Chrome plating process characteristics
Compared with other plating types, chrome plating is a rather complicated type of plating, which has the following characteristics:
(1) Chromium is easy to passivate, so it is stable in many media. From the perspective of atomic structure, it has different characteristics compared . Chromium is a very active metal. When chromium plating is performed in chromic acid, a continuous coating can only be obtained at a very low potential . Compared with the electroplating process of other metals, the cathode reaction of chromium plating is more complicated, including the deposition of metallic chromium and the generation of trivalent chromium, and a large amount of hydrogen is reduced, so the cathode current efficiency is particularly low (10-18%) . The electrode reaction from chromate ion to reduction to metallic chromium is also complicated, and its intermediate process has been a matter of debate until now . In addition, there is a certain amount of Cr 3+ in the chromium plating electrolyte , and the chromium plating process can be realized.
(2) The chromium plating solution uses strong oxidizing chromic anhydride (CrO 3 ) instead of chromium salt, so in the process of plating , it is necessary to add external ions such 
as F - and Cr 3+ to realize the deposition of chromium The process of cathodic polarization is complicated, and multiple reactions occur at the same time, and most of the electric energy is consumed in the side reaction of hydrogen evolution. Therefore, an experienced chrome-plating worker can determine the actual condition of the cathode efficiency by how much the cathode is "spend", thereby judging whether the chrome plating is normal. This "flower" is the hydrogen gas released from the cathode.
(3) The current density used in chromium plating is very high, dozens of times higher than that of general plating types, and the cell voltage during chrome plating is also very high , which is higher than that of other plating types (6V). 1 times, usually around 12V.
(4) The anode used in chrome plating is not metal chromium, but lead + antimony or lead + tin alloy as insoluble anode. This is because chromium metal is brittle and easily broken, making it difficult to make plates. In addition, when metal chromium dissolves, it enters the solution in different valence states, which will cause large changes in the solution and be difficult to control. Therefore, an insoluble anode is used, and the dispersibility of the chromium plating solution is extremely low, and an auxiliary anode is required to obtain a uniform thickness coating for complex-shaped plating parts.
(5) During the chrome plating process, power failure is not allowed in the middle, and the temperature and current must be stable. Parts of different sizes and thicker chrome plating parts should not be in the same tank. In addition, different shapes of parts require different types of hangers, and attention must be paid to the choice of hangers.
(6) In order to ensure that the plating layer has a strong bonding force, the parts should be hung in the plating tank or hot Water Tank in advance before chrome plating, so that the temperature of the parts and the plating solution is consistent. For copper and decorative chrome-plated parts, chrome parts should not be put into the plating tank. Preheat in tank, can preheat in hot water .
(7) For parts with complex shapes, in order to improve the deep plating ability, when the power is turned on, an impact current can be used, that is, a current that can be 50%-60% higher than the normal current is used. Chrome plated under workmanship specifications .
（8）铬镀层在0.25μm时是微孔性的，其厚度超过0.25μm，铬层便出现网状裂纹，铬层厚度超过20μm时，对基体才有机械保护作用，其铬层产生裂纹的原因之一，在应力镍部分对高应力镍表面层产生微裂原因已作过讨论，这里还需要从铬镀层上作具体研究与分析。之所以产生铬裂纹的原因，是因为铬在电沉积时，吸附了一定量的氢而形成氢化铬，同时还吸附了一定量的氧，具有六方晶格构的氢化铬是很不稳定的，它分解生成体心立方晶格的铬层，由于分解时体积收缩使铬层具有很高的内应力，铬镀层便形成了微孔或网状裂纹。
镀铬的特殊性
除了上述一些特点外，在实际镀铬生产过程中，除了具有其他镀种的共同点外，应用中还要特别注意：
（1）由于其镀液分散能力差，要使镀层均匀，需要According to镀件几何形状，设计特殊的挂具、夹具（包括象形阳极），工件挂法、挂具绝缘涂覆等都很重要。
（2）需要注意镀铬过程中阴极上产生大量氢气和阳极产生大量氧气，如果排气设备抽风不良，氢氧会发生爆炸，大量氢、氧析出，带出有毒铬雾、酸雾，均需有良好的抽风装置，同时可适当添加抑雾剂，从工艺上抑制和减少污染，并注意生产安全。
（3）为获得镀铬稳定镀层，镀铬生产需要高电流，不仅需要大容量电流，同时汇流量很大，按每升镀液1~1.2A的比例（其他电镀一般0.3-0.5A/L进行电镀，必要时需冷却设置，日常生产中应注意设备维护，进而保证镀铬产品质量。
(4) The electrodeposition stress of the chromium plating layer is large, the thinner the chromium plating layer has more pores, and the thicker it is, the cracks occur. Therefore, it is necessary to be good at grasping the reasonable thickness of the plating layer layer is generally 0.1-0.5μm , and the plating time is 1-4min , Compared , the time is fast and the coating is thin. Due to its poor dispersion and covering power, the high current density parts at the end of some workpieces tend to have thick coatings and cracks, while low current density parts such as recesses often cannot be plated, so the operation must be handled flexibly .
Classification of chrome plating
Chromium plating can be divided into two categories according to its use and the characteristics of chrome plating: one is protective decorative chrome plating, commonly known as decorative chrome; the other is functional chrome plating.
For protective decorative chrome plating, copper, nickel, nickel-iron alloy or copper-tin alloy are usually used as the intermediate layer. Plating 0.2-0.5μm of chromium on the surface of the bright intermediate layer , so that products such as mechanical parts, light industrial products, instruments, medical equipment, etc. can improve their decoration, corrosion resistance and service life. Ordinary chrome plating with sulfuric acid and chromic anhydride in the protective decorative chrome plating : 
composite chrome plating with the composition of the plating solution; fast chrome plating with a certain amount of H 3 BO 3 and MgO added to the standard chrome plating electrolyte; use SrSO 4 and K 2 SiF 6 is used as a catalyst for automatic adjustment of chromium plating, as well as micro- crack chromium, microporous chromium and tetrachromic acid, salt chromium plating; trivalent chromium plating, barrel chromium plating, etc.
Uses of chrome plating
The main purpose of functional chrome plating is to increase the surface hardness of some parts, improve wear resistance, or increase functions according to the special needs of the product surface , such as hard chrome plating and milk white chrome plating are used to prevent light reflection and improve friction conditions. , pine hole chrome plating and black chrome plating and other functional chrome plating.
