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Selection of plastic Materials for injection cover Mould and PET bottle embryo Mold

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Selection of plastic Materials for injection cover Mould and PET bottle embryo Mold

Release date:2019-05-14 Author: Click:

Most of the engineering plastic products are processed by injection molding, and the planning of the parts must simplify the structure and mold as much as possible, save data and facilitate molding on the premise of satisfying the application requirements and meeting the characteristics of the plastic material itself. 


The following elements should be taken into account in part planning: 

First, the shape of the parts should be as simple as possible and easy to form. 

Under the premise of ensuring the application requirements, strive for simplicity, easy demoulding, prevent or reduce core-pulling structure as far as possible, such as selecting the structure of (b) in the following illustration, it can not only greatly simplify the mold structure, facilitate molding, but also improve production efficiency.

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Second, the confirmation of the wall thickness of the parts should be reasonable. 

The wall thickness of plastic parts depends on the application requirements of plastic parts, the thin injection cover mold will cause the lack of strength and stiffness of the products, warping deformation will occur briefly after the force, and the movement resistance is large during molding, so it is difficult for large and messy products to fill the mold cavity. 


On the contrary, the wall thickness is too large, not only bad material, but also lengthen the molding cycle, bottle embryo mold manufacturers reduce the yield, but also a brief occurrence of bubbles, shrinkage, warping and other defects. 


Therefore, the following points should be paid attention to when confirming the wall thickness of the parts when planning the parts: 

1. 

Under the premise of satisfying the application requirements, the wall thickness should be reduced as much as possible. 


2。. 

The wall thickness of each part of the part is as uniform as possible to reduce the internal stress and deformation. 


3. 

To accept the fastening force, the compression strength must be ensured. 


4. 

Prevent shrinkage and depression in too thick parts; 


5. 

It can accept the impact force when it is molded and ejected. 

The introduction wall thickness of some commonly used plastics abroad is as follows:

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Data wall thickness (mm). 

PA, POM 0.45Musi 3.2. 

PC, PSV 0.95 color 4.5. 

ABS 0.8Mur3.2. 


Third, the necessary demoulding angle must be set. 


In order to ensure the smooth demoulding of the parts during molding, the demoulding angle must be set in the demoulding direction, which is related to the plastic function, the shortening rate and the shape of the parts. Generally, the demoulding angle should be minimized on the premise of ensuring smooth demoulding. 


The following table shows the release angles introduced according to different data: 

Data demoulding angle. 


PA, POM, ABS 40'- 10 °30' 


PC, PSV 50mm 2 °. 


PE, PP 30% color 1 °. 


Thermosetting plastics 20 ℃, 1 °. 


The following points should be considered when confirming the release slope: 


  1. For plastic parts with large shortening rate, a larger demoulding angle should be selected; 


2. For large-scale parts or parts with high scale precision, a smaller demoulding angle should be selected. 


3. When the wall thickness of the part is thick, the forming shortens and increases, so the demoulding angle should be larger; 


4. The demoulding slope of reinforced plastics should be larger; 


5. Easy demoulding plastics such as self-lubricant can be taken small; 


6. In general, the demoulding angle is not included in the scope of public service.


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Four. lack of strength and stiffness can be considered for planning reinforcement. 


In order to satisfy the strength and stiffness of parts, it is often unreasonable to add wall thickness alone. Not only the weight of pet injection mold parts is greatly added, but also defects such as shrinkage and indentation are easy to occur. Reinforcement should be considered in part planning, which can satisfactorily deal with these problems. It can improve the strength of parts, prevent and prevent plastic deformation and warping. 

The direction of setting the reinforcement should be consistent with the direction of the material flow as far as possible, so as to prevent the material flow from being disturbed during mold filling, reducing the toughness of the parts or affecting the appearance quality of the parts. 


Five. under the premise of satisfying the application requirements, all the corners of the parts are planned into fillets as far as possible, or arc transition is used. 


The fillet has the following features: 

1. The fillet can prevent the stress from converging and improve the strength of the parts. 

Stress convergence is easy to occur at the corner of the parts, and cracks will occur when subjected to stress or impact or vibration, especially like the commonly used engineering plastic material-polycarbonate, if the forming conditions are inappropriate or the structure of the parts is unreasonable, there will be a lot of internal stress, especially stress cracking. 


The experimental data show that the stress convergence increases sharply when the fillet radius is less than 0.3 times of the wall thickness and decreases significantly when the fillet radius is greater than 0.8 times of the wall thickness. 


2. Fillet can be beneficial to mold filling and demoulding. 

For some inactive plastics or plastics with fillers, the product planning fillet is particularly important, which can not only improve the mold filling function, but also improve the product application function. 


3. The fillet is beneficial to the mold manufacturing and improve the mold strength. 

The fillet is planned on the part, and the corresponding part of the die is also filleted, which adds the firmness of the mold, so that the mold will not crack due to stress convergence during quenching or application, so the strength of the die is also added. 

Six. the standard public service of the parts should be reasonably confirmed according to the application requirements of the parts and the characteristics of the plastic materials. 


The factors that affect the scale accuracy of plastic parts are many and very messy, which can be summed up in the following aspects: 

The main results are as follows: 1. According to the characteristics of plastic raw materials, the shortening rate of crystalline and semi-crystalline plastics is larger and wider than that of amorphous plastics, so the scale accuracy of products is different. 


2. The forming process conditions, such as material temperature, mold temperature, injection pressure, holding pressure, plasticizing back pressure, injection speed, forming cycle and so on, will affect the size and fluctuation range of the molding shortening rate. 


3. The structure of the mold, such as the selection of parting surface, the planning of the gating system, exhaust, the cooling and heating of the mold, as well as the stiffness of the mold, will affect the dimensional accuracy of the parts. 


4. The wear of the die in the process of application and the wear of the guide parts of the die will also directly affect the scale accuracy of the parts. 

Therefore, it is very important to confirm the standard public service correctly and reasonably in the product planning. 

With regard to engineering plastic parts, especially those that use plastic instead of steel, planners often briefly apply the standard public service of mechanical parts, which is very unreasonable. Many industrialized countries have drawn up the standard public service of plastic parts according to the characteristics of plastics. 


China also issued GB/T14486-93 "Standard Public Service of Engineering plastic molded plastic parts" in 1993. Planners can confirm the standard public service of parts according to the requirements of plastic raw materials and parts used and according to the rules in the code. 

Seven. the planning of engineering plastic parts should not only pay attention to the above points, but also pay attention to the design of various holes, side concave (convex), threads and inserts. They are no longer listed here one by one. If you need to know, you can refer to the relevant professional books. you are also welcome to communicate and comment with us.


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Foshan Shunde Zongsheng Precision Mould Co., Ltd. 

Tel: 0757 Tel: 22269630 / 13923298099 (Mr. Nie). 

Web site: www.fszongsheng.com. 

Add: no. 1, Rongye 6 road, Fengxiang industrial zone, Daliang, Shunde district, Foshan, Guangdong


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