Thermally insulating tubes

Claim 1

Method of jacketing a tube with a foamed, thermal insulation, and including providing a thermoplastic resin powder or granulate, conveying and heating the thermoplastic resin powder or granulate in a device such as a screw extruder in order to melt the powder or granulate; feeding the heated thermoplastic melt from the device into a shear head which includes a fast rotating, hollow mandrel for further heating the plastic, the tube passing through the hollow mandrel, the melt being shaped and discharged from the shear head onto and around the tube as the tube emerges from the mandrel, the improvement comprising: adding a chemical blowing agent to the thermoplastic melt prior to said feeding step for rendering the melt foamable, said blowing agent reaching a decomposition temperature for subsequently obtaining foaming just prior to the discharge of the foamable, plastic melt onto and around the tube; and adding a cross-linking agent to the foamable, plastic melt when inside said shear head and at a location in the shear head in which the thermoplastic has a temperature so that it is completely melted, but the temperature of the thermoplastic, as further heated in the shear head, has not yet reached said decomposition temperature of said chemical blowing agent at said location said cross-linking agent causing the plastic to begin cross-linking at a temperature below said decomposition temperature.

Claim 9

A method of jacketing a tube with foamed plastic for thermally insulating the tube, using a blend of high- and low-density poly-ethylene, comprising the steps of: adding a blowing agent to the blend, the blowing agent having a higher decomposition temperature than the melting point of the high-density polyethylene; raising the temperature of the blend, as blended with the blowing agent, to a temperature well above the melting point of the high-density polyethylene so that the blend is completely melted: adding to the heated and completely melted blend, in a second adding step, a peroxide as a cross-linking agent having a reaction temperature below the temperature that the blend has when the cross-linking agent is added, the reaction temperature being well below said decomposition temperature so that the cross-linking reaction begins right after the second adding step; continuously heating the blend after the second adding step by means of shear forces applied to the melted blend and in a channel surrounding said tube, the heating to continue up to a temperature above said decomposition temperature; and depositing a tube-like envelope of the heated blend onto the tube as foaming begins and cross-linking continues.

Claim 10

A method of jacketing a tube with foamed plastic for thermally insulating the tube, using a blend of high- and low-density poly-ethylene, comprising the steps of: adding a blowing agent to the blend, the blowing agent having a higher decomposition temperature than the melting point of the high-density polyethylene; raising the temperature of the blend, as blended with the blowing agent, to a temperature well above the melting point of the high-density polyethylene so that the blend is completely melted: adding to the heated and completely melted blend, in a second adding step, a peroxide as a cross-linking agent having a reaction temperature below the temperature that the blend has when the cross-linking agent is added, the reaction temperature being well below said decomposition temperature so that the cross-linking reaction begins right after the second adding step; continuously heating the blend after the second adding step by means of shear forces applied to the melted blend and in a channel surrounding said tube, the heating to continue up to a temperature above said decomposition temperature; and depositing a tube-like envelope of the heated blend onto the tube as foaming begins and cross-linking continues.