| 摘要 |
<p>A disc flap for a corrosion resistant valve comprises a metal core enveloped in a seamless covering of synthetic plastic material. One face is flat whilst the other has reinforcing ribs and provision for a pin or bolts on which it is hinged inside the plastic lined housing of the valve. In the first stage of production, the flat face of the core is placed on the top face of a bolster, smaller in diameter than the core, and a preheated plastic sheet, clamped by a blank holder is drawn down over the core by a tubular tool into which compressed air is introduced, during a cooling period. The collar is then cut off leaving the circular overlap and a disc of plastic is laid on the uncovered centre of the core and welded seamlessly in place. A simple method using cheap tools, and capable of being applied over the whole range from the smallest to the largest nominal bore valves, with only the critical zone needing inspection.</p> |
