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How to prevent and remedy the burrs(flash) in the TPU injection parts during injection process
May 10 , 2021

Burr is a common problem encountered in TPU injection products. A burr (also known as a “flash”) is an unwanted raised edge or small piece of TPU material left in a part after a injection manufacturing process. Burrs not only disfeature the appearance of plastic parts but also affect it’s properties.

How to analysis and solve the burrs problem during TPU injection process. Burrs of a TPU injection part can occur for several reasons-from raw material problems, injection molding machine problems, improper set-up of injection molding machine to the mould. Improper handling in the process and material all can cause the flash in the TPU injection parts. so recognizing the cause of burrs when it is occurring can point you in the right direction. It is necessary to proceed from obvious and easy to unconspicuous and difficult when estimate the cause of burrs. Below four sequential steps for your reference.

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1.Check the material: check whether the raw materials are thoroughly dried, whether they are mixed with impurities, whether different types of raw materials are mixed, and if the viscosity of the raw materials is affected;

2.Check the pressure and injection speed of the machine: Correctly adjust the pressure control system of the injection molding machine and the injection speed to match the clamping force;

3.Check the mould and vent,runner of the injection machine: Whether the mould are worn, whether the vent is blocked, and whether the runner design is reasonable;

4.Check the parts of the injection machine: whether there is deviation in the parallelism between the injection molding machine templates, whether the force distribution of the template tie rods is uniform, whether the screw check ring and the melt barrel are worn out.

Cause Remedies
Raw material is moist Dried thoroughly
Raw materials are contaminated Check raw materials and impurities to find out the source of pollution
The viscosity of the raw material is too high or too low Check the viscosity of the raw material and the operating conditions of the injection molding machine
Clamping force is too low check the pressure value and adjust
The injection and holding pressure are too high Check the set value and adjust
The injection pressure change over is too late Check the change over pressure position, re-adjust and change it earlier
Injection speed is too fast or too slow Check and adjust the flow control valve
The temperature is too high or too low Check the electric heating system and screw speed
Insufficient template rigidity Check clamping force and adjustment
The melt barrel, screw or non-return ring is worn out Repair or replace
Back pressure valve worn Repair or replace
Uneven clamping force Check the force of the tie rod
Templates are not parallel Adjust
Mold ventis blocked Cleanup
Mold is abrasion Check mold use times and clamping force, repair or replace
Mold parting does not match Check whether the relative position of the mold is offset, and re-adjust
Imbalance of mold runner check design and modify
Low mold temperature and uneven heating Check electric heating system and repair

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