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The injection molding process of TPU is discussed briefly

The injection molding process of TPU is discussed briefly
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  • Categories:Industry news
  • Author:
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  • Time of issue:2021-08-02 14:21
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(Summary description)

The injection molding process of TPU is discussed briefly
Top

(Summary description)

  • Categories:Industry news
  • Author:
  • Origin:
  • Time of issue:2021-08-02 14:21
  • Views:
Information

      

In other thermoplastic materials, when the processing temperature is higher than the melting temperature of the raw material, the melt is mainly viscous flow state. When the processing temperature is low: the fluidity of the melt is poor, or even does not flow, the melt shows less elasticity. For TPU elastomers, such as molecular when machining temperature higher than a temperature between virtual crosslinking completely lifted, the melt flow, melt appear to be more viscous flow sex when processing temperature below a certain temperature, molecular virtual crosslinking between partially lifted, melt showed both liquidity and show that the elastic, is a kind of viscoelastic body.

 

When the melt temperature is high in injection molding and filling, TPU, like other thermoplastic materials, mainly shows viscous flow, and the product can obtain a better shape, stable size and small deformation. When the melt temperature is low, TPU shows viscoelasticity. Due to poor fluidity, the product does not naturally fill the mold cavity, but fills the mold cavity with elastic expansion. When the injection pressure is withdrawn, the external force of elastic expansion disappears, and the expanded part recovers deformation.

 

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Therefore, TPU injection molding process adjustment should be paid attention to

1, processing temperature control on the final size of the product, shape and deformation has a critical impact. The processing temperature depends on the grade of TPU and the specific situation of mold design. The general trend is that IN order to obtain a small shrinkage ratio, THE processing temperature needs to be increased.

 

2. Slow and long time holding pressure will lead to molecular orientation. Although it is possible to obtain a smaller product size, the product has a larger deformation and a large difference in transverse and longitudinal shrinkage. Large holding pressure will also lead to the colloid in the mold over compression, when the product is released after the size of the cavity is larger than the size of the phenomenon.

 

3. The position of injection molding speed and pressure conversion should be set accurately. Inaccurate position setting will increase the difficulty of cause analysis and is not conducive to rapid and accurate process adjustment.

 

4, the choice of injection molding machine model should be appropriate. Small size of injection molding products should be as far as possible to choose a small model of injection molding machine, in order to increase the injection stroke, convenient for position control reasonable injection molding speed, pressure conversion. If the size of mobile phone accessories is relatively small, such as the injection molding machine is relatively large, sometimes the screw only forward 1mm product is full of glue, it is impossible to control the position.

 

5. When the moisture content of TPU is more than 0.2%, not only the appearance of the product is affected, but also the mechanical properties are obviously bad. The elasticity and strength of the injected product are poor. Therefore, it should be dried at 80℃/110℃ for 2/3 hours before injection.

 

6. The cleaning of the cylinder of the injection molding machine should be clean, and the mixing of few other raw materials will lead to the reduction of the mechanical strength of the product. The cylinder cleaned by ABS, PMMA and PE should be cleaned again with TPU nozzle material before injection, and the residual material in the cylinder should be removed with TPU nozzle material. When cleaning the hopper, special attention should be paid to the cleaning of a small amount of residual raw materials of other properties in the connection part of the hopper and the injection molding machine base. This part is easily overlooked by most technical workers in production (the above content is for reference only).

 

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