The purpose of hard chrome plating is mainly to utilize the high hardness, wear resistance, and corrosion resistance of the chrome plating layer to improve the wear resistance and repair the dimensions of worn mechanical parts.The restoration of worn machine parts' dimensions, etc.

Hard chrome plating is essentially no different from decorative chrome plating, and the conventional chrome plating solution is still widely used. To increase the chrome plating speed, recent research has successfully developed efficient hard chrome plating processes that have also been widely applied in industrial production.Currently, the best in the world is Germany.Chrome plating additive VOP-Cr879is suitable for a wide range of hard chrome and Germanchrome plating additives.873VOP-Cris suitable for gravure printing hard chrome!Efficient chrome plating solution is based on traditional chrome plating solutions, with the addition of one or more organic additives and a small amount of inorganic compounds to achieve excellent performance.

1. Characteristics of efficient chrome plating process1) It has a high current efficiency and deposition speed, with a cathodic current efficiency of 22%~27%, which is twice that of traditional chrome plating solutions, thereby reducing energy consumption. Since efficient chrome plating allows for higher current densities, the deposition speed can be significantly increased. Table 3-5-14 lists the deposition speed comparison, and Figures 3-5-15 and 3-5-16 show the comparison of cathodic current efficiency and deposition speed.

2) The hardness of the chrome layer is high, with a microhardness of HV800~HV1000. Figure 3-5-17 shows the hardness retention percentage of the plating layer after 2 hours of heat treatment.

3) Wear resistance can generally be improved by 20%, and sliding friction can be increased by 25%.4) The chrome layer has a high crack density, generally 400 cracks/cm, with microscopic images of the crack surface shown in Figure 3-5-18. Since the chrome layer has a micro-crack structure, it disperses corrosion and enhances the corrosion resistance of the chrome layer.5) High current densities can be used, and electroplating below 70A/d㎡ generally does not cause burning or roughness of the plating layer. In addition,

this plating solution does not contain fluorides, and there is no erosion in the low current density area of the workpiece.6) The dispersion ability of the plating solution is better than that of traditional chrome plating.

7) The traditional chrome plating process can easily be converted to efficient chrome plating. As long as the metal impurities in the plating solution are below 7.5g/L, fluorides do not exceed 0.2g/L, and chloride ions do not exceed 100m, and an appropriate amount of additives is added.

2. Operating conditions of efficient chrome plating solutionHard chrome plating requires a thicker plating layer, which differs significantly from decorative chrome in practical operations. These differences are mainly reflected in the following aspects:

1) A considerable number of parts are locally hard chrome plated, and the areas not plated must be insulated. The insulation materials must have good adhesion, be easy to strip after plating, and be resistant to chrome acid corrosion;2) There is a saying that hard chrome plating is three parts technology and seven parts hanging tools, which shows that the design of hanging tools is very important. Attention must be paid to the conductive cross-sectional area to minimize energy loss and prevent local overheating;

3) Medium to low temperatures are often used, and high current densities are applied as much as possible to achieve high hardness and high deposition speeds;

5) Due to the poor dispersion and coverage ability of the plating solution, it is necessary to pay attention to the use of auxiliary cathodes and shaped anodes;6) The thickness of hard chrome plating is generally 2μm~50μm, with special wear-resistant chrome plating being 50μm~30μm. Repairing worn parts often requires plating 80μm~1000μm, and usually, post-plating hydrogen removal and machining are also required.The applicable thickness range for hard chrome plating on various parts is listed in Table 3-5-18.氯离子不超过100mg/L ,再加适量的添加剂即可。

2.高效镀铬液的操作条件

镀硬铬由于要获取较厚镀层，此在实际操作中与装饰铬有较大的差别，这些差别上主要表现在以下几方面:

1）相当多的零件是局部镀硬铬，不镀之处要绝缘，绝缘材料要求附着力好、镀后易剥离、耐铬酸腐蚀;

2)镀硬铬有三分技术，七分挂具的说法，可见挂具设计十分重要、要允分注意导电截面积，尽量减少电能损失，防止局部过热;

3）常采用中等偏低的温度和尽量应用大电流密度，以获得高硬度和高沉积速度;

5）由于镀液分散能力和覆盖能力差，必须注意应用辅助阴极和仿形阳极;

6）镀硬铬厚度一般为2μm~50μm，特殊耐磨镀铬为50μm~30μm,修复磨损零件往往需镀800μm~1000μm ,通常还要进行镀后除氢和机加工。

各种零件镀硬铬适用厚度范围，列于表3一5一18。