The two main innovations at the Fakuma stand of Kunststoff Institut Lüdenscheid (KIMW) both offered solutions to remove visible knitlines, phenomena that can be particularly noticeable in high gloss parts.
In the ThermoOpt process, a passive temperature control ceramic thermal barrier layer applied to a mould means less heat is absorbed into the mould metal. As a result, the higher temperature in the mould causes the knit line to practically melt away. Stefan Schmidt, managing director of KIMW said the ThermoOpt coating is 20-25µm thick and that this approach has been conceived for dealing with knitlines on large surface area parts.
KIMW displayed ThermoOpt examples in the form of a Gigaset telephone handset and a remote-control garage door opener housing produced by Mayweg Kunststofftechnik during the Fakuma show.
The other temperature control knitline solution uses partial application of additional heat just in the areas where visible knitlines occur. This is applied using electric heating cartridges from Hotset Heizpatronen und Zubehör.
In what Hotset calls its Z-System partial dynamic temperature control, developed jointly with KIMW, dynamic heating is applied to relevant points in the mould cavity at a heating rate of up to 60°K per second. This raises the temperature from just over 40°C to just over 50°C within 7 seconds, followed by cooling to 10.5°C.
Looking at a black high-gloss polycarbonate version of KIMW's standard ice scraper as a test piece, it was apparent that if there had ever been any knitlines, the Z-System solution made them melt away.
Aside from knitline removal, HotSet says the reduction of temperature in the overall mould structure enables faster cycle time and low energy use – 100W in the case of the ice scraper. The technique has been patented, but is licence-free.
Schmidt said KIMW now has seven advanced mould rapid heating and cooling (RHC) techniques at its disposal. These include the two new knitline removal ones, RocTool induction, BFMould ball-filled moulds, carbon dioxide and Greenmould. The latter involves electrically heated conductive mould coating and was one of the KIMW highlights at Fakuma 2014.