Acrylic PMMA Process characteristics

                                                                   Acrylic PMMA Process characteristics

1. Polymethyl methacrylate contains polar side methyl groups and has obvious hygroscopicity. The water absorption rate is generally 0.3% -0.4%. It must be dried before molding. The drying conditions are 80 ℃ -85 ℃ for 4-5h. .

2. Polymethyl methacrylate has obvious non-Newtonian fluid characteristics in the temperature range of the molding process. The melt viscosity will decrease significantly with the increase of the shear rate, and the melt viscosity is also very sensitive to temperature changes. Therefore, for the molding process of polymethyl methacrylate, increasing the molding pressure and temperature can significantly reduce the melt viscosity and achieve better fluidity.

3. The temperature at which polymethyl methacrylate starts to flow is about 160 ° C, and the temperature at which it starts to decompose is higher than 270 ° C, which has a wide processing temperature range.

4. The melt viscosity of polymethyl methacrylate is higher, the cooling rate is faster, and the product is prone to internal stress. Therefore, the process conditions are strictly controlled during molding, and post-processing is also required after the product is molded.

5. Polymethyl methacrylate is an amorphous polymer, and the shrinkage rate and its variation range are relatively small, generally about 0.5% -0.8%, which is conducive to molding plastic parts with high dimensional accuracy.

6. Polymethyl methacrylate has very good cutting performance, and its profiles can be easily machined to various required sizes.

Processing technology

Polymethyl methacrylate can adopt casting, injection molding, extrusion, thermoforming and other processes.

Casting

Cast molding is used to form profiles such as plexiglass sheets and rods, that is, profiles are formed by bulk polymerization. Post-casting products need to be post-treated. The post-treatment conditions are heat preservation at 60 ° C for 2 hours and 120 ° C for 2 hours.

Injection molding

Injection molding uses pellets prepared by suspension polymerization, and molding is performed on ordinary plunger or screw injection molding machines. Table 1 is the typical process conditions of polymethyl methacrylate injection molding.

Acrylic Bar

Injection products also require post-treatment to eliminate internal stress. The treatment is carried out in a 70-80 ° C hot air circulation drying oven. The treatment time depends on the thickness of the product.

Extrusion molding

Polymethyl methacrylate can also be extruded to form plexiglass sheets, rods, pipes, sheets, etc. using the pellets produced by suspension polymerization. The mechanical properties, heat resistance, and solvent resistance are not as good as those of cast molding. Its advantage is high production efficiency, especially for pipes and other molds using the casting method. Profiles that are difficult to manufacture. Extrusion molding can use single-stage or double-stage exhaust type extruder, screw length to diameter ratio is generally 20-25. Table 2 is the typical process conditions of extrusion molding.


Acrylic crafts

Thermoforming is the process of making plexiglass sheets or sheets into products of various sizes and shapes, clamping the blank cut to the required size on the mold frame, heating it to soften it, and then pressing it to fit the mold surface To obtain the same shape as the molding surface, and after cooling and shaping, the edge is trimmed to obtain the product. Pressing can be done by vacuum drawing or direct pressing of the punch with a profile. The thermoforming temperature can refer to the recommended temperature range in Table 3. When using rapid vacuum low drafting shaped products, the temperature should be close to the lower limit. When forming deep drawing products with complex shapes, it should be close to the upper limit temperature. Normally, the normal temperature is used.

Engraving and cutting

Is mainly for hollowing and carving of already formed acrylic or colored acrylic materials. Ordinary laser engraving and cutting machine can meet the engraving and hollowing needs of most acrylic products.