Defects and abnormal phenomena of injection molding

The defects and abnormal phenomena of injection molding are finally reflected in the quality of injection molded products. The disadvantages of injection molded products can be divided into the following points:

(1) Insufficient product injection;

(2) Product overflow;

(3) Product dents and bubbles;

(4) The product has contact mark;

(5) The product is brittle;

(6) Plastic discoloration;

(7) The products have silver wire, stripes and flow marks;

(8) The product gate is muddy;

(9) Product warpage and shrinkage;

(10) The product size is not accurate;

(11) Product paste in mold;

(12) Material paste flow channel;

(13) The nozzle salivates.

The following one by one describes the causes and solutions.

1. How to overcome the shortage of product injection

The insufficient injection of product is often due to the fact that the material has solidified before filling the cavity. Of course, there are many other reasons.

(1) equipment reasons:

① The hopper stops feeding;

② The necking of hopper is partially or completely blocked;

③ The feeding quantity is not enough;

④ Abnormal operation of feeding control system;

⑤ The plasticizing capacity of injection press is too small;

⑥ The injection cycle caused by the equipment is abnormal.

(2) reasons for injection molding conditions:

① The injection pressure is too low;

② The injection pressure loss is too large in the injection cycle;

③ The injection time is too short;

④ The injection time is too short;

⑤ The injection rate is too slow;

⑥ The material flow in the cavity is interrupted;

⑦ The filling rate is different;

⑧ The injection cycle was abnormal due to the operation conditions.

(3) temperature reason:

① Increase the temperature of barrel;

② Increase the temperature of nozzle;

③ Check millivoltmeter, thermocouple, resistance electric heating coil (or far infrared heating device) and heating system;

④ Increase the mold temperature;

⑤ Check the mold temperature control device.

(4) causes of die failure

① The flow channel is too small;

② The gate is too small;

③ The nozzle hole is too small;

④ The gate position is unreasonable;

⑤ The number of gates is insufficient;

⑥ The cold hole is too small;

⑦ Insufficient exhaust;

⑧ The injection cycle caused by the mold is abnormal;

(5) material reason: poor material fluidity.

2. How to overcome product flash overflow:

The product overflow is often caused by the defects of the mold, other reasons are: injection force is greater than the locking force, the material temperature is too high, insufficient exhaust, excessive feeding, foreign matter on the mold, etc.

(1) mold problems:

① The cavity and core are not closed tightly;

② Cavity and core offset;

③ The template is not parallel;

④ Deformation of formwork;

⑤ The mold plane falls into the foreign matter;

⑥ Insufficient exhaust;

⑦ The exhaust hole is too large;

⑧ Abnormal injection cycle caused by mold.

(2) equipment problems:

① The projection area of the product exceeds the maximum injection area of the injection press;

② Incorrect installation and apintejinustment of injection press template;

③ Incorrect mold installation;

④ The clamping force cannot be kept constant;

⑤ The injection press template is not parallel;

⑥ The deformation of the pull rod is uneven;

⑦ Abnormal injection cycle caused by equipment

(3) injection conditions:

① Too low clamping force

② The injection pressure is too high;

③ The injection time was too long;

④ The injection time of full pressure is too long;

⑤ The injection rate is too fast;

⑥ The filling rate is different;

⑦ The material flow in the cavity is interrupted;

⑧ The control of feeding quantity is too large;

⑨ The injection cycle was abnormal due to the operation conditions.

(4) temperature problem:

① The barrel temperature is too high;

② The nozzle temperature is too high;

③ Mold temperature is too high.

(5) equipment problems:

① Increase the plasticizing capacity of the injection press;

② The injection cycle was normal;

(6) cooling conditions:

① The cooling time of the parts in the mold is too long to avoid shrinkage from the outside to the inside and shorten the cooling time of the mold;

② Cool the parts in hot water.

3. How to avoid dent and air hole

Product dents usually appear in the thick wall part which is close to the thin wall due to insufficient force on the product, insufficient material filling and unreasonable product design. The cause of the air hole is that the plastic in the mold cavity is insufficient, the plastic in the outer ring is cooled and solidified, and the plastic in the inner part shrinks to form a vacuum. Most of them are caused by poor drying of hygroscopic materials and residual monomers and other compounds in materials. To judge the cause of air hole, we only need to observe whether the air bubble of plastic products appears instantaneously during mold opening or after cooling. If it occurs instantaneously when the mold is opened, it is mostly a material problem. If it occurs after cooling, it is a mold or injection condition problem.

(1) Material problem:

① Drying materials

② Add lubricant

③ Reduce volatile matter in materials

(2) Injection molding conditions

① The injection volume was insufficient;

② Increase the injection pressure;

③ The injection time was increased;

④ Increase the total pressure time;

⑤ Increase the injection speed;

⑥ The injection cycle was increased;

⑦ The injection cycle was abnormal due to operation.

(3) Temperature problem

① Too hot material causes excessive shrinkage;

② The material is too cold, resulting in insufficient compaction;

③ The mold temperature is too high, resulting in the mold wall material can not be cured quickly;

④ Too low mold temperature leads to insufficient mold filling;

⑤ There are local hot spots in the mold;

⑥ Change the cooling scheme.

(4) Mold problems;

① Increase the gate;

② Increase the shunt channel;

③ Increase the main channel;

④ Increase the nozzle hole;

⑤ Improve the mold exhaust;

⑥ Equilibrium filling rate;

⑦ Avoid the interruption of filling material flow;

⑧ The gate feeding is arranged in the thick wall part of the product;

⑨ If possible, reduce the wall thickness difference of products;

⑩ The injection cycle caused by the mold is abnormal.

(5) Equipment problems:

① Increase the plasticizing capacity of the injection press;

② The injection cycle was normal;

(6) Cooling conditions:

① The cooling time of the parts in the mold is too long to avoid shrinkage from the outside to the inside and shorten the cooling time of the mold;

② Cool the parts in hot water.

4. How to prevent product seam (seam line)

The product joint mark is usually caused by low temperature and low pressure at the joint.

(1) temperature problem:

① The barrel temperature is too low;

② The nozzle temperature is too low;

③ The mold temperature is too low;

④ The mold temperature at the joint is too low;

⑤ The temperature of plastic melt is uneven.

(2) injection problem:

① Injection pressure too low:

② The injection speed is too slow.

(3) Mold problems:

Poor exhaust at the joint;

Poor exhaust of components;

The shunt is too small;

The gate is too small;

The inlet diameter of three channel is too small;

The nozzle hole is too small;

 

About PTJMould Industrial Company Limited

PTJmould is a China mold maker of plastic molds- injection mold, die casting moulds, plastic blow molding, rotational molding, medical plastic injection molding, two shot plastic injection molding, insert molding, overmolding, metal injection molding, micro injection molding, powder injection molding, ceramic injection molding, liquid injection molding, husky injection molding, household mold, casting mold, die mold tool, custom molds, china moulds, rapid prototyping tooling, plastic prototyping tooling, punch press tooling, die and tooling for mobile/ cell phone parts, automotive parts, vacuum cleaners, rechargeable tools, telephones, copiers, computers, multimedia speakers, and many other electronic products and household appliances. And also a plastic product manufacturer, mold manufacturer China– plastic parts, plastic water tank, plastic balls, plastic containers, plastic buckle, plastic anchor, plastic hanger, plastic spoon, plastic pipe fitting, plastic tumble, plastic tableware, plastic cups, plastic bottles, plastic tray, plastic cosmetic container, plastic case, plastic food container, plastic chairs, plastic caps, plastic cap closure, plastic tubes, plastic water pipes, plastic knobs, plastic tubing, plastic utility boxes, plastic racks and so on.