Discussion on Electroplating Equipment for Super Strong Neodymium Electroplating

- Nov 09, 2017 -

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Due to its excellent magnetic properties, rare earth magnet materials have been developed rapidly since its introduction in 1983 and are now widely used in many fields such as electromechanical, communication, instrumentation, computer and medical equipment. However, due to the potential of neodymium-iron-boron magnets, the surface is easily oxidized. Therefore, strict antiseptic treatment must be carried out before use. Otherwise, the performance and life of the whole machine will be directly affected. China is a neodymium iron boron power, but also a weak country, the reason is more than the magnetic properties of the magnet is not poor, but the surface treatment level is low. Therefore, the surface treatment technology in the production of NdFeB products occupy a pivotal position. Electroplating as a mature means of metal surface treatment, NdFeB magnets in the field of anti-corrosion is widely used. NdFeB plating relative to the ordinary parts plating, its particularity is difficult to obtain good adhesion of the coating, it is difficult to coordinate the relationship between coating thickness and magnetic properties, coating surface easily damaged. Neodymium iron boron plating equipment also has the same special equipment and the special nature of the equipment as a control device outside the bath coating quality means that the status of the NdFeB plating is particularly important. This must be fully understood, otherwise, it is difficult to obtain the desired acceptable coating even with the advanced electroplating process. This article will elaborate on the particularity of NdFeB plating equipment from the following points.

1, roller

NdFeB products to the majority of small parts, it is generally the method of barrel plating, and mostly horizontal barrel-based. As we all know, horizontal barrel plating equipment is the key component of the drum, drum quality is directly related to the pros and cons of plated product quality. This is especially true for neodymium iron boron plating, where the roller is the most important part of the entire equipment and only the right roller can be chosen for its high quality product.

 

1.1 roller size

Choose a reasonable drum size is the most important NdFeB plating equipment. This sentence is no exaggeration, such as in earlier years, there have been many neodymium iron boron plating enterprises blindly pursue luxury in the selection of equipment, high degree of automation, equipment capacity, etc., while ignoring the most fundamental reasonable size of the drum . Therefore, plating the poor quality of products, pass rate is not high, the market sluggish, and often accompanied by returns, claims and other incidents.

NdFeB material is a multi-phase structure, the potential of each phase are different, in particular, the grain boundary Nd-phase potential of the lowest, with the formation of the other phases of the original battery electrochemical corrosion occurred. And its corrosion rate is much faster than ordinary steel parts. Therefore, neodymium iron boron parts into the drum, it should be as quickly as possible sinking the surface of the coating to prevent the oxidation process. The faster the deposition of the coating, the smaller the degree of oxidation of the surface of the part, the better the bonding between the coating and the substrate. So, from the roller point of view, how to make the coating deposition rate faster? As we all know, parts in the drum only roll to the exposed surface layer and the solution in full contact, in order to have a chance to be sinking coating, if tumbling to the inner parts of the flow, the only part of the current through the electrochemical reaction and the basic stop. So, as a NdFeB plating roller, should be more exposed parts of the exposed surface layer and solution full access opportunities, the more opportunities, the coating deposition speed faster, the better the binding force. And the roller that can provide more of this opportunity is only a small roller.

Small drum due to small size, less drum load, the accumulation of parts in the drum lighter, the mixing cycle of parts (parts from the surface into the inner layer and then back to the surface of the time) is short, and the full access to the solution more opportunities , The chance of plating more. The loading capacity of the drum, due to the serious accumulation of parts, the parts have more time can not fully contact with the solution, not in contact with the solution electrochemical reaction will stop, but the part itself will not stop the oxidation. The more serious the accumulation of parts, the greater the degree of surface oxidation. Imagine, in the oxidation of the surface of the deposited parts of the coating, how to ensure that its good binding it? In addition, the drum load (especially large diameter), parts in the drum tumbling strength is large, and because the neodymium iron boron material is more brittle, prone to parts surface damage such as "knocking", "knock angle" and so on. Therefore, the choice of neodymium iron boron plating drum, we must follow the "small" principle, only a small number of rollers in order to ensure high-quality coating. Years of NdFeB plating practice also fully proved this point. Even many enterprises have paid a heavy price for this. This cost is not only a direct economic loss, but more often the enterprise can not embark on a path of sound development for a long time.

In order to make high-quality products, NdFeB plating drum should not be too large, it is an indisputable fact. However, small drum load, output will inevitably be affected, this is a real situation. For example, a larger NdFeB manufacturer typically produces more than 1 tonne electroporation a day, with a load of 3 kg per drum and a 1 tonne / day production at a load of 3 kg / drum It does not seem easy. Therefore, in order to make up for the lack of production capacity of small drums, the only way is to increase the number of drums. Only a small number of small drums to meet the "quality" and "volume" of NdFeB plating dual requirements. At present, most domestic NdFeB plating drum manufacturers, even if NdFeB plating technology more advanced Japanese (or Sino-Japanese joint venture), South Korean-owned (or Sino-South Korea joint venture) business is basically the case.

 

1.2 drum speed

NdFeB products more parts of the sheet, the sheet parts due to "sticking" phenomenon prone to the coating blossoming, "drum eye", the thickness of the uneven quality problems. The solution is that parts in the barrel plating process should occur as little as possible, "clumps" phenomenon and more "single" state. Single parts and solution full contact, then there will be no "adhesion" brought about the quality of the coating. Improve the speed of the drum is to solve the problem of "adherent" a good way, drum speed, parts tumbling good, the probability of each other is small paste.

However, due to the brittleness of the neodymium-iron-boron material, surface damage to varying degrees can occur if the part is tumbled too much inside the drum. From this perspective, NdFeB plating drum speed should not be too fast. Slow drum speed, parts easy to paste; drum speed, surface and easily damaged. It seems that really dilemma! Finally, the solution to this problem is still the drum size. In order to ensure that the parts roll evenly in the drum to improve the drum speed is necessary, but in order to ensure high speed parts damaged less, while allowing the use of the drum diameter reduced. Roller diameter is small, the drop when the parts fall drop small parts collide with each other to reduce the intensity of the parts surface damage naturally reduce. That is, reducing the drum diameter at a rotational speed of the drum, ie, the angular velocity can not be reduced, reducing the linear speed at which the part runs within the drum. Angular velocity, fully tumbling parts; line speed is small, a small extent of damage to the parts. In this way, not only solve the "sticking" problem of thin-walled parts, but also to reduce the extent of damage to the surface of the parts.

However, when the drum diameter is reduced, the drum load will inevitably be affected, and the capacity of the equipment will be reduced. At this time, the length of the drum may be lengthened properly to increase the load of the drum as much as possible. In this way, suitable for electroplating neodymium iron boron thin-walled parts is actually an elongated drum. In addition, the slender roller also has advantages in terms of thickness fluctuation of the plating layer and improvement of current efficiency. However, not the finer the longer the cylinder, the better the length and diameter of the cylinder must meet a certain ratio, otherwise the mechanical strength of the cylinder will be affected.

In addition, the thin cylinder suitable for electroplating neodymium iron boron thin-walled parts is also suitable for other non-plate neodymium iron boron parts (such as magnet, etc.), but also will receive unexpected results. The reason is that compared with the same volume of thick and short roller cylinder, the parts in the drum spread out large area, parts of the mixing cycle is short, of course, the chance of plating more. However, non-plate coated NdFeB parts, the drum speed is not too fast, to further reduce the degree of damage in the drum parts.

Therefore, the speed of neodymium iron boron plating drum should be able to adjust, so that when used according to the circumstances choose a different speed. There are two common roller speed control methods. One is variable speed, it is commonly used roller speed made of several stalls, and then according to the situation using different stalls speed. Just like the manual transmission of a car, the driver can change different gears according to the driving conditions of the road. The other is infinitely variable speed, that is, the design of a maximum speed, and then the drum speed can be continuously adjusted from zero to the speed. Two kinds of speed control methods have their own advantages and disadvantages, variable speed gear position clear, small fluctuations in speed, but occasionally there is no useful useful speed involved; Promise speed optional large, suitable for many, but the speed fluctuations , Less stable equipment. The best solution is to combine the two speed control modes. In the normal case, the variable speed control is used. When the variable speed control is used, the stepless speed control system can be started. Once the Promise speed system damage, you can still use the variable speed governor for normal production.


1.3 Drum water permeability and reliability

Due to the closed structure of the drum, the drum plate becomes a natural barrier that influences the exchange of ions inside and outside the drum. Therefore, the plating current resistance, low current efficiency, uneven coating thickness. Finding ways to improve the water permeability of the drum, drum plate will reduce the shielding effect, the consumption of metal ions in the plating process is easy to add, barrel plating, many of the drawbacks will be reduced. Neodymium iron boron plating on the drum of the water permeability is even more demanding, the drum water permeability, deposition speed on the fast, the degree of oxidation of the part surface is small, coating adhesion is also good. In particular, NdFeB deep hole parts (such as magnets), drum water permeability, not only can accelerate the deposition of parts on the surface coating, but also to make the deep hole plating ability is improved.

To improve the permeability of the drum, if only from the roller itself to consider, there are generally two ways: First, increase the rate of open the drum, the second is to reduce the thickness of the roller board. The high drum opening rate and the thinness of the drum plate make the resistance encountered by the ions in and out of the drum small and the water permeability of the drum can be improved.

However, to improve the water-permeable performance of the drum is not to blindly increase the opening ratio of the drum and to reduce the thickness of the drum. Otherwise, the mechanical strength of the drum will be affected and the reliability of the drum will be reduced. Especially for super strong neodymium plating, the drum that is required to use not only has good water-permeable performance but also has good and reliable performance. From the above analysis know that although the use of NdFeB plating roller size small, but a large amount of plating, but also because of the high requirements of the protective parts of each cylinder plating time is very long. Therefore, NdFeB plating roller usage is very high, fatigue strength when used is also very large. Common NdFeB plating business endless, twenty-four hour shift production, even though this may still not be completed production tasks. Imagine, if the reliability of the drum is not good, how can withstand the high strength NdFeB plating it?

Therefore, the use of neodymium iron boron plating drum both permeable performance, but also fatigue, durability, high reliability, to achieve the unity of water permeability and reliability.

 

1.4 drum open the door

Neodymium iron boron plating roller door opening and closing speed must be fast, this can shorten the parts into the cylinder after the residence time in the air to minimize the degree of oxidation of the surface of parts. In addition, NdFeB products more sheet parts, so the drum must be strict open the door, otherwise it is easy to be part of the folder, card and become defective. Neodymium iron boron plating product qualification requirements are high, so in the production equipment, any one of the easy to bring hidden dangers of the plating are not allowed to ignore. NdFeB manufacturers often due to electroplating pass rate is not high and was returned or claims, so that businesses suffer unnecessary losses.

 

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2 production line

NdFeB parts variety of products varied, electroplating drum size used small, the number of large and plating production is large, high product quality requirements, so choose a suitable production line is essential.

 

2.1 Self-driven barrel plating equipment

NdFeB domestic electroplating started late, about the late 1980s to early 1990s, when there is no dedicated barrel plating equipment. However, most companies are able to master the principle of smaller drum size used in NdFeB electroplating, while the small drums were self-driven roller coaters at the time, so the self-driving barrel plating equipment is more prevalent. Since the drive roller plating machine that comes with motor barrel plating machine, this barrel plating machine drive motor is generally located directly above the drum, and through the gear drive drum rotation. Since it comes with motor drive, the operation of the production line by the impact of small, so the flexibility of this device is relatively strong. Neodymium iron boron plating enterprises as long as the choice of the right size drum, the use of such equipment generally can achieve good results.

However, since self-driven roller coater motor and drum together, will inevitably make their own heavier, and most of this equipment is hand-operated, large-scale electroplating workers labor intensity is bound to be great. In addition, as the motor is located above the drum, the chances of corrosion during plating are bound to be high, the damage rate of the motor is relatively high, and the normal plating production will be affected. Therefore, if it is used for NdFeB plating production, self-driven barrel plating equipment has obvious advantages in the case of small electroplating amount, for example, less investment, quick loading, flexible operation and guarantee of electroplating quality. However, in mass production, Defects such as equipment will show a lot, for example, labor-intensive workers, production management difficulties, high equipment damage, unstable plating quality.

 

2.2 barrel automatic plating line

Self-driven barrel plating equipment can not meet the requirements of large-scale production of NdFeB plating, so automatic plating for NdFeB plating barrel line came into being. High degree of automatic plating line barrel automation can reduce the labor intensity of workers, beautiful equipment, generous, high-end, business visit, appears to high corporate grade. However, after years of practice has proved that automatic plating roller plating is not the ideal NdFeB plating equipment.

(1) NdFeB parts varieties, large quantities, but a single species of small quantities. And different varieties, the requirements of the coating is also different. Therefore, neodymium iron boron plating equipment required to make timely changes in circumstances, and lack of flexibility of automatic lines, obviously not easy to meet this requirement.

(2) NdFeB plating using nickel - copper - nickel more technology. Rollers that are self-priming are prone to cross-contamination of nickel-copper-nickel solutions by inadequate cleaning.

(3) NdFeB plating business practitioners overall poor quality, high technology content of the automation equipment difficult to use and grasp of flexibility.

(4) equipment investment, long cycle, high maintenance costs.

Nevertheless, it does not mean that NdFeB plating can not use automatic lines. Instead, the automatic wire of NdFeB plating should be designed and manufactured according to the particularity of NdFeB products combined with the process, and can not simply be used to pick up ordinary automatic lines. Just like people wear clothes, everyone should wear suitable clothes, is it just suitable for wearing on the body?


2.3 multi-head barrel plating equipment

Multi-barrel plating (machine) equipment refers to a plating tank equipped with a plurality of drums, a plurality of drums share a motor drive, a drive through the chain drive each station's drum rotation. Bulls roller plating machine generally have two machines, four or six six-head machine specifications to choose from, and then according to the size of the production capacity and the use of technology to determine the number of Bulls roller plating machine, but also according to the situation on the equipment Increase or decrease the number.

Bulls roller plating machine of this form originated in South Korea, first appeared in China in late 1999 to early 2000. The mechanical structure of the equipment in our country and the equipment in South Korea are not the same, but the manifestations are basically the same. Bulls roller plating machine can also be said to have evolved from self-driven roller plating machine, so retains all the advantages of self-driven roller plating machine. For example, flexible and flexible equipment, controllable, easy to ensure the quality of the coating. Moreover, bump mill also overcome many of the shortcomings of self-driven roller coater. For example, after the separation of the motor from the drum, the labor intensity of the worker is reduced; the stability of the equipment is increased; the single station adopts a multi-cylinder with one tank and multiple units to form a group; Difficult. Therefore, this long barrel plating equipment is easily accepted by a large number of NdFeB plating manufacturers.

NdFeB multi-head barrel plating equipment than self-driving barrel plating equipment has been greatly improved, but still manual operation, the use of the larger number of rollers, there is still a large labor-intensive workers. Therefore, in order to further reduce the labor intensity of workers, you can consider for multi-head barrel plating equipment with hand-held cantilevered traffic car. However, due to the fact that the current multi-head barrel plating equipment is in good overall use, whether it will affect some of the equipment's advantages (such as flexibility, handleability, etc.) after driving, remains to be further proved.

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3 plating power

 

NdFeB products due to the higher corrosion resistance, so the surface coating is often very thick. However, the thicker the coating, the more severely the magnetic shield to the magnet and the worse the magnetic properties of the part. Therefore, trying to reduce the coating and improve corrosion performance is one of the focuses of the development of NdFeB plating.

The coating obtained with pulsed power supplies is dense, bright and has low porosity. The corrosion resistance is still good with thin coatings. Therefore, many NdFeB plating manufacturers in China have done work in this area, with a view to control the means through the tank - electroplating power supply, to solve plagued the NdFeB plating thickness and magnetic properties for many years the contradiction between the problem. However, it has been found that the poor adhesion of the plated product using the pulsed power source and the poor bonding strength are the number one quality issues for plating of the NdFeB products. Analysis shows that: the pulse current is an on-off DC, current is very large when the turn-off current is zero. Due to the extremely negative potential of neodymium iron boron material, it is possible in the pulse off period oxidation corrosion occurs on the surface of the parts so that the coating adhesion decreased. Based on this, the current supplied for electroplating of NdFeB products should be a continuous DC current without interruption.

However, in theory, it is not allowed to have intermittent current plating on the surface of neodymium iron boron products, if the bottom is still using DC and thickening pulse, the result will be like? After adjusting the program to re-test. The results showed that coating adhesion problems have been solved, but no significant anti-corrosion performance. So, whether it can be considered that the pulse plating is not suitable for NdFeB products? I am afraid that the answer should be unknown. Because the effect of preservative is not obvious, there may be many reasons, such as the choice of pulse parameters is appropriate, whether the electroplating process should be adjusted, the test conditions are stringent, the quality of the pulse power pass and so on. Can not simply come to a conclusion with a few simple tests.

Therefore, the current NdFeB plating power supply is still the DC power supply. Early use of single-phase full-wave rectifier power more, this power without filter, the output waveform for the continuous half-cycle sine wave. Originally did not think that this power is wrong, but later introduced the switching power supply and found that the use of switching power supply made products, coating adhesion, surface finish. The analysis shows that although the single-phase full-wave current has a continuous waveform, when the current approaches the position of the sine wave trough, the electrochemical reaction may be stopped due to the inability to reach the deposition potential of the metal ions. Electrochemical reaction to stop the plating of ordinary products may have little effect, but the NdFeB plating means that the surface of parts of the oxidation corrosion began. Even if it is not single-phase full-wave waveform, as long as the ripple coefficient is not desirable. Because NdFeB electroplating the initial part, while the deposition and surface oxidation of the two competing process of deposition, rapid deposition of the surface oxidation of the small, slow deposition of the surface oxidation degree is large. Large ripple coefficient of the waveform current alternating size, when the current is large surface oxidation slow, the current is small when the surface oxidation fast, the coating can not be continuously and consistently deposited. Therefore, in order to exclude the quality of the coating caused by the power waveform, NdFeB plating should try its best to use plating power with smaller ripple coefficient. Can not be as early as that, just use a power to use, the result of a problem that is pre-improper handling or solution problems, even as a problem may not be solved for several years. Like hard chrome, just use a power supply can get satisfactory results?

Switching power supply ripple factor is small, saving, for NdFeB plating can achieve good results. However, the special requirements of NdFeB plating, no matter what equipment used, must have leather, durable, high reliability. Otherwise, parts of the whole drum may be scrapped due to equipment damage, and the price of a drum neodymium iron boron product will not be much lower than a single power supply. Obviously, the stability of the switching power supply is slightly less. However, if you must use the switching power supply, you should try to remedy its shortcomings: First, choose the power of the power margin should be large, and second, the use of remote control power away from the plating tank to reduce corrosion, it is best to have a special power supply engine room. Although the waveform of the three-phase bridge rectifier power supply is slightly worse than the switching power supply, the plated product is almost the same as the switching power supply. The stability of the three-phase bridge rectifier power supply is the best of all plating power. Therefore, the current supply of NdFeB plating industry is basically still based on three-phase bridge rectifier power supply.

 

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In short, no matter what kind of products are used, the public opinion propaganda in the society can only play a guiding role and the market plays a decisive role in the end. The market is always out of the product is not suitable for their own, leaving the end-use products tend to rationalize. Neodymium iron boron plating is also true, no matter what kind of equipment used, must meet the special Neodymium Iron Boron products, or will eventually be neodymium iron boron plating market eliminated. China's NdFeB plating industry has experienced years of ups and downs, regardless of technology or equipment have basically stabilized. However, it must be clearly understood that the days of the NdFeB plating industry can only say that it has just reached the "adequate food and clothing," and at present there are still many enterprises still living a "poor clothing and eating less" life. Neodymium iron boron electroplating advanced countries in the world lead us a lot, we also need advanced, we also need to modernize, but modernization can only be a step by step, must not engage in "Great Leap Forward," or heavy losses can only be exchanged for a profound lesson. Therefore, placed in front of our country NdFeB plating workers will be a long way, far away, very difficult.

After ultrasonic cleaning, the pretreatment process of neodymium-iron-boron magnetic materials is generally as follows: (1) Alkaline degreasing - water bleaching - water bleaching - ultrasonic bleaching - dilute nitric acid treatment (neutralization and bleaching) - water rinsing - water Rinsing - Ultrasonic Bleaching - Activation - Electroplating (2) Alkaline Degreasing - Water Rinsing - Water Rinsing - Ultrasonic Bleaching - Dilute Nitric Acid (Neutralization, Bleach) Treatment - Water Rinsing - Water Rinsing - Ultrasonic Bleaching - Activation - Water rinsing - Water rinsing - Ultrasonic finishing - Plating (3) Ultrasonic alkaline degreasing - Water rinsing - Water rinsing - Ultrasonic finishing - Dilute nitric acid (neutralizing, bleaching) treatment - Water rinsing - Water rinsing - Ultrasonic finishing - Activation Processing - water rinsing - water rinsing - ultrasonic finishing - plating analysis The above three processes, the difference is that: Process (1) is characterized by: direct plating after activation treatment while (2) (3) After the activation treatment and further use of ultrasonic polishing. The reason for using the first process is that the activated magnetic material after the best surface condition of the workpiece, it is suitable for combination with the plating layer. Easy to ensure the quality of the plating. And use 2 , 3 kinds of craft reasons Is that the activation solution is acidic, the residual acid in the workpiece micropores must be removed by ultrasonic cleaning to ensure the quality of the plating.The common points of these processes are the use of ultrasonic cleaning after alkaline cleaning and acid cleaning, the process (3) Using up to four ultrasonic cleaning. We recommend the conditions of the enterprise using process (3), especially for high-grade magnetic materials with multi-pass ultrasonic cleaning more appropriate, it can well guarantee the quality of electroplating products.Of course, Here does not rule out the user according to their own operating habits and product objects choose a different cleaning process. ?? NdFeB nickel plating is actually multi-layer coating, the need to pre-nickel plating, and then plated copper thickened, and then coated bright surface nickel.

Pre-nickel plating

Nickel sulfate 300g / L?

pH 4. O ~ 4.5

Nickel chloride 50g / L?

Temperature 50 ~ 60 ℃

Boric acid 40g / L?

Current density 0.5 ~ 1.5A / dm2

The amount of additives

Time 5min

② pyrophosphate copper thickening. As the intermediate coating, though the acid bright copper plating process is popular, acidic copper plating is not suitable for thickened plating for the neodymium iron boron material since the cathode material has been pre-plated in the strong acid plating bath Will be prone to micro-corrosion matrix; for the future delay bubble left hidden dangers. More appropriate process is close to neutral pyrophosphate copper plating.

Copper pyrophosphate 70g / L

Brightener amount

Potassium pyrophosphate 300g / L

pH 8 ~ 8.5

Ammonium citrate 30g / L

Temperature 40 ~ 50 ℃

Ammonia 3mL / L

Current density l ~ 1.5A / dm2

③ bright nickel plating

300g / L nickel sulfate

Commercial brightener according to the instructions to join

Nickel chloride 40g / L

pH 3.8 ~ 5.2

Boric acid 40 g / L

Temperature 50 ℃

Low foam wetting agent lmL / L

Cathode current density 2 ~ 4A / dm2

For neodymium iron boron materials that require other surface coatings, additional surface plating may be performed after the copper plating of the intermediate plating has been completed. Sometimes in order to increase the thickness and reliability of the coating, you can also add rapid acid copper plating process after pyrophosphate coating, in order to obtain good surface decoration, and then plating other coatings will have better results. The key point for these plating operations is that it must be energized and can not be de-energized in the middle of the tank. Otherwise, the plating solution in the pores will also cause micro-corrosion on the substrate and affect the bonding force.


Article from NdFeB Industry Network

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