Frequently asked questions on the moulding process
How much waste do you get with this process?
Typically the material in the runner and gate is waste. This can represent anything from a few percent to 35% for very small components. When runners can be recycled for less critical applications, the waste is zero. With hot runner equipment, most applications will have zero waste.
Can a conventional heated screw and barrel type machine be used for moulding?
This has been accomplished a few times and unsuccessfully a lot of times. Technomelt® has very low viscosity at the correct processing temperatures compared to engineering plastics. This low viscosity can cause the material to bleed backwards through the screw and essentially glue it together. Moldman® machines use positive displacement gear pumps designed for lower viscosity fluids to inject the molten material into the cavities.
How do you ensure sealing of the component?
Selecting the appropriate Technomelt® material best suited to the application is the key to sufficient sealing of the component. Typically the best surface wetting of the component occurs with lower viscosity material at relatively high temperatures. Higher packing pressure may also help ensure surface wetting and sealing. The component design is also crucial. Low-Pressure moulding works best when encapsulating around a component versus filling into the housing.
How are the moulds cooled?
The Moldman® machines have permanent water connections on the side of the machines. This feature allows you to run chilled water through the mould platens. Mould-sets are then cooled via the water-cooled mould platens. Typical mould temperature is around 20°C (68°F).
Are any special de-gating tools required?
How do you control the filling of the cavity?
The Moldman® machines offer programmable injection profiles. A typical profile would consist of filling 90% of the volume into the cavity at relatively high flow rate and then packing at low pressure. Packing pressures are typically from 50 to 150 psi and such pressures will not over-pack a cavity. Packing is critical to prevent sink and voids as the Technomelt® material will shrink when they transition from liquid phase to a solid.
What is the lowest pressure that parts can be moulded?
2 Bar (30 psi) is typically the lowest practical pressure. For anything lower the runner and gate design become very critical. Injection pressures from 4 bar to 20 bar (60 psi to 300 psi) are typical.
Do the moulds need to be heated?
No, mould-sets are typically cooled to approximately 20ºC (68ºF). The Moldman® series of machines require no direct mould-set cooling since the mould platens have chilled water circulating through them.
What is a typical injection temperature for these materials?
Melt reservoir temperature ranges from 190 to 230°C (370 to 450ºF). Depending on mould-set design, this would typically correspond to cavity temperatures of 135 to 180oC (275 to 355ºF).
How long is a typical injection cycle?
The moulding cycle is dependent on the size and material section thickness of the component. Typical cycle times range from 15 to 45 seconds. Multiple cavity mould-sets can be used to reduce the actual moulding drop rate.