EP0327581B1

EP0327581B1 - Sealing apparatus for sealing a movable blanket

Info

Publication number: EP0327581B1
Application number: EP19870907389
Authority: EP
Inventors: Bernard C. Bell; David V. Lange
Original assignee: Beloit Corp
Current assignee: Beloit Corp
Priority date: 1986-10-24
Filing date: 1987-10-19
Publication date: 1991-10-16
Also published as: EP0327581A1; AU8171187A; CA1307156C; AU605804B2; JPH0355599B2; JPH02500455A; BR8707859A; WO1988003192A1; DE3773942D1

Abstract

A sealing apparatus for sealing a movable blanket (18) which extends through an extended nip (16) defined by first and second cooperating press members (12, 14). The apparatus seals the blanket (18) relative to, and between, a first (32) and second end (36) of the first press member (12). The apparatus includes first and second rotatable heads (30, 34) which are disposed adjacent to the first and second ends respectively of the first press member. The heads are coaxial relative to the first press member (12). First and second annular seals (38, 40) are disposed between the blanket (18) and the first and second heads respectively for sealing the blanket (18) relative to the heads such that when the seals (38, 40) are in an inflated first position thereof, the blanket (18) is permitted to rotate coaxially around the first press member (12). When the seals (38, 40) are disposed in a deflated second position, the blanket (18) is movable axially relative to the seals for replacing the blanket.

Description

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

This invention relates to a sealing apparatus for sealing a movable blanket relative to a first press member of an extended nip press. More specifically, this invention relates to a sealing apparatus for sealing a movable blanket relative to a first press member of an extended nip press wherein the first press member is of the so-called "apple" configuration.

BACKGROUND OF THE INVENTION

Many variations of the basic extended nip press concept have been proposed. Basically, an extended nip press includes a first and second cooperating press members which define therebetween an extended nip. The arrangement is such that as the paper web extends through such extended nip, the residence time of the paper web between the cooperating press members is increased relative to the residence time of a more conventional nip defined by a pair of cooperating rolls. The increased residence time has a profound effect on the amount of water removed from the paper web, partially because the water removing pressure is exerted more gradually and for a longer period than is the case with a conventional nip defined by a roll couple.
Although many different extended nip press designs have been proposed, a particularly effective proposal was disclosed in U.S. patent numbers 4,287,021 and RE 31,923 to Justus et al. This extended nip press design has been commonly termed the "apple" design. This is because the lower first press member resembles an apple when viewed in a cross-machine direction.
With the so-called "apple" extended nip press, a major problem has been the containment of the lubricating oil disposed between the inner surface of the blanket and the outer surface of the apple-shaped first press member. As the looped blanket in operation of the extended nip press moves around the stationary first press member, there has been a tendency for the lubricating oil to seep laterally towards the edges of the blanket thereby permitting particles of the lubricating oil to be thrown radially outwards, thus causing possible contamination of the treated paper web.
In DE-A-3 338 487 there is described a sealing apparatus according to the preamble of claim 1. More specifically, DE-A-3 338 487 discloses an apparatus sealing a blanket relative to and between a first and second end of a first press member, the sealing apparatus comprising a first rotatable head disposed adjacent to the first end of the first press member, the first head being coaxial relative to the first press member, a second rotatable head disposed adjacent to the second end of the first press member, the second head being coaxial relative to the first head and the first press member respectively, first annular seal means disposed between the blanket and the first head for sealing the blanket relative to the first head, and second annular seal means disposed between the blanket and the second head for sealing the blanket relative to the second head such that when the first and second seal means are in an inflated first and third position thereof, the blanket is permitted to rotate coaxially around the first press member, the first position of the seal means being attained when the seal means are inflated and rotating relative to the first press member prior to passage of the seal means through the extended nip, the third position of the seal means being attained when the seal means are inflated and compressed during passage of the seal means through the extended nip, the first and second annular sealing means being each of hollow toroidal configuration, the sealing apparatus further including flow control means connected respectively to the first and second seal means for controlling the inflation and deflation of the first and second annular seal means.
It is an object of the present invention to provide an unstressed and unbiased second disposition of the seal means such that during stressing of the seal means during use of the sealing apparatus, the life of the seal means is extended. The present inventions also seeks to overcome the aforementioned problem associated with seepage of the lubricating oil and thereby provides a significant contribution to, and advancement over, the prior art proposals.
To achieve this, the sealing apparatus of the invention is characterized by the features set forth in the characterizing portion of claim 1. According to the invention, when said first and second seal means are disposed in a deflated second position thereof, the blanket is movable axially relative to the seal means for replacing the blanket, and the flow control means control the inflation and deflation of the first and second annular seal means such that each of the seal means defines, in an unstressed and unbiased disposition thereof, a cross-sectional configuration substantially equivalent to the cross-sectional configuration of the seal means when disposed in the second position thereof, such unstressed and unbiased disposition of the seal means being disposed between the first and third positions of the seal means so that during stressing of the seal means during use of the sealing apparatus, the life of the seal means is extended.
Advantageous embodiments of the invention are claimed in the subclaims.
A feature of the present invention is the provision of a sealing apparatus in which when the seals are inflated, the blanket is permitted to rotate relative to, and around, the first press member.
Another feature of the present invention is the provision of a sealing apparatus in which when the seals are disposed in a deflated second position thereof, the blanket is permitted to be moved axially relative to the first press member for replacement of the blanket.
Another feature of the present invention is the provision of a sealing apparatus in which when the seals are disposed in an inflated first position thereof, the blanket is permitted to move axially relative to the first press member while maintaining a sealing engagement with the inner surface of the blanket.
Other objects and advantages of the present invention will be evident to those skilled in the art by a consideration of the following detailed description taken in conjunction with the annexed drawings.
The arrangement is such that when the first and second seal means are in an inflated first position thereof, the blanket is permitted to rotate coaxially around the first press member. When the first and second seal means are disposed in a deflated second position thereof, the blanket is movable axially relative to the seal means for replacing the blanket.
In a more specific embodiment of the present invention, the first and second heads are each of discshaped configuration and are rotatable relative to the first member. The first and second seals are fabricated from an elastomeric material and are of a hollow, toroidal configuration such that when the seals are inflated, a sealing member of each seal is urged radially outwardly relative to the respective head into sealing conformity with the inner surface of the movable blanket. A base portion of each seal is connected with a respective head so that when the seals are inflated, the blanket is supported by the seal members and enabled to rotate with the heads around the stationary first press member.
Due to the elastomeric nature of the seals, any axial movement of the blanket relative to the first press member can be accommodated when the seals are inflated.
In another embodiment of the present invention, the base portion defines a convex surface in a cross-machine direction and the first and second rotatable heads each define a concave rim surface in a cross-machine direction. The concave rim surface cooperates with the convex surface of the base portion for permitting axial mounting of the respective seal means onto the respective head.
In another embodiment of the present invention, the first and second rotatable heads each further include a rim portion with the rim portion of each head defining a plurality of radial slots. A plurality of threaded fasteners are anchored within the base portion with the threaded fasteners having threaded portions extending radially inwards relative to the base portion. The arrangement is such that the inwardly extending threaded portions cooperate with the radial slots so that when the seal means is moved axially relative to the rim portion, the threaded portions are received within the radial slots. A plurality of internally-threaded members cooperate with the threaded portions for anchoring the base portion relative to the rim portion.
In each of the aforementioned embodiments, the sealing member is movable to a compressed third position thereof when the respective seal means is inflated. The third position is attained during compression of the respective seal means when that portion of the respective seal means passes through the extended nip.
In a preferred embodiment of the present invention, the seal means defines, in an unstressed and unbiased disposition thereof, a cross-sectional configuration of the seal means when disposed in the second position thereof. This unstressed and unbiased second disposition of the seal means with the seal means being disposed between the first and third positions thereof, is such that during stressing of the seal means during use of the sealing apparatus, the life of the seal means is extended.
In yet another embodiment of the present invention, the first and second seal means each further include a base portion for connecting the respective seal means to the respective rotatable head and a sealing portion disposed diametrically opposite to the base portion with the sealing portion defining a plain sealing surface disposed adjacent to an inner surface of the movable blanket.
In another embodiment of the present invention, means are provided for connecting a compartment defined between the blanket, the first press member and the first and second seal means to a source of pressurized fluid. The source of pressurized fluid is preferably pressurized air, such that during use of the apparatus with the seal means disposed in the inflated first position thereof, the pressurized air within the compartment is above ambient atmospheric pressure.
Preferably, the pressurized air within the compartment is within the range .07-.14 Kg/SQ CM (1-2 pounds per square inch) and the seal means are each internally pressurized within the range 1.44-2.9 Kg/SQ CM (20-40 pounds per square inch) in the first position thereof.
The present invention also includes a method of sealing a blanket extending through an extended nip so that the blanket is sealed relative to the first press member. The method includes the steps of deflating the seals, moving the blanket axially relative to, and around, the first press member so that the blanket encircles and enwraps the first press member, then inflating the seals so that the seals are urged radially outwardly against the inner surface of the blanket for maintening a seal between the blanket and the stationary first member when the blanket rotates relative to, and around, the stationary first press member.
Although the present invention, as described hereinafter, is described particularly with regard to one manner of carrying out the invention, it will be evident to those skilled in the art that there are many variations of the present inventive concept and that these numerous variations and modifications fall within the spirit and scope of the present invention as defined by the appended claims and that the invention is not limited to the particular embodiment to be described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a side-elevational view of an extended nip press of the "apple" type showing a stationary "apple" shaped first press member and a cooperating rotatable second press member with an inflatable sealing apparatus disposed between the blanket and the first press member.
Figure 2 is a sectional view taken on the line 2-2 of figure 1.
Figure 3 is an enlarged fragmentary view taken on the line 3-3 of figure 2 showing the disposition of the first and second seals relative to the blanket and the first and second heads when the seals are inflated.
Figure 4 shows one of the seals in the deflated second position thereof.
Figure 5 is an enlarged sectional view of one of the seals in an air inflated first position thereof, the seal being subjected to radial deflection by the blanket, and
Figure 6 shows the seal of figure 5 in an inflated first position thereof with the blanket having been moved axially relative to the first press member while maintaining a sealing relationship between the blanket and the first press member.
Figure 7 is a sectional view of an embodiment of the present invention showing one of the seal means with the base portion thereof defining a convex surface.
Figure 8 is a sectional view of another alternative embodiment of the present invention showing one of the seal means viewed in a cross-machine direction and showing an alternative means of anchoring the seal means to the rotatable head.
Figure 9 is a sectional view of the seal means shown in figure 3 in the inflated first disposition thereof.
Figure 10 is a sectional view of the seal means shown in figure 9 but with the seal means in the second deflated disposition thereof.
Figure 11 is a sectional view of the seal means shown in figure 9 with the seal means disposed in the compressed third disposition thereof.
Figure 12 is a sectional view of a further embodiment of the present invention showing an alternative seal means in which the sealing portion defines a plain surface; and
Figure 13 is a fragmentary sectional view of the seal means showing the compartment and the means for connecting the compartment to a source of pressurized air.
Similar reference numerals refer to similar elements throughout the detailed description of the various embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 is a side-elevational view of a typical "apple" type extended nip press having a sealing apparatus according to the present invention. The apple type extended nip press is generally designated 10 and includes a first stationary apple-shaped press member 12 and a cooperating rotatable second press member 14. The first and second press members 12 and 14 respectively, define therebetween, an extended nip 16 for the passage therethrough of a paper web W to be pressed. A felt F simultaneously extends through the extended nip 16 such that as water is removed from the web W such water is taken up and absorbed by the felt F. A blanket 18 extended through the nip 16 with the blanket 18 being disposed between the felt F and the first press member 12. The first press member 12 defines a concave surface 20 for the cooperating reception therein of the rotatable second press member 14. During operation of the extended nip press 10 the blanket 18 moves substantially at the same speed as the felt F and web W during passage through the extended nip 16 so that there exists relative movement between the inner surface 22 of the blanket 18 and the concave surface 20 of the first stationary press member 12. This relative movement of the blanket 18 relative to the first press member 12 necessitates the provision of a lubricating medium between the inner surface 22 of the blanket 18 and the concave surface 20 of the first press member 12.
With the prior art proposals, the provision of a lubricating medium such as oil, has resulted in the seepage of such oil laterally relative to the machine direction as indicated by the double-headed arrow 24 as shown in figure 2. When such oil seepage occurs, an oil film may reach the respective edges 26 and 28 of the blanket 18 as indicated in figure 2 and due to the rotation of the blanket 18 around the stationary first press member 12, particles of contaminating oil have been thrown outwardly and have sometimes caused contamination of the surface of the paper web W.
As shown in figure 2, the present invention includes a first rotatable head 30 disposed adjacent to the first end 32 of the first press member 12. The first head 30 is disposed coaxial relative to the first press member 12. Furthermore, a second rotatable head 34 is disposed adjacent to the second end 36 of the first press member 12 so that the second head 34 is disposed coaxial relative to the first head 30 and the first press member 12. A first annular seal means 38 is disposed between the blanket 18 and the first head 30 for sealing the blanket 18 relative to the first head 30. Also, a second annular seal means 40 is disposed between the blanket 18 and the second head 34 for sealing the blanket 18 relative to the second head 34 such that when the first and second seal means 38 and 40 respectively are in an inflated first position thereof as shown in figure 2, the blanket 18 is permitted to rotate coaxially around the first press member 12. However, when the first and second seal means 38 and 40 respectively are disposed in a deflated second position thereof, the blanket 18 is movable axially relative to the seal means 38 and 40 for replacing the blanket 18.
More particularly, figure 2 shows the first and second rotatable heads 30 and 34 respectively as each defining a disc-shaped configuration with the first and second heads 30 and 34 respectively, each being rotatable relative to the stationary first press member 12.
Figure 3 is an enlarged fragmentary sectional view of the first and second seal means 38 and 40 respectively. The seal means 38 and 40 are of an elastomeric material and are preferably fabricated from rubber. Each of the seal means 38 and 40 are of hollow, toroidal configuration as shown in figure 3. The first and second seal means 38 and 40 are able to be inflated or deflated by means of a flow control means generally designated 42 which is connected respectively to the first and second seal means 38 and 40 for controlling the inflation and deflation of the annular seal means 38 and 40.
As shown in figure 3, the first annular sealing means 38 includes a base portion 44 for connecting the seal means 38 to the rotatable head 30. A sealing member 46 is disposed diametrically opposite to the base portion 44 such that when the sealing means 38 is inflated, the sealing member 46 is urged into sealing conformity with the inner surface 22 of the movable blanket 18. As shown in figure 3, the sealing member 46 defines a serrated surface 48 with the serrations extending in a machine direction such that as the sealing member 38 is urged against the inner surface 22, an effective seal is established thereby.
Similarly, the second sealing means 40 also includes a base portion 50 and a sealing member 52 with a correspondingly serrated surface 54 defined thereby.
In a specific embodiment of the invention, the seals 38 and 40 expand radially by a distance of two inches (5.08 centimeters) between the deflated and inflated positions of the seals. In effect, this means that if the serrated surface 48 of the sealing member 46 defines a circle having a diameter of fifty-six inches (142.24 centimeters) when inflated. Such movement of the serrated surfaces 48 and 54 between the deflated and inflated positions thereof is ample for allowing lateral removal of the blanket when the seals 38 and 40 are in the deflated position thereof whereas when the seals 38 and 40 are inflated, the serrated surfaces 48 and 54 move radially outwardly sufficient to establish an effective seal relative to the inner surface 22 of the blanket 18 for inhibiting any cross-machine directional seepage of lubricating oil that would otherwise cause contamination of the treated paper web.
Figure 7 is a sectional view showing an alternative embodiment of the present invention. Similar reference numerals are used throughout the detailed description to indicate similar elements of the various embodiments of the present invention however, such numerals include alphabetical suffixes added thereto.
In figure 7, the sealing means 38a includes a sealing member 46a and a base portion 44a. However, the base portion 44a defines a convex surface 45 which cooperates with a concave surface 47 defined by the first rotatable head 30a. This arrangement facilitates mounting of the seal means 38a onto the head 30a.
Figure 8 shows an alternative embodiment of the present invention in which a rim portion 49 of the first rotatable head 30b defines a plurality of radial slots 51,53 and 55. A plurality of threaded fasteners 57,58 and 59 are anchored within the base portion 44b such that inwardly extending-threaded portions 60,61 and 62 cooperate with the radial slots 51,53 and 55 respectively so that when the seal means 38b is moved axially relative to the rim portion 49, the threaded portions 60-62 are received within the radial slots 51,53 and 55 respectively. A plurality of internally-threaded members 63,64 and 65 cooperate with the threaded portions 60-62 for anchoring the base portion 44b relative to the rim portion 49.
As shown in figures 9 to 11, the sealing member 38 is movable between a first, second and third position thereof as shown in figures 9-11 respectively. This third, compressed position, as shown in figure 11 is attained during compression of the seal means 38 when the inflated seal means 38 passes through the extended nip 16.
Preferably, when manufacturing the seal means 38, 38a or 38b, the seal means defines, in an unstressed and unbiased disposition thereof, a cross-sectional configuration substantially equivalent to the cross-sectional configuration of the seal means when disposed in the second position thereof, as shown in figure 10. This unstressed and unbiased disposition of the seal means is disposed between the first and third positions as shown in figures 9 and 11 respectively so that during stressing of the seal means during use of the sealing apparatus between the first and third positions as shown in figures 9 and 11, the life of the seal means is extended.
In an alternative embodiment of the present invention as shown in figure 12, in addition to the base portion 44c for connecting the respective seal means 38c to the respective rotatable head 30c, a sealing portion 66 is provided with the sealing portion 66 being disposed diametrically opposite to the base portion 44c. The sealing portion 66 defines a sealing surface 68 which is disposed adjacent to the inner surface 22c of the movable blanket 18c. The sealing surface 68 is a plain surface.
In yet another embodiment of the present invention, as shown in figure 13, channel means 70 defined by the stationary first press member 12d connect a compartment 72 defined between the blanket 18d, the first press member 12d and the first and second seal means 38d and 40d to a source of pressurized fluid 74 such that during use of the apparatus, with the seal means 38d and 40d disposed in the inflated first or third disposition thereof, the pressure within the compartment 72 is above ambient atmospheric pressure. Preferably, the pressurized fluid is air and the pressure within the compartment 72 is within the range .07-.14 Kg/SQ CM (1-2 pounds per square inch) and the pressure within the seal means 38d and 40d is 1.44-2.9 Kg/SQ CM (20-40 pounds per square inch) when the seal means 38d and 40d are in the first or third position thereof.
In operation of the apparatus according to the present invention, the flow control means 42 is operated in order to deflate the seals 38 and 40 so that the blanket 18 can be moved axially to encircle and enwrap the first press member 12. When the blanket 18 has been correctly aligned over and around the first press member 12 with the annular seals 38 and 40 adjacent to the respective edges 26 and 28 of the blanket 18, the flow control means 42 is operated to inflate the seals 38 and 40 such that the serrated surfaces 48 and 54 thereof move radially outwardly into sealing engagement with the inner surface 22 of the blanket 18 so that the blanket 18, seals 38 and 40 and heads 30 and 34 can, together, rotate around the stationary first press member 12. Furthermore, when the blanket passes the concave surface 20 of the "apple" shaped first press member 12, the seals 38 and 40 can compress and deform in conformity with the configuration of the extended nip while maintaining the required sealing relationship between the blanket 18 and first press member 12.
As shown in figure 4, when the blanket 18 is to be removed, the seals 38 and 40 are deflated. Figure 4 merely shows seal means 38 in the deflated position. With the seal means 38 deflated, a clearance of approximately two inches (5.08 centimeters) is provided between the inner surface 22 of the blanket 18 and the sealing means 38 and this is ample to permit the sideways removal of the blanket 18.
Figure 5 shows the seal 38 in an inflated position thereof with the seal 38 being subjected to radial deflection by the blanket 18. Also any lateral deviation of the blanket 18 relative to the stationary first press member 12 when the seal 38 is inflated can be adequately accommodated by the sealing relationship established between the serrated surface 48 and the inner surface 22 of the blanket 18 as particularly shown in figure 6.
Those skilled in the art will appreciate that the radius of each of the heads 30 to 34 is slightly less than the distance between the axis of the first press member 12 and the lowest point of the concave surface 20.
The present invention provides a simple and low cost means for overcoming the problem of web contamination by oil sprayed from the press blanket.

Claims

1. A sealing apparatus for sealing a movable blanket (18) which extends through an extended nip (16) defined by first and second cooperating press members (12,14), said apparatus sealing the blanket (18) relative to and between a first (32) and second (36) end of the first press member (12), said apparatus comprising:
a first rotatable head (30) disposed adjacent to the first end of the first press member, said first head being coaxial relative to the first press member;
a second rotatable head (34) disposed adjacent to the second end of the first press member (12), said second head being coaxial relative to said first head and the first press member respectively;
first annular seal means (38) disposed between the blanket and said first head for sealing the blanket relative to said first head; and second annular seal means (40) disposed between the blanket (18) and said second head for sealing the blanket (18) relative to said second head such that when said first and second seal means (38,40) are in an inflated first and third position thereof, the blanket is permitted to rotate coaxially around the first press member;
said first position of said seal means being attained when said seal means are inflated and rotating relative to the first press member prior to passage of said seal means through the extended nip;
said third position of said seal means being attained when said seal means are inflated and compressed during passage of said seal means through the extended nip;
said first and second annular sealing means being each of hollow toroidal configuration; and
said sealing apparatus further including: flow control means (42) connected respectively to said first and second seal means (38,40) for controlling the inflation and deflation of said first and second annular seal means,
characterized in that, when said first and second seal means (38,40) are disposed in a deflated second position thereof, the blanket (18) is movable axially relative to the seal means for replacing the blanket,
said flow control means (42) controlling the inflation and deflation of said first and second annular seal means (38,40) such that each of said seal means defines, in an unstressed and unbiased disposition thereof, a cross-sectional configuration substantially equivalent to the cross-sectional configuration of said seal means when disposed in said second position thereof, such unstressed and unbiased disposition of said seal means being disposed between said first and third positions of said seal means so that during stressing of said seal means during use of the sealing apparatus, the life of said seal means is extended.

2. A sealing apparatus as set forth in claim 1, wherein said first and second rotatable heads (30,34) each define a disc-shaped configuration.

3. A sealing apparatus as set forth in claim 2, wherein said first and second heads (30,34) are each rotatable relative to the first press member.

4. A sealing apparatus as set forth in claim 1, wherein said first and second seal means (38,40) are of an elastomeric material.

5. A sealing apparatus as set forth in claim 4, wherein said first and second seal means (38,40) are of rubber.

6. A sealing apparatus as set forth in claim 1, wherein said first and second annular sealing means (38,40) each further include:
a base portion (44,50) for connecting said respective seal means to the respective rotatable head;
a sealing member (48,54) disposed diametrically opposite to said base portion such that when said respective sealing means is inflated, said sealing member is urged into sealing conformity with an inner surface (22) of the movable blanket (18).

7. A sealing apparatus as set forth in claim 6, wherein said base portion (44a) defines a convex surface (45) in a cross-machine direction;
said first and second rotatable heads each define a concave rim surface (47) in a cross-machine direction, said concave rim surface (47) cooperating with said convex surface (45) for permitting axial mounting of said respective seal means onto said respective head.

8. A sealing apparatus as set forth in claim 6, wherein said first and second rotatable heads each further include:
a rim portion (49);
said rim portion of each head defining a plurality of radial slots (51,53,55);
a plurality of threaded fasteners (57,58,59) anchored within said base portion, said threaded fasteners having threaded portions (60,61,62) extending radially inwards relative to said base portion such that said inwardly extending threaded portions cooperate with said radial slots so that when said seal means is moved axially relative to said rim portion, said threaded portions are received within said radial slots;
a plurality of internally threaded members (63,64,65) for cooperating with said threaded portions for anchoring said base portion relative to said rim portion.

9. A sealing apparatus as set forth in claim 6, wherein said sealing member defines a serrated surface (48) which moves radially relative to said axis of said respective head such that when said respective sealing means is inflated, said sealing member moves radially outwards such that said serrated surface moves into sealing engagement relative to said inner surface of the blanket.

10. A sealing apparatus as set forth in claim 8, wherein said sealing member is movable axially relative to said first and second heads when said annular seal means are inflated while such sealing member maintains sealing engagement relative to said inner surface of the blanket.

11. A sealing apparatus as set forth in claim 1, wherein said first and second annular seal means each further include:
a base portion (44c) for connecting said respective seal means to said respective rotatable head;
a sealing portion (66) disposed diametrically opposite to said base portion, said sealing portion defining a plane sealing surface (68) disposed adjacent to an inner surface (22c) of the movable blanket (18c).