Hot runners build on solid origins

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Necessity forces innovation

Hot runners helped to trim production expenses by minimising the amount of waste generated when cutting off the sprue, the solidified residue left in the passage which feeds the liquid material into the mould and which needs to be removed from the finished part. The larger the mould, the bigger the sprue due to the distance between the injection cylinder nozzle and the moult cavity, whilst most manufacturers chose to recycle waste material rather than scrap it.

“One benefit is the material saving because you do not have to melt unnecessary material, cool it again and then regrind it,” explains Harald Schmidt, president at Mold Hotrunner Solutions (MHS), citing a second advantage of savings in energy costs associated with the sprue recycling - again a particular problem in the 1970s as electricity prices fluctuated during the oil crisis. Schmidt estimates that potential power savings for hot runners could reach as high as 25% compared to cold runners, for example.

“Not only do you have to plasticise the material that goes into a cold runner, but you have to extract that heat again through a cooling system. Once up to temperature and running 24/7 a hot runner usually comes in at 20-40% power consumption maximum, whereas with a cold runner mould you waste energy with every cycle,” he says.

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Craig Reynolds is director of business development for hot runners and controllers at Canada-based injection moulding system specialist Husky which currently manufactures a range of hot runner systems, controllers and nozzles under the Altanium, Ultra, Unify and Pronto brands. He agrees that hot runners reduce wasted resin, lower the required fill pressure and improve the part quality which all contributes to a net reduction on the volume of scrap, whilst cutting electricity bills in as much as the need to re-process that same scrap is removed.

Mold-Master released its V-Series hot runners in the 1970s with similar systems introduced by Incoe and other manufacturers. What followed was a series of upgrades designed to deliver ever more precise temperature control through more accurate nozzles with the 1980s seeing new approaches to valve gating in particular.

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