There’s snow mistaking quality ski boots thanks to precision injection moulding

A manufacturer of some of the world’s biggest brands of ski boots has said that the precision machine technology used to produce the boots is paramount for optimum performance on the slopes.

For Plastor SA, which produces component parts and bindings for the ‘Salomon’ and ‘Atomic’ ski boot ranges, precision is paramount. The Romanian manufacturer uses a fleet of injection moulding systems to maintain the high performance characteristics and biomechanics of the leading downhill ski boot brands.

Starting with just one injection moulding machine from Sumitomo (SHI) Demag in 1993, Plastor SA’s Romanian production facility now has over 10 hydraulic systems in operation with clamping forces of between 1,000 and 4,200 kN. More recently, the company enhanced its plastic moulding capabilities, investing in a fully electric IntElect 100-430 machine.

“When producing components for high performance ski boots, it is necessary to have simultaneous movement of moulds and core pulling”, explained Plastor’s Managing Director, Ion Sereş.

Citing the versatility of Sumitomo (SHI) Demag machines as a key benefit, he added: “These plasticising units are suitable for processing a wide range of thermoplastics and create a high quality melt. For instance, we get excellent results when we work with transparent and translucent TPU’s coloured with liquid dyes.

“The machines are also characterised by a highly precise repeatability,” he continued. “The five-point twin toggle system makes for highly precise tool movements. Furthermore, the NC4 and NC5 machine control systems are very user-friendly, as the parameters for the detail controls are grouped.”

Aside from developing and moulding the end products, Plastor also undertakes the surface decoration, employing techniques such as screen and pad printing and hot stamping.

Dave Raine, Technical Sales Manager at Sumitomo (SHI) Demag explained the challenges that this presents when decorating products like the outer shells of ski boots. “Part stability is key in ensuring consistent transfer of the decoration onto the moulded part, whether it be pad printed or hot foiled. Achieving and maintaining a consistent stable process on the moulding machine is essential when employing post moulding decorative processes.”

The complex process involves moulding small insert pieces from TPE, which must pass high precision quality tests. They are then reworked and inserted into bigger two-component or three-component parts made of translucent TPU in larger injection moulds. Production is semi-automated on moulds with two or four cavities; fully automated on others, achieving cycle times of less than 50 seconds.

The IntElect machine is equipped with a dust extractor and a gravimetric dosing device, which can dose up to four different components. Expanding on the dust extraction system, Raine added: “Another issue with foil and printed decoration processes is contamination of the surface. Any imperfections or contaminants on the moulding will be highlighted on the decorated area. Dust particles under the foil show up as uneven or incomplete printing, and compromise the visual impact, which to some customers, can be just as important as the boots’ technical performance.”

Lower noise emissions are another feature of the all-electric machine that Sereş noted. “We also benefit from the many opportunities for fine adjustments, i.e. during opening and closing of the mould, the ejection movement or during venting of the mould,” he added.