Doctor blades

Description

[0001] The present invention relates to doctor blade sub-assemblies and doctor blade assemblies, more particularly but not exclusively for stripping excess ink from a rotating printing roll in the surface of which there are arranged depressions for filling with printing ink. The doctor blade is attached to a holder carried by an adjustable apparatus which determines the force with which the doctoring edge of the blade lies against the printing roll. Such blades are exposed to wear and must be changed after a period of use.

[0002] A conventional doctor blade consists of a strip which is formed along its length with a thinner forward portion and a thicker rear portion. The thinner forward portion is formed by a comparatively expensive grinding operation.

[0003] The free edge of the thinner portion is intended for use as a stripping edge, while the thicker portion is intended for clamping in a standard type of blade holder for the printing machinery in question. The advantage of the thin portion of even thickness is that wear on it can take place without the wear causing any unacceptable alteration of the profile of the scraping or doctoring edge engaging the printing roll.

[0004] In long printing runs, the blade may have to be removed, either for replacement due to wear or for cleaning. When changing blades, the blade is removed together with a relatively heavy removable portion of the standard holder and is carried to a place for changing the blade or to a hot steam bath in which the blade is to be cleaned. This work is often arduous, since the weight of the removable holder and the blade attached thereto is considerable, and the walking distance in the printing hall to the work bench or to the steam bath is in many cases so long that the holder portion with the blade needs to be transported on a trolley.

[0005] G.B. Patent Specification No. B-287,565 discloses the use of a replaceable strip as doctor blade. The strip is clamped in a doctor blade holder which is, close to the strip itself, relatively stiff lengthwise. Such a holder cannot fully support the doctor blade strip in its effort to maintain even pressure between the doctor blade edge and the printing cylinder. As a result the print quality and the doctor blade life will be low.

[0006] U.S. Patent Specification No. 2007418 also discloses a doctor blade holding assembly for a strip, this holding assembly also being relatively stiff lengthwise with disadvantages. The device is designed for negative doctoring, i.e. scraping the roll, consequently without special requirements a doctor blade for a printing roll.

[0007] The invention concerns a doctor blade sub-assembly as defined in the claim 1 and a doctor blade assembly as defined in claim 7.

[0008] A preferred embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of a complete doctor blade assembly.

Fig. 2 is an exploded view in cross section, through the complete doctor blade assembly shown in Fig. 1.

Fig. 3 is an exploded view in cross section of the flexible doctor blade sub-assembly.

Fig. 4 is a view in cross section of the flexible blade sub=assembly when assembled.

Fig. 5 is a fragmentary plan view of one end of the flexible blade sub-assembly.

Fig. 6 is a schematic perspective view of the blade sub-assembly showing the lengthwisde flexibility of the sub-assembly.

Figs. 7, 9 and 11 are plan views of alternative presser plates, and

Figs. 8, 10 and 12 are respective cross sections on the lines VIII, X and XII of Figs. 7, 9 and 11.

[0009] Figures 1 and 2 show a doctor blade assembly consisting of a flexible doctor blade sub-assembly 2 including the doctor knife blade 21 with its back up blade 22 and a light-weight rigid holder 1.

[0010] As shown in Fig. 1 and 2 the light-weight doctor blade holder 1 consists of three sheet-metal elements of different cross sections, each accurately straight. The bottom element 12 is formed like a Z and has an upstanding rear flange 12a and a depending front flange 12b. The middle element 11 is formed as an L having a small depending front flange 11a. The top element 14 is formed like an inverted U having depending front and rear flanges 14a and 14b. The middle element 11 is clamped to the bottom element 12 by a row of bolts 16a having corresponding nuts 16b. Between the middle element 11 and the bottom element 12 is clamped the flexible sub-assembly, normally permanently. To give the middle member 11 an accurate and straight edge to support the springy flexible blade sub-assembly 2 a metal rod or tube 13 is positioned in the corner of the middle element. A range of rods or tubes 13 may be made available of different diameters to enable the pressure of blade application to be adjusted. The top element 14 completes the holder 1 by giving it stiffness, straightness and a convenient overall thickness corresponding to the thickness of the conventional, heavy solid metal holder which the holder replaces. The top element 4 is clamped to the other two elements 11, 12 by means of say four or six bolts 17a with corresponding nuts 17b along the length of the holder. The heads of bolts 16a and 17a are counter-sunk into the bottom element 12 so that the bolt heads lie flush with the bottom surface of the bottom element 12. This surface is directed towards the doctor blade holder bed in the printing press unit which is a straight plane parallel to the printing cylinder axis demanding an accurate and plane surface of the doctor blade holder.

[0011] The holder is preferably provided with two handles 15a fixed to the top element by means of bolts 15b passing through the top element 14.

[0012] The doctor blade 21 is a length of thin, steel strip cut from stock of uniform thickness and is supported by a back-up blade 22 which also is a thin steel strip of uniform thickness but narrower than the doctor blade 21. Both blades are resiliently clamped, as shown in Fig. 4 in the flexible sub-assembly. This consists of a wider flexible carrier plate 23, which is clampable or fixable in the holder 1 or in a conventional solid metal holder, and a narrower flexible presser plate 24, which is disposed with its front edge almost flush with the front edge of the carrier plate 23. Both plates 23, 24 are of spring steel about 0.3 mm thick. As shown in Fig. 3 the arched narrower plate 24 is transversely curved but can also be bent to a corresponding degree, thus comprising two flat portions at an obtuse angle to each other. The plates 24, 23 are held in position by a plurality of ties 25 arranged in a straight row, and each having a flange 25a at one end in the shape of a bolt head and a groove 25b near the other end to receive a circlip 26.

[0013] The free length between the two clamping surfaces presented respectively by the flange 25a and the circlip 26 is substantially greater than the combined thickness of the plates 24, 23 and the blades 22, 21.

[0014] This free length of the ties and the curvature of the narrower presser plate 24 are so selected relative to each other that the desired clamping pressure is obtained between the front edge portions of the plates 24, 23.

[0015] Elongated holes 24a, 23a in the plates 24, 23 through which the ties 25 pass, accurately fit the ties 25 transversely of and lie with their extended longer dimensions in a straight row parallel to the longitudinal edges of the plate 23. This permits convenient insertion of the blades 22, 21 to an accurately determined position by first the back-up blade 22 being inserted up to engagement with the ties 25 and then the doctor blade 21 being inserted up to engagement with the ties 25, which thus also serve as stops for the two blades 22,21.

[0016] The doctor blade 21 consists of a thin, steel strip of constant thickness and width, the thickness of the strip being in the range 0.05-0.15 mm. The thickness and width of the doctor blade is thus so small that the blade 21 can be curved in the plane of Fig. 5, the right hand side of the blade being then wrinkled, enabling the blade to be drawn progressively out from or pressed progressively between the plates 24, 23 along the length of the blade, from one end to the other with the aid of a rag.

[0017] The back-up blade 22 is normally identical to the doctor blade 21 except for the width which is 1 to 2 mm less than the width of the doctor blade.

[0018] Since the doctor blade and the back-up blade consist of thin steel strips, the doctor blade supported by the back-up blade can easily adjust itself to unevennesses on the printing cylinder, and this adjusting capacity is further substantially increased by the two blades being resiliently clamped in the flexible sub-assembly. The flexibility of this sub-assembly is shown in Fig. 6, from which it is clear that the front edge of the flexible sub-assembly 2 has a flexing capacity both lengthwise and crosswise relative to a straight reference line R-R when the holder is fixed straight and stiffly along a lone F-F and to the left of this line. This flexibility lengthwise directly results from the elongated holes 23a, 24a, these holes being extended at least 30 percent along the hole-row-axis, both in the wider plate 23 and in narrower plate 24. These holes allow the two plates 23, 24 to slide relatively to one another when the blade flexes lengthwise, as can be seen in Fig. 6.

[0019] The flexible sub-assembly and the doctor blade 21 have a slightly greater length than the printing cylinder, so that the blade covers the entire length of the printing cylinder. The back-up blade 22 however may be slightly shorter than the doctor blade as shown in Fig. 5, so that the doctor blade 21 itself can be easily and separately gripped at one end when changing blades.

[0020] As shown in Figs. 7 and 8 the presser plate means can alternatively consist of a row of separate sections 124, each having one or more elongated aperture 24a, replacing the single presser plate 24. Alternatively the presser plate 24 can on the other hand be notched or slotted transversely as shown in Figs. 9 and 10 and Figs. 11 and 12 respectively to increase the lengthwise flexibility of the presser plate still more.

Claims

1. A doctor blade sub-assembly comprising a resiliently flexible carrier plate (23), an arched presser plate means (24 or 124) extending along one edge of the carrier plate with its concave side directed towards the carrier plate (23), a resiliently flexible doctor blade strip (21) of constant thickness clamped between said one edge of the carrier plate (23) and an adjacent edge of the presser plate means and a row of ties (25) passing through apertures (23a and 24a respectively) in the carrier plate (23) and the presser plate means (24, 124) to hold the presser plate means in a stressed condition to clamp the doctor blade strip, the apertures (23a and 24a) in the carrier plate and pressure plate means being elongated in a direction parallel to the said edge to permit movement of the ties (25) relative to the carrier plate and/or the presser plate means in the said direction.

2. A sub-assembly according to claim 1, characterised in that the presser plate means (24) comprises a continuous resilient strip.

3. A sub-assembly according to claim 2, characterised in that the presser plate strip is slotted or notched transversely to the said direction (Figs. 9 to 12).

4. A sub-assembly according to claim 1, characterised in that the presser plate means comprises a plurality of short lengths (124) of arched resilient strip.

5. A sub-assembly according to any of the preceding claims characterised in that a resilient flexible back-up blade strip (22), narrower than the doctor blade strip (21) is located between the presser plate means (24 or 124) and the doctor blade strip (21).

6. A sub-assembly according to any of the preceding claims characterised in that the ties (25) each comprise a separate tie rod having a head (25a) at one end and a groove (25b) near the other end, the groove receiving a circlip (26).

7. A doctor blade assembly comprising a doctor blade sub-assembly according to any of claims 1 to 6 and a holder including a top channel element (14) having front and rear downwardly depending flanges bearing on an intermediate element in the form of a plate (11) of width greater than the top element, and a bottom element (12) having an upstanding rear flange (12a) behind the rear flange of the top element and a depending front flange (12b) below a forward region of the intermediate element (11), and means (16,17) clamping the three elements (11, 12, 14) together with the carrier plate portion (23) of the doctor blade sub-assembly between the forward portions (11, 11 a and 12) of the intermediate and bottom elements.

8. A doctor blade and holder assembly according to claim 7 characterised in that the forward portion of the intermediate element has a short depending flange (11a) to form a corner to receive a cylindrical packing element (13) whereby to adjust the position of a doctoring edge of the doctor blade.

Revendications

1. Un sous-ensemble de raclette comprenant une plaque de support flexible et élastique (23), une structure de plaque de pression arquée (24 ou 124) qui s'étend le long d'un bord de la plaque de support avec son côté concave dirigé vers la plaque de support (23), une bande de raclette flexible et élastique (21) d'épaisseur constante, serrée entre ledit bord de la plaque de support (23) et un bord adjacent de la structure de plaque de pression, et une rangée d'éléments de liaison (25) traversant des ouvertures (respectivement 23a et 24a) dans la plaque de support (23) et dans la structure de plaque de pression (24, 124), pour maintenir la structure de plaque de pression sous contrainte, afin de serrer la bande de raclette, les ouvertures (23a et 24a) dans la plaque de support et dans la structure de plaque de pression étant allongées dans une direction parallèle audit bord, pour permettre le mouvement des éléments de liaison (25) par rapport à la plaque de support et/ ou à la structure de plaque de pression, dans ladite direction.

2. Un sous-ensemble selon la revendication 1, caractérisé en ce que la structure de plaque de pression (24) consiste en une bande élastique continue.

3. Un sous-ensemble selon la revendication 2, caractérisé en ce que la bande de plaque de pression est fendue ou encochée transversalement à ladite direction (figures 9 à 12).

4. Un sous-ensemble selon la revendication 1, caractérisé en ce que la structure de plaque de pression comprend un ensemble de longueurs courtes (124) d'une bande élastique arquée.

5. Un sous-ensemble selon l'une quelconque des revendications précédentes, caractérisé en ce qu'une bande de lame de renfort flexible et élastique (22), plus étroite que la bande de raclette (21), est placée entre la structure de plaque de pression (24 ou 124) et la bande de raclette (21).

6. Un sous-ensemble selon l'une quelconque des revendications précédentes, caractérisé en ce que chaque élément de liaison (25) comporte une tige de liaison séparée ayant une tête (25a) à une extrémité et une gorge (25b) près de l'autre extrémité, la gorge recevant un circlip (26).

7. Un ensemble de raclette comprenant un sous-ensemble de raclette selon l'une quelconque des revendications 1 à 6, et un porte-raclette qui comprend un élément en U supériuer (14) comportant des ailes avant et arrière qui s'étendent vers le bas, cet élément reposant sur un élément intermédiaire ayant la forme d'une plaque (11) de largeur supérieure à celle de l'élément supérieur, et une élément inférieur (12) qui comporte une aile arrière (12a) qui s'étend vers le haut, derrière l'aile arrière de l'élément supérieur, et une aile avant (12b) qui s'étend vers le bas au-dessous d'une région avant de l'élément intermédiaire (11), et des moyens (16, 17) destinés à bloquer ensemble les trois éléments (11, 12, 14) avec la partie de plaque de support (23) du sous-ensemble de raclette située entre les parties avant (11, 11a et 12) des éléments intermédiaire et inférieur.

8. Un ensemble d'une raclette et d'un porte-raclette selon la revendication 7, caractérisé en ce que la partie avant de l'élément intermédiaire comporte une aile courte (11a) dirigée vers le bas, dans le but de former un coin destiné à recevoir une cale cylindrique (13), ce qui permet de régler la position d'un bord de raclage de la raclette.

Ansprüche

1. Rakel-Baugruppe mit einer elastisch biegsamen Trägerplatte (23), einer gewölbten Druckplatte (24 oder 124), die sich längs der einen Kante der Trägerplatte erstreckt, wobei ihre konkave Seite der Trägerplatte (23) zugekehrt ist, einen elastisch biegsamen Rakelstreifen (21) von konstanter Dikke, der zwischen der erwähnten einen Kante der Trägerplatte (23) und einer benachbarten Kante der Druckplatte eingeklemmt ist, und eine Reihe von Bolzen (25) durch Öffnungen (23a bzw. 24a) in der Trägerplatte (23) und der Druckplatte (24, 124) hindurchgeführt sind, um die Druckplatte in einem gespannten Zustand zum Festklemmen des Rakelstreifens zu halten, welche Öffnungen (23a und 24a) in der Trägerplatte und in der Druckplatte in einer Richtung parallel zu der erwähnten Kante länglich sind, um eine Bewegung der Bolzen (25) mit Bezug auf die Trägerplatte und/oder die Druckplatte in der erwähnten Richtung zu ermöglichen.

2. Rakel-Baugruppe nach Anspruch 1, dadurch gekennzeichnet, daß die Druckplatte (24) durch einen kontinuierlichen elastischen Streifen gebildet wird.

3. Rakel-Baugruppe nach Anspruch 2, dadurch gekennzeichnet, daß der Druckplattenstreifen quer zu der erwähnten Richtung (Fig. 9 bis 12) geschlitzt oder gekerbt ist.

4. Rakel-Baugruppe nach Anspruch 1, dadurch gekennzeichnet, daß die Druckplatte durch eine Vielzahl kurzer Längen (124) gewölbter elastischer Streifen gebildet wird.

5. Rakel-Baugruppe nach einem oder mehreren der vorangehenden Ansprüche, dadurch gekennzeichnet, daß ein elastischer biegsamer Rakelabstützstreifen (22), der schmäler als der Rakelstreifen (21) ist, zwischen der Druckplatte (24 oder 124) und dem Rakelstreifen (21) angeordnet ist.

6. Rakel-Baugruppe nach einem oder mehreren der vorangehenden Ansprüche, dadurch gekennzeichnet, daß die Bolzen (25) je durch einen gesonderten Bolzenschaft mit einem Kopf (25a) an seinen einen Ende und einer Nut (25b) in der Nähe des anderen Endes gebildet werden, welche Nut einen Sicherungsring (26) aufnimmt.

7. Rakel mit einer Rakel-Baugruppe nach einem oder mehreren der Ansprüche 1 bis 6 und einem Halter aus einem oberen Kanalelement (14) mit einem vorderen und einem hinteren nach unten gerichteten Flansch, welche Flansche auf einem Zwischenelement in Form einer Platte (11) von größerer Breite als das obere Element aufsitzen, und aus einem unteren Element (12) mit einem nach oben gerichteten hinteren Flansch (12a) hinter dem hinteren Flansch des oberen Elements, und einem nach unten gerichteten vorderen Flansch (12b) unter einem vorderen Bereich des Zwischenelements (11), und Mitteln (16, 17) zum Zusammenspannen der drei Elemente (11, 12, 14) mit dem Trägerplattenteil (23) der Rakel-Baugruppe zwischen den vorderen Teilen (11, 11 a und 12) des Zwischenelements und des unteren Elements.

8. Rakel und Halterbaugruppe nach Anspruch 7, dadurch gekennzeichnet, daß der vordere Teil des Zwischenelements einen kurzen nach unten gerichteten Flansch (11a) hat, um eine Ecke zur Aufnahme eines zylindrischen Dichtungselements (13) zur Einstellung der Stellung einer Streichkante der Rakel zu bilden.

Drawing