PLASTIC INJECTION MOLDING – MECHANICAL INJECTION PROCESS
GREAT ADVANTAGE – ALWAYS REFORM – ANYWHERE
Unlike elastomer injection molding, no chemical vulcanization process is initiated in thermoplastic or plastic injection molding. It is therefore a purely thermal, mechanical injection process. This process is reversible, i. e. it can be repeated as often as required by cooling and reheating to the molten state, as long as the so-called thermal decomposition of the material does not occur due to overheating. SPT manufactures classic hard component parts, but specializes in the processing of thermoplastic elastomers (TPE) in injection molding.
THE PROCESS IN PLASTIC INJECTION MOLING:
- In resin form, the thermoplastics enter the gaps between the rotating screw. This transports the granulate in the direction of the screw tip. The resin is melted due to the temperature control of the injection cylinder and the frictional heat generated when the material is sheared. As soon as a sufficient amount of material for the component volume has accumulated, the dosing process is completed and the screw no longer rotates.
- For injection, the injection unit is moved to the clamping unit. The melt is injected under high pressure through the opened nozzle into the mold. A non-return valve prevents the melt from flowing back to the hopper.
- Unlike rubber injection molding, the mold is colder tempered than the plastic melt. The melt solidifies when it reaches freezing point.
- To compensate for the shrinkage caused by cooling, a reduced pressure is maintained after filling the mold. This repression can take place until the sprue has solidified.
- After pressing, the nozzle is closed and the next cycle begins while the cooling time is running and the workpiece has solidified or sufficient rigidity has been achieved for demolding.
- The demolding can be done by ejector pins and the components fall down (bulk material). Alternatively, the parts can also be removed by a robot and placed in a controlled manner on conveyor belts.
A HOT RUNNER PLASTIC INJECTION MOLDING
The sprue can either be granulated and returned to the melt or recycled separately. Sprueless injection molding is possible with a hot runner that keeps the melt permanently above the solidification temperature. A hot runner is particularly useful for large components and larger quantities, as the entire injection process can be better controlled and no handling of sprue waste is required.
SPT supports the use of plastic recyclate to protect the environment whenever possible and approved by the customer.