Common problems and solutions of PVC injection molding processing for pvc foam shoes

September 16, 2019

 

Common problems and solutions of PVC injection molding processing for pvc foam shoes 
 

1, the flashing edge
(1) The mold is not tightly sealed and the mold should be repaired.
(2) The cooling rate is too slow. The cooling efficiency should be increased, and the cooling rate should be increased. It is better to pass the cooling water in the bottom mold, and the cooling effect is better.
(3) Excessive injection volume and feed. Should be appropriately reduced.
(4) Plasticizing time and injection pressure are not properly matched. After determining the relationship between the pressure and the foaming time, the injection pressure and the foaming time were appropriately adjusted.
(5) Warping deformation of the mold inner liner. The inner liner should be repaired or replaced.
(6) The oil leakage caused by the hydraulic system is insufficient. The hydraulic system should be repaired.
(7) The spring on the pin hook is too loose. The spring should be replaced to increase the pulling force of the hook.
(8) The setting time is not enough, the surface of the product is not cold enough, and the middle part of the hot material breaks through the surface overflow when the mold is opened for the first time. The first mold opening time should be extended as appropriate.

 

2, the big bubble
(1) The pvc compound/granule size of the foaming agent is too coarse and the dispersion is uneven. Generally, the foaming agent needs to be ground through three rolls, and the mill is ground in the barrel for 2~4 times, and then it is ground and used.
(2) The processing temperature is too high during kneading and granulation, the foaming agent decomposes prematurely, and the pvc compound have a foaming phenomenon. The kneading and granulation temperatures should be appropriately lowered, and the extruded particles should not have vesicles when cut.
(3) The residence time of the melt in the cylinder is too long or the processing temperature is too high. Rapid pre-plasticization should be adopted, and the plasticized melt should be injected once and used as much as possible in a multi-mode production.
(4) The back pressure of the screw is too small, and the melt is thermally expanded in the barrel. The back pressure should be increased so that the blowing agent contained in the melt is decomposed without thermal expansion.
(5) The end of the barrel leaks, forming a low pressure zone at the end exit, causing the melt to expand at the outlet to form bubbles. The discharge port temperature should be appropriately lowered. It is preferable to use a throttle valve structure at the discharge port to seal the end outlet.
(6) Proportion of recycled materials is improper. The amount should be appropriately reduced.

 

3, the expansion rate is too large
(1) The blowing agent is supplied in too much amount, resulting in excessive gas generation. The amount of gas generated should be measured and accurately fed.
(2) Too much plasticizer. Should be appropriately reduced.
(3) The mold temperature is too high. The mold should be cooled down.
(4) The holding time is too short. The product should be guaranteed to be molded after it has been completely shaped.

 

4, the expansion rate is not enough
(1) The blowing amount of the blowing agent is too small, resulting in insufficient gas generation. The amount of gas generated should be measured and accurately fed.
(2) The amount of plasticizer is too small. The amount of feed should be increased appropriately.
(3) When the product is processed for the second time, the second expansion time is too short. The cooking foaming time during processing should be appropriately extended, and the first and second foaming time intervals should not exceed 12 hours.
(4) When there is a baking pattern on the surface of the product, it indicates that the first expansion of the mold is too slow. The first mold opening time should be shortened as appropriate.
(5) When small bubbles bulge on the surface of the product, it indicates that the injection temperature is too low. The injection temperature should be increased appropriately. However, if the foaming does not occur after the molding temperature is increased, the first mold opening time should be further shortened.

 

5, the aperture is uneven
(1) The pvc granule size of the blowing agent is inconsistent and the dispersion is not good. The foaming agent should be used after being ground.
(2) If the injection pressure is too low or the injection speed is too slow, the melt will expand during the filling process to form cells of different sizes. The injection speed should be appropriately increased to increase the injection pressure.
(3) The molding temperature is too high. Should be appropriately reduced.
(4) The material in the cartridge is too much. Should try to reduce the stock through a multi-cavity and other methods.
(5) The screw back pressure is insufficient. Should be properly improved.

 

6, solid depression
(1) The product is too thin, and the melt receives a large flow resistance during filling, causing insufficient pressure in some parts. The thickness of the product should be reasonably designed. Generally, the unfoamed thickness should be more than 6mm, and the thickness should be made as uniform as possible.
(2) Uneven cooling, some parts are cooled too fast, and foaming is difficult. The product should be cooled evenly, and the cooling system of the mold must be properly set according to the physical characteristics of the product.

 

7, gate depression
(1) The gate cross-section size is too large. Should be appropriately reduced.
(2) The holding time is too short and the mold is too fast. The pressure holding time should be extended appropriately.
(3) The molding temperature is too high or too low. Should be adjusted appropriately.
(4) The hydraulic system of the molding machine is faulty and the injection pressure is insufficient. The hydraulic system should be repaired to increase the injection pressure.

 

8, flow marks
(1) The molding temperature is too low or the temperature difference in each heating zone is too large. The molding temperature should be appropriately increased, and the heating temperature of each part should be adjusted.
(2) The injection speed is too slow. Should be accelerated as appropriate.
(3) Insufficient supply. The amount of feed should be increased appropriately.

 

9, poor gloss
(1) The viscosity of the resin is too high, and the plasticizer is not uniformly absorbed. The resin should be reasonably selected.
(2) Foaming shrinkage forms uneven pockmarks. The cause of the big bubble should be detected to eliminate the large bubble failure.
(3) The molding die temperature is too low. The molding temperature should be appropriately increased.
(4) The surface finish of the mold cavity is poor or corroded. The surface finish of the mold should be improved.
(5) There is residue on the surface of the mold cavity. The mold cavity should be cleaned.
(6) Due to the decomposition and foaming of the foaming agent on the surface of the melt during the filling process, some of the cells are torn during the flow process to form a baking varnish pattern, which affects the surface gloss of the product. In this regard, auxiliary methods such as spray coloring and glazing can be used to improve the surface gloss.

 

10, uneven color
(1) The color material is not approved. Should be accurately weighed.
(2) The color material is unevenly dispersed. The colorant should be ground and grouted using a grinder.
(3) The quality of the color material is poor, the color is easy to change, and the coloring power itself is not strong. Colorants with better coloring properties should be used.
(4) The local plasticizing temperature is too high, causing discoloration. Check the heating system to reduce the local temperature.
(5) The surface has a baking-like pattern to form a color difference. The first mold opening time should be shortened as appropriate.

 

11. Raw materials
(1) The molding temperature is insufficient and the plasticization is poor. The heating system should be checked to increase the molding temperature.
(2) The formulation of raw materials is unreasonable. The formula should be adjusted.

 

12, layering
(1) Too much amount of blowing agent. Should be appropriately reduced.
(2) The molding temperature is too high. Should be appropriately reduced.
(3) The setting time is too short. The cooling set time should be extended appropriately.

 

13, deformation
(1) The expansion ratio of the bottom surface and the top surface of the product is inconsistent or the partial expansion ratio is too high. The heat transfer of the mold should be checked. The thickness ratio of the mold must be appropriate and the temperature must be uniform.
(2) The cooling setting time is too short. The cooling set time should be extended appropriately.
(3) The stress distribution of the product condensation layer is uneven. The temperature distribution of the mold should be checked to adjust the condensation stress of the melt.
(4) The mold release time is improperly controlled, or the mold is too early, and the mold is overheated; or the mold is too late, and the mold is too cold. The mold time should be reasonably controlled.

 

14, dimensional instability
(1) Foaming limit control is different. The foaming limit should be strictly controlled.
(2) When single-batch single-mode production, or molding temperature and qualitative time control are different. The consistency of the process conditions should be strictly controlled, and the uniformity of the products can be improved by a multi-cavity method.
(3) The mold error exceeds the error of the expansion ratio. The mold should be trimmed to reduce mold errors.
(4) Uneven mold filling or long-term deformation of the mold. The structural dimensions of the mold casting system should be adjusted to trim the mold to reduce errors.
(5) The mold leaks. The mold should be trimmed.
(6) The product cooling is inconsistent. The mold heating and cooling system should be checked to ensure that the mold surface temperature is uniform.
(7) The clamping force is not enough. The pulling force of the hook spring should be adjusted to appropriately increase the clamping force.

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