PET plastic is generally a common raw material for plastic bottled beverages. Its advantages are low viscosity, good fluidity, and large specific heat capacity. The disadvantages are easy sticking of the material, high moulding temperature, narrow material temperature adjustment range, poor processability, etc.
Selection Suggestion
According to the characteristics of PET plastic, we can choose PET injection molding machine from the following aspects:
1. Screw, screw length-to-diameter ratio, design special PET screw, generally plastic screw length-to-diameter ratio is about 18-22, PET screw length-to-diameter ratio is generally more than 1:24, the larger the ratio, the better the plasticizing ability it is good.
2. The mold capacity space is determined by the mold size to determine whether the large column distance, mold thickness, minimum mold size, and template size of the machine are appropriate to confirm whether the mold can be placed. The width and height of the mold must be smaller than or at least one size smaller than the inner distance of the large column; the width and height of the mold should preferably be within the size of the template; the thickness of the mold must be between the thickness of the injection molding machine; Meet the minimum mold size recommended by the PET injection molding machine.
3. The product removal space is determined by the mold and the finished product whether the mold opening stroke and the mold supporting stroke are sufficient for the finished product to be removed. The mold opening stroke must be at least more than twice the height of the finished product in the direction of opening and closing the mold; the mold supporting stroke and the supporting force must be sufficient to eject the finished product.
4. The clamping force depends on the product and plastic to determine the tonnage of the clamping force of the machine. When the raw materials are injected into the mold cavity at high pressure, a mold supporting force will be generated. Therefore, the clamping unit of the injection molding machine must provide sufficient clamping force to prevent the mold from being expanded. The calculation of the clamping force demand is as follows:
Calculate the projected area of the finished product in the direction of the switch mold from the appearance size of the finished product;
Die support force = projected area of the finished product in the direction of the switch mold (cm²) × number of mold cavities × pressure in the mold (kg/cm²);
The clamping force of the machine must be greater than the clamping force, and for the sake of safety, the clamping force of the machine is usually 1.17 times greater than the clamping force.
Preliminarily determine the specifications of the clamping unit, and roughly determine the tonnage of the PET machine, and then the following steps must be performed to confirm which injection unit's screw diameter is more suitable.
5. The injection is full. Determine the required "injection volume" from the weight of the finished product and the number of cavities and select the appropriate "screw diameter". Calculating the weight of the finished product needs to consider the number of cavities (one mold and several cavities); for the sake of stability, the injection volume must be more than 1.35 times the weight of the finished product, that is, the weight of the finished product must be within 75% of the injection volume.
6. Good injection. Conditions such as "screw compression ratio" and "injection pressure" are determined by PET plastic. PET plastic needs better plasticizing ability and proper screw compression ratio design to have better molding effect. Therefore, in order to make the finished product shot better, the plasticization requirements and compression ratio must also be considered when selecting the screw.
7. Enlarge the storage motor. PET plastic is easy to stick to materials, high molding temperature and other reasons, which require a large screw torque, and often choose a storage motor two or more stages larger than ordinary machines to meet machine needs.
8. Increase the power system. The storage motor increases the screw speed and reduces the speed of the screw. While increasing the storage motor, it also increases the power system to ensure more stable operation of the machine and shorten the product cycle time. There are some special issues that may also have to be considered:
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