Problems Often Encountered in The Production Process Of PP-coated Rubber And Plastic
Sep 19, 2024
We all know that PP-coated rubber has many advantages, such as: accurate product size, smooth surface, good product appearance and size repeatability, complex structures can also be formed at one time, and secondary processing does not need to damage the product. However, in the production process of PP-coated rubber and plastic, there will also be bad defects, resulting in defective products, mainly in the following aspects:
1. Lack of materials:
Lack of material means that the PP-coated rubber-plastic molded parts are not completely filled, and the production parts are mostly concentrated on the edges of the PP-coated rubber-plastic products, especially the roots and tops of the corners.
Cause Analysis:
(a) The amount of discharge is small, (bPP-coated rubber and plastic have poor fluidity, (c) the equipment pressure is not sufficient (d) the curing is too fast.
Generation mechanism and countermeasures:
① After the PP-coated rubber plastic is heated and plasticized, the melt viscosity is large, and there is not enough time, pressure, and volume to fill the mold cavity with the melt before the cross-linking and curing reaction is completed.
② The storage time of PP-coated rubber plastic is too long, and the styrene volatilization is too much, resulting in a significant decrease in the fluidity of PP-coated rubber plastic.
③ The resin paste does not penetrate the fibers. During molding, the resin paste cannot drive the fibers to flow, resulting in material shortage. For the shortage of materials caused by the above reasons, the direct solution is to remove these molding materials when cutting materials.
④Insufficient feeding amount causes material shortage. The solution is to appropriately increase the feeding amount.
⑤ There is too much air and a lot of volatiles in the molding material. The solution is to appropriately increase the number of exhausts; appropriately increase the feeding area to clean the mold for a certain period of time; appropriately increase the molding pressure.
⑥ The pressure is too late, and the molding material has completed cross-linking and curing before filling the mold cavity. ⑦ The mold temperature is too high, the cross-linking curing reaction is advanced, and the temperature should be appropriately lowered.
2. Stomata
There are regular or irregular small holes on the surface of the product, and most of them are generated at the top of the product and the thin wall in the middle.
Generation mechanism and countermeasures:
① The PP-coated rubber and plastic are wrapped in a large amount of air and the volatile content is large, and the exhaust is not smooth; the thickening effect of the PP-coated rubber and plastic is not good, and the gas cannot be effectively driven out. For the above-mentioned causes, it can be effectively controlled by a combination of increasing the number of exhausts and cleaning the mold.
② If the feeding area is too large, it can be controlled by appropriately reducing the feeding area. In the actual operation process, human factors may also cause trachoma. For example, if the pressure is too early, the gas wrapped in the molding material may not be easily discharged, resulting in surface defects of pores on the surface of the product.
3. Warping deformation
The main reason is the uneven curing of the molding compound and the shrinkage of the product after demolding.
Generation mechanism and countermeasures:
During the resin curing reaction, the chemical structure changes, causing volume shrinkage, and the uniformity of curing causes the product to have a tendency to warp toward the side that is cured first. Secondly, the thermal expansion coefficient of the product is larger than that of the steel mold. When the product cools, its unidirectional shrinkage is greater than the unidirectional thermal shrinkage of the mold. To this end, the following methods are used to solve it:
①Reduce the temperature difference between the upper and lower molds to make the temperature distribution as uniform as possible.
③ Use a cooling jig to limit deformation.
④ Properly increase the molding pressure, increase the structural compactness of the product, and reduce the shrinkage rate of the product.
⑤ Properly extend the holding time to eliminate internal stress.
⑥ Adjust the curing shrinkage of PP-coated rubber.
4. Foaming
A semicircular bulge on the surface of the cured product.
Generation mechanism and countermeasures:
It may be that the material is not fully cured, the local temperature is too high or the volatile content in the material is large, and the air is trapped between the sheets, causing the semicircle on the surface of the product to bulge.
① Properly increase the molding pressure.
②Extend the holding time.
③ Reduce the mold temperature.
④ Reduce the discharge area.
5. The surface color of the product is uneven
Generation mechanism and countermeasures:
① The mold temperature is uneven and locally too high, so the mold temperature should be properly controlled.
②The fluidity of the molding material is poor, resulting in uneven distribution of fibers. Generally, the molding pressure can be increased to increase the fluidity of the melt.
③ In the process of color paste deployment, the pigment and resin are not well miscible.