Rigid polyurethane foam plastics
foam process is the isocyanate, polyol, water, catalyst and other auxiliary materials together blend to make the chain growth under high speed stirring, crosslinking and foaming reaction is almost complete and foam system at the same time, this method is called one-step foaming process. Molding methods mainly include foam injection molding, reaction injection molding, compound foam and so on. Foam is a commonly used of rigid PUR foam plastics injection molding method, the various raw materials, after mixing injection mold or cavity in the foam molding parts.
RIM molding process is a highly active reaction material under high pressure of the liquid is sprayed into the mixing chamber at the same time, instantaneous mixing, then quickly get molding in injection mold cavity. The production of foam plastic into a foam inner core and skin is not foam compact structure, from the skin to the core density gradually reduce, the internal and external form an organic whole. Structure of rigid PUR foam plastics high-density skin make it has good mechanical properties, low density foam core and has the advantages of qualitative light, adiabatic, is good performance of engineering structure materials.
polyether and polyester can be used as injection foaming materials, widely used but is type polyether polyol. Such as glycerol polyether, trimethylolpropane polyether, etc. Give priority to with MDI isocyanate, catalyst is given priority to with tertiary amine compounds, can also be appropriate to add some organic tin compounds, foaming agent generally choose a fluorine chloroform. Production according to the formula in the injection mold after mixing all kinds of raw materials or parts inside the cavity of foam molding.
due to the mixing time is short, the uniformity of material mixing is very important. Mixing, bubble hole is fine and uniform, good quality; On the contrary, the bubble pore is bulky and uneven, and even the phenomenon of local chemical composition do not conform to the requirements of the formula, affect the quality of products. In the production of environmental temperature on 20 - It is advisable to 30 ℃, temperature can be controlled in 20 - material 30 ℃ or a little higher. The temperature too high or too low are not the quality of products. When the environment temperature is difficult to control, can be appropriately control raw material temperature, and catalyst dosage adjustment.
rigid PUR foam plastics is highly crosslinked structure, basic for the obturator structure, under certain load effect is not obvious deformation, deformation happened when the load is too large can not restore to its original shape. This kind of foam plastic has good insulation effect, the quality of light, is better than strength, chemical stability, etc. Rigid PUR foam plastics by using MDI and 4 - Eight functional groups of polyether polyols, change the component can obtain a half rigid PUR foam plastics.
the mold temperature directly affects the speed of reaction heat removing. Low mold temperature, injection molding products processing density is big, thick skin, high mold temperature, on the other hand. 40 - general mold temperature control early 50℃。 General mixture to solidify around 10 min after injection mould, premature release may be due to insufficient curing bubble deformation. Complete the RIM process mainly has the following steps: material preparation and polymerization, high pressure measurement and instantaneous mixing, molding and curing, unloading, stripping, cleaning the mold and injection mold release agent, curing finishing products, etc.
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