The preparation of BMC (DMC) is divided into two steps: ① First add the resin, colorant, mould release agent, part of the filler, etc. into the high-shear mixer to mix evenly, the mixing temperature reaches about 50 ℃, and then slowly add the remaining The filler is mixed and stirred evenly to prepare the resin premixed slurry; ②Add the premixed slurry to the Z-type reamer mixer or other mixers, add the dried chopped glass fiber, and stir for 10~15 minutes Then pour out the bulk material, squeeze it into strips and pellets with an extruder, dry and seal the package with polyester film, and store it for later use.
Points for attention in BMC moulding
1) Barrel temperature and mould temperature. During processing, BMC is required to maintain low viscosity flow for a long time at the temperature of the barrel. Generally, the temperature of the barrel should meet the low limit of BMC. The temperature of the barrel is generally divided into two or three stages of control. The temperature near the hopper is lower and the temperature near the nozzle is higher. Generally, the difference is 20~60℃, and the mould temperature is generally controlled at 135~185℃.
2) Injection pressure. Due to the poor fluidity of BMC, fast curing, and complicated mould structure, the injection pressure should be selected to be higher, generally 80~160MPa.
3) Injection speed. The increase in injection speed helps to improve the surface quality of the plastic parts, shorten the curing time but is not conducive to exhaust and increase the degree of orientation of the glass fiber. Therefore, lower injection speed should be adopted under the premise of ensuring the surface quality of plastic parts, usually 1.8~3.5m/min.
4) Screw speed and backpressure. If a screw-type injection moulding machine is used, the screw damages the glass fiber greatly when injecting BMC. In order to minimize the damage of the glass fiber, the screw speed should be selected at a low value, generally 20-50r/min. According to the viscosity of BMC, the use of low back pressure is appropriate, generally 1.4 ~ 2.0MPa.
5) Moulding cycle. Due to the different size and complexity of plastic parts, the processing time of each section is also different. The general injection time is 2~20s and the holding time is 10~20.
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Taizhou Huangyan MDC Mould&Plastic Co.,ltd
No.35-1 Qingfeng Rd, Huangyan North Industrial estate, Taizhou, Zhejiang, china 318020
Website: compression mould