Abstract:
A doctor blade device ( 01 ) for cleaning a surface has a doctor blade ( 03 ) and a tub ( 09 ) for receiving the material stripped from the surface by the doctor blade. The doctor blade is movable between a position in which it projects out of an opening ( 13 ) of the tub and a position in which it is submerged in the tub. A closure element ( 07 ) closes the opening in the submerged position of the doctor blade.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a doctor blade device. 
   BACKGROUND OF THE INVENTION 
   Washing apparatuses are known for the automatic cleaning of ink-carrying rolls in a printing press, which washing apparatuses comprise spray nozzles or similar means for applying a cleaning fluid to the surface which is to be cleaned, and also comprise a doctor blade device which serves for pressing a flexible doctor blade against the surface which is wetted with the washing fluid, and thus for wiping off the washing fluid together with ink which is dissolved in it. The ink solution which is obtained in this way runs off into a trough of the doctor blade device and is led away via the latter. After the end of the washing process, ink residues remain on a conventional doctor blade device of this type, which ink residues have to be removed by hand, as they would otherwise dry on the doctor blade and damage the surface of the roll to be cleaned when said doctor blade is used again. 
   The invention is based on the aim of providing a doctor blade device. 
   SUMMARY OF THE INVENTION 
   According to the invention, the object is achieved by a doctor blade device for cleaning a surface, having a doctor blade and a trough for receiving material which is wiped off from the surface by the doctor blade wherein the doctor blade can be moved between a position in which it protrudes from an opening in the trough and a position in which it is lowered into the trough, and in that the trough has a closure element which, in the lowered position of the doctor blade, is capable of closing the opening. 
   The advantages which can be attained with the invention consist, in particular, in the fact that it is possible to avoid ink drying and solidifying on the doctor blade when the latter is not in use, as a consequence of the capability to lower the doctor blade into the trough and to close the trough. 
   As the trough in general has an elongate shape with a slot-shaped opening for the emerging doctor blade, a possibility for closing the trough can be provided in a simple manner by the trough being configured in the shape of a cylindrical chamber, about the axis of which the closure element can rotate between an open and a closed position. Here, the closure element is preferably arranged within the chamber. 
   The movement of the doctor blade between the position which protrudes out of the trough and the lowered position is preferably a pivoting movement, and an actuator for driving this pivoting movement is provided on the doctor blade device. 
   The doctor blade is preferably deformed elastically in the lowered position. 
   A particularly simple construction results if the closure element can be pivoted by the same actuator which also drives the movement of the doctor blade between the position which protrudes out of the trough and the lowered position. 
   In order not only to prevent the drying of wiped off ink on the doctor blade but also, moreover, for it to be possible for wiped off ink residues to be removed automatically from the doctor blade, it is desirable for the trough to be provided with a feed line and a discharge line for a cleaning fluid. In the closed state of the trough, the cleaning fluid can be pumped through said trough at a high flow speed, in order to release and rinse away ink residues over time which adhere tenaciously to the doctor blade. 
   In order to attain an effective flow through the chamber, it is desirable for the feed line and the discharge line to open into in each case opposite ends of the trough. 
   The doctor blade device preferably also comprises a pump for circulating cleaning fluid through the trough. Expediently, this pump can be assigned a control apparatus which is coupled to the position of the closure element and, when the chamber is closed, permits a higher throughput of the pump than when the chamber is open. It is appropriate to allow a flow of cleaning fluid when the chamber is open, even if said flow is weak, in order continuously to rinse off ink residues which the doctor blade wipes off from the roll surface which is to be cleaned during operation of the doctor blade device. The throughflow rate when the chamber is open has to be selected to be low enough that cleaning fluid does not spray out of the opening of the chamber. In contrast, when the chamber is closed, substantially higher throughflow rates can be used advantageously for the cleaning fluid. 
   It is desirable for ecological and economical reasons for the cleaning fluid to circulate in a closed circuit. This circuit expediently has at least one filter element for separating ink residues out of the flow of the cleaning fluid. 
   Exemplary embodiments of the invention are shown in the drawings and will be described in greater detail in the following text. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the figures: 
       FIG. 1  shows a diagrammatic section through a first refinement of a doctor blade device, in which the doctor blade is extended out of the chamber; 
       FIG. 2  shows a diagrammatic section through the doctor blade device from  FIG. 1 , in which the doctor blade is lowered into the trough; 
       FIG. 3  shows an axial section along the line III-III from  FIG. 1 ; 
       FIG. 4  shows a section, which is analogous to that of  FIG. 1 , through a second embodiment of the doctor blade device; 
       FIG. 5  shows a section through the doctor blade device according to a second embodiment, with a lowered doctor blade; and 
       FIG. 6  shows a block diagram of the doctor blade device. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a diagrammatic section through a doctor blade device  01  with a doctor blade  03  which is set against an inking roll  02  of a printing press. The inking roll  02  is shown only as a detail, over a quarter of its circumference. 
   The doctor blade  03  is a strip which extends at least over the active axial width of the inking roll  02  and is composed of a flexible plastic or rubber material. In the extended position of the doctor blade  03  which is shown in  FIG. 1 , one longitudinal edge  04  of the doctor blade  03  is in contact with the surface of the inking roll  02 . 
   An opposite longitudinal edge  06  of the doctor blade  03  is clamped in a closure element  07  in the shape of a cylinder sector, for example a holding element  07 . The holding element  07  is accommodated rotatably in a cylindrical chamber  08  of a trough  09 . As shown in  FIG. 3 , the trough  09  is composed of two end plates  11  which lie opposite one another and a cover  12  which connects the two end plates  11 . The cover  12  has substantially the shape of a cylinder, with an elongate opening  13 , for example a slot  13 , on its upper side and an elongate tongue  14  which is bent outward at one end of the slot  13  and serves as a support  14  for the doctor blade  03  when the inking roll  02  is being wiped. 
   Both end plates  11  are provided with a hole  16 , to which in each case a feed line or discharge line  17  for a cleaning fluid is connected. 
   When the inking roll  02  is being cleaned, a nozzle rail (not shown) sprays a cleaning fluid onto the entire width of the cover of the inking roll  02 . The inking roll  02  rotates in the counterclockwise direction in relation to  FIG. 1 . The doctor blade  03  presses against the surface of the inking roll  02  at an acute angle. The friction which occurs here increases the pressure between the doctor blade  03  and the inking roll  02  and, moreover, presses the doctor blade  03  against the supporting tongue  14  of the trough  09 . A mixture of cleaning fluid and ink residues which is moved over the surface of the inking roll  02  is wiped off by the doctor blade  03  and flows downward on the latter into the trough  09 , where it is entrained by a flow of cleaning fluid which flows through the trough  09  in the longitudinal direction from the feed line to the discharge line  17 . The throughput of the cleaning fluid in this state is measured to be just sufficient to ensure that the ink residues are rinsed away reliably and are not deposited in the trough  09 . For this purpose, it is not necessary for the flow to fill the entire cross section of the trough  09 . 
   After the inking roll  02  has been cleaned, the holding element  07  together with the doctor blade  03  is rotated about the longitudinal axis A of the chamber  08  into the position which is shown in  FIG. 2 . For this purpose, the holding element  07  merges at its two longitudinal ends into a cylindrical ring  18  which is closed in the circumferential direction and fills the inner cross section of the likewise cylindrical chamber  08  exactly. An external toothing system  19  which meshes with a pinion  21  is formed on each of these rings  18 . The pinions  21  at both ends of the trough  09  are driven by an identical actuating motor (not shown). The external toothing systems  19  are protected in each case by sealing rings  22  against the infiltration of rinsing fluid and possibly ink. 
     FIG. 2  shows the doctor blade device  01  in a configuration, in which the holding element  07  with the doctor blade  03  is rotated in the clockwise direction by not quite 180° compared with the configuration of  FIG. 1 . Here, the doctor blade  03  is situated in a position which is withdrawn completely into the chamber  08 . Instead of against the inking roll  02 , the longitudinal edge  04  of the doctor blade  03  presses against the cover  12  of the trough  09 , and the doctor blade  03  is bent elastically into itself. The holding element  07  blocks the slot  13 , with the result that the holding element  07  and the cover  12  form a tube which is closed all around. In order to clean the doctor blade  03 , cleaning fluid is pumped at high speed through the chamber  08  in this configuration of the doctor blade device  01 . In contrast to the configuration of  FIG. 1 , where a uniform, laminar flow is required to prevent cleaning fluid from spraying out of the trough  09 , a turbulent flow can be accepted here and is even desirable, in order to improve the cleaning action on the doctor blade  03 . The flow through the chamber  08  can be maintained for as long as is necessary to clean the doctor blade  03  with a desired accuracy. 
   As can be seen in the cross section in  FIG. 2 , the withdrawn doctor blade  03  separates a small region  23  of the cross section of the chamber  08 , which small region  23  does not communicate directly with the holes  16  on the end plates  11  of the trough  09  and in which small region  23  no significant flow of the cleaning fluid therefore occurs. However, this is insignificant for the efficacy of the cleaning of the doctor blade, as that lateral face of the doctor blade  03  which delimits the region  23  is not reached by the ink/cleaning fluid mixture when the mixture is being wiped off the inking roll  02  and remains clean. If it should prove necessary in an individual case also to clean that surface of the doctor blade  03  which faces the region  23 , it is not a problem to generate a flow of cleaning fluid in this region also, for example by the position at least of the hole  16  which is connected to the feed line in its end plate  11  being displaced in such a way that at least part of its cross section opens into the region  23 . 
     FIG. 4  shows a second embodiment of a doctor blade device  01  in an illustration which is analogous to  FIG. 1 . Identical elements which are present in both embodiments are denoted by identical designations and will not be described again. The doctor blade device  01  from  FIG. 4  is designed for an inking roll  02  which rotates in the clockwise direction in the perspective of this figure. The doctor blade  03  is composed of a rigid doctor blade lip  24  made from plastic and a spring  26 , for example a leaf spring  26  which, like the doctor blade lip  24 , extends over the entire width of the inking roll  02 . The leaf spring  26  is screwed on one side to the doctor blade lip  24  and on the other side to a holding element  07  which has the same functions as the holding element  07  from  FIG. 1 . The tongue  14  of the embodiment from  FIG. 1  is replaced by a rail  27  which is screwed to the cover  12  and holds the free longitudinal edge  04  of the doctor blade  03  pressed against the inking roll  02 . The rail  27  can be removed, in order to gain access to the interior of the trough  09  for maintenance and repair purposes. 
   The feed and discharge lines  17  for cleaning fluid are not guided through the end plates  11 , but through the cover  12  of the trough  09  near the ends which lie opposite one another. 
   If the doctor blade  03  is situated in the withdrawn position which is shown in  FIG. 5 , it divides the free inner space of the chamber  08  into two regions  23 ,  28 . The feed line  17  is arranged in such a way that it opens into the region  23  which is delimited by that lateral side of the doctor blade  03  which bears wiped-off ink in this embodiment. The discharge line  17  opens into the region  28 . A flow of cleaning fluid which is pumped through the chamber  08  via the feed and discharge lines  17  rinses the chamber  08  not only in the longitudinal direction, but it also displaces the doctor blade  03  a little away from the cover  12  back into the interior of the chamber  08 , with the result that a narrow gap is produced along the longitudinal edge  04  of the doctor blade  03 , through which narrow gap the cleaning fluid moves at high speed from the region  23  into the region  28 . In this way, highly effective cleaning is attained, above all of the longitudinal edge  04  which is provided for contact with the inking roll  02 . 
   Two sealing strips  29  made from rubber are let into the body of the holding element  07  and rotate with the latter. They are placed in such a way that, in the closed configuration which is shown in  FIG. 5 , they come to rest on both sides of the slot  13  and prevent egress of the cleaning fluid toward the inking roll  02  reliably. 
   As the block diagram from  FIG. 6  shows, the doctor blade device  01  also comprises a pump  30  which circulates the cleaning fluid in a closed circuit. The pump  30  is coupled to a control circuit  32  which also drives the actuating motor  33  for the pivoting movement of the holding element  07  and the doctor blade  03 . Coupled to the respective position of the holding element  07 , the control circuit  32  regulates the throughput of cleaning fluid to a low value in the open position and to a high value which favors a turbulent flow of cleaning fluid in the closed position. Furthermore, filters  31  for trapping ink residues which are dissolved in the cleaning fluid are arranged in the closed circuit, with the result that the doctor blade device  01  can be operated for a long time without maintenance.