Vented lead blade

Abstract

A vented lead blade for use in a paper making machine located so that the stock jet impinges the forming fabric at, or near to, its trailing edge. The vented lead blade serves to bend the forming fabric before it enters the forming section, and to vent at least a substantial proportion of any air which becomes trapped in the wedge shaped space between the surface of the forming fabric and the surface of the stock jet, together with at least some of any liquid carried with the air. The vented lead blade of this invention thus enables the forming fabric to be positioned so that the angle of impingement of the stock jet onto the forming fabric can be minimized to become substantially zero. It also makes it possible to reduce the unsupported length of the stock jet. The vented lead blade of this invention can be used in both an open surface forming section with one forming fabric, or in the forming section of a two fabric paper making machine.

What is claimed is:  
     
         1 . A curved vented lead blade for use in a paper making machine upstream of, and immediately adjacent to, the point of impingement of a stock jet ejected from a head box slice onto a moving forming fabric carrying an amount of liquid, which lead blade has a leading edge, a shaped trailing edge portion, including a trailing edge, and a convexly curved surface located between the leading edge and the trailing edge portion, over which the forming fabric moves in sliding contact and wraps through an angle of wrap θ, the convexly curved surface and the trailing edge portion including a plurality of grooves which begin at the leading edge and end at the trailing edge constructed and arranged to vent at the lead blade trailing edge at least a substantial proportion of any air trapped in the forming fabric from a wedge shaped space between the stock jet and the forming fabric surface, and at least some of the liquid carried by the forming fabric.  
     
     
         2 . A papermaking machine, having a machine direction and a cross machine direction, which includes: 
 a forming fabric moving in the machine direction;    a head box including a head box slice which provides a jet of paper making stock which impinges at an angle of impingement onto the forming fabric at a point of impingement;    a roll, having a cylindrical surface whose axis is in the cross machine direction, about which the forming fabric passes, and which is located upstream of the head box slice;    a forming section, located downstream of the point of impingement, including static support elements which define a fabric path through which the forming fabric passes; and    a vented lead blade, located upstream of, and immediately adjacent to, the point of impingement of a stock jet ejected from a head box slice onto a moving forming fabric, about which a forming fabric wraps through a wrap angle θ;    wherein the vented lead blade has a leading edge, a shaped trailing edge portion, including a trailing edge, and a convexly curved surface located between the leading edge and the trailing edge portion, over which the forming fabric moves in sliding contact and wraps through an angle of wrap θ, the convexly curved surface and the trailing edge portion including a plurality of grooves which begin at the leading edge and end at the trailing edge constructed and arranged to vent at the lead blade trailing edge at least a substantial proportion of any air trapped in the forming fabric from a wedge shaped space between the stock jet and the lead blade curved surface, and at least some of the liquid carried by the forming fabric.    
     
     
         3 . A papermaking machine, having a machine direction and a cross machine direction, which includes: 
 a first and a second forming fabric each moving in the machine direction;    a head box including a head box slice which provides a jet of paper making stock which impinges at an angle of impingement onto at least one of the forming fabrics at a point of impingement;    two rolls, each having a cylindrical surface whose axis is in the cross machine direction, about each of which one of the forming fabric passes, and which are located adjacent the head box slice;    a forming section, located downstream of the point of impingement, including static support elements which define a fabric path through which the forming fabric passes; and    two vented lead blades, each located upstream of, and immediately adjacent to, the point of impingement of the stock jet, about the first of which the first forming fabric wraps through a wrap angle θ 1 , and about the second of which the second forming fabric wraps through a wrap angle θ 2 ;    wherein each vented lead blade has a leading edge, a shaped trailing edge portion, including a trailing edge, and a convexly curved surface located between the leading edge and the trailing edge portion, over which the forming fabric moves in sliding contact and wraps through an angle of wrap, the convexly curved surface and the trailing edge portion including a plurality of grooves which begin at the leading edge and end at the trailing edge constructed and arranged to vent at the lead blade trailing edge at least a substantial proportion of any air trapped in the forming fabric from a wedge shaped space between the stock jet and the lead blade curved surface, and at least some of the liquid carried by the forming fabric.    
     
     
         4 . A curved vented lead blade according to  claim 1  wherein the convexly curved surface is essentially circular, with a constant radius.  
     
     
         5 . A curved vented lead blade according to  claim 1  wherein the shaped trailing edge portion conforms to the convexly curved surface.  
     
     
         6 . A curved vented lead blade according to  claim 1  wherein the convexly curved surface is not circular, and the radius of curvature increases towards the trailing edge.  
     
     
         7 . A curved vented lead blade according to  claim 1  wherein the convexly curved surface is not circular, the radius of curvature increases towards the trailing edge, and the shaped trailing edge portion is essentially flat.  
     
     
         8 . A curved vented lead blade according to  claim 1  wherein the convexly curved surface has an effective radius of curvature that is from about 50% to about 100% of the radius of the adjacent upstream roll.  
     
     
         9 . A curved vented lead blade according to  claim 1  wherein the angle θ is from about 10° to about 40°.  
     
     
         10 . A curved vented lead blade according to  claim 9  wherein the angle θ is from about 15° to about 30°.  
     
     
         11 . A curved vented lead blade according to  claim 10  wherein the angle θ is from about 20° to about 25°.  
     
     
         12 . A paper making machine according to  claim 3  wherein the two vented lead blades are the same, and their convexly curved surfaces are the same shape.  
     
     
         13 . A paper making machine according to  claim 3  wherein the two vented lead blades are not the same, and their convexly curved surfaces are not the same shape.  
     
     
         14 . A paper making machine according to  claim 3  wherein the two vented lead blades are the same, the angles θ 1  and θ 2  are the same, and the convexly curved surfaces are the same shape.  
     
     
         15 . A paper making machine according to  claim 3  wherein the two vented lead blades are not the same, the angles θ 1  and θ 2  are not the same, and the two convexly curved surfaces are not the same shape.  
     
     
         16 . A paper making machine according to  claim 2  including a vented lead blade according to claims  4 ,  5 ,  6 ,  7 ,  8 ,  9  or  10 .  
     
     
         17 . A paper making machine according to  claim 3  including a first vented lead blade according to claims  4 ,  5 ,  6 ,  7 ,  8 ,  9  or  10 .  
     
     
         18 . A paper making machine according to  claim 3  including a second vented lead blade according to claims  4 ,  5 ,  6 ,  7 ,  8 ,  9  or  10 .