Patent ID: 8459159

Claim:
A method for producing an element by punching from a starting material that is a web of bonded fibrous material, comprising: employing a punching tool in a form of at least one punch knife mounted in a press plate and pressed through the web and then pulled out again, wherein the tubular punch knife used projects through the press plate and is of a length which is 80 to 350%, of a thickness of the web of bonded fibrous material, and wherein the punching is carried out against a first back-pressure plate provided with a hole, and wherein the punching is carried out such that initially an element just punched out is temporarily retained in the punch knife, but after a stepwise advancing of the web of fibrous material, and a renewed pressing inwards of the tubular punch knife, the element is pressed backwards through the punch knife by the element now punched out; wherein the web comprises a mineral wool suitable for use as heat insulation casings for pipes, wherein the punch knives used are formed by a tubular punch knife of large diameter and a tubular punch knife of small diameter, wherein the large and small diameter tubular punch knives are arranged on their respective sides of the web comprising mineral wool, and wherein the punch knives are individually pressed into the web and into one another, the small diameter tubular punch knife being moved into the hole of the first back pressure plate, the small diameter tubular punch knife pressing against a second back-pressure plate, with a result that an annular element formed between the punch knives settles as a plug in the large-diameter tubular punch knife and once the two punch knives have been pulled apart the web comprising mineral wool is advanced one step, and the two tubular punch knives are again individually pressed into the web comprising mineral wool with a result that a first annular element now punched out presses a second annular element punched out during the previous step out of the large-diameter tubular punch knife, the second annular element being rearwardly released from the large-diameter tubular punch knife, wherein the starting material used comprises glass wool, rock wool, and/or plant fibers with a density of 15 to 80 kg/m 3 , and the web has a thickness ranging from 4 to 20 cm.