EP0395911B1 - Sealing assembly for an offset printing machine - Google Patents

Description

The invention relates to a sealing arrangement for each end of a pair of rollers of a dampening unit of an offset printing press, the pair of rollers comprising an operationally rotating first roller in the form of a dampening solution applicator roller and an operationally rotating second roller in the form of a metering roller which is employed in a contact zone on the first roller is formed, the directions of rotation of the two rollers in the contact zone result in downward vectors of the peripheral speeds of the two rollers, a reservoir for a fountain solution is provided in the form of a channel formed from a gusset located above the contact zone between the two rollers, the respective ends of which by means of a respective sealing arrangement are completed, a respective sealing arrangement has a sealing element and a holder receiving it, the respective sealing element has a flat first sealing surface and a In a region of a respective end face of the first roller starting from the contact zone, by means of a first end face of a respective sealing element, a curved second sealing surface is formed which adjoins the first sealing surface and which conforms to the cross section of the second roller and which is operationally attached to a abuts the respective end section surrounding the contact area of the lateral surface of the second roller, the respective sealing element is pressed against the respective end face of the first roller by means of the respective holder under the action of a spring device, the pair of rollers extends between a pair of opposing bearing plates supporting the pair of rollers, which respective holder is articulated on a bearing plate by means of a swivel connection with a swivel axis parallel to an axis of rotation of the pair of rollers, and the curved second sealing surface of the respective sealing element in a working position of the respective holder by means of a holding projection of the respective holder preventing rotation of the sealing element in the direction of rotation of the second roller in a sealing position exerting a sealing force on the respective jacket section of the second roller.

From DE-OS 22 06 498 it is known to stow a fountain solution in the trough between a metering roller and an applicator roller. With regard to the sealing arrangement of this known device, a sealing element, which consists of resilient sealing material, is attached to both end faces of the metering roller and the applicator roller. The sealing element also consists of a storage plate in which the resilient sealing material is received. The storage plate is held in an upwardly open guide and can be pulled out in this direction for the purpose of replacement. The position is secured by locking projections that snap into corresponding locking recesses in the storage plate.

EP 0 047 350 B1 has disclosed a sealing arrangement with the features mentioned at the beginning with respect to a dampening unit. In this known sealing arrangement, the sealing element accommodated in the holder is biased both axially and radially by spring loading. Sealing takes place in two directions, ie with respect to one direction on the end face of the application roller and with respect to the other direction on the outer surface of the metering roller. The design of this known sealing arrangement is unsatisfactory, particularly with regard to the need to replace the sealing element designed as a wearing part. In this known sealing arrangement, an upper edge region of the sealing element is acted upon by a support spring, which rests on an angled portion that adjoins the upper one Edge area of the sealing element overlaps, supports. This affects accessibility and complicates the exchange work, which proves to be time-consuming.

Based on the last-described prior art, the object of the invention is to design a generic sealing arrangement in such a way that an easy-to-use replacement of the sealing element is possible.

This object is achieved by the features specified in claim 1.

The subclaims indicate advantageous developments of the subject matter of the invention.

According to the invention, the holder leaves a pivoting path for the sealing element from a sealing position into a ready-for-removal position. The sealing element can be pivoted into the ready-for-removal position by rotating it around the second roller. As a result of this configuration, assembly and subsequent replacement of the sealing element can be carried out extremely simply. Necessary retaining projections are not formed in an area that the sealing element sweeps over when pivoting around the second roller. In order to be able to simply pivot the sealing element into the removal-ready position, it is preferably provided that the sealing element has a freely accessible extension.

In the case of a sealing arrangement according to the invention, not only are special guides for the sealing element dispensed with, but rather there is a further advantage of an automatic readjustment of the sealing element with increasing wear of the curved second sealing surface of the sealing element.

To adjust the curved second sealing surface of a respective sealing element to a respective end section of the lateral surface of the second roller, the invention makes use of the frictional force between the flat first sealing surface of the sealing element and the end face of the first roller which cooperates with this sealing surface. The second roller is used as a kind of "pivot". The frictional force always holds the holding projection in a working position in which the sealing element is set against the second roller.

As a result of the mutual engagement of the two rollers, elastic deformations will occur on the dampening roller which is generally formed with an elastic surface. After the two rollers have come to a standstill, restoring forces occur which endeavor to "turn back" the dampening solution application roller in particular. In this case, the sealing element can leave its sealing position with respect to the metering roller as a result of a frictional force acting on its first sealing surface.

To avoid this, a further development of the invention provides that the sealing element is provided with a securing part which prevents it from pivoting against the direction of rotation of the second roller and which is held under the action of a spring force in a respective blocking position corresponding to a sealing position of the sealing element and manually overcome by overcoming the spring force an unlocked position is displaceable.

The securing part is also arranged to be movable and thus follows wear-induced migration of the sealing element. It is further provided that a wedge is formed on the securing part and the wedge is held in the locked position by means of a spring arrangement in contact with a second end face of the sealing element on the one hand opposite the curved second sealing surface and on the other hand with a cam which is stationary with respect to the dampening unit formed wedge angle opens in the direction of rotation of the second roller.

The wedge-shaped design enables the aforementioned movable arrangement of the securing part in a simple manner. Characterized in that a wedge surface of the wedge cooperates with a fixed cam, the securing part can automatically readjust even with a rotational movement caused by wear. It is understood that the cam has a rounded with this a cooperating circumferential region.

Advantageously, it is further provided that the securing part is held in a locked position by means of a leg which engages in a groove of a spring arrangement supported on a bearing plate.

The spring arrangement provided always ensures the positive engagement of the securing part on the sealing element even when the sealing element migrates due to wear. The groove formed in the securing part facilitates the establishment of an operative connection of the spring arrangement with the securing part when it is inserted into the dampening unit. A spring leg acting on the securing part can be caught as it were by means of the groove.

For the movable arrangement of the securing part, it is further provided that the securing part moves out of a blocking position along a guide slot formed therein an unlocked position and vice versa is articulated on a bearing plate.

An advantageous embodiment results with regard to the movable arrangement of the securing part in connection with the wedge provided on it, in that a wedge surface of the wedge, which is in contact with the cam at least in a locked position, represents a longitudinal side of a guide slot formed in the securing part and penetrated by the cam, by means of which the securing part is articulated on a bearing plate from a locked position into an unlocked position and vice versa.

A particularly simple manufacture and a shape of the securing part which is advantageous in terms of handling results with an embodiment in which a first wedge surface and a second wedge surface opposite this are formed by means of respective boundary surfaces of a plate-shaped securing part, the plate-shaped securing part between a bearing plate and an end face opposite this the first roller is arranged and an end of the plate-shaped securing part located in a direction in which the wedge tapers extends beyond the bearing plate at least in a locked position of the securing part and has a projection pointing in a longitudinal direction of the pair of rollers, by means of which the securing part on the bearing plate is supported.

The sealing element is released for pivoting about the intended pivoting path and for removal from the dampening unit by manually moving the securing part against the action of the spring arrangement and along the guide slot. Here, due to the wedge-shaped design of the securing part, a gap is created between it and the sealing element in the sealing position. This gap then enables the sealing element to pivot in its readiness for removal. When the sealing element is removed and the securing part is left to itself, this is intercepted by means of the protrusion formed thereon on the adjacent bearing plate, so that the securing part does not fall into a gap provided for its installation between this bearing plate and the end faces of the two rollers and is no longer accessible .

The projection preferably projects above a respective plate surface of the plate-shaped securing part. Initially, this has particular advantages in terms of production technology. The same securing part can be installed at both roller ends in such a configuration. In addition, the one-sided, but in particular also the two-sided projection also has handling advantages with regard to an actuation of the securing part.

Also with regard to the arrangement of the holder itself, the focus is on handling that is as simple as possible and as completely tool-free as possible. In particular, this is achieved in that the holder is pivotally mounted on a bearing plate of the dampening unit. The bracket is thus optimally accessible. It proves to be advantageous that the holder is pivotally mounted about a pivot axis parallel to the axes of rotation of the two rollers, which is formed with a pin fastened in a bearing plate. The swiveling takes place in the narrow gap between the end faces of the pair of rollers on the one hand and a bearing plate on the other hand without hindrance. This configuration is optimized in that a bearing hook is formed on the holder for cooperation with the pin. The removal of the holder is limited to simply unhooking it. The pin projects beyond a guide surface of the seal holder, on which the sealing element with one of the first sealing surface opposite sliding surface. This leads, creating a kind of double function of the pin, to a limit stop for the sealing element, which can be grasped at the highest point. A preferred feature is that the sealing element may have a thickening above the channel on its side facing the channel. This thickening preferably extends essentially radially with respect to the metering roller over the sealing element up to its end that is accessible for manual access. This thickening can - alone or in combination with the extension mentioned above - contribute to easy handling of the sealing element. In addition, a sealing element can be individualized due to a thickening on one side with respect to the side on which it is to be installed in the dampening unit. This thickening is preferably pulled through to the second sealing surface. As a result, a further combinative effect is achieved, since the greatest wear attack usually also occurs in the region of the sealing element located above the groove.

The invention is explained in more detail below with reference to the accompanying drawings, which, however, only show exemplary embodiments.

Fig. 1

im Vertikal-Querschnitt einen Endbereich des Feuchtwerks,

Fig. 2

eine Draufsicht auf den Gegenstand gemäß Fig. 1,

Fig. 3

eine Schnittdarstellung durch den Gegenstand gemäß Fig. 1, geschnitten entlang der Linie III-III,

Fig. 4

eine Darstellung gemäß Fig. 1, mit heruntergedrücktem Sicherungsteil,

Fig. 5

eine Darstellung gemäß Fig. 4, nach einem Drehen des Dichtelementes in eine Entnahme-Bereitschaftsstellung, und

Fig. 6

eine perspektivische Darstellung der mit dem Dichtelement bestückten Dichtungshalterung, in Zusammenwirkung mit dem Sicherungsteil, mit in strichpunktierten Linien angedeutetem Walzenpaar.

Herein shows:

Fig. 1

in vertical cross-section an end area of the dampening unit,

Fig. 2

2 shows a plan view of the object according to FIG. 1,

Fig. 3

2 shows a sectional illustration through the object according to FIG. 1, cut along the line III-III,

Fig. 4

1, with the securing part pressed down,

Fig. 5

4, after rotating the sealing element in a removal standby position, and

Fig. 6

a perspective view of the seal holder equipped with the sealing element, in cooperation with the securing part, with roller pair indicated in dash-dotted lines.

A dampening unit F is shown and described - in particular with reference to FIGS. 1 and 6 - which has an application roller 7 as the first roller of a pair of rollers and a metering roller 6 as the second roller of a pair of rollers. The metering roller 6 and the application roller 7 are in mutual contact in a contact zone 11. With their upper gusset they form a channel 5 in which a dampening solution supply 4 is received. In detail, the metering roller 6 and the applicator roller 7 are arranged and driven such that the vectors of the respective peripheral speeds are directed downward in the contact zone 11.

The dampening unit F also has a sealing arrangement 1, which consists of an actual sealing element 2 and a holder 3 receiving it.

One end of each pair of rollers is supported in one of opposing bearing plates 8, only one of which is shown. The metering roller 6 has a somewhat smaller diameter than the application roller 7. The axes of rotation 9 and 10 of the metering roller 6 and the application roller 7 are approximately the same height. Due to the relatively rigid design of the metering roller 6 and the more elastic Execution of the application roller 7, the application roller 7 forms a slightly concave shape in the contract zone 11.

The directions of rotation of the metering roller 6 and the application roller 7 in the operating state are indicated by the arrows 12 and 13. The outer surfaces of the metering roller 6 and the applicator roller 7 thus rotate downward via the contact zone 11.

The sealing element 2 has a flat first sealing surface 36 (see FIGS. 3 and 6), which in operational contact rests on a region of an end face of the application roller 7 starting from the contact zone 11, and a curved second sealing surface 17. This is formed by a first one The end face of a respective sealing element 2, adjoins the first sealing surface 36, stands vertically thereon and is fitted to the cross section of the metering roller 6. In operation, this curved second sealing surface lies against a respective end section of the outer surface of the metering roller 6 surrounding the contact zone 11. To avoid a water ring on the applicator roller 7, the first and the second sealing surfaces (36 and 17) adjoin each other with sharp edges.

In the area of the sealing element 2 in contact with the metering roller 6, the latter has a metal ring 14 with a hardened surface (FIG. 2). Dampening solution which has reached this metal ring 14 is guided into the channel 5 by means of a bevel 2 'at the upper end of the sealing element 2 in order not to be flung out in an uncontrolled manner.

The sealing element 2 consists for example of PTFE. This material is advantageous both in terms of wear and in terms of its low tendency to add dirt.

A level control of the dampening solution supply 4 in the channel 5 can be carried out using measures known per se. Corresponding measures can be found, for example, in the prior art mentioned at the beginning.

The sealing element 2 can be replaced in a user-friendly manner, since the holder 3 leaves a swivel path x for the sealing element 2 in a ready-for-removal position (see FIG. 5), into which the sealing element 2 can be brought about by pivoting the same about the axis 9 of the metering roller 6 . The sealing element 2 is positively supported on the metal ring 14 of the metering roller 6. During the pivoting, the sealing element 2 moves from the sealing position (FIG. 1) to the ready-for-removal position (FIG. 5). To facilitate handling, the sealing element 2 has an extension 15 in the region of its end face 2 ″ (FIG. 2) which points upward in the sealing position. This extension 15 has a finger insertion groove 16 on its back.

The second sealing surface 17 of the sealing element 2 bearing against the metal ring 14 has a length which does not exceed a length corresponding to the angle of 180 ° of the circumference of the metal ring 14. In the exemplary embodiment, this second sealing surface 17 extends over an angle alpha of approximately 90 °, the contact zone 11 being approximately in the lower third of the 90 ° angle range. The lower end of the sealing element 2 extends sufficiently far downward beyond the contact zone 11, in the exemplary embodiment by approximately 30 °.

A holding projection 19 is formed on the holder 3.

The sealing element 2 has a second end face 2 ″ ″ opposite the curved second sealing face 17, which interacts with a securing part 20. The essentially wedge-shaped securing part 20 is biased upwards by a spring arrangement 21. This acts on a lower end face 20 'of the securing part 20. The end face 20' also has a groove 38, in which a leg 21 'of the spring arrangement 21, which is supported on a bearing plate 8 and is designed as a leg spring, engages.

In the example shown, the second end face 2 '' 'of the sealing element 2 runs at a distance parallel to a tangent to the metering roller 6 or to the second sealing face 17 of the sealing element 2, in such a way that a perpendicular end which cuts the end face 2' '' in the middle Line goes through a point P on the circumference of the metering roller 6, as shown in FIG. 1. The point P also lies on a radial line passing through the axis 9 of the metering roller 6, which includes an angle of approximately 25 ° with the horizontal.

The securing part 20 has a wedge K. A first wedge surface K 'of the wedge K interacts with the second end surface 2' '' of the sealing element 2, while a second wedge surface K '' interacts with a cam 22. The cam 22 is fixed in the bearing plate 8 of the dampening unit F and is represented by a bolt in the example shown (cf. also FIG. 2).

The second wedge surface K ″ simultaneously forms a longitudinal side of a guide slot 23 formed in the securing part 20, into which the cam 22 enters when the securing part 20 is pressed into an unlocked position. To form this guide slot 23, the wedge K continues into a section 24 which lies opposite the second wedge surface K ″.

In the lower region of the wedge K in the installed position, the second wedge surface K ″ merges into a receptacle 25, against which the cam 22 comes to rest when the sealing element 2 is removed under the action of the spring arrangement 21 already explained. With appropriate handling, the securing part 20 can be pulled from the cam 22 through an opening 26. 2, the cam 22 has at its end facing the applicator roller 7 a collar 27 which overlaps the securing part 20 in some areas. The securing part 20 is prevented by this collar 27 from moving in the longitudinal direction of the pair of rollers 6, 7.

At its upper end in the installed position, the securing part 20 has a projection 28 which projects perpendicular to the plane of extent of the securing part 20. This projection 28 is formed on both sides of the plate forming the securing part 20. It prevents the securing part 20 from tilting around the cam 22 when the sealing element 2 is removed and from sliding with its upper region downward into the gap Sp between the bearing plate 8 and an end face of the application roller 7. Due to the design of the projection 28 on both sides, a securing part 20 can be used on both sides of the dampening unit F. The holder 3, which has a guide surface F1 for the sealing element 2, is pivotable about a pin 29 parallel to the axes of rotation 9, 10. The pin 29 is arranged above the metering roller 6, projects beyond the guide surface F1 of the holder 3 and forms a pivot axis 37 for the holder 3. At the same time, the pin 29 forms a limit stop for the sealing element 2 when it is pivoted into the ready-for-removal position (cf. FIG. 5).

In order, for example, to be able to remove the holder 3 completely for cleaning purposes, it is provided that on the holder 3 for interaction with the one in storage Pin 29 a bearing hook 30 is formed. Its mouth, which opens downwards, forms diverging flanks 31 starting from a basic hook contour. The flanks 31 have a centering effect.

The holder 3, which is accommodated in the relatively narrow gap Sp between the end faces of the metering roller 6 and the application roller 7 on the one hand and the bearing plate 8 of the dampening unit F on the other hand, stands in the axial direction of the pair of rollers comprising the metering roller 6 and application roller 7 under the action of a pressure spring 32 accommodated in a pressure piece 33, the flat, curved head surface of which constantly acts on the holder 3 on its side facing away from the guide surface F1 for the sealing element 2 (cf. in particular FIG. 3).

The corresponding lateral offset of the pin 29 of the holder 3 to the channel 5 leaves a sufficient free space above the channel 5 for access to the sealing element 2.

A bend 35 on the bracket 3 is not only advantageous in terms of handling the bracket 3 when it is removed from the dampening unit, but also prevents the bracket 3 from pivoting down so far about the pin 29, for example with the sealing element 2 removed, that it can only be gripped with difficulty. Otherwise, the bend 35 is operationally at a distance above an upper side of the bearing plate 8. The position of the holder 3 is determined by the sealing element 2, via its support on the holding projection 19. Since the sealing element 2 is approximately in the direction due to wear arrow Pf moves down during operation, there is also a certain movement of the holder 3.

To replace the sealing element 2, the securing part 20 is pressed down on the projections 28 against the action of the leg 21 ′ of the spring arrangement 21. 4, the securing part 20 is shifted accordingly. An operator can do this by hand. Due to the resulting gap Z (see FIG. 4), the sealing element 2 can be pivoted from the sealing position into the ready-for-removal position by pivoting around the metering roller 6. 5 shows the sealing element 2 after such a pivoting operation with the securing part 20 still depressed (the respective depressing hand not being shown in FIGS. 4 and 5). 5, the sealing element 2 can be easily removed upwards.

It goes without saying that a corresponding sealing arrangement is formed at both ends of the channel 5, even if only the sealing arrangement is shown at one end in the drawing.

The sealing element 2 advantageously has a thickening 18 which is formed above the groove 5 on the side of the sealing element 2 facing the groove 5. This thickening 18 extends essentially radially to the metering roller 6. In the exemplary embodiment, the slope 2 'passes directly into the thickening 18. The thickening 18 merges into the extension 15. As a result, the extension 15 and the finger insertion groove 16 itself can be grasped better. In addition, for example, an edge of the thickening 18 also offers an attachment option for a tool in order to pivot the sealing element 2 into its ready-for-removal position. Last but not least, the thickening 18 extending to the curved sealing surface 17 also provides advantages with regard to the wear behavior of the sealing element 2 as a result of the widening of the curved sealing surface 17 associated therewith.

REFERENCE SIGN LIST

1

Sealing arrangement

2nd

Sealing element

2 '

Weird

2 '' '

second end face of the sealing element 2

3rd

bracket

4th

Fountain solution supply

5

Gutter

6

Metering roller (second roller)

7

Dampening roller (first roller)

8th

Bearing plate

9

Roller axis

10th

Roller axis

11

Contact zone

12th

arrow

13

arrow

14

Metal ring

15

Continuation

16

Finger insertion throat

17th

curved second sealing surface of the sealing element 2

18th

thickening

19th

Holding tab

20th

Safety part

21

Spring arrangement

21 '

leg

22

cam

23

Guide slot

24th

section

25th

Intake curvature

26

opening

27

Federation

28

head Start

29

pen

30th

Storage hook

31

Flanks

32

Pressure spring

33

Pressure piece

34

Head area

35

Angling

36

flat first sealing surface of the sealing element 2

37

Swivel axis

38

Groove

F

Dampening system

Fl

Leadership area

K

Area

K '

Wedge surface

K ''

Wedge surface

Sp

gap

x

Swivel path

Claims (12)

1. Sealing arrangement for each end of a pair of rollers of a dampening unit of an offset printing machine,

   - the pair of rollers being formed from a first roller (7) rotating during operation and taking the form of a dampening-medium applicator roller and from a second roller (6) rotating parallel thereto during operation, thrown onto the first roller (7) in a contact zone (11) and taking the form of a metering roller,

   - the directions of rotation of the two rollers (6 and 7) in the contact zone (11) producing downwardly directed vectors of the circumferential speeds of the two rollers (6 and 7),

   - a reservoir for a dampening-medium supply (4) being provided, in the form of a gutter (5) which is formed between the two rollers from a gusset located above the contact zone (11) and the respective ends of which are closed off by means of a respective sealing arrangement,

   - a respective sealing arrangement having a sealing element (2) and a mounting (3) receiving the latter,

   - the respective sealing element (2) possessing a plane first sealing face (36) and, during operation, bearing with the latter against a region of a respective end face of the first roller (7), the said region extending from the contact zone (11),

   - there being formed by means of a first end face of a respective sealing element a curved second sealing face (17) which adjoins the first sealing face (36), is perpendicular thereto and matches the cross-section of the second roller (6) and which, during operation, bears against a respective end portion of the cylindrical surface of the second roller (6), the said end portion surrounding the contact zone (11),

   - the respective sealing element (2) being pressed, during operation, against the respective end face of the first roller (7) by means of the respective mounting under the effect of a spring device (32, 33),

   - the pair of rollers extending between a pair of bearing plates (8) located opposite one another and supporting the pair of rollers,

   - the respective mounting (3) being articulated on a bearing plate (8) by means of a pivoting connection (29, 30) having a pivot axis (37) parallel to an axis of rotation of the pair of rollers, and

   - in a working position of the respective mounting (3), the curved second sealing face (17) of the respective sealing element (2) being held, by means of a holding projection (19) preventing a rotation of the sealing element (2) in the direction of rotation of the second roller (6) and belonging to the respective mounting (3), in a sealing position bearing against a respective end portion of the cylindrical surface of the second roller (6), an adjusting force resulting from the frictional forces between the pair of rollers (6, 7) and the sealing element (2) and being transmitted from the sealing element (2) via the holding projection (19) to the mounting (3),

   characterized in that

   - the mounting (3) is held in the working position automatically by the adjusting force exerted on it, and

   - the sealing element (2) is arranged relative to the axis of rotation (9) of the second roller (6) so as to be pivotable opposite to the direction of rotation of this roller (6) over a pivoting travel (x) out of the sealing position into a position of readiness for removal.
2. Sealing arrangement according to Claim 1, characterized in that one end of the sealing element (2), the said end leading during a pivoting of the sealing element (2) into its position of readiness for removal, has an extension (15) which is freely accessible at least in the position of readiness for removal.
3. Sealing arrangement according to Claim 1, characterized in that the respective pivoting connection is formed from a cylindrical pin (29) fastened to the respective bearing plate (8) and from a bearing hook (30) which is formed on the mounting (3) and is matched to the cross-section of the pin (29) and which is suspended on the pin (29).
4. Sealing arrangement according to Claim 1, characterized in that a pin (29) fastened to the respective bearing plate (8) in order to form the pivoting connection is designed as a stop for one end of the sealing element (2), the said end leading during a pivoting of the sealing element (2) into its position of readiness for removal.
5. Sealing arrangement according to Claim 1, characterized in that one end region of the curved second sealing face (17) of the sealing element (2), the said end region being located above the contact zone (11) during operation, is widened relative to the remaining curved sealing face (17) in the longitudinal direction of the pair of rollers (6, 7).
6. Sealing arrangement according to Claim 5, characterized in that there adjoins the widened end region of the curved second sealing face (17) located above the contact zone (11) during operation a thickening (18) of the sealing element (2) which extends approximately radially relative to this sealing face (17) and which forms an extension (15) which is freely accessible at least in the position of readiness for removal of the sealing element (2).
7. Sealing arrangement according to Claim 1, characterized in that there bears against the sealing element (2) a retaining part (20) which blocks a pivoting of the said sealing element (2) opposite to the direction of rotation of the second roller (6) and which is held under the effect of a spring force in a respective blocking position corresponding to a sealing position of the sealing element (2) and, with the spring force being overcome, can be displaced manually into an unblocking position.
8. Sealing arrangement according to Claim 7, characterized in that there is formed on the retaining part (20) a wedge (K) which, by means of a spring arrangement (21), is held in the blocking position in bearing contact with a second end face (2''') located opposite the curved second sealing face (17) and belonging to the sealing element (2), on the one hand, and with a boss (22) fixed relative to the dampening unit (F), on the other hand.
9. Sealing arrangement according to Claim 7, characterized in that the retaining part (20) is held in a blocking position by means of one leg (21') of a spring arrangement (21) supported on a bearing plate (8), the said leg (21') engaging into a groove (38) of the said retaining part (20).
10. Sealing arrangement according to Claim 7, characterized in that the retaining part (20) is articulated on a bearing plate (8) so as to be displaceable along a guide slot (23) formed in the said retaining part (20) out of a blocking position into an unblocking position, and vice versa.
11. Sealing arrangement according to Claim 8, characterized in that a wedge face (K'') of the wedge (K) bearing against the boss (22) at least in a blocking position of the retaining part (20) constitutes one longitudinal side of a guide slot (23) which is formed in the retaining part (20) and through which the boss (22) passes and by means of which the retaining part (20) is articulated on a bearing plate (8) so as to be displaceable out of a blocking position into an unblocking position, and vice versa.
12. Sealing arrangement according to Claim 8, characterized in that

    - a first wedge face (K') and a second wedge face (K'') located opposite the former are formed by means of respective edge faces of a plate-shaped retaining part (20),

    - the plate-shaped retaining part (20) is arranged between a bearing plate (8) and an end face of the first roller (7) located opposite the latter, and

    - one end of the retaining part (20), the said end projecting above the bearing plate (8) in a blocking position of the retaining part (20), has a projection (28) which points in a longitudinal direction of the pair of rollers (6, 7) and by means of which the retaining part (20) can be supported on the bearing plate (8).

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