CAUSES OF FLASH IN INJECTION PRODUCTS
Why do injection products flash? Flash burr may occur during injection molding, which is largely due to the failure of mold or machine clamping force. It affects the quality of the product, we need to understand the cause of flash.
Why do injection products flash?
The material temperature is too high
For low viscosity melt materials such as polyamide, if only by changing the molding conditions to solve the spillage defect is very difficult, spillage, should consider appropriate to reduce the temperature of the barrel, nozzle and mold, shorten the injection cycle.
Insufficient clamping force
When the injection pressure is greater than the clamping force, the parting surface of the mold is not close enough to produce spillage flash. In this case, check whether the supercharging is excessive or not, and check whether the product of the projected area of the plastic part and the forming pressure exceeds the clamping force of the equipment. The forming pressure is the average pressure in the mold, which is calculated by 40mpa under normal circumstances. The molding pressure of polyethylene, polypropylene, polystyrene and ABS is about 30mpa in the production of box plastic parts. When producing deep plastic parts, the forming pressure is about 36mpa. When producing small plastic parts with volume less than 10cm3, the forming pressure is about 60mpa. If the calculated result is that the clamping force is less than the product of projection area and molding pressure, it indicates that the clamping force is insufficient or the injection positioning pressure is too high. The injection pressure should be reduced or the cross-sectional area of the injection orifice should be reduced, the pressure holding time and pressurization time can be shortened, the injection stroke can be reduced, or the cavity number should be reduced and the injection molding machine with large mold closing tonnage should be used.
Mold defects are the main cause of spillage, when there are more spillage, the mold must be carefully checked, the parting surface should be checked again, so that the moving mold and fixed mold alignment, and check whether the parting surface closely fit, cavity and mold core part of the sliding parts wear gap is out of tolerance. Whether the formwork is parallel, whether there is bending deformation, whether the opening distance of the formwork is adjusted to the correct position according to the thickness of the mold, whether the surface of the guide pin is damaged, whether the tie rod is uneven in deformation, whether the exhaust slot is too big and too deep. According to the results of the above step by step inspection, the errors can be eliminated by machining.
Improper control of process conditions
If the injection speed is too fast, the injection time is too long, the injection pressure is not distributed evenly in the mold cavity, the mold filling rate is not balanced, as well as too much feeding amount, excessive use of lubricant will lead to the spillage. It is worth paying attention to that, to eliminate the overflow flash fault must start from the mold fault, if because of the overflow flash and change the molding conditions or raw material formula, often have adverse effects on other aspects, easy to cause other molding fault.
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