PP is a translucent, semi-crystalline thermoplastic with high strength, good insulation, low water absorption, high heat forming temperature, low density, and high crystallinity. Modified fillers usually include glass fiber, mineral filler, thermoplastic rubber, etc.
The fluidity of PP varies greatly from application to application, and the general flow rate of PP used is between ABS and PC.
1. Handling of plastic.Pure PP is translucent ivory white and can be dyed into various colors. the dyeing of PP in a general
injection molding machine can only use color masterbatch. There is an independent plasticizing element on the WADA machine that strengthens the blending effect, and it can also be dyed with color powder. For products used outdoors, UV stabilizers and carbon black filling are generally used. The proportion of recycled material used should not exceed 15%, otherwise, it will cause a decrease in strength and decomposition, and discoloration. PP injection molding process generally does not require special drying treatment before.
2. Injection molding machine selectionThere is no special requirement for the choice of an injection molding machine. Because PP has high crystallinity. Need to use high injection pressure and multi-stage control of computerized injection molding machine. The clamping force is generally determined by 3800t/m2 and the injection volume is 20%-85%.
3. Mold and gate designMold temperature 50-90℃, high mold temperature for high size requirement. The core temperature is more than 5℃ lower than the cavity temperature, the diameter of the runner is 4-7mm, the length of needle-shaped gate is 1-1.5mm, the diameter can be as small as 0.7mm, the shorter the length of wedge-shaped gate is, the better, about 0.7mm, the depth is half of the wall thickness, the width is twice of the wall thickness, and the length of melt flow in the cavity increases with each time. The mold must have good exhaust, the exhaust hole is 0.025mm-0.038mm deep and 1.5mm thick, to avoid shrinkage marks, we should use a large and round injection port and round runner, the thickness of reinforcement should be small (for example, 50-60% of the wall thickness). For products made of homopolymer PP, the thickness cannot exceed 3mm, otherwise, there will be bubbles (thick-walled products can only use copolymer PP).
4. Melting temperatureThe melting point of PP is 160-175℃, and the decomposition temperature is 350℃, but the temperature setting cannot exceed 275℃ during injection processing. The melting section temperature should be 240℃.
5. Injection speedIn order to reduce internal stress and deformation, the high-speed injection should be selected, but some grades of PP and molds are not applicable (human mantle now bubbles, airlines). If the surface with pattern is engraved with bright and dark stripes spread by the gate, low-speed injection and higher mold temperature should be used.
6. Melt glue back pressureThe backpressure of melt glue can be 5bar, and the backpressure of color powder can be adjusted higher.
7. Injection and pressure-holdingUse high injection pressure (1500-1800bar) and holding pressure (about 80% of injection pressure). About 95% of the full stroke, turn to pressure-holding and use a longer pressure-holding time.
8. Post-processing of the productIn order to prevent shrinkage and deformation from post-crystallization, the product should be treated by hot water soaking.
Latest blog posts
Custom molds injection molding
Custom molds injection molding is a manufacturing process that involves creating custom molds to produce plastic parts. Injection molding is a popular technique used in various industries such as...
Plastic injection molding companies
Plastic injection molding is a manufacturing process that involves injecting molten plastic into a mold to create a wide range of plastic products. From car parts to medical devices and household items, plastic injection molding is used to create a variet
PET Preform Injection Moulding Machine
PET preform injection molding is a manufacturing process that is used to create PET (polyethylene terephthalate) preforms that can be later blown into bottles, jars, and other containers. This process...
You may like
Inventory of the advantages of all-electric injection molding machines
The reason why all-electric injection molding machine is popular in the market is that it has the performance that cannot be achieved by the all-hydraulic injection molding machine, mainly in...
Plastic Chair Mould for sale
Every year produce more than 400 sets chairs moulds.
Interchangeable insert block for different versions of chair
Cycle time 35 to 40 seconds for high speed running cycle.
Suitable mould structure ( arm sliders, ejector pins, air vent, etc.)
What should I do if my injection molded products produce nozzle saliva?
Spraying, also called spray marks and spray saliva, refers to the 65 thread-like flow lines that appear at the gate of the product, mostly appearing when the mold is a side gate. When the plastic melt...
Does the external environment affect the quality of injection molded products?
Injection mold manufacturers rare ten people, hundreds and thousands of people. Some environments are very good, some are normal, and some are very bad. Does the external environment affect the product...