Abstract:
An apparatus for doctoring a roll in a paper machine, comprising a doctor blade and an integral blade holder including a support tray carrying fluid actuated tubes for applying the doctor blade to the roll. The blade holder is removably mounted on and releasably secured to the doctor back.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from provisional application Ser. No. 60/068,463 filed Dec. 22, 1997 and entitled REMOVABLE DOCTOR BLADE HOLDER. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to doctors used, in papermaking machines, and is concerned in particular with the provision of a blade holder which is readily separable from the doctor back and removable from the papermaking machine for cleaning, inspection and repair. 
     2. Description of the Prior Art 
     The main components of a doctor system include the doctor blade, the blade holder, the doctor back and the loading mechanism. The doctor blade keeps the roll clean and/or sheds the sheet. It must be perfectly flat, straight and parallel, and its composition must be compatible with the roll to be doctored. 
     The blade holder exerts a uniform, designated load pressure on the blade. It holds the blade firmly against the roll, accommodates roll irregularities and, within limits, compensates for thermal expansion. 
     The doctor back is in essence the backbone of the doctor. It serves as the support structure for the blade holder. The loading mechanism pivots the doctor back to load the doctor blade against the roll. 
     Doctor blade holder designs used in recent years are more complex and have more components than the simpler blade holders used in the past. As a result, the more recent holder designs require more routine cleaning and maintenance. The doctor blade holders are normally mounted to the doctor back rigidly with a series of fasteners. Maintenance and cleaning of the blade holder can take place while the doctor remains in the machine but only in installations where the holder is accessible. However, in many cases, papermachine framework or other equipment prevents access to the blade holder while it is in the papermachine. In these cases, the complete doctor structure including the doctor back and attached holder must be removed from the papermachine to perform any cleaning or maintenance work. This task involves removing heavy equipment which requires extensive manpower and machine downtime. After making the necessary repairs, the entire doctor assembly must be re-installed in the papermachine, consuming more valuable manpower and time. In addition to the re-installation, the doctor must be re-aligned to the roll surface for optimum doctor performance. 
     SUMMARY OF THE INVENTION 
     The present invention avoids or at least significantly minimizes the above mentioned problems by providing a doctor blade holder which is readily separable from the supporting doctor back. Thus, while the doctor back remains undisturbed in the papermachine, operating personnel can remove the blade holder for cleaning and maintenance. Thereafter, the blade holder is returned to its operative position on the doctor back and locked in place. Certain embodiments of the invention further include the provision of a releasable clamping mechanism for clamping the blade holder in place on the doctor back during papermachine operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objectives, features and advantages of the present invention will be described in greater detail with reference to the accompanying drawings; wherein: 
     FIG. 1 is a side view of a doctor assembly in accordance with the present invention; 
     FIG. 2 is an enlarged view of the doctor blade holder shown in FIG. 1; 
     FIG. 3A is a sectional view taken along line  3 A— 3 A of FIG. 2 showing the blade holder in its operative position clamped to the doctor back; 
     FIG. 3B is a view similar to FIG. 3A showing the blade holder unclamped from the doctor back; 
     FIG. 3C is a horizontal sectional view taken along line  3 C— 3 C of FIG. 3A; 
     FIG. 4 is a view similar to FIG. 2 showing an alternative embodiment of a blade holder in accordance with the present invention; 
     FIG. 5 is a horizontal sectional view taken along line  5 — 5  of FIG. 4; 
     FIG. 6 illustrates another embodiment of a blade holder in accordance with the present invention; 
     FIG. 7 is a horizontal sectional view taken along line  7 — 7  of FIG. 6; 
     FIG. 8 illustrates another embodiment of a blade holder in accordance with the present invention; 
     FIG. 9 is a perspective view of one of the dovetail washers employed in the arrangement shown in FIG. 8; 
     FIG. 10 illustrates still another embodiment of a blade holder in accordance with the present invention; 
     FIG. 11 is a perspective view of one of the stepped washers used in the arrangement shown in FIG. 10; 
     FIG. 12 is a perspective view showing a further modification to blade holders embodying the concepts of the present invention; and 
     FIG. 13 is a partial plan view of the blade holder and doctor back at one side of the papermachine. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference initially to FIG. 1, a doctor assembly in accordance with the present invention is generally depicted at  10  adjacent to a papermachine roll  12 . Roll  12  is driven by conventional means (not shown) for rotation about an axis A, extending in the cross-machine direction. The doctor assembly includes a doctor blade  14 , a blade holder  16 , a doctor back  18 , and a loading mechanism  20 . The doctor back is mounted on the papermachine frame for pivotal movement about an axis A 2  extending in the cross-machine direction parallel to the rotational axis A 1 , of roll  12 . The loading mechanism  20  includes a piston-cylinder unit  22  acting through lever arm  24  to pivot the doctor back  18  about its axis A 2  in order to load the doctor blade  14  against the surface of the roll  12 . 
     With reference additionally to FIGS.  2  and  3 A- 3 C, it will be seen that the blade holder  16  includes a tray  26  with upstanding brackets  28  located between an unloading tube  30  and a loading tube  32 . A top pressure plate  34  overlies the tubes  30 ,  32  and has depending brackets  36  which are connected to the brackets  28  by a rod  38  for pivotal movement about a third axis A 3  parallel to axes A 1 , and A 2 . 
     Fingers  40  cooperate with the underside of the top pressure plate  34  to retain the doctor blade  14  in its forwardly extending position. The tubes  30 ,  32  are fluid actuated, with tube  32  serving to coact with the force being applied by the loading mechanism  20  to apply the blade  14  to the surface of the roll  12 . Tube  30  serves to unload the blade from the roll surface, in addition to acting as a front seal. 
     A pair of L-shaped confronting mounting strips  42   a ,  42   b  are secured to the underside of the tray  26 . The mounting strips have horizontal ledges  44   a ,  44   b  spaced one from the other to define a continuous slot  46  communicating with an interior recess  47 . 
     A shelf  50  extends forwardly from and forms an integral part of the doctor back  18 . Shoulder screws  52  are threaded into the shelf  50  at spaced locations along the length of the slot  46 . A locking strip  54  in interposed between the ledges  44   a ,  44   b  and the heads of the shoulder screws  52 . The locking strip is slotted as at  56  to accommodate the shoulder screws, and the slots  56  are partially bordered by resilient tabs  58  which are bent upwardly out of the lane of the locking strip. 
     The locking strip  54  is slidable longitudinally with respect to the shelf  50  of the doctor back and the mounting strips  42   a ,  42   b  on the underside of the tray  26 . When in the locked position as shown in FIGS. 3A and 3C, the tabs  58  are deflected downwardly by the heads of the shoulder screws  52  into the plane of the strip  54 , thereby exerting a downward force which clamps the ledges  44   a ,  44   b  against the shelf  50 , thus fixing the doctor holder  16  in its operative position on the doctor back  18 . As can be best seen in FIG. 3A, a pin  60  or the like at one side of the papermachine is employed to releasably fix the locking strip  54  in its locked position. 
     When it becomes necessary to clean or maintain the blade holder, the pin  60  is removed and the locking strip  54  is shifted to its unlocked position as shown in FIG.  3 B. This relieves the clamping force exerted by the resilient tabs  58 , thus allowing the blade holder and doctor blade to be extracted longitudinally as a unit out of the papermachine. After cleaning and maintenance, the blade holder is longitudinally reinserted into the papermachine, and the clamping strip returned to its locked position. 
     An alternative embodiment of the invention is depicted in FIGS. 4 and 5, where a mounting strip  62   a  is secured to the underside of the tray  26 . A second mounting strip  62   b  is connected to strip  62   a  by means of shoulder screws  64  extending through angled slots  66 . The strips  62   a ,  62   b  coact to define a dovetailed slot  68  for receiving a dovetail strip  70  secured to the doctor back shelf  50  by screws  72 . Longitudinal movement of the strip  62   b  in direction A will urge it laterally against the dovetail strip  70 , thus clamping the blade holder in place. 
     Longitudinal movement of the strip  62   b  in the opposite direction B will shift the strip  62   b  laterally away from strip  70 , thus freeing the doctor holder for removal from the doctor back. If the strip  62   b  is only shifted slightly laterally, the blade holder can be slid longitudinally into and out of its operative position, whereas a more pronounced lateral shifting of the strip will permit the blade holder to be lifted from and lowered onto the doctor back. 
     In the embodiment shown in FIGS. 6 and 7, a male dovetail strip  74  is secured to the underside of the tray  26  and a female dovetail strip  76  is secured to the doctor back shelf  50 . A set screw  78  at one side of the papermaking machine serves to fix male dovetail the strip  74  against sliding movement relative to the female dovetail strip  76 . When the screw  78  is backed off as shown in FIG. 7, the blade holder is free to slide longitudinally into and out of its operative position on the doctor back. 
     In the embodiment shown in FIGS. 8 and 9, a female dovetail strip  80  is secured to the underside of the tray  26 , and frustoconical dovetail washers  82  are secured to and spaced along the length of the doctor back shelf  50 . 
     In FIGS. 10 and 11, stepped washers  84  are secured at spaced locations along the underside of the tray  26 , and a mounting strip  86  is secured to the doctor back shelf  50 . The mounting strip  86  has an undercut channel  88  along which the stepped washers slide during longitudinal extraction and insertion of the blade holder. 
     FIG. 12 illustrates another embodiment where a mounting strip  90  with an undercut channel  92  is secured to the doctor back shelf  50 . The channel  92  is interrupted as at  94  at spaced locations along its length. This allows either the stepped washers  84  of FIGS. 11 or  12  stepped strip segments  96  which are secured to the underside of the blade holder tray  26  to slide along the channel  92  to positions at which they may exit via the interrupted sections  94  either laterally in direction A or vertically in direction B. 
     In the embodiments shown in FIGS. 8 to  12 , a locking means of some type is provided at one side of the machine to prevent removal of the blade holder from the doctor back during operation of the papermachine. As shown in FIG. 13, locking can be achieved by providing a bracket  98  on the tray  26  at one side of the papermachine which is detachably connected to the doctor back shelf  50  by a pin  100  or the like. 
     In light of the foregoing, it will now be appreciated by those skilled in the art that the present invention provides for ready separation of the doctor blade holder from the doctor back for removal from the papermachine. The embodiments illustrated in FIGS. 1-5 provide means for securely clamping the blade holder to the doctor back during operation of the papermachine. Other embodiments as illustrated in FIGS. 6-13 lock the blade holder in its operative position, but do not exert additional clamping forces. All arrangements are advantageous in that removability of the blade holder provides maintenance personnel with the opportunity to clean and perform maintenance outside of the papermachine, without disturbing the doctor back.