US3809907A - Calender roll apparatus with device for controlling the thickness of the bank of material in front of the rolling gap - Google Patents

Abstract

A device for controlling the bank of viscous material in front of the nip of a pair of calender rolls comprises a source of coherent radiation which is trained, across a surface of the rolling bank turned away from the nip, toward a receiver sensitive to such radiation so that a growth of thickness of the rolling bank obstructs the receiver and produces one signal condition while excessive reduction in the size of the bank creates a second signal condition whereby the calendering operation is regulated. The source of coherent radiation is preferably a laser beam while the receiver is a photocell arrangement juxtaposed with the source which is oscillated to sweep the beam angularly or is reciprocated at high frequency to reciprocate the beam in a plane generally perpendicular to the plane of the roll axes.

Description

United States Patent 1191 Schuller etal.

1111 3,809,907 1451- May 7, 1974 [75] Inventors: Reinhard Schuller; Heinz Kopsch,

both of Munich, Germany [73] Assignee: Krauss-Maflei AG, Munchen,

Germany [221 Filed: Aug. 7, 1972 21 Appl. No.: 278,438

[30] Foreign Application Priority Data Aug. 20, 1971 Germany 2141741 [52] U.S. 250/219 TH, 356/160, 250/219 LG [51] Int. Cl. G0lb 7/04 [58] Field 0I'Search.,250/2l9 WD,-219TH,219 DR, 250/219 S, 219 LG, 222 R; 356/l5616 1, 163, 167; 72/DIG. 4

[56] References Cited UNITED STATES PATENTS 3,518,441 6/1970 Selgin ..250/2l9Tl-1X 3,588,513 6/1971 Akamatsu 250/2l9DF s l\ 1 I 54 A11 H1962 Bailey 250/219 TH 3,037,156 5/1962 Koulikovitch..... 250/235 X 3,600,591 8/1971 Thier 250/219 DF 3,659,950 5/1972 Troll 'et al 250/219 S Primary Examiner-Walter Stolwein Attorney, Agent, or Firml(arl F. Ross; Herbert Dubno [5 7 ABSTRACT A device for controlling the bank of viscous material in front of the nip of a pair of calender rolls comprises a source of coherent radiation which is trained, across a surface of the rolling bank turned away from the nip,

toward a receiver sensitiveto such radiation so that a growth of thickness of the rolling bank obstructs the receiver and produces one signal condition while excessive reduction in the size of the bank creates a second signal condition whereby the calendaring operation is regulated. The source of coherent radiation is preferably a laser beam while the receiver is a photoa cell arrangement juxtaposed with the source which is oscillated to sweep the beam angularly or is reciprocatedat high frequency to reciprocate the beam in a plane generally perpendicular to the plane of the roll axes. 1

10 Claims, 6 Drawing Figures PATENTED MY 7 I974 SHEET 2 [1F 3 PATENTEDHAY H914 3,809,907

SlllEl 3 [1F 3 Phofocell 15 I50 LWWJ' Operclror W x Fig. 6 ff v l5c l Roll-speed control Roll-position control Roll -be ndin colnlrol Stripperplate control CALENDER ROLL APPARATUS WITH DEVICE FOR CONTROLLING THE THICKNESS OF THE BANK OF MATERIAL IN FRONT OF THE ROLLING GAP FIELD OF THE INVENTION The present invention relates to calendering apparatusand, more-particularly, to a calender-roll arrangement providedwith a device for monitoring the thickness of the bank of viscous material collecting ahead of the nip or gap between the rolls, and feeding through the latter to form a foil or band.

BACKGROUND OF THE INVENTION gap. As it is well known in the production of synthetic resin (thermoplastic) foils, wherein a layer of a pasty or doughy substance is received from a roll-type mill at a thickness controlled by the position of a stripper blade, the viscous material forms a layer, band, strip or foil as it ispassed between two rolls or through a series of roll ing nips or gaps such that the foil emerges from the final nip or gap at the desired thickness. Ahead of the nip or gap, there accumulates a mass of the viscous materials, having generally a bulbous cross-section converging toward the nip, which is termed the bank and constitutes a supply of the pasty material entering the gap. Within the bank, the viscous material may circulate until it enters the gap and, when the bank is too thick, such movement often carries the viscous materials away from the nip for a period sufficient to cause cooling. This substantially reduces the quality of the final foil.

On the other hand, when the bank becomes too thin or fails altogether, the foil is disrupted and the calender rolls. may come into contact with one another, thereby size of the bank of material built up ahead of the nip or I OBJECTS'O F THE INVENTION It is the principal object of the present invention to provide an improved calender-roll apparatus, especially for the calendering of viscous synthetic resin, whereby the aforedescribed disadvantages are obviated. A

Another object of the invention is to provide a calender-roll apparatus with an improved system for controlling the calendering operation in accordance with the condition of the bank of viscous materials built up ahead of the nip or gap.

Still another object of the invention is to provide a sensingdevice for the bank of viscous materials ahead of the nip of a pair of calendering rolls which will be less sensitive to environmental and other potentially interfering influences associated with the calendering of viscous materials to produce bands or foils that has been thecase heretofore and which also is highly accurate, has a short response time and does not detrimen tally affect the bank.

SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are attained in accordance with the present invention in a system for the calendering of viscous manalcondition in the event of excessive reduction in the size (thickness) of the bank and a second signal condition in response to the maintenance of a satisfactory the bank to remain in an excessively thick condition with consequent reduction in the quality of the product.

Efforts to avoid these disadvantages have included continuous monitoring by operating personnel by visual observation which is not always satisfactory because the response time of the observer may be excessive if it is desired to protect against elimination of the bank with calender rolls operating at high speed. In another effort to avoid this disadvantage, the bank was sensed by a roll engaging the bank surface opposite the nip. This contact-type sensor, however, has the drawback that it adversely affects the bankand hence the quality of the resulting foil.

Systems which are incapable of preventing elimination of the bank. and direct contact of the calendering surfaces of the'rolls with each other are of little value since contact of the calendering rolls with each other causes such damage as requires time consuming and expensive repair of the surfaces.

thickness of the bank or an increase in the thickness beyond a desired level, the signal conditions operating control means determining the rate at which the viscous materials traverses the calendering ,roll arrangement and hence restoring the bank or otherwise modifying the calendering operation, eg by preventing the rolls from coming into contact with one another.

In other words, the present invention makes use of a sensor for monitoring the size or thickness of the bank in the form of a parallel beam of coherent radiation, preferably from a laser source which provides a contactless detection of the thickness of the bank of viscous materials and controls the regulators for the calendering operation to maintain an optimum bank thickness while preventing the rolls from coming into contact with one another.

When the beam of coherent radiation is a laser or like luminous beam, the receiver disposedat the end of the roll assembly opposite thesource maybe a photodetector (photo-cell) and the nondivergent or columnated beam is preferably trained along the surface of the bank turned. away'from the rolling gap or nip and generally along a path parallel to the axis of the rolls.

The beam is either screened by the bank from the receiver so that no voltage output is derived or is permitted to reach the receiver without interruption by the bank (as in the case of an excessively small bank thickness) whereby a voltage signal is generated by the receiver.

Advantageously, the device for monitoring the thickness of the bank is so arranged on the roll support stands that the beam glances along thesurface of the bank in its optimum thickness. A signal is thus produced when the bank thicknessfalls below the optimum and no signal is produced when the bank thickness exceeds the optimum.

The signals generated by the receiver are applied to a controller which can increase or decrease the width of the nip or rolling gap and therefore the amount of material retained in the bank or drawn therefrom in accordance with whether the signal voltage is obtained or not, thereby maintaining a substantially constant thickness of the bank. Should the signal remain over a predetermined time period, whose length is depended uponthe rolling speed, the rolls may be brought to a standstill or backed away from each other to prevent contact. An acoustic signal or optical signal may. also be operated to alert responsive personnel. The time interval can be determined by a time delay relay and the correction of the bank failure condition can be accomplished by modifying the thickness of the layer of viscous materials delivered to the calender rollers (e.g. by controlling the position of a stripper blade, by controlling the roll adjustment devices etc.).

While the system of the present invention, for monitoring the bank of viscous material ahead of the nip or gap of the calendering rolls is somewhat more complex with respect to irregularities in the bank, by comparison with mechanical sensing systems, it is possible to compensate for such local distortions of the bank by oscillating and/or reciprocating the source of the coherent radiation as will become apparent hereinafter.

The use'of a beam or columnar nondivergent) coherent radiation has a significant advantage in that, because of its sharp delineation and high intensity, it is not materially affected by the plasticizer vapors which form in the region of the bank of viscous materials and practically is transparent to the monitoring beam. in other words, no error or substantial signal reduction results from the presence of the cloud of plasticizer vapor around the bank of viscous material when a laser source is applied.

It has been found to be advantageous, both for rapid response to changes in the condition of the bank of viscous material ahead of the roll gap and for convenience in signal processing, to impart a high-frequency angular oscillation or high-frequency parallel reciprocation, or both, to the monitoring beam of coherent radiation in a plane which is substantially perpendicular to the plane of the roll axes, while the receiver, sensor or detector has an elongated sensitive zone extending along this plane.

The high-frequency angular oscillation thus causes the beam to sweep across the length of this sensitive zone and, when the latter comprises a plurality of photocells connected in parallel, generates a pulse train of constant frequency and amplitude provided that the beam is not intercepted by the bank of viscous material. When this output pulse train is integrated over each sweep to and fro across the sensitive zone, the resulting pulses have a duration and, consequently, an average voltage level which is inversely proportional to the thickness of the bank. in fact, the loss of signal from the unobstructed-path condition is a precise measurement of the thickness of the bank.

The resulting signal, which continuously varies in accordance with the thickness of the bank, increases the information available for the process controller, facilitates a rapid response to deviations of the bank thickness from its set point value and provides, if desired, a

digital output which can facilitate process regulation by output of the photocell arrangement, generally after differentiation thereof to permit differential control or rate control responses, to operate any of the several devices associated with the calerider assembly for restoring the bank to its optimum condition. For example, the material feed to the roll gap can be increased by adjusting the spacing of the stripper blade arrangement of a roll mill ahead of the calendering roll, may vary the gap width of the calendering rolls, or may otherwise modify the rate at which material is fed to the bank and through the calender gap to maintain the-optimum bank thickness.

The circuitry associated with the system, according to the present invention, should be designed so that the system has two signal conditions to which thecontroller responds, namely, an output condition in which a voltage is generated of a suff cient level to operate the controller and indicates a failure or diminution of the bank and a no-output condition in which the bank is of satisfactory width.

When the beam is reciprocated parallel to itself in a plane perpendicular to the plane of the axes through the calendering rolls, it is possible to provide a system in which the output voltage is not excessively dependent upon the thickness of the bank and it is also possible to avoid excessive spacing between the beam and the gap.'Each change in the thickness of the bank produces an output which is thus independent of the distance of the monitoring beam from the rolls at the instant the output is generated. The parallel reciprocation of the beam has also the advantage that a change in the set-point value of the bank thickness does not require a mechanical shifting of the laser source or detector, it being merely necessary to introduce an altered set-point signal into the circuitry which can include a comparator.

According to a further feature of the invention, the oscillation of the beam can be carried out by angularly displacing the laser source about an axis parallel to the plane of the axes of the rolls or by reflecting the beam from the source with an oscillatable mirror. In place of an oscillatable mirror, the angular oscillation of the beam may be effected by a rotary polygonal mirror arrangement, a rotary prism or other beam-deflecting means. The parallel reciprocation may make use of an actual mechanical displacement of the source although it also may employ a shiftable' beam deflector, e.g. an angularly displaceable radiation-transparent refractive plate having parallel optical surfaces. v

The oscillation frequency is so selected that it exceeds the possible frequency of alteration of the bank thickness although a lower frequency may be also used, it being merely necessary to provide a substantial difference between the oscillation frequency and the fre quency at which the bank thickness varies.

Since, during starting of the calender rolls, no bank is present at the rolling gap, it has been found to be desirable to provide means for controlling the gap width until the bank is formed, thereby preventingthe rolls from coming into direct contact with oneanother. To this end, a pair of coherent-radiation (laser) beams are projected through the roll gap at each end of the rolls, the beams being intercepted by respective receivers (photocells) and being connected to the process controller'for regulating the gap by operation of the conventional roll-adjustment means or like. A switch is provided between these gap-monitoring devices and the bank-monitoring device for operation by hand or automatically in response to buildup of the bank, for cutting off the gap monitors and cutting in the bank monitor when the bank has reached a satisfactory thickness.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the presentinvention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a partial perspective view, in diagrammatic form with parts broken away, of a vertical calendering roll apparatus provided with a system for monitoring .bank thickness according to the invention;

FIG. 2 is a diagrammatic perspective view of a system for angularly oscillating the monitoring beam in accordance with an embodiment of the invention;

FIG. 3 is a view similar to FIG. 2 of an embodiment for the high-frequency parallel reciprocation of the beam;

FIG. 4 is a view similar to FIG. 2 of an embodiment in which other means is employed to achieve parallel reciprocation of the beam;

FIG. 5 is a view similar to FIG. 1 showing the gapmonitoring means; and

FIG. 6 is a block circuit diagram illustrating another feature of the invention.

SPECIFIC DESCRIPTION 6 ing optimal bank thickness. The set-point input is shown, by way of example, to be a variable resistor 2b in FIG. 6.

The controller 7 for the calendering process may have a number of outputs including an output 7a for regulating roll speed, an output 7b for adjusting the roll position, an output 7c for controlling the roll-bending device, an output 7d for operating the stripper plate of the millfeeding the viscous material to the calender apparatus andan output 7e constituting an acoustic or optical alarm.

The coherent radiation source also comprises, as illustrated in FIG. 1, a drive 8 for angularly oscillating the beams 5 through an anglea at a high frequency, e.g. of the order of kHz whereby the oscillating plane is perpendicular to the plane of the axes of the rolls.

The beam thus sweeps across the sensitive zone 6 and is of band-like configuration. When the sensitive zone 6 comprises a multiplicity of photocells 2a connected in parallel, the detector 2 includes an integrator, the system generates a pulse train of constant frequency having a mean voltage output. This differs from the .case in which the beam either impinges upon the receiver or is obstructed, whereby the output values are either zero or the maximum amplitude. The mean output of the system illustrated in FIGS. 1 and 6, however, varies between zero with an excessively thick bank and a maximum corresponding to disappearance of the bank. The set-point value corresponds to an average voltage level. Since the zone at which the beam encounters the receiver is substantially a point, the travel of this point can be used to generate a pulse train whose pulse duration is inversely proportional to the bank thickness. j 7

From FIG. 2, it will be apparent, that the lasermay be fixed and optical means can be employed for imparting the oscillation to the beam. In this case, the optical means is a .mirror 9 driven by an oscillating motor whose pumping circuitry and associated apparatus has not been illustrated, is mounted upon the other roll support not illustrated) while a photocell arrangement 2, constituting the detector, is carried by the roll-' journaling structure represented at 3. The beam of coherent radiation shown at 5, is trained along the surface of the bank 4 of viscous material turned away from the rolling gap.

The sharply columnated beam 5 from the radiation source 1 is trained upon the elongated sensitivity zone 6 of the detector 2, the sensitivity zone lying generally in a plane perpendicular to the plane of the axes of the roll 53 and 54, between which the bank of viscous material feeds to form the synthetic-resin foil.

The detector 2 may comprise a plurality of photocells connected in parallel to a control circuit 7 as represented at 2a in FIG. 6. The system 2 may also include an integrator from the output of the parallel-connected photocells 2a, a differentiator having the integrated signal as its input, and a comparator for comparing the detected bank thickness with a set-point value representabout an axis perpendicular to the plane of oscillation. FIG. 3 shows a system in which the laser 1 is shifted to and fro with the beam parallel to itself bya crankdrive 10, a similar motion of the beam being obtained by the use of a transparent plate 11 having planar andparallel incident and radiation surfaces. The beam is refracted through the plate to an extent determined by the angle so that angular oscillation of the plate by a motor of the type described in-connection with element 8 in FIG. 1, will generate a planar sweep of the beam parallel to it self.

In FIG. 5, there is shown the vertical calender arrangement of FIG. 1 with the bank monitor omitted to enable the positions of the gap-monitoring system to be seen with greater clarity. This system comprises a pair of coherent radiation sources 12, e.g. lasers, mounted adjacent opposite ends of the rolls and projecting coherent beams 14 through the gap betweenthe rolls. The cross-section of the beams 14' is so selected that during movement of the rolls together during starting Should the rolls approach too closely, controller 7 responds to terminate advance of the rolls. The switch has a further contact 150 which connects the detector 2 with a-sw'itch operator l6 responding to the buildup of the bank to operate the switch and close the contacts 15d which applies the output of detector 2 to the controller 7 as already described. The switch may also be operated by hand.

We claim:

1. A calendering apparatus comprising at least two closely juxtaposed calendering rolls having a nip defining a gap between them and rotatable to produce a band from viscous material forming a bank thereof ahead of said gap; and a device for monitoring the thickness of said bank in a plane substantially perpendicular to the plane of the axes of the rolls, said device comprising a coherent-radiation source projecting a collimated beam of radiation substantially along but adjacent to said gap and interceptable by said bank and a detector disposed opposite said source and responsive to variations in a radiation in a plane substantially perpendicular to the plane of the axes of the rolls for producing an output representing the condition of said bank.

2. The apparatus defined in claim 1 wherein said source is a laser disposed at one end of said rolls and said detector includes photocell means disposed at the opposite ends of said rolls along said gap whereby said beam extends substantially parallel to the axes of said rolls along the surface of said bank away from said gap.

substantially perpendicular to the plane of the axes of said rolls, said detector having an elongated sensitive zone lying in said plane of oscillation.

4. The apparatus defined in claim 3 wherein said beam is oscillated by reflecting it from a surface and angularly oscillating said surface.

5. The apparaus defined in claim 2, further comprising means for reciprocating said beam parallel to itself in a plane perpendicular to the plane of the axes of said rolls, said detector having an elongated sensitive zone lying in the plane .of reciprocation of said beam.

6. The apparatus defined in claim 5 wherein said means for reciprocating said beam includes a radiationtransparent plate having planar mutually parallel incident and refraction surfaces.

7. The apparatus defined in claim 2, further comprising gap-monitoring means respective to the separation between said rolls, a calendering-process controller and switch means for selectively connecting said detector and said gap-monitoring means to said controller.

8. The apparatus defined in-claim 7 wherein said gapmonitoring means includes a source of coherent radiation at each end of said rolls training respective beams through said gap and respective photocells arrnagements intercepting the last-mentioned beams on the opposite sides of said gap.

9. The apparatus defined in claim 8, further comprising means responsive tosaid detector for automatically operating said switch upon buildup of said bank.

10. The apparatus defined in claim 9, further comprising means for switching said laser beam in a plane perpendicular to the plane of the axes of said rolls, said detector having an elongated sensitive zone lying in the plane of said beam.

Claims (10)

1. A calendering apparatus comprising at least two closely juxtaposed calendering rolls having a nip defining a gap between them and rotatable to produce a band from viscous material forming a bank thereof ahead of said gap; and a device for monitoring the thickness of said bank in a plane substantially perpendicular to the plane of the axes of the rolls, said device comprising a coherent-radiation source projecting a collimated beam of radiation substantially along but adjacent to said gap and interceptable by said bank and a detector disposed opposite said source and responsive to variations in a radiation in a plane substantially perpendicular to the plane of the axes of the rolls for producing an output representing the condition of said bank.

2. The apparatus defined in claim 1 wherein said source is a laser disposed at one end of said rolls and said detector includes photocell means disposed at the opposite ends of said rolls along said gap whereby said beam extends substantially parallel to the axes of said rolls along the surface of said bank away from said gap.

3. The apparatus defined in claim 2, further comprising means for oscillating said beam angularly in a plane substantially perpendicular to the plane of the axes of said rolls, said detector having an elongated sensitive zone lying in said plane of oscillation.

4. The apparatus defined in claim 3 wherein said beam is oscillated by reflecting it from a surface and angularly oscillating said surface.

5. The apparaus defined in claim 2, further comprising means for reciprocating said beam parallel to itself in a plane perpendicular to the plane of the axes of said rolls, said detector having an elongated sensitive zone lying in the plane of reciprocation of said beam.

6. The apparatus defined in claim 5 wherein said means for reciprocating said beam includes a radiation-transparent plate having planar mutually parallel incident and refraction surfaces.

7. The apparatus defined in claim 2, further comprising gap-monitoring means respective to the separation between said rolls, a calendering-process controlleR and switch means for selectively connecting said detector and said gap-monitoring means to said controller.

8. The apparatus defined in claim 7 wherein said gap-monitoring means includes a source of coherent radiation at each end of said rolls training respective beams through said gap and respective photocells arrnagements intercepting the last-mentioned beams on the opposite sides of said gap.

9. The apparatus defined in claim 8, further comprising means responsive to said detector for automatically operating said switch upon buildup of said bank.

10. The apparatus defined in claim 9, further comprising means for switching said laser beam in a plane perpendicular to the plane of the axes of said rolls, said detector having an elongated sensitive zone lying in the plane of said beam.

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