Mold plating nickel-tungsten alloy process and analytical

Mold quality and workpiece quality are closely related. Many molds (such as die-casting mold) on the surface must be plated to improve its corrosion resistance, abrasion resistance, oxidation resistance and hardness properties. Despite the traditional chrome plating technology, process maturity, quality, relatively stable, but because hexavalent chromium is a toxic substance, seriously polluting the environment. Therefore, to eliminate pollution, protect the environment, clean production, the path of sustainable development.

Electroplating nickel-tungsten alloy is to improve the quality of mold and prolong die life, cleaner production a good choice. Nickel, tungsten metal, high hardness, good wear resistance, and substrate adhesion of molten high temperature. Crystal nickel-tungsten alloy plating bright detail, good wear resistance, and the strong substrate, high hardness, high temperature Vickers hardness of more than 1,000. The technology has been widely in recent years, attention will gradually replace the mold chrome plating, but the technology prevailing coating rough, uneven pitting and other defects, severe constraints on their application development.

2 bath formula and process

Bath mainly by sodium tungstate, nickel sulfate and sodium citrate, whose contents were 40 ~ 45gL, 20 ~ 30gL, 40 ~ 50gL.

Process:

Blasting → Check → degreasing → washing → plating → test

3 Analysis of coating quality defects and their causes

Common quality defects of nickel-tungsten coating is pitting large, side, and rough white coating spherical particles, the central plating and side, corner, and R Division is seriously imbalanced, and even corner, R occurring at the micro-cracks.

3.1 Pits

Ma is a white coating on the tiny black dot defect, shape, variety, and some obvious rules, easy to find, relatively good control; a small amount of the naked eye "invisible", and only use equipment checks.

Analysis:

Die trachoma matrix, porosity, pitting, adhesion caused by bad material, etc.; die when the adhesion in a blasting grit, or sandy poor or sandy are impurities, oil, foreign matter, dust and other pollution caused by; die in degreasing when the emulsion adhesion, cleaning impurities in the water, etc.; with liquid used in compressed air, pure water and the pipes, tools and environment pollution caused by impurities; bath, activation fluid does not dissolve the salt particles, such as acidification of the electrode metal can cause pitting.

The Hemp intuitive point can be seen, while the mold surface, some of the thin adhesive materials, mainly through the analysis of pre-contaminated sandy-plated carbon compounds. It is solid, strong adhesion gradually becomes acid and alkali, anti-vibration high-viscosity jelly. In the degreasing, cleaning difficult to remove, once the negligence, into the plating process, must be covered by coating the naked eye difficult to find, can not make up.

3.2 Coating roughness

Analysis:

Basic bath composition is nickel sulfate, sodium citrate, sodium tungstate, etc., as well as salts, organic complexes and so on. Test found that: Mold plating defects mainly related to the content of impurities in the bath. Chemical purity is not high, the foreign body in the bath, the frequent use of bath, so that the bath of metal impurities in Cu, Fe, Cr, Co content exceeds the allowable range, may also lead to coating rough, hemp-point increase and white particles.

3.3 The coating thickness is seriously imbalanced

The central and side, corner, R Division coating is seriously imbalanced, and even corner, R occurring at the micro-cracks.

Analysis:

Plating the use of longer time, the coating increases the odds of defects, side, and the white spherical particles, corner, R is particularly evident at the micro-cracks. Test found that: When the bath of impurities Cu, Fe, Cr, Co contents were significantly increased 20,20,20,50 mgl, the plating quality has declined markedly.

Results also found that: the distribution of plating current situation directly affects the coating uniformity. Die edge, corner, R Department, current density was significantly higher than other parts of the corresponding quantity of metal deposition, coating thickness is large. Under normal circumstances, the central and side, corner, R Department plating thickness difference of about 4μm. Uneven current distribution will lead to poor coating thickness to 15μm and above, and in severe local metal deposition coating because of the amount of excessive shedding.

In addition, the mold shape, structure, materials, etc. also affect the coating quality.

4 responses

(1) sand blasting prior to inspection, to eliminate trachoma mold matrix, porosity, pitting, adhesion and other materials.

(2) when the first test sand blasting, if impurities, foreign matter, oil and other pollution, should be replaced immediately and completely. Promptly after blasting the remnants of sand mold surface cleaning, and other adhesive material.

(3) In addition to oil degreasing surfaces prior to testing, if oily emulsion aggregation, it is timely spray to break up; degreasing after the die surface if adhesion of oily emulsion to be cleaned.

(4) The acid activation would strictly control the time, to avoid excessive corrosion of mold; the same time, under the control of a good die groove depth, to prevent the electrode plate, connectors and other corrosion. Its corrosion will pollute the bath, resulting in plating bad.

(5) when the bath preparation of high purity chemicals, as far as possible, and timely analysis of impurities. In addition, the bath should be timing analysis, filtering, and regular replacement.

(6) According to the mold structure and shape, scientific design and reasonable current balance sheet, you can effectively inhibit the deposition of thick metal part to ensure the quality of coating.

(7) ensuring the mold to meet the premise of the production process, optimizing the mold design, in particular, help improve the coating quality.

(8) provide timely relief to the anode, repair, accessories, regular cleaning of plating sludge tank and carry out "three wastes" a comprehensive way.

(9) purification, and protection of the environment, comply with technical rules to enhance operator accountability, avoidance of environmental, mechanical impurities into the bath.

5 Conclusion

Nickel-tungsten alloy plating of new technologies, have broad application prospects. However, to improve plating quality, and must process technology, production management, and integrated control and management of.