| 摘要 |
PURPOSE:To manufacture the external screw of high accuracy without deterioration of corrosion resistance, inexpensively, with high efficiency by engraving a screw thread with the cold thread rolling die working of the shaft part of the iron external screw base material subjected to the zinc plating in optimum thickness on the surface. CONSTITUTION:The whole body of an iron external screw base material 1 is dipped in a molten zinc melted at about 450 deg.C and the zinc plated layer 4 in 50-70mu thickness is formed on the surface. A screw thread is cut with the cold work of the shaft part 3 thereof between a pair of thread rolling dies 6. The rolling screw thread part becomes black and looks like the zinc plated layer 4 being separated apparently, but there is no separation via the alloy layer 5 of the plating boundary part and no deterioration in the corrosion protection is caused. The screw part is therefore made a good anti-corrosion and the product of high screw precision and yet can be manufactured inexpensively with high efficiency. A silver powder, etc. may be painted on the rolling discoloring screw part for increasing the commodity value.
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