The defects and abnormal phenomena of
The defects and abnormal phenomena of injection moldingare finally reflected in the quality of injection molding products. The disadvantages of injection molding products can be divided into the following points:
(1) Insufficient injection
(2) Product overflow
(3) Product dents and bubbles
(4) Product has joint mark
(5) Crispy product
(6) Plastic discoloration
(7) Products have silver wire, stripes and flow marks
(8) Turbidity at product gate
(9) Product warpage and shrinkage
(10) Incorrect product size
(11) Product paste in mold
(12) Material paste flow channel
(13) Spout salivation
The following describes the causes and the ways to overcome them.
1. How to overcome the lack of injection
There are many other reasons for the insufficient injection of the product.
(1) Equipment reason:
Hopper interruption;
Hopper necking partially or completely blocked;
Insufficient feeding quantity;
Abnormal operation of feeding control system;
Plasticizing capacity of injection press is too small;
Abnormal injection cycle caused by equipment.
(2) Injection condition reason:
Injection pressure is too low;
The loss of injection pressure is too large in the injection cycle;
Injection time is too short;
The injection time of total pressure was too short;
Injection rate is too slow;
Die cavity material flow interruption;
The filling rate is different;
Abnormal injection cycle caused by operating conditions.
(3) Temperature cause:
Raise the barrel temperature;
Increase nozzle temperature;
Check millivoltmeter, thermocouple, resistance heating coil (or far infrared heating device) and heating system;
Increase mold temperature;
Check the mold temperature control device.
(4) Mold reason
The flow passage is too small;
Gate too small;
Nozzle hole too small;
Gate location is unreasonable;
Insufficient number of gates;
Too small cold hole;
Insufficient exhaust;
Abnormal injection cycle caused by mould;
(5) Material reason
Material fluidity is too poor.
2. How to overcome the product flash overflow:
The edge overflow of the product is often caused by the defects of the mold. Other reasons include: the injection force is greater than the mold locking force, the material temperature is too high, the exhaust is insufficient, the feeding is excessive, and the mold is stained with foreign matters.
(1) Mold problem:
The cavity and core are not closed tightly;
Cavity and core offset;
Formwork is not parallel;
Formwork deformation;
The mold plane falls into foreign matters;
Insufficient exhaust;
Vent too large;
Abnormal injection cycle caused by mold.
(2) Equipment problems:
The projection area of the product exceeds the maximum injection area of the injection press;
Incorrect installation and adjustment of injection press formwork;
Incorrect mold installation;
The clamping force cannot be kept constant;
The injection press formwork is not parallel;
Uneven deformation of pull rod;
Abnormal injection cycle caused by equipment
(3) Injection conditions:
Mold locking force too low
Too much injection pressure;
Injection time is too long;
The time of injection full pressure is too long;
Injection rate is too fast;
The filling rate is different;
Die cavity material flow interruption;
Too much control of feeding quantity;
Abnormal injection cycle caused by operating conditions.
(4) Temperature problem:
Too high barrel temperature;
Nozzle temperature too high;
Mold temperature is too high.
(5) Equipment problems:
Increase the plasticizing capacity of the injection press;
Make the injection cycle normal;
(6) Cooling conditions:
The cooling of parts in the mold is too long to avoid shrinkage from outside to inside and shorten the cooling time of the mold;
Cool the parts in hot water.
3. How to avoid product dents and air holes
The product dents usually appear in the thick wall which is close to the thin wall because of the insufficient force on the product, the insufficient filling of the material and the unreasonable design of the product.
The air hole is caused by the lack of plastic in the mold cavity, the cooling and solidification of the outer plastic, and the shrinkage of the inner plastic to form a vacuum. Most of them are caused by the non drying of hygroscopic materials and the residual monomers and other compounds in the materials. To determine the cause of air hole, only observe whether the air bubble of plastic products appears instantaneously or after cooling when the mold is opened. If it occurs instantaneously when the mold is opened, it is mostly material problem. If it occurs after cooling, it belongs to mold or injection condition problem.
(1) Material issues:
Dry materials
Add lubricant
Reduce volatiles in materials
(2) Injection conditions
Insufficient injection volume;
Increase injection pressure;
Increase injection time;
Increase the total pressure time;
Improve injection speed;
Increase injection cycle;
Abnormal injection cycle caused by operation.
(3) Temperature problem
Excessive shrinkage caused by too hot material;
The material is too cold to be compacted;
Too high mold temperature makes the material on the mold wall unable to solidify quickly;
Mold temperature is too low to fill mold;
Mold has local hot spots;
Change cooling plan.
(4) Mold problem;
Increase the gate;
Increase the shunt channel;
Increase the main channel;
Increase nozzle hole;
Improve mold exhaust;
Balance filling rate;
Avoid mold filling material flow interruption;
The gate feed is arranged at the thick wall part of the work in progress;
If possible, reduce the difference of wall thickness of products;
Abnormal injection cycle caused by mold.
