US3077134A

US3077134A - Shear for cutting billets, beams, and the like

Info

Publication number: US3077134A
Authority: US
Inventors: Ronick Murray
Original assignee: Baldwin Lima Hamilton Corp
Current assignee: Baldwin Lima Hamilton Corp
Priority date: 1958-12-04
Filing date: 1958-12-04
Publication date: 1963-02-12
Anticipated expiration: 1980-02-12

Description

M. RONICK Feb. 12, 1963 SHEAR FOR CUTTING BILLETS, BEAMS, AND THE LIKE Filed Dec. 4, 1958 4 Sheets-Shee t v 1 INVENTOR MURRAY RONICK HIS AGENT Feb. 12, 1963 M. RONICK 3, 7

SHEAR FOR CUTTING BILLETS, BEAMS, AND THE LIKE Filed Dec. 4, 1958 4 Sheets-Sheet 2 FIG. 3. *i"

HIS AGENT Feb. 12, 1963 M. RONICK 3,077,134

SHEAR FOR CUTTING BILLETS, BEAMS, AND THE LIKE Filed Dec. 4, 1958 4 Sheets-Sheet 3 FIG. 4.

' PUMP UNIT l '78 INVENTOR MURRAY RONICK WNW HIS AGENT Feb. 12, 1963 M, omc 3,077,134

SHEAR FOR CUTTING BILLETS, BEAMS, AND THE LIKE Filed Dec. 4, 1958 FIG. 5. 49 50 4 Sheets-Sheet 4 INVENTOR MURRAY RONICK HIS AGENT United States Patent Ofliee 3,077,134 Patented Feb. 12, 1963 3,077,134 dfrlEAR FUR CUTTING lllhLElS, BEAMS, AND THE LlKE Murray Ronick, East Meadow, N.Y., assignor to Baldwin- Lirna liiamilton Corporation, Philadelphia, Pa, a corporation of Pennsylvania Filed Dec. 4, 1958, Ser. No. 778,181 Claims. (til. 83-559) This invention relates to shears for cutting metal, and more particularly to vertical shears of the so-called universal type for handling a great variety of materials such as billets, bars, angles, beams, channels, and other profiles.

Conventional shears of the above type normally have a lower knife which is in a fixed position onthe shear housing or frame, and an upper knife which is rigidly secured to a knife actuator or ram. Thus, both knives are within the confines of the shear housing and all knife changes must be made within the shear proper. Such changes and the necessary realignment of the parts are extremely time consuming and cause the machine to remain idle while these steps are carried out, which results in a very considerable loss in production.

It has been proposed to provide a removable lower knife carrier sliding laterally out of the shear so that the lower knife or knives may be replaced outside the machine. The upper knife or knives, however, must still be changed within the confines of the shear where accessibility is limited so that the work requires much time. Likewise, the alignment of the upper and lower knives must be carried out within the shear. The machine is idle while the upper knives are changed and the parts are aligned so that the loss in production is still very considerable.

Another difliculty encountered in conventional shears of the above type is due to the fact that normally the lower knife is vertically fixed relative to the frame. In such arrangement, the material to be cut must be supplied to the shear at the fixed level of the lower knife, which, if the shape of the material varies, requires cumbersome and expensive handling equipment.

it is an object of the invention to provide an improved shear in which a change of knives will cause a minimum of down time.

It is also an object of the invention to provide a vertical shear in which the upper and lower knives may be changed, as well as aligned with each other, outside the machine in a simple manner.

it is another object of the invention to provide a shear with an integrated knife assembly in which cutting movements may be simulated outside of the shear for precise alignment of the knives.

Another object of the invention is to provide a vertical shear in which the upper knife system cooperates with its actuator merely under resilient pressure without being fastened thereto so that the upper knife system may be readily separated from its actuator.

Still another object of the invention is to minimize the transmission of eccentric forces from the reciprocating knife system of a shear to the actuator thereof, and practically to eliminate play between the reciprocating parts during operation.

A further object of the invention is to equip a vertical shear with a plurality of interchangeable assemblies which are used in rotation, and each of which comprises a complete set of upper and lower knives.

It is a still further object of the invention to provide a vertical shear with a movable lower knife holder and compact means for positioning the holder at a desired level prior to a shearing operation.

Various other objects, features and advantages of the invention will become apparent as the description proceeds.

In the drawings which illustrate an embodiment of the invention by way of example,

FIG. 1 shows a vertical shear according to the invention in section taken generally along line 11 of FIG. 3, certain parts being broken away for better illustration;

FIG. 2 shows a portion of FIG. 1, some of the parts being in different positions for cutting another size of material;

FIG. 3 is an enlarged section taken generally along line 3-3 of FIG. 1, but showing some of the parts in the FIG. 2 position, the material to be sheared being omitted;

FIG. 4 is a plan view taken in the direction of the arrow 4 of FIG. 1, certain parts being broken away for better illustration;

FIG. 5 is an enlarged, fragmentary section taken along line 5-5 of FIG. 4;

FIG. 6 is an enlarged, fragmentary section taken along line 66 of FIG. 1;

FIG. 7 is an enlarged, fragmentary section taken along line 7-7 of FIG. 6; and

FIG. 8 is an enlarged, fragmentary section showing a detail.

Referring to the drawings, an upright housing or frame generally indicated at It) and mounted on a foundation block 11 is adjacent its top equipped with split bearings 12 for journalling a crankshaft 14 which has a connecting rod 15 attached thereto to operate a knife actuator or ram 26 reciprocable in vertical guideways 22 of the frame. It will be clear that instead of the

mechanical drive

14, 16, hydraulic operating means may be provided if desired.

Below its vertical guideways 22, the frame 10 has a large opening 24 therethrough in which horizontal guideways 26 (FIG. 3) are positioned to accommodate a carriage generally indicated at 3%. The latter is interchangeable and used in rotation with similar carriages, one of which is indicated at 31 in FIG. 4. An upper knife 34 and its backer 35 (FIG. 3) are secured at 37 (FIG. 1) to an upper knife holder 36 which is vertically movable in guideways 38 positioned particularly in the corner regions of carriage 30. The upper knife holder has a raised portion 39 at its top for engaging the ram 20 and normally is resiliently urged upwardly by biasing means such as four cylinder and piston units 40 arranged adjacent the four corners of the knife holder. Each of the units ill which are single-acting comprises a cylinder 41 (FIG. 5) mounted in a bore 42 of the upper knife holder and secured to the latter at 42A, a cylinder head 43 fastened at 43A, a piston 44, and a piston rod 45, each cylinder having an upper chamber 46. The lower ends 47 of the piston rods are spherically shaped and supported on mating surfaces of replaceable: wear disks 43 (FIG. 3) inserted in carriage 3t).

Attached to lateral ports 49 (FIG. 5) of the cylinder heads 43 are pipes 5%. (see carriage 31, FIG. 4) which are positioned in grooves 51 of the upper knife holder 36 and connected to a common pipe line 52 accommodated in a groove 53 of the upper knife holder. A conventional quick disconnect coupling comprising portions or halves 54, 55 (see carriage 30, FIG. 4) serves for the attachment to pipe line 52 of a flexible hose 56 which is in turn connected to a pipe line 57.1eading to a source of pressure such as an accumulator 58 containing oil under pneumatic pressure.

Conventional hold-down or stripper pins till (FIG. 3) are movable in hushed bores 61 of the upper knife holder 36 against the pressure of springs 62. Nuts 53 attached to the threaded upper ends of the pins serve to limit downward movement of the pins relative to the knife holder 36.

A lower knife 6d and its backer as are secured at or (FIG. 1) to a lower knife holder 65 which is vertically movable in guideways 68 of carriage 3%. The knife holder 66 is provided with upwardly extending portions 69 for better guidance and with lateral projections 7t), 71 (FIG. 3) which in the lowermost position of the knife holder rest on shoulders 72, '73 of the carriage. These shoulders terminate in

inclined faces

74, 75 which cooperate with shields '75 made of plate material and mounte on the frame in to deflect pieces of metal dropping down during a shearing operation. Mechanism for lifting the lower knife holder to a level above its rest position will be described later.

A pair of spaced track members 8%, 81 are attached at one end to frame it? by fastening means 84 (FTG. 6) while the other ends of the track members are secured by fastening means as (FIGS. 1 and 4) to a base 9% mounted on a foundation block hit so that the members 89, 81 bridge the space between blocks 11 and 91 The track members have guideways 94 aligned with the guideways 26 of frame it} and forming a continuous track therewith so that the carriage 39 may readily be shifted on this track from the cutting station in frame Iii) onto the

members

80, 81 and vice versa. For such movements, a driving mechanism is provided comprising a reversible electric motor 96 attached to a gear unit 98 which is mounted on the base 90; a brake 99 for stopping the mechanism at a desired instant; a threaded spindle Tilt} rotatable by means of unit 98 and arranged in the space between the

track members

80, 81; a travelling nut 192 meshing with spindle 100 and engaging guideways liil'3 of the track members; and a pin 164 secured to the top of nut 162. One end of spindle 1% is journalled in the base 9d and the other end is supported in a bearing which is secured to the track members 8%, 31 at 199 (FIG. 6). The carriage St} has a rearward extension 110 provided with a hole ill into which the pin 164 projects. Since the spindle 1% is secured against axial movement by reason of its attachment to gear unit 98 at 114 and by means such as its shoulder 116 (FIG. 1), and since the travelling nut 162 is prevented from rotating due to its engagement with guideways itlfz, the nut 10-;- and carriage do will be caused to move along the track in a selected direction when spindle tea is turned in a corresponding way.

To determine the shearing position positively, the car riage 3b is provided with two lateral arms 11% which stop inward movement of the carriage upon engagement with frame 10. The arms have holes 12o (FIG. 7) therein to receive pins 122, secured to the frame. Tapered keys 124 provided with eyebolts 125, and keyways 126 in the pins serve to lock carriage 3t} releasably in its shearing position.

Referring now again to the lower knife holder arrangement, mechanism for lifting the knife holder 66 from its rest position comprises a slide 13% (FIGS. 1 and 3) mounted for vertical movement in guideways 132 of the frame. The slide 13d has a recess 13 at its bottom and is provided with an inclined guideway 136 mating with the top of a wedge 14% which is accommodated in the recess 134. The wedge having a liner 142 at its bottom is movable on a horizontal face 144 in an opening 146 (FIG. 3) which extends through frame lit at right angles to the path of travel of carriage 363. A pressure-operate double-acting cylinder and piston unit 14% is mounted on frame It} and connected to one end of the wedge to move the latter. Facing the other end of the wedge is an abutment member in the form of a threaded rod 158 which is supported in a pillow block 152 mounted on frame Til. Rod 150 is axially shiftable to a selected position relative to pillow block 152 by means such as a worm drive located at 154 in 2. lug of the pillow block.

An auxiliary, relatively long flexible hose 172 (FIG. 14) is equipped with a coupling portion 175 identical with portion 55. The hose 172 is connected to a pipe line 176 which includes a manually controlled exhaust or bleeder valve 177 and leads to an auxiliary source of pressure such as a pump unit 17%.

Operation When carriage 343 is in its cutting position shown in full lines in FIG. 1, both knife holders 36 and 65 are aligned with the ram or actuator 2d. The chambers 46 of cylinders ii communicate freely with the accumulator 5% so that the upper knife holder is urged upwardly and its top 3? is in engagement with actuator 26'. The lower knife holder 66 may rest on the

shoulders

72, 73 of the frame as shown in FIG. 1. As the knives, 34, 64; are shaped for triple cuts, three elements such as angles 1% (FIG. 1) may be placed in the machine simultaneously. When crankshaft 14 is turned and the actuator 2d descends to perform the shearing operation, the cylinders 41 will be caused to move downwardly over their pistons 24 so that fluid under pressure will be forced to flow from chambers 36 back to the accumulator. When the out has been completed and ram 29 ascends again, fluid will return from the accumulator to the cylinders 41 and cause them to move upwardly over their pistons 44 so that the upper knife holder 35 will follow the upward motion of the ram in engagement therewith. It should be noted that cha1n bers 132 (H6. 5) in cylinders 41 are connected to the atmosphere through ports 133 and clearance 134 at the circumference of the cylinders to allow for free flow of air to and from these lower chambers.

To guide knife 34 safely when it approaches knife 64, each or" the upwardly extending portions 6? of the lower knife holder has a recess or guideway 1&6 therein as shown in cross-section in FIG. 8. These guideways cooperate with lateral extensions 187 on the upper knife holder 36.

During the downward movement of knife 34, the holddown pins 69 will engage the angles lilo in conventional manner and firmly bear thereupon under the pressure of their springs as to avoid tilting of the angles. At this stage the pins are stopped from further participation in the downward movement of the upper knife holder and its drive. Therefore, holes 188 (FIG. 3) are provided in ram 2b to accommodate the upper ends of the pins, as well as their nuts 63 which are disengaged from the upper knife holder 36 at this time. When knife 34 starts to move upwards upon completion of the cut, the pressure exerted by pins on will counteract any tendency of the angles 34) to stick to the knife and will be effective to strip the angles therefrom as well known in the art. At a predetermined point of the upward stroke of knife 34, the nuts 63 are engaged again by knife holder as and the stripper pins are then lifted together with the holder. The shearing operation may then be repeated after further material to be cut has been placed on the lower knife.

When it is necessary to change the knives due to a change in the shape of the material to be handled or for other reasons, the tapered keys 124 are removed from their pins 122 and the flexible hose 56 is disconnected from pipe line 52. The

halves

54, 55 have built-in check valves 1%, 192 which, upon disconnection of the coupling, close automatically to seal the cylinders 41 as well as the accumulator 58 so that uncontrolled escape of fluid is prevented. The coupling portion positioned on the auxiliary hose 172 and having a built-in check valve 194 is now connected to coupling portion 54, which by reason of the construction of these standard parts will result in both check valves 1%, 194 being automatically pushed to open positions. The manually operated bleeder valve 177 is then opened temporarily with the pump 178 being shut off to release a small amount of fluid from cylinders 41 so that the upper knife holder 36 will descend slightly due to the action of gravity and thus will be disengaged from ram 2% Thereafter, hose 172 may be disconnected from the carriage. Slide 139 and Wedge Mt} should be in their withdrawn positions at this time. Motor 96 is started to move carriage 34} along track members 8 3, 81 from the cutting or shearing station where the carriage is in the position shown in full lines in FIG. 1, to a transfer station where the carriage is in the withdrawn position indicated in phantom at 30' in FIG. 1. Lifting equipment such as a crane is connected to hooks 198 on carriage 3! to raise the latter from the track and move it to a convenient location on the floor. Pin tilt. of the travel mechanism is readily released from engagement with hole 112 when the carriage is lifted.

The next carriage 31 having the required knives attached thereto ready for operation is then raised by means of the crane and placed on the track so that its hole 112 accommodates pin 104. The cylinders 41 of carriage 31 contain a predetermined amount of fluid and their position is such that the top of the upper knife holder will clear ram 26. Motor 96 is now started in the reverse direction to move carriage 31 into the shear frame and is then stopped and the brake 99 is applied to bring the arms 118 of carriage 31 into smooth engagement with frame it whereupon the tapered keys 124 are inserted in pins 122 to lock the carriage in position. Flexible hose 56 is connected to carriage 31 and thereby both check valves 1%, 192 of the coupling will be automatically pushed to open positions so that the cylinders 41 will communicate freely with the accumulator 58 and additional fiuid under pressure will enter the chambers 46 to bring the upper knife holder 36 of carriage 31 into engagement with ram 29. The cylinders 41 will communicate continuously with the accumulator while the flexible hose 56 remains connected to the carriage. The shear is now ready again for operation with the lower knife holder 66 being in its rest position on

shoulders

72, 73 of carriage 31.

While operation of the shear is resumed after a minimum of down time and proceeds without interruption, a knife change may be performed on the withdrawn carriage 30 in accordance with the requirements of the production program. After the upper and lower knives have been changed, they can be completely aligned with each other in the withdrawn carriage which is outside the shear on the floor where the parts are easily accessible. For this purpose, the auxiliary hose 172 may be connected to pipe 52 on carriage 3t) and the upper knife holder of this withdrawn carriage may then be reciprocated with the aid of bleeder valve 177 and pump unit 178 to perform idle movements, that is, to simulate the shearing motion. This renders it possible to check the alignments of the parts outside the shear frame. Before the auxiliary hose 172 is disconnected from the withdrawn carriage, the cylinders 41 thereof are partly but not entirely filled with fluid by means of pump unit 178 so that the upper knife holder 36 of this carriage is in the proper position to clear ram 2% when carriage 3t is moved into the shear again upon withdrawal of carriage 31.

The reason for the movable arrangement of the lower knife holder 66 will be best understood from a comparison of FIGS. 1 and 2. In FIG. 1, the lower knife holder is in its rest position to shear the relatively small angles 180 which are advanced to the shear on a feeding table and then received on a depressihle delivery table, the normal level of the tables being indicated in chain lines at 2G2. In the case of larger angles 2% (see FIG. 2) the legs thereof extend further downwards. Therefore, in conventional shears having the lower knife in a fixed vertical position, it is necessary to make the feeding and delivery tables vertically shiftable and lower the tables when larger angles are handled, so that the inner contour of the angles will properly register with the top of the lower knife. As the feeding and delivery tables are relatively long and heavy and, moreover, the delivery table is depressible, shiftable supports for such tables are cumbersome and relatively expensive. The movable arrangement of the lower knife eliminates these drawbacks since 6 only one single, compact assembly need be shifted as will be clear from the following description.

Wedge Mil is initially in its withdrawn position shown in phantom at 149 in FIG. 3 and, accordingly, slide 136 is in its lowermost position as shown in phantom at 136 in FIG. 3. This initial arrangement of the parts is illustrated in full lines in FIG. 1 and it will be seen that the top surface of slide 13% now clears the lower knife holder as and the carriage 3-3 by a predetermined distance so that the carriage may be moved along its track. At the same time, the lower knife is in its proper position for shearing the small angles 13d shown in FIG. 1. For cutting the larger angles 2%, the threaded rod 15%) is moved axially by means of worm drive 154 to a predetermined extent, which may be done while the carriage 30 is within or outside the frame it When the carriage is in the frame, pressure is admitted to the cylinder and piston unit 148 to move the far end of wedge 149 into engagement with the adjacent end of rod 15-0 and lift slide a corresponding distance. The top of the slide will thereby engage the bottom of the lower knife holder 65 and shift the latter to the desired level as shown in full lines in FIGS. 2 and 3. It may be mentioned here that the total vertical movement of slide 13%) is somewhat larger than that of the lower knife holder as there is initial clearance between these parts. Slide 13$) and wedgelitl may be withdrawn by admitting pressure to the return side of unit 143 whenever required. It will be clear that with this arrangement small and large angles may be fed to the shear at the same level 2&2 and will be discharged at the same general level so that it is no longer necessary to shift the feeding table and the depressible delivery table upon a change in the angle size.

The removal of a carriage assembly from the shear and the replacement thereof by another completely assembled carriage can be achieved very rapidly. Operation of the machine is interrupted for a brief period of time only since the upper knife holder 36 is not fastened to its actuator 20 and is disengageable therefrom simply by operating the cylinder and piston units 49. Rod 15% may be preset while the exchange of carriages takes place so that wedge and slide 13% can be actuated to bring the lower knife to the desired level as soon as the respective carriage is locked to frame 10. On a large shear built according to the invention and capable of exerting a shearing force of 700 tons, the changeover has been carried out within seven minutes. As compared therewith, a complete change of upper and lower knives including alignment causes five hours down time in one conventional type of shear while eight hours are required in another type.

It should be noted that as the upper knife holder is not rigidly connected to the ram but is guided in the carriage, no appreciable eccentric forces will be transmitted to the ram which has a beneficial effect upon the operation of the shear drive. Further, the resilient pressure exerted by the cylinders 41 will practically eliminate: play between the reciprocating parts so that they will operate smoothly.

As will be understood, the embodiment described herein does not illustrate all the ways in which the broad invention may be employed. In case of a relatively simple production program, for example, it may not be necessary to make the lower knife movable relative to

carriage

39 or 31. The basic advantages of the carriage will be obtained regardless of whether the lower knife is rigidly or movably mounted thereon, though the latter arrangement is superior where a large variety of different shapes is to be handled.

Other possible modifications relate to the hydraulic means. A bleeder or control valve may be provided on the upper knife holder proper so that the latter may be lowered readily without connecting the auxiliary hose 172 thereto. Further, a single source of pressure and suitable control valves may replace the two separate hydraulic systems and bleeder valve shown in the drawings as will be readily clear to those skilled in the art. Structural details may likewise be changed in that, for example, the pistons 44 may operate in bores of the upper knife holder proper'though the use of separate cylinders is preferable, or the pistons may be attached to the upper knife holder and the cylinders may then be supported on the carriage. Various other modifications and changes may be made without departing from the scope of the invention as defined in the appended claims.

Having described my invention, what I claim and de sire to secure by Letters Patent is:

1. A vertical shear for cutting billets, beams and the like, comprising a source of fluid under pressure, a frame, an actuator mounted in said frame for reciprocation along a substantially vertical aids, operating means on said frame for reciprocating said actuator, substantially horizontal guide means intersecting said axis and extending from a cutting station in said frame to a transfer station remote therefrom, an assembly movable on said guide means independently of said actuator between said cutting and transfer stations; said assembly including a carriage, an upper knife holder mounted in said carriage for substantially vertical movement, an upper knife secured to said holder, 21 lower knife arranged on said carriage for cooperation with said upper knife, and cylinder and piston means supported on said carriage and connectible to said source, said cylinder and piston means being operable at the cutting station to urge said upper knife holder resiliently towards said actuator for engagement therewith; and a valve for releasing a selected amount of fluid from said cylinder and piston means to disengage said upper knife holder from its actuator prior to withdrawal of the carriage from the cutting station; said assembly being removable from said guide means at the transfer station as a unit whereby said assembly may be replaced by another carriage assembly interchangeable therewith.

2. A shear as specified in claim 1, including conduit means connecting said source to said cylinder and piston means and establishing continuous communication therebetween while said carriage is at the cutting station.

3. A shear as specified in claim 1, including conduit and valve means operable when said carriage is outside said frame to introduce fluid under pressure into said cylinder and piston means and then to withdraw fluid therefrom to perform idle movements of the upper knife holder and knife.

4. A vertical shear for cutting billets, beams and the like, comprising a frame, an actuator mounted in said frame for reciprocation along a substantially vertical axis, operating means on said frame for reciprocating said actuator, a substantially horizontal guide means intersecting said axis, an assembly movable on said guide means independently of said actuator between a cutting station in said frame and a transfer 'ation remote therefrom; said assembly including a carriage, an upper knife holder mounted in said carriage for substantially vertical movement, an upper knife secured to said holder, biasing means supported on the carriage and operative at the cutting station to urge said upper knife holder resiliently towards said actuator for effective engagement therewith, a lower knife for cooperation with said upper knife, a lower knife holder supporting said lower knife and mounted in said carriage for substantially vertical movement relative thereto, and abutment means on the carriage for supporting said lower knife holder in a lower rest position, said assembly being removable from said guide means at the transfer station as a unit; and positioning means mounted on said stationary frame and engageable with the lower knife holder for lifting said lower knife holder from its lower rest position and returning it thereto; whereby said assembly may be replaced by another carriage assembly interchangeable therewith at the transfer station and said lower knife holder with the lower knife thereon may be shifted to a selected level at the cutting station prior to a cutting operation.

5. A shear as specified in claim 4, in which said positioning means include a slide mounted in said frame for substantially vertical movement, and said carriage has a downwardly open slideway therein accommodating the lower knife holder, said slide being arranged to enter said slideway and to engage said lower knife holder when said carriage is at the cutting station, power-operated, actuating means being supported on said frame for causing said slide to shift said lower knife holder at predetermined distance.

References Cited in the file of this patent UNITED STATES PATENTS 891,359 Morse June 23, 1908 949,807 Nyman Feb. 22, 1910 1,834,919 Altrater Dec. 8, 1931 2,013,976 Wales Sept. 10, 1935 2,209,497 Lindsay et al. July 30, 1940 2,355,344 Wales Aug. 8, 1944 2,760,575 Taylor Aug. 28, 1956

Claims

1. A VERTICAL SHEAR FOR CUTTING BILLETS, BEAMS AND THE LIKE, COMPRISING A SOURCE OF FLUID UNDER PRESSURE, A FRAME, AN ACTUATOR MOUNTED IN SAID FRAME FOR RECIPROCATION ALONG A SUBSTANTIALLY VERTICAL AXIS, OPERATING MEANS ON SAID FRAME FOR RECIPROCATING SAID ACTUATOR, SUBSTANTIALLY HORIZONTAL GUIDE MEANS INTERSECTING SAID AXIS AND EXTENDING FROM A CUTTING STATION IN SAID FRAME TO A TRANSFER STATION REMOTE THEREFROM, AN ASSEMBLY MOVABLE ON SAID GUIDE MEANS INDEPENDENTLY OF SAID ACTUATOR BETWEEN SAID CUTTING AND TRANSFER STATIONS; SAID ASSEMBLY INCLUDING A CARRIAGE, AN UPPER KNIFE HOLDER MOUNTED IN SAID CARRIAGE FOR SUBSTANTIALLY VERTICAL MOVEMENT, AN UPPER KNIFE SECURED TO SAID HOLDER, A LOWER KNIFE ARRANGED ON SAID CARRIAGE FOR COOPERATION WITH SAID UPPER KNIFE, AND CYLINDER AND PISTON MEANS SUPPORTED ON SAID CARRIAGE AND CONNECTIBLE TO SAID SOURCE, SAID CYLINDER AND PISTON MEANS BEING OPERABLE AT THE CUTTING STATION TO URGE SAID UPPER KNIFE HOLDER RESILIENTLY TOWARDS SAID ACTUATOR FOR ENGAGEMENT THEREWITH; AND A VALVE FOR RELEASING A SELECTED AMOUNT OF FLUID FROM SAID CYLINDER AND PISTON MEANS TO DISENGAGE SAID UPPER KNIFE HOLDER FROM ITS ACTUATOR PRIOR TO WITHDRAWAL OF THE CARRIAGE FROM THE CUTTING STATION; SAID ASSEMBLY BEING REMOVABLE FROM SAID GUIDE MEANS AT THE TRANSFER STATION AS A UNIT WHEREBY SAID ASSEMBLY MAY BE REPLACED BY ANOTHER CARRIAGE ASSEMBLY INTERCHANGEABLE THEREWITH.