Several factors affecting service life of plasticizing components of injection molding machines

Time:2022-05-10 08:22:35 / Popularity: / Source:

Plasticizing components of injection molding machine, here refers to: screw, glue barrel, glue head, glue ring, glue washer.
Several factors affecting service life of plasticizing components of injection molding machines 
When injection molding machine is working, plasticizing component is like wheel of a motor vehicle. As long as it is started, it will be subjected to pressure, impact, friction and extrusion. For same tires, driving on smooth roads and skilled drivers can often extend life of tires. And often driving on uneven roads with more gravel, coupled with frequent emergency braking actions, pattern of tire tread is quickly ground and scrapped.
Therefore, to ensure that injection molding machine is always in good condition, it is necessary to clarify performance of injection molding machine used, understand performance and quality of plastic materials used, strengthen use and management of injection molding machine to reduce failure rate, reduce maintenance costs, and extend purpose of service life.
Generally speaking, service life of plasticizing system that affects injection molding machine has following aspects:

First, effect of mechanical wear

Minerals, glass fibers, metal powders, etc. are added to some modified plastics. Existence of these materials will cause uniform mechanical wear to screw, three small parts and melt cylinder over time in process of plasticization and injection processing. Nitride and chrome plating can be removed. After wear, gap between screw and melt barrel increases, which reduces plasticizing effect, increases leakage of injection molding, reduces injection molding efficiency, and reduces processing accuracy.
Therefore, in order to minimize wear and prolong service life of plasticizing components, temperature should be appropriately increased and screw speed should be reduced during processing. Choose chrome plating or use a bimetallic solution to prevent wear more effectively.

Second, mechanical fatigue and overload work

Adjustment personnel habitually set low temperature work, high speed and high pressure work habitually, which gradually deteriorates performance of plasticizing components. For example, when processing PC and PA plastics, when temperature does not meet requirements, plastic viscosity is very large. If sol action is forced at this time, sol pressure must be increased, and sol torque must be increased, thus increasing stress fatigue of screw.
At the same time, because viscosity of plastic melt is very high at this time, injection pressure and injection speed must be increased for injection molding, which increases impact and load of three small parts, accelerates their wear and stress fracture.

Third, human factors (including operational errors or illegal operations, etc.)

1) When metal impurities are mixed in plastic and enter melt cylinder together, due to extrusion action, screw rib, screw groove, rubber ring and rubber gasket of screw are worn to different degrees, resulting in unstable injection molding and easy to produce black spots and black lines;
2) Artificially adding wrong plastic, adding high temperature plastic to melt barrel set to low temperature, resulting in excessive torque of screw during sol, causing screw to produce stress fatigue;
3) Cold start is a kind of anxious and irresponsible work attitude. When temperature of sol cylinder has not reached set required temperature or just reached it, outer layer of residual material in material tube absorbs heat from heating ring to make temperature higher, while inner layer temperature is still very low. Therefore, torque of screw is very large during cold start, which causes screw to produce stress fatigue. In severe cases, screw will be broken quickly, rubber head and rubber ring will be broken. Most of metal impurities entering sol cylinder are brought in together with crushed material.
Therefore, damage of blades of crusher should be checked frequently, and if blades are found to be worn, they should be replaced immediately. On the other hand, magnets in blanking hopper should be checked frequently. When metal scraps adsorbed around magnet are saturated, adsorption force for iron filings on outer layer will weaken.

Fourth, correct assembly, debugging and replacement of parts

plasticizing components of injection molding machines 
This aspect is also very important. If assembly of sol cylinder is not tight enough, screw will hit sol cylinder during sol or injection action, causing screw or sol cylinder to wear out. Therefore, technical status of equipment should be checked regularly, and attention should be paid to abnormal phenomena of parts during processing.

Fifth, damage caused by improper workmanship

1) Long-term use of high back pressure sol can speed up wear of three small plasticized parts. This situation generally occurs when toner is used. Since toner is difficult to disperse, method of increasing back pressure is adopted.
2) For plastics with high viscosity, fast sol is used for sol, so that screw produces stress fatigue.
3) For high-temperature plastics, especially plastics with glass fiber added, high-speed sol method should not be used.

Sixth, chemical corrosion

Corroded metal material is an iron component. Common corrosive plastics are: flame retardant plastics, acid plastics, PVC plastics, etc. After screw, melt barrel and flange are corroded, some pits are formed on the surface, and surface is rough, which makes flow resistance of molten material large when injection molding machine is working. Some materials tend to adhere to surface, causing decomposition and carbonization. If corrosion is severe, gap between screw and the melt cylinder will become larger, leakage flow will increase, and injection molding efficiency will be reduced.
Whether it is a flame retardant plastic or an acid glue, acid gas will be decomposed when plastic is processed at high temperature, plastic melt will easily carbonize and stick to metal. Therefore, on the one hand, plasticizing components should be made of stainless steel or surface chrome plating; on the other hand, low back pressure, low temperature and low shear processes should be used as far as possible in production and processing to reduce degradation of plastics;
Thirdly, due to thermal sensitivity of above plastics, too high temperature or too long heating time will easily cause plastic decomposition, degradation and carbonization. Therefore, unreasonable shutdowns should be avoided and reduced in production process. If it is necessary to stop machine, temperature should be lowered first, material gate should be closed, and after molten material in sol cylinder is finished, sol cylinder should be cleaned with PP material or PS material before shutdown.

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