Bronze is an alloy. Characteristics of bronze

Bronze is an alloy based on copper. The auxiliary metals can be nickel, zinc, tin, aluminum and others. In this article we will consider the types, technological features, chemical. Composition of bronze, as well as methods of its production.

Classification

1. The chemical composition of this metal is divided into two groups. The first is tin bronzes. In them, tin is the main alloying element. The second is tinless. Below, we will discuss this in more detail.

2. On the basis of technological features, bronze is usually divided into deformable and foundry ones. The former are well processed under pressure. The latter are used for shaped castings.

This metal in comparison with brass has much better antifriction, mechanical properties, and also corrosion resistance. In fact, bronze is an alloy of copper and tin (as the main auxiliary element). Nickel and zinc here are not the main alloying elements, for this use components such as aluminum, tin, manganese, silicon, lead, iron, beryllium, chromium, phosphorus, magnesium, zirconium and others.

Tin bronzes: Foundry

Let's see what a metal is like. Tin bronze (the photo below shows cast details) is an alloy that has a lower fluid flow than other types. However, it has an unimportant volumetric shrinkage, which makes it possible to obtain shaped bronze castings. These properties cause the active use of bronze when casting antifriction parts. Also, the alloy in question is used in the manufacture of valves intended for use in an aqueous medium (including in seawater) or in steam, in oils and under high pressure. There are also so-called non-standard foundry bronzes of responsible designation. They are used in the production of bearings, gears, bushings, parts of pumps, low-sealing rings. Such parts are designed to work under high pressure conditions, at high speeds and small loads.

Lead bronze

This subspecies of foundry tin alloys is used in the manufacture of bearings, seals and shaped castings. Such bronzes are characterized by low mechanical properties, so that in the process of manufacturing bearings and bushings they are simply applied to the steel substrate in the form of a very thin layer. Alloys with an increased content of tin have higher mechanical properties. Therefore, they can be used without a steel base.

Tin bronzes: deformable

The alloys processed by pressure are usually divided into the following groups: tin-phosphorous, tin-zinc and tin-zinc-lead. They have found their application in the pulp and paper industry (from them make grids) and mechanical engineering (production of springs, bearings and machine parts). In addition, these materials are used in the manufacture of bimetallic products, bars, belts, bands, gears, gears, bushings and gaskets of high-loaded machines, tubes of instrumentation, pressure gauges. In electrical engineering, the widespread use of bronze (deformable) is explained by excellent mechanical properties (along with high electrical characteristics). It is used in the manufacture of current-carrying springs, plug-in connectors, contacts. In the chemical industry, tin wire is made of tin bronze, in precision mechanics - reinforcement, in the paper industry - scrapers, in automotive and automotive - bushings and bearings.

These alloys can be supplied in a particularly hard, solid, semi-solid and soft (annealed) state. Tin bronzes are usually treated cold (rolling or drawing). Hot metal is only subjected to compression. Under pressure, bronze is perfectly processed both in cold and hot form.

Beryllium bronze

It is an alloy belonging to the group of precipitation-hardening metals. It has high mechanical, physical and elastic properties. Beryllium bronze has a high level of heat resistance, corrosion resistance and cyclic strength. It is resistant to low temperatures, it does not magnetize and does not give out sparks when striking. Tempering of beryllium bronzes is carried out at temperatures of 750-790 degrees Celsius. Addition of cobalt, iron and nickel contributes to the thermal processing slowing the rate of phase transformations, this greatly facilitates the technology of aging and hardening. In addition, the addition of nickel promotes an increase in the temperature of recrystallization, and manganese can replace, albeit not fully, expensive beryllium. The above bronze characteristics make it possible to use this alloy in the manufacture of springs, springing parts, and membranes in the watch industry.

Copper Alloy with Manganese

Such bronze is characterized by special high mechanical qualities. It is processed by pressure, both in the cold and in the hot state. This metal is characterized by high heat resistance, as well as corrosion resistance. A copper alloy with the addition of manganese has found wide application in furnace fittings.

Silicon Bronze

This alloy, which includes nickel, less often - manganese. Such a metal is distinguished by ultrahigh mechanical, antifrictional and elastic properties. At the same time, silicon bronze does not lose its plasticity in conditions of low temperature. The alloy is well soldered, processed by pressure at both high and low temperatures. The metal in question is not magnetized, it does not spark at impacts. This explains the wide use of bronze (silicon) in marine shipbuilding in the manufacture of antifriction parts, bearings, springs, grids, evaporators, nets and guide bushings.

Foundry all-tin alloys

This type of bronze is characterized by good corrosion, antifriction properties, as well as high strength. They are used to manufacture parts that are used in particularly difficult conditions. These are, for example, gears, valves, bushings, gears for powerful turbines and cranes, worms that work in the paddle with reinforced steel parts, bearings operating under high pressure and shock loads.

How to make bronze?

The manufacture of this metal must be carried out in special furnaces used for the smelting of copper alloys. Charge for bronze can be made of fresh metals or with the addition of secondary waste. The smelting process is usually carried out under a layer of flux or charcoal.

The process using a mixture of fresh metals occurs in a certain sequence. First, the required amount of flux or charcoal is loaded into a heavily heated furnace. Then put copper there. After waiting for its melting, raise the heating temperature to 1170 degrees. After this, the melt must be deoxidized, for which phosphorous copper is added. This process can be carried out in two steps: directly in the furnace, and then in the ladle. In this case, the additive is introduced in equal proportions. Further, the necessary alloying elements heated up to 120 degrees are added to the melt. Refractory components should be introduced in the form of ligatures. Further, the molten bronze (the photo below demonstrates the smelting process) is mixed until all the added substances have dissolved completely and is heated to the prescribed temperature. When issuing the resulting alloy from the furnace, before casting, it must be finally deoxidized by a residue (50%) of copper phosphorous. This is done to release bronze from oxides and increase the fluidity of the melt.

Smelting on the basis of negotiable materials

In order to produce bronze using secondary metals and waste, the smelting should be carried out in the following order. First, the copper is melted and deoxidized by phosphorous additives. Then they add circulating materials to the melt. After this, complete melting of the metals is awaited and the alloying elements are introduced in the appropriate sequence. In the event that the burden consists of a small amount of pure copper, you must first melt the recycled metals, and then add copper and alloying elements. Melting is carried out under a layer of flux or charcoal.

After melting the charge and heating it to the required temperature, the mixture is finally deoxidized with phosphorous copper. The melt is then covered with calcined carbon or dried flux from above. The consumption of the latter is 2-3 percent of the mass of the metal. The heated melt is aged for 20-30 minutes, periodically mixed, and then the separated slag is removed from its surface. All bronze is ready for casting. For better removal of slag in the ladle, you can add quartz sand, which thickens it. To determine whether bronze is ready for casting into molds, a special technological test is carried out. The fracture of such a sample must be homogeneous and pure.

Aluminum bronze

It is an alloy of copper and aluminum as an alloying element. The process of melting this metal differs significantly from the above, which is explained by the chemical characteristics of the auxiliary component. Consider how to make bronze using aluminum alloying components. In the manufacture of this type of alloy using recycled materials in the charge, the deoxidizing operation with phosphorous components is not used. This is explained by the fact that phosphorus is characterized by a lower affinity for oxygen molecules than aluminum. You should also know that this type of bronze is very sensitive to overheating, so the temperature should not exceed 1200 degrees. In an overheated state, aluminum is oxidized, and the bronze alloy is saturated with gases. In addition, the oxide formed during the melting of this type of bronze is not restored by the addition of deoxidizers, and it is very difficult to remove it from the melt. The oxide film has a very high melting point, which significantly reduces the fluidity of bronze and causes rejection. Melting is carried out very intensively, on the upper limits of the heating temperatures. In addition, do not delay the ready melt in the oven. When melting aluminum bronze as a covering layer, it is recommended to use flux, which consists of 50% of soda ash and 50% of cryolite.

The finished melt is refined by molding it into manganese chloride or zinc chloride (0.2-0.4% of the total mass of the charge) before casting. After this procedure, the alloy should be allowed to stand for five minutes until the gas evolution ceases completely. After that, the mixture is brought to the required temperature and poured into molds.

In order to prevent segregation into the melt of bronze with a high content of lead impurities (50-60%), it is recommended to add 2-2.3% nickel in the form of copper-nickel ligatures. Or as a flux, it is necessary to use the alkali metal sulphate salt. Nickel, silver, manganese, if they are part of the bronze, should be introduced into the melt before the tin additive procedure. In addition, to improve the quality of the resulting alloy, it is sometimes modified with minor additives based on refractory metals.