US3759077A

US3759077A - Method and apparatus for feeding elongated rotary workpieces in straightening machines or the like

Info

Publication number: US3759077A
Application number: US00189213A
Authority: US
Inventors: H Hartkopf
Original assignee: TH Kieserling and Albrecht GmbH and Co
Current assignee: TH Kieserling and Albrecht GmbH and Co
Priority date: 1970-10-17
Filing date: 1971-10-14
Publication date: 1973-09-18
Anticipated expiration: 1990-09-18
Also published as: DE2051087A1; FR2112303B1; CA954540A; HU162602B; FR2112303A1; GB1344702A; NL7107174A

Abstract

A straightening machine for tubular or rod-like workpieces has concave straightening rolls which treat successive workpieces while such workpieces move lengthwise and rotate about their own axes. The feeding unit which advances workpieces into the range of the straightening rolls employs a pair of driven concave advancing rollers whose axes are inclined with reference to the axis of a workpiece between their concave surfaces. The advancing rollers can move successive workpieces at a higher speed so that the leading end of the workpiece between the advancing rollers catches up with the trailing end of the preceding workpiece which is being treated by the straightening rolls, and thereupon at a lower speed which corresponds to the speed of lengthwise transport of the workpiece at the straightening station. The speed of workpieces which are being transported by the advancing rollers can be varied by changing the inclination of the axes of rollers with reference to the axis of the advanced workpiece or by changing the operating speeds of series-connected hydraulic motors which rotate the advancing rollers.

Description

Uited States Patent m1 Hartkopi 1 Sept. 18, 1973 METHOD AND APPARATUS FOR FEEDING ELONGATED ROTARY WORKPIECES IN STRAIGHTENING MACHINES OR THE LIKE [75] Inventor: Heinz Hartkopt, Solingen, Germany [73] Assignee: TH. Kieserling & Albrecht, Solingen,

Germany [22] Filed: Oct. 14, 1971 [2i] Appl. No.: 189,213

[30] Foreign Application Priority Data Primary Examiner-Richard J. Herbst Attorney-Michael S. Striker [57] ABSTRACT A straightening machine for tubular or rod-like workpieces has concave straightening rolls which treat successive workpieces while such workpieces move lengthwise and rotate about their own axes. The feeding unit which advances workpieces into the range of the straightening rolls employs a pair of driven concave advancing rollers whose axes are inclined with reference to the axis of a workpiece between their concave surfaces. The advancing rollers can move successive workpieces at a higher speed so that the leading end of the workpiece between the advancing rollers catches up with the trailing end of the preceding workpiece which is being treated by the straightening rolls, and thereupon at a lower speed which corresponds to the speed of lengthwise transport of the workpiece at the straightening station. The speed of workpieces which are being transported by the advancing rollers can be varied by changing the inclination of the axes of rollers with reference to the axis of the advanced workpiece or by changing the operating speeds of seriesconnected hydraulic motors which rotate the advancing rollers.

20 Claims, 7 Drawing Figures Patented Sept. 18, 1973 6 Sheets-Sheet 1 Patented Sept. 18, 1973 3,759,077

6 Sheets-Sheet 2 FIE Patented Sept. 18, 1973 3,759,077

6 Sheets-Sheet 5 Patented Sept. 18, 1973 6 Sheets-Sheat 4 IXI Patented Sept. 18, 1973 6 Sheets-Sheet 5 Patented Sept. 18, 1973 3,759,077

6 Sheets-Sheet 6 METHOD AND APPARATUS FOR FEEDING ELONGATED ROTARY WORKPIECES IN STRAIGIITENING MACHINES OR THE LIKE BACKGROUND OF THE INVENTION The present invention relates to a method and machine for treating elongated workpieces, such as metallic rods or tubes. More particularly, the invention relates to improvements in a method and machine for treating elongated workpieces which rotate about their own axes during lengthwise transport through a treating station. Still more particularly, the invention relates to improvements in a method and apparatus for feeding elongated tubular or rod-shaped workpieces to a treating station at which successive workpieces undergo a straightening or analogous treatment.

It is well known to employ in a straightening machine for tubular or rod-shaped metallic stock pairs of mutually inclined hyperbolical rolls whose concave peripheral surfaces engage and treat successive increments of workpieces while such workpieces move lengthwise and rotate about their own axes. A drawback of such straightening machines is that the trailing end of a freshly treated workpiece is subjected to substantial bending stresses and is deformed so that its axis is inclined with reference to the axis of the major portion of the respective workpiece. Such stresses develop as a result of the release of substantial amounts of energy which are stored in the machine frame and in the tensioning anchors when the trailing end of a workpiece moves beyond the straightening rolls. It was found that the deformation of the trailing end of a freshly straightened workpiece is due to such feeding of workpieces that the distance between the trailing end of a preceding workpiece and the leading end of the next-following workpiece exceeds the length of that portion of a workpiece which is being engaged by the straightening rolls. Thus, the energy which is released when the trailing end of a workpiece leaves the straightening rolls can deform the trailing end so that the workpiece must be subjected to a secondary treatment or the deformed trailing end must be separated from the major portion of such workpiece.

It was further found that, when an elongated tubular or rod-like workpiece is treated in a straightening machine and the trailing end of such workpiece is spaced from the leading end of the next-following workpiece, and when the workpiece which is being engaged by the mutually inclined straightening rolls rotates during straightening, its trailing portion swivals to travel along a conical path and strikes with a great force against the guide means wherein the workpiece is led during treatment. Such swiveling of the trailing portions of workpieces which advance through the straightening station is due to rotation of the workpieces about their own axes and can cause considerable damage to a tubular workpiece as well as to the guide means. At any rate, the wear on the guide means is considerable, especially if the workpieces are metallic tubes or rods of large diameter.

Attempts to avoid excessive damage to the guide means include the replacement of tubular guides with several pairs of conical (hyperbolic) rollers which form two rows. The rollers of one row are adjustable toward and away from the rollers of the other row. To this end, one roller of each pair is mounted in a holder and all such holders are pivotable about an axis which is parallel to the axis of the workpiece between the two rows of rollers. The means for pivoting the holders comprises a double-acting cylinder which can move the -,holders away from the path of workpieces so that a fresh workpiece can be introduced from above and is properly engaged by the two rows of rollers when the holders are returned to their operative positions. The cylinder is preferably designed to yieldably urge the rollers which are mounted in the holders against the workpiece between the two rows of rollers. The rollers are adjustable to allow for proper guidance of workpieces having larger or smaller diameters. Such guide means reduces the likelihood of swiveling of the trailing ends of workpieces which are being fed lengthwise and rotate about their own axes. However, a straightening machine which embodies such guide means is still incapable of preventing deformation of the trailing end of a workpiece which has been advanced beyond the straightening rolls. A machine of the just outlined character is disclosed in German Pat. No. 725,630.

It is further known to feed successive workpieces end-to-end in machines wherein the workpieces need not rotate about their axes. For example, it is known to employ in a shaving machine for metallic tubes or rods a system of feeding or advancing rollers which transport successive workpieces lengthwise while the workpieces perform no angular movement about their own axes. When a preceding workpiece reaches the shaving station and is treated by one or more orbiting knives, the speed of its lengthwise movement is reduced and the thus decelerated workpiece decelerates the nextfollowing workpiece whereby the advancing rollers slip with reference to the peripheral surface of the nextfollowing workpiece. The resulting scoring of the peripheral surface by the rollers presents no problems be cause the workpiece is about to enter the shaving station.

SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved method of feeding elongated tubular or rodlike workpieces toward a straightening or a like treating station (at which the workpieces rotate about their own axes during treatment) in such a way that the feeding action reduces the likelihood of deformation of the trailing ends of freshly treated workpieces and also reduces the likelihood of damage to the guide means and- /or other component parts of the treating machine.

Another object of the invention is to provide a novel and improved apparatus for feeding successive elongated rod-shaped or tubular metallic workpieces into a straightening or analogous treating station.

A further object of the invention is to provide the feeding apparatus with novel and improved means for driving and otherwise moving the advancing elements for a succession of elongated rod-shaped or tubular workpieces which are caused to move lengthwise and to simultaneously rotate about their own axes.

An additional object of the invention is to provide a novel and improved straightening machine for tubular or rod-shaped workpieces which embodies the above outlined feeding apparatus.

Still another object of the invention is to provide a novel and improved method of controlling the speed of elongated workpieces which are fed toward, through and beyond a straightening station.

An ancillary object of the invention is to provide a novel and improved hydraulic system for a straightening machine which is used to treat elongated tubular or rod-like workpieces.

The method of the present invention is employed for the feeding of elongated workpieces, such as metallic tubes or rods, toward and through a treating station, especially a straightening station. The method comprises the steps of rotating a first workpiece about its own axis and simultaneously conveying the workpiece lengthwise along a predetermined path toward and through a treating station so that the workpiece moves through the. treating station at a first speed (which may but need not be constant), introducing into the path a second workpiece so that the leading end of the second workpiece is spaced from the trailing end of the first workpiece while the trailing end of the first workpiece is still located upstream of the treating station, conveying the second workpiece lengthwise toward the treating station at a second speed which exceeds the first speed so that the leading end of the second workpiece at least closely approaches but preferably moves into abutment with the trailing end of the first workpiece upstream of the treating station, and thereupon conveying the second workpiece toward the treating station at the first speed, i.e., so that the leading end of the second workpiece enters the treating station at the same time when the trailing end of the first workpiece leaves such station. The third, fourth and further workpieces are thereupon manipulated in the same way as the second workpiece.

If the (first) speed of the workpiece which passes through the treating station varies, the second speed is preferably changed as a function of variations in the first speed so that the location where the leading end of a next-following workpiece catches up with the trailing end of the preceding workpiece need not change due to eventual variations in the first speed. The second workpiece preferably rotates about its own axis during lengthwise movement at the second speed and thereupon at the first speed, and the speed of such rotary movement during lengthwise transport at the first speed preferably equals the speed of rotary movement of the first workpiece.

The method may further comprise the steps of producing a signal in response to movement of the leading end of the second workpiece (and/or the trailing end of the first workpiece) beyond a predetermined portion of the path between the introducing and treating stations, and utilizing such signal to decelerate the second workpiece from the second speed to the first speed.

The workpieces are preferably accelerated upon completed transport beyond the treating station for the purpose of separating the trailing end of each preceding workpiece from the leading end of the nextfollowing workpiece. This allows for unimpeded sidewise removal of treated workpieces from the path downstream of the treating station. The introduction of successive workpieces into the path upstream of the treating station preferably takes place by moving the workpieces sideways.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved feeding apparatus itself, however, both as to its construction and its mode of operation, together with additional features and-advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic plan view of a straightening machine for tubular or rod-shaped workpieces including a feeding apparatus which is constructed and assembled in accordance with a first embodiment of the invention;

FIG. 2 is an enlarged transverse vertical sectional view of the feeding apparatus, substantially as seen in the direction of arrows from the line IIII of FIG. 1;

FIG. 3 is a sectional view as seen in the direction of arrows from the line A-B of FIG. 2;

FIG. 4 is a sectional view as seen in the direction of arrows from the line C-D of FIG. 2;

FIG. 5 illustrates a portion of the hydraulic circuit of the machine shown in FIG. 1;

FIG. 6 is an enlarged fragmentary sectional view as seen in the direction of arrows from the line VIVI of FIG. 1; and

FIG. 7 is a diagrammatic plan view of a straightening machine including a feeding apparatus which is constructed and assembled in accordance with a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, there are illustrated certain components of a straightening machine for elongated solid rod-shaped or tubular metallic workpieces. For the sake of convenience, the workpieces will be called rods with the understanding, however, that the machine can be used with equal advantage for the straightening or analogous treatment of tubes or the like. The rods are stored in a magazine in the form of a rack 2 which includes a front stop 2a and a lateral stop 93 (see FIG. 6) and serves to feed

successive rods

68, 68a, sideways into a tubular guide or channel member 1 having a pivotable section la which can be moved to and from the closed position of FIG. 6 by a hydraulic or pneumatic motor here shown as a cylinder and piston unit 96. When the motor 96 moves the section la to its open position, the foremost rod 68 can be trans-- ferred from the rack 2 into the stationary section lb of the guide 1 and is then ready to be rotated about its own axis as well as to be transported lengthwise so that its leading end enters a straightening station ST which accommodates a straightening unit 3 shown in FIG. 1 by broken lines and including two mutually inclined concave (hyperbolical) straightening rolls 9, 10. Prior to entry into the stationary section lb of the guide 1, the foremost rod 68 abuts against the lateral stop 93 and rests on a pivotable transfer member which is actuatable by a hydraulic or pneumatic motor in the form of a cylinder and piston unit 94 shown in FIG. 6. When the motor 94 pivots the transfer member 95 in a clockwise direction, as viewed in FIG. 6, the member 95 lifs the foremost rod 68 over the lateral stop 93 and causes it to roll sideways along a suitably inclined guide surface 93a so as to descend (either immediately or with a certain delay) into the section lb. The motor 96 thereupon returns the section la to the closed position of FIG. 6 and the rod 68 in the guide 1 is ready to start its lengthwise movement (accompanied by rotary movement about its own axis) in order to advance the leading end into the straightening unit 3 at the station ST. The

rods

68, 68a, are placed onto the rack 2 in such a way that their front end faces abut against the stop 2a.

The space between the front end of the guide I and the straightening station ST accommodates a feeding apparatus 4 which includes two mutually inclined concave (hyperbolical) feeding or advancing

rollers

5, 6 serving to engage the leading end of that rod (68) which is received in the guide 1. To this end, the advancing

rollers

5, 6 are mounted rearwardly of the front stop 2a, as considered in the direction (arrow 100) of lengthwise movement of rods toward the straightening station ST. At least one of the advancing rollers 5, 6 (namely, at least the advancing roller 5) is movable to and from a retracted position in which it allows for unimpeded entry of the foremost rod into the guide 1. The movable advancing roller (5) is thereupon returned to the operative position shown in FIG. 1 in which the two advancing rollers cooperate to rotate the foremost rod about its own axis and to simultaneously move the rod lengthwise toward the straightening station ST. The

- feeding apparatus 4 is followed by an auxiliary tubular guide 7 which may but need not have a movable section and is disposed between the feeding apparatus 4 and a ring-shaped signal generating device 8 here shown as an inductance which can produce signals in response to entry of the leading end as well as in response to passage of the trailing end of a rod through and beyond its interior. A similar ring-shaped signal generating device 11 is disposed downstream of the straightening unit 3 and upstream of a second auxiliary tubular guide 12.

The latter is followed by an accelerating unit 13a which includes cooperating upper and lower accelerating rollers 13 (only one shown) and is followed by a tubular guide or channel member 14 which is adjacent to one side of a second magazine or rack serving to receive and store straightened rods. The construction of the guide 14 is preferably somewhat similar to that of the guide 1, i.e., the guide 14 may also comprise a stationary section and a pivotable section which must be moved to an open position in order to allow for evacuation of a freshly straightened rod onto the rack 15 whereon the rod rolls sideways into abutment with a lateral stop or into abutment with the previously straightened rod.

The length of the auxiliary guide 7 is'selected in such a way that the leading of a next-following rod (e.g., the rod 68a) can catch up with the trailing end of that rod (e.g., 68) which is being caused to pass through the straightening station ST. The arrangement is preferably such that the leading end of the next-following rod catches up with the trailing end of the preceding rod in the space between the straightening rolls 9, l0 and the signal generating device 8. The length of the auxiliary guide 12 is such that it can properly guide the leading end of a rod which is being advanced through the straightening station ST while the trailing end of the preceding (freshly straightened) rod is being moved away from the treated rod by the rollers 13 of the accelerating unit 13a. This is desirable in order to insure that the sidewise transport of the preceding rod from the guide 14 onto the rack 15 cannot be impeded by the rod which is being moved through the straightening station ST. The leading end of a next-following rod preferably reaches the accelerating rollers 13 at a time when the transfer of the preceding rod from the guide 14 is already completed. The guide 14 can be designed to allow for evacuation and transfer of straightened rods onto the rack 15 under the action of gravity.

Referring now to FIGS. 2 to 4, there is illustrated the manner in which the advancing roller 5 of the feeding apparatus 4 can be moved to and from its operative position, i.e., from and to an inoperative or retracted position in which the member of FIG. 6 is free to effect the transfer of a fresh rod into the guide 1. The advanc ing roller 6 is mounted at that side of the path for a rod (68) in the guide 1 which is adjacent to the rack 2, and the advancing roller 5 is mounted at the opposite side of such path. The feeding apparatus 4 comprises a stationary frame 16 having an upwardly extending portion or extension 17 which constitutes a vertical guide member for an aggregate AG] which carries the advancing roller 6. The level of the aggregate AGl can be adjusted by a feed screw 18. The aggregate AGI comprises means for pivoting the axis 6a of the roller 6 with reference to the axis ofa rod (68) in the guide 1. A second aggregate AG2 serves to support the advancing roller 5 for pivotal movement between operative and inoperative positions. Since the two aggregates are similar (and preferably nearly identical), only the details of the aggregate AG2 are fully illustrated in the drawing because the mounting of the aggregate AG2 is more complex due to the fact that the roller 5 is pivotable toward and away from the guide 1. FIGS. 2 and 4 show that the frame 16 is provided with two spaced upwardly extending supporting brackets 20 for plate-like arms or checks 19 which are turnable about the common axis of two horizontal shafts 19a in response to actuation of a hydraulic or pneumatic motor here shown as a double-acting cylinder and piston unit 21. The cylinder of the motor 21 is pivotably secured to the frame 16, as at 21a, and the piston rod 21b of this motor is articulately connected with the arms 19. The arms 19 are rigidly connected with a plate-like carrier 22 which normally assumes an upright position (in a substantially vertical plane) as shown in FIG. 2. The carrier 22 forms a vertical guide member for the parts which support the advancing roller 5. Such parts can be adjusted with reference to the carrier 22 (i.e., up or down, as viewed in FIG. 2) by a feed screw 23 which can be rotated by a hand wheel or the like.

The parts which support the advancing roller 5 include a two-piece casing 24 for a shaft 25 which is mounted in the casing 24 for movement radially of the path for the rod 68 and can be moved toward and away from the rod 68 shown in FIG. 2 by a threaded sleeve 26 which is rotatable in a nut 26a of the casing 24 by a hand wheel 27. The axis of the shaft 25 in operative position of the aggregate AG2 is at least substantially normal to the axis of a rod in the guide 1 and is preferably located in a horizontal plane. The portions of the casing 24 define a pair of vertically aligned

slots

24a, 24b (see FIG. 2) for a device which can turn the shaft 25 and hence the advancing roller 5 about the axis of the shaft 25. Such turning device comprises a sleeve or hub 28 which is fixed to the shaft 25 by a key 25a and has two radial projections or

extensions

28a, 28b which respectively extend

throughthe slots

24a, 24b of the casing 24. The extension 28a is articulately connected with the piston rod 29a of a hydraulic or pneumatic cylinder 29 which is mounted on the casing 24. The piston 67 of the cylinder 29 is shown in FIG. 5. The extension 28b passes through the slot 24b and into a housing 30 which is mounted on the casing 24. The housing 30 accommodates two

stops

32, 32a which are disposed at the opposite sides of the extension 28b and are adjustable axially toward and away from each other by two

feed screws

31, 31a. The cylinder 29 for the hub 28 is a double-acting cylinder and the extent of strokes of the piston 67 in this cylinder is determined by the selected axial positions of

stops

32, 32a in the housing 30. This is clearly shown in FIG. 3. In other words, the axial positions of the

stops

32, 32a in the housing 30 determine the extent to which the shaft 25 can turn the advancing roller 5 about the axis of the hub 28. The roller 5 is rotatably mounted in a bifurcated holder 33 which is rigidly connected with the inner end portion of the shaft 25, namely, with that end portion which is nearer to the path for the rod 68 shown in FIGS. 2 and 4. The holder 33 further serves to support a hydraulic motor 34 which serves to rotate the advancing roller 5. The motor 34 can rotate the roller 5 by way of a clutch 35.

The aggregate AGI comprises a second holder 33A (FIG. 4) which accommodates the motor 34A (FIG. 5) for the advancing roller 6. The shaft which supports the holder 33A is analogous to the shaft 25 for the holder 33 and is mounted in a casing similar to the member 24.

The piston 54 (FIG. 5) in the cylinder of the motor 21 for the arms 19 shown in FIG. 2 has a downwardly extending rod 210 which carries a conical acutating member or trip 36 for an electric limit switch 37. The switch 37 and the aforementioned

signal generating devices

8, 11 constitute component parts of a programming system which serves to operate various movable parts of the machine in a predetermined sequence. The operation of the machine which includes the parts shown in FIGS. 1 to 4 and 6 will be described with reference to FIG. 5 which shows additional parts of the programming system. FIG. 5 further shows two electric or fluid-operated motors 38, 39 which respectively serve to rotate the straightening rolls l and 9. The motor 38 drives the straightening roll 10 by way of a transmission 76 which has a take-off 76a serving to drive a variable-delivery pump 75. The pump 75 serves to supply pressurized fluid (e.g., oil) for the aforementioned motors 34, 34A which respectively drive the advancing rollers and 6. It will be seen that the rotational speed of the advancing

rollers

5, 6 can be varied as a function of changes in rotational speed of the straightening roll which is preferably driven at the same speed as the straightening roll 9.

FIG. 5 further shows a main pump 41 which is driven by an electric motor 40 and serves to draw oil from a tank or fluid source 42 through a supply conduit 44 containing an oil filter 44. The outlet of the pump 41 is connected with a conduit 46 which contains a oneway ball check valve 45 and is connected with an adjustable pressure relief valve 57 by way of a conduit 58. When the oil pressure in the conduit 46 exceeds a predetermined value which is selected by appropriate adjustment of the valve 57, the conduit 58 is free to admit oil into a return conduit 59 which conveys the oil into the tank 42. The conduit 46 serves to deliver pressurized oil to three conduits 47, 48, 49 which respectively serve to supply pressurized oil to the motor 21, cylinders 24, 24A and pump 75 for the motors 34, 34A. The conduit 47 delivers pressurized oil to an electromagnetically operated valve 51 by way of a ball check valve 50. The valve 51 is connected with the upper and lower chambers of the cylinder of the motor 21 by conduits 52, 56 which respectively contain flow regulating devices 53, 55. The devices 53, 55 respectively comprise flow restrictors 53a, 55a and ball check valves 53b, 55b.

The conduit 48 serves to supply pressurized oil to a second electromagnetically operated valve 61 by way of a ball check valve 60. The valve 61 delivers pressurized oil into one of two conduits 62, 73. The conduit 62 is respectively connected with the lower chambers of the cylinders 29, 29A (below the pistons 67, 67A by conduits 63, 64 which respectively contain flow regulating devices 65, 66. The conduit 73 communicates with conduits 71, 72 which are respectively connected with the upper chambers of cylinders 29, 29A and respectively contain flow regulating devices 69, 70. Each of the flow regulating devices 65, 66, 69, is identical with the device 53 or 55.

The conduit 49 contains a ball check valve 74 and is connected with the inlet of the pump 75 as well as with a conduit 84 which is connected with the motor 34A by way of a further conduit 81 containing a check valve 82. The conduit 81 further contains an adjustable pressure relief valve 83. The outlet of the pump 75 is connected with a conduit 77 which is connected with an adjustable pressure relief valve 80 and contains a ball check valve 78. A conduit 79 which is connected with the conduit 77 downstream of the check valve 78 is connected with the motor 34 and with a conduit which by-passes the motor 34 and contains a flow restrictor 86.

The operation of the machine shown in FIGS. 1 to 6 is as follows:

Several

untreated rods

68, 68a, are placed onto the rack 2 in such a way that their leading ends abut or nearly abut against the front stop 2a and that the rightmost rod, as viewed in FIG. 6, abuts against the lateral stop 93. The stop 93 is adjustable substantially radially of the tubular guide 1. The machine is thereupon set in operation by starting the motors 38, 39 for the straightening rolls 10, 9 and the motor 40 for the main pump 41. The latter draws oil from the tank 42 by way of the supply conduit 44 and through the oil filter 43 and forces pressurized oil through the ball check valve 45 and into the conduits 46, 47, 48 and 49. The pressurized oil opens the ball check valve 50 in the conduit 47 and passes through the valve 51 into the conduit 52 or 56. FIG. 5 shows the valve member of the valve 51 in that position in which the conduit 47 is free to communicate with the conduit 52 while the conduit 56 communicates with the tank 42. The pressurized oil then flows through the flow regulating device 53 and enters the lower chamber of the cylinder in the motor 21 to move the piston 54 upwardly, as viewed in FIG. 5. This causes the piston rod 21b to pivot the aggregate A62 to the operative position shown in FIG. 2. If the tubular guide 1 does not accommodate a rod when the aggregate AGZ is moved to the operative position of FIG. 2, the arms 19 are caused to come into abutment with a suitable stop, not shown. As the piston 54 moves upwardly, it expels oil from the upper chamber of the cylinder in the motor 21, and such oil is returned into the tank 42 by way of the flow regulating device 55 in the conduit 56 and valve 51. The fluid pressure in the conduit 47 begins to rise when the aggregate AG2 reaches the operative position of FIG. 2 but such pressure cannot exceed a predetermined value because the relief valve 57 then opens and connects the conduit 58 (and hence the conduits 46, 47) with the return conduit 59 which delivers oil back into the tank 42. I

The oil which enters the conduit 48 opens the ball check valve 60 and flows into the conduits 62, 63, 64 or 73, 71, 72. If the valve 61 connects the conduit 48 with the conduit 62, pressurized oil flows through the flow regulating devices 65, 66 to enter the corresponding chambers of the cylinders 29, 29A. This causes the shafts (see the shaft 25 of FIGS. 2-3) for the advancing

rollers

5, 6 to move the corresponding

holders

33, 33A to such angular positions (see FIG. 4) which are determined by the positioning of the respective stops (see the stop 32a for the sleeve 28 on the shaft 25 of FIG. 3) so that the angle between the axes 5a, 6a of the

rollers

5, 6 is best suited to insure the lengthwise movement of a rod in the guide 1 at a speed which suffices to enable the leading end of such rod to catch up with the trailing end of the preceding rod while the preceding rod is being moved through the straightening station ST. The oil which is expelled from the cylinders 29, 29A by the pistons 67, 67A flows back into the tank 42 by way of the conduits 71, 72, flow regulating devices 69, 70, conduit 73 and valve 61. When the extension 28b of the hub 28 shown in FIG. 3 already abuts against the stop 32a but the conduit 63 continues to admit pressurized oil into the corresponding chamber of the cylinder in the motor 29, the relief valve 57 opens and allows the conduit 59 to return surplus oil into the tank 42. The same holds true for the aggregate AGl, i.e., the buildup of oil pressure in the conduit 64 after the axis 611 of the roller 6 has reached the position shown in FIG. 4 will also cause the relief valve 57 to open so as to prevent excessive stressing of the machine by pressurized oil.

The pressurized oil which enters the conduit 49 opens the ball check valve 74 and flows into the pump 75 which is driven by the take-off 76a of the transmission 76 between the motor 38 and the straightening roll 10. The pump 75 conveys oil into the conduit 77 so that the ball check valve 78 opens and admits oil into the conduits 79 and 85. The motors 34, 34A are connected in series and the adjustment of the relief valve 80 is such that the pressure of oil at the downstreamside of the pump 75 cannot exceed a preselected value. The flow restrictor 86 in the bypass conduit 85 insures that the RPM of the motor 34 equals the RPM of the motor 34A. The suction side of the pump 75 draws oil from the conduit 84 which receives oil from the motor 34A by way of the conduit 81 and ball check valve 82. Thus, the pump 75 recirculates oil which flows from the conduit 77, through conduits 79, 85, 81 and back through the conduit 84. The relief valve 83 controls the oil pressure in the conduits 81 and 84.

It will be seen that, shortly after the pump 41 is started, the arms 19 move the aggregate A02 to the operative position of FIG. 2 and that the axes 5a, 6a of the advancing

rollers

5, 6 are caused to make with the axis of the rod 68 in the guide 1 a predetermined angle which is best suited to insure accelerated transport of a rod from the guide 1 toward the straightening station ST. The rotational speed of the advancing

rollers

5, 6 is determined by the motors 34, 34A and is a function of the speed of the straighteing roll because the pump 75 which supplies oil to the motors 34, 34A is driven by the transmission 76 which rotates the roll 10.

The straightening operation is regulatedby a programming system which includes the aforementioned detectors 8, Ill and the limit switch 37. The treatment of a first rod 68 and the transport of the second rod 68 are carried out as follows: In the first step, the programming system causes the motor 94 of FIG. 6 to pivot the transfer member in a clockwise direction so that the foremost or rightmost rod 68 which abuts against the lateral stop 93 is transferred onto the guide surface 93a and is ready to be introduced into the guide 1. If desired, the rod 68 which is transferred onto the guide surface 93a can come to rest in the broken-line position 68A of FIG. 6 in which it abuts against a portion of the carriage 96a for the movable section la of the guide I. The programming system then comprises a suitable time delay relay or the like which causes the motor 96 to move the pivotable section 10 to its open position with a predetermined delay following actuation of the transfer member 95 by the motor 94. As the section 1a pivots in a clockwsie direction (reference being had to FIG. 6), the rod 68 leaves the position 68A and descends into the section 1b to assume the full-line position of FIG. 6. The same time delay device can serve to reset the electromagnetically operated valve 51 of FIG. 5 so that the valve 51 connects the conduit 47 with the conduit 56 and the conduit 52 with the tank 42. The pressurized oil furnished by the pump 4] and conduit 46 is then free to flow through the conduit 56 and flow regulating device 55 to enter the upper chamber of the cylinder in the motor 21 whereby the arms 19 move the aggregate AG2 with the advancing roller 5 to the retracted position. The oil which is expelled from the lower chamber of the cylinder in the motor 21 can flow through the regulating device 53, conduit 52, valve 51 and back into the tank 42. Thus, the roller 5 is retracted and allows the leading portion of the rod 68 which descends into the guide 1 to enter the space between the

rollers

5 and 6. The programming system resets the valve 51 to the condition shown in FIG. 5 after the elapse of a predetermined interval (for example, after the elapse of an interval determined by the delay device which actuates the motor 96 for the guide section la) so that the lower chamber of the cylinder in the motor 21 is again connected with the conduit 47 and the motor 21 returns the aggregate A62 to the operative position shown in FIG. 2. The return movement of the aggregate AG2 to the operative position of FIG. 2 can take place simultaneously with return movement of the guide section 1a to the closed position shown in FIG; 6. As the motor 21 returns the aggregate AGZ to the operative position of FIG. 2, its piston rod 210 causes the trip 36 to actuate the limit switch 37 which causes the motor 94 to again pivot the transfer member 95 in a clockwise direction, as viewed in FIG. 6, so that the member 95 transfers the next-following rod 68a from the rack 2 onto the surface 930 whereby such rod rolls against the carriage 96a to assume the brokenposition 68A of FIG. 7 above the closed guide I. Thus, the engagement of a preceding rod 68 by the advancing

rollers

5, 6 automatically entails the transfer of the next-following rod 68 into a position of readiness above the guide 1.

The

rollers

5, 6 are respectively driven by the motors 34, 34A and cause the rod 68 to perform a lengthwise movement accompanied by a rotary movement along its own axis so that any selected point on the periphery of the rod 68 travels along a helical path. Such composite movement of the rod 68 is due to mutual inclination of the axes 5a, 6a of advancing

rollers

5, 6 as shown in FIG. 4. The large angle between the axes a, 6a of the advancing

rollers

5, 6 insures that the rotational speed of the rod 68 about its own axis is relatively small but that the rod 68 advances lengthwise at a substantial speed.

When the leading end of the rod 68 reaches the space within the detector 8, the latter produces a signal which energizes the solenoid of the valve 61. The latter then connects the conduit 48 with the conduit 73 and the conduit 62 is connected with the tank 42. The oil is then free to flow from the conduit 48, via conduits 73, 71, 72 and flow regulating devices 69, 70 into the respective chambers of the cylinders 29, 29A. This causes the shafts 25 for the

holders

33, 33A to turn about their own axes whereby the extension 28b of FIG. 3 returns into abutment with the stop 32 and the corresponding extension of the aggregate AGl also returns into abutment with a stop corresponding to the stop 32 of FIG. 3. In other words, the angle between the axes 5a, 6a of the advancing

rollers

5, 6 decreases to equal or approximate the angle between the axes of the straightening rolls 9, 10. Thus, the angle which the axis 5a makes with the axis of the rod 68 between the advancing

rollers

5,6 equals the angle between the axis of the straightening roll and the rod in the straightening station ST, and the angle between the axis 6a and the axis of the rod 68 between the

rollers

5, 6 equals the angle between the axis of the roll 9 and the rod at the straightening station.

The diameters and rotational speeds of the advancing

rollers

5, 6 are selected in such a way that the peripheral speed of the

rollers

5, 6 equals the peripheral speed of the straightening rolls 9, 10 when the angle between the axes 5a, 6a is reduced. Consequently, once a trailing rod has caught up with the preceding rod (which passes through the straightening station ST), the speed of lengthwise movement of both rods is the same. The speed at which the two rods rotate about their own axes is also the same. The preceding rod enters the space between the straightening rolls 9, l0 and is subjected to a straightening operation. When the straightening operation upon the preceding rod progresses to such an extent that the trailing end of the rod which is being treated by the rolls 9, 10 leaves the space between the advancing

rollers

5, 6, the programming system causes the valve 51 to connect the conduit 47 with the conduit 52 for a short interval of time so that the extension 28b of the holder 28 for the shaft 25 is returned into abutment with the stop 32a and the angle betwen the axes 5a, 6a of the

rollers

5, 6 increases. The rod 210 moves the trip 36 upwardly so that the latter releases the limit switch 37 which causes the motor 96 to move the section 1a of FIG. 6 to the open position so that the rod 68a which was held in the position 68A is free to enter the stationary section lb of the guide 1. The limit switch 37 also resets the valves 51 and 61 so that the aggregate AG2 is pivoted to its retracted position in order to allow the rod 680 which has left the position 68A to enter into the space between the advancing

rollers

5, 6. The aggregate AG2 then returns to the operative position of FIG. 2. This is caused by the valve 51. The valve 61 thereupon causes the axes 5a, 6a of the

rollers

5, 6 to assume the angular positions shown in FIG. 4. The limit switch 37 also energizes a time delay relay of the programming system which causes the motor 94 to return the section In of the guide 1 to the closed position of FIG. 6 with a predetermined delay and to reset the valve 51 so that the aggregate AG2 is moved to the operative position in order to allow the roller 5 to engage the leading portion of the rod 68a in the guide 1. When the guide 1 is closed again and the

rollers

5, 6 engage the rod 68a in the guide 1, the trip 36 causes the limit switch 37 to actuate the motor 94 which transfers a further rod (not shown) into the position 68A of FIG. 6.

The rod 68a which is engaged by the advancing

rollers

5, 6 is rapidly transported toward the straightening station ST so that its leading end catches up with the trailing end of the rod 68 which is being treated by the straightening rolls 9, 10. When the trailing end of the treated rod 68 moves beyond the detector 8, the latter produces a signal for actuation of a scanning device (not shown) which forms part of the programming system and monitors the movements of rods between the detector 8 and the center of the straightening station ST. The leading end of the next-following rod 68a (which is being advanced by the rollers 5, 6) reaches the detector 8 shortly after the latter detects the trailing end of the preceding rod 68. The detector 8 then actuates an adjustable time delay relay of the programming system which relay changes the condition of the valve 61 after the elapse of a predetermined interval of time. This causes the cylinders 29, 29A to reduce the angle between the axes 5a, 6a of the advancing

rollers

5, 6 so that the rod 68a whose leading end has advanced beyond the detector 8 begins to move lengthwise at a reduced speed. The just mentioned delay is selected in such a way that the rod 68a which is being advanced by the

rollers

5, 6 catched up with the rod 68 which is being treated by the straightening rolls 9, 10 while the leading end of the rod 68a travels between the straightening rolls 9, 10 and the detector 8. The aforementioned scanning device which monitors the rods between the detector 8 and the centers of the straightening rolls 9, 10 then produces a signal which causes the rollers 13 of the accelerating unit 13a to move into engagement with the uppermost and lowermost portions of the adjacent rod 68 and to rapidly introduce such rod into the guide 14. The accelerating rollers 13 are driven in opposite directions and are movable radially of the adjacent rod 68 by a mechanism which forms no part of the present invention. When the trailing end of the rod 68 which is being accelerated by the rollers 13 reaches the detector 11, the latter produces a signal which energizes a time delay relay of the programming system so that the relay produces a signal after elapse of a predetermined interval of time from the generation of signal by the detector 11. The signal from the relay triggers the following operations: The accelerating rollers 13 are moved away from the freshly treated rod 68 and are brought to a standstill. The movable section of the guide 14 is moved to the open position so that the rod 68 which has entered the guide 14 under the action of the accelerating rollers 13 is free to roll sideways onto the rack 15. A further time delay relay produces a signal when the rod 68 reaches the rack 15. Such signal is used to close the guide 14. In the meantime, the rod 68a which is being advanced by the

rollers

5, 6 moves its leading end into the space between the straightening rolls 9, l0 (and its trailing end beyond the rollers 5, 6) and the treatment, acceleration and storage of such rod 680 are then carried out in the same way as described above for the preceding rod-68. The rods are treated one after the other as long as the rack 2 contains a supply of untreated rods and as long as the programming system for the straightening machine is An important advantage of the improved advancing apparatus 4 is that the output of the straightening machine is increased because the straightening unit 3 operates at maximum capacity, i.e.., without any gaps between successive workpieces. Another advantage of the feeding apparatus 4 is that it prevents the straightening machine from deforming the trailing ends of those workpieces which move beyond the straightening rolls 9, at the station ST. All this is achieved by the simple expedient of temporarily transporting a freshly introduced workpiece at a relatively high speed so that the thus accelerated workpiece catches up with the preceding workpiece before the trailing end of the preceding workpiece moves beyond the straightening rolls 9, 10.

The advancing

rollers

5, 6 reduce the extent of (or completely prevent) the swinging movements of the trailing end of the workpiece in the guide 1 so that this guide can stand long periods of use. Also, when the leading end of a freshly introduced workpiece reaches the trailing end of the workpiece which is being treated by the rolls 9, 10 the trailing end of the preceding workpiece is held against excessive lateral movements. The frame of the straightening machine cannot release energy which would result in deformation of the trailing end of a freshly treated workpiece when such trailing end moves beyond the rolls 9, 10 because the leading end of the next-following workpiece enters the straightening station ST simultaneously with movement of the trailing end of the freshly treated workpiece beyond such station. This insures that each workpiece is properly treated from end to end and that the rack receives workpieces with undeformed trailing ends.

Referring to FIg. 7, there is shown a modified straightening machine wherein the acceleration of workpieces (not shown) which are being transported toward the straightening station ST is not effected by pivoting the axes of the advancing

rollers

5, 6 but rather by changing the speed of the

motors

91, 91A for such advancing rollers. This results in substantial simplification of the aggregates for the advancing

rollers

5, 6 because these rollers need not be pivoted with their holders. The change in speed of the

motors

91, 91A for the advancing

rollers

5, 6 is effected by changing the inclination of the customary tilting plate (not specifically shown) in an axial piston pump 87 which is driven by the transmission 76 for the straightening roll 10. The mechanism for changing the inclination of the tilting plate in the pump 87 comprises a feed screw 88, a gear train 89 which can move the feed screw 88 axially, and a servomotor 90 which rotates the first gear of the gear train 89. The feed screw 88 changes the inclination of the tilting plate in the pump 87. The servomotor90is controlled by a circuit 92 which receives signals from the detector 8. The circuit 92 further receives signals from the limit switch 37 (not shown in FIG. 7). The circuit 92 may comprise a time delay relay and an amplifier; such parts determine the length of intervals during which the motor 90 causes the feed screw 88 to increase theinclination of the tilting plate in the axial piston pump 87 so that the latter conveys more fluid through the series-connected

motors

91, 91A whereby the advancing

rollers

5, 6 drive the adjacent workpiece at a higher speed so that such workpiece can catch up with the workpiece which is being treated by the straightening rolls 9, l0.

Otherwise, the operation of the machine shown in FIG. 7 is identical with that of the machine shown in FIG. 6. The only important difference is that the advancing

rollers

5, 6 of the machine shown in FIG. 7 need not be pivoted with their holders, i.e., it is merely necessary to move the roller 5 to and from a retracted position so as to permit the introduction of a fresh workpiece from the rack 2 into the guide 1. All other parts which are shown but not specifically mentioned in FIG. 7 are denoted by characters identical with those employed in FIGS. 1 to 6.

The straightening machine of FIG. 7 can be used with particular advantage for the treatment of largediameter tubes or rods which are normally moved lengthwise at a relatively low speed. This renders it possible to temporarily increase the speed of lengthwise movement of a freshly introduced workpiece by increasing the operating speeds of the

motors

91, 91A to such an extent that the leading end of the freshly introduced workpiece catches up with the trailing end of the workpiece which is being treated at the station ST before such trailing end moves beyond the rolls 9, 10. The temporary increase in rotational speed of the accelerated workpiece about its own axis during travel toward the workpiece which passes through the station ST is of no consequence because the difference between the normal rotational speed and the increased rotational speed about the axis of such workpiece is relatively small. However, when the diameters of the workpieces are relatively small (e.g., less than I00 millimeters), the difference between the rotational speeds while a workpiece moves lengthwise at a first and second speed is substantial so that such workpieces are preferably treated in machines of the type shown in FIGS. 1 to 6 wherein the rotational speed of a next-following workpiece is preferably caused to match that of the preceding workpiece immediately before or at the time the two workpieces meet upstream of the straightening station.

The machine of FIG. 7 can be modified by replacing the pump 87 with an adjustable electromagnetically operated valve which can temporarily change the rate of oil delivery to the

motors

91, 91A in response to signals from the detector 8.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A method of feeding elongated workpieces, such as tubes or rods, to and through a treating station, especially a straightening station, comprising the steps of rotating a first workpiece about its axis and simultaneously conveying the workpiece lengthwise along a predetermined path toward and through said treating station so that the workpiece moves through the treating station at a first speed; introducing into said path a second workpiece so that the leading end of said second workpiece is spaced from the trailing end of said first workpiece while such trailing end is still located upstream of said treating station; conveying said second workpiece lengthwise at a second speed which exceeds said first speed so that the leading end of said second workpiece at least closely approaches the trailing end of said first workpiece upstream of said treating station; and reducing the speed of said second work piece from said second to said first speed and thereafter conveying said second workpiece through said treating station at said first speed.

2. A method as defined in claim I wherein said first speed is variable and further comprising the step of changing said second speed as a function of variations of said first speed.

3. A method as defined in claim 1, further comprising the step of rotating said second workpiece about its axis during lengthwise movement at said first and second speeds.

4. A method as defined in claim 1, further comprising the steps of producing a signal in response to movement of the leading end of said second workpiece beyond a predetermined portion of said path, and utilizing such signal to decelerate said second workpiece from said second to said first speed.

5. A method as defined in claim 1, further comprising the step of accelerating said first workpiece upon completed transport of the trailing end of said first workpiece beyond said treating station so that the trailing end of said first workpiece moves away from the leading end of said second workpiece.

6. A method as defined in claim 1, wherein said second workpiece is introduced into said path by moving sideways.

7. In a machine for straightening or analogous treatment of elongated workpieces, such as metallic rods or tubes, a combination comprising a treating unit having means for rotating successive workpieces about their own axes and for advancing such workpieces lengthwise at a first speed; and a feeding apparatus for supplying successive workpieces to said treating unit, said apparatus comprising advancing means for advancing successive workpieces lengthwise along a predetermined path at a second speed exceeding said first speed so that the leading end of a next-following workpiece which is introduced into said path with a delay following the introduction of preceding workpiece catches up with the trailing end of the preceding workpiece, and for thereupon advancing such next-following work piece at said first speed so that the next-following workpiece enters said treating unit at least substantially simultaneously with lengthwise movement of the preceding workpiece beyond said treating unit.

8. A combination as defined in claim 7, wherein said advancing means comprises a pair of concave advancing rollers, motor means for rotating said rollers about their respective axes, holder means for maintaining said rollers in positions of contact with a workpiece therebetween so that the axes of said rollers are inclined with reference to the axis of such workpiece whereby the workpiece is caused to move lengthwise and to rotate about its own axis, and adjusting means for changing the inclination of the axes of said rollers to thereby change the speed of lengthwise movement of the workpiece which is engaged by said rollers.

9. A combination as defined in claim 8, wherein said adjusting means comprises fluid-operated motor means for turning said holder means about axes which are at least substantially normal to the axes of workpieces in said path.

10. A combination as defined in claim 9, wherein each of said fluid-operated motor means comprises a double-acting cylinder and piston unit actuatable to turn the respective holder means and the associated roller about the corresponding axis.

11. A combination as defined in claim 10, further comprising signal generating detector means adjacent to said path between said unit and said apparatus and arranged to produce signals for actuation of said cylinder and piston units in response to detection of predetermined portions of successive workpieces.

12. A combination as defined in claim 11, further comprising electromagnetically operated valve means arranged to control the actuation of said cylinder and piston units in response to signals from said detector means.

13. A combination as defined in claim 11, wherein said detector means comprises at least one inductance.

14. A combination as defined in claim 7, wherein said advancing means comprises a pair of conical rollers, holder means for maintaining said rollers in positions of contact with a workpiece therebetween so that the axes of said rollers are inclined with reference to the axis of the workpiece therebetween, motor means for rotating said rollers whereby the rotating rollers cause the workpiece therebetween to rotate about its own axis and to move lengthwise toward said treating unit, and adjusting means for changing the speed of said motor means to thereby change the speed of lengthwise movement of the workpiece which is engaged by said rollers.

15. A combination as defined in claim 14, wherein said motor means comprises a discrete fluid-operated motor for each of said rollers, variable-delivery pump means for supplying a pressurized fluid to said motors, and means for changing the rate of fluid delivery by said pump means.

16. A combination as defined in claim 15, wherein said means for rotating the workpieces in said treating unit comprises a plurality of straightening rolls and motor means for rotating at least one of said rolls, said pump means receiving motion from said last mentioned motor means.

17. A combination as defined in claim 7, wherein said treating unit comprises a plurality of concave straightening rolls and first motor means for rotating at least one of said rolls, said advancing means comprising a pair of concave advancing rollers, second motor means for rotating said advancing rollers, and means for changing the speed of said second motor means as a function of changes in the speed of said first motor means.

18. A combination as defined in claim 7, further comprising a source of workpieces and transfer means for delivering successive workpieces from said source into said path at predetermined intervals.

19. A combination as defined inclaim 7, wherein said advancing means comprises a pair of rotary concave advancing rollers located at the opposite sides of a predetermined portion of said path and means for moving at least one of said advancing rollers away from and toward said path to thus permit entry of a fresh workpiece into said path when said one roller is moved away from said path.

20. A combination as defined in claim 7, further comprising means for accelerating successive workpieces downstream of said treating unit.

*3 I: t l i

Claims

1. A method of feeding elongated workpieces, such as tubes or rods, to and through a treating station, especially a straightening station, comprising the steps of rotating a first workpiece about its axis and simultaneously conveying the workpiece lengthwise along a predetermined path toward and through said treating station so that the workpiece moves through the treating station at a first speed; introducing into said path a second workpiece so that the leading end of said second workpiece is spaced from the trailing end of said first workpiece while such trailing end is still located upstream of said treating station; conveying said second workpiece lengthwise at a second speed which exceeds said first speed so that the leading end of said second workpiece at least closely approaches the trailing end of said first workpiece upstream of said treating station; and reducing the speed of said second workpiece from said second to said first speed and thereafter conveying said second workpiece through said treating station at said first speed.

2. A method as defined in claim 1 wherein said first speed is variable and further comprising the step of chaNging said second speed as a function of variations of said first speed.

7. In a machine for straightening or analogous treatment of elongated workpieces, such as metallic rods or tubes, a combination comprising a treating unit having means for rotating successive workpieces about their own axes and for advancing such workpieces lengthwise at a first speed; and a feeding apparatus for supplying successive workpieces to said treating unit, said apparatus comprising advancing means for advancing successive workpieces lengthwise along a predetermined path at a second speed exceeding said first speed so that the leading end of a next-following workpiece which is introduced into said path with a delay following the introduction of preceding workpiece catches up with the trailing end of the preceding workpiece, and for thereupon advancing such next-following workpiece at said first speed so that the next-following workpiece enters said treating unit at least substantially simultaneously with lengthwise movement of the preceding workpiece beyond said treating unit.

19. A combination as defined in claim 7, wherein said advancing means comprises a pair of rotary concave advancing rollers located at the opposite sides of a predetermined portion of said path and means for moving at least one of said advancing rollers away from and toward said path to thus permit entry of a fresh workpiece into said path when said one roller is moved away from said path.