Heat-recoverable metallic couplings

A hollow, generally tubular coupling member formed of a metallic material which exists in a martensitic phase at a first temperature and in an austenitic phase at a second temperature higher than the first temperature, which member, when cooled from a temperature at which it is in a first configuration with the metallic material in the austenitic phase to a temperature at which the metallic material is in the martensitic phase, can be deformed to a second configuration and will recover from said second configuration substantially towards said first configuration when reheated to a temperature at which the metallic material is in the austenitic phase, and which member is provided on its inner surface with at least three teeth in the form of radially extending rings, the distance (t) between corresponding points on any pair of adjacent teeth having a value which is less than 0.95 d and less than 4 w, where d is the internal diameter of that portion of the tubular member between the teeth, and w is the wall thickness of that portion of the tubular member between the teeth, the distance from the center of the member to the tooth nearest the center of the member being from 0 to 0.3 d, there being at least one tooth either side of the tooth nearest the center of the member, and the distance (p) between corresponding points on the two teeth adjacent the tooth nearest the center of the member having a value which is more than the smaller of 0.4 d and 3 w.

A method of preparing a coupling which comprises diametrically expanding a hollow generally tubular coupling member having a first configuration and formed of a metallic material which is in a martensitic phase while the material is being expanded but which exists in an austenitic phase at a higher temperature, said diametric expansion being effected by driving a tapered mandrel through the tubular member, and said member being provided on its inner surface with at least three teeth in the form of radially extending rings, the distance (t) between corresponding points on any pair of adjacent teeth having a value which is less than 0.95 d and less than 4 w, where d is the internal diameter of that portion of the tubular member between the teeth and w is the wall thickness of that portion of the tubular member between the teeth, the distance from the center of the member to the tooth nearest the center of the member being from 0 to 0.3 d, there being at least one tooth either side of the tooth nearest the center of the member, and the distance (p) between corresponding points on the two teeth adjacent the tooth nearest the center of the member being more than the smaller of 0.4 d and 3 w, whereby the coupling member is deformed to a second configuration while the metallic material is in the martensitic phase, but on heating to a temperature at which the metallic material is in the austenitic phase, recovers substantially towards said first configuration.