The invention relates to a profiling bar for a web coating device used in paper making processes, and in particular to a mechanism for controlling the amount of deformation of the bar during profile adjustment.
In the manufacture of paper, it is often desirable to coat one or both sides of the paper web. The coating mixture is applied to the running paper web, which is typically supported on a rotating roll, and just downstream of the coating application zone, there is positioned a metering blade that controls the thickness of the coating to remain on the web. An example of a coating apparatus is disclosed in U.S. Pat. No. 4,903,632, which patent is incorporated herein by reference.
The purpose of the metering blade, which is also often referred to as a doctor blade, is to control the thickness of the coating on the web. It is often desirable to modify the profile of the edge of the metering blade across the width of the web. A commonly utilized mechanism for doing this is a profile bar typically made of stainless steel and having an edge that engages a side face of the metering blade and extends the entire width of the web. Spindles or other adjustment mechanisms, such as air bags or pivoting actuators, engage the opposite edge of the profile bar at spaced apart directions along the axis of the bar and apply tensile or compressive forces to deform the bar so as to change the profile of the leading edge of the bar. This in turn deforms the metering blade so that the spacing of the metering blade edge from the surface of the web can vary across the width of the web.
A problem with prior art profile bars is that the bar can be deformed locally beyond its elastic limit to thereby cause permanent plastic deformation of the bar. Such plastic deformation of the bar will result in a permanent distortion of the leading edge thereby causing difficulties in making precise adjustments thereafter.