Abstract: In a method of producing a double-walled structure, such as a silencer for use in a ventilation duct system, use is made of an arrangement having a forming head for forming helically-wound lock-seam tubing. In the forming head, a perforated metal strip is helically would together with an air-permeable cloth strip such that the tubing fed out of the forming head has an outer cover of said cloth. The tube assembly consisting of the perforated tube and the cloth cover is provided with an outer tubular layer of insulating material and then inserted in a casing which makes the silencer complete.

Abstract: An improved apparatus for forming and cutting spirally formed pipe, particularly spiral pipes having a diameter of approximately one inch or less, is disclosed. The device for slitting the spiral pipe into sections includes a first knife that is positioned inside the spiral pipe and a second knife positioned outside of the pipe. A support sleeve is also positioned outside of the pipe and is in a fixed radial position with respect to the pipe. The inner and outer knives and the support sleeve move axially with the pipe as the pipe is severed.

Abstract: A self-drilling blind rivet includes a deformable sleeve and a shaft having a drill bit at one end. The shaft extends through the sleeve and the drill bit is connected to one end of the sleeve. The shaft and sleeve are rotatable as a unit. A method for making a riveted joint with a self-drilling blind rivet includes the steps of passing the drill bit through a work piece and pulling the drill bit entirely within the sleeve so that the drill bit does not extend beyond the end of the sleeve to which it is connected. Thus, the diameter of a portion of the sleeve in increased and the riveted joint is rendered pressure tight.

Abstract: In a method and an apparatus for producing helically-wound lock-seem tubing from a metal strip having longitudinal edge portions, the strip is fed to a forming head and formed into helical shape. A lubricant is locally supplied on that side of the strip which forms the outside of the tube, said lubricant being supplied over only a limited portion of the width of the strip.

Abstract: A kit for producing a non-straight connector for fluid pipe elements comprises loose sleeve couplings and at least one flat blank which has been given such a shape and such dimensions that, after forming thereof and interconnecting its opposite ends, it is connectable with the sleeve couplings by means of a peripheral joint, thereby forming an intermediate segment.

Abstract: A kit for producing a non-straight connector for fluid pipe element comprises loose sleeve couplings and at least one flat blank which has been given such a shape and such dimensions that, after forming thereof and interconnecting its opposite ends, it is connectable with the sleeve couplings by means of a peripheral joint, thereby forming an intermediate segment.