Reactive injection molding of foam plastics
DATE：2022/4/6 8:37:28 / READ： / SOURCE：This station
Reactive injection molding of foam plastics
Reactive injection molding of foam plastics is actually a combination of chemical processes and injection processes. But compared with injection molding, it has two main differences. One is that the mold pressure for reaction injection is very high, which makes the energy consumption and equipment cost of reaction injection system lower than that of conventional injection molding. The other is that the raw materials for reaction injection are not prepared compounds, but various chemical components, which form compounds after injection molding into parts. In the process of reaction injection, each chemical component is fully mushroom, which leads to a very fast chemical reaction. Breathable membrane production line www.handern.com com1. Raw materials and processing parameters for rim forming are shown in table 9-3.
(1) Urethane (polyurethane after rim molding) rim molding is first applied to urethane, and many corresponding processing equipment are also designed for polyurethane rim molding. At present, rim molding of polyurethane is still the rim field with the most commercial value, and in the increasing competition, rim technology of polyurethane also continues to make new progress. The curing time of parts is reduced from 60s to 30s, and the dimensional stability of flexible automobile instrument panel is improved by adding 10% ~ 15% glass fiber. At present, rim molded parts of polyurethane not only still occupy an advantage in the field of auto industry accessories, but also have hit the markets of agricultural equipment, telephone communication equipment, household appliances and structural materials. Breathable membrane production line www.handern.com com
(2) At present, urea has not formed a rim forming system based entirely on urea, because the reaction between isocyanate and amine is too fast. However, in most standard polyurethane formulations, a variety of important commercial formulations are used. This formulation uses polyols instead of ethylene glycol as a supplement to inhibit the diamine chain. The diamine filling system increases the viscosity rapidly after mixing, which can reduce the degree of turbulence during mold filling and lead to faster and cleaner demoulding. However, even if blocked, diamine is still very fast (adiabatic gelation time is 2 ~ 3S), which is too fast for some complex parts. Because the reaction speed is too fast, it is impossible to produce high elastic modulus products by increasing the proportion of diamine. Breathable membrane production line www.handern.com com
The activation energy of urea listed in table 9-3 is smaller than that of ethyl carbamate. In fact, it only shows that the initial reaction of urea is very fast, and the time taken for the final 10% conversion is longer than that of ethyl carbamate. This is because the temperature rise caused by the release of chemical energy can not accelerate the reaction of urea. Breathable membrane production line www.handern.com com
(3) Nylon 6 the thermal deformation temperature of nylon 6 is about 160 ℃. Nylon 6rim products are tough, and its crystalline shrinkage makes it easy to demould. The elastic modulus of nylon 6 can be changed by block copolymerization with polyol or rubber filler. The RIM product of the whole nylon foam has been made, and its material price is slightly higher than that of polyurethane. The existing rim forming method uses 473
Nylon 6 is also affected by water absorption, demoulding time, hot mold and knot rate.
(4) The functional group of class B resin is often called polyester, because its m formula is composed of thermosetting molding resin including unsaturated polyester and styrene. It can freely attract many varieties to form its system, so it has a certain competitiveness in material cost. As shown in table 9-3, the polyester reaction is also fast. It can be formed on the standard polyurethane rim molding machine at a hotter mold temperature. However, this system is brittle and needs some reinforcement treatment, and the polymerization shrinkage of this system is also large. Breathable membrane production line www.handern.com com
(5) Epoxy resin although epoxy resin is more expensive than phenylethylene resin, it has stronger mechanical properties and excellent electrical properties. The existing epoxy resin RM molding also needs a reinforcing agent. The epoxy resin can also be formed in a standard polyurethane machine, but its curing time is longer than that of polyurethane.
2. Rim molding process breathable film production line www.handern.com com
The monomers or oligomers are mixed into the mixing head and mixed into the mould after a certain proportion in the liquid state by the metering pump. After injection, the mold is rapidly reacted and cross-linked and solidified in the mold, and the product is foam plastic after demoulding. Component a metering mixing - mold filling - curing - pre discharge - post-treatment component B metering mechanical energy exothermic heating
(1) Storage and measurement of stock solution stock solution is usually stored in the storage tank at a certain temperature, so it is necessary to heat the stock solution storage tank. The temperature of raw liquid for polyurethane rim molding is generally 20 ~ 40 ℃, and the temperature control accuracy is ± 1 ℃. In addition, because there is a certain pressure when quantitatively pumping the stock solution, the stock solution is usually circulated at a low pressure of 0.2 ~ 0.3MPa. When the raw liquid is ejected, it is converted to the set high-pressure ejection through the raw liquid circulation low-pressure and high-pressure conversion device. The raw liquid is measured and output by hydraulic quantitative pump. In order to strictly control the correct proportion of each stock solution injected into the mold cavity for reaction, the measurement accuracy is required to be at least + 1.5%, preferably controlled at about ± 1%.
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