Several factors affect the service life of plasticized components of injection molding machines

Plasticizing components of the injection molding machine here refer to screw, melt cylinder, over rubber head, over rubber ring, over rubber washer.

When the injection molding machine is working, the plasticizing components are like the wheels of a motor vehicle, which are subject to pressure, impact, friction, and extrusion as soon as they are turned on. For the same tires, driving on a flat road and operated by a skilled driver can often extend the service life of the tires. And often in the uneven, gravel road driving, coupled with regular emergency braking action, the tire tread pattern is soon worn flat, scrap.

Therefore, to ensure that the injection molding machine is often in good condition, it is necessary to clarify the performance of the injection molding machine used, to understand the performance and quality of the plastic materials used, and to strengthen the management of the use of injection molding machine, to reduce the failure rate, reduce maintenance costs and extend the service life of the purpose.

Generally speaking, the plasticizing system of the injection molding machine affects the service life of the following aspects.
 

First, the role of mechanical wear and tear

Some modified plastics added minerals, glass fibers, metal powder, etc., the presence of these materials, in the plasticization and injection processing process, will accumulate overtime on the screw, three small parts, and melt cylinder for uniform mechanical wear. The nitriding layer and chrome plating layer can be worn away. The wear increases the gap between the screw and the melting cylinder, which reduces the plasticizing effect, increases the leakage of injection, reduces the injection efficiency, and reduces the processing accuracy.

Therefore, to minimize wear and extend the service life of the plasticizing components, the temperature should be increased and the screw speed should be reduced during processing. The choice of chrome plating or the use of bimetallic solutions can be more effective in preventing the role of wear.
 

Second, mechanical fatigue and overload operations

Tuning personnel habitually set low-temperature work, habitually set high speed and high-pressure work, so that the performance of plasticizing components gradually deteriorate. For example, when processing PC, PA plastic, in the temperature has not reached the requirements, the plastic viscosity is very large, if this time to force the melting action, must increase the melting pressure, increase the melting torque, thus increasing the stress fatigue of the screw.

At the same time, because the plastic melt viscosity is very large at this time, to carry out the injection molding process must increase the injection pressure and injection speed, increasing the impact and load of the three small parts, accelerating its wear, and stress fracture.
 

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

(1), there are metal impurities mixed in the plastic together into the melting cylinder, due to the extrusion effect, so that the screw prongs, screw groove, over rubber ring, over rubber washers produce different degrees of wear, resulting in injection molding processing instability, easy to produce black spots and black lines phenomenon.

(2), artificially adding the wrong plastic, adding high-temperature plastic to the melting cylinder set to low temperature, resulting in excessive torque of the screw during dissolution, resulting in stress fatigue of the screw.

(3), cold start, a rush mentality, and irresponsible work attitude. In the melting barrel temperature has not reached the set required temperature or just reached, the residual material in the material tube, its outer layer absorbed the heat from the heating ring to make the temperature higher, while the inner layer temperature is still very low, so the cold start when the screw torque is large so that the screw produces stress fatigue, the serious soon twist off the screw, twist off the over glue head and glue ring. Most of the metal impurities that enter the dissolving barrel are brought in with the crushed material.

Therefore, the broken blades of the crusher should be checked frequently, and found to have worn blades should be replaced immediately. On the other hand, the magnet in the drop hopper should be checked and cleaned frequently. When the magnet around the adsorption of metal chips is saturated, the adsorption force for the outer layer of iron chips will be weakened, even if it is sucked, it is easy to be washed away by the continuous flow of plastic, together with the soluble cylinder.
 

Fourth, the correct assembly, commissioning, and replacement of parts

This aspect is also very important, if the assembly of soluble barrel fashion is not tight enough, soluble or injection action will occur when the screw touches the soluble barrel phenomenon, resulting in the screw or soluble barrel wear. Therefore, the technical state of the equipment should be regularly checked, pay attention to the abnormalities of the parts in the processing.
 

Fifth, the damage caused by improper technology

(1), long-term use of high back pressure sol, speeds up the plasticization of the three small parts of the wear and tear. The situation generally occurs in the use of color powder occasions, because the color powder is difficult to disperse, so the method of increasing the backpressure.

(2), for plastics with high viscosity, the dissolution is done with fast dissolution, which causes stress fatigue of the screw.

(3), for high-temperature plastics, especially the addition of glass fiber plastic, also shall not use high-speed dissolving method.
 

Sixth, the role of chemical corrosion

Corroded metal material is the iron component. Common corrosive plastics are flame retardant plastics, acidic plastics, PVC plastics, etc. After the screw, melt cylinder, and flange are corroded, the surface produces some pits and a rough surface, which makes the injection molding machine work with high resistance to the flow of molten material. Some materials are easily attached to the surface, causing decomposition and charring. The serious corrosion makes the gap between the screw and the melt barrel bigger, and the leakage flow increases so that the injection efficiency is reduced.

Whether it is flame-retardant plastic or acidic glue, plastic will decompose acidic gas when processed at high temperature, and the plastic melt will easily char and stick to the metal. Therefore, on the one hand, plasticizing components should be selected from stainless steel or surface chrome plating program; on the other hand, low back pressure, low temperature, and the low shear process should be used as much as possible in the production and processing to reduce the degradation of plastic.

Third, due to the heat sensitivity of the above plastics, too high a temperature or too long a heating time can easily cause plastic decomposition and degradation, and carbonization, so the production process should avoid and reduce the artificial unexplained downtime. If you need to stop, you should first reduce the temperature, close the material gate, finish the molten material in the soluble cylinder, and then switch to PP material or PS material to clean the soluble cylinder before stopping.