EP0454403A1

EP0454403A1 - A doctor blade with integral mounting means and a method of making the same

Info

Publication number: EP0454403A1
Application number: EP91303608A
Authority: EP
Inventors: Earl R. Mileson; Robert B. Ramey; Normand Boucher
Original assignee: Albany International Corp
Current assignee: Albany International Corp
Priority date: 1990-04-23
Filing date: 1991-04-23
Publication date: 1991-10-30

Abstract

A doctor blade (10) is made with two sets (20, 22) of integral recesses. One set (20) is shaped to retain the blade in a standard holder (34). The second set (22) is shaped to act as a spring for biasing the blade within the holder. The blade may be made of metallic or a composite plastics material.

Description

This invention pertains to a blade used as a doctor for a pulp or papermaking machine, and more particularly to a blade with integral mounting means for mounting it on a blade holder.
Pulp or papermaking machines utilize machine rolls. Such machine rolls are used during various aspects of the process, for example, in the forming, pressing, drying or calendering sections. The operation of machine rolls requires a device to remove contaminants which form on the roll surface and/or to peel off a sheet or web from the rolls. A traditional method of achieving this is through the use of a mechanical device commonly referred to as a doctor or doctor blade. The failure to remove the contaminants or the sheet effectively can have a catastrophic effect on the quality of the product being produced.
The doctor blade is typically fastened by a doctor blade holder to a structural beam which is adjustably supported across the papermaking machine on which the blade holder and replaceable blade is provided. The doctor blade comes in direct contact with the roll surface so as to scrape off any contaminants from the roll surface, or to scrape off the whole pulp or paper web sheet, or parts thereof.
There is a plurality of different doctor blade types having dimensions and materials commonly available in the industry, as well as different designs of blade holders. Laminated plastic doctor blades and blade holders such as type KF-35, KF-35A or PNEUFLEX blade holder are manufactured by Albany International Corp.. For obvious reasons the blade should be securely attached to the blade holder as a doctor without a blade will not scrape anything from the roll, and as aforesaid, this will have a catastrophic effect on the machine production. But even worse, the blade or a part thereof can come off and fall in the machine and may irreparably damage the pulp or paper machine clothing; the roll may also be damaged because of direct and sudden contact with the blade holder.
The ultimate solution to prevent the aforesaid catastrophic situation would be to permanently fasten the blade to the holder or to make it as an integral part of the holder. But, doctor blades do wear with time. Depending on the application, they can last anywhere from a few hours to several months. Therefore, a doctor blade must be a replaceable item. The blade and holder design should allow for easy, fast and safe blade replacement so as to ensure that neither the blade, nor a part thereof, like the fastening devices for example, will come off and fall into the machine.
A common design in the industry is to put along one edge of the blade some types of rivets, or some other mechanical retainers that could be, for example, rivetted, glued, or press-fitted to the blade. The holder is then manufactured with a slot incorporating a step or a groove. The edge of the blade with the retainers can be slid into the groove though one end of the holder. One such doctor blade and a common holder are disclosed in Canadian Patent no. 803,198. Alternative designs are also available which allow a blade to be removed from the front of the holder, for the few applications where the access through the ends is limited. However, all these designs although widely used in the industry have a significant drawback as very often a retainer will come off the blade, and will either fall into the machine, or will stay in the holder but become wedged into the blade slot, thus making the blade very difficult to slide in or out.
Another design used in the industry consists of making the blade with built-in retainers whereby there is no mechanically fastened part on the blade that can come off. One know way to do this is to machine the blade out of thicker material, leaving a narrow step along one edge that will retain the blade in the holder slot. This method is widely used to manufacture polyethylene doctor blades, where machining is fast and easy, and where thicker material is also required to add strength or to increase wear life. Theoretically, this method can be used to manufacture blades out of other popular materials, like metal or laminated plastics.
However, the increase in cost of the material, and in machining time, combined with the high amount of tooling required, render this method simply undesirable. Moreover, it would not be suitable for the front removable blade design.
Another known way of making integral retainers to the doctor blade is to stamp or punch straps formed of two parallel cuts along one edge of the blade at a certain spacing, to simulate the function of the rivets of the first design. However, this design has been used only to manufacture metallic doctor blades, such as bronze or stainless steel for example. It was believed that the mechanical properties of synthetic material used in the doctor blade industry, such as, for example, those of laminated glass fiber reinforced plastics, did not allow this method to be used on plastics blades. All the laminated composite doctor blades known to be used on the pulp or paper machines today, are manufactured with add-on retainers that are either rivetted, glued, or press-fitted along one edge of the blade, a design with major disadvantages as described above.
Moreover, all the prior art blades discussed above required a biasing spring member for maintaining the blade in a preselected position. This spring member complicated the production and assembly of the doctor blade installation and was also prone to breaking and falling into the papermaking machine.
It is therefore a principal objective of the invention to provide a doctor blade with integral biasing means and retainers, thereby offering all the advantages relating to this design yet cost effective to manufacture.
The present invention provides a doctor blade for installation in a doctoring blade holder in a papermaking machine, said holder comprising two opposed jaws, said doctoring blade comprising an elongate strip defined by a first longitudinal and a second longitudinal side, said first longitudinal side having a doctoring surface, first recess means formed integrally from said strip and extending in a first direction away from said strip, and, second recess means formed integrally from said strip and extending in a second direction opposite said first direction, said first and second recess means being arranged and constructed to maintain said blade within said holder by contacting said first and second jaws respectively.
Preferably, said first and second recess means have respective regions maintained in a spaced relation from said strip by the plastic deformation thereof.
The strip may have first and second surfaces and the first recess means may extend above said first surface and said second recess may extend below said second surface.
In a preferred embodiment, the second recess means is flexible to apply a biasing force on said blade when said blade is inserted in said holder.
The first and/or second recess means may be formed by arcuate cuts in the strip. The first recess means may be defined by arcuate cuts extending away from said second side, and the second recess means may be defined by arcuate cuts extending toward said second side. The first recess means may comprise longitudinal straps cut from the strip, and may be formed by pairs of cuts parallel to said second side. The second recess means may be defined by transversal cuts in said strip, which cuts preferably extend from the second side of the strip.
The doctoring blade may be made of a metallic or plastics composite material.
The present invention further provides a doctor blade assembly for doctoring a roll in a papermaking machine comprising a blade holder having first and second jaws defining a cavity therebetween and a blade, as specified above, capable of being retained in the cavity.
The assembly may comprise a blade holder having first and second longitudinal jaws defining a cavity therebetween, and, a blade adapted to be disposed in said cavity, said blade including an elongate strip having a first side with a doctoring surface disposed away from said blade holder, and a second side disposed in said cavity, first recess means formed integrally from said strip, said first recess means co-operating with said first longitudinal jaw to retain said blade, and, second recess means formed from said strip and arranged and constructed to bias said strip away from said second longitudinal jaw.
The present invention also provides a method of making a doctor blade, as specified above, which method comprises forming an elongate strip with a first side having a doctoring surface, and a second side opposite said first side, and, forming first and second recess means integrally from the strip, preferably by plastically deforming said strip, and optionally, shaping said first recess means to retain said blade in a holder, and shaping said second recess means to bias said blade against said holder.
A blade may be made by taking an elongate strip of suitable blade material and punching two sets of recess means adjacent to a longitudinal side of the material, one set of recesses being deformed to form retainers and the second set of recesses being deformed to form the biasing means.
Various embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 shows a plan view of a first doctor blade;
Figure 2 shows a sectional side view of the doctor blade of Figure 1 taken along lines 2-2;
Figure 3 shows a sectional side view of the doctor blade of Figure 1 taken along lines 3-3;
Figure 4 shows the doctor blade inserted into a blade holder;
Figure 5 shows a plan view of a second doctor blade;
Figure 6 shows a side view of the second doctor blade; and
Figure 7 shows a side view of the second doctor blade inserted into a blade holder.

The doctor blade 10 shown in Figures 1-4 consists of a strip 12 made of a metal, a metal alloy or a fiber reinforced laminated plastics material such as a plastics laminated base of, for example, a vinyl ester reinforced by fiberglass fibers. In a preferred embodiment of the invention, strip 12 is about 0.060˝ (1.5 mm) thick, and 3˝ (78 mm) wide. One side 14 of strip 12 may be bevelled at an angle of about 45° to form a doctoring surface 16. Adjacent to the other side 18 of the strip 12, there are two sets of tabs 20, 22 extending along the length of the strip. At least one end of the strip 12 is provided with a through hole 24 by which the strip can be grabbed so that it can be removed from a holder.
As shown in detail in Figure 1, tabs 20, 22 are formed by making semi-circular cuts 26, 28 in the strip 12. As clearly shown in Figure 1 the tabs 20, 22 are cut symmetrically along axes normal to the longitudinal axis of blade 12. Moreover, tabs 20 and tabs 22 are cut so they are facing in opposite directions.
Preferably, simultaneously with the cutting, the tabs 20, 22 are pushed out laterally with respect to the strip 12. Importantly, tabs 20 are bent toward one side of the strip 12 while tabs 22 are bent toward the other side. The size of the cuts 26, 28 and their distance from side 18 are selected to ensure that the tabs are formed by plastically deforming the strip 12 (i.e. the tabs remain in the bent position after the bending force is removed).
Importantly, tab 20 is shaped so that, as shown in Figure 3, it first moves outwardly away from strip 12 but just before its tip, the tab curves back toward the blade to define an arc. Preferably, tab 20 is also curved in the longitudinal direction to reinforce the tab structurally. As a result, tab 20 is formed with a contact zone or point 30 which is the furthest point on tab 20 from strip 12. Similarly, tab 22 is curved in two dimensions to form a contact zone or point 32.
Referring now to Figure 4, a typical doctor blade holder 34 consists of two jaws 36, 38 joined by nut-and-bolt arrangements 40. Jaw 38 may be a single longitudinal unit, or may consist of a plurality of parallel fingers. Jaw 36 has a longitudinal channel 40 defined between a lip 42 and a wall 44. Jaw 38 is also formed with a channel 46 defined at one end by a step 48.
After strip 12 is formed as described above and in Figures 1-3, it may be inserted into the holder by sliding it into the cavity formed by channels 40, 46. A sharp tool may be used to engage hole 24 to pull the blade into the holder. The holder 34 and blade 12 are dimensioned so that once the blade is seated in its place it is maintained there by interference fit with the holder. More particularly, tabs 20 are seated so that the contact point 30 is resting on the web 50 of jaw 36 with the tip of the tab 20 being in contact with lip 42. Tab 22 rests against jaw 38 and it is flexible to bias the blade. The doctoring surface 16 rests on a roller 52 in the usual manner.
An alternative embodiment of the invention is shown in Figures 5 and 6. In these Figures, strip 100 is made with a set of straps 102, formed by making two longitudinal cuts 104, 106. The opposite edge 110 is slanted to form a doctoring surface.
After the straps have been cut they are punched to be plastically distorted to extend by about 1/16˝ (0.16 cm) away from blade 100.
Importantly, blade 100 is also provided with transversal tabs 112. Tabs 112 are formed by making two transversal cuts 116, 118 extending from edge 108 inwardly.
Tabs 112 are bent away from blade 100 in a direction opposite from straps 102 as shown in Figure 6.
Straps 102 and tabs 112 are dimensioned so that when blade 100 is inserted into holder 34 (Figure 7), straps 102 are in contact with or at least adjacent to lip 42 to retain the blade within the holder. Tabs 112 bear against step 48 to bias the blade within the holder.
Blades 10, 100 may be made of a metallic or plastics material which is resilient enough so that the integral tabs 20, 22, 112 or strap 102 cut therefrom maintain some degree of springiness sufficient to keep the blade within the holder.
It is important to note that in either embodiment, the tabs and/or straps which form the recesses used to retain the blade within the holder, each have a zone or region disposed on one side or another of the blade. These zones are maintained in their position by the plastic deformation of the blade used to generate the recesses.

Claims

A doctor blade for installation in a doctoring blade holder in a papermaking machine, said holder comprising two opposed jaws, said doctor blade comprising:
an elongate strip defined by a first longitudinal and a second longitudinal side, said first longitudinal side having a doctoring surface;
first recess means formed integrally from said strip and extending in a first direction away from said strip; and
second recess means formed integrally from said strip and extending in a second direction opposite said first direction;
said first and second recess means being arranged and constructed to maintain said blade within said holder by contacting said first and second jaws respectively.
A doctor blade as claimed in claim 1, wherein said first and second recess means have respective regions maintained in a spaced relation from said strip by the plastic deformation thereof.
A doctor blade as claimed in claim 1 or claim 2, wherein said strip has first and second surfaces and wherein said first recess means extends above said first surface and said second recess means extends below said second surface.
A doctor blade as claimed in any one of claims 1 to 3, wherein said second recess means is flexible to apply a biasing force on said blade when said blade is inserted in said holder.
A doctor blade as claimed in any one of claims 1 to 4, wherein said first recess means are defined by arcuate cuts extending away from said second side.
A doctor blade as claimed in any one of claims 1 to 5, wherein said second recess means are defined by arcuate cuts extending toward said second side.
A doctor blade as claimed in any one of claims 1 to 4, wherein said first recess means comprises longitudinal straps cut from said strip.
A doctor blade as claimed in any one of claims 1 to 4 or claim 7, wherein said second recess means are defined by transversal cuts in said strip.
A doctor blade as claimed in any one of claims 1 to 8, which is made of a metallic or plastics composite material.
A doctor blade assembly for doctoring a roll in a papermaking machine comprising a blade holder having first and second jaws defining a cavity therebetween and a blade capable of being retained in the cavity and as specified in any one of claims 1 to 9.
A doctor blade assembly as claimed in claim 10, for doctoring a roll in a papermaking machine, said assembly comprising:
a. a blade holder having first and second longitudinal jaws defining a cavity therebetween; and,

b. a blade adapted to be disposed in said cavity, said blade including:
i. an elongate strip having a first side with a doctoring surface disposed away from said blade holder, and a second side disposed in said cavity;

ii. first recess means formed integrally from said strip, said first recess means co-operating with said first longitudinal jaw to retain said blade; and

iii. second recess means formed from said strip and arranged and constructed to bias said strip away from said second longitudinal jaw.
A method of making a doctor blade as specified in any one of claims 1 to 9 comprising:
forming an elongate strip with a first side having a doctoring surface, and a second side opposite said first side; and
forming first and second recess means integrally from the strip, preferably by plastically deforming said strip, and optionally, shaping said first recess means to retain said blade in a holder, and shaping said second recess means to bias said blade against said holder.