1432375 Drawing STD SERVICES Ltd 11 Sept 1973 [19 Sept 1972] 43319/72 Heading B3P A tube drawing plug 10 is formed mainly or wholly from an oxide, carbide, nitride or boride of a metal or semi-conductor such as silicon and is compressively stressed so as to counteract the tensile stress generated during drawing. In one embodiment, the ceramic plug 10 is positioned between steel abutments 14, 15 which are interconnected by a screw thread 18 on a stem 17, extending from the abutment 14 and passing through the plug 10, and a coacting screw thread 19 in a bore of the abutment 15. A projection 16 on the abutment 14 and flats 20 on the abutment 15 enable the abutments 14, 15 to be turned to apply a compressive stress to the plug 10. The abutment 15 may be screwed to a plug bar. In another embodiment, a brass or copper spacer (21) (Fig. 2, not shown) having a higher coefficient of expansion than the abutments 14, 15 is positioned between the plug 10 and the abutment 15 to prevent relaxation of the compressive stress on the plug 10 in use.
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