Paper making and fiber liberation – Apparatus – Web creping or crinkling type
Reexamination Certificate
2000-01-24
2001-12-11
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Apparatus
Web creping or crinkling type
C015S256510, C162S272000
Reexamination Certificate
active
06328853
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to web processing machines, e.g., paper machines, coaters and the like, and is concerned in particular with an improved apparatus for doctoring the rolls of such machines.
2. Description of the Prior Art
The three main components of a doctor system include a rigid doctor structure or beam, a doctor blade holder, and a doctor blade. The doctor system is adapted to be mounted in a paper machine, coater or other like web processing machine and is used to scrape the rotating rolls for cleaning or dewatering purposes. At some critical roll positions in the paper machine, the doctor system is also used during the threading process to remove or “shed” either a full width sheet of paper or a portion of the sheet.
In conventional doctoring, the working edge of a doctor blade is applied to the rotating roll surface from which the material, water or other solutions are to be removed. The critical factors contributing to an effective doctoring operation include a uniform load between the working edge of the blade and the rotating roll surface for the full length of the blade, and maintenance of an optimum blade angle with respect to the roll surface.
FIGS. 1-3
illustrate examples of prior art doctoring systems. In
FIGS. 1 and 2
, a doctor system includes a doctor back
10
mounted in bearings
12
for rotation about an axis A
1
. An actuator
14
operates to rotate the doctor back about axis A
1
in order to load the working edge of a doctor blade
16
against the surface
18
of a rotating roll
20
. A blade holder
22
is mounted to the front of the doctor back
10
.
In the following description, it is to be understood that the doctor blade and the principal associated components of the doctoring system, e.g., the doctor back and blade holder, each extend in the “cross machine direction”, i.e., parallel to the rotational axis A
1
of roll
20
, for at least the full width of the web being processed. Moreover, as herein employed, the term “machine direction” is to be understood as referring to the direction of travel of the web through the machine.
As can best be seen in
FIG. 2
, the blade holder includes a relatively rigid top plate
24
and an underlying jaw
26
. The doctor blade
16
is removably received in a slot
28
where it is supported between the top plate
24
and the jaw
26
.
The top plate is fastened to the doctor back by threaded screws
30
or the like. Adjustable set screws
32
are provided to adjust the blade holder and doctor blade along the length of the roll
20
in order to accommodate localized roll surface variations. Even though the set screws
32
provide some measure of adjustability, achieving a uniform load between the blade working edge and the varying roll surfaces continues to be problematical. The main drawback of this type of apparatus is that because the doctor blade
16
is held between the top plate
24
and the jaw
26
, both being relatively rigid members, there is a lack of flexibility needed to satisfactorily accommodate the often encountered roll surface irregularities.
FIG. 3
illustrates a more advanced prior art doctoring system. Here, a blade holder
34
is again mounted to the doctor back
10
. A top plate
36
is pivotally mounted for rotation about an axis A
2
defined by a pivot pin
38
extending for the full length of the holder. The pivot pin is threaded through top brackets
40
depending from the top plate
36
, and similar base brackets
42
extending upwardly from a channel-shaped base
43
. A jaw
44
is mounted to the underside of the top plate
36
in a forward position. The jaw
44
together with the top plate
36
defines a slot
46
in which the doctor blade
16
is removably received for application to the surface
18
of roll
20
.
An air or liquid filled load tube
48
extends for the full length of the holder and lies parallel to the pivot pin
38
in a position furthest from the doctor blade
16
. The load tube
48
is either inflated to generate a doctor blade loading force, or it provides a reactionary force with the top plate
36
when the doctor back
10
is rotated towards the roll surface
18
.
An additional air filled tube
50
is located parallel to the pivot pin
18
in a forward position. When it is necessary to unload the doctor blade
16
, either the air filled tube
50
is inflated while the load tube
48
is deflated, or the doctor back
10
is rotated away from the roll surface
18
. The air filled tube
50
also creates a seal to prevent debris from entering the holder cavities.
The main disadvantage of this type of doctoring system is that friction between the pivot pin
38
and the top plate brackets
40
along with a relatively low mechanical advantage provided by the load tube
48
combines to make the contact load between the doctor blade and the roll surface somewhat variable and unpredictable. An additional disadvantage is that the necessary clearances present between the pivot pin
38
and the associated brackets
40
,
42
makes the doctoring apparatus susceptible to vibration and chatter problems.
Examples of other prior art doctoring arrangements are provided by U.S. Pat. Nos. 4,789,432; 4,367,120; and 3,748,686.
SUMMARY OF THE INVENTION
The objective of the present invention is to provide a uniquely configured and improved doctoring apparatus which avoids or at least significantly minimizes the problems and drawbacks associated with the above described prior art systems, and is thus well suited for a wide range of applications on high speed paper machines or other like web processing equipment.
A more specific objective of the present invention is the provision of a doctoring apparatus which is capable of providing a substantially uniform loading between the doctor blade and the rotating roll surface while accommodating surface irregularities in the roll surface. This uniform loading characteristic is due largely to the flexural characteristics of the components and their unique geometry. Uniform loading between the doctor blade and the rotating roll surface is critical to achieving a more effective cleaning of the roll surface and/or more reliable sheet shedding, while also minimizing roll surface wear and minimizing and promoting even wear of the doctor blade.
The present invention achieves these objectives by relying primarily on the flexural properties of the top plate in combination with a strategically placed resilient member. In contrast to prior art holders utilizing a pivoted top plate assembly, the invention has minimum clearance or play between holder components. This in turn reduces any tendency of the blade holder components to vibrate or chatter. Additionally, the geometry of the present invention is such that doctor blade wear has a minimum effect on the operating doctor blade load or application angle.
These and other objectives, advantages and features of the present invention will now be described in greater detail with reference to the accompanying drawings wherein:
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patent: 3748686 (1973-07-01), Winterburn et al.
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patent: 3803665 (1974-04-01), Winterburn et al.
patent: 3854162 (1974-12-01), Russell
patent: 3866266 (1975-02-01), Dunlap
patent: 4367120 (1983-01-01), Hendrikz
patent: 4665859 (1987-05-01), Dunlap et al.
patent: 4906335 (1990-03-01), Goodnow et al.
patent: 5230775 (1993-07-01), Goodnow et al.
patent: 5279710 (1994-01-01), Aikawa
patent: 5284516 (1994-02-01), Sieberth
patent: 5408720 (1995-04-01), Miles
Benoit David
Brauns Allen
Goodnow Ronald F.
Chin Peter
Hug Eric
Samuels Gauthier & Stevens
Thermo Web Systems, Inc.
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