Mold for retreading pneumatic tires

In tire retreading apparatus comprising heating means for receiving and heating a circular, radially inextensible, radial tire body having on the peripheral surface thereof a circumferentially continuous layer of uncured rubber which softens on heating, said layer having a thickness selected to provide the tire tread and having a normal outer diameter and said heating means having means for heating said layer to vulcanize said layer, and a mold for producing a tread pattern in said layer, wherein the improvement comprises a mold of elastomeric material for surrounding said rubber layer during the heating thereof and for embossing said tread pattern in said rubber layer without applying stretching forces to said body which increase said diameter of said layer above said normal diameter thereof, said mold being made of an elastomeric material and having the shape of a generally circular, continuous band and having an inner face extending around and facing the axis of said band, said inner face having a normal diameter when said mold is in its unstretched condition which is at least as small as said outer diameter of said layer, said band having a plurality of spaced, tread pattern forming projections of a first dimension in the radial direction extending from said inner face toward said axis and said band having a pair of axially spaced lips, one on one side and the other on the other side of said projections, extending toward said axis and inwardly of said inner face, said lips being substantially continuous in a direction circumferentially of said axis and being of a second dimension in the radial direction from said inner face toward said axis which is greater than said first dimension so as to be adapted to extend along axially opposite sides of said layer, the normal diameter between the innermost extents of said projections when said mold is in said unstretched condition thereby being both less than said normal diameter of said inner face and less than said outer diameter of said layer but said band being stretchable to a size such that the diameter between said innermost extents of said projections is at least equal to said normal diameter of said layer, the elasticity of said band being sufficient to permit stretching of said band to said size without exceeding the elastic limit thereof, and said band after being stretched around said layer and released being adapted to cause said projections to contact said layer before said inner face returns to its normal diameter whereby by reason of the inherent tendency of said band to return to its unstretched condition, said projections have radial forces applied thereto which urge them against said layer and into said layer during heating and softening thereof and said elastomeric material of said mold having a tensile strength at break of at least 500 p.s.i., an elongation at break of at least 20 percent, a modulus at 300 percent elongation of at least 100 p.s.i., a hot tear strength of at least 100 p.s.i., a Shore hardness of at least 50, a compression set not exceeding 40 percent and a Lupke rebound in the range from 15 to 30 at temperatures up to about 70.degree. C.