1. Plastic processing
PMMA has a certain degree of water absorption, with a water absorption rate of 0.3-0.4%, and injection molding must have a humidity below 0.1%, usually 0.04%. The presence of moisture causes bubbles, gas lines, and reduced transparency in the melt. So it needs to be dried. The drying temperature is 80-90℃, and the time is more than 3 hours. Recycled materials can be used 100% in some cases. The actual amount depends on the quality requirements, usually over 30%. Recycled materials should avoid pollution, otherwise it will affect the transparency and the properties of the finished product.
2. Injection molding machine selection
PMMA has no special requirements for injection molding machines. Because of its high melt viscosity, a deeper screw groove and a larger diameter nozzle hole are required. If the strength of the product is higher, a screw with a larger aspect ratio should be used for low-temperature plasticization. In addition, PMMA must be stored in a dry hopper.
3. Mold and gate design
The mold temperature can be 60℃-80℃. The diameter of the main runner should match the inner taper. The best angle is 5° to 7°. If you want to inject 4mm or more products, the angle should be 7°, and the diameter of the runner should reach 8 to 10mm, the overall length of the gate should not exceed 50mm. For products with wall thickness less than 4mm, the diameter of the runner should be 6-8mm
For products with wall thickness greater than 4mm, the runner diameter should be 8-12mm. Diagonal, fan-shaped and tabular gate depth should be 0.7 to 0.9t (t is the thickness of the product wall), and the diameter of the needle gate should be 0.8 to 2mm; smaller size should be used for low viscosity.
The common vent hole has a depth of less than 0.05 and a width of 6mm, and the demolding slope is between 30'-1° and 35'-1°30° of the cavity part.
4. Melting temperature
It can be measured by the air injection method: ranging from 210°C to 270°C, depending on the information provided by the supplier.
Withdraw the back seat, make the nozzle of the injection molding machine leave the main runner bushing, and then manually carry out plasticization injection molding, which is air injection molding.
5. Injection temperature
Fast injection can be used, but to avoid high internal stress, it is advisable to use multi-level injection, such as slow-fast-slow, etc. When injecting thick parts, use slow speed.
6. Detention time
If the temperature is 260℃, the residence time should not exceed 10 minutes, if the temperature is 270℃, the residence time should not exceed 8 minutes
