Now with the development of economy in our country, the use of high precision plastic mould and the number increasing, and the user requirements for the use of plastic mold is becoming more and more high, in this paper, the mold design of plastic bottle cap, shows the process method and the common quality problems, and puts forward some more reasonable solution, in order to improve the efficiency of the use of plastic bottle cap mould, improve the overall quality of the plastic bottle cap.
 
In general, in the process of plastic processing because of the mold cavity filling, resulting in the appearance of parts does not accord with the design of phenomenon is the lack of material.
 
Methods (1) devices
 
A lot of technological factors leads to lack of material for plastic parts, one of the most important reason is the filling pressure is small, injection time is short and low mold temperature caused by three factors. Hours filling pressure, injection molding machine in injection molding, lead to the cavity pressure is insufficient, the plastic is hard to fill the cavity, causing parts of material; Short time can also lead to plastic injection not completely fills the cavity, causing parts of material; Mold temperature is low, will accelerate plastic solidification, liquid liquidity decreases, and also leads to fill the cavity with plastic cannot and due to lack of material.
 
(2) equipment reasons
 
Equipment cause of the lack of material for plastic parts mainly nozzle part, generally for the nozzle clogging, general method of clearing the nozzle can be solved. Nozzle leak adhesive can also lead to lack of material, such failures generally need to replace the nozzle.
 
(3) the mould
 
Generally caused by mold inside the exhaust not unobstructed, due to the accumulation of air in cavity can't discharge, will cause the plastic filling quantity is not enough, which leads to lack of material, the measures is to reduce plastic filling speed or increase the vent on the mould.
 
Due to hot runner block or plastic melt due to unbalanced flow material flow is not smooth, cause the lack of material, general measures is to improve the lack of material products corresponding to the temperature of hot water the flow path, and use the delicate and clean raw material.
 
Flash generally occur in the mold parting position, such as: mold parting surface, with the slide block position, insert the side gap, the porosity of the push rod, etc. When the material overflow problem not timely solve will flash. Insert the side gap and push rod pore material overflow can make the plastic card on the mold, die.
 
(1) process
 
General due to the large injection molding machine injection pressure or injection speed faster. Due to its high speed within the mold cavity mould of the tension increase produce material overflow phenomenon. General settlement measures is to extend the period of injection molding and the holding time.
 
(2) equipment
 
The machine itself clamping force is not enough. Mould can't normal compaction, which generally when choosing injection molding machine model, the calibration of the machine rated generally must be greater than the injection mould clamping force von berg systeme axial cross-sectional area formed by tension when injection, otherwise will cause demoulding, form a flash. When the injection molding machine clamping device adjust the inappropriate will produce mould clamping disequilibrium itself can also cause flash insufficient parallelism.
 
(3) the mould
 
Is generally due to the mould design is not reasonable, it is difficult to solve this problem, need to design mold.
 
shrink
 
Plastic shrinkage phenomenon is mainly because of the volume contraction, the surface of the wall thickness of the raw material is pulled in, after cooling in the finished product surface appear sag. Shrinkage defects is what happens to the finished surface of most, most of the dry wall thickness.
 
(1) process
 
Injection molding machine injection molding speed and pressure maintaining time is less, make plastic illiquid, first into the mold cavity plastic cooling fast, not enough pressure maintaining time for feeding, general solution measures is to use a higher injection pressure.
 
(2) the mould
 
Plastic bottle cap mould inside the exhaust not unobstructed, can also lead to cavity with excess air cannot be ruled out, also takes less feeding of plastic, parts of shrinkage is larger, the general measures for the mold maintenance and increase the vent.