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Process for electroplating nickel-tungsten alloy it is known in the art that the quality of the mold is closely related to the quality of the article


The surface of many dies, such as die-casting dies, must be plated to improve their corrosion resistance, wear resistance, oxidation resistance and hardness. It is understood that the traditional chrome-plating technology, though mature and stable in quality, is very stable in quality, but because the six-valent chromium is a toxic substance, it seriously pollutes the environment. Therefore, the road of pollution prevention, environmental protection, clean production and sustainable development can be eliminated. The electroplating nickel-tungsten alloy is a good choice for improving the quality of the die, prolonging the service life of the die and cleaning the production. the nickel and the tungsten metal have the advantages of high hardness, good wear resistance and high adhesion temperature with the molten matrix. The nickel-tungsten alloy coating has the advantages of fine and bright crystal, good wear resistance, strong binding force with the matrix, high hardness, and the Vickers hardness of the nickel-tungsten alloy coating reaches more than 1000. In recent years, the technology has been paid close attention by all parties, which will gradually replace the electric chrome plating of the mold. However, it is known that the technology is widely used in the defects of roughness, non-uniformity and pitting of the coating, which seriously restricts the development of the application. in that follow, the formula and process flow of the nickel-tungsten alloy for you to analyze the mold are given below. Plating solution formula and process flow The plating solution is mainly composed of sodium tungstate, nickel sulfate and sodium citrate, and the content is 40-45gL, 20-30gL, and 40-50gL, respectively. Process flow: Inspection of the cleaning and plating of the oil-cleaning agent by the sand-blasting machine Analysis of the quality defects of the coating and its causes the quality defects of the common nickel-tungsten coating are more and more, and the coating on the side surface and the spherical surface is rough and has white particles, and the central coating layer and the side surface, the corner part and the R part are seriously uneven, even at the corner part, a fine crack or the like occurs at the R. 1. Hemp The pitting is tiny white on the coating, black dot-like defect, various shapes, some obvious and regular, easy to find, relatively good control; a small amount of naked eye “canundefinedt see” can only be checked by the instrument. Cause analysis: the sand hole, the air hole, the point corrosion, the adhesive and the like of the mould base are not caused by the bad; the mould is adhered to the sand in the sand blasting, or the sand is poor, or the sandy is caused by the pollution of the impurities, the oil, the foreign matters, the dust and the like; the mould is an emulsion which is adhered when the mould is removed, the impurities in the water when the mould is cleaned, and the like; The compressed air, pure water and its pipelines, tools and other impurities in the environment shall be caused by the pollution of the compressed air, pure water and the pipelines, tools and environment of the solution; the unmelted salt particles in the plating solution and the activating liquid, the acidified electrode metal, and the like can cause the pitting. The above-mentioned points are directly visible, and some thin-layer adhesive on the surface of the mould is mainly used as the carbon compound in the sand before plating. It is firm, and the adhesive force is gradually changed into the high-viscosity rubber with acid and alkali resistance and anti-vibration. In addition to the oil, the cleaning is not easy to remove, and once it is neglected, the plating process is not easy to be covered by the coating, and the naked eye is not easy to find or make up for it. 2. The coating is rough Cause analysis: The plating liquid is mainly composed of nickel sulfate, sodium citrate, sodium tungstate and the like, and salts, organic complexes and the like. It is found that the defects of the plating of the mold are mainly related to the content of the impurities in the plating solution. The purity of the chemical is not high, the foreign matters in the plating solution and the frequent use of the plating solution, so that the content of the metal impurities Cu, Fe, Cr and Co in the plating solution exceeds the allowable range, and the like can lead to the roughness of the coating, the increase of the twist point and the white particles. 3. The thickness of the coating is not uniform. The coating at the center and the side, corner and R is very uneven, and even the corner and R are micro-cracks. Cause analysis: After the plating solution is used for a long time, the probability of the defect of the plating layer is increased, and the fine cracks at the corner part and the corner part of the side surface and the spherical surface are particularly obvious. The results show that when the content of Cu, Fe, Cr and Co in the plating solution is increased to 20, 20, 20, 50mgl, the plating quality is obviously reduced. It is also found that the distribution of the electroplating current directly affects the uniformity of the coating. The current density at the edge, corner and R of the die is obviously higher than that of other parts, and the corresponding metal deposition amount is much, and the thickness of the plating layer is large. In normal cases, the thickness difference between the center and the side, the corner and the R is about 4. m The uneven current distribution can cause the thickness difference of the plating layer to be more than 15. m u.m, and the plating layer will fall off because the local metal deposition amount is too much. In addition, the shape, structure, material and the like of the mold also affect the quality of the coating.