Tires building machine with rigid radially expansible drum

Abstract

A simple two-stage process is disclosed for economic mass production of premium-quality heavy-duty belted tubeless and tube-type radial truck tires of various sizes using standard 30-year-old semi-automatic tire building machines heretofore used in the manufacture of bias-ply tires by the flat-band process. The old automatic machines are modified at minimal cost to receive a unique rigid expansible drum which is radially expanded 35% or more during the first-stage tire building operation. The drum may be adjusted to make tires of various widths and diameters and has a series of closely spaced radially movable segments defining a rigid segmental open-ended externally cylindrical shell having an annular rubber cover on which a complete green tire carcass is built prior to application of the belts and the tread at the second-stage machine. The shell has rigid beveled shoulders at the ends of the drum which are inclined at an angle of from 40.degree. to 50.degree. relative to the drum axis and which are shaped to facilitate high-speed production, and to permit effective use of the ply turn-up tools and stitching means normally used on such automatic tire building machines with open-ended cylindrical drums. The rubber-covered shell expands radially in a precisely controlled manner in response to rotation of the drum, and it maintains uniform cord spacing and prevents the formation of wrinkles and air pockets during the ply down and ply turn-up operations. The unique drum facilitates accurate positioning of the wire beads and more precise control of bead-to-bead cord lengths and provides an ideal support during the stitching operations at the drum shoulders so as to improve tire quality and uniformity.