Injection pressure is one of the basic processes of rubber floor mat rubber products processing. It is a production process method in which the rubber material is directly injected into the model from the machine barrel to complete the molding and vulcanization. It is mainly used in the manufacture of rubber shoes, sealing products and shock-absorbing products. The advantage of this method is that the molding vulcanization cycle is short, the waste edge is less, the production efficiency is high, the molding and vulcanization process are integrated, the process is simple, the labor intensity is reduced, the degree of mechanization and product quality are improved, but there is an anisotropy problem of the product.
The injection process consists of five processes: feeding, plasticizing, injection, vulcanization and demoulding. According to the structure, the injection machine can be classified into four types: screw type, plunger type, reciprocating type and screw pre-molded plunger type. The structure of the vulcanization mold is relatively complex, consisting of two parts: a fixed mold and a movable mold. It needs to be made of high-strength steel and finely processed to withstand high temperature and high pressure. The operation of the mold clamping device is all mechanized and automated, and its transmission mode has two modes: hydraulic and mechanical, but the hydraulic-mechanical combination is commonly used, which requires sufficient clamping force. The key to the injection molding process is to obtain good fluidity of the rubber material under appropriate temperature and pressure conditions, and to produce qualified products in the shortest possible molding cycle. The main factors affecting the injection process are as follows.
1 temperature
Temperature is a necessary condition to ensure smooth injection and rapid vulcanization of rubber flooring. The choice of barrel temperature is related to the characteristics of the extruder and the vulcanization characteristics of the rubber. Generally, the temperature of the plunger type barrel is controlled at 70~80°C, and the temperature of the reciprocating barrel is 80~100°C, and generally should not exceed 120°C. The injection temperature should be as close to the mold temperature as possible under the premise of scorch safety permitting. The mold temperature is generally chosen to be 3~5°C lower than the scorch temperature of the rubber material, and the highest vulcanization temperature of natural rubber can be 180~200°C.
2 pressure
The injection pressure has a decisive effect on the rubber floor mold filling, and its size depends on the nature of the rubber material, the type of injection press, the structure of the model, and the injection process conditions. The pressure in the mold is generally in the range of 19. 6~68. 6 MPa. As the injection pressure increases, the viscosity of the rubber material decreases, the fluidity increases, the injection temperature increases, and the vulcanization time shortens, so increasing the injection pressure is beneficial to production.
3 hours
The time to complete a molding is the sum of the vulcanization time and the action time. In the injection cycle, the most important are the filling time and curing time. It is required that the filling time is less than the scorch time of the rubber material, and the curing time is equal to the positive curing time. Therefore, it is required that the rubber material adopts a high-temperature rapid vulcanization system, which has good anti-scorch performance at a temperature that is not too high. Once the high temperature is reached, the rubber material quickly reaches positive vulcanization, so as to achieve the purpose of shortening the curing time as much as possible.
4 Screw speed and plunger advance speed
Generally, the screw speed should not exceed 100 r/min. If the speed is too fast, it will cause the shaft wrapping phenomenon and easy to generate air bubbles; if the speed is too low, the glue temperature will be low, the injection temperature will drop, and the vulcanization time will increase. As the plunger temperature increases, the injection temperature increases, the vulcanization speed increases, and the injection time shortens. However, if the vulcanization speed is too fast, it will cause a large amount of heat generation, resulting in scorch of the rubber.
5 Compound properties
According to the requirements of the injection molding process, the rubber material should be easy to flow, the Mooney viscosity is 30~90, it has good scorch safety, it can be vulcanized quickly after being injected into the mold, the vulcanization flatness is good, the rubber material does not contain moisture, is volatile and easy to decompose Components, sizing materials have no pollution or adhesion to the model, etc.
Thermoplastic rubber can be processed by ordinary plastic injection molding machines, which has the advantages of high production efficiency, convenient processing, and reusable scraps.
