Heat treatment technology of copper alloy

What is copper alloy?

Copper alloy is an alloy made of pure copper and one or several other elements. Pure copper is purple red, also known as red copper. The density of pure copper is 8.96, the melting point is 1083 ℃, and it has excellent conductivity, thermal conductivity, ductility and corrosion resistance. It is mainly used for making electrical equipment such as generator, bus, cable, switch device, transformer, heat exchanger pipeline, flat collector of solar heating device, etc.


20200213092304 83728 - Heat treatment technology of copper alloy
Common copper alloys are divided into three categories: brass, bronze and white copper.

White copper

Copper alloy with nickel as the main additive. The binary alloy of copper and nickel is called common white copper; the alloy of white copper with elements such as manganese, iron, zinc and aluminum is called complex white copper. Industrial white copper can be divided into structural white copper and electrical white copper. The structural white copper is characterized by good mechanical properties, corrosion resistance and beautiful color. The white copper is widely used in manufacturing precision machinery, glasses accessories, chemical machinery and ship components. White copper for electrical engineering generally has good thermoelectric properties. Manganin, constantan and Kaotong are manganin white copper with different manganese content. They are materials for manufacturing precision electrical instruments, varistors, precision resistors, strain gauges, thermocouples, etc.

Brass

Brass is an alloy of copper and zinc. If it is only composed of copper and zinc, it is called ordinary brass. Brass is often used to make valves, water pipes, connecting pipes of air conditioners and radiators.
If it is composed of more than two elements of a variety of alloys called special brass. Such as copper alloy composed of lead, tin, manganese, nickel, iron and silicon. Special brass is also called special brass. It has high strength, high hardness and strong chemical corrosion resistance. The mechanical properties of cutting are also outstanding. Brass has strong wear resistance. The seamless copper tube drawn by brass is soft and wear-resistant. Brass seamless pipe can be used for heat exchanger and condenser, low temperature pipeline, subsea transportation pipe. Manufacturing sheet, bar, flange, pipe, casting parts, etc. It contains 62% – 68% copper, has strong plasticity and can be used to manufacture pressure equipment.
According to the different kinds of alloy elements in brass, brass can be divided into two kinds: common brass and special brass. Brass used for pressure processing is called deformed brass. Brass is a copper alloy with zinc as the main additive element, which has a beautiful yellow color, collectively known as brass. Copper zinc binary alloy is called common brass or simple brass. Brass with more than three elements is called special brass or complex brass. Brass alloy containing less than 36% zinc is composed of solid solution and has good cold working performance. For example, brass alloy containing 30% zinc is often used to make bullet case, commonly known as bullet
Case brass or 73 brass. The brass alloy with zinc content between 36% and 42% consists of and solid solution, of which the most commonly used one is 64 brass with zinc content of 40%. In order to improve the performance of common brass, other elements are often added, such as aluminum, nickel, manganese, tin, silicon, lead, etc. Aluminum can improve the strength, hardness and corrosion resistance of brass, but it can reduce the plasticity, so it is suitable to be used as condensation tube and other corrosion-resistant parts of sea going vessels. Tin can improve the strength and corrosion resistance of brass to sea water, so it is called Navy brass, which is used for ship thermal equipment and propeller, etc. Lead can improve the cutting performance of brass; this kind of free cutting brass is often used as clock parts. Brass castings are often used to make valves, pipe fittings, etc.

Bronze

Bronze is the earliest alloy used in China, which has a history of more than 3000 years.
Bronze originally refers to copper tin alloy. Later, all copper alloys except brass and white copper are called bronze, and often preceded by the name of the first major added element. Tin bronze has good casting, antifriction and mechanical properties, and is suitable for bearing, worm gear, gear, etc. Lead bronze is a widely used bearing material for modern engines and grinding machines. Aluminum bronze has high strength, good wear resistance and corrosion resistance. It is used for casting high load gears, shaft sleeves, marine propellers, etc. Phosphor bronze has high elastic limit and good conductivity, which is suitable for making precision spring and electric contact components. Beryllium bronze is also used to make non sparking tools used in coal mines and oil depots. Beryllium copper is a supersaturated solid solution copper base alloy, which has good mechanical, physical, chemical and corrosion resistance properties. When p / M is used to make dies made of tungsten steel, high carbon steel and high temperature resistant superalloy, due to large electrode loss and slow speed, tungsten copper is an ideal material. Bending strength ≥ 667mpa.

Heat treatment of copper alloy

The heat treatment of copper alloy is mainly heating and annealing for different purposes. Only some alloys, such as beryllium bronze, can be quenched and tempered. Annealing for different purposes includes softening annealing, finished annealing and billet annealing.

Softening annealing

That is to say, recrystallization annealing for softening between two cold rolling is also called intermediate annealing. After cold rolling, the alloy will produce fiber structure and work hardening. After heating the alloy above the recrystallization temperature and cooling it slowly after holding for a certain period of time, the alloy will recrystallize into fine grain structure to obtain good plasticity and low deformation resistance, so as to continue cold rolling. This kind of annealing is the most important heat treatment in copper alloy rolling.

Finished product annealing

That is to say, after cold rolling to the finished product size, the final annealing of different states and properties can be obtained by controlling the annealing temperature and holding time. The annealing of finished products has the requirements of controlling state and properties, such as obtaining soft (m) state, semi-hard (Y2) products and obtaining better deep drawing products by controlling the grain structure. In addition to the annealing above the recrystallization temperature, there are also low temperature annealing at the recrystallization temperature.

Blank annealing

It is a kind of heat treatment method to eliminate the hardening caused by incomplete hot deformation during hot rolling by recrystallization annealing and to make the structure uniform by annealing. Quenching and tempering (aging): for some solid solution alloys that can be dissolved and precipitated and undergo eutectoid transformation, when the temperature is higher than the transformation point, the strengthened phase is fully dissolved through heat preservation, forming a uniform solid solution, and then forming a supersaturated solid solution in quench. After low temperature or room temperature, the strengthened phase is precipitated or transformed to control the heat of alloy performance Rationale.

Annealing process system

The annealing process is determined according to the alloy properties, work hardening degree and product technical conditions. The main technological parameters of annealing are annealing temperature, holding time, heating speed and cooling mode. The determination of annealing process system shall meet the following three requirements:

  • ① To ensure the heating uniformity of the annealed material, so as to ensure the uniform structure and performance of the material;
  • ② Ensure that the annealed material is not oxidized and the surface is bright;
  • ③ Save energy, reduce consumption and improve yield. Therefore, the annealing process system and equipment of copper should meet the above conditions. Such as reasonable furnace design, fast heating speed, protective atmosphere, accurate control, easy adjustment, etc. Table 1 lists the annealing process of some common copper alloys.

Selection of annealing temperature

In addition to the properties and hardening degree of the alloy, the purpose of annealing should also be considered. For example, for intermediate annealing, the upper limit of annealing temperature should be taken and the annealing time should be appropriately shortened; for finished annealing, the emphasis should be placed on ensuring the product quality and performance are uniform, the lower limit of annealing temperature should be taken and the fluctuation of annealing temperature should be strictly controlled; for thick specification, the annealing temperature should be higher than that of thin specification The annealing temperature of the sheet is higher than that of the strip.

Heating rate of annealing

It shall be determined according to the alloy property, charging amount, furnace structure, heat transfer mode, metal temperature, temperature difference in furnace and product requirements. Because the rapid heating can improve the productivity, fine grains and less oxidation, the intermediate annealing of semi-finished products mostly adopts the fast heating; for the annealing of finished products, less loading and thin thickness, the slow heating is adopted.

Heat preservation time

In the design of furnace temperature, in order to improve the heating speed, the temperature of heating section is relatively high. When the temperature reaches a certain temperature, heat preservation shall be carried out. At this time, the furnace temperature is close to the material temperature. The holding time is to ensure the uniform heat penetration of annealed materials.

Cooling mode

Air cooling is the main way for the annealing of finished products. Sometimes water cooling can be used for the intermediate annealing. For the alloy with serious oxidation, the oxide skin can burst and fall off under rapid cooling. However, quenching is not allowed for alloys with quenching effect.

Table 1 annealing process of some common copper alloys

Grade of alloy

Annealing temperature/℃

Holding time/min

Intermediate annealing

Finished product annealing

HPb59-1HMn58-2QAl7QAl5

600~750

500~600

30~40

HPb63-3QSn6.5-0.1QSn6.5-0.4

QSn7-0.2QSn4-3

600~650

530~630

30~40

BFe3-1-1BZn15-20Bal6-1.5BMn40-1.5

700~850

630~700

40~60

QMg0.8

500~540

30~40

B19B30

780~810

500~600

40~60

H80H68HSn62-1

500~600

450~500

30~40

H95H62

600~700

550~650

30~40

BMn3-12

700~750

500~520

40~60

TU1TU2TP1TP2

500~650

380~440

30~40

T2H90HSn70-1HFe59-1-1

500~600

420~500

30~40

QCd1.0QCr0.5QZr0.4QTi0.5

700~850

420~480

30~40

Solution aging

The process parameters of solution (quenching) – aging (tempering) are mainly determined by heating temperature, heating speed, holding time, cooling speed, heating medium and transfer time interval during water cooling. The upper limit of quenching temperature is lower than the eutectic temperature, and the lower limit is higher than the solid solubility line temperature. The holding time mainly depends on the dissolution rate of strengthening phase. In order to maintain a good quenching effect, the shorter the quenching transfer time is, the better, and the water temperature is generally not higher than 25 ℃. The cooling rate mainly considers two factors. One is that the particles will be precipitated if the cooling rate is too slow, and the residual stress or crack will be produced if the cooling rate is too fast. During tempering (aging), the uniform precipitation and distribution of strengthening particles are mainly ensured. Table 2 shows the process system of solution (quenching) – aging (tempering) for some copper alloys.

Table 2 Process system of solid solution (quenching) – aging (tempering) for some copper alloys

Grade of alloy

Solution (quenching)

Aging (tempering)

Heating temperature/℃

Holding time/min

Cooling medium

Heating temperature/℃

Holding time/min

QBe2

700~800

15~30

water

300~350

120~150

QCr0.5

920~1000

15~60

400~450

120~180

QZr0.2

900~920

15~30

420~440

120~150

QTi7.10

850

30~60

400~450

120~180

Bal6-1.5

890~910

120~180

495~505

90~120

Atmosphere control in heat treatment furnace

According to the characteristics of the interaction between the medium and the surface of the material in the furnace, the heat treatment is divided into ordinary heat treatment (i.e. air as the medium), protective atmosphere heat treatment (i.e. bright annealing) and vacuum heat treatment.

Flame furnace atmosphere

This is an old-fashioned common heat treatment method, which uses combustion heating such as gas as fuel.
Oxidizing atmosphere means that the fuel is burned under the condition of excess air, so that there is more oxygen in the furnace.
Reducing atmosphere, the air in the furnace is insufficient in the combustion process. Due to the insufficient combustion of fuel, there are more CO and CO2.
The neutral atmosphere is the atmosphere controlled between oxidation and reduction in the furnace. The micro oxidation atmosphere, which contains a small amount of oxygen in the furnace, has a certain oxidation effect.
The atmosphere in the furnace is controlled according to the properties and technical requirements of the alloy. Generally, copper and copper alloy do not use oxidizing atmosphere, because not only the surface quality is damaged, but also the components with low melting point, such as Sn, Pb, Sn, Zn, CD, are easy to evaporate. Therefore, reductive or neutral furnace atmosphere is mostly used. For the alloy which is easy to absorb hydrogen to produce “hydrogen embrittlement” and sulphurization during heat treatment, micro oxidation atmosphere is usually used, such as nickel alloy, pure copper and so on. The flame heating furnace will be gradually replaced by the annealing furnace with electric heating and continuous heating of protective gas.

Protective atmosphere

Due to the progress of sealing technology and protective gas manufacturing technology, most of them are heated in protective atmosphere. The composition of the protective gas shall not react with the alloy during heating; it shall not corrode the components, thermocouples and resistance devices of the furnace; it shall be stable in composition, simple in manufacture and convenient in supply.
Most of the protective atmosphere is heated by electric heating. It is a continuous annealing furnace with electric induction heating after the 1990s. It is annealed online with protective atmosphere and forced circulation air, which simplifies the process and improves the surface quality and production efficiency. In the past, the protective atmosphere used to be nitrogen, carbon dioxide, purified gas or water vapor after gas combustion, etc. due to the poor sealing of the furnace, low concentration of the protective gas used, high cost and other reasons, no satisfactory results have been achieved. Now, the main component of shielding gas is nitrogen hydrogenation. According to the different ratio of nitrogen and hydrogen, hydrogenation protection is more effective for brass. Because the thermal conductivity of hydrogen is 1.7 times that of nitrogen, the heat conduction velocity can be greatly increased. After hydrogenation, the heating time can be shortened, especially under the action of strong wind, the convective heat transfer effect is better, the annealing material can be heated uniformly, and the homogeneity of structure and property of heat-treated copper material can be ensured. Under the action of strong wind, the volatiles of lubricant are removed and the surface quality is improved.

Several methods of manufacturing protective gas:

  • ① Ammonia decomposition gas: after vaporization, liquid nitrogen enters into the cracker filled with nickel catalyst. At the temperature of 750-850 ℃, ammonia and hydrogen are generated by cracking, and then they are sent into the furnace after purified water and residual ammonia removal. This protective gas is suitable for annealing brass. According to the calculation, 1.97m3 hydrogen and 0.66m3 nitrogen can be generated from 1kg ammonia.
  • ② Ammonia decomposition gas combustion purification: if the proportion of ammonia needs to be reduced, part of hydrogen can be burned out, and nitrogen can be added in the combustion process.
  • ③ The ammonia decomposition gas is added to the air separation nitrogen (or liquid nitrogen vaporization) and sent to the furnace after purification, so as to obtain the protective gas with different proportion of hydrogenated nitrogen according to the needs.
  • ④ When the dosage is small, bottled nitrogen and hydrogen can be used as protective gas.
  • ⑤ The gas after gas combustion, generally containing 96% nitrogen and less than 4% carbon monoxide and hydrogen, needs to be purified before use.
  • ⑥ The purity of pure nitrogen can reach 99.9%. The new process of nitrogen production by pressure swing adsorption air separation of coke molecular sieve adopts oil-free compressor. The oxygen content in nitrogen is less than 5 × 10-6, and the dew point is – 65 ℃. This is the most suitable annealing for pure copper and Tin Phosphorus Bronze with high oxygen content.

Vacuum heat treatment

In the process of annealing and heating, the space of the charge is vacuumized, and the annealed material does not contact with any medium. There are two forms of vacuum annealing: external heat and internal heat. The external heating type is that the heating element is placed outside the furnace tank, which is electrically heated. The external heating type vacuum furnace is simple in structure, easy to manufacture and convenient in loading and discharging. However, the temperature rise is slow, the heat loss is large, and the life of furnace is low. The internal heating type is that the heating element is in the furnace tank, and the heat treatment material is also placed in the furnace tank. Usually, tungsten, molybdenum, graphite and other materials are used as the heating element. It is characterized by fast temperature rise, high heating temperature and long furnace life. However, the structure of the furnace is complex, the investment is large and the cooling is slow. When vacuum annealing is used, pure copper is (10-1 ~ 10-2) × 133.3pa, and most copper alloys are (10-2 ~ 10-3) × 133.3pa. During the vacuum annealing, the vacuum can be broken only when the temperature is below 100 ℃ to prevent the oxidation of the annealed material. In recent years, vacuum annealing is not recommended for the heat treatment of copper alloy, because vacuum is a bad conductor of heat, it only relies on heat radiation heat transfer, especially for the surface bright material, which is more difficult to heat by radiation. In addition to the low thermal efficiency, it is difficult to get heat-treated products with uniform performance. Therefore, it is gradually replaced by protective atmosphere and air cushion continuous annealing.

Heat treatment furnace

Heat treatment equipment is mainly heat treatment furnace. The following conditions shall be considered when selecting the heat treatment furnace: that is, to meet the requirements of the heat treatment process, to ensure the quality and performance; to select the appropriate heat source, to meet the needs of production; the furnace has simple structure, accurate temperature control, durability, and less investment; it has high degree of automation, high production efficiency, good working conditions and convenient operation.

Heat treatment furnace for common copper and copper alloy

Common annealing furnace for copper alloy: according to the structure, there are box furnace, well furnace, walking furnace, car bottom furnace, roller bottom furnace, chain type water seal furnace, single chamber furnace, double chamber furnace, bell type furnace, etc. According to the production mode: monomer batch annealing furnace, air cushion continuous annealing furnace, etc. According to the atmosphere in the furnace, there are annealing furnace with or without protective atmosphere, annealing furnace with protective atmosphere and vacuum annealing furnace. According to the heat source, there are coal furnace, gas furnace, heavy oil furnace, resistance furnace and induction furnace. There are three types of quenching furnace: vertical type, horizontal type and well type.

Common copper alloy heat treatment furnace

At present, the main trends of the development of heat treatment furnace are: improving design, finding new process and improving heat utilization efficiency; adopting low or high temperature rapid annealing to reduce oxidation and dezincification; adopting protective gas annealing and forced circulation ventilation to make it rapidly heated, evenly temperature and improve the quality of annealing products; enhancing sealing effect, simplifying process and improving integration and continuity level.
Air cushion furnace is a common annealing furnace for copper alloy single strip, which has both on-line annealing and separate annealing. Nowadays, air cushion annealing furnace often combines pickling, washing, drying, surface coating, passivation treatment, etc. Compared with bell type annealing furnace, it has high furnace temperature and short annealing time, which can realize high temperature and rapid annealing. For example, for 0.05 ~ 1.5mm thick strip, it only takes a few seconds to heat, and for thick strip, it only takes more than one minute. The heating speed is adjustable, the heating is even, the annealed surface quality is good, and the microstructure and properties are even.
The ratio of the maximum thickness to the minimum thickness is 10:15, the ratio of the maximum width to the minimum width is 2, and the ratio of the thickness to the width of the same strip is less than 1 / 250. At present, it can realize annealing of strip with thickness of 0.05-1.5m m and width of 250-1100mm. The annealing speed is (4-100) m / min, the production capacity is 5t / h, the thermal efficiency is 85%. The heat source can be heated by electricity or gas.
Air cushion furnace is composed of uncoiler, welding, degreasing, furnace, pickling, shearing, coiling and roll, control roll, looper tower, etc.
Air cushion annealing furnace is a new technology of continuous heat treatment. When the strip passes through the furnace, the upper and lower surfaces are lifted and suspended in the heat treatment furnace by the high-temperature air flow evenly sprayed, the distance between the upper and lower air jets is 80mm, and the strip lifted and floated is contactless. For continuous annealing, there are two uncoilers and two coilers. In order to improve the surface quality of the strip and remove the rolling oil or emulsion on the surface of the strip, the strip should be degreased, washed and dried after entering the annealing furnace. When annealed pure copper or bronze strip, the surface of the strip will not be oxidized or pickled, and the heating zone and cooling zone will be filled with 2% ~ 5% H2, containing 95% ~ 98% N2. When annealing brass strip, heating zone and cooling zone are not filled with protective gas, but acid pickling, water washing and drying are needed. For some special purpose copper alloys, coating and drying are carried out after annealing. In order to prevent the strip from running off, photoelectric centering device and rectifying roller are set at the upper and lower nozzles of the heating area and cooling area, and the edge unevenness rate of the strip after coiling is less than ± 1mm. Some air cushion annealing continuous furnaces also have tension leveling devices. The adoption of air cushion continuous furnace greatly improves the surface quality and the uniformity of the product structure and performance.

Pickling and surface cleaning

Pickling

Pickling process

In the process of hot rolling and heat treatment of copper alloy, the surface of slab or strip is easy to be oxidized. In order to remove the oxide skin on the surface, pickling is needed. The usual pickling procedure is: Pickling – cold water washing – hot water washing – drying. The working process of the pickling train used at present also needs to go through this procedure.
The pickling process of the production workshop has the following requirements: the pickling of the material surface shall be clean, the effective acid and acid concentration shall be adopted, the pickling time shall be short, the utilization efficiency of the acid shall be high, the anti pollution measures shall be taken, the protection of human body shall be paid attention to, and the recycling of waste liquid and products shall be considered.
Sulfuric acid or aqueous solution mixed with nitric acid is mainly used in acid pickling. The reaction process is: the oxide skin is dissolved, or is peeled by the mechanical action of the oxide skin by the gas (hydrogen bubble) generated by chemical reaction. The chemical reaction formula of copper and copper alloy with acid solution is as follows:

  • CuO+H2SO4→CuSO4+H2O
  • Cu2O+H2SO4→Cu+CuSO4+H2O
  • Cu+2HNO3→Cu(NO3)2+H2

For the surface oxidation of copper and its alloys, the outermost layer is copper oxide Cuo, and the inner layer is cuprous oxide Cu2O. The dissolution of cuprous oxide in sulfuric acid is very slow. In order to make the surface treatment clean and accelerate the dissolution of cuprous oxide, an appropriate amount of oxidant potassium dichromate K2Cr2O7 or NO3 should be added to the sulfuric acid solution. But this will worsen the working conditions and reduce the service life of the acid tank. The chemical reaction formula is as follows:

  • K2Cr2O7+2H2SO4+3Cu2O→CuSO4+Cu5(CrO­4)2+2H2O+K2SO4
  • 4HNO3+H2SO4+CuO→CuSO4+Cu(NO3)2+2NO2+3N2O

For pure copper, bronze, zinc and white copper and copper alloy containing be, Si and Ni which are not easy to clean, the reaction with dilute acid is slow, and 0.5% ~ 1% potassium dichromate can be added. Some add 0.5% ~ 1% hydrochloric acid or hydrofluoric acid to the acid wash solution in order to purify the oil and enhance the pickling effect.
Pickling time is related to the concentration and temperature of pickling solution. Generally, the concentration of acid washing solution is 5% ~ 20%, the temperature is 30 ~ 60 ℃, and the time is 5 ~ 30min. It can be adjusted according to the effect of pickling, such as room temperature in summer, steam heating in winter, upper limit for pure copper and lower limit for brass. The higher the acid concentration and temperature is, the more severe the acid mist will be and the worse the equipment, environment and working conditions will be. In order to reduce the pollution of smoke, a certain amount of buffer is often added to the acid wash solution, and low temperature pickling is used as far as possible.
The defects during pickling include over pickling, corrosion spots, residual acid traces, water traces, etc. Over pickling is mainly caused by high acid concentration, high temperature and long time. Over pickling not only produces corrosion spots, but also reduces the surface quality, and also excessively consumes acid and metal. On the contrary, if the acid concentration, temperature and time are too low, the oxide skin will not be cleaned thoroughly. The residual acid trace and water trace are mainly caused by unclean cleaning or incomplete drying. In order to achieve rapid pickling and improve the surface quality, a new method of electrolytic pickling and ultrasonic pickling has emerged.
In the pickling process, the concentration of pickling solution will continue to decrease. When the sulfuric acid content of acid solution is less than 50-100g / L and the copper content is more than 8-12g / L, new acid solution shall be added or replaced in time. When preparing new acid solution, water must be drained before adding acid to ensure safety. It is forbidden to use iron tools in the acid tank to prevent spots on the surface of the strip. The replaced waste acid can be neutralized with ammonia, copper sulfate and copper powder can be extracted and made into microelement fertilizer, and Regenerated Copper and acid can also be obtained by electrolysis. The specific gravity of acid is measured by Baume when preparing acid solution.

Surface cleaning

There are many methods of surface cleaning, acid pickling is one of them. There are also commonly used mechanical cleaning methods, such as surface cleaning machine cleaning and manual repair.

Surface cleaning machine cleaning and manual repair

The purpose is to remove the residual copper oxide powder and acid trace on the surface of the rolled piece after pickling, so as to improve the surface quality. Common surface cleaning machines are: single roll cleaning machine and double roll cleaning machine, as shown in Figure 1.
The single roller cleaning machine can only clean one surface at a time, each brush roller has a support roller, which plays a compaction role. The linear speed of the brush roller is 0.6-6m/s, the feed speed of the compaction roller is 0.2-0.8m/s, and the linear speed of the brush roller is 3-10 times higher than the linear speed of the compaction roller. The rotation direction of the brush roller is the same or opposite to the feed direction of the pressing roller. The brush roller can be made of brown, nylon wire, steel wire, Tin Phosphorus Bronze Wire and other materials. The diameter of the brush roller is about 200 ~ 300 mm. For the double roller cleaning machine, the upper and lower surfaces can be cleaned at the same time. When wet brushing, it can avoid the flying of copper oxide powder, but the brush wire material should avoid corrosion and rust. Dust collector shall be set for dry brushing to recover copper oxide powder.
Local copper oxide powder, discoloration, water stains and spots on the surface of the rolled piece can be removed by wire brush or sandpaper, and defects such as pockmarks, cracks, peeling, pressing pits and ash inclusions on the surface can be repaired by scraper.
In order to prevent surface oxidation and discoloration, inhibitors are sometimes used for surface treatment. Chromate can be used as an effective antirust agent, but + 6 chromic acid is toxic and will pollute the environment. Now, an organic inhibitor, benzotriazole (BTA,C6H5N3), is used to form a protective coating on the surface of copper alloy, i.e. CuBTA coating. The thickness and shape of BTA solution are different due to the temperature, pH value and the type of alloy. This method is suitable for treatment in clean environment, but not ideal in corrosive environment. At present, chromic acid is still used to remove the oxide on the surface of copper and the matrix polluted on the surface.

Calendering

For products requiring high surface finish, sometimes the process of calendering or polishing is used. Generally, roll mill is used for calendering, with large roll diameter, low rolling speed, and very high surface finish. The total reduction processing rate during calendering is 3% ~ 10%. By multi pass calendering, the surface of the product can be close to the surface finish of the roller. When calendering, the use of lubricating oil requirements are very high, viscosity is very small, such as white oil, kerosene and so on.

Polishing

The surface polishing is a roller type polishing machine with nylon roller or flax roller. Its structure is similar to the double roller cleaning machine. Two or three pairs of nylon rollers are used. Polishing agent and talcum powder with a particle size of 3.5-5 μm are sprayed during polishing. The polishing agent is a mixture of water and Cr2O3, with a ratio of 10:1.

Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

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heat treatment technology of copper alloy - Heat treatment technology of copper alloy
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Heat treatment technology of copper alloy
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The heat treatment of copper alloy is mainly heating and annealing for different purposes. Only some alloys, such as beryllium bronze, can be quenched and tempered. Annealing for different purposes includes softening annealing, finished annealing and billet annealing.
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