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Production process of zinc alloy products

1. The influence of zinc alloy material selection
Standard zinc alloy materials contain about 4% aluminum, 0.75%~1.25% copper, 0.03%~0.08% manganese, and the remaining 95% is the main component zinc. But sometimes our friends in the hardware factory will not pay attention to buying the materials that are returned to the furnace for many times. There is a kind of material that has too high lead content. (Some friends in the electroplating factory will find that some products are very white after the same pretreatment The secondary product is very black, and the release powder is not white.) Lead corrodes and breaks in the boundary layer between the metal particles. During electroplating, the intergranular corrosion part expands and the plating layer is topped to produce blisters, so zinc should be controlled. The alloy composition, especially the harmful impurity lead, prevents the waste material from bringing in the impurities during the smelting operation;
2. The influence of mold and product design
1. At the beginning of the design of zinc alloy products, it is necessary to consider the mold inlet, slag outlet and exhaust settings. Because the flow path of the workpiece for feeding and slagging is smooth, no air, no water stains, no dark bubbles, which directly affects whether the subsequent electroplating is blistered, the qualified feeding and slagging molds are die-casting the workpiece, and the surface is smooth and white. No water stains.
2. As far as possible, do not design vertical planes in product design. It is best to design a few degrees of arcs without affecting the appearance (a few degrees of arcs are often invisible to the naked eye but are good for all subsequent processes)
A. Face the product, especially the large flat surface, the die-casting parts are prone to scars
B. The fullness of the face product after polishing and electroplating is poor
3. Electroplating is water plating. Everyone knows that at the beginning of product mold opening and design, it is necessary to consider whether electroplating will hide water. Avoid blind hole design as much as possible, consider whether the potion is easy to pour, and whether there is a slot for discharging potion in the combination of the workpiece, and ensure that there is enough clearance. Many finished watermark pits and whitening are related to this design.
Three, the influence of die-casting process
Die casting should avoid blank blistering
(1) To control the generation of pores, the key is to reduce the amount of gas mixed into the die casting. The ideal metal flow velocity should be continuously accelerated, and the nozzle enters the cavity through the splitter cone and runner to form a smooth and consistent metal flow. (Therefore, a tapered runner design is adopted, that is, the area of ​​the runner is gradually reduced from the nozzle to the runner, which can achieve this goal). In the filling system, the mixed gas forms pores due to the mixing of turbulence and the liquid phase of the metal. From the study of the simulated die-casting process in which the molten metal enters the cavity from the gating system, it is obvious that the sharp transition and increasing pouring in the runner The cross-sectional area of ​​the channel will cause the molten metal flow to appear turbulent and entrain gas, and the stable molten metal is conducive to the gas entering the overflow groove and exhaust groove from the runner and cavity, and expelling the air out of the mold.
(2) For water and cold barrier lines, the mold temperature can be increased, the flow speed of the alloy liquid in the inner runner, or the overflow groove in the cold barrier area can be increased to reduce the appearance of cold barrier lines. Increasing the mold temperature and increasing the flow speed of the alloy liquid in the runner can reduce the generation of water marks.
(3) It is necessary to control not to open the mold prematurely and eject the casting. The mold temperature may be too high when the casting is ejected prematurely. Due to the large number of bubbles inside the casting, when the molten metal solidification time is not enough, the strength is not established, and the mold is opened prematurely to eject the casting, the pressure bubble expands and the surface of the casting is raised and hot cracks are generated.
(4) Mold loading must consider the tonnage and pressure of the mold loading machine. We personally experienced a 20-30 blistering event after zinc alloy electroplating. A friend from a hardware factory received a large order of several million, and 8 molds were opened. The pressure was insufficient and the exhaust was poor. No matter how the pre-plating treatment was solved, there would always be 20-30% blistering. Finally, 4 molds were blocked. Change to a mold to produce 4 pieces, and then there will be no bubbles after plating.
Fourth, the influence of the machining and polishing of the rough blank
Zinc alloy die-casting products have dense and smooth surface structure and low porosity, but the thickness of the surface dense layer is relatively thin, generally only 0.05 to 0.2 mm. The inner layer is porous and loose structure. If we improperly grasp the subsequent processing procedures, after damaging the dense layer on the surface, it will make the subsequent electroplating procedures difficult to do. Normally we are through two processes
1. Sanding, hemp wheel, cloth wheel polishing, here it is necessary to pay attention to the sand line not to be too thick, do not finish sanding the dense layer of the surface, and the polishing paste should not accumulate too much, which will cause difficulty in dewaxing after electroplating (most of the wax removal With chemical agents, in principle, the longer the wax is removed, the greater the risk to product quality). In addition, the product will flow to electroplating as quickly as possible after polishing. The longer the time, the harder the polishing wax will become and the more difficult it will be to process.
2. The surface of the rolled-polished workpiece is bright; many employees in the pickling process of electroplating plants just pick it up casually, so that the roller polish attached to the surface is not cleaned, and foaming often occurs. In addition, the tumbler used in the tumbler polishing plant has a great relationship, and some surfactants in the tumbler polish are extremely difficult to wash off.
Five, the influence of electroplating process
1. Zinc is an amphoteric metal, the electrode potential is relatively negative, and it is more sensitive to acid and alkali, and is prone to chemical reactions leading to corrosion. A slight negligence in the pretreatment degreasing and activation process will cause the aluminum-rich phase or zinc-rich phase to be preferentially dissolved, and uneven corrosion on the surface will cause pitting and blistering, which will affect the product quality. Therefore, the degreasing should not be too alkaline. Strong, such as sodium hydroxide and other strong bases should be controlled, and strong acid should not be used for activation