Melting point of brass and bronze: melting at home

Bronze is a copper-based alloy that does not contain nickel and zinc as the main alloying components. Characterized by a relatively high melting point, the metal becomes liquid in the range from +940°C to +1300°C. The most refractory is tin-phosphorus. Bronze alloys are used to produce long products, sheets and pipes, engine parts, elements of transmission devices, liners for shut-off valves, fittings, taps, souvenirs, instrument parts and much more. You can make casting at home. Bronze is smelted in muffle furnaces or furnaces. At the melting temperature, bronze becomes thick and does not flow well into the mold; you need to know some tricks in order to do casting yourself.

A little history

Bronze is actually the first alloy that humanity began to use. In the 3rd millennium BC. e. craftsmen actively used copper for a variety of purposes. Some types of ore contained a small percentage of tin. When processing this material, people noticed that such copper is denser and harder than ordinary copper. Thus, this became the birth of a new historical and cultural period, which is now known as the “Bronze Age”. Further research led to the discovery of tin, which began to be specially added to copper to obtain a high-quality alloy for making tools and jewelry.

Bronze metallurgy qualitatively increased the productivity of a wide variety of industries in which humanity was occupied at that time. Melting gradually improved, and people began to make special stone molds in which various products could be cast repeatedly. Gradually, closed molds were invented, which made it possible to make weapons and jewelry with complex designs and patterns.

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Casting brass into plaster molds

Gypsum hemihydrate CaSO4 mixed with the semianhydride substance γCaSO4 is used for castings from non-ferrous alloys, as well as for the manufacture of models and model plates; for small castings a mixture of 20% gypsum, 80% asbestos + water is made. The mechanism of strength formation is hydration (the more asbestos, the less water is taken).

For thin-walled castings with thin relief and a clean surface, instead of asbestos, fine-grained quartz powder is recommended; this mixture is stronger than cement and has low gas permeability, so it is melted in autoclaves at a pressure of 2 MPa for 8 hours, after which it is dried for 10-20 hours. To enhance gypsum mixtures, a surfactant can be introduced into them - this will allow, when foaming the gypsum slip, an increase in the number of gas bubbles, which, during the studied hardening of the mixture, promotes gas permeability.

This gypsum mold has microporosity and high gas permeability, which makes it possible to produce castings from alloys that release an increased amount of gases during hardening.

Making molds for casting

The quality of products produced by casting from bronze alloys is seriously influenced by the correct manufacturing of the casting mold, which makes it possible to create a part of the required configuration and with given geometric parameters from molten metal. For the manufacture of casting molds, special devices are traditionally used - flasks. The flask, the dimensions of which should be approximately one and a half times greater than the parameters of the finished product, consists of:

• top frame;
• bottom drawer.

The upper and lower parts of the flask, into which the molding mixture is poured, can be reliably connected to each other for greater reliability, for which special clamps are used on their side surfaces.

The composition of the most commonly used molding sand includes:

• fine sand – 75%;
• clay – 20%;
• coal dust – 5%.

As a result of mixing these components, a homogeneous mass should be obtained.

To make a casting mold, you will also need a model that is made from wood or other soft material (you can use a finished product of the required quality in its role).

The production of the casting mold itself is carried out as follows.

• The molding mixture is poured into the bottom drawer of the flask and lightly compacted.
• A model is placed into the resulting compacted mass, the surface of which must first be coated with talc or powdered graphite.
• Place the upper frame on the lower part of the flask and fill it to the top with molding mixture, also compacting it. Before filling the upper half of the flask, it is necessary to form a sprue hole in the future shape, for which a special conical plug is used.
• After compacting the molding mixture, you need to divide the finished mold into two halves - upper and lower, for which you can use any sharp object.
• After removal from the resulting casting mold, the internal cavities of the model are carefully inspected and any defects that may be present are corrected.

The finished mold must be dried, after which it can be assembled and started to be used for casting bronze products. The production of a casting mold is shown more clearly in the video below.

Mold casting: manufacturing, sand, shell molds

According to historians, the bronze casting is 12 thousand years old. Initially, using this technology, jewelry and simple tools were made from bronze. Over time, this technology has been improved, and today it is a method by which many unique products are created from this alloy.

The current level of development of bronze casting makes it possible to produce various objects from this copper alloy not only in production, but also at home.

Thanks to the invention of bronze, as well as the development of its processing technologies, the main of which is casting, we can still enjoy the sight of works of art that were created by masters back in the Middle Ages and ancient times.

Antique bronze set of writing instruments

Bronze casting, as well as brass casting, another alloy based on copper, gained the greatest popularity in the era of classicism and European Baroque. It was in those days that people learned to use these materials to create unique interior elements and decor.

Such alloys created on the basis of copper are still actively used in the manufacture of:

• items used for interior decoration;
• gates and fences that perform not only a decorative, but also a protective function;
• sculptural compositions and souvenirs;
• bas-reliefs and design elements of lighting fixtures - chandeliers and sconces;
• elements of staircase structures and entrance groups.

Bronze casting for making knife handles

Many of these products, which are not large in size or complex in shape, can be made from bronze and brass not only in production, but also at home.

Stages of artistic bronze casting

In order to perform high-quality casting from a metal such as bronze, it is necessary to adhere to a certain sequence of actions. First of all, you should reflect in the sketch the shape of the product that you plan to cast from bronze.

Based on the sketch, which is created by professional artists and designers at modern enterprises, specialists create a drawing that accurately reflects all the dimensions of the future casting.

It is the drawing that is the basis for making an accurate model, which is used to produce a casting mold.

To create a model of a product that will subsequently be made from bronze by casting, various materials can be used, in particular:

• Ivory;
• wood (in this case, preference is given to such varieties of this material as pine, alder, beech, linden);
• gypsum;
• various types of polymer materials.

The cavities of the wax model of the future figurine are filled with clay, which will be removed after casting

To make the surface of the model as smooth as possible, it is primed, puttied and covered with several layers of varnish. When making a casting model, not only different materials can be used, but also different design approaches. So, models can be:

• detachable (these are complex structures consisting of several component elements that can be connected to each other along flat or complex surfaces);
• one-piece (monolithic models, the simplest type, most often used for casting at home);
• special (this includes skeletal or molding templates used in cases where it is necessary to make a casting mold for the manufacture of objects with a complex configuration).

The next step after creating an accurate model of the future bronze product is the production of a casting mold. For this purpose, special devices and equipment are used, and the main materials used in this case are molding mixtures created on the basis of clay and carefully cleaned quartz sand.

The longest stage of bronze casting is molding - making a casting mold

In such a technological process as casting, made from bronze and any other metal, the casting mold plays a decisive role.

It is into such a mold, the internal cavity of which must exactly repeat the product being cast, that the molten metal is poured, and in it it cools, forming the finished casting.

Foundry molds, used both in production and at home, can be single-use or reusable, which is determined not only by the material from which they are made, but also by the features of their design.

Microcasting at home

A lot of cast parts made of non-ferrous metals and their alloys are used in technology, including quite complex and miniature ones, the serial production of which can only be afforded by enterprises with precision technology.

However, single (or even small-scale) microcasting can be organized at home.

It turns out that modern technology can be rivaled by the ancient method of injection molding using a simple manual centrifuge.

Almost everything that is needed for such micro-casting can be made by hand. Costs are minimal.

Indeed, the flask required for casting in this case is a piece of ordinary steel pipe with a diameter of 50-60 mm and a wall thickness of 2-3 mm. For casting products of different sizes, it is good to have several flasks of different diameters, provided that each one fits freely in the centrifuge bucket. If you have such a set, you can cast a whole series of parts one by one.

A centrifuge matches the flask in simplicity. Its wooden handle has a length of about 200 mm and a diameter of 20-30 mm. An M8 bolt is inserted into the axial hole of the handle. A metal earring is attached to it using a locked nut so that both the handle and the earring rotate easily without interfering with each other.

A bucket for a flask is suspended from the earring on a rocker arm made of 6 mm steel wire. The side of the bucket is made of a 60 mm piece of 80x3 mm steel pipe, and the welded bottom is made of a steel sheet 3 mm thick. The 200 mm high bow is made of the same 6 mm steel wire.

In order to confidently use such a centrifuge, you must first practice a little, remembering how in your school years in the physics room you had to twist a bucket of water on a string while studying centrifugal force.

True, now, instead of string and a bucket of water, in my hands I have a homemade centrifuge with a bucket, on the bottom of which there is a plastic cup (to prevent it from breaking).

But the water in it is ordinary, like it was in school physics experiments. And the action of centrifugal force is similar.

Holding the handle firmly, you need to rotate the entire chain (earring - rocker - bucket and vessel with water) around the bolt-axis, trying not to spill a drop.

Technology for producing high-quality micro-injection molding of non-ferrous metals and alloys using a manual centrifuge:

1 — bolt-axle; 2 - wooden handle; 3 — metal, easily rotating earring; 4 — locked nut; 5 — steel wire rocker; 6— bow; 7 — side of the bucket; 8 — bottom of the bucket; 9 — flask; 10 - molding compound; 11 — wax model; 12 — wax ball with technological wire pins; 13—casting mold with sprue channels, formed after melting the wax and removing the pins; 14—molten metal (alloy); 15 — flame of a gasoline burner; filling the mold with the melt while rotating the centrifuge and subsequent operations for removing and finishing the finished product are not shown

Once you get the hang of it, you can subsequently deal not with water, but with molten non-ferrous metal (or alloy), which will be pressed by centrifugal force through the gating channels into the casting cavity in the flask installed in a bucket instead of a plastic cup.

Perhaps the most difficult and time-consuming thing in micro-casting is the production of a three-dimensional, life-size wax model.

This one is molded from wax by hand, using a heated eye scalpel or a hot darning needle. Even small details are worked out with the utmost care, because molten metal (as well as any alloy) does not forgive mistakes and sloppiness. Moreover, casting, performed in a centrifuge under pressure, reveals all the flaws of the model!

In my practice, I use wax models whose height is no more than 40 mm and diameter is 50 mm. At the same time, I try to maintain proportionality so that the mass of metal in the casting does not exceed 40 g. The limitations are mainly due to the low power of the burner I use for melting.

Safety rules at work

Any work with products heated to high temperatures must be accompanied by strict compliance with labor safety standards.
This is the only way to prevent accidents and injuries. The person working with the stove must have protective clothing. This should be a heat-resistant apron that covers the entire front part of the body, thick leather gloves and boots with large soles. There should be no shirts or pants made of synthetic materials under protective clothing. Such products ignite very quickly and do not extinguish well. Give preference to items made from cotton or wool.

If you're wondering where you can get these safety gear, don't worry. Most likely, the same place where you will find crucible tongs and other equipment for melting metals. You can also buy safety glasses, a face mask or a respirator with a special filter there. These devices will help protect your face, eyes and lungs from the harmful effects of waste fumes emanating from molten metal.

Characteristics of brass

The manufacture of products from this alloy is achieved primarily through casting . Therefore, it is very important to know at what temperature brass melts. This greatly depends on its chemical composition, and more specifically, on the zinc content in it, because the more of this metal, the less heat is required to melt it. If brass contains a significant amount of bismuth or lead impurities, this has a very negative effect on its flow, complicating the processing of products. Therefore, its melting point ranges from 880-950 degrees Celsius.

When making brass products, it is very important to cover them with a protective layer. For this you can use regular varnish. Despite its resistance to corrosion, it is very susceptible to oxidation in the open air. Many exposed parts or furnishings need to be cleaned regularly to prevent them from discoloring. But this is easy to do, because brass polishes very well .

Technical characteristics of the alloy

In addition to its melting point, brass has several other important characteristics due to which it is so widely used in various fields. Here are some of them:

• Specific electrical resistance is in the range of 0.07−0.08 microohms per meter.
• Density is about 8.3−8.7 tons per cubic meter.
• Heat capacity is 0.377 kilojoules per kilogram Kelvin.

Depending on the composition, brass is:

• Double - an alloy containing only copper and zinc.
• Multicomponent - containing a large number of other metals and impurities.

How is brass melted in metallurgical plants?

The alloy is usually melted in metallurgical plants, since favorable conditions for remelting are created there. During factory melting, the material retains all its physical properties - strength, electrical conductivity, retention of shape during deformation, and so on. The technology for remelting brass at a factory depends on what category of brass the material belongs to. Two-component alloys (with added zinc) are usually melted in induction furnaces that have quartz-lined walls. This coating minimizes overheating of the furnace and also protects the walls from deformation and cracking.

Double brasses melt at relatively low temperatures (the liquidus point for them is in the region of 910-930 degrees Celsius). Therefore, there is no point in melting dual alloys in powerful electric arc furnaces. For the melt, it is recommended to use a charcoal-based protective layer. It is also recommended to introduce a small amount of cryolite into the melt (about 0.01-0.1%) - this helps reduce metal defects during smelting. Instead of charcoal, you can use a flux consisting of glass and spar in a 1 to 1 ratio.

To remelt two-component brass, you must first melt the copper and then the zinc. To melt metal, you need to heat it to a temperature of about 1000-1100 degrees. After this, zinc and alloying additives, if available, should be added. Please note that there is no need to deoxidize brass, since zinc performs this function perfectly.

Complex non-siliceous brass

Melted according to a similar algorithm. These alloys contain zinc in small quantities. Therefore, such a metal must be deoxidized in order to preserve all its beneficial physical properties. Phosphorus is suitable for deoxidation, although other deoxidizers can be used. When melting, complex brass often produces large debris fractions - to get rid of them, you should perform manganese refining or filtration.

Complex silicon brasses

They have complex crystallization dynamics, which is explained by the presence of silicon and aluminum additives in the alloy composition. Due to the presence of these components, the alloy has an increased tendency to absorb atmospheric hydrogen at high temperatures (more than 1000 degrees).

When the alloy is heated to temperatures above 1100 degrees, batch releases of dissolved carbon may occur, which can lead to the formation of “blisters” on the alloy after it hardens. Therefore, approach the remelting of silicon steels responsibly. To avoid the release of dissolved carbon, smelting should be carried out in an acidic environment. Saturating the air with an acid flux based on sodium carbonate, calcium fluoride and silicon oxide works well. It is important to monitor the heating temperature, since the protective properties of the gas oxidizer noticeably decrease when the temperature reaches 1100 degrees.

After melting all components in a protective environment, it is necessary to perform a mandatory check of the metal for all main indicators (fracture, saturation, presence of contaminants, and so on).

Brass grades and applications

The brand of brass and its scope of application depend on the composition. For example, tombak, which belongs to the class of wrought brasses, which contains more than 95% copper, can easily combine with steel, forming a bimetal with it. This compound is used in the manufacture of insignia and various objects of art and interior design - figurines, frames, candlesticks .

LO grade brass is used for the manufacture of condenser tubes used in various heating equipment, for example, gas boilers, autoclaves, and bellows.

The LS brand is used to create parts for watch mechanisms, adapters and connecting bushings. Printing matrices are also made from it.

LMC - is found in old Soviet coins with denominations up to 5 kopecks, fittings, nuts and bolts, and its subtype with the prefix “A” is found in parts of river and sea vessels.

Brass, marked LA or LZhM (and its subtypes), is also used for the construction of sea ships and aircraft, various electrical machines and bearings. Very common in parts for various chemical equipment.

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Is it possible to solder brass?

brass soldering

Many beginners, as a rule, are concerned with the questions: can brass be soldered or not and to how many degrees can it be heated. The answer is clear: you can solder brass. It is quite possible to solder brass surfaces, although it will require more skill than when joining with conventional solder. Solder for brass should consist of copper and silver, combined in a ratio of 1 to 2. Parts placed on an asbestos base are moistened with flux (borax, boric acid, water), sprinkled with crushed solder, then heated with a gas burner. The temperature should not exceed 700° C to avoid deformation of parts; heating should be done gradually.

The difference between the melting temperatures of solder and brass parts does not exceed 50 °C, so if overheated, there is a risk of getting a large ingot instead of a quality product. If the work was done efficiently, the seam will have the same color as the brass surface of the part. This is explained by chemical diffusion. The last stage of soldering is removing flux residues. To do this, hot three percent sulfuric acid is used, which is then washed off the product with water.

Bronze classification

Despite the fact that the “Bronze Age” has long passed, several variants of this material are used today. Based on composition, the alloy is divided into the following types:

• tin-free (does not contain tin);
• tin.

The first group additionally includes beryllium, aluminum, lead and silicon-zinc types.

• Beryllium bronze is the most resistant and durable alloy, which in its basic characteristics surpasses even high-quality steel.
• The silicon-zinc type in the molten state is characterized by high fluidity rates.
• Lead bronze is a type of alloy that has increased durability and stability.
• Aluminum bronze differs from other types in its resistance to chemical irritants and negative environmental influences.

As for the second subtype of bronze, the tin type is by far considered the most common in industry, despite the fact that other types of alloys are superior to it in certain characteristics.

Soldering brass

In our practice we often have to deal with brass parts. They are well processed, soldered and then blackened. Most people solder brass with a soldering iron using regular tin solder. This method, along with its simplicity, has three serious drawbacks: the seam turns out white, noticeable, and few people manage to immediately make this seam thin; the seam turns out to be relatively weak; when bent, it can easily come apart; When blackened, tin may behave differently than brass and the weld will turn out to be a completely different color or shade. This article will tell you about the method of soldering brass using a gas torch with special solder and flux. The resulting weld is practically indistinguishable in color from the main parts, very durable and chemically much closer to brass than tin.

Features of the described metal

What is bronze? This is an alloy consisting of a main component (copper) and an additional alloying element. Depending on what acts as an alloying additive, several grades of the material being described are distinguished, therefore each type of bronze has its own melting point. The physical and chemical properties of bronze depend on the percentage of additional components. Its marking helps to understand what impurities are contained in the alloy.

All bronze compositions can be divided into two large groups:

• Tin.
• Tinless.

Tin alloys are a type of bronze that contains tin as an alloying element. This metal is stronger than copper, but it is fusible. The combination of copper (80%) and tin (20%) is the first alloy that humanity has learned to create. With its help, church bells were cast in Rus'. The metal sounded good, but was fragile. Therefore, there was a need to look for more advanced alloys.

Tin-free alloys do not contain brittle tin. Beryllium, silicon, lead and aluminum can be used as alloying additives. Depending on which of the listed metals is combined with copper, the alloy acquires its physical and chemical properties. For example, beryllium makes it possible to create alloys whose strength characteristics are much superior to high-quality steel. The addition of silicon makes bronze more resistant to mechanical friction. Lead helps to form high resistance to corrosion, aluminum improves the friction characteristics of the alloy.

The process of melting bronze must begin with studying its composition. All tin grades melt at a temperature of 900–950°C, tin-free grades melt at a temperature of 950–1080°C.

Note! When casting, another indicator of the alloy is taken into account - its viscosity. Tin bronze has a higher temperature than brass, so when heating it it must be very overheated. Then, after cooling, the described brand gives minimal shrinkage, so this type of bronze is ideal for shaped casting.

Is it possible to cast bronze at home?

Many of us wonder whether the process of melting the described alloy is possible at home. It is impossible to recreate industrial casting. Since bronze has a high melting point, special conditions are required to work with hot metal. You can try to master small casting, which allows you to create jewelry or small crafts. To carry out this process, you will have to allocate a separate room, as well as take all fire safety measures and provide high-quality ventilation. Large bronze parts can be made where there is an earthen or concrete floor (this could be a garage with good forced ventilation).

To work you will need certain equipment and special tools. Only a muffle furnace will allow casting (the presence of a thermostat will greatly simplify the solution of the task). For large pours, you will have to install a forge. You can melt metal in a cast iron container that is shaped like a spout. It helps to gently pour the molten metal into the mold. This cast iron container is called a crucible.

The crucible is removed from the furnace using long tongs and a special hook. There should be a casting mold at hand. Charcoal is best suited for lighting a muffle furnace, and coke for a forge.

What is brass made of?

Brass, the alloy composition of which can vary significantly, necessarily contains copper in an amount of at least 55%. The remaining 45% of the two-component alloy consists of zinc. Zinc in the copper alloy significantly increases the mechanical strength of the alloy and corrosion resistance.

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In addition to zinc, multicomponent brass may contain:

• Aluminum.
• Tin.
• Nickel.
• Manganese.
• Silicon.

Additional additives are necessary if it is necessary to provide the metal alloy with new properties that will facilitate easier formation of the product during casting and during machining.

To melt brass, the alloy must be heated to 880 - 950 degrees. Exactly what temperature is required for melting a particular type of brass depends on its composition, but when melting metals at home, it is not always possible to determine the grade of the alloy.

To guarantee melting of brass at home, you should purchase a special device in which the metal is heated to the maximum melting temperature.

Making a melting device yourself will require significant time and special knowledge. Therefore, it is much easier to purchase ready-made melting furnaces in specialized stores that run on gas or AC power.

Furnace and tools for melting brass

To cast brass at home, you need to purchase a special furnace.

At home, it is best to use small devices with a maximum heating temperature of 1300 degrees. Such a limitation is necessary to prevent burnout of the zinc contained in this copper alloy.

1. Graphite crucibles are used as a container for melting brass.
2. You will also need to purchase tongs and a large spoon. Tongs are needed to install and remove the crucible from the furnace, and a spoon is used to remove slag that forms on the surface of the melt.
3. A casting ladle is used to pour the molten brass from the crucible into the mold. Without this device, it is impossible to safely tilt the hot crucible during smelting operations.

Work with the melt must be carried out without any deviations from safety regulations, therefore, in addition to equipment for melting, you should definitely purchase protective clothing, eye and breathing protection.

When brass melts, harmful fumes are formed that negatively affect human health.

1. It is strictly prohibited to carry out smelting work without a respirator. Special glasses or a mask are used to protect the eyes from exposure to infrared radiation, which, with prolonged exposure, can cause damage to the organ of vision.
2. It is also necessary to use a heat-resistant apron to protect clothing from possible contact with molten metal and thick gloves to avoid burning your hands during melting work.

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When all the necessary tools and fixtures have been purchased, you can begin preparing to melt the brass.

Preparatory work

In order for the melting of a copper alloy to be carried out according to all the rules, it is necessary to prepare tools and a place for work.

The best option for placing a furnace for melting brass is a canopy in the fresh air. Installing a stove outdoors allows you to minimize the harmful effects of zinc vapor, as well as ensure good fuel combustion when using a gas stove.

In terms of fire safety, placing a high-temperature furnace outdoors is the most appropriate. If it is not possible to install the melting furnace in this way, then the room in which the melting work is planned to be carried out must be equipped with a forced air ventilation system.

The surface on which the stove is installed, regardless of its location, must be made of non-combustible materials. It is also recommended to install a box with dry sand to safely move the crucible with molten metal. To prevent splashing of molten metal, it is recommended to carry out mold pouring work only over a container with sand.

1. If scrap metal will be used to obtain the melt, then before starting melting, the brass surface should be thoroughly cleaned of dirt and paint.
2. When using rolled non-ferrous metal, it is enough to cut it into pieces, the size of which will not exceed the parameters of the crucible of the melting furnace.

Such preparatory work will allow for better melting of metal with less slag, and the process itself will be more fireproof.

Brass melting process

After the preparatory stage, you can begin to directly melt the copper alloy.

The work is carried out in the following sequence:

1. In the oven, the molds are heated to a temperature of +100 degrees. It is also necessary to warm the spoon well before use. This procedure is necessary to completely evaporate moisture from the surface of the instruments. After warming up, the molds must be placed on dry sand.
2. Pre-prepared brass scrap or crushed rolled metal for melting is placed in the crucible in the required quantity.
3. The oven heats up to a temperature of +500 degrees.
4. The crucible with brass is installed in the furnace and the temperature rises to 950 degrees.
5. When the metal has completely melted from its surface, you must carefully remove the resulting slag and oxidation products using a spoon.
6. When the brass acquires a bright yellow color, you can begin filling out the prepared forms. For this purpose, the crucible is removed from the furnace with special tongs and installed on a casting ladle. Then the molds are filled with melt.

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If it is necessary to continue melting the metal, the crucible must be filled again with the prepared material and installed in the melting furnace.

Tips and tricks

1. There are a large number of furnaces for melting metals on the market and it is not always possible to make the right choice of device. Especially if you have no experience in smelting. So that the furnace can be used not only for melting brass, it is recommended to choose a device with the ability to heat up to 1300 degrees. For example, the melting point of bronze is about 1150 degrees and low-power devices will not allow the melting of this non-ferrous alloy.
2. For each type of non-ferrous metal it is necessary to use a separate crucible, therefore it is not recommended to melt bronze or any other metal or alloy in a container in which brass was melted.
3. It is not recommended to wear synthetic clothing while performing smelting work. This fabric ignites and melts easily. In case of fire, may cause serious burns.
4. In the immediate vicinity of the place where the melting furnace will be installed, it is necessary to place a container with cold water. Such a protective measure will allow, in the event of a burn, to instantly reduce the temperature of the affected area of ​​the body.
5. The fire extinguisher must be located in direct access to the place where smelting work is carried out.
6. The moment of complete melting of brass can be determined by eye. It is necessary to pour products from this alloy when the surface of the molten metal begins to glow yellow with a slight orange tint.
7. During melting, brass is strictly prohibited from stirring. This action can lead to the formation of air bubbles, which will negatively affect the density of the material, its mechanical and aesthetic properties.
8. The exact melting point of brass depends on its brand. When determining the melting point experimentally, care must be taken not to overheat the mixture so as not to accelerate the oxidation process of the metal alloy.
9. You can make a furnace for melting brass yourself, but only with special knowledge. If difficulties arise in this matter, you can seek advice from experienced craftsmen.

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Significant savings can also be achieved by replacing the graphite crucible with a ceramic product. If you purchase special refractory clay, you can learn how to make containers for melting furnaces yourself.

Ceramic crucibles have a significantly shorter lifespan, but in cases where it is possible to independently manufacture such parts, the money savings will be significant.

Conclusion

At what temperature copper and its alloys melt is described in the article, but theoretical knowledge alone is not enough to become a professional in this matter.

Once a brass melting furnace has been purchased or installed, it is necessary to melt a small amount of metal to test the functionality of the equipment. And gain experience in melting copper alloys at home.

Comparative characteristics and differences between metals

In the metallurgical industry, there are clear criteria for distinguishing between bronze and brass. However, if a person is not associated with this field of activity, he will not be able to determine by eye what material is in front of him. Combining copper with tin or zinc produces alloys that have different properties and are used in specific areas.

Bronze and brass have different properties and belong to completely different categories. The first alloy can be tin or tin-free, while the second can be two- or multi-component.

Bronze alloy consists of tin to which lead may be added. The color of the metal will depend on the percentage of one element or another. The main additive element in brass is zinc.

Bronze is resistant to chemical and aggressive compounds. In addition, its negative reaction to salty sea water made it possible to use the alloy in shipbuilding and navigation. Brass cannot boast of this, so to give it improved qualities, additional elements must be introduced into the alloy. In addition, bronze has better strength and anti-friction characteristics than brass. This allows you to significantly expand the scope of application of the alloy.

The high zinc content in brass gives the alloy a variety of colors from pink-red to golden yellow. This is what makes it similar to noble gold.

What does brass look like?

The silvery-white color of bronze is achieved by adding more than 35% Sn to its composition. An alloy containing at least 85% copper is brownish-red in color. Since compounds with high levels of impurities are rare, it can be argued that basically brass is a metal of golden yellow color, and bronze is closer to red, sometimes dark brown. The same colors of brass and bronze will appear on the broken objects. This allows you to easily distinguish brass products from bronze ones.

From a metal such as brass, not only decorative elements are made, such as furniture fittings or artistic objects for interior decoration, but also main parts used in various industrial fields.

Bronze and brass have a lower melting point than pure copper. This makes it possible to make various products from them for home use. Artistic casting made of bronze and brass looks very beautiful. However, for this you need to have the appropriate equipment and know the technology and rules for performing such a procedure.

Physical features of melting multicomponent alloys

Multicomponent compositions consist of several elements. This imposes a number of features on the melting of such materials:

1. Multicomponent alloys consist of several elements. Together they also form a strong crystal lattice. The properties of such a material are identical to one-component alloys, and sometimes can exceed them. Basic examples are higher strength, lower risk of corrosion, higher shelf life, and so on.
2. When a multicomponent alloy is heated, the potential energy of individual atoms increases. But the crystal lattice retains its strength, so the substance retains its original shape.
3. When the critical heating temperature is reached, the crystal lattice gradually disintegrates. But since the alloy contains atoms of different categories, the lattice disintegrates unevenly (different atoms have their own boiling point). At the physical level, such a substance will be a mixture of solid and liquid fragments.
4. The temperature at which low-melting atoms begin to enter the liquid phase is called the solidus point. If you reduce the fuel supply, low-melting atoms will begin to form a crystal lattice again, which will lead to solidification of the alloy. For brass, the solidus point is 880 degrees Celsius (zinc is a more fusible material).
5. The temperature at which all atoms begin to enter the liquid phase is called the liquidus point of the substance. The liquidus point indicates how hot a material must be heated to completely melt it. The dynamics here are standard - as the fire supply decreases, a gradual crystallization of molten atoms will occur. For brass, the liquidus point is 950 degrees Celsius.

Manufacturing methods and characteristics

Physical data

The characteristics of the alloy are determined by its chemical composition and can vary within certain limits. Bronze is less susceptible to corrosion and provides better metal-to-metal glide than brass. It has higher strength and is less susceptible to atmospheric influences (water and air) and better resists salts and organic acids. It is easy to machine, it can be soldered and fastened by welding. Some physical characteristics of bronze:

• specific gravity from 7.8 to 8.7 tons/cu.m. meter;
• melting point of bronze – melts when heated from 930 to 1140 degrees;
• color changes from red - the color of copper, to white - the color of tin;
• wear resistance and good sliding on metal determine the scope of application as sliding bearings; they work well in any temperature conditions;
• There is high electrical conductivity and heat transfer, resistance to steam, which contributes to the manufacture of parts for equipment operating in extreme situations.

How to make bronze

Melting and mixing copper melts and additives of different metals, which make it possible to give the alloy certain required characteristics, leads to the production of an alloy metal such as bronze. The manufacturing process involves electric induction furnaces and crucible forges; with their help, any alloys with copper can be produced.

Melting is carried out with flux additives, and the initial raw material for smelting can be either copper ore or copper scrap. Typically, scrap copper is added to the melt along with the filler metal during the smelting process. When smelting only copper ore, the following operations are performed:

• the furnace is heated, copper ore with flux additives is placed in it, and melted at a temperature of about 1200 degrees;
• a chemical oxidizer is added - phosphorous copper, half could be loaded as part of the flux, and the rest is additionally loaded with a ladle;
• during melting, filler metals are added to the deoxidized molten copper, preheated to one hundred degrees;
• After settling the melt for half an hour, the floating slag is removed from its surface, and the resulting alloy is distributed into molds.

When using scrap copper, the procedure for making bronze is the same.

What tools are needed to melt brass

Melting steel in induction furnaces

To melt brass before subsequent casting, it must be heated to almost +900 degrees Celsius. To do this, you will need to purchase or make a special oven. An induction type oven heats up most efficiently.

The frame of a homemade forge can be assembled from refractory bricks with a bond of refractory clay, and be sure to be tied with metal to avoid destruction of the structure at elevated temperatures inside. A removable lid is placed on top.

The interior decoration of the stove is an electric spiral, evenly fixed along the entire perimeter of the walls using ceramic tubes. The device where metal parts are directly placed is called a crucible. This is a special container that can withstand high thermal loads. Therefore, it is not made of metal. Factory models of crucibles are often made of graphite. For home use, you can make a crucible from fireclay bricks.

To create the required heat inside the furnace, the power of the electric coil must be designed for at least 20 kilowatts. When making a spiral yourself, when choosing nichrome wire, you need to take this point into account. Additional tools you need to have to work with molten brass:

• Tongs for removing a hot crucible with metal from the furnace of the furnace;
• Steel spoon to remove film and slag from the melt;
• A casting ladle into which liquid brass is poured before pouring the mold;
• Personal protective equipment for vision, breathing and skin;
• Fire extinguishing agents (fire extinguisher).

In addition to all of the above, the room in which the brass composition is melted must be equipped with supply and exhaust ventilation - zinc vapor is very harmful to the body.

Nuances of spectral comparative analysis

Due to the variety of copper-based alloys, it is difficult to accurately determine the type of their connection. Any of the methods to distinguish brass and bronze, even the most effective, does not provide a 100% guarantee. If you need an accurate answer to the question of what kind of alloy it is, then the only way to a reliable answer is to use spectral analysis. You can contact a scrap metal collection point, which may have the appropriate equipment.

Spectral analysis allows you to determine the chemical composition of a metal alloy based on its spectrum. In addition, this method has other advantages:

• high sensitivity;
• accuracy of results;
• studying the composition of brass and bronze products without destroying their structure;
• you can study the composition even on a small sample.

To carry out spectral analysis, a special tool is used - a steeloscope. It is designed for rapid visual qualitative and quantitative assessment of ferrous and non-ferrous alloys in the visible region of the spectrum.

Processing Features

The home craftsman uses many different parts in everyday life that are made from brass.

In addition, quite a lot of different tools are produced that contain this component. Very often brass is found in an alloy based on bronze and copper.

Knowing the melting point of this metal, as well as the methods by which it can be melted, you can independently repair and manufacture some products that will be useful on the farm.

Melting this universal component based on bronze and copper has certain subtleties and nuances, knowing which you can avoid a variety of difficulties in your work.

Of course, in order to independently smelt this bronze-based metal, you must have certain knowledge in this area, as well as some tools that may be required in the work.

In addition, in order to melt brass yourself at home, you need to be patient.

To work, you should definitely have technical silver on hand, as well as a manual gas burner. You will also need a copper alloy and a special graphite torch.

Article on the topic: Where to put an old gas stove in St. Petersburg

Borax should be purchased in sufficient quantity. In addition, in order to maximize the safety of the surrounding area for melting brass, you should purchase an asbestos sheet.

This process is quite labor-intensive and requires compliance with certain safety precautions.

If the brass alloy is based on copper or bronze, then when melting it is necessary to take into account certain subtleties, and also know some nuances that will help to carry out this work correctly and as efficiently as possible.

First of all, it should be taken into account that an alloy based on bronze and copper has slightly different melting parameters, and, accordingly, some characteristics of the metal, both physical and chemical, change.

Once all the necessary tools and materials have been prepared, you can proceed to melting brass with your own hands at home.

METHODS OF MELTING BRASS AT HOME

Melting brass at home can occur in several ways, depending on the equipment used.

Melting brass with a gas torch

The burner is installed in a vertical position under the crucible. The crucible can be either ready-made, made of ceramics or graphite, with a permissible temperature of 1300 degrees, or made at home from silica, liquid glass, or fireclay chips. The heated area is shielded with a sheet of iron or other fire-resistant material. A strong stand is created to mount the product.

Molds for parts are made from:

• Plaster;
• Mixtures of cement and brake component.

Melting brass in a home furnace

Most often, stoves are made of high-quality refractory bricks. The heating element is created from induction heating devices, which are ceramic tubes with a winding of nichrome wire. The temperature of such heaters can reach 1000 degrees or more. Electrical power must be at least 25-30 kW.

What is brass?

Copper and zinc - these two chemical elements in their pure form are not very similar, but together they form one of the most popular alloys in the world - brass. The base substance contains about 70% copper, and 28%+ is zinc. The remaining 2% are various impurities, which can be lead, silicon and even tin.

Interesting facts about brass:

• the Romans called brass orichalcum “golden copper” because of its characteristic golden hue;
• Western countries prefer to make gun casings from high-quality brass - this reduces the amount of mechanical damage to the barrel during operation;
• Zipp lighters are made of galvanized brass;
• in Rus', brass was an indispensable material in the production of samovars;
• Brass has not bypassed African countries either. Local aborigines make ritual masks from it;
• It is practical to make the housings of magnets and compasses from brass, since this alloy does not have magnetic properties;
• L68 and L62 are two grades of decorative brass used by beginners in jewelry making to learn how to machine gold objects.

There is a special recipe for brass made from a nickel-copper alloy, where 2.4% aluminum is used as an alloying additive. The specified material is extremely popular among jewelry manufacturers, because it is extremely difficult to distinguish it from 583-carat gold. Often this property of the alloy is used for the purpose of fraud, therefore it is best to purchase jewelry in certified places where there are persons responsible for the quality of the product and the accompanying documentation is issued.

6 steps on how to distinguish copper from brass at home

1) Classification of brass + its advantages/disadvantages

Brass is a bright and practical material that has found itself in solving many household and industrial issues. The yellowish tint and ease of polishing the metal surface, coupled with weak oxidation in the external environment, make the alloy objectively the best for solving a number of problems associated with the construction of transport systems and in the manufacture of certain equipment parts. The table below will tell you more about the pros and cons of brass.

In practice, the variability in the proportion of components in a brass alloy is much higher. For example, if an alloy contains 50% zinc, then the resulting material is considered low-quality, and its production technology is based on secondary waste. The table below will tell you more about the classification of brass.

By analyzing the data above, it is easy to replace the pattern of changes in the properties of the alloy as the dosage of zinc and other alloying additives increases/decreases. Chemically, brass is a mixture of zinc, copper and α-solution. The structure of the material usually consists of 2 phases - α- or α+β'. In the first case, we obtain a copper fcc structure, and in the second, a CuZn solution, the concentration of which is 1.5, and the shape of the cells is as simple as possible.

Important: greater elasticity of brass is observed in the α phase, but increased strength is observed in the β' phase.

Therefore, when purchasing material intended for further melting, pay attention to the markings. The average value for strength and ductility is achieved thanks to 30% zinc in the alloy.

2) Properties of brass + areas of its application and markings

It is problematic to provide a clear overview of the chemical properties of the material, because the parameters vary depending on the proportion of zinc and alloying additives.
Each new alloy has its own characteristics that make the material unique in its own way. The maximum is to provide generalized characteristics for the reference percentage of zinc/copper in a brass alloy (30% to 70%). Properties of brass:

• density varies between 8,400 – 8,800 kilograms per cubic meter;
• is non-magnetic in the absence of an external magnetic field, that is, it is not ferromagnetic;
• at normal temperatures, the specific heat capacity of brass is 0.4 kilojoules per kilogram to the -1 degree per kelvin to the -1 degree;
• The thermal conductivity of brass increases as the proportion of pure copper within the alloy increases. The lower limit is 0.3 cal. per centimeter* second in Celsius, and the upper limit is 0.6;
• easy to polish.

Classic fusion welding is not suitable for brass. The optimal option is to use resistance welding. The properties above are given for two-component brass. For multicomponent alloys, different rules apply. The roles of the main alloying components within brass alloys are provided below.

The lead alloy brass alloy is the most common of all those considered. In terms of marking, brass is designated by the letter “L”. After it comes the percentage of copper and alloying components in the template.

Two-component brass is used for the production of automotive parts, devices in the chemical/thermochemical industry, and for stamping products (nuts, bolts, condensers, thick-walled pipes, etc.).

There are many more multi-component varieties of brass. You can judge this yourself from the scale of the table above. The main areas of application of the material include the production of parts in shipbuilding, the development of capacitors in thermochemical equipment, various small parts of watches, printing assemblies and other small products.

According to GOSTs, cast-type brass is classified into a separate category. The basic properties of the material are corrosion resistance, high-quality anti-friction properties, fluidity and a slight tendency to liquidation. Regarding the scope of application, these are cast-type fittings and other small items with the need to resist corrosion.

The last category of brass alloys is jewelry. Here, raw materials are supplied only in yellow or golden granules, for further processing at high temperatures and melting into low-quality “jewelry”. Admirers of costume jewelry will have something to enjoy.

Application by rental type

Brass is present everywhere, although not in large quantities (unlike steel). If you want to learn more about the classifications, typifications and markings of brass alloys, we recommend studying GOST 1019-47. Next, we will consider the thermal characteristics of brass and its most common alloys.

Process sequence

• Individual pieces of metal are placed in the crucible, and the crucible itself is placed in the furnace. Then a heating regulator is installed, and bronze, the melting point of which depends on its constituent elements, begins to change shape.
• After this, the crucible is removed from the furnace using a hook, and the alloy itself is poured into the prepared mold.
• Bronze, whose melting point is relatively low, allows you to replace the muffle furnace with an autogen or a blowtorch.

A similar sequence is also suitable for working with other copper alloys. Since, for example, the melting point of bronze and brass is approximately in the same range - 930-1140 and 880-950 degrees, respectively.

Metal characteristics

There are several varieties of brass materials available that have a wide range of applications. The most common metal compounds include:

• multicomponent composition;
• double made of zinc-copper alloy.

The melting point of brass depends on its components. In addition to industry, various interior items and parts of furniture structures are made from it. This became possible thanks to casting, which makes it possible to give the product any shape. Melting at home does not pose any particular problems if you have the appropriate knowledge and the necessary special equipment. To do this, you must know at what temperature this metal composition melts. It has a yellowish color, which without additional protection turns black when exposed to air.

The lower limit at which the brass composition melts is about 880 °C, and its upper value reaches 950 °C. To lower the melting point of brass, more zinc is added to it. The characteristics of the metal are negatively affected by bismuth or lead. Please note that the melting point of copper is different from brass. When the material is heated, they significantly reduce its ability to undergo plastic deformation.

Brass is capable of providing high resistance to corrosion, has increased fluidity and excellent anti-friction characteristics. Thanks to all these properties, it is actively used both in general industrial products and in highly specialized components. The surface of the composition is perfectly polished, which allows it to maintain its magnificent appearance for a long time. Brass and bronze have different melting points, which is taken into account when choosing the operating mode.

Main characteristics of the alloy

Paradoxically, brass itself and the method of its manufacture were known long before the discovery of zinc as a separate metal.
The ancient peoples of the Southern Black Sea region made copper-based alloys with the addition of a substance called galmey, or zinc spar. Very often, products from this combination were used as fake jewelry, which were passed off as gold. In ancient Rome, because of this, brass was called orichalcum, that is, gold-copper. It was used there for minting coins.

The physical parameters of the alloy look like this:

• The specific heat capacity is 0.377 kilojoules per kilogram kelvin at room temperature.
• The specific heat of fusion of brass is 210 Joules per kilogram.
• The melting point is highly dependent on the content of alloying metals and varies from 850 to 950 degrees Celsius.
• Density is about eight and a half tons per cubic meter.
• Resistance per unit length is within 0.07 microohms.

As you can see, brass melts much easier than copper, and therefore is well suited for the manufacture of decorative elements and objects of art, even without the help of specialists.

Physical features of melting homogeneous metals

Brass is a multicomponent alloy based on copper and zinc. It may also contain some other components - tin, lead, iron, nickel, manganese. Copper acts as the main substance, while additional components improve the physical properties of the material (strength, elasticity, electrical conductivity, corrosion potential). Melting of single-component and multi-component alloys has many differences. Therefore, before considering the issue of melting brass, it is necessary to consider the features of melting a homogeneous metal based on copper.

In physics, smelting is a procedure in which a solid metal turns into a liquid state. To melt copper, it must be heated to a temperature of 1.085 degrees Celsius. Typically, heating is carried out with a small temperature increase (~1150 degrees), since in practice copper alloys with the addition of alloying substances are often used, which increases the melting point.

Heating at the chemical-physical level

1. Copper atoms are in a solid state before heating. On a chemical level, this means that they form a strong crystal lattice that is resistant to deformation and retains its shape upon impact.
2. When heated, the potential energy of copper atoms increases, which leads to a deterioration in the strength of the crystalline structure of the material. However, the material retains its hardness because the crystal lattice is not destroyed (although it becomes less dense).
3. When the temperature reaches 1.085 degrees, the copper atoms receive an excess amount of energy, which causes the crystal lattice of the alloy to disintegrate. At the physical level, the alloy changes from a solid to a liquid state.
4. Now several situations are possible. Let's consider the first situation. If the material continues to be heated, it will retain its liquid state. At a temperature of 2.567 degrees, copper goes into a gaseous state (that is, the liquid begins to boil). In metallurgy, evaporation of copper is very rarely performed, since it has no practical benefit.
5. But another situation is also possible. If liquid copper is not heated after melting, then the liquid will gradually begin to cool. This will cause the material to return to a solid form. At the chemical level, the crystal lattice will re-form.

One simple conclusion can be drawn from these theoretical calculations. For one-component compositions, the crystallization temperature and melting temperature are the same. In practice, it is simple to regulate the melting procedure - you just need to reduce or increase the temperature of the fire. During work, it is also necessary to monitor the distribution of fire over the entire area of ​​the metal object. If the temperature distribution is uneven, some components will be in a liquid state, while others will be in a solid state.

Precautionary measures

Melting metals at home does not mean that this can be done simply in a residential area without any restrictions. For bronze casting, you will need a separate room that serves as a workshop, which must be equipped with all the necessary equipment and personal protective equipment for this process. The workshop must be equipped with a working fire extinguisher, and flammable materials and substances cannot be stored in the room itself.

In addition, melting bronze is considered a rather traumatic activity, so all the necessary stages of this procedure should be carried out only by a trained person.

Main areas of use of brass alloys

In mechanical engineering, brass alloys are used for the production of adapters, bushings, and cooling systems for engines. In construction, this alloy is often used in the manufacture of pipe fittings and individual elements of plumbing equipment.

Brass often becomes a material popular in the design environment: its presentable appearance allows numerous interior components to be made from alloys.

April 16, 2017

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Casting process

The process of casting bronze is extremely simple. The oven heats up to certain parameters. Let us remind you once again that to melt tin alloys it is necessary to heat the furnace to a temperature of 900–950°C; the melting temperature of tin-free alloys is an order of magnitude higher – 950–1080°C.

Melting of any bronze composition must begin with calcination of the mold for pouring in a muffle furnace or in a forge. To do this, the oven is first heated to a temperature of 600°C. Then the mold is immersed in it, after which the temperature in the oven must be increased to 900°C. The mold should spend a couple of hours in the oven. After the timer ends, the mold is removed from the oven and cooled to a temperature of 500°C.

The bronze is placed in a cast iron tray and sent straight into a well-heated oven. After the alloy has melted, the metal must be kept in the oven for another five minutes. This way it will warm up well, which means it will be easy to ensure high-quality filling of the casting mold. The crucible is removed from the furnace using a hook, and the process of pouring the molten alloy into the mold is ensured with tongs. It is important to pour the metal in a thin, continuous stream. This is the only way to prevent the process of blurring the shape.

How to properly pour molten bronze into a casting mold

Pouring molten bronze into a mold is a real science. Filling out a large form will be easy. The liquid alloy, under the influence of gravity and its own weight, will itself be evenly distributed throughout the container and displace all existing air. There will be a certain problem with filling out small forms. The fact is that air prevents the uniform redistribution of the alloy over all planes. Therefore, often melting bronze at home does not allow creating high-quality products.

Is it possible to solve a similar problem on my own? Yes, if you have a centrifuge at hand. Centrifugal force will displace the air and allow the alloy to be evenly redistributed over the entire area of ​​the mold. It is necessary to act according to this plan very quickly, before the bronze has time to harden.

You need to remove the pouring from the mold when the alloy has completely hardened. The surface of the workpiece will be rough, and in some places metal deposits will definitely appear. Such defects are eliminated by mechanical grinding. If the oven has been heated correctly, the amount of mechanical grinding will be minimal.

Creating a casting mold

Given the fact that each type of bronze has its own melting point, it is important to have on hand a mold that can withstand the highest heating point of the alloy being described. It is difficult to create it with your own hands at home, but you can try if you carefully study the following instructions.

First you need to create a molding box (foundry workers call it a flask). Its dimensions are one and a half times larger than the dimensions of the future part. The flask is assembled from unplaned boards according to the following scheme: first, the upper frame is knocked down (outwardly it looks like an ordinary box without a bottom and top, but with two crossbars in the middle), then the lower frame (box with a bottom) is knocked down.

Then they begin to create the molding soil. It has a special composition: 75% fine-grained sand, 20% clay and 5% coal dust. All ingredients are combined and mixed thoroughly.

The next stage is making a model that will help form a mold for future casting. Experts recommend making it from wood. The further process is reproduced according to the following algorithm.

• The wooden model is first generously sprinkled with talcum powder, and then carefully placed exactly halfway in the bottom drawer of the flask.
• Then it is filled to the top with ready-made molding soil.
• The entire resulting composition is generously sprinkled with graphite.
• After this, the lower part of the flask (with a bottom) is covered with an upper frame (without a bottom).
• A metal cone is inserted into the upper frame, the narrow part of which should touch the surface of the wooden model. The cone will allow you to form a sprue - a part through which molten bronze will be poured.
• The top box is also filled to the top with molding soil. The filling is carefully compacted with a special mortar.
• After this, the metal cone is carefully removed. Using a sharp knife, the upper flask is removed from the lower frame along with the molding sand. A wooden blank is removed from it. After all the manipulations performed, there should be indentations on both flasks that accurately copy the geometry of one half of the wooden model.

Note! At this stage, you can use a knife to correct slightly crumbling lines. If some of the earth sticks to the model, its deficiency in the flask is made up for. The excess is simply removed.

• We leave the lower and upper parts of the flask until completely dry, and then connect them together so that there is no gap between them. The bronze casting mold is ready.

Using this form, it is possible to create bronze products that do not have a clear pattern and small details.

Casting brass into plaster molds - Metalworker's Guide

Gypsum hemihydrate CaSO4 mixed with the semianhydride substance γCaSO4 is used for castings from non-ferrous alloys, as well as for the manufacture of models and model plates; for small castings a mixture of 20% gypsum, 80% asbestos + water is made. The mechanism of strength formation is hydration (the more asbestos, the less water is taken).

For thin-walled castings with thin relief and a clean surface, instead of asbestos, fine-grained quartz powder is recommended; this mixture is stronger than cement and has low gas permeability, so it is melted in autoclaves at a pressure of 2 MPa for 8 hours, after which it is dried for 10-20 hours. To enhance gypsum mixtures, a surfactant can be introduced into them - this will allow, when foaming the gypsum slip, an increase in the number of gas bubbles, which, during the studied hardening of the mixture, promotes gas permeability.

This gypsum mold has microporosity and high gas permeability, which makes it possible to produce castings from alloys that release an increased amount of gases during hardening.

Chemical processes during hardening of gypsum mixtures

Hardening gypsum-water system

After mixing the gypsum mixture (its basis is anhydrous calcium sulfate, semihydrous gypsum and semianhydride) with water, solid hydrated calcium sulfate is formed in accordance with the equation

2 (CaSO4)• H2O+ 3H2O= 2 (CaSO4• 2H2O). (14)

The hardening time of gypsum depends on the grade of gypsum, the amount of water, the temperature of the water, and the dispersion of the gypsum. With a low water content, the mixture is poorly poured, hardens quickly, and releases an increased amount of heat, with a simultaneous increase in the amount of volume. The hardening time of gypsum increases with increasing water temperature, so cold water should be used.

Technological properties
of gypsum mixtures
With a sufficient amount of water, the gypsum mixture is mushy, quite fluid, hardens slowly and does not have a tendency to increase in volume. After the mixture hardens and the mold is heated before pouring, shrinkage occurs, which can cause cracking of plaster molds. The more water semi-aqueous gypsum contains, the greater its shrinkage when heated.

To reduce shrinkage, an increased amount of pulverized quartz, a minimal amount of gypsum and additives that cause expansion of the gypsum are introduced into the gypsum mixture.

The strength of dried gypsum mixtures increases with a decrease in the content of water and pulverized quartz. Mixtures of gypsum with quartz filler are relatively low-elastic, so forms made from them are deformed slightly. Quartz mixtures require less water than asbestos, since they absorb less of it. The linear shrinkage of such mixtures is also less than asbestos mixtures.

Advantages of gypsum mixtures:

— Satisfactory strength

- easy knockout

Flaws:

- insufficient heat resistance

- limited scope

— the presence of shrinkage of the mixture and possible cracking of the molds. To reduce cracking, pulverized quartz is introduced and the amount of gypsum is reduced.

Casting in ethyl silicate molds

Ceramic molds are used in the production of investment castings or the Shaw process. The molding mixture has a mushy consistency and consists of a solid ceramic component and a liquid binder.

The following refractory fillers are used for ceramic molds:

1. dusty quartz (marshallite) PC1, PC2, PC3. For ceramic molds PK2, PK3.
2. electrocorundum Used for refractory Me and Mg-based alloys.
3. zircon flour
4. titanium dioxide. Used for high-alloy steels and other alloys with a basic oxide nature.

Most often, silica SiO2 is used for ceramic forms in the form of dusted quartz (marshallite). As noted above, quartz, due to changes in its crystalline modifications, is characterized by a sharp change in volume when heated and melts at a temperature of 1550°C.

In addition to quartz, the following is used in the manufacture of ceramic molds:

Alumina

A12O3 - artificial corundum - is used in the form of powder and crumbs, the melting point is 2045 ° Q when heated, no significant volumetric changes occur.

Silimanite

А12О3• SiO2—natural aluminum silicate—suitable for precision casting of non-ferrous alloys; melts at a temperature of 1545° C.

mullite

3A12O3• 2SiO2—aluminum silicate obtained artificially from kaolin; melts at a temperature of 1810°C.

Zircon

ZrSiO4—zirconium silicate; melting temperature up to 2430° C.

Molochit

is calcined kaolin, which, in addition to SiO2 and Al2O3, contains oxides of titanium, iron and alkali metals.

The following is used as a liquid binder:

Alcosols,

or
hydrosols
, which are colloidal solutions of certain organic silicon compounds.
Among them, the most important is tetraethyl orthosilicate,
the chemical formula of which is SiO4 (C2H5)4. The connection of individual filler grains is ensured by a gel film formed under the action of water and an acidic hydrolyzed catalyst.

Heterosiloxanes

are aluminosilicate esters, which, under the influence of moisture contained in the air, hydrolytically split into colloidal solutions of aluminum and silicon compounds. The resulting gel after firing binds the ceramic grains in the form of strong aluminosilicates.

-Chloro-ethoxytitanate

used in benzene solution as a binder for alloys of titanium and other metals with high reactivity.

Aminoalkyl silicate

and
basic aluminum nitrate
are used in the form of alcohol solutions, the hydrolysis and gelation of which are caused by ammonia.

The mushy molding mixture is applied to the model in several layers, sprinkled with ceramic chips and dried. After removing or melting the model, a ceramic mold is formed. Drying is carried out slowly by raising the heating temperature to 120 ° C for several hours.

After removing the remaining carbon compounds and strengthening the silicate gel, the molds are sequentially fired at temperatures of 400, 600, 800, 1000 ° C for 6-8 hours. The molds are poured with metal immediately after firing, until they absorb moisture from the air.

As already indicated, in quartz materials, upon cooling, reverse recrystallization occurs, which can cause cracking of the forms.

Copper casting

Copper is one of the first metals mastered by mankind.

Copper

Thanks to its low melting point and high plasticity, it has not lost its popularity for the fifth millennium. Red metal is widely used both in industry and at home to make jewelry, crafts and parts by casting copper.

In industrial settings, technologies such as

Copper casting

• Casting copper into molds
• Powder metallurgy
• Electroplating
• Hot and cold rolled
• Sheet stamping
• Wire drawing
• Mechanical restoration

They require complex and expensive professional equipment, highly qualified personnel and are accompanied by high energy costs.

Wire drawing of copper

At home, in a small workshop, simple technologies are used, largely repeating the work techniques of the Copper Age masters. This includes copper casting and wire drawing, as well as forging and embossing. Despite the simplicity and antiquity of technological techniques, home craftsmen achieve high quality products. Sufficient casting accuracy is ensured by careful production of the mold.

Characteristics of copper

Copper is a metal with a relatively low melting point (1083C), a density of 8 g/cm3 and high ductility. It occurs in nature in the form of nuggets.

Thanks to these qualities, it became the first metal mastered by mankind. Archaeologists have found tools and weapons in burials dating back to the 3rd millennium BC.

Most likely, humanity mastered copper casting even earlier, at the end of the Stone Age.

Basic properties of metals of the copper subgroup

The Latin name of the metal, Cuprum, is associated with the name of the island of Cyprus, a famous ancient center for the production of bronze products. Copper-based alloys - bronze and brass - have high strength and are less susceptible to oxidation. Bronze was widely used as the main metal of mankind until the development of mass steel production technologies.

Copper has excellent electrical and thermal conductivity. This leads to its widespread use in electrical and thermal engineering.

In addition, copper has pronounced bactericidal properties.

Copper smelting and casting equipment

Casting copper at home does not require particularly complex or expensive equipment. Buying it or making it yourself is quite within the capabilities of a home craftsman.

Required

• Crucibles are cylindrical open vessels.

Examples of graphite crucibles

• Steel tongs for removing and placing the crucible in the furnace.
• Muffle furnace or gas burner.
• Steel hook for removing oxide crust from the surface of the melt.
• Casting mold.

First of all, you need to melt the copper. The better the feedstock is crushed, the faster the melting will occur. Melting will occur in a crucible made of ceramic or refractory clay.

The muffle furnace must be equipped with a thermometer and a glass window for visual inspection.

Electronic temperature control and maintenance system will make copper casting easier and provide better casting quality.

Molds for copper casting are made based on the model. Depending on the chosen technology, the molds can be disposable (from a mixture specially molded in the formwork) or reusable - steel molds. Recently, molds made from high-temperature silicone have become widespread.

At home, disposable forms are more often used. The model is made from wax or special types of plasticine. The model completely repeats the spatial configuration of the future product. When a hot melt is poured into a mold, the wax melts and is replaced by metal, which takes its place and repeats all the details of the mold's relief. This form is called lost wax.

Burnout mold for copper casting

There are also burnt forms. They use a model made of flammable material, such as papier-mâché. In this case, the model burns when a high-temperature melt is poured, the combustion products in the form of gases exit through the filling hole.

SAFETY INSTRUCTIONS WHEN MELTING BRASS

During the process of smelting brass at home , or in industrial enterprises, precautions must be taken.

• The molds are removed using tongs with long handles.
• Work clothes should be made of non-flammable or flame-retardant fabrics and cover the maximum area.
• The face must be protected with a one-piece mask, or goggles and a visor.
• The casting process is carried out under the condition of ensuring high-quality ventilation.
• Surrounding surfaces must be insulated using non-flammable coatings. The most popular and affordable option for such coating is asbestos.
• All manipulations with the molten alloy are carried out over previously prepared sand.
• The presence of moisture is not permissible due to the risk of splashing of molten material.

The melting time of the alloy directly depends on its composition, and the final result depends on compliance with all necessary conditions. Upon completion of the process and complete cooling of the workpiece, it is given the proper appearance. This is achieved by cleaning and polishing.

Copper smelting equipment

The preparatory stage involves the purchase of special equipment. You can melt copper at home if you have:

1. Muffle furnace. Modern design options make it possible to control the heating power with high precision, due to which the melting process is significantly simplified and a better result can be achieved.
2. A crucible designed to hold the charge and melt it.
3. Tongs with which the crucible is pulled out of the furnace. It is worth considering that the surface will heat up, so you need to use a special mechanism made of a heat-resistant alloy.
4. Hook and household vacuum cleaner.
5. Charcoal for surface coating.
6. A mold made of heat-resistant material into which casting will be carried out.
7. Gas burner or forge to increase the ductility of the alloy.

Melting with a gas burner

Purchase professional equipment only if copper casting is carried out periodically. It is characterized by high cost, as well as efficiency in use.

Muffle furnace

The easiest way to melt copper at home is to install a muffle furnace. Among its features we note:

1. The charge can be heated to higher temperatures, thereby increasing fluidity. This is due to high efficiency, since the walls of the structure reflect and accumulate heat.
2. The melting process is accelerated.
3. High performance. Uniform heat distribution allows large quantities of copper to be melted simultaneously.

Melting copper in a homemade furnace

In addition, the muffle furnace is quite easy to install if you follow all safety rules. Problems with installing such equipment at home often arise due to the large size of the structure.

Gas-burner

Copper casting at home using a gas burner is often carried out if copper products are made extremely rarely. Such a process is characterized by low financial costs. When choosing such a technology, the following are taken into account:

1. Low efficiency indicator.
2. At the time of melting, difficulties arise with uniform heat distribution.
3. Work should be carried out in an open space in compliance with fire safety rules.

A gas burner can heat the crucible within a few minutes. It is worth considering that copper will oxidize quickly.

Blowtorch

Melting when using blowtorches is extremely rare. This is due to the low efficiency of this method. As in the previous case, when using a blowtorch, active oxidation of the surface occurs.

Melting copper in a homemade furnace using a blowtorch

When using a blowtorch, take into account the fact that it takes quite a lot of time to heat up the metal. In this case, heating must take place without interruption, since the metal cools quickly, after which it begins to crystallize.

At home, casting copper blanks can be done in a forge. This oven is characterized by the following features:

1. It is often used in blacksmithing.
2. It is worth taking into account the low efficiency indicator, due to which it takes much longer to melt copper.
3. There are two designs: open and closed.

The melting temperature when using a forge is relatively low. Therefore, not all copper can be melted using this method.