Doctor blade mounting assembly
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an assembly for mounting a doctor blade, such as is used in connection with the roll or cylinder in a paper making machine or other machine for making webs of fibrous material or in laminating, coating or printing machines. 
     2. The Prior Art 
     In order for a doctor blade to function effectively, it should be in uniform contact with the coacting roll or cylinder throughout the length of the roll or cylinder, and the blade should be capable of accommodating itself to a crowned or cambered roll or cylinder irrespective of any sagging or distortion to which the blade-mounting assembly may be subject. It is also preferable that provision be made for quickly adjusting a blade in its mounting assembly to its optimum setting with regard to the condition of the material being doctored from the roll or cylinder. A further preferred requirement of a doctor blade and its mounting assembly is that the passage of paper or pulp removed by the blade should not lead to blockages between adjacent rolls or cylinders. 
     In a typical previous proposal for a doctor blade mounting system a number of &#34;fingers&#34; bear down on the blade, urging it onto the coacting cylinder or roll. Each finger is freely and independently pivotally mounted on a rigid common pivot shaft running parallel to the axis of the coacting cylinder. In order to afford a system of clamping the blade firmly and of averaging out the clamping force exerted by the fingers, it is common practice to provide continuous plates interposed between the doctor blade and the fingers. However, this limits the degree of distortion required of the doctor blade in order that it may accommodate itself adequately to the crowning or distortion of the coacting cylinder. 
     SUMMARY OF THE INVENTION 
     The present invention provides a doctor assembly for doctoring a cylinder which comprises a doctor blade; a main support bar extending parallel to the cylinder for applying pressure to the doctor blade so as to urge it into contact with the cylinder; a rigid support member extending forwardly from the main support bar towards the cylinder; a pivot shaft disposed beneath and fixed to the rigid support member and disposed parallel to the cylinder; a blade holder which accommodates the rear end of the doctor blade and extends forwardly towards the cylinder from the pivot shaft, the blade holder being constituted by a multiplicity of closely adjacent rigid pivot plates which are mounted side-by-side on the pivot shaft and capable of independent pivotal movement on the pivot shaft; and a fluid-filled bag which extends parallel to the length of the doctor blade between the support member and the pivot plates at a location between the rear end of the doctor blade and the pivot shaft. 
     As is conventional, the support bar is biased in use, either by its own weight, by springs or otherwise, to urge the forward end of the doctor blade into contact with the cylinder and the blade is readily able to adapt itself to curvature or discontinuities in the surface of the cylinder since all of the pivot plates can pivot independently to maintain uniform doctoring pressure having regard to the resilience of the inflatable bag which bears against them. 
     As will be appreciated, the number of pivot plates should be as large as convenient. Their width, measured in the direction of the length of the roll, is preferably 1/8 inch to 11/4 inch. In a typical case the width is 11/4 inch, and with a doctor blade having a length of 120  inches the number of pivot plates constituting the blade holder is approximately 96. 
     One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a portion of a doctor blade assembly according to the present invention, 
     FIG. 2 is a section taken along the line II--II in FIG. 1 and including a portion of a cylinder to be doctored, and 
     FIG. 3 is the view similar to FIG. 2 but showing an air-bag inflated. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The doctor blade assembly 1 shown in the drawings includes a rigid support member 10 attached to a main support bar 11 pivotally mounted on an axis 2 and extending parallel to a cylinder 12 to be doctored. A support bar 13, fixed to the underside of the rigid support member 10, carries a pivot shaft 14 which extends parallel to the axis of the cylinder 12. The shaft 14 is supported along its entire length by the support bar 13 so as to eliminate bending. 
     A doctor blade 17 for doctoring the cylinder 12 is supported by a blade holder constituted by a multiplicity of juxtaposed steel pivot plates 15, each provided at the rear end with a circular aperture 9 through which the shaft 14 passes. The plane of each pivot plate is perpendicular to the axis of the shaft 14, and the plates are mounted closely together on the shaft for individual independent pivotal rotation about the shaft. 
     The front end of each pivot plate is cut away and shaped to provide a means for locating and holding the rear end of the doctor blade 17. Each pivot plate locates and holds a portion of the doctor blade in a manner to be described and the entire length of the doctor blade is held and supported by the multiplicity of pivot plates. The cut away and shaped portion of each pivot plate 15 is provided by: 
     (a) a recess 20 extending diagonally upwards and through the thickness of the plate into the pivot plate from the front end facing the cylinder 12, 
     (b) a bottom portion of the pivot plate which extends upwardly into the entrance to the recess 20 to form a lip 22, and 
     (c) a top portion of the pivot plate which extends downwardly and forwardly of the lip 22 to form a finger 23 terminating in a flat bearing surface 24. 
     The finger 23 and the lip 22 are so disposed that the corner 25 between the rear wall and the bottom wall of the recess 20 is substantially coplanar with the bearing surface 24 and the top of the lip 22 so that the doctor blade 17 is supported, when it is inserted into the recess, by the bearing surface 24 contacting the upper surface of the blade, by the lip 22 contacting its lower surface, and at its rear edge by the corner 25. The blade is resiliently retained in the recess by a spring 26 compressed between the underside of the finger 23 and the blade 17 and attached to the blade by a rivet 27. 
     An inflatable, tubular air-bag 28 is located between the underside of the support member 10 and the upper sides of the pivot plates 15 and extends for the length of the plate 10 substantially parallel to the shaft 14. The ends of the air-bag are retained in place by screw-on plates 30 located at the ends of the support plate 10. 
     The weight of the support plate 10 pivoting about the axis 2 of the main support bar 11 causes the doctor blade 17 to bear against the cylinder 12 in opposition to the resilience of the air-bag 28 when inflated to a suitable pressure (e.g. 2-4 lbs. per sq. inch). The doctor blade assembly may be lifted from the cylinder 12 by rotating the bar 11 clockwise (as viewed in FIG. 3) in the direction of the arrow 3 about its axis 2 to a release position. Lifting of the doctor blade from the cylinder 12 is then effected by engagement of a projection 32 on the front of the support member 10 with rearwardly extending lugs 31 on the pivot plate 15, as shown in FIG. 3. 
     It will be seen that the doctor blade is supported by a multiplicity of pivot plates 15 and, owing to the resilience of the air-bag 28, can flex relative to other sections of the blade by virtue of the independent pivoting of the pivot plates 15 about the shaft 14. The doctor blade is thus enabled to conform to the exact shape of the cylinder 12 despite any reasonable amount of crown, camber or other irregular shape the cylinder may have. The narrowness of each pivot plate coupled with the closeness of the pivot plates to each other, effectively provides continuous control over the length of the doctor blade. 
     Each pivot plate is provided with a circular aperture 40. By inserting a rod through the apertures 40 of a number or all of the pivot plates they may be fixed relative to each other if so desired. 
     The pivot plates may be easily and cheaply stamped out of sheet steel in large quantities. An individual pivot plate may be easily replaced by sliding it off the shaft 14 and sliding a new pivot plate on. 
     The sloping fingers 23 enable material to be doctored cleanly off the cylinder without risk of fouling adjacent cylinders or machinery. 
     If desired a liquid filled bag may be used in place of the air bag 28.