BAG-WELDING FOR HERMETIC SEALS

Press, Volume XCVIII, Issue 28935, 1 July 1959, Page 19

BAG-WELDING FOR HERMETIC SEALS

A £l5O machine which has been put to work at the National Airways engineering store is sealing thousands of aircraft spare parts in plastic packs.

The machine was made specially to order by the Christchurch factory of Weltex Plastics Ltd. Individual parts in the store are being placed in bags and have air, dust and moisture sucked from them by the machine which makes a hermetic seal by welding the bag mouth shut. In this way valuable instruments and delicate motor parts will be stored indefinitely free from dust damage and corrosion. Of the Weltex factory’s 100 different fabricated plastic products, the übiquitous plastic packing bag, used for holding everything from peanuts to stock food, is in keenest demand. The pol.-thene material for these bags comes in thicknesses from 1.5 thousandths of an inch to 5 thousandths of an inch and is in the form of tubes up to a third of a mile long.

Weltex claims it scored a world “first” in the plastic bag field when it was asked to produce a large order of 6ft wide bags for packing foam rubber mattresses.

There was no machine capable of sealing bags that size, so Weltex engineers produced their own. Now, they not only machineproduce the large-size bags, which formerly were all hand made, but also make them two at a time. A line of seven welders are the key members of a production team that turns out, among other things, handbags, purses, wallets, curtains and key cases. Heat is applied to the pieces to be joined by passing through them a high-frequency electric current. The current oscillates the molecules of the material, producing friction (and, therefore, heat) from the "inside.”

External application of heat would damage the material, as anyone knows who has let a piece of plastic get near a fire or radiator.

On one particular machine a good operator could produce up to 100 bags in an hour. Weltex began operations seven years and a half ago as a partnership between Mr R. J. Blackburn and Mr W. Green. They used then a 24ft by 12ft shed as their factory but today the firm has a 7000 square feet building of modern design and extensions are already planned.