US2947248A

US2947248A - Doctor blade mechanism

Info

Publication number: US2947248A
Application number: US744112A
Authority: US
Inventors: Fuchs Friedrich
Original assignee: Westfalendruck & Co Ko GmbH
Current assignee: Westfalendruck & Co Ko GmbH; Westfalendruck & Co Kommandit-Gesellschaft GmbH
Priority date: 1957-06-26
Filing date: 1958-06-24
Publication date: 1960-08-02
Anticipated expiration: 1977-08-02

Description

Aug. 2, 1960 F. FUCHS DOCTOR BLADE MECHANISM 7 Sheets-Sheet 1 Filed June 24, 1958 INVENTOR FR znmcn'rucns BY 41%, 2/4042! ATTORN Aug. 2, 1960 F. FUCHS DOCTOR BLADE MECHANISM 7 Sheets-Sheet 2 Filed June 24, 1958 m m M 5 BY r gmcw rug: 7

j ATTOR Aug. 2, 1960 uc s 2,947,248

DOCTOR BLADE MECHANISM Filed June 24, 1958 7 Sheets-Sheet s INVENTOR TRIERDGH FUCHS Aug. 2, 1960 F. FUCHS DOCTORBLADE MECHANISM '7 Sheets-Sheet 4 Filed June 24, 1958 g m w T \R W O 4 m w T A "I m t M W H W ,F [M f ,ll av w NNQfi w w M m 1 @R F W M0 NR B W U m N m m N m.\ A m MN 2 R m m- I- h i n W0, NM MN 1 WM, WM MN I V SW NW WM, 9 MW l Aug. 2, 1960 F. FUCHS DOCTOR BLADE MECHANISM Sheets-Sh eet 5 Filed June 24, 1958 INVENTOR F'RJEDRILH FUC. HS

ATTOR Aug. 2, 1960 F. FUCHS DOCTOR BLADE MECHANISM 7 Sheets-Sheet 6 Filed June 24, 1958 INVENTOR FRIFDRICH FUCHS ATTO EYS Aug 2, 1960 F. FUCHS 2,947,248

DOCTOR BLADE MECHANISM Filed June 24, 1958 '7 Sheets-Sheet 7 FRIEDR H FUC ATTORN '5 2,947,248 Patented Aug. 2, 1960 2,947,248 DOCTOR BLADE MECHANISM Friedrich Fuchs, Ende uber Dortmund, Germany, assignor to Westfalendruck G.m.b.H. & Co., Kommandit-Gesellschaft, Dortmund, Germany, a firm of Germany Filed June 24, 1958, Ser. No. 744,112 Claims priority, application Germany June 26, 1957 12 Claims. (Cl. 101-157) The present invention relates to improvements in a doctor blade mechanism for rotary printing machines,

particularly for intaglio printing.

It is the principal object of the invention to provide a new mechanism which permits a doctor blade which has beendamaged during the operation of the rotary printing machine to be exchanged for anew blade without requiring the machine to be stopped for such exchange.

. Although prior to this invention .various efforts have been made to attain this result, they have all been inadequate. Thus, for example, it has been proposed to mount a plurality of doctor blades above each other in such a manner as to permit one blade to take over the function of apreviously damaged blade while the printing machine continues to operate. Since in such a mechathem the individual damaged blades themselves can, however, not be exchanged for new. blades during the continued operation of the machine, it means that, after the reserve blades have been used up, the machine has to be stopped to permit a new set of blades to be inserted. Since with a poor grade of paper containing gritty particles, the individual doctor blades may be damaged within a short time, such a mechanism may extend the period during which the machine might continue to run, but it does not avoid the necessity of stopping it at one time'or another for an exchange of the entire set of doctor blades. p

In another doctor blade arrangement two doctor blades are mounted above each other, so that one blade is in the operative position while the other is in the reserve position. A suitable mechanism then permits thereserve blade to be advanced and to take over the function of the damaged blade before the latter is withdrawn. The damaged blade may then be exchanged for a new blade which will then be in the reserve position. Although this mechanism permits an exchange of blades while the machine continues to run, the two blades do not engage with the printing cylinder at the same point but at a considerable distance from each other. This affects the adjustment of the doctor blades relative to the printing cylinder, resulting in an inaccurate function of one or both blades and consequently in poor printing results,

particularly during the time while the reserve bladeis being exchanged for the damaged blade. g

It is therefore more specifically an object of the invention to provide a blade mounting and exchanging mechanism which permits the doctor blade to be exchanged as frequently as may be desirable and without causing any interruption in the rotation and normal operation of the printing machine, and which for such exchanging operation does not require any change in the position of the individual doctor blades relative to the printing cylinder and does not cause any changes in the printing results due 'to the blade changing operation.

7 The new doctor blade mechanism replaces the conventional doctor blade shaft'and all its accessories, and it may be mounted in a similar manner on the frame of the printing machine and also be adjusted by conventional means so that the respective operating blade 2 engage the printing cylinder at the most suitable wiping angle.

The mechanism according to the invention essentially consists of a blade supporting structure comprising two supporting trails which are disposed at an acute angle to each other and the front edges of which facing toward the printing cylinder are spaced a small distance from each other so as to form a narrow slot at the apex of the two supporting rails through which the doctor blade may be passed at the required angle toward the printing cylinder. One of these supporting rails is adapted .to secure the doctor blade which is in the operative position in engagement with. the printing cylinder, while the other is adapted to holdt-he reserve blade temporarily during the exchanging operation which may thus be carried out in such. a manner that one or the other blade will be in constant engagement with the printing cylinder and at almost the identical point thereon so that one blade will take over the wiping operation when the other is to be Withdrawn because it has become defective and has to be replaced.

The mechanismjaccording to the invention further consists of a sliding mechanism which is pivotable to the extent of the angle between the two supporting rails and by means .of'which the reserve blade together with its blade holder may be passed into the angle between the two supporting rails and along one of them into the operating position, while the other blade holder together with its blade, after. being disconnected from its supporting rail and after the new blade has previously thereto been inserted into the reserve position and into engagement with the printing cylinder, may then be Withdrawn from the printing cylinder and be removed from the mechanism, whereupon the new blade on its holder may bepivoted from the reserve position to the normal operating position on the supporting rail from which the previous blade holder has been removed, permitting a new blade for. the next exchanging operation to be mounted on the other supporting rail in the reserve positi on.

K The doctor blades, as well as their supporting structure, that is, primarily the two supporting rails, extend along the entire width of the printing cylinder, while a pivotable sliding mechanism as above described is disposed on each end, and these two mechanisms are connected to each other by a single actuating device so that both of them will be operatedin unison.

Further objects, features, and advantages of the present invention will be apparent from the following detailed description thereof, particularly when read with reference to the accompanying drawings, in which- Figures 1 to 6 illustrate diagrammatically the principle of the present invention by showing the different stages of the blade exchanging operation;

Figure 7 shows a front view of the entire doctor blade mechanism;

Figure 8 shows a cross section taken along line CC of-Figure 7;

Figure 9 shows a plan-view of the pivotable sliding mechanism at one end of the blade supporting structure;

Figure 10 shows a cross section taken along line BB in Figure 9; I

Figure 11 shows a cross section taken along line A-A of. Figure 9; w I

liigure 12. shows a plan view of an upper supporting ra1 r a l Figure 13. shows a cross section taken along line D-D in Figure 12; l a .Figure. ;14 shows a plan view of a blade holder-with the doctor blade mounted therein; while Figure 15 shows a cross section taken along. line.

. 13 s of Figure 14. r

The present invention will first be described primarily with reference to Figures 1 to 6 which only show the most essential parts of the new mechanism and are only intended to illustrate the principle of the invention and the different stages of the blade exchanging operation so as to render the subsequent detailed description and the other drawings of the mechanism according to the invention more easily understandable.

The two supporting

rails

50 and 53 which extend at an acute angle to each other and the front ends of which are separated from each other by a narrow slot together form a single rigid unit by being connected to each other by a pair of sector-shaped plates 52 which are secured to the opposite ends of rail 50' and have the other rail 53 bolted to their upper surfaces. Each sectorshaped member 52 has an arcuate gear section 55 into which a spur gear 78 engages which is rotatably mounted on an arm 74 which, in turn, is pivotable about the axis of member 52. Thus, when arm 74 is pivoted, gear 78 rolls along gear sector 55. The pivotable arm 74 has a slide member 80 slidably guided therein by means of which the blade holder 54 or 54' with a doctor blade 64 or 64', respectively, therein may be inserted into and withdrawn from the angular area formed between the two supporting

rails

50 and 53. The upper surface of supporting rail 50 has a suitable recessin which an electromagnet 50a is mounted which is adapted to hold temporarily the reserve blade holder in a fixed position with the blade thereon in operative engagement with the printing cylinder F, until such blade holder can be transferred to and secured in the normal operating position on the lower surface of the other supporting rail 53. The upper surfaces of arm 74, slide 80, and supporting rail 50 including electromagnet 50a are disposed substantially within the same plane when arm 74 is pivoted to its lower end position. For this purpose, supporting rail 50 is provided with suitable recesses at its outer ends. The other supporting rail 53 is provided with a clamping device which includes a clamping bolt 59 for securing one of the blade holders 54 or 54' in the normal operating position on rail 53. The front ends of

rails

50 and 53 are provided with longitudinal slots into which steel bands 72 are fitted which resiliently engage each other ahead of

rails

50 and 53 and are adapted to serve as a forwardly-extended support of the respective doctor blade 64 or 64'. The apparatus according to the invention further includes a pressure control mechanism which is adapted to exert a pressure upon the operative doctor blade andto regulate the pressure with which such blade acts upon the printing cylinder F. This pressure control mechanism, although required for a proper operation of the respective doctor blade, may be made according to any one of several designs but preferably according to the design as described and claimed in my copending application, Serial No. 721,246, filed on March 13, 1-958, now Patent No. 2,920,357, issued January 12, 1960. However, since this pressure control-mechanism does not form a part of the present invention and has no effect upon the blade mounting and exchanging operation, it does not'need to be described or illustrated herein in detail.

Figure 1 illustrates the position of the blade exchanging mechanism before it is taken into operation. The blade holder 54 rests on the pivotable arms '74. In Figure 2, slide members 80 carrying the blade holder 54 are pushed forwardly and into the angular area between the two supporting

rails

50 and 53 so that blade 64 penetrates through the narrow slot between the front ends of the two rails and also through the two steel bands 72until its free edge engages with printing cylinder F. Then, according to Figure 3, arm 74 is pivoted upwardly until blade holder 54 engages with and rests flatly against the lower surface of supporting rail 53. The blade holder isthenclamped tightly to rail53 by means of the clamping bolt 59, whereupon the rotation of printin g the front.

4 cylinder F may be started and the printing operation may begin. Thereupon, slide member 80 is retracted and arm 74 is pivo'ted downwardly to its original position to receive the other blade holder 54' with the blade 64' clamped therein which thus lies in the reserve position, as illustrated in Figure 4. In the event that blade 64 has to be exchanged because it has become damaged during the continuous operation of printing cylinder F by gritty matter contained in the paper, the reserve blade holder 54 is pushed with slide member 80 forwardly so that doctor blade 64' likewise penetrates through the slot between the two supporting

rails

50 and 53 and the two steel bands 72, and in sliding engagement with the upper blade 64 until its front edge engages directly underneath blade 64 with the printing cylinder F, as illustrated in Figure 5. Electromagnet 50a is then energized to hold blade holder 54 temporarily in a fixed position. Blade 64' then takes over the wiping operation from blade 64 without requiring any interruption in the operation of printing cylinder F. Ann 74 is then again pivoted to the upper position, clamping bolt 59 is loosened, slide member 80 is moved forwardly and by means of a suitable hook or the like, not shown in Figures 1 to 6, engaged with blade holder 54, whereupon the latter with blade 64 thereon is retracted from the upper supporting rail 53, as shown in Figure 6. Blade holder 54 may then be removed from slide member 80 and the latter may be pivoted downwardly on arm 74. Thereupon, slide member 80 is pushed forwardly into engagement with blade holder 54, permitting the electromagnet 50a to be switched off. Arm 74 with blade holder 54' thereon may then be pivoted upwardly until the latter engages against supporting rail 53 and may then be secured thereto in its normal operating position by clamping bolt 59. Arm 74 is then again free to be pivoted downwardly to its original position as shown in Figure 4, whereupon another blade holder with ,a new blade therein may be placed upon arm 74 and be thus held in reserve for the next blade exchanging operation.

Figure 7 illustrates the entire apparatus as seen from It is mounted at both ends on shaft stubs 51 on the frame of the printing machine, not shown. Aside from the actual invention concerned herein which consists of the doctor blade mounting and exchanging mechanism, Figure 7 also indicates diagrammatically a pressure control mechanism 49 which is mounted on a pair of arms 48 on shaft stubs 51, and which is preferably of a design as disclosed in my aforementioned application Serial No. 721,246, although it may also be of any other suitable design without affecting the proper function of the blade mounting and exchanging mechanism according to the present invention.

Figure 8 shows a cross section of the blade mounting and exchanging mechanism with blade holder 54 in the normal operative position and the other blade holder 54' in thereserve position. It also shows the pivotable slide mechanism, as seen in a side view. The blade mounting mechanism consists of the supporting rail 50 withthe two sector-shaped plates 52 secured to its two ends by means of which rail 50 is connected to the other supporting rail 53 which is bolted upon the upper surface of plates 52. The two supporting rails '50 and 53 which thus form a single rigid unit are disposed at a fixed acute angle to each other but are separated from each other at their front ends by a narrow slot 57. The opposite outer surfaces of the front ends'of rails 50 and 53 are provided with recesses in each of which clamping strips 70 and 71, respectively, are mounted between which the resilient steel bands 72 are securely clamped, the free ends of which engage and resiliently press upon each other. Supporting rail 53, which is illustrated in its entirety on a reduced scale-in Figures 12 and 13, is provided with guide bushings 53 for receiving the clamping bolt 59. Each bushing 58 is further provided'with a ring .60 for guiding bolt 59 and supporting a coil spring operative position on supporting rail 53. Each bolt 59 is for this purpose provided With a head 65 of a rectangular shape which corresponds to that of a recess 66 in supporting rail 53, as shown particularly in Figure 13. Thus, if no doctor blade is mounted on supporting rail 53, the rectangular heads 65 of bolts 59 are sunk into recesses 66 by the action of springs 62 and the bolts are pressed outwardly. After the blade holder 54 or 54 is placed in engagement with the supporting rail 53, each clamping bolt 59 is depressed and passed through a slot 67 in the blade holder, as shown in Figure 14, until head 66 will be clear thereof so that the entire bolt may then be turned 90 about its axis by means of handle 63. If bolt 59 is then released, its head 65 will, under the action of spring 62, rest transversely in slot 67. When check nut 61 is then tightened on bolt 59, the respective blade holder 54 or 54 will be firmly secured to supporting rail 53 in the normal operative position. As shown in Figures 14 and 15, each blade holder 54 or 54 is made in the shape of an angle iron, and doctor blade 64 or 64' is clamped thereon by beinginserted and bolted by screws between one web of the angle iron and a clamping strip 68.

In this normal operative position, doctor blade 64 extends through slot 57 between the front ends of supporting

rails

50 and 53, with its front edge engaging with printing cylinder F, while its unclamped part in front of the beveled ends of blade holder 54 and clamping strip 68 is arcuately bent and the blade is thus resiliently pressed upon the lower supporting rail 50 and further supported ahead of the latter by steel bands 72. These steel bands 72' have the additional purpose of serving as sealing meansifor preventing the ink, which has been wiped off by the doctor blade and runs down along the outer surface of the lower supporting rail 50 into the ink tank,.from penetrating into the blade exchanging mechanism. Still, in the event that any ink might penetrate between steel band 72 and doctor blade 64, such ink will run down along ink channels 50b. As shown in Figure 9, the individual ink channels 56b are separated from each other by small partitions or ridges 500 which form intermediate supporting surfaces on which clamping strips 70 are mounted. As previouslyindicated, the entire doctor blade apparatus may be adjusted to the proper angle relative to the curved plane of printing cylinder Fby being pivoted about the axis of shaft stubs 51 by means of a setting mechanism St of a typeknown in this art.

The pivotable slide mechanism is illustrated in greater detail in Figures 9 to 11. On each end of this mechanism a bolt 73 which is secured in an eye 56 in the sectorshaped plate 52 forms a pivot pin on which arm 74 is pivotably mounted which, in turn, carries a housing 75 in which a ball bearing 76 supports a shaft 77. Each end of. this shaft carries a spur gear 78 which engages with the'teeth of gear sector 55 on plate 52. Thus, shaft 77 forms the rigid connection between the two pivotable arms 74, so that the two gears 78 thereon will roll in unison along gear sectors 55 when shaft 77 is rotated. Arm 74. further has a lateral extension 79 in which the slide member 80- is slidably guided within an elongated recess .and by being held therein by a pair of strips79a which are screwed upon element 79 and'are connected at their rear ends by a plate 791). On its lower side, each slide member 80 carries a'rack 81 into which a gear 82 engages which is secured to a tubular shaft 83. This tubular shaftis rotatably mounted on a pin bearing 84 on shaft 77. Thus, a rotation of the tubular shaft 83 will be transmitted through gears 82 and racks 81 to slidemembers 80 to shift the same longitudinally ina direction'tfoward printing cylinder F. Each slide member 80 further carries a square 85 for determining the proper lateral position of a blade holder 54' when being inserted in the reserve position. Each slide member 80 also carries a bracket 86 which forms a stop to limit the rearward movement of the respective slide member by then engaging with end plate 79b. The extent of the forward movement of slide members 80 is limited by stops 94 which are bolted to supporting rail 50. Each bracket 86 has a threaded bore in which a setscrew 87 is adjustable to the extent limited by a check nut 87' thereon. Setscrew 87 is used for adjusting the proper distance of the newly inserted reserve blade holder 54' between squares 85 from the surface of printing cylinder F. Each bracket 86 also supports a hook 88 which when arm 74 with all of its elements thereon is pivoted upwardly, is adapted to be pivoted counterclockwise from its inoperative position as shown in Figure 10 to engage with the upper blade holder 54 to permit the latter to be retracted after clamping bolt 59 has been disengaged therefrom. A slotted ring 89 surrounding the tubular shaft 83 and connected to arm 74 may be clamped tightly upon theshaft by means of a bolt and a handle 90 on such bolt. Shaft 83 which by being rotated shifts slide member 80 in its longitudinal direction, may thus be locked in either of its required positions by the operation of handle 90. For rotating the tubular shaft 83 and the solid shaft 77 therein, a ring 91, as shown in Figure 7, is mounted on shaft 83. A suitable rod may be inserted in ring 91 or if desired, a ratchet lever may be attached thereto to turn ring 91. For locking the pivotable arm 74 in its upper end position, a two-armed lever is provided at least at one end of the apparatus and pivotably mounted on a bracket 93. One arm 92 of this lever serves as a locking pawl, while the other arm 92a serves as a handle as well as a counterweight to hold pawl 92 in engagrneent with a smooth arcuate surface on plate 52 adjacent to gear sector 55. At its upper end, plate 52 has a notch 52a. Thus, when arms 74 with the various elements thereon are pivoted upwardly, pawl 92 will slide along the smooth surface adjacent to gear sector-55 until it automatically engages into notch 52a and thus locks arms 74 in the upper or operative position.

When the printing machine is readied for operation, blade holder54 with doctor blade 64 therein is placed upon the upper surfaces of arms 74 between squares 85 on slide members 80 and adjusted by means of setscrews 87 to a certain predetermined distance from the surface of printing cylinder F, so that blade holder 54 with blade 64 will then be in the lower position, that is, in

the loading or reserve position. If the tubular shaft 83 is then turned, such motion will be-transmitted through gears 82 and rack teeth 81 to slide member 80 to shift the same forwardly, whereby blade holder 54 will be moved until it engages with the front stops 94. In this position, the tubular shaft 83 will be locked by tightening handle 90 so that the blade holder resting on slide member 80 will then be in a fixed position.

Thereupon, doctor blade 64 will be adjusted by means of the pressure-regulating

mechanism

47, 48, 49 to engage at the proper pressure against the ink-coated surface of printing cylinder F. 7

Before the printing operation is started, the doctor blade is moved from its reserve position to the operative position by pivoting it upwardly together with the locked tubular shaft 83 on arms 74 until the upper surface of blade holder 54 engages upon the lower side of sup porting rail 53 and pawl 92 engages into notch 52a of atleast one of thesector-shaped plates 52. Blade 64 then remains in this bent operative position and is secured therein by clamping bolts 59 which lock blade holder 54 against supporting rail 53. Thereafter, clamping ring 89 is released by loosening lever 90, and slide members are retracted by turningthe tubular shaft 83 accordingly by means of ring 91." Pawl 92 is then disengaged from notch 52a by an operation of handle 92a permitting arms 74 and all of the elements s pported thereby to be pivoted downwardly to the original position. Thereupon, another blade holder with a reserve blade therein may be inserted in the manner as previously described.

When the respective new doctor blade is transferred from the lower loading or reserve position to the upper operative position, it will, as previously described, be bent arcuately intermediate the beveled front end of the blade holder 54 and slot 57. Due to such bending, the effeetive length of the blade will be slightly shortened with the result that the blade edge will be slightly drawn back to the extent of about 1.5 mm. This slight retraction has no effect upon the ink-Wiping action of the doctor blade since the pressure control mechanism follows such movement and always maintains the doctor blade edge at a constant pressure upon the surface of the printing cylinder F.

Although my invention has been illustrated and described With reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments, but is capable of numerous modifications within the scope of the appended claims:

Having thus fully disclosed my invention, what I claim is:

-1. A doctor blade mechanism for rotary printing machines comprising supporting means, said means comprising a pair of supporting rails disposed at an acute angle to each other and rigidly secured to each other near their ends so as to form a single unit, and having a narrow slot separating their front edges forming the apex of said angle, one of said rails being adapted to sup-- port a blade holder with a doctor blade thereon in the normal operative position in which said blade extends through said slot and its front edge engages with the surface of the printing cylinder of said machine, means for removably securing said blade holder to said first rail in said normal operative position, sliding means adapted to receive a second blade holder in a reserve position outside of the angular area between said rails and substantially within the plane of said second rail, and for sliding said second blade holder from said reserve position substantially along said plane into said angular area and into a temporary operative position in which the doctor blade on said second blade holder likewise extends through said slot and its front edge engages with the surface of said printing cylinder, means for temporarily securing said second blade holder in said temporary operative position, means for then pivoting said sliding means alone substantially from the plane of said second rail substantially to the plane of said first rail, means for retracting said first blade holder with its blade on said sliding means from said normal operative position after said blade holder has been disengaged from said securing means thereof and for then permitting said first blade holder with its blade to be removed, said pivoting means then being adapted to pivot said sliding means in said retracted position to said reserve position, said sliding means then being adapted to be moved into engagement with said second blade holder, whereupon said temporary securing means are disconnected from said second blade holder and said sliding means with said second blade holder is pivoted into engagement with said first rail, and secured thereto by said securing means thereof, while the front edge of the doctor blade on said second blade holder remains in engagement with said printing cylinder, whereupon said sliding means may again alone be pivoted to said loading position to receive another blade holder with a doctor blade thereon for the next blade exchanging operation.

2. A doctor blade mechanism as defined in claim 1, wherein said supporting means further comprise a pair of sector-shaped plates mounted on the opposite ends of said supporting rails and securing said rails to each other, each of said plates having a gear sector thereon, said pivoting means comprising a pair of arms pivotably mounted on the opposite ends of said supporting means and coaxially to the axis of said plates, a gear mounted on each of said arms and in engagement with one of said gear sectors, and common actuating means connecting said arms to each other.

3. A doctor blade mechanism as defined in claim 2, wherein said sliding means comprise a slide member slidably guided within each of said arms and having a gear rack at its lower side, and a gear rotatably mounted on each of said arms and in engagement with said gear rack, and means for rotating said gears in unison for shifting said slide member back and forth.

4. A doctor blade mechanism as defined in claim 3, wherein said common actuating means comprise a tubular shaft, said gears engaging with said racks for actuating said slide members being mounted on said tubular shaft, and further comprising a shaft disposed Within said tubular shaft and rotatably mounted within a bearing within each of said arms, and carrying said gears engaging with said gear sectors.

5. A doctor blade mechanism as defined in claimv 1, wherein said means for retracting said blade holder from said normal operative position comprise a hooklike member pivotably mounted on said sliding means and adapted to grip said blade holder to permit the same to be retracted from the angular area between said supporting rails.

6. A doctor blade mechanism as defined in claim 1, further comprising a lateral stop means and threaded adjusting means for adjusting a blade holder with a new blade thereon properly in said reserve position.

7. A doctor blade mechanism as defined in claim 4, further comprising means for locking said tubular shaft in different positions, said means comprising a clamping ring surrounding said tubular shaft and mounted on one of said arms.

8. A doctor blade mechanism as defined in claim 2, further comprising means for locking said arms in the upper end position for retracting said blade holder from said first rail, said means comprising a recess in at least one of said sector-shaped plates and a pawl pivotably mounted on one of said arms and adapted to engage into said recess.

9. A doctor blade mechanism as defined in claim 1, wherein said means for temporarily securing said second blade holder in said temporary operative position comprise an electromagnet embedded within the upper surface of said second supporting rail, and means for energizing said electromagnet.

10. A doctor blade mechanism as defined in claim 1, wherein each of said blade holders comprises an angle iron, and a mounting strip secured to one side of said angle iron, said doctor blade being clamped between said angle iron and said mounting strip.

11. A doctor blade mechanism as defined in claim 1, wherein said means for removably securing said blade holder to said first rail in said normal operative position comprise a plurality of bolts, and quick-acting means for connecting said bolts to said rail and for disconnecting the same therefrom.

12. A doctor blade mechanism as defined in claim 1, further comprising a pair of resilient steel bands mounted on the front ends of said rails and projecting forwardly therefrom in the direction toward said printing cylinder and their front ends resiliently pressing from opposite sides upon said doctor blade to support the same.

Caulfield May 2, 1950 Ross Oct. 13, 1953