Technical Serialization - Maintenance and Maintenance of Plastic Injection Molding Machines (5)

Three aspects of technology:
(1) Improper mold temperature or improper cooling circuit causes mold temperature control to be unreasonable.
(2) Injection pressure is low.
(3) The injection pressure holding time is not enough or fluctuates.
(4) The barrel temperature is high or the injection cycle is unstable.
Four raw materials:
(1) There is a change in the resin properties when changing batches.
(2) Irregularities in the size of the material particles.
(3) Large moisture content.
(4) Replacement of additives has an effect on the contraction law.
1.6.14 cracked steam white mold: the ejection mechanism is not good.
Second craft:
(1) The barrel temperature is low or the mold temperature is low.
(2) High injection pressure.
(3) The pressure holding time is long.
Three raw materials:
(1) Improper lubricants or release agents or too much amount.
(2) Grades and grades do not apply.
Four product design aspects: The product design is irrational, leading to local stress concentration.
1.6.15 Tiered peeling A process aspect:
(1) The barrel and nozzle temperature is low.
(2) Back pressure is low.
(3) For PVC plastics, too rapid injection speed or low mold temperature may also cause delamination.
Two raw materials:
(1) Contamination of raw materials or foreign matter.
(2) Different plastics are mixed.
1.6.16 Swelling and blistering Some plastic products will quickly appear swollen and blistering on the back of metal inserts or in particularly thick areas after molding. This is due to the effect of internal pressure on the incomplete cooling of the hardened plastic. Under the release of gas expansion caused. solution:
(1) Reduce the mold temperature and extend the mold opening time.
(2) Reduce the drying temperature and processing temperature of the material; reduce the filling rate; reduce the molding cycle; reduce the flow resistance.
(3) Improve pressure holding pressure and time.
(4) To improve the condition that the wall surface of the product is too thick or varies greatly in thickness.
1.6.17 Slow production (1) The plastic has a high temperature and the product has a long cooling time. Should reduce the barrel temperature, reduce the screw speed or back pressure, adjust the barrel temperature.
(2) The mold temperature is high, which affects the shaping, and causes the card and the clamp to stop. It is necessary to strengthen the cooling of waterways in a targeted manner.
(3) The molding time is not stable. Should use automatic or semi-automatic operation.
(4) The barrel heat supply is insufficient. Machines with large plasticizing capacity should be used or preheating of materials should be strengthened.
(5) Improve machine production conditions such as oil pressure, oil volume, mold clamping force, etc.
(6) Nozzle flow. The barrel and nozzle temperatures should be controlled or replaced with self-locking nozzles.
(7) The wall thickness of the part is too thick. The mold should be improved to reduce the wall thickness.
2. Injection system The injection system is the heart of the injection molding machine. Its role is to ensure that the material is heated in a timed and quantitative manner, and then a certain amount of molten plastic is injected into the mold cavity with a certain amount of pressure and speed as quickly as possible. After the injection, there must be a period of holding time to supplement the mold cavity with a part of the molten material that shrinks due to cooling, so that the product is compacted and the material in the cavity is prevented from flowing back. Therefore, the injection device must ensure that the plastic is uniformly plasticized and has sufficient injection pressure and pressure holding pressure. The injection devices that can meet these requirements mainly include plunger type, plunger-screw type, and screw type.