Barrel Electroplating The process of plating large numbers of small parts in a rolling container. Such as steel parts galvanized, barrel copper plating, barrel plating high-tin bronze; copper and copper alloy parts such as nickel plating. The barrel plating solution and the plating conditions are basically the same as the groove plating, and some adjustments may be made depending on the material and the shape of the plating. I. Overview Barrel plating is applicable to the electroplating of small parts that cannot be or cannot be influenced by shape, size, etc. It saves labor and labor compared to the way that early small parts were electroplated using rack plating or basket plating. Production efficiency, but also the surface quality of the plating is greatly improved. Therefore, the invention and application of barrel plating are undoubtedly very positive in the field of electroplating of small parts. Barrel plating was already applied industrially as early as the 1920s. Domestic barrel plating appeared earlier in Shanghai in the mid-to-late 1950s. Mechanized continuous barrel plating equipment began to be used around the 1960s, but at the time the equipment was only manually controlled, and the large-scale automatic barrel plating line was probably from the 20th century. Only a relatively wide range of applications began in the 1990s. At present, the barrel plating production accounts for about 50% of the entire electroplating process, and involves tens of plating species such as galvanized, copper, nickel, tin, chromium, gold, silver and alloys. Barrel plating has become an electroplating process that is very common and is almost in parallel with plating. 2 The concept of barrel plating Barrel plating is strictly called roller plating. It is a kind of electroplating in which a certain number of small parts are placed in a special roller, and in the rolling state, a variety of metal or alloy plating is deposited on the surface of the part to achieve surface protection decoration and various functional purposes. Processing methods. The typical barrel plating process is as follows: The small parts that have been plated before processing are loaded into the drum, and the parts rely on their own gravity to press the cathode conductive device inside the drum tightly to ensure the current required when the parts are plated. Can transmit smoothly. Then, the drum is rotated in a certain direction at a certain speed, and the parts are continuously rolled and dropped after being rotated by the drum. At the same time, the main metal ion is reduced to metal plating on the surface of the part after being acted by the electric field. The fresh solution outside the drum is continuously added to the drum through numerous small holes in the roller wall plate, and the old liquid in the drum and the electroplating process are generated. Hydrogen gas also exits the cartridge through these holes. Second, several basic characteristics of barrel plating 1. Barrel plating is the barrel plating in the roller and the small parts of the plating difference is that it uses a roller, the roller is carrying small parts in the process of rolling constantly A filled device that is plated. The typical drum is hexagonal and horizontally placed horizontally. One side of the wall of the drum is open, a small number of small parts are loaded into the drum from the opening during plating, and then the drum door is closed to close the opening. The roller wall is covered with a number of small holes, the current conduction between the parts and the anode during plating, the renewal of the solution inside and outside the cylinder, and the exhaust gas discharge are all required to pass through these holes. The cathode conductive device in the drum passes through the central axis hole on both sides of the drum through a copper wire or a bar, and is then fixed on the conductive footrests of the left and right wall panels of the drum. The part is naturally connected to the cathode conductive device by its own gravity in the drum. The barrel plating of small parts is performed in such a device. The drum's structure, size, size, rotation speed, electrical conductivity and hole opening rate are all related to barrel plating production efficiency, coating quality and so on. Therefore, the drum is one of the focuses of the entire barrel plating technology research. 2. Barrel plating is a barrel plating process in which small parts are tumbling. The small parts are not stationary in the drum, but are always rolled as the drum rotates. This tumbling to a specific part is that it is buried inside the entire stacked part for a while and then turned to the outer surface again. This is repeated until the entire barrel plating process is over. So, why keep small parts rolling inside the drum? (1) Ensure that each part can be uniformly plated. Small parts are stacked together in the drum. Some of the parts are distributed inside the stack, called inner parts; the other parts are distributed on the outer surface of the stack, called surface parts (as shown in Figure 1). . During barrel plating, the main metal ions are actually reduced only on the surface of the surface parts to form a metal plating layer, and only the current passes through the inner layer parts due to the shielding and shielding of the surface parts, but almost no electrochemical reaction occurs. Therefore, in order to have the opportunity to be plated, the inner part needs to be turned from the inside of the stack to a surface part. The surface parts can not stay for a long time. After electroplating for a while, they are turned into inner parts by the rotation of the drum. In this way, the small parts can only be rolled constantly, so that the inner parts and the surface parts can be continuously changed and changed, and each part can be evenly plated. 1-Inner parts; 2 - Slab parts Figure 1 Schematic diagram of the inner parts and surface parts (2), to avoid "burning black" or "burning" the surface parts. If a small part is in a stationary state in the drum if it does not roll, then the use of a small current density may result in the lack of metal ions near the surface parts and a "burning" phenomenon. Particularly close to the surface parts of the wall of the drum, the current entering the drum from the perforation is obstructed, so that it concentrates on the narrow surface of the part immediately following the perforation, causing the coating to burn and leave a black eye, ie the so-called "Drum eye prints." At this time, the effect of the small parts rolling in the drum is similar to the solution stirring or cathode movement of the rack plating. If there is no effect of solution stirring or cathode movement during rack plating, the upper limit of the current density cannot be easily increased, and the deposition rate of the plating layer is also difficult to accelerate. 2.3 The current required for the small parts during barrel plating is transmitted in an indirect manner. During rack plating, the current required by the part is directly transmitted by the hanger, and the part is in close contact with the hanger without any medium in between. Therefore, the plated current is transmitted smoothly, the contact resistance is small, and the current obtained by each component is basically not different due to the transmission problem. However, during barrel plating, the parts are pressed against the cathode conductive means in the drum as a whole, and there are only a few parts directly connected to the cathode conductive means, and most of them can only be conducted to the cathode through stacked overlapping parts. Therefore, the cathode-conducting device in the drum can only deliver current to parts that are in direct contact with itself, and then can be transported from these parts to other parts and transported one by one between other parts and parts. This is barrel plating. Indirect conductivity. This indirect conductivity is undoubtedly another important feature of barrel plating. It is mainly due to indirect conduction between parts and parts, rather than the parts directly contact with the cathode conductive, so when the barrel plating contact resistance than the corresponding increase in hanging plating. III. Classification of Barrel Plating 1. General The classification of barrel plating is scientifically based on the shape and axial direction of the barrel used for barrel plating. The drum shape refers to what the shape of the drum is similar to, and the axial direction of the drum refers to the relationship between the direction of the axis of rotation and the horizontal plane when the drum rotates. According to the difference between the two aspects of the drum, the common barrel plating methods in electroplating production are divided into three categories: horizontal barrel plating, inclined barrel plating, and vibration plating. 2. Horizontal Barrel Roller horizontal drum plating has the shape of "bamboo tube" or "pillar" and is placed horizontally when in use. The axial direction of the drum is horizontal, so horizontal barrel plating is also called horizontal horizontal barrel plating. Hexagonal cylinders, chrome-plated cylinders, rod-shaped (or spoke) cylinders, and sewing needle cylinders, which are common in production, are among the areas of horizontal barrel plating. Among them, hexagonal rollers are widely used. A typical horizontal drum structure is shown in Figure 1. 2.1 Roller cross-sectional shape Horizontal drums have hexagonal, octagonal, and circular cross-sectional shapes. With a hexagonal roller, the drop of the part during turning is large, and the mixing of the parts is sufficient. Therefore, the thickness fluctuation of the coating is superior to other types of rollers. This advantage is even more pronounced when the loading does not exceed one-half the drum volume. In addition, the hexagonal roller parts have a strong mutual polishing effect, which is more conducive to improving the brightness of the coating. 2.2 Roller Axial Horizontal The axial direction of the drum is horizontal. Therefore, when the horizontal drum is tumbling to drive the parts, the running direction of the parts is perpendicular to the horizontal plane, which is favorable for the full mixing between the various parts and improving the brightness of the coating. And, the vertical running of the parts also gains advantages for the loading of the horizontal drum. For example, it is not uncommon for a horizontal roller to load about 150 kg of parts in production, which is incredible for other barrel plating methods. Especially in recent years, the length and diameter of the horizontal roller have been greatly developed, and the size and weight of parts suitable for barrel plating have also increased. Many of the original plated parts can also be barrel plated. All of these make the superiority of barrel plating labor production efficiency better reflected. Horizontal barrel plating has many advantages such as high labor productivity, good surface quality of plated parts, and wide range of applicable parts, and it is widely used in barrel plating production. The application scope of horizontal barrel plating covers the vast majority of small parts electroplating processing of hardware, household appliances, automobile and motorcycle, bicycles, electronics, instruments, watches, pens, magnetic materials and other industries. It is the main force of electroplating processing of small parts. . Therefore, for many years, the research focus of barrel plating technology has always centered on horizontal barrel plating. However, due to the closed structure of the horizontal drum, defects such as long time of horizontal barrel plating, uneven thickness of the coating, poor quality of the coating in the low current area of ​​the part, and the like are impaired, thereby affecting its application in production. 3. Inclined barrel plating The barrel type of inclined barrel plating is in the form of a "bell" or "bowl". Therefore, the inclined drum is also referred to as a bell drum. The axial direction of the roller is approximately 40º ~45º the angle, then the running direction of the part is inclined to the horizontal plane, and the name of the inclined barrel plating comes from this. 1-motor; 2-drum; 3-cathode; 4-plating bath; 5-anode; 6-conductor trough; 7-lift handle. Fig. 2 Tilting immersed barrel plating machine The currently used inclined barrel plating equipment is called Tilt-immersion type barrel plating machine (as shown in Figure 2). The tilt-type submerged immersion barrel plating machine was used in the Shanghai area in the 1960s and is popular for its ease of operation, flexibility, and ease of maintenance. In addition, the use of oblique barrel plating machine damage is lighter, more suitable for parts that are vulnerable or require high dimensional accuracy. However, the barrel load of the inclined barrel plating machine is small, the rolling strength of the parts is not enough, and the productivity and plating surface quality are inferior to the horizontal barrel plating machine. Therefore, the application and development of inclined barrel plating has always lagged behind horizontal barrel plating for many years. 4. Vibration Electroplating Vibratory electroplating is a new small part electroplating new technology that was developed in the early 1980s and developed in the late 1970s. It has more outstanding advantages than conventional barrel plating technology, so it is rapidly applied and developed once it is available. Domestic vibrating electroplating occurred in the late 1980s and has gradually become widespread in the electroplating of small parts since the late 1990s. 1-Vibrator; 2-Vibrator; 3-Vibrating shaft; 4-Choccock Figure 3 Vibrating Screen Vibrating plated roller is in the shape of a "round screen" or "disc". The vibration force of the device is achieved. Therefore, vibrating plated rollers are generally referred to as "vibrating screens" (as shown in Figure 3). The vibration axis of the vibrating screen is perpendicular to the horizontal plane, and the direction of movement of the components in the vibrating screen is the horizontal direction. The vibrating plated vibrating screen structure and vibrating axial direction are essentially different from the traditional horizontal roller, so it will produce different effects compared with the traditional horizontal roller plating. 1 The upper part of the feed basket of the vibrating screen is completely opened and completely breaks the traditional horizontal type. The closed structure of the roller eliminates the difference in ion concentration inside and outside the roller. Therefore, the barrel plating defects brought about by the drum-enclosed structure are greatly improved. For example, the deposition speed is high, the thickness is uniform, and the quality of the coating in the low current area of ​​the part is good. 2 By controlling the vibration frequency or amplitude of vibrating screens, the purpose of controlling the mixing conditions of the parts in the vibrating screen can be achieved, so that the thickness fluctuation of the plating of each part can be controlled to be small. 3 The electroplating uses a large current density and at the same time performs mechanical finishing. The coating is crystallized with a high degree of surface brightness. 4 The abrasion and abrasion of parts are less than other barrel plating methods. In addition, the cathode conducts electricity steadily during electroplating and the clips and card components are light, and parts can be sampled at any time for quality inspection. However, due to the restrictions of the vibrating screen structure and the vibration axis, the loading capacity of the vibrating screen is relatively small, and the cost of the vibrating plating equipment is also relatively high, so the current vibratory plating is not suitable for a single piece with a slightly larger volume and a larger quantity. Plating of parts. But for the parts that are not suitable or can not be used for conventional barrel plating or high quality requirements, such as needle-shaped, small, thin-walled, easy to scratch, easily deformed, high-precision parts, etc., vibration plating has other barrel plating methods unparalleled superior Sex. Therefore, vibration plating is a powerful supplement to conventional barrel plating. Four, barrel plating precautions 1. Current density difference Large barrel current cathode current density is large, but due to the great difference in current density, most of the current consumption in the workpiece of high current density, the average current density is very small, the result is Cathode current efficiency is low, and if the operation is slightly inadvertent, the coating thickness is difficult to guarantee. 2. Chemical dissolution at the same time in the barrel plating process. When the workpiece is tumbling, the current will be intermittent. It is required that the thick plating layer needs to extend the barrel plating time. However, it is still difficult to thicken the plating layer in the local area. 3. Adjust the main salt concentration in time The main salt in the barrel plating solution is consumed quickly. This is mainly caused by the fact that the area of ​​the anode is often insufficient and the workpiece is worn out. When the main salt content is too low, the current efficiency will be reduced and the plating will be difficult to plate. For this reason, it is necessary to make timely adjustments based on laboratory analysis data. 4. Barrel plating parts are difficult to pre-treat Barrel plating parts can only be pre-treated in the basket, which inevitably overlaps, making it difficult to completely remove dirt. Therefore, the barrel plating solution is apt to be contaminated. Since the barrel plating solution is more sensitive to impurities, the purification treatment of the solution requires a large amount of work and is often liable to delay the production. 5. Change in pH of the barrel plating solution The change in the pH value is particularly noticeable in the case of barrel nickel plating. This is because the partial hydrogen evolution is intense during the barrel nickel plating process. To maintain production, the pH needs to be diligent. V. Summary The three methods of barrel plating have their own different characteristics, advantages and disadvantages, and the scope of application. In the production, according to the specific conditions such as the shape, size, batch, and quality requirements of the plating parts, an accurate and reasonable barrel plating method should be selected. To achieve the purpose of saving efficiency and improving product quality for the company. For example, horizontal barrel plating should be preferred for conventional small parts. For the small parts that are not suitable or cannot be used for horizontal barrel plating or with high quality requirements, vibration plating methods are generally considered. But vibration plating is not a kind of "salvage", sometimes for vibrational plating can not solve the small parts, you can use some of the more special plating methods, such as basket plating, screen plating or cloth pocket plating.
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