Conveyor unit

A conveyor unit for conveying a web of material, in particular for conveying a web of corrugated board in a corrugating machine, comprises a machine frame; a delivery roller, which is lodged in the machine frame rotatably about a first axis of rotation; a drive for actuation of the delivery roller; a draw roller, which is lodged in the machine frame rotatably about a second axis of rotation, the first axis of rotation and the second axis of rotation being substantially parallel to each other, a nip for the web of material to pass through being formed between the delivery roller and the draw roller, the draw roller having a draw-roller-surface coefficient of friction which is selected so as to ensure power transmission from the draw roller to the web of material that rests thereon, and the delivery roller having a delivery-roller-surface coefficient of friction which is less than or equal to the draw-roller-surface coefficient of friction; and a torque transmission arrangement, which acts between the delivery roller and the draw roller for transmission of torque from the delivery roller to the draw roller, a free-wheel being disposed between the torque transmission arrangement and the draw roller.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a conveyor unit for conveying a web of material, in particular for conveying a web of corrugated board in a corrugating machine.

2. Background Art

Conveying a web of corrugated board at a given velocity and accelerating the web to a certain velocity is of major importance in a corrugating machine so as to ensure that given portions of the web of corrugated board reach the processing devices to the moment. Upon changes of format in the lengthwise cutting and grooving unit, individual portions of the web must be accelerated for a gap to be produced, big enough to allow renewed positioning of the cutting tools. Conveyor units exist for conveying a portion of a web of corrugated board at a pre-determined velocity; they comprise a driven pair of rollers between which the web of corrugated board is passed. Permanent actuation of both rollers causes a comparatively high degree of wear.

SUMMARY OF THE INVENTION

It is an object of the invention to embody a conveyor unit for webs of material which will deliver the web of material with lowest possible wear.

This object is attained in a conveyor unit for conveying a web of material, in particular for conveying a web of corrugated board in a corrugating machine, comprising a machine frame; a delivery roller, which is lodged in the machine frame rotatably about a first axis of rotation; a drive for actuation of the delivery roller; a draw roller, which is lodged in the machine frame rotatably about a second axis of rotation, the first axis of rotation and the second axis of rotation being substantially parallel to each other, a nip for the web of material to pass through being formed between the delivery roller and the draw roller, the draw roller having a draw-roller-surface coefficient of friction, which is selected so as to ensure power transmission from the draw roller to the web of material that rests thereon, and the delivery roller having a delivery-roller-surface coefficient of friction, which is less than or equal to the delivery-roller-surface coefficient of friction; and a torque transmission arrangement, which acts between the delivery roller and the draw roller for torque transmission from the delivery roller to the draw roller, a free-wheel being disposed between the torque-transmission arrangement and the draw roller. The gist of the invention resides in providing the conveyor unit with a bottom delivery roller which is constantly actuated by a drive. A draw roller of a high coefficient of friction is provided, which is coupled with the delivery roller via a torque transmission arrangement with a free-wheel. The transmission ratio of the torque transmission device is selected such that the free-wheel acts when the velocity of the web of corrugated board, and thus the rotational speed of the draw roller, falls short of a pre-determined value.

Additional features and details of the invention will become apparent from the ensuing description of an exemplary embodiment, taken in conjunction with the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The corrugating machine1, part of which is seen inFIG. 1, is described below as seen in the conveying direction2. A web of corrugated board3is supplied by a heating and pulling device4. The heating and pulling device4has a continuous drivable hold-down belt5which cooperates with a table6to define a nip7in which to compress the web of corrugated board3. The heating and pulling device4is followed by a cross cutter8for cross-wise severing the web of corrugated board3.

Disposed downstream of the cross cutter8is a lengthwise cutting and grooving unit9. In this lengthwise cutting and grooving unit9, grooves and longitudinal cuts, inclusive of a marginal cut, are applied to the web of corrugated board3. Downstream of the lengthwise cutting and grooving unit9, provision is made for a conveyor unit10, which will be described in detail in the following and which serves for specific conveyance of the web of corrugated board3when the actual velocity vB(actual) thereof falls short of a nominal velocity vB(nominal). Downstream of the conveyor unit10, provision is made for a shunt11, dividing up various parts of the web of corrugated board3along two tables12and then supplying them to a double cross cutter13where the strips of corrugated board are cut into individual sections. In a wider sense, the term conveyor unit10means a unit which conveys a web of material or, possibly, sections of a web of material. It is also conceivable that several webs of material are conveyed side by side. Conveyor units in corrugating machines also imply automatic cutting and grooving machines.

The following is a description of the detailed structure of the conveyor unit10, taken in conjunction withFIGS. 2to4. The conveyor unit10comprises a machine frame14with lateral vertical walls15and16which are parallel to each other. Disposed between the walls15and16is a horizontal delivery roller17which is perpendicular to the conveying direction2and has two journals18,19projecting on each end; the journals18,19are run on bearings20,21in the walls15and16rotatably about an axis of rotation22. The delivery roller17is a hollow roller with a jacket23to each end of which are fixed the journals18,19. The jacket23is made of metal, in particular steel. The coefficient of static friction μ between the surface of the delivery roller17and a web of paper is in the range of 0.05≦μ≦0.25, in particular μ≈0.15.

Above the delivery roller17, a draw roller24is run on bearings25,26for rotation about an axis of rotation27. The bearings25and26are mounted on the walls15and16by arms28. The draw roller24has a shaft29which extends from the bearing25to the bearing26and on which several rolls30are mounted, which are spaced apart axially. The rolls30are made of plastic material, in particular rubber, having a cylindrical surface31. The draw-roller-surface coefficient of friction is selected so as to ensure power transmission from the roll30, and thus from the draw roller24, to the web of corrugated board3. Consequently, the draw-roller-surface coefficient of friction is considerably greater than the delivery-roller-surface coefficient of friction. The coefficient of static friction μ between the surface of the draw roller24and a paper web is approximately 0.6≦μ≦0.8, in particular μ≈0.7. Formed between the draw roller24and the delivery roller17is a nip32through which passes the web of corrugated board3while bearing against both the delivery roller17and the draw roller24. The rolls30have uniformly distributed laminae33, which extend substantially radially outwards and are closed in the radial direction. It is also possible to use solid rolls30without laminae33. The axes of rotation22and27are parallel to each other.

A driving motor34is mounted on the wall15; it is connected for torque transmission via a belt drive35to a pulley36. The pulley36is joined to the journal18. A gearwheel37is mounted on the journal18in vicinity to the pulley36. The delivery roller17, the pulley36and the gearwheel37are rotary about a common axis of rotation22. Above the gearwheel37, a driving shaft40, which is rotary about an axis of rotation39, is run on a bearing38in the wall15. On its left end inFIG. 2, the driving shaft40has a gearwheel41which is connected to the driving shaft40and engages with the gearwheel37. The opposite end of the driving shaft40is joined to an articulated shaft42, the other end of which is again connected to the shaft29. A free-wheel43is disposed between the gearwheel41and the driving shaft40. The free-wheel43is a commercial free-wheel, allowing the gearwheel41to rotate in one sense relative to the driving shaft40and blocking it in the other sense. The axes39and27are parallel to one another and misaligned.

The following is a description of the mode of operation of the conveyor unit10. During trouble-free conveyance, the web of corrugated board3has a nominal velocity vB(nominal) within the conveyor unit10. The web of corrugated board is primarily pulled through units downstream of the conveyor unit10and possibly accelerated. The delivery roller17is driven by the driving motor34, the belt drive35and the pulley36so that it has a tangential rotational speed vTin the vicinity of the nip32and an associated angular velocity ωT. The delivery roller17is run at a higher speed i.e., the tangential rotational speed vTexceeds the nominal velocity vB(nominal) of the web of corrugated board3. vT/vB(nominal)>1 applies, in particular vT/vB(nominal)>1.01 and, by special advantage, vT/vB(nominal)>1.04. The draw roller24has a tangential rotational speed vZ(nominal) and an associated angular velocity ωZ(nominal), with vZ(nominal)≈vB(nominal) i.e., the rolls30travel substantially free from slippage on the web of corrugated board3. Consequently, the angular velocity of the driving shaft40is also ωZ(nominal). The gearwheel41is constantly driven by the gearwheel37, with the transmission ratio being selected such that, if the web of corrugated board3is conveyed at the velocity vB(nominal) and the driving shaft40has the angular velocity ωZ(nominal), no torque is transmitted from the gearwheel41to the driving shaft40; consequently, the free-wheel43allows free relative rotation. This has the advantage that upon trouble-free conveyance of the web of corrugated board3at the desired velocity vB(nominal), the rolls30are not driven and the wear of these rolls30is considerably reduced as compared to a situation in which the rolls30are permanently driven.

If for example a change of format in the lengthwise cutting and grooving unit9occasions a drop in velocity of the web of corrugated board3in the conveyor unit10and thus malfunction, an actual velocity vB(actual) of the web of corrugated board3ensues, which is less than the nominal velocity vB(nominal). The delivery roller17, which is tightly joined to the driving motor34, continues to run with slippage at a tangential rotational speed vTwhich exceeds the nominal velocity vB(nominal) of the web of corrugated board3. However, the draw roller24that rests on the web of corrugated board3slows down so that another tangential rotational speed vZ(actual) and an associated angular velocity ωZ(actual) result, to which applies: vZ(actual)≈vB(actual)<vB(nominal). The gearwheel41is driven by the gearwheel37at a speed that is independent of the velocity of the web of corrugated board3. Due to the reduction in velocity of the web of corrugated board3, the angular velocity of the driving shaft40decreases. The transmission ratio of the gearwheels37and41is selected such that, if the ratio a that the actual velocity vB(actual) bears to the nominal velocity vB(nominal) undershoots a pre-determined threshold aLIMand the angular velocity of the driving shaft40undershoots a certain threshold, the free-wheel takes action and the shaft29is driven by the driving motor34. The following applies to aLIM: aLIM<1, aLIM≦0.99 and, by special advantage, aLIM≈0.98. It is important that aLIMis in a range outside the customary fluctuation of the conveying velocities vB(nominal) during troublefree operation. This is intended to prevent the free-wheel43from being permanently switched on and the shaft29from being driven in the case of usual fluctuations in the conveying velocity of the web of corrugated board3. Apart from wear symptoms, this would result in the system building up. If the fluctuations in velocity of the web of corrugated board3in trouble-free operation are in the range of approximately 1 percent, then it is reasonable that the drive of the draw roller24is switched on when the velocity of the web of corrugated board3falls short by more than 2 percent, corresponding to a factor aLIM=0.98. If the fluctuations in velocity of the web of corrugated board3in trouble-free operation are inferior, aLIMmay be in a range closer to 1, for example aLIM=0.99. If the fluctuations are greater, aLIMmust be in a range more remote from 1.

A special advantage of the conveyor unit10resides in that no electronic control is required. In trouble-free operation the draw roller24is not actuated, its wear being comparatively low. If the velocity of the web of corrugated board3falls short of a pre-determined threshold, torque is exerted by the driving motor34via the free-wheel43on the draw roller24which continues to convey the web of corrugated board3at least at the given limit velocity. This is important for example in case of a change of format in the corrugating machine1. For the change of format to be put into practice, the web of corrugated board3is cut through by the cross cutter8. The portion of the web of corrugated board3that is upstream of the cross cutter8is accelerated so that a gap is produced for the lengthwise cutting and grooving unit9. This gap is needed for renewed positioning of the cutting tools in the unit9. If the gap is too small, because the portion of the web of corrugated board had not been delivered rapidly enough, the renewed positioning of the tools must be disrupted, which produces a back-up. The corresponding delivery of the section of the web of corrugated board is implemented by the conveyor unit10, which pulls the portion of the web of corrugated board out of the unit9. It is also possible to dispose the conveyor unit upstream of the unit9, which is roughly outlined by the reference numeral10′.