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Why
A welder for plastic sheet can help farmers to increase post harvest income. Such a plastic sheet welding machine, produced in the region, has to be cheap enough to be purchased by a small farmer. With it, he is be able to SEAL and store his dried produce in plastic sheet. In plastic food is protected against moisture and dirt. Pcked in plastic will facilitate its bringing it to the market at the most appropriate time.
This machine has no need for electricity, or complex timers, however it should be able to make reliable seals of any shape or length. Experience in Thailand learned people recovering bits of plastic sheets by cleaning and drying. This welding machine should be able to make good use of this lowest grade plastic sheet and turn it into reliable packaging.
How
Welding is done between aluminum plates, partly immersed in oil, heated on burning charcoal. The plastic parts are inserted between the hot plates in an cardboard envelop, exposing only the place where the seal has to come. Heat is transferred from plate to plastic by metal strips embedded in the cardboard, on both sides of the envelop. These strips are kept oily, so they do not stick to the plastic when molten.
Time needed for making a weld is learned by doing. So adaptation to change of temperature of the oil can easily be compensated for.
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