The molding temperature range depends on the following aspects.
① The minimum temperature at which the material can be molded with sufficient accuracy.
The highest temperature refers to the temperature when the material does not have thermal damage. Thermal damage may be caused by surface burning, color change, over-brightness, bubbles, surface cracking, or the material cannot be reworked (the surface is no longer smooth when passed through the machine).
HIPS sheet has a molding temperature range of 80K wide: molding temperature of 120~150°C (200°C) during pressure molding; The forming temperature of vacuum forming is 165 (140°C) ~ 190°C (200°C).
OPS materials only have a molding temperature range of 10K; Pressure and vacuum molding molding temperature 110 ~
115°C (120°C).
The main purpose of hot forming sheet heating is to heat the whole forming surface evenly. For radiation heating, it is worth noting that the mold frame and mold core in the heating area should also play a good role.
Every thermoplastic in a certain temperature range, will have a large draft, in the best forming temperature range of drafting only requires a small force. If the thermoforming machine cannot provide the necessary forming force, it is necessary to further heat the forming material in order to obtain the required dimensional accuracy of the product. This is equivalent to the sheet not being molded in the optimal stretchability range. If the accuracy requirements are high in the actual processing, and high draft rate is required, the molding material needs a higher temperature, such as the vacuum molding of the refrigerator liner with a positive mold, the radius of the edge part is less than 6mm, or the bottom radius of the beverage cup with a negative mold pressure molding is less than 1.5mm. The higher the design requirements, the further it will deviate from its optimal stretchability, which will cause the wall thickness distribution to be uneven, and thin spots on the side wall of the molded product. When forming very sharp parts, some forming materials can become unstable when thermoforming. Very small dimensional tolerances on the thickness of the molding material are very easy to produce defective products. Process support design is very meaningful, but designers often do not pay enough attention to it. If the unformed sheet is marked with a grid, the draft can be evaluated after hot forming.