Polymethyl methacrylate (PMMA) by introducing the basic knowledge of
Polymethyl methacrylate (PMMA) is an organic glass, commonly known as"Maria" (Acrylic), is a non crystalline plastic.
PMMA purposes are as follows:
Mainly used for making ornaments, sun glasses, stationery, surface,instrument case, shade, on billboard's.
The following properties of pmma:
1, PMMA to fire, can slow burning.
2, high transparency, lightweight, easy to deformation, good guide light.
3, impact resistance and surface hardness are slightly worse, easy toscratch, so higher requirements for packaging.
4, no resistance to alcohol, ketone, alkali, soluble in aromatic hydrocarbons, chlorinated hydrocarbons (three ethyl chloride can be used as a stick full agent).
5, molding shrinkage of small (0.2-0.8%), often take 0.5-0.6%. Easy molding, dimensional stability. Commonly used in pattern material (S136H,for ordinary steel material to the province to the high degree of finish, must use the mirror steel)
Knowledge of molding process of PMMA as follows:
1, die surface to maintain smooth, chrome plated corrosion. In order not to affect the production of transparency, color, as little as possible with a release agent should increase the die die angle, convenient demoulding.
2, mold temperature and high product transparency, and reduce adverse weld, especially can reduce the product of internal stress, and easily filledcavity, the mold temperature is generally 70-90 C
3, acrylic high transparency, plastic beer defect post bubble, rhyolite,impurities, black, silver and other significant exposure, thus forming a high degree of difficulty, low rate of production of Minamata lattice.
4, raw materials are sufficient drying inadequate silver bubble phenomenonoccurs. Drying time: 6HRS, material house, the layer thickness of not more than 30mm, and with the premise of adequate filling of the die cavity,temperature should not be too high, in order to reduce the defects such asdiscoloration, silver. The temperature parameter: the front feed cylindertemperature is 200-230 DEG C, the temperature of 215-235 DEG C afterthe barrel, barrel temperature of 140-160 DEG C.
The design of channel 5, mould should be simple, smooth, usually made ofS shape to improve the cloud, gas lines product surface defects, broadgate favorable molding. Various forms of inlet. When the wall thickness is less than 4mm, the channel size 0 16.0- client in 0 18.0mm. When the wall thickness is greater than 4mm, the channel size 0 18.0- client in 0112.0mm. The vent size 0.05-0.07mmX1.5mmX6.0mm. Gate size 0.7-0.9tX2t.
6, to reduce the internal stress of heat treatment temperature of 70-80 DEG C (hot air or hot water slow cooling treatment time as the products of wall thickness and general 4HRS).
7, to reduce plastic beer spots:
1) guarantee the raw material clean (clean environment)
2) clean the mold (regular)
3) machine cleaning (cleaning barrel screw, nozzle front end, etc.).
