Foreign heat treatment technology and heat treatment equipment

Foreign heat treatment technology and heat treatment equipment
1. Current status of heat treatment technology

(1) Promote the application of high-pressure air quenching

Foreign heat treatment manufacturers attach great importance to cooling during the heat treatment process. According to the technical and technological requirements of the product, slow cooling, oil quenching, and one-time gas quenching can be performed. Rapid atmosphere circulation cooling uses high-pressure gas injection into the cooling chamber, and the computer controls the flow rate and flow rate changes to achieve the cooling rate within a specific time, so as to achieve the required cooling curve during the heat treatment process and ensure the heat treatment quality of the parts. In the past, the quenching gas used in the gas quenching method was nitrogen, helium, etc., but now it is strongly sprayed with air to cool the workpiece at a very rapid rate. After quenching, the surface has only a very thin oxide film, which is off-white, and the color of the parts is still beautiful. , And save a lot of nitrogen and inert gas, so that the cost of heat treatment is further reduced.

The combination of vacuum low pressure carburizing and high pressure gas quenching is an advanced carburizing and quenching process today. It has fast carburizing speed, excellent carbide structure, small quenching cracking and deformation, energy saving and carburizing agent raw materials, carburized parts The surface quality is good and it is conducive to environmental protection.

(2) The heat treatment equipment adopts oil cooling

Fan cooling, heat exchanger cooling, quenching oil tank cooling and other cooling devices all adopt oil-sealed self-cooling, completely replacing the water-cooled circulation system, and the entire heat treatment furnace does not require any cooling water. For example, hot air circulation fan cooling: change the inlet and outlet pipes of the original water cooling jacket to oil pipes, and place a small oil tank with a diameter of 102mm near the fan. The oil cooling system is fully enclosed. When the fan bearing heats up, the proportion of heated oil is small. , Naturally float upward, causing natural circulation of oil. In the case of a small oil tank with oil storage and natural heat dissipation, the hot oil is added to the circulation after being cooled, so as to completely replace water cooling without fuel consumption and no power. The water in the plate heat exchanger of the quenching oil tank is replaced with cooling oil. The cooling oil is heated by the heat exchange of the hot oil. The change in the specific gravity of the oil causes the cooling oil to circulate by itself. A heat sink is added to the oil tank on the top of the furnace to match the fan. It can achieve the effect of full oil cooling and save a lot of cooling water.

(3) Hydrogen probe is used on the nitriding furnace

The German company Ipsen has applied hydrogen probes and corresponding technologies to measure and control the nitrogen potential in the nitriding furnace to adjust and control the atmosphere of the nitriding furnace and realize the modernization of the nitriding furnace.

(4) Gas radiant tube

At present, most of the heat treatment equipment in Europe has adopted gas radiant tubes and natural gas heating. Gas heating technology and equipment are very mature in Europe. Natural gas burners have a standard series, which are manufactured and supplied by professional burner factories. The inner tube of the gas radiant tube is replaced from stainless steel to ceramic to extend the service life and increase the power. Natural gas heating improves energy utilization and reduces production costs.

2. Heat treatment deformation and prevention methods

There are two types of heat treatment deformation: one is the change of size, and the other is the change of part geometry. The heat treatment technology is different, the deformation of the part size and geometry and the method of preventing deformation are also different.

In the process of heat treatment heating austenitization, the longer the holding time and the higher the temperature, the more carbon is dissolved into austenite and the greater the expansion during martensite transformation. During cooling, martensite expands the most, followed by upper bainite, and the volume changes of lower bainite and troostite are small. When tempering at low temperature, martensite shrinks, and the shrinkage is proportional to the supersaturated carbon content. When heated at room temperature -200°C, part of the retained austenite will be transformed into martensite and will expand. However, due to the decomposition of martensite near 200°C, the expansion has little change in performance.

In conventional heat treatment, the main reason for the shape change of parts is the thermal stress and phase transformation stress that occur during heat treatment heating and quenching. The heating speed is too fast, the parts are too large compared to the heating furnace, and the temperature of each part of the parts is different, which will cause thermal deformation. During heat preservation, the residual stress of processing will be released and deform, and the weight of the part will also cause deformation. When cooling, due to the different cooling rates of different parts of the part, thermal stress will be formed and the part will be deformed. Even if the cooling rate is the same, the cooling is always fast on the surface and slow at the heart. Therefore, the previously transformed surface plastically deforms the untransformed core. If there is segregation of alloy components in the material, or the surface is decarburized, the phase transformation stress will be more uneven and the parts will be more likely to deform. In addition, if the thickness of the parts is uneven, the cooling rate will be different.

In the heat treatment of forgings, the ways to place the parts to reduce deformation are as follows: one is to hang vertically as much as possible, the other is to place it vertically at the bottom of the furnace, and the third is to use two points of horizontal support. The fulcrum positions are at one-third and four of the full length. Among them, the fourth is to lay flat on the heat-resistant steel tooling.

In the cooling process of parts, the type of quenching medium, cooling performance, hardenability, etc. are related to deformation. The change of cooling performance can be adjusted by changing the viscosity, temperature, surface pressure of the medium, using additives, and stirring. The higher the viscosity of the quenching oil and the higher the temperature, the smaller the elliptical deformation. In a static state, the deformation is small.

The spring factory can effectively reduce the deformation in the following ways: ①Salt bath quenching; ②High temperature oil quenching; ③QSQ method; ④Reduced pressure quenching; ⑤One trough three-stage quenching. Salt-bath quenching is similar to high-temperature oil quenching, both of which are quenched at the martensite transformation temperature to increase the uniformity of the martensite transformation. QSQ is double liquid quenching. Decompression quenching is to reduce the liquid surface pressure of the quenching medium, thereby extending the vapor film stage, the cooling rate of the high temperature zone is reduced, and the cooling rate of each part of the part is uniform. The structure of one-tank three-stage quenching is simple. First, the parts are oil-cooled from the quenching temperature to a temperature slightly higher than the Ms point, then out of the furnace, and maintained in the atmosphere to make the overall temperature of the parts uniform, and then oil-cooled to transform the martensite Evenly, the irregularity of deformation is greatly improved.

Galvanizing process

Galvanizing process
1. Process introduction

Zinc is a silver-white metal, brittle at room temperature, with an atomic weight of 65.38 and a density of 7.17g/cm3. It is an amphoteric metal that can interact with acids and alkalis. The actual zinc coating is passivated. Because the galvanized layer is passivated in a solution containing chromic acid, a chromate film of various colors with higher chemical stability can be obtained on the galvanized surface, and its protective ability can be increased by 5 to 8 times, and the surface Beautiful, increased decorative effect.

2. Process characteristics

1. Available gloss, smooth coating

2. It can be directly plated on carbonized, nitrided steel and cast iron

3. Higher current efficiency

4. The waste liquid is easy to handle, just use high pH to precipitate zinc

5. Good conductivity, save power

6. Low hydrogen embrittlement

7. Glossy coating can be obtained at higher temperature

8. Stable plating bath, low toxicity and low cost

3. Various performance parameters

Film thickness (μm) Hardness Gloss Color difference Adhesion Corrosion resistance Galvanized 7~12 90° bending without cracking 12H (National standard neutral salt spray test)

Professional production of heat treatment is booming

Since the country implemented a market economy, the specialized production of heat treatment has developed rapidly since 1995, which is mainly reflected in the rapid growth of private and joint-stock companies specializing in heat treatment processing. In 2003, the total number of such enterprises mainly concentrated in coastal cities was at least 2,000. In recent years, private heat treatment companies in North China, Northeast China and the Mainland have also seen a significant growth trend. There may be 3,000 specialized heat treatment plants nationwide. The average annual turnover of each enterprise is conservatively set at 2 million yuan. The annual turnover of such enterprises in the country can reach 6 billion yuan, accounting for about 20% of the total turnover of heat treatment in the country. This ratio is greater than 10% in the United States and less than 30% in Japan. It is undeniable that this is the greatest achievement made in recent years since the country promoted specialized production in the 1980s, and it is also an inevitable product of deepening reform and promoting a socialist market economy.

Heat treatment production technology transformation and equipment renewal are in full swing

Most private enterprises recognize the importance of a high-tech starting point in maintaining their strong competitiveness. They have sufficient funds and capabilities to purchase advanced heat treatment equipment. Aviation, weapons, and shipbuilding industries have benefited from the country’s national defense modernization policy in recent years and have carried out large-scale technological transformations and equipment updates. The unprecedented development of the automobile industry has created a large demand for advanced heat treatment technology and high-precision heat treatment equipment. Aviation industry companies and coastal private enterprises that mainly target light industrial product molds have added a large number of vacuum heat treatment equipment in recent years, especially high pressure gas quenching equipment. . Automobile and weapon industry enterprises and private enterprises mainly focusing on automobile and motorcycle parts use the multi-purpose furnace production line as the main technical transformation content. The heat treatment department of individual automobile companies has also introduced low-pressure carburizing and high-pressure gas quenching heat treatment production lines. Shipbuilding enterprises take the large-scale pit carburizing furnace with precise control of the carbon potential of the blast furnace temperature uniformity as the technical transformation target. In these enterprises, due to the vigorous development of production technology transformation, the proportion of non-oxidizing heat treatment has reached more than 90%. Basically realize the advanced heat treatment production with less oxidation, less distortion, less pollution, less waste, less labor, less quality dispersion.

The prevalence of ion heat treatment

As early as the early 1970s, Beijing Machine Tool Research Institute successfully developed the first 10A ion nitriding test device in China. Since then, research on ion nitriding technology has sprung up all over the country. The relationship between process parameters, structure and properties of the infiltration layer was systematically studied, and the effects of carbon content and alloying elements in the steel as well as the original structure, temperature, time, pressure, and gas medium composition on the structure of the infiltration layer were explored. The conditions for the formation of γ, ε phase, γ’+ε or ε+Fe3C composite phase compound layer and compound-free layer were identified, and the most suitable structure of steel under various service conditions was determined. These conclusions laid a good foundation for the expanded application of ion nitriding. By the end of 1980, there were thousands of ion nitriding equipment and dozens of ion nitriding equipment manufacturing plants across the country, and there was a climax of popularizing ion nitriding technology. Tension spring

In addition to ion nitriding, many scientific research institutions, universities and colleges have also carried out the research and development of ion carburizing, carbonitriding, ion soft nitriding, sulfur nitrogen and carbonitriding sulfur, ion boronizing and other technologies. Factors such as complex technology, high production costs, environmental protection, safety and sanitation have not been widely used, and ion nitriding is the most widely used in production.

The research and application of ion plating technology is also an example of the progress of heat treatment technology in my country. Taiyuan University of Technology, Beijing Union University and the First Research Institute of the Ministry of Electronics have conducted in-depth research on the ion plating mechanism, optimization of process parameters, the relationship between coating quality and process, and developed multi-layer glow ionizing metal and multi-arc ion Plating technology can not only obtain a dense TiN deposition layer on the surface of metal products, and obtain single element plating layers such as W, Mo, Cr, Ni, but also make W, Cr, Mo, V and other elements at the same time in different combinations and proportions. Infiltrate ordinary steel to obtain a relatively thick plating layer similar to high-speed steel on the surface, thereby replacing expensive high-speed steel.

Popularization of vacuum heat treatment technology

In the 1970s, the oil and gas quenching and cooling cold-wall vacuum heat treatment furnace began to be developed, and it was mass-produced in series in the 1980s. At present, local manufacturing enterprises have been able to provide a series of vacuum heating, oil and gas quenching furnaces, low pressure carburizing furnaces, 1MPa (10bar) high pressure gas quenching furnaces, vacuum sintering furnaces, and brazing furnaces. The maximum temperature of vacuum quenching and high-pressure gas quenching furnace can reach 1350℃, and that of vacuum sintering furnace can reach 1800℃. The output of various furnace types and furnace types is more than 200 sets. In recent years, the development of the aviation industry and the mold industry has put a lot of demand on vacuum heat treatment furnaces, vacuum brazing furnaces, especially vacuum heating and high pressure gas quenching furnaces, which has promoted the prosperity of vacuum equipment manufacturing. The combination of low-pressure carburizing and high-pressure gas quenching technology provides a new way for vehicle gears to extend life, reduce distortion (distortion) and reduce noise. The development of a semi-continuous production line that embodies this advanced technology is a mass production of automotive gears. The technical transformation of heat treatment provides the possibility. At the beginning of the new century, several domestic automobile and diesel gear manufacturers have introduced such equipment and production lines. Stainless steel spring

Due to the high requirements of molds for surface quality and distortion, vacuum high pressure gas quenching has almost become an irreplaceable technology for mold heat treatment. At present, in the coastal areas of South China and East China, large-scale private heat treatment processing enterprises have at least one 0.4MPa vacuum heating and high-pressure gas quenching furnace (the largest number is 6). In the cutting tool industry, the wide application of CNC and machining centers strongly requires tools with high quality and long life, and urban environmental protection also puts forward stricter requirements on heat treatment. Vacuum heating and high pressure gas quenching has therefore become a substitute for high-speed steel tool heat treatment. The preferred process for bath heating and quenching.

Cold formed spring manufacturing process

Cold formed spring manufacturing process
When using materials that do not need to be quenched and tempered to make springs after forming, the process is spiral springs, compression springs: rolling, stress relief annealing, grinding on both ends, (shot blasting), (aligning), ( Stress relief annealing), standing or pressure treatment, inspection, surface anti-corrosion treatment, packaging.

Spiral tension spring: coiling, stress relief annealing, hook and loop production, (tail trimming), stress relief annealing, standing treatment, inspection, surface anticorrosion treatment, packaging.

Spiral torsion spring: coiling, stress relief annealing, torsion arm making, tail trimming, stress relief annealing, standing treatment, inspection, surface anticorrosion treatment, packaging.

The manufacturing processes of the spiral tension and torsion springs described above are all the hook loops or torsion arms at both ends after being wound on the ordinary coil spring. In recent years, many domestic and foreign manufacturers have produced and used computerized forming machines or special forming machines. The shape of the spring body and tail can be completed on the forming machine at one time, eliminating the need for processing hooks or torsion arms.

When using materials that need to be quenched and tempered after forming, the main difference from the above process is that they need to be quenched and tempered after forming. Sometimes the spring end processing needs to be normalized.

The process with brackets is a non-fixed process, and whether it is performed depends on the performance requirements of the spring.

Tips for bright heat treatment of metals in oxidizing atmosphere furnace

Tips for bright heat treatment of metals in oxidizing atmosphere furnace
It is to burn off the oxygen in the airtight container where the workpiece is placed to form a stable solid compound, so that the metal product is heated under oxygen-free and low vacuum conditions.

The specific method is to put the metal spring products (single piece or batch) in an iron (low carbon steel) container, and put a small piece of metal sodium or lithium into the container at the same time, and then cover the lid to weld the seam. . Heat the sealed container in an air oven. When the container is heated to a low temperature, the sodium or lithium burns and the oxygen in the container (accounting for 21% of the container volume) combines to form a stable solid compound. The reaction is as follows:



Further heating is carried out in pure nitrogen below atmospheric pressure, and after heating is maintained, it is cooled in the furnace or taken out of the furnace. That can make the metal achieve the purpose of bright annealing or normalizing. After processing, take out the workpiece with gas cutting method.

The amount of sodium or lithium (XNa, Xli) put in the container can be calculated according to the volume (V. in L) of the container,



That is to say, only 0.86gNa or 0.26gLi is required for a 1L container. However, in actual applications, the calculated value should be slightly excessive, such as adding 105%.

Attention should be paid to the application of this method for heat treatment:

1. When welding a closed container, cooling measures should be taken to prevent sodium and lithium from burning in advance.

2. Metal sodium and lithium are easily oxidized in the air, so they must be stored in gasoline, kerosene or inert gas when not in use.

7005 aluminum alloy heat treatment process

7005 aluminum alloy heat treatment process
Through the determination of mechanical properties and stress corrosion resistance, the heat treatment process of 7005 aluminum alloy has been studied. The results show that the ideal heat treatment system for this alloy is 470 ℃ solution treatment followed by water quenching, and the artificial aging system is two-stage aging 100 ℃ ×8 h +120 ℃×24 h. After heat treatment, the room temperature tensile strength of the alloy reaches more than 400 MPa, the corrosion resistance is good, and the precipitates are fine and dispersed, which has a good strengthening effect on the alloy.

Spring copper plated

Preparation of electroless copper plating bath

(1) Dissolve the required sodium cyanide with cold water.

Add the required cuprous cyanide slowly to the sodium cyanide water to dissolve. This process is an exothermic reaction and cannot be overheated.

(2) Add other additives, stir evenly, take samples for analysis.

(3) According to the analysis results, supplement and correct each component.

(4) Weak electrolysis to remove impurities at low current density for several hours.

4.4.9 Defects of electroless copper plating and their causes

1. The coating is dark red, black, and hydrogen and oxygen are violently precipitated. The reasons are:

Current density is too high bath temperature is too low

Too little copper salt, too much arsenic cyanide

2. The coating is uneven, and some are not plated. The reasons are:

Improper installation, too low current

Too much cyanide

3. The coating blisters, peels, and has poor adhesion due to:

Incomplete surface pretreatment, oil film, oxide film bath temperature is too low

Too much current

4. The plating layer has a white film layer, blue crystals appear, and the plating solution turns blue. The reasons are:

Small anode area, insufficient potassium and sodium tartrate

Insufficient sodium cyanide

4.4.10 Formula for copper plating

(1)  Sodium cyanide NaCN 65~89g/l

Cuprous cyanide CuCN 45~60g/l

Sodium carbonate Na2CO3? 15g/l

Sodium hydroxide NaOH 7.5~22.5g/l

Potassium Sodium Tartrate (rochelle salt) 45g/l

Free sodium cyanide 15~22.5g/l

Bath temperature 60~70℃

(2) Full potassium bath

Potassium cyanide KCN 80~110g/l

Cuprous cyanide CuCN 45~60g/l

Potassium carbonate K2CO3? 15g/l

Potassium hydroxide KOH 7.5~22.5g/l

Rochelle salt 45g/l

Free sodium cyanide 12~22.5g/l

Bath temperature 60~70℃

4.4.11 Gloss cyanide copper plating

1. Add gloss agent:

(1) Lead: use lead carbonate or lead acetate to dissolve in water 0.015~0.03g/l

(2) Sodium thiosulfate: Dissolve in water with Haibo 1.9~2g/l

(3) Sulfur: Use sulfur to dissolve in water 0.1~0.5g/l

(4) Arsenic: Dissolve in NaOH 0.05~0.1g/l with arsenous acid

(5) Selenium: Dissolve in NaOH 1~1.5g/l with selenite

(6) Potassium thiocyanide: Potassium thiocyanide is soluble in water 3~10g/l

2. Use current waveform

(1) PR current:

a. Smoothing: 35 seconds for the cathode and 15 seconds for the anode.

b. Glossing: 15 seconds for cathode and 5 seconds for anode.

(2) AC and DC combined use:

a. Smoothing: DC 25 seconds, AC 10 seconds.

b. Glossing: DC 20 seconds, AC 6 seconds, the cycle of AC is 1.25-10 cycle.

(3) DC interruption: interrupt the current instantly and then resume the current.

4.5 Copper Pyrophosphate Plating Bath

It needs more control and maintenance, but the solution is less toxic than the copper cyanide bath. It is mainly used in printed circuit plastic plating and electroforming. Steel and zinc castings will produce replacement coatings and poor adhesion. You must first strike with a cyanide copper plating bath or a 10:1 P2O7Cu low pyrophosphate copper plating bath.

4.5.1 Copper pyrophosphate base plating bath formula (Strike Bath)

Copper pyrophosphate Cu2P2O7‧3H2O 25~30g/l

Potassium pyrophosphate K2P2O7 95.7~176g/l

Potassium acetate potassium nitrate 1.5~3g/l

Ammonium Hydroxide ?1/2~1ml/l

pH value 8~8.5

Bath temperature 22~30℃

Current density 0.6~1.5A/d㎡

Stirring machine or air

Filter continuous

Copper content 9~10.7g/l

Pyrophosphate 63~107g/l

P2O7/Cu ratio 7~10.1

4.5.2 Maintenance and control of copper pyrophosphate plating bath

1. Ingredients:

(1) Ammonia (ammonia) can help dissolve the anode and make the crystallization fine, and the evaporation loss needs to be supplemented every day.

(2) Acetate (nitrate), increase the current density operating range and remove the cathodic polarization.

(3) The pH value is adjusted and controlled by pyrophosphate or potassium hydroxide.

2. Temperature: Temperature over 60°C will hydrolyze pyrophosphate into ortho phosphate.

3. Stirring: Adequate stirring is required. Air stirring or mechanical stirring is generally used. Ultrasonic wave and solution spraying methods can also be used.

4. Impurities: It is very sensitive to organic impurities such as the decomposition products of oil and organic additives, which will make the coating dark and uneven, and the operating range will be smaller. Cyanide and lead impurities will also make the coating uneven and the operating range smaller. Organic impurities are treated with activated carbon. Add hydrogen peroxide or potassium permanganate before treatment to remove cyanide. Lead can be removed by weak electrolysis.

5. Phosphate: Too high temperature and too low pH will increase phosphate rapidly. Back to list

4.6 Copper Fluoborate Bath

Since the copper borofluoride salt is soluble in water in a large amount and has a large solubility, a higher current density can be used to increase the plating speed. Its disadvantage is corrosiveness, and the use of materials is limited to hard rubber, polypropylene and PVC plastic or carbon.

4.6.1   borofluorate copper plating bath formula

Copper pyrophosphate Cu2P2O7‧3H2O 57.8~73.3g/l

Potassium pyrophosphate K2P2O7? 231~316.5g/l

Potassium acetate 8.2~15.8g/l

Ammonium hydroxide 2.7~7.5m1/1

Additives (improve the ductility and uniformity of the coating) as indicated

pH value 8~8.4

Bath temperature 49~54

Current density 2.5~6A/d㎡

Stirring mechanical or air

Organic impurities will affect the appearance, uniformity and mechanical properties of the coating, especially ductility.

This plating bath requires continuous activated carbon filtration.

Additives usually do not use organics. Molasses will harden the coating and reduce edge effects. Some copper sulfate bath additives can be used.

4.6.2   Advantages of borofluoride copper plating bath

Allows high current density, smooth coating, good appearance

The coating is soft and easy to grind, additives can be used to increase the hardness and strength of the coating

Cathodic current efficiency is nearly 100%, low anodic polarization

No crystallization in the tank, easy to equip with plating bath

Stable plating bath, easy to control, high-speed plating permit

General copper plating process:

Steam degreasing

Inspection before plating (R) Solvent washing (R) Mounting (R) Chemical degreasing (R) Hot water washing (R) Cold water washing (R) Acid leaching (R)

Electrolytic degreasing

Cold water washing (R) Electrolytic degreasing (R) Hot water washing (R) Activation (R) Neutralization (R) Cold water washing (R) Cyanide coating (R) Cold water washing (R) Acid copper plating (R) Cold water washing (R) ) Light emitting (R) Cold water washing (R) Drying (R) Unloading (R) Drying (R) Inspection

4.7 Stainless steel copper plating process

4.8 Stripping of copper plating

(1) Chemical method:

Chromium CrO3? 200~300g/l

Ammonium sulfate (NH4)2SO4? 80~100g/l

Bath temperature room temperature

(2) Electrolysis method:

Sodium nitrate NaNO3? 800~100g/l

Current density 2~4A/d㎡

Bath temperature room temperature

Spring copper plated

Low-concentration copper bath formula (base plating bath formula)

Coprous cyanide CuCN 20g/l

Sodium cyanide (sodium cyanide) NaCN 30g/l

Sodium carbonate (sodium carbonate) Na2CO3? 15g/l

pH 11.5

Temperature 40℃

Current efficiency 30~60%

Current density 0.5~1A/cm2

4.4.2 The formula of the concentration bath in copper

Coprous cyanide CuCN 60g/l

Sodium cyanide (sodium cyanide) NaCN 70g/l

Sodium hydroxide (sodium hydroxide) NaOH 10~20g/l

Free cyanide 5~15g/l

pH 12.4

Temperature 60~70℃

Current density 1~2A/dm2

Current efficiency 80~90%

4.4.3 Copper cyanide high concentration bath formula

Cuprous cyanide CuCN 120g/l

Sodium cyanide NaCN 135g/l

Caustic soda NaOH 42g/l

Brightener 15g/l

Free sodium cyanide) 3.75~ 11.25g/l

pH 12.4~12.6

Temperature 78~85℃

Current density 1.2~11A/dm2

Current efficiency 90~99%

4.4.4 Cyanide copper plating full potassium bath formula

Cuprous cyanide CuCN 60g/l

Potassium cyanide KCN 94g/l

Potassium carbonate 15g/l

Potassium hydroxide KOH 40g/l

Free potassium cyanide 5~15g/l

pH value <13

Bath temperature 78~85℃

Current density 3~7A/dm2

Current efficiency 95%

4.4.5 Advantages and disadvantages of electroless copper plating full potassium bath

High current density can also get gloss, coating, high conductivity

Wide gloss range brings out less loss

Good gloss, more expensive medicine

Good smoothing effect

4.4.6 Potassium sodium tartrate cyanide copper plating bath formula (Rochelle cyanide Buths)

Cuprous cyanide CuCN 26g/l

Sodium cyanide NaCN 35g/l

Sodium carbonate Na2CO3? 30g/l

Sodium potassium tartrate NaKC4H4O6‧6H2O 45g/l

Free sodium cyanide 5~10g/l

pH 12.4~12.8

Bath temperature 60~70℃

Current density 1.5~6A/d㎡

Current efficiency 50~70%

4.4.7 The role and influence of the components of the electroless copper plating bath

1. Main salt: NaCu(CN)2 and Na2Cu(CN)3 exist in two forms, and its functions are:

CuCN+NaCN=NaCu(CN)2? CuCN+2NaCN=Na2Cu(CN)3? Na2Cu(CN)3? 2Na + (aq) +Cu(CN)3-(aq) Na2Cu(CN)3? 2Na+ (aq ) +Cu(CN)3-(aq) Cu(CN)3-? Cu++3CN- Cu(CN)2-? Cu++2CN-

Because the ionization constants of copper complex ions Cu(CN)2- and Cu(CN)3- are very small, the cathode has a great polarization effect, making it difficult for copper to be replaced and precipitated. Therefore, copper can be plated directly on steel. The current efficiency is reduced, hydrogen is generated, and the plating output is reduced. The main salt has a great influence on the cathode polarization, and the increase of the main salt concentration can reduce the cathode polarization, help the anode dissolve, and prevent the formation of anode passivation.

2. Free cyanide, NaCN, KCN, help anode dissolve, prevent wrong salt precipitation, stabilize the plating bath. Too much content will deepen the polarization and produce a large amount of hydrogen and reduce the current efficiency.

3. Sodium carbonate prevents sodium cyanide from being hydrolyzed, reduces anode polarization and helps anode dissolution.

4. Caustic soda, reduce hydrogen ion concentration, increase conductivity, improve current efficiency and use of electricity

Flow density.