GB2074761A

GB2074761A - Control of roll gap

Info

Publication number: GB2074761A
Application number: GB8112978A
Authority: GB
Original assignee: Buehler AG
Current assignee: Buehler AG
Priority date: 1980-04-30
Filing date: 1981-04-28
Publication date: 1981-11-04
Also published as: DE3016786C2; GB2074761B; DE3016786A1; CH654223A5; FR2481610A1

Abstract

An automatic control system is provided for regulating the roll gap between at least two parallel cooperating rolls 15, 16 of a multiple roll mill, especially for processing chocolate and pigments, in which the roll gap can be changed by means of hydraulic piston- in-cylinder devices 33 and by changing the temperature of the rolls. A predetermined roll pressure and roll gap are selected for the rolling task in hand and the roll gap is held constant by adjusting the cooling and/or heating of the rolls, by control of the flow of water to sprays 22, which changes the temperature thereof and the viscosity of the product passing through the mill in response to an inductive gap width transducer 31. If insufficient control is available in this way the rolling pressure is varied to restore the roll gap to the desired value. By changing over a switch 32 the system alternatively controls the temperature of the water in response to a temperature sensor 28. <IMAGE>

Description

SPECIFICATION A method and apparatus for regulating the gap width between at least two cooperating rolls in a multiple roll mill The invention relates to a method of regulating the gap width between at least two parallel cooperating rolls in a multiple roll mill which contain variable intensity heating and/or cooling apparatus and which can be clamped together or moved apart from one another by means of hydraulic piston-incylinder arrangements which are arranged between adjacent ends of the rolls and are subjected to a control pressure.

Multiple roll mills of this kind generally have from three to five rolls and serve to crush, disperse, mix, homogenize etc. pasty masses such as a mass of chocolate. Such multiple roll mills can also be used to process printing dies, paint colourings, pigment dispersions, crayon compositions, coating compositions, toilette soap, confections etc.

The hydraulic piston-in-cylinder arrangements at the end faces of the rolls make it possible to select a specific gap width or a specific rolling pressure individually for each side of the roll.

Arrangements are known in which such rolls are predominantly cooled or, in special cases, heated in order to be able to match them in an ideal manner to the temperature of the material to be processed. By way of example the cooling or heating of rolling mills is necessary when using such multiple roll mills in the pigment and chocolate industries. In the known arrangements thermostatic temperature control is used to hold the rolls at a specified and constant temperature.

As a rule each roll is equipped with a thermostatic temperature control system which is set manually to a predetermined temperature. The known system is disadvantageous because of the relatively large deviation between the desired and actual temperatures and also because of the low water pressure from 0.8 to 1.8 bar together with the thereby resulting lowthroughputofwaterand pressure strength of the water jet. Temperature control is made difficult because, in a five roll mill for example, five desired temperature values must be adjusted if it is desired to carry out a change of the temperature level. The known temperature control system is in particular not suited to automation.

The invention is now based on the problem of providing a method of the initially named kind in which the gap width between at least two rolls of the multiple roll mill is controlled by means of the temperature. The invention thus starts from the recognition that the ideal rolling pressure, which depends on the camber ground on the rolls, is the controlling factor in achieving a product of optimum quality. It is also important for the attainment of an ideally processed product that the layer thickness during processing has a predetermined desired value and remains as far as possible constant.

In order to solve this problem the invention envisages that a predetermined rolling pressure and roll gap are selected for the rolling task in hand, that on change of the gap width during the rolling process the intensity of cooling and/or heating is first adjusted, without changing the rolling pressure, in the sense of restoring the predetermined gap width and, if the range of variation of the intensity of cooling and/or heating is not sufficient, that the rolling pressure is changed to produce or restore the predetermined gap width.

Thus, in accordance with the invention, the roll temperature is first of all changed in order to maintain the roll gap, and thus the thickness of the material layer, constant. Because an increasing gap width is caused by the viscosity of the material being too high, i.e. by the material being too cool it is necessary in this case to bring about an increase in temperature. Conversely, the temperature has to be lowered when the gap width falls below the desired gap width. The rolling pressure control is, in accordance with the invention, only switched on when the range of variation of the temperature change of the rolls is no longer sufficient, i.e. the rolling pressure is increased when the gap width is too large and vice versa.

For a normally adjusted machine both the gap width and also the temperature and rolling pressure will initially remain constant. On the occurrence of changes of the gap width brought about by the material being processed the temperature is first of all changed in the above described manner. If this is not sufficient then changes of the rolling pressure are used in addition.

The control proposed in accordance with the invention is not only directed to holding the roll gap constant but is instead additionally directed toholding the temperature constant. With uniformly softened material and constant material characteristics the gap width will in any event remain constant.

With temperature fluctuations and changes of the material characteristics the gap width changes and this is compensated for by the closed loop temperature control proposed by the invention.

The temperature range of the rolls can preferably be changed between 15 and 65"C and in exceptional cases up to 1500C.

In a rolling mill with more than two rolls all the roll gaps should be jointly adjusted in dependence on a reference input from the temperature of one of the rolls. The temperatures of the rolls which follow and/or precede the roll from which the reference temperature is derived are then successively changed by a predetermined fixed amount.

The invention also relates to an apparatus for carrying out the method of the invention. This apparatus is characterized in that a gap width transducer is connected to both a temperature controller and also, via a switch device, to a pressure controller for the rolling pressure, in that the temperature controller reduces the intensity of cooling or raises the roll temperature when the gap width increases and vice versa and in that, on exceeding or falling below the- predetermined temperature control range, a minimum-maximum detection stage of the temperature controller closes the switch device and thus initiates the control of the rolling pressure.

In this arrangement the hydraulic piston-in cylinder arrangements provided at the end faces of the rollers can each be connected to a main pressure source with their clamping chambers being individually connected to the main pressure source via fixed, pre-adjusted pressure reducing valves and the release chambers can be connected to the main pressure source via a common counterpressure reduction valve. This arrangement is advantageous because in this way the pressures in the clamping chambers can be initially set to a predetermined ideal maximum value in the works of the manufacturer whereas, in operation, it is only necessary to adjust the one counterpressure reduction valve.A particularly simple pressure control results if, in accordance with a particularly preferred embodiment, the counterpressure reduction valve is connected via a servodrive to the closed loop pressure controller.

In order to produce, one the one hand, a start-up without overshoot and, on the other hand, a complete regulation without permanent control deviation during steady state operation the closed loop temperature controller should, in accordance with a preferred embodiment, be a PDPl closed loop controller.

It is particularly advantageous for a start-up circuit stage to be provided in the closed loop temperature controller with the start-up circuit stage switching off the cold water supply and switching on a warm water supply at the start of operation until the rolls have heated up.

In order to be able to control the temperature of each ro!l there is provided, in accordance with a specially preferred embodiment of the invention, an arrangement in which each roll has a temperature controller with an adjustable, desired temperature input with one controller serving as the master temperature controllerforthe reference temperature.This arrangement is preferably so contrived that a temperature difference adjustment stage is arranged before each of the slave temperature controllers, with a temperature signal from the master temperature controller also being passed to the temperature difference adjustment stage which adds or subtracts the temperature difference and the reference temperature, and with the output signal being passed as a desired temperature signal to the further temperature controller to which the actual temperature signal from the associated roll is supplied, with the output of this temperature controller forming the cooling control signal. In this manner desired temperature differences can be preselected between the remaining rolls and the temperature of the temperature controlled master roll.By adjusting the reference temperature the temperatures of the remaining rolls will then likewise be adjusted while retaining the preselected differences in temperature.

Thus the overall temperature ievel of the remaining rolls with the predetermined differences in temperature can be changed in simple manner using the master temperature controller and the associated desired value input for the control temperature.

It is readily possible to change over from the fuily automatic control of temperature and gap width to a semi-automatic control when the master temperature controller is controlled manually as a desired valve input in place of the gap width transducer.

The roll gap can be measured to an accuracy of the order of magnitude of 1 CL by means of an inductive displacement transducer and carrier frequency measurement amplifier or by means of a layer thickness measurement apparatus. The roll temperature or rolling pressure can then be fully automatically controled in accordance with the change of the roll gap. If the roll gap approaches the value zero the automatic control takes over the function of the dry run safety mechanism so that, in operation, metallic contact of the rolls can be avoided.

The control system of the invention has the following advantages when compared with thermostatic temperature control: The electrically or electronically controilable temperature regulator has a PDPI control characteristic.

The permissable water pressure can amount to a maximum of 10 bar. As the arrangement is electricaily steplesslyvariable it is also possible to carry out a semi-automatic roll temperature control with only one desired value input for from 2 to 5 rolls. In addition a fully automatic roll temperature control can be carried out by measurement of the roll gap width or of the layer thickness.

The invention will now be described in the foilowing by way of example and with reference to the drawing the single figure of which shows a schematic illustration of the apparatus of the invention for regulating the gap width and/or the temperature of the rolls of a multiple roll mill.

In the drawing there are shown, in schematic form just two rolls 15, 16, their rotational axes 14', 14" and their support bearings. The rolls and their roll necks are hollow and thus provide a passage way for a conduit 21 for heating or cooling water. Bores 21 are provided in the top of the conduit 21 within the rolls 15, 16 so that water jets 23 can spray upwardly onto the inner walls of the rolls 15, 16. A bath of cooling water 24 forms in the lower half of the roll 15. The excess water flows away out of the side opening of the roll 15 at 25. A water supply of this kind is provided in each of the rolls of the multiple roll mill.

The water conduit 21 is connected to two solenoid valves 26, 27 which are respectively supplied with cold water K and hot water W. Of the two solenoid valves 26, 27 one is open at any one time whereas the other is closed. The two solenoid valves 26, 27 are controlled by a switching stage 17b within the temperature regulation circuit.

The controller 17 is a PDPI closed loop controller and the actual temperature of the roll 15 as measured by a temperature sensor 28 is supplied to the control input 1 of the controller. The temperature controller 17 is also supplied with a desired temperature signal T15 from a desired value input 20 following closing of the switch 32.

A temperature control signal ST1, which is applied to a control slide 30 in the manner described further below, is created at the output of the temperature controller.

An actual value signal representative of the temperature of the second roll 16 is supplied from a temperature sensor 28' in this roll to the control input 2 of a further PDPI closed loop controller 17'.

A temperature signal T1 from the PDPI closed loop controller 17 is applied to a temperature difference adjustment stage 34. The stage 34 forms by choice either the sum or the difference of the preselected temperature difference At and the guide temperature signal T1. The outputT2s represents the desired temperature signal for the second roll 16. This signal is passed to the second PDPI closed loop controller 17'.

The output signal ST2 of the closed loop controller 17' is supplied to a control slide similar to the control slide 30 in a manner not illustrated in detail in the drawing.

Further PDPI closed loop controllers can be provided in completely analogous manner in the event that any further rolls are provided and each individual roll can be adjusted to have a freely selectable, desired difference from the master temperature T1. The master temperature controller 17 does not have to be arranged at the first roll but can instead be associated with any desired roll inside the multiple roll mill.

The control output ST1 of the temperature controller 17 is, as stated, applied to the control slide 30 which covers over to a greater or lesser degree the cross-section of the water conduit 21 in response to the signal ST1 in such a way that the temperature of the roll 15 can be regulated to a predetermined desired value. This desired value can be input into the master temperature controller 17 by the desired value input of signaller 20. If the control range of the control slide 30 is not sufficient to hold the selected desired temperature constant the solenoid valves 26, 27 can, if necessary, be switched over in order for example to feed warm water W into the water conduit 21 in place of the cold water K. This is necessary in particular at the start of operation of the multiple roll mill.

In the drawing the desired input 20 is connected via a tandem switch 32 to the closed loop controller 17. In the illustrated position the tandem switch 32 separates the desired value input 20 for the temperature from the closed loop controller 17 and connects instead a gap width transducer 31 with the input of the closed loop temperature controller 17.

The gap width transducer is inserted between two or more rolls or takes the form of a layer thickness measuring apparatus. On an increase in the size of the gap width the gap width transducer activates the temperature controller 17 in the sense that the temperature of the roll is increased and vice versa. In this manner the gap width is held constant.

The pressure at which two or more rolls can be clamped together is determined by a hydraulic piston-in-cylinder arrangement 33 which is provided between the bearings of the two rolls. The clamping chamber 11 a of the piston-in-cylinder arrangement 33 is connected via an individual pressure reducing valve 13a which is capable of fine adjustment to a main pressure source P. The clamping chambers 11 b, 1 Ic, 1 it, ... of further piston-in-cylinder arrangements 33 provided at the other end faces of the rolls are likewise connected to the main pressure source P via the correspondingly designated connections in the drawing and further individual pressure reduction valves 13b, 13c, 13d, ... which are capable of fine adjustement.The optimum or maximum pressure values in the individual piston-in-cylinder arrangements 33 are previously set in the manufac turer'sworks by means of the pressure reducing valves 13.

The release chambers 12a, 12b, 13c, 12d of the piston-in-cylinder arrangements 33 which can be subjected to pressure during separation of the rolls and of which only one is illustrated in the drawing are however jointly connected to the main pressure source P via a single counterpressure reduction valve 14. By an adjustment of the counterpressure reduction valve 14 by means of a servo drive 29 the roll pressures at all sides of the rolls can be uniformly changed.

In this way it is possible, with one closed loop pressure controller 19 to change all the roll pressures by a single adjustment step. This can, for example, take place manually by means of a rotatable selection knob 42. Using this rotational selection knob the roll pressures are ideally adjusted for any specific material which is to be processed.

During automatic control the closed loop pressure controller is however additionally connected via an electronic switch 18 to the gap width transducer 31.

The electronic switch 18 is in turn connected with a minimum-maximum detection stage 17a of the closed loop temperature controller 17. The electronic switch 18 closes when the temperature range of the temperature controller 17 is exceeded or not attained.

As soon as this is the case the control slide 30 remains in one of its extreme positions and the gap width is controlled to the desired value as a result of the closed loop pressure controller 19 becoming active.

As soon as the temperature has changed again so that it lies within the control range of the closed loop temperature controller 17 the switch opens again so that operation can continue with the constant preselected roll pressure and the gap width is now once again held constant only by the closed loop temperature controller 17.

The described apparatus for regulating the material infeed conditions and/or the gap width in a hydraulic multiple roll mill can be used with particular advantage in a hydraulic multiple roll mill as is described in the simultaneously filed patent application entitled "hydraulic multiple roll mill". The disclosure of the parallel application (German Patent Application P 30 16785.2 is hereby also made the subject of the present application.

Claims

1. A method of regulating the gap width between at least two parallel cooperating rolls in a multiple roll mill which contain variable intensity heating and/or cooling apparatus and which can be clamped together or moved apart from one another by means of hydraulic piston-in-cylinder arrangements which are arranged between adjacent ends of the rolls and are subjected to a control pressure, characterized in that a predetermined rolling pressure and roll gap are selected for the rolling task in hand and in that, on change of the gap width during the rolling process, the intensity of cooling and/or heating is first adjusted, without changing the rolling pressure, in the sense of restoring the predetermined gap width, and in that, if the range of variation of the intensity of cooling and/or heating is not sufficient, the rolling pressure is changed to produce or restore the predetermined gap width.

2. A method in accordance with claim 1 and characterized in that the temperature range of the cooling and/or heating means of the rollers (15, 16) can be varied between 15 and 150"C and preferably from 15 to 65or.

3. A method in accordance with claim 1 or claim 2 and characterized in that the reference input for the roll temperature can be specified at each roll (e.g.

roll 15).

4. A method in accordance with one of the preceding claims in a roll mill with more than two rolls, characterized in that all the roll gaps can be jointly adjusted in dependence on one roll temperature.

5. A method in accordance with claim 3 or claim 4 and characterized in that the temperatures of the rolls following or preceding the roll at which the reference temperature is measured are successively changed by a selectable, predetermined, fixed amount and are preferably increased.

6. Apparatus for carrying outthe method of one of the preceding claims, characterized in that a gap width transducer (31) is connected to a temperature controller (17) and also, via a switch device (18), to a pressure controller (19) for the rolling pressure, that the temperature controller (17) reduces the intensity of cooling or raises the roll temperature when the gap width increases and vice versa and that, on exceeding or falling below the predetermined temperature control range, a minimum-maximum detection stage (17') of the temperature controller (17) closes the switch device (18) and thus initiates the control of the rolling pressure.

7. Apparatus in accordance with claim 6 and characterized in that the hydraulic piston-in-cylinder arrangements (33) provided at the end faces of the rollers are each connected to a main pressure source (P) with their clamping chambers (11 a, b, c, d) being individually connected to the main pressure source (P) via fixed preadjusted pressure reducing valves (13a, bc, d) and the release chambers (12a, b, c, d) being connected to the main pressure source (P) via a common counterpressure reduction valve (14).

8. Apparatus in accordance with claim 6 and claim 7, and characterized in that the counterpressure reduction valve (14) is connected via a servodrive (29) to the pressure controller (19).

9. Apparatus in accordance with one of the claims 6 to 9 and characterized in that the temperature controller is a PDPI controller (17) and that each roll has a PDPI controller of this kind with desired value adjustment.

10. Apparatus in accordance with one of the claims 6 to 9 and characterized in that a start-up circuit stage (17b) is provided in the temperature controller (17) with the start-up circuit stage switching off the cold water supply (K) and switching on a warm water supply (W) at the start of operation until the rolls (15, 16) have heated up.

11. Apparatus in accordance with one of the claims 6 to 10 and characterized in that each roll (15, 16) has a temperature controller (17, 17') with an adjustable desired temperature input and with one controller (17) serving as the master (or guide) temperature controller for the reference temperature (T1).

12. Apparatus in accordance with claim 11 and characterized in that before each of the slave (or guide) temperature controllers (17') there is arranged a temperature difference adjustment stage (34) to which a temperature signal (T1) from the master (or guide) temperature controller (17) is also passed and which adds or subtracts the temperature difference and the reference temperature, and in that the output signal (T2s) is passed as a desired temperature signal to the further temperature controller (17') with the actual temperature signal of the associated roll (16) being passed to this temperature controller (17') and with the output (ST2) forming and heating or cooling control signal.

13. Apparatus in accordance with one of the claims 6 to 12 and characterized in that the master (or guide) temperature controller (17) has a desired value input (20) on which a signal of the gap width transducer (31) can be superimposed.

14. A method substantially as herein described with reference to the accompanying drawing.

15. An apparatus substantially as herein described with reference to the accompanying drawing.