im rim reaction molding
im rim reaction molding
reaction injection moulding is also known as low pressure reaction molding. it is a new process applied to the production of rapid moulding products. it is a new process in which the two-component polyurethane materials are mixed and injected into the rapid moulding at room temperature and low pressure to form the products through the chemical and physical processes such as polymerization, cross-linking and curing of the materials. it has the advantages of high efficiency, short production cycle, simple process and low cost. it is suitable for the trial production of small batches in the process of product development, as well as the production of small batches of covering parts with simple structure and large thick and non-uniform wall thickness products.
applicable mold: resin mold (more than 100 pieces); abs mould (more than 300 pieces); aluminum alloy mould (more than 1000 pieces).
pouring material: two-component polyurethane pu. materials used: hd-pu4210, dcp-rim, axson-rim 875.
physical properties: similar to pp/abs. products with aging resistance, impact resistance, high anastomosis, easy to load and unload and other characteristics.
injection pressure: about 10mpa. flow control: 600g/s.
general working time: 15-30 minutes/parts, mould temperature can be controlled below 40 ℃, parts under the environment of 80 ℃ after demoulding curing performance best 2-4 hours.
standard reproduction accuracy: 0.20mm/100mm.
casting sample thickness: the optimal casting thickness is 4~6mm, and the maximum casting thickness is 10mm.
maximum pouring workpiece: 2000mmx1200mmx1000mm, 10kg.
rim process: monomer or prepolymer in liquid state by the metering pump to a certain ratio into the mixing head for mixing. after the mixture is injected into the mold, it is rapidly reacted and cross-linked to solidify in the mold. this process can be simplified as: storage metering mixing filling mold curing demoulding post-treatment.
(1) storage. the two components used in rim processes are usually stored in two separate tanks, usually pressure vessels, at a given temperature. when it is not formed, the original liquid is usually at a low pressure of 0.2-0.3mpa and circulates continuously in the reservoir, heat exchanger and mixing head. for polyurethane dope temperature generally is 20 ~ 40 ℃, the temperature control precision of plus or minus 1 ℃.
(2) measurement. the measurement of two-component raw liquid is generally completed by the hydraulic system, which is composed of pump, valve and auxiliary parts (the pipeline system controlling the liquid material and the oil circuit system controlling the work of the distribution cylinder). in addition, the injection shall be converted into the pressure required by the high and low pressure conversion device. the original liquid is metered by hydraulic quantitative pump, the metering accuracy is required to be at least 1.5%, and the best control is 1%.
(3). in rim product molding, the quality of the product largely depends on the mixing quality of the mixing head, and the production capacity completely depends on the mixing quality of the mixing head. generally, the pressure is about 10mpa to achieve better mixing effect.
(4) mold filling. the characteristic of reaction-injection material filling is high speed of material flow. for this reason, it is required that the viscosity of the original solution should not be too high. for example, the viscosity of the polyurethane mixture when filling the mold is about 0.1pa.s. flow control: 600g/s.
(5) curing. polyurethane two-component mixture has high reactivity after injection into the mold cavity and can be cured in a short time. but due to the poor thermal conductivity of plastic, a large number of reaction heat can not be distributed in a timely manner, so that the internal temperature of the molding material is much higher than the surface temperature, resulting in the curing of the molding material from the inside out. in order to prevent the temperature in the mold cavity is too high (not higher than the thermal decomposition temperature of the resin), the heat transfer function of the mold should be given full play to dissipate heat.
the curing time in the reaction injection mold is mainly determined by the formula of the molding material and the size of the product. in addition, a secondary heat cure is required after the product is removed from the mold.