Popularization of knowledge points: chrome-plated mounting, insulation and common minefields

chrome plating installation

Because of the low dispersibility of the chromium plating solution and the high current density, it is difficult to obtain a uniform chromium coating for thick chromium plating. The following points must be paid attention to when mounting:

(1) The parts should be placed in the tank not less than 100mm from the bottom of the tank, and not less than 50mm from the tank liquid level. (2) The shape of the anode should be selected and designed according to the shape of the chrome-plated parts and the distribution characteristics of the power line. The distance between the corresponding positions between the cathode and anode should be approximately equal (to make the power lines evenly distributed), and the protruding parts and edges should be protected by the cathode or properly shielded. (3) The hanger should have enough cross-section to maintain good conductivity. The current load of the conductive cross-section should not exceed 1.5A/mm2 for steel, 2.0Amm2 for aluminum, 2.5A/mm2 for brass, and 3.0A/mm2 for copper. (4) The hanger used for the parts should be convenient for loading and unloading, and the thick chrome plating should meet the uniform size and special special fixtures should be used. (5) The hanger should consider not causing “air pockets” on the parts. The small holes and grooves on the surface of the parts that are not plated should be blocked with lead or plastic in advance. In the chromium plating bath containing fluorine, the non-chromium plating surface should be insulated and protected. Especially the contact with the fixture will generate heat due to the passage of current, which is very easy to corrode, so pay attention to strengthen the protection. (6) When plating single-hole inner cavity products, to ensure the uniformity of the inner surface of the inner circle, the profiling anode (pictographic anode) must be used, the conductive material is made of copper and lead-antimony alloy strips (S6%~8%) are soldered. , This can increase the anode area, light weight and easy to use. The pole distance between the cathode and the anode is 28mm~30mm when chrome-plating the cast iron cavity; when chrome-plating the rolled steel cavity, 30mm-40mm is adopted. The diameter of the small anode is one-third of the aperture. In order to ensure the correct distance between the upper and lower poles, a double-layer hollow positioning frame is used to allow the chromium plating solution to escape through a large amount of hydrogen to make the plating solution circulate and renew. For chrome plating of two-way inner cavity products, profiling anodes must also be used. Two single-layer hollow positioning frames are used to bolt the two ends of the anode. The upper and lower ends of the plated parts are equipped with cathodic protection rings to weaken the two-wire power line. , Make the plating layer uniform up and down, and other process conditions are the same as single-hole inner cavity chromium plating. For non-through holes, the inner cavity should be chrome plated. In order to ensure a certain concentration of the bath liquid in the hole, the bath liquid should be circulated to ensure uniform chromium plating. Otherwise, the chromium plating layer at the root of the cavity without a through hole is thinner, and the upper part The chromium layer is too thick to achieve the upper and lower uniformity of the chromium coating.

Chrome-plated insulation

The following materials can be used for insulation during chrome plating: ①Metal materials: lead sheet, lead wire, iron sheet, iron wire. ②Non-metallic materials: organic glass, plastic (such as polyethylene, polyvinyl chloride, etc.) films, plates, tubes, silk, adhesive tape, and varnishes (perchloroethylene paint, nitro coating varnish and nitro varnish, glue Liquid, etc.), after adding Sudan Red, it becomes a red transparent varnish for easy inspection of the paint film. At the junction of the insulating part and the part to be plated, a protective cathode should generally be installed. This is particularly important for parts insulated with non-metallic materials.

Precautions for chrome plating

The process parameters during chromium plating have a great influence on the appearance and performance of the chromium coating. As long as a slight change, the appearance and hardness of the chromium coating will change. Therefore, the operating conditions should be determined and strictly controlled before the parts are placed in the groove. (1) The temperature of the solution does not change more than +2C, and automatic temperature control should be used. When performing size chromium plating, it should be controlled to ±1℃ as much as possible, and the change of current density should not exceed 5A/dm2. (2) Requirements for the power supply: The ripple factor of the power supply during hard chrome plating is not more than 5%. It is best to use a power supply with a smooth waveform. (3) The accuracy requirements of the ammeter and voltmeter used in production are not less than 1.5. (4) The chromium-plated parts should be immersed in the chromium-plating bath, 50mm away from the liquid surface. If the coating is thicker, it should be more than 50mm. Because the bath liquid is heated and gradually evaporates during chromium plating, the bath liquid is reduced, and the parts are easily exposed to the liquid surface. It is not allowed to directly add water to the vicinity of the chrome-plated parts during work. Because cold water will affect the quality of the chrome-plated layer, it is allowed to slowly add water around the chrome-plating tank. (5) The chromium plating solution should be prepared with water ionized water, and deionized water should also be added to the usual supplement. (6) For 30CrMnSiNizA steel parts such as rework, hydrogen must be removed to eliminate stress before chromium removal. If necessary, remove the chromium and then remove the hydrogen again, and then allow the replating. The number of repairs should be marked on the part specified on the part for verification. (7) In order to reduce the hydrogen embrittlement of the parts, the hydrogen should be removed within 4h after chromium plating, according to the process documents. The domestic conditions for hydrogen removal are: ①When using an air furnace to remove hydrogen: temperature: 200℃~230℃, time: 2h-4h②When using an oil tank to remove hydrogen: temperature: 180℃~200℃, time: 2h-4h Note: a. Oil tank The oil used for hydrogen removal should be an oil whose open flash point is more than 30 cents higher than the hydrogen removal temperature. The acid value of the oil is not allowed to exceed 0.5. Overheated cylinder oil should be used. b. For parts with tensile strength above 1240MPa, the hydrogen removal time shall not be less than 3h. (8) For the preparation and adjustment of the chromium plating solution, the catalyst adjustment method, etc., please refer to the methods introduced in Chapter 7 Decorative Chromium Plating Process. (9) The electroplating of important high-strength steel parts with tensile strength above 165MPa should be subject to itemized approval.