Plastic receive gas at a filling process disturbances often forming blooming within blooming or silver markings or small thick-walled articles on product surface. The main sources of gas contained in the raw material gas is the degradation of moisture or volatile substances or excess lubricant, it may be too high temperature plastic material heating time degradation occur to produce long.
A Equipment: nozzle hole is too small, the material drooling at the nozzle or drawing, barrel or nozzle obstructions or burrs generated when the high-speed stream through the friction heat make the material decomposition.
Two molds: (1) due to defects in design, such as: poor gate location, gate is too small, multi-gate parts asymmetric arrangement gates, runners small, mold cooling system is unreasonable to make the mold temperature caused by too different melt flow discontinuity in the mold cavity, blocking the air passage. (2) mold parting surface lacked sufficient necessary or exhaust vent bore tunnel, congestion, poor location, and no inserts, machining gap exhaust thimble and the like, resulting in a cavity in the plastic when air can not enter At the same time leave. (3) the difference between the mold surface roughness, friction large, resulting in local hot spots, through the decomposition of the plastic.
Three technological aspects
(1) The material temperature is too high, resulting in decomposition. Barrel heating temperature is too high or disorders, should piecewise reduce cylinder temperatures. Feed zone temperature is too high, a portion of the plastic melt prematurely full of grooves, the air can not be discharged from the charging port.
(2) injection pressure is small, dwell time is short, so that the melt and the cavity surface is not dense paste.
(3) injection speed is too fast, the molten plastic is decomposed by a large shearing effect, generation of decomposition gas; injection speed is too slow, can not be filled cavity surface density caused by lack of products produced crazing.
(4) insufficient quantity, feeding cushion is too large, the material temperature is too low or too low mold temperature will affect the melt flow and molding pressure blooming.
(5) multi-stage injection reduce crazing: injection speed filling runner gate → → Slow fill bolus injection → low pressure slowly fill the mold, the inner mold and remove and clean gas energy in each segment.
(6) when the pre-plastic screw back pressure is too low, the speed is too high, the screw is retracted too fast, easy air together with the material to the front end of the barrel.
Four raw materials
(1) heterogeneous mixed plastic materials incorporating a lot of powder or pellets, easily entrained air melted, sometimes crazing. When contaminated raw or scrap materials containing hazardous materials readily decomposed by heat.
(2) renewable materials pellets loose structure, large air pores in the reservoir; renewable excessive number of recycled materials or materials with a high proportion of new (generally less than 20%)
(3) the raw material or feedstock comprising a volatile solvent such as dyeing assistant auxiliary liquid white oil, silicone oil lubricant, a plasticizer, dibutyl and stabilizers, antistatic agents, etc. The amount of excess or uneven mixing, to product set state into the cavity formed crazes.
(4) plastic handle without drying or moisture absorption from the atmosphere. Respond sufficiently dried raw material and use the drying hopper.
(5) Some brands of plastic, itself can not withstand higher temperatures or longer heating time. Especially when containing traces of moisture, catalytic cracking reactions may occur. For this type of plastic you want to consider adding external lubricant such as stearic acid and its salts (10kg material can be added to each 50g), to minimize the processing temperature.
Five product design: the thickness is too thick, the cooling rate different list. Mold manufacturing should increase at an appropriate sprue, runner and gate size.