ERJ staff report (PR)
Ternitz, Austria – Rubber injection moulders could reduce cure times by almost a third on many parts through using simple conical die devices, researchers at Montan University, Leoben, Austria have established.
The finding is based on work to characterise and model the contribution of elongational flow effects to the heating of rubber during the injection process, according to professor Walter Friesenbichler, chair of the university's injection moulding department.
Unlike other effects, such as shear and conduction, elongational heating has up to now not been covered by simulation, Friesenbichler explained at machinery maker Maplan GmbH's 'days of technology 2014' event, held 4-5 June in Ternitz.
But, as shown in a paper by PhD student Leonhard Perko – and carried out in partnership with Maplan and two other industrial partners – by far the highest contribution to heating is caused by elongation as the polymer mass flows into a conical die. This was found to account for 84 percent of heat introduced into the compound, compared to just 7 percent caused by shear at the die walls.
Friesenbichler went on to show how elongational heating could reduce curing in parts with thicknesses from 4mm and above by almost 30 percent, adding that the research team's modelling of the process was found to be accurate to within 5 percent.
"This is a really, scientifically new model," Friesenbichler concluded. "This combined shear and elongational heating in [specially designed] conical dies can be easily used for cure-time reduction in a fast and simple way without the need for complicated, special units to heat up the material.
"We can rely on elongational heating, which contributes significantly to temperature increase."