Title of Invention

RIGID THIN SHEET MATERIAL

Abstract

The present invention relates to a set of rolls for manufacturing a thin sheet metal, each roll comprising an outer surface, the rolls having rows of teeth on the outer surface of the rolls, each tooth having four flanks of involute form, each flank facing in a direction between an axial direction and a circumferential direction, the rolls being spaced apart in use by a distance such that the teeth on one roll extend into gaps between the teeth on the other roll, whereby projections are formed on both surfaces of the sheet during its passage between the rolls, the teeth being arranged in parallel helical rows, wherein the tops of the teeth are radiused in two areas; at the peak and at the corners of the peak, the radius at the peak being from 1.0 to 2.5 mm and that at the corners of from 0.2 to 1 mm.

Full Text

The invention relates to a set of rolls for manufacturing a thin sheet metal. In our prior patent WO 94/12294 published on June 9, 1994 we have disclosed a method for forming projections in a thin sheet to increase stiffness of the sheet. We have now discovered an improved method of treating the sheet material. Accordingly the present invention relates to a set of rolls for manufacturing a thin sheet metal, each roll comprising an outer surface, the rolls having rows of teeth on the outer surface of the rolls, each tooth having four flanks of involute form, each flank facing in a direction between an axial direction and a circumferential direction, the rolls being spaced apart in use by a distance such that the teeth on one roll extend into gaps between the teeth on the other roll, whereby projections are formed on both surfaces of the sheet during its passage between the rolls, the teeth being arranged in parallel helical rows, wherein the tops of the teeth are radiused in two areas; at the peak and at the comers of the peak, the radius at the peak being from 1.0 to 2.5 mm and that at the comers of from 0.2 to 1 mm. We have realized that when flexible sheet material of relatively thin guage is passed in the nip between rollers having teeth, the sheet surface can be damaged so that fragments of the sheet come away and accumulate in the spaces between teeth. The fragments than cause further damage to the sheet material which is following behind. We have discovered that by radiusing portions of the teeth this risk can be reduced; the teeth are radiused in two areas; at the corners of the peak and at the peak. In other words it has been found according to the invention that by radiusing the corners of the teeth, both at the peak and the root thereof, it is possible to cause the sheet material to flow in the clearance between opposed teeth to become more rigid with little or no thinning and without spalling of the sheet material or of the teeth. As a result the rolls suffer less wear and need less cleaning and last longer; the sheet material is rigid and yet lightweight. So far as we are aware it has not previously been the practice to radius the corners of teeth on rolls, and the benefits of doing so were unrealized. The extent of radius is related to the size of the tooth which in turn relates to the gauge of the sheet being processed. Where the tooth is relatively small for use with thin gauge sheet, the corner radius is about 0.2 mm and the peak is preferably about 1 mm; where the tooth is relatively large for thicker gauge sheet the corner radius is about 1 mm and the peak about 2.5 mm. The ratio of the corner radius to the peak radius thus decreases with increasing size of the tooth. It has been observed that outside these parameters the tooth tends to have corners which can cut into the surface of the sheet material being treated. By virtue of the radiusing of the corners and the peaks of the teeth there is no risk that a sheet material will be cracked in such a way that the fragmenting e.g. spalling or the like will occur. Such cracking releases fragments of the sheet material which tend to foul the space between the teeth of the roll which risk breaking the integrity of the surface of the sheet following on behind. We have surprisingly discovered that in the method of the invention not only does the sheet surface maintain its integrity but the formed sheet undergoes an enhanced stiffening effect as a result of which the mechanical strength e.g. rigidity of the sheet is enhanced. The method of the invention may even be applied to a thin flexible sheet carrying a coating, e.g. a paint or like film without risk that it will be harmed. In another aspect of the invention provides a method of making thin sheet metal rigid by cold rolling using the set of rolls the method comprising passing flexible sheet metal of relatively thin guage between two rolls each having teeth, each tooth having four flanks, each flank facing between an axial direction and a circumferential direction, the rolls being arranged so that the teeth of one roll extend into the gaps between the teeth on the other, the teeth being arranged in parallel helical rows, the rolls being rotated at substantially the same speed about parallel axes to form rows of projections on both faces of the sheet material passed therethrough, wherein the teeth are radiused in two areas; at the peak and at the comers of the peak, the radius at the peak being from 1.0 to 2.5 mm and that at the comers from 0.2 to 1 mm, whereby the sheet is made rigid without damage to the surface material of the sheet. In another aspect the invention provides sheet material having projections on both of its surfaces, a corresponding depression being on the surface opposite cash projection, the relative positions of the projections and depressions being such that lines drawn on the surface are non-linear, the sides of the projections lying a line extending between a longitudinal direction and a lateral direction, the overall thickness of the sheet material being no more than four times the guage g, the pitch distances between adjacent projections and depressions being within the range of 2mm to 5mm and in the range of four to ten times the guage, wherein the comers of the projections and depressions have been rediused by the method disclosed herein. In order that the invention may be well understood it will now be described with reference to the accompanying drawings in which; Figure 1 is a diagrammatic representation of the overall method; Figure 2 is a fragmentary representation of part of tine circumferential surface of the first set of rolls (shown at the left hand end of Figure 1) with the positions of the teeth of an adjacent roll indicated by broken lines; Figure 3 is a sectional view taken on lines III - III on Figure 2; Figure 4 is a sectional view taken on lines IV - IV on Figure 2; and Figure 5 is an enlarged sectional view showing the shape of a relatively small tooth form; Figure 6 is the same as Figure 5 for a relatively large tooth form; Figure 7 is a perspective view of the form of the teeth on the roll of Figure 2; and Figure 8 is a perspective view of the projections formed on the sheet. In the process shown in Figure 1 thin sheet material S, typically metal, having a thickness of the order 0.05 mm to 2.5 mm is drawn from a coil and passed between a pair of identical rolls R1,R2 each of which has at its periphery a mmiber of teeth T shown in Figure 2. The rolls are rotated about their respective parallel axis P1,P2 and the sheet material is engaged and formed by the teeth T of the rolls. Each tooth pushes a part of the sheet material into a gap between teeth T on the other roll to form a projection facing that other roll and a corresponding depression facing the one roll. Thus, the overall thiclcness of the sheet material is increased by forming projections on both of its faces. From the roll pair Rl and R2, the sheet material passes between the rolls of further pairs A,B,C which form the sheet material into a profile. The roll pair R1,R2 and the roll pairs A,B,C are driven for example by common drive means D of known form and including for example an electric motor E. The rolls are driven at substantially the same peripheral speed so that the sheet material passes continuously and at the same speed between the rolls R1,R2 and then between the rolls of the subsequent pairs. After shaping, the sheet is cut into lengths for transportation and use. As shown in Figure 2 each roll R1,R2 has on its periphery a number of identical teeth T arranged in a plurality of helical rows which are inclined to the axis of the roll at an angle of 45°. Each tooth has a peak 1 having a radius on each of the flanks 2,3,4,5 with each flank being inclined to the axis at an angle of 45*^. From each edge of the peak, there extends a corresponding flank 2,3,4 and 5. Adjacent flanks meet at respective edges of the tooth. In the embodiment shown and as viewed in a direction from one of these edges to the other, the flank between the two edges has the form of an involute curve. All flanks of all of the teeth have the same form. It will be noted that the flanks of the teeth on the rolls face in directions which are between a circumferential direction and an axial direction. Figure 7 is an enlarged perspective view of the teeth of the roll. The sheet material S is gripped by and stretched by the teeth T when it passes between the rolls Rl and R2 so that the overall length of the sheet material is reduced only a little or not significantly. The reduction in the overall length (if any) depends upon a number of factors, including the thickness of the sheet material and the increase in the overall thickness which is caused by the rolls. We prefer that the length of the sheet material should not be reduced by more than r5% of the initial length. Generally, the length of the sheet material which leaves the rolls is at least 90% of the initial length and we prefer to maintain the length of the sheet material within the range 95% to 100% (or more) of the initial length. We prefer that the overall thickness of the sheet material leaving the rolls should be between two and three times the gauge of the sheet material. Subsequent treatment of the sheet material by the roll pairs A,B,C slightly reduces the overall thickness of the material. As can be seen from Figure 2, the flanks of the teeth of one roll R1,R2 face those of adjacent teeth across gaps 6 which gaps 6 are not occupied by teeth T of the other roll. At the nip between the rolls R1,R2, the teeth T enter gaps between edges of the teeth T with edges of each tooth T facing edges of adjacent teeth T. In the gaps 6, the sheet metal S is free to adopt a form determined by forces applied to the sheet at the tips of the teeth T. These forces are such that the sheet does not remain flat in the gaps 6. Figure 5 and 6 show in enlarged scale the preferred small tooth form and a large tooth form for use with relatively thin and relatively thick gauge sheet material respectively. The broken vertical line is the axis of the tooth and the horizontal broken line is the pitch diameter. The extent of radiusing is selected to avoid comer shapes at any location which could damage the sheet material " whicH it is being formed. We prefer to determine the extent of radiusing by a measurement technique used in relation to gears. Figure 6 shows, in the case of the large tooth form, the centres of the radii which are preferably 1.0 mm for the comer radius and 2.5 mm for the peak. The corresponding values for the small tooth are 0.2 mm and 1.0 mm in both cases. As a result of these radiuses when the projections and depressions are formed in the sheet by passage through the rollers R1,R2 there is no cause for the sheet material to crack and release fragments which can lie in the space between the teeth of the rolls. Such fragments tend to accumulate and mar the projections and depressions formed on the subsequent sheet of the coil S and are avoided in this invention. Figure 8 shows the projections formed on sheet material of the invention. It will be noted that the projections and depressions are relatively smooth as a result of the radiused teeth of the rolls. WE CLAIM: 1. A set of rolls for manufacturing a thin sheet metal, each roll comprising an outer surface, the rolls having rows of teeth on the outer surface of the rolls, each tooth having four flanks of involute form, each flank facing in a direction between an axial direction and a circumferential direction, the rolls being spaced apart in use by a distance such that the teeth on one roll extend into gaps between the teeth on the other roll, whereby projections are formed on both surfaces of the sheet during its passage between the rolls, the teeth being arranged in parallel helical rows, wherein the tops of the teeth are radiused in two areas; at the peak and at the comers of the peak, the radius at the peak being from 1.0 to 2.5 mm and that at the comers of from 0.2 to 1 mm. 2. The set of rolls as claimed in claim 1, wherein the tops of the teeth have a comer radius of 1.0 mm and a peak radius of 2.5 mm. 3. The set of rolls as claimed in claim 1, wherein the tops of the teeth have a comer radius of 0.2 mm and a peak radius of 1.0 mm. 4. A method of making thin sheet metal rigid by cold rolling using the set of rolls as claimed in any one of the preceding claims, the method comprising passing flexible sheet metal of relatively thin guage between two rolls each having teeth, each tooth having four flanks, each flank facing between an axial direction and a circumferential direction, the rolls being arranged so that the teeth of one roll extend into the gaps between the teeth on the other, the teeth being arranged in parallel helical rows, the rolls being rotated at substantially the same speed about parallel axes to form rows of projections on both faces of the sheet material passed therethrough, wherein the teeth are radiused in two areas; at the peak and at the comers of the peak, the radius at the peak being from 1.0 to 2.5 mm and that at the comers from 0.2 to 1 mm, whereby the sheet is made rigid without damage to the surface material of the sheet. 5. A set of rolls for manufacturing a thin sheet metal substantially as herein described with reference to the accompanying drawings.

Documents:

0623-mas-1997 abstract-duplicate.pdf

0623-mas-1997 abstract.pdf

0623-mas-1997 claims-duplicate.pdf

0623-mas-1997 claims.pdf

0623-mas-1997 correspondence-others.pdf

0623-mas-1997 correspondence-po.pdf

0623-mas-1997 description (complete)-duplicate.pdf

0623-mas-1997 description (complete).pdf

0623-mas-1997 drawings.pdf

0623-mas-1997 form-2.pdf

0623-mas-1997 form-26.pdf

0623-mas-1997 form-4.pdf

0623-mas-1997 form-6.pdf

0623-mas-1997 petition.pdf