Plastic Plating-influencing Factors Of Plastic Plating

Plastic plating-influencing factors of plastic plating.
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1. Material selection of plastic parts.
There are many kinds of plastics, but not all of them can be electroplated. Some plastics have poor adhesion to the metal layer and have no practical value; some of the physical properties of some plastics and metal coatings, such as the coefficient of expansion, are too different, so it is difficult to guarantee their performance in high temperature difference environment. At present, ABS is the most commonly used in electroplating, followed by PP. In addition, PSF, PC, PTFE and so on also have successful electroplating methods, but they are difficult.
two.. Modeling design of plastic parts.
Under the premise of not affecting the appearance and use, the modeling design of plastic parts should meet the following requirements as far as possible.
(1) Metal luster will make the original shrinkage become more obvious, so it is necessary to avoid uneven wall thickness of the products, so as to avoid shrinkage, and the wall thickness should be moderate, lest the wall is too thin (less than 1.5 mm), otherwise it will cause poor rigidity, easy to deform during electroplating, poor adhesion of the coating, and easy to deform and make the coating fall off in the process of use. (2) avoid the blind hole, otherwise the treatment solution left in the blind hole is not easy to clean, which will cause pollution in the next process, thus affecting the quality of electroplating. (3) the sharp edge becomes thicker in the electroplating process. The sharp edge in electroplating will cause tip discharge, resulting in the uplift of the corner coating. Therefore, the fillet transition should be adopted as far as possible, and the fillet radius is at least 0.3 mm. The plated parts are difficult to be electroplated, the central part of the plated part is thinner, the more close to the edge, the thicker the coating is, and the whole coating is uneven, so the plane shape should be changed to a slightly curved surface or a matte surface made of orange peel pattern. The larger the surface area of electroplating, the greater the gloss difference between the center and the edge, and the slightly parabolic surface can improve the gloss uniformity of the plating surface. (4) minimize grooves and protruding parts on plastic parts. Because the deep concave part is easy to be exposed during electroplating, and the protruding part is easy to be scorched. The depth of the groove should not exceed 1 of the width of the groove, and the bottom should be an arc. When there is a grille, the hole width should be equal to the beam width and less than 1 prime 2 of the thickness. (5) the plated parts should be designed with sufficient mounting position, and the contact surface with the hanger should be 2 or 3 times larger than that of the metal parts. (6) the plastic parts should be designed to make it easy to release the mold when sinking, otherwise the surface of the plated parts will be strained or sprained, or the internal stress of the plastic parts will be caused and the adhesion of the coating will be affected. (7) when knurling is needed, the knurling direction should be linear and consistent with the demoulding direction. The distance between the knurled stripes and the stripes should be as large as possible. (8) plastic parts should not use metal inserts as far as possible, otherwise the inserts are easy to be corroded during pre-plating treatment. (9) the surface of plastic parts should have a certain surface roughness.
3. Mold design and manufacture.
In order to ensure that there are no defects on the surface of plastic plated parts, no obvious directional structure and internal stress, the following requirements should be met in the design and manufacture of moulds.
The main results are as follows: (1) the mold material should not be made of beryllium bronze alloy, but should be made of high quality vacuum cast steel. the surface of the cavity should be polished to mirror light along the exit direction, the roughness is less than 0.2 m, and the surface should be plated with hard chromium. (2) the surface of the plastic parts truthfully reflects the surface of the mold cavity, so the mold cavity of the electroplated parts should be very smooth, and the surface roughness of the mold cavity should be 1 or 2 levels higher than that of the parts. (3) parting surface, weld line and core mosaic line can not be designed on the plating surface. (4) the gate should be designed in the thickest part of the product. In order to prevent the melt from cooling too fast when filling the mold cavity, the gate should be as large as possible (about 10% larger than the ordinary injection mold), it is better to use the gate and gate with circular cross-section, and the length of the gate should be shorter. (5) exhaust holes should be left to avoid defects such as gas filaments and bubbles on the surface of the parts. (6) the ejection mechanism should be selected to ensure the smooth demoulding of the parts.

4. Selection of injection machine.
Improper selection of injection machine, sometimes because the pressure is too high, the nozzle structure is not suitable or mixing makes the parts produce greater internal stress, thus affecting the adhesion of the coating.
5. Forming process of plastic parts.
Due to the characteristics of the molding process, the injection molding parts inevitably have internal stress, but if the process conditions are properly controlled, the internal stress of the plastic parts will be reduced to the minimum, which can ensure the normal use of the parts. On the contrary, if the process is not controlled properly, there will be a lot of internal stress, which will not only reduce the strength and performance of the parts, but also warp or even crack in the process of storage and use, resulting in the cracking and even shedding of the coating. Therefore, the control of process parameters should make the internal stress of the parts as small as possible. The process conditions to be controlled are raw material drying, mold temperature, processing temperature, injection speed, injection time, injection pressure, holding pressure, holding time, cooling time and so on.
6. Effect of Post-treatment of plastic parts on Electroplating.
Due to the reasons of injection molding conditions, injection machine selection, product modeling design and mold design, there will be internal stress in different parts, which will cause insufficient local coarsening and difficulty in activation and metallization. Finally, the metallized layer is not resistant to collision and the adhesion decreases. The experimental results show that both heat treatment and finishing agent treatment can effectively reduce and eliminate the internal stress of plastic parts and increase the adhesion of the coating by 2060%.
In addition, the molded plastic parts should be specially packed and isolated, and it is strictly forbidden to scratch or scratch the surface, so as not to affect the appearance of electroplating. During the inspection, the inspector should wear skimmed gloves to prevent contamination of the plated surface and affect the adhesion of the coating.