Plastic packaging bags composed of a laminate which comprises a layer of ethylene polymer of low density and a layer of polyethylene of high density

摘要

A light and strong tube structure for frames of bicycles and motorcycles has its cross sections with a variable thickness of the tube wall (1). Said wall (1) is formed by two or more layers of different materials (2, 3), of which at least one is metallic material and at least another one has a preferential direction of tensible strength. Preferably, the straight cross sections of the tube are outwardly defined by a circle and inwardly defined by an ellipse and the said layers comprise an external metallic layer and an internal layer of fibers incorporated into resin.