Multi-stage finishing for plastic mouldings

A new cleaning system, introduced to finish lightweight mobile telephone casings, combines high speed precision beadblasting with higher volume saturation spray, washing, rinsing and drying

Surface imperfections such as scuff-marks, smooth patches, light burrs and similar defects appearing after ejection from the moulding tool adversely affect the quality of the matt cosmetic finish produced on polycarbonate mouldings.

Removing these imperfections and simultaneously restoring the matt cosmetic finish can now be done automatically at a production target rate of 30,000 mouldings per 24 hours, using the latest 'Blast and Wash' system designed specially for the purpose by surface cleaning and finishing machinery specialists Guyson International Limited.

The new system, introduced to finish lightweight mobile telephone casings, combines the performance of a higher speed precision beadblasting process using a Guyson Multiblast TR900 twin track, multi-gun machine with a lower speed, higher volume saturation spray, washing, rinsing and drying machine, a Guyson Marr-Line 500.

The multi-stage process starts with a continuous flow of mouldings being positioned on to custom built jigs, moving on a twin track, parallel belt conveyor into an eight gun blast chamber where, using a specially selected beadblast media, the surface imperfections are removed and a matching, uniform, matt cosmetic finish produced along both sides of each moulding as it passes through four blast guns, strategically positioned, two on each side of both tracks, at a speed of between two to five metres per minute.

An overhead, continuous retaining belt keeps the lightweight mouldings in position on their fixtures during the blasting process.

Excess blast media and dust is removed by a de-ionised air wash, as they are gravity fed into a newly designed automatic transfer system which compensates for the differing process speeds of the blast finishing and wash machine conveyors.

By discharging and then distributing the mouldings in an array which not only makes full use of the greater available area of the slower moving, 300mm per minute, 500mm wide stainless steel honeycomb mesh conveyor of the wash and dry machine, but also ensures that the mouldings do not mask each other.

The mouldings pass through the wash, rinse and dry sections at a constant speed and are kept on the conveyor by a stainless steel cage.

Inside the wash chamber stainless steel spray bars positioned around the conveyor deliver pressurised, heated washing solution.

This is followed by rinsing using a demineralised water trickle feed to complete the removal of any contamination remaining on the surface.

After passing under a blow off bar, which also assists the final drying process, the mouldings enter the drying chamber where blown heated air, convected through adjustable louvres positioned above and below the conveyor ensures that they are thoroughly dry and ready for immediate packaging.

Back to top