Rubber, plastics and polymer–metal joints

Plastic pipes are used for drinking water, drains, hot water and greenhouse heating systems. Their advantages are that damp does not corrode them and they keep their shape under outside force; the drawback is poor heat resistance. Pipes are cut with an ordinary saw or a pipe cutter. For them straight couplings, elbows (90° and 120°), tees, reducers, metal-plastic transitions and stop valves are made. Pipes are joined with a special heating tool (an «iron»): the pipe end and fitting are pushed onto the heating tips, and when the melting point is reached they are taken off quickly, pressed together firmly and not moved until cool. Sequence: measuring and marking, cutting, heating, joining. The heating tool is very hot (about 260 °C), so only a master or the teacher does this; pupils measure, mark and prepare, and watch from a safe distance; the room is ventilated. A polymer–metal item such as a dustpan is made by screwing a plastic scoop to a metal handle (or a sheet-metal scoop to a plastic handle); adults cut and drill the sheet metal and plastic, and gloves are worn because sheet-metal edges are sharp.