RIM process is: monomer or prepolymer in liquid state through the metering pump with a certain ratio into the mixing head for mixing. After the mixture is injected into the mold, the rapid reaction and crosslinking curing in the mold, after demolding is RIM products. This process can be simplified as follows: storage → measurement → mixing → mold filling → curing → demolding → post-treatment.
1. Storage:
RIM process used in the two-component stock solution is usually stored at a certain temperature in two separate storage, storage is generally a pressure vessel. When not being molded, the stock solution is usually circulated continuously in the reservoir, heat exchanger and mixing head at a low pressure of 0.2~0.3 MPa. For polyurethane, the temperature of the raw liquid is usually 20~40℃, and the temperature control accuracy is ±1℃.
2. Metering:
The metering of the two-component stock liquid is generally done by the hydraulic system, which consists of pumps, valves and auxiliary parts (piping system for controlling the liquid material and the oil system for controlling the work of the distribution cylinder). Injection also needs to go through the high and low pressure conversion device will be converted to the pressure required for injection. Raw liquid with a hydraulic quantitative pump for metering output, the requirements of metering accuracy of at least ± 1.5%, preferably controlled in ± 1%.
3. Mixing:
In RIM product molding, product quality depends largely on the mixing quality of the mixing head, the production capacity depends entirely on the mixing quality of the mixing head. Generally the pressure used is about 10MPa to get a better mixing effect.
4. Mold filling:
Reaction injection material mold filling is characterized by the high speed of the material flow. For this reason, it is required that the viscosity of the original liquid can not be too high, for example, the viscosity of polyurethane mixture when filling the mold is about 0.1Pa.s. The viscosity of polyurethane mixture is about 0.1Pa.s. Flow control: 600g/s.
5. Curing:
Polyurethane two-component mixture has high reactivity after injected into the mold cavity, and it can be cured and shaped in a very short time. However, due to the poor thermal conductivity of the plastic, a large amount of reaction heat can not be emitted in time, so the internal temperature of the molding object is much higher than the surface temperature, resulting in the curing of the molding object from the inside to the outside. In order to prevent the temperature inside the cavity from being too high (not higher than the thermal decomposition temperature of the resin), the heat exchange function of the mold should be fully utilized to distribute heat.
The curing time in the reaction injection mold is mainly determined by the formulation of the molded material and the size of the product. In addition, the reaction injection products from the mold out of the second thermal curing needs to be carried out.
Applications:
Automotive models and accessories, medical equipment shells, toys, digital products, home electronics, fitness equipment, and other small production, if you are doing large products, but the number of large and did not reach the number of molds, you can use low-pressure injection processing, so as to keep the products made without deformation.