Method and apparatus for producing openings in sheet material

#The present invention relates to a method of and an apparatus for the production of openings in sheet material as well as to perforated sheet material thus produced.

#Two kinds of method are known of producing through bores or openings in an otherwise solid or unperforated starting material, such as sheet steel. One method provides for punching holes into the initial sheet steel by use of suitable punching tools. This mechanical processing, namely the punching and the relatively great proportion of waste, namely the punched-out parts of the starting material render the punched steel band so expensive that it is used only in cases where such material as expanded metal mesh, wire mesh, and the like cannot be applied for other reasons. The second possibility of obtaining openings passing through the sheet material is to produce expanded metal mesh. With this method cutting tools are used to cut slits into the starting material. Subsequently the slitted material is expanded axially whereby the webs which remained between the slits are deformed about their longitudinal axes by as much as 90.degree.. The expanded metal mesh can withstand only minor mechanical stress because of the bending of the webs and cracks or tensions present in the material. Therefore, such expanded metal mesh can be applied only where the mechanical forces occurring are small. Thus it is utilized as cover over slots in buildings or as safety cover for protection from rotating elements, as air shaft covering, and the like. It is another disadvantage of punched sheet steel as well as expanded metal mesh that the configuration of the edges of the holes passing through the material is limited to a few examples. This is disadvantageous if the punched metal or expanded structure are to be processed together with plastics to establish a composite material or article because it is difficult to coat the edges of the openings in such known materials with plastics.

#So far, a problem is encountered when it is desired to produce inexpensive materials of large surface areas which, on the one hand, have good mechanical loading capacity and, on the other hand, are corrosion-proof. Cheap mass-produced sheet metal does have the desired mechanical properties, yet the risk of corrosion is quite great. Cheap plastics do not tend to corrode, but they lack the required mechanical strength and sufficient permanent temperature resistance. In order to combine the advantages of plastics and sheet metal it has already been suggested to coat punched metal sheets or expanded metal mesh with plastics, thus producing the so-called composite materials. Yet even these composite materials have the above mentioned disadvantages of punched metal or expanded metal mesh. Composite materials of punched sheet metal and plastics are so expensive because of the loss of material in producing the punched sheet metal that, in most cases, stainless steel could compete with such composite materials from the point of view of the price. In the production of mass articles, such as drinking water pipe and sectional material of any kind composite materials of punched metal sheet coated with plastics consequently are out of the question because of the cost factor. A composite material of expanded metal mesh and plastics still has the insufficient mechanical load bearing capacity of the expanded metal mesh.

#The invention will be described further, by way of example, with reference to the accompanying drawings, in which:

#FIG. 1 is a diagrammatic side elevational view of a sheet steel rolling apparatus in accordance with the invention,

#FIGS. 2a and 2b are diagrammatic cross sectional views of part of another sheet steel rolling apparatus according to the invention, showing only the two roller pairs on separate roller stands,

#The invention will be described below with refence to the manufacture of perforated sheet steel bands which are a cheap mass-produced article. However, it is to be understood that the invention is suitable also for use with other metallic materials and some thermoplastics.

#FIG. 1 diagrammatically shows a rolling apparatus suitable for production of the openings in the band. The band 1 is wound on a reel 4 which is supported in per se known manner on a bracket 5. The band is passed from reel 4 through a band guide means 6, a tension regulating means 8 toward the nip between a notching roller 10 and a counter-roller 12, around the counter-roller 12 to a second nip between the counter-roller 12 and a profile roller 14, another band guide means 16 toward a second reel 18 on which the band 3 which is now perforated is wound up. Reel 18 is likewise supported on a bracket 20 in per se known manner. The band guide means 6, 16, the tension regulating means 8, and rollers 10, 12, 14 are arranged in per se known manner on a roller stand 22 which need not be described in detail. By a socket 24 roller stand 22 rests on the floor 26. Such a roller stand comprising three rollers is known per se, with the exception of the design of rollers 10 and 14 which is characteristic of the invention. In such roller stands comprising three rollers the nips are adjustable and at least one of the rollers is driven. For the sake of simplicity the means for adjusting the roller nips and for driving the apparatus are not shown because they are likewise known per se. With the apparatus according to the invention driving of the rollers themselves may be dispensed with if the band transport is taken over by the reel on which the perforated band is wound up. Presumably, driving of the rollers themselves may be dispensed with because the rollers 10 and 14 are taken along, if external band transport is provided, because of their specific function in the apparatus according to the invention, namely to produce notches and reduce the thickness and stretch partial areas of the band, respectively.

#As will be described in more detail below, it may be desirable to subject the perforated band several times to the thickness reducing and stretching processing step. For this purpose, the rolling apparatus according to FIG. 1 may be of the reversing kind, a band drive means being provided at both reels 4 and 18. During the repeated processing by profile roller 14 and counter-roller 12 the notching roller 10 is taken out of operation.