Specific Process Knowledge/Back-end processing/Polymer Injection Molder: Difference between revisions
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== Mold temperature setup == | == Mold temperature setup == | ||
Injection molding processes can be divided into two different types: | Injection molding processes can be divided into two different types: Constant mold temperature processes and Variable mold temperature (Variotherm) processes. | ||
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=== 1. Constant mold temperature processes === | === 1. Constant mold temperature processes === | ||
In this type of process the mold remains at the same temperature during the entire injection molding cycle. The temperature should not exceed the glass transition (or melting point) temperature of the polymer being used. Otherwise the polymer will never get cold enough to solidify to a degree where it can be demolded without being deformed/damaged. How close one can get to the glass transition temperature depends on several factors like e.g. polymer type, cooling time and whether the polymer has a tendency to stick to the shim (especially an issue when replicating high aspect ratio structures). With Topas 5013L-10 (which has a Tg around 135°C) one can often go up to 100°C and for samples that are easy to demold even higher (110-120°C). For polymers with very low Tg (such as e.g. flexible polyurethanes) one often has to run as cold as possible. With the mold heating switched completely off and mold cooling water fully open, the lowest achievable mold temperature is around 15°C. | In this type of process the mold remains at the same temperature during the entire injection molding cycle. The temperature should not exceed the glass transition (or melting point) temperature of the polymer being used. Otherwise the polymer will never get cold enough to solidify to a degree where it can be demolded without being deformed/damaged. How close one can get to the glass transition temperature depends on several factors like e.g. polymer type, cooling time and whether the polymer has a tendency to stick to the shim (especially an issue when replicating high aspect ratio structures). With Topas 5013L-10 (which has a Tg around 135°C) one can often go up to 100°C and for samples that are easy to demold even higher (110-120°C). For polymers with very low Tg (such as e.g. flexible polyurethanes) one often has to run as cold as possible. With the mold heating switched completely off and mold cooling water fully open, the lowest achievable mold temperature is around 15°C. | ||
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*Every time you open the gate (door) at the mold (either the front gate or the back gate) mold heating will switch off and the insert cooling water valves ('''f''' + '''h''') will open due to a safety interlock. To switch heating back on and close the cooling water vales, the 'Activate' conditions have to be fulfilled again. | *Every time you open the gate (door) at the mold (either the front gate or the back gate) mold heating will switch off and the insert cooling water valves ('''f''' + '''h''') will open due to a safety interlock. To switch heating back on and close the cooling water vales, the 'Activate' conditions have to be fulfilled again. | ||
*Avoid circulation of mold cooling water while the mold heating is switched on. The machine will give an error stating that the mold heating is defective. Mold heating should always be switched off before opening mold cooling water valves. | *Avoid circulation of mold cooling water while the mold heating is switched on. The machine will give an error stating that the mold heating is defective. Mold heating should always be switched off before opening mold cooling water valves. | ||
== Injection == | == Injection == | ||