COOLANT FLOW CONTROL

Abstract: A method and apparatus for controlling the temperature of a machine tool (e.g. mill rolls (7, 8)). A coolant or lubricant is fed from a header supply (22) to the primary inlet (21) of a fluidic device (20) such as a vortex valve. The outlet (23) of the fluidic device (20) is directed to or at the machine tool (7, 8). A second flow (36) of coolant or lubricant from reservoir (25) is fed to the control inlet (30) of the fluidic device (20) the second flow (36) being controlled via a feedback signal (27) and valve (26) to vary the second flow (36) in response to workpiece shape or temperature so that the total outflow from the outlet (23) of coolant or lubricant can be varied. The second flow (36) may be at a temperature which differs from that of the first flow so that as the flow rate from outlet (23) to the workpiece rises the temperature of the coolant or lubricant falls.

Description: TITLE: COOLANT FLOW CONTROL FIELD OF THE INVENTION The present invention relates to means for supplying a coolant or lubricant to a tool or a work piece. The invention is applicable for supply of a coolant or lubricant to a mill roll. The term "tool" is used broadly in this specification to include a mill roll as well as machine tools and the term work piece includes ingots, strip and other forms of workpiece. BACKGROUND ART In rolling mills such as are used for production of high quality rolled flat metal strip, any variation in temperature over a work roll surface may cause differential radial expansion of the mill roll, referred to as thermal camber, and thus result in transverse variations in thickness and flatness of the rolled product. Control of strip flatness (shape) requires maintenance of mill roll thermal camber within close tolerances. Variations in the transverse thickness profile during rolling may cause non-uniform lengths to be produced at different locations across the strip width and these result in a non-uniform transverse stress distribution which may cause buckling. When rolling under tension, the buckling usually does not occur and a shapemeter then measures the transverse stress variation which is interpreted as the tendency to subsequent buckling (or bad shape) . It is usual to provide at least one row of spray nozzles through which a coolant and/όr lubricant is applied to the roll surface. Usually the nozzles are disposed in three or more transverse zones, the nozzles in each zone being supplied with fluid at a pressure which differs from each other zone. The flow rate of coolant through the pressure supplied to each zone of nozzles, or through each individual nozzle, is adjusted to control roll expansion and/or level of lubrication to suit the current rolling requirements. The latter' depend in a complex manner upon mill loads, roll deflections and ground profiles, workpiece thickness and temperature profile and roll bending settings. It has been practiced to locate a shape meter downstream of the mill roll and to use feedback signals indicative of strip shape variation to control thermal camber in the roll. The shape meter is adapted to measure variations in the transverse stress and/or temperature distribution in the product resulting from rolling, including the effect of mill roll distortion. The measurements are made at a plurality of points in the product width direction. Each spray nozzle may then be provided with a separate valve and the shape meter may be used for generating feedback signals to control individual valves. Individual valves are controlled to provide a greater flow rate of coolant to parts of the mill roll or work piece which are excessively hot or have more radial expansion than is desirable. In this way, variations in thermal distortion and consequent variations in strip shape, may be minimized. On-off control, rather than analogue control, of valves is often used to reduce the complexity of communication interfaces between automation equipment and the valve actuators and to reduce valve costs, variable flow being achieved by use of multiple valves of different sizes in each zone and/or by varying the ratio of "on-time" to "off-time". Known systems for roll shape feedback control utilize a large number of electric or pneumatically controlled valves which must be operable in an extremely hostile environment and are consequently each of costly construction. The valve nozzles are susceptible to blockage and because one blocked valve nozzle could result in roll overheating, it is usual to have a redundant set of "stand-by" valves and to stop the line if a severe blockage occurs. An object of the present invention is the provision of means for supplying a coolant or lubricant to a mill roll or other tool or work piece which avoids at least some of the disadvantages of the prior art. DISCLOSURE OF THE INVENTION According to one aspect the invention consists in a method for controlling the temperature of a tool or workpiece comprising the steps of: (a) providing a first flow of a coolant or lubricant to the primary inlet of a fluidic device; (b) providing a second flow of a coolant or lubricant to the control inlet of a fluidic device; (c) conducting the outflow from an outlet of said fluidic device to said tool or workpiece; and (d) controlling the flow rate of the second flow whereby to control the flow rate of said coolant or lubricant provided to said tool or workpiece. In preferred embodiments of the invention at least a portion of the spent coolant or lubricant after extraction of heat is recycled to the primary inlet. Also for preference, the temperature of the coolant or lubricant provided to the primary inlet of the fluidic device differs from that provided to the control inlet. A preferred fluidic device for use in the invention is a vortex valve. The invention will herein be described primarily with reference to a vortex valve as the fluidic device but it will be understood that all fluidic devices operating in a similar manner may be substituted for vortex valves. The fluid supplied to the primary inlet may be at a different concentration from the fluid supplied to the control inlet. This configuration enables a different concentration of lubricant to be used selectively on individual headers or, if required, for individual nozzles. The latter facility has advantages in that it allows the edge regions of a hot strip rolling mill to be preferentially lubricated with major advantages in wear reduction and without excessive contamination of the coolant system by lubricant. Use of a vortex valve allows excellent mixing to be achieved and, at the same time, provides variable control over the concentration. A vortex valve may be used in the manner described to achieve effective mixing of rolling oils with a recirculating coolant system. A high pressure control flow should then be used to ensure maximum turbulence in the exit region of the vortex valve. Desirably, two valves are used at each location across the work roll of a rolling mill, one valve for selectively applying lubricant and the other valve to selectively apply coolant so as to control the roll expansion, thereby maintaining a more constant strip thickness profile and reducing the amount of customary edge thickness tapering in the region up to 200 mm from the strip edge. BRIEF DESCRIPTION OF DRAWINGS Various embodiments of the invention will now be described by way of example only with reference to Figures 1 to 5 wherein: Figure 1A is a schematic plan view of a vortex valve for use in the invention. Figure IB shows the valve of Figure 1A in schematic elevation, Figure 2 is a graph useful for illustrating characteristics typical of a vortex valve such as shown in Figure I wherein exit flow is shown on the upright axis and control flow pressure is shown on the horizontal axis, and Figure 3 is a schematic diagram of an embodiment of the invention. Figures 4 and 5 show schematically a configuration -which may optionally be used in the embodiment of Figure 3. DESCRIPTION OF PREFERRED EMBODIMENTS With reference to Figure 1, there is shown a vortex valve comprising a generally cylindrical conical or frustro conical valve chamber 1 having a primary inlet 2 which is radially directed; a control inlet 3 which is tangentially directed in a direction transverse primary inlet 2; and having an outlet 4 which preferably extends in an axial direction. In the absence of a flow through the control inlet 3, a primary flow admitted to valve chamber 1 via primary inlet 2 exits from outlet 4. If a control flow is admitted through control inlet 3 at a high pressure in comparison with the primary flow, the exit flow from the outlet 4 is reduced. Figure 2 is a graph showing total flow (L/min) on the vertical axis 5 and control pressure (kPa) on the horizontal axis 6 for a typical vortex valve operating with main supply pressure equal to 100 kPa. The vortex valve to which Figure 2 applies has a chamber 1 of 50 mm diameter, an inlet tube 2 of 12.5 mm diameter and a single entry control flow tube 3 of 2.6 mm diameter. As shown by the graph, the total flow at outlet 4 reduces as a function of increase in the control flow and approaches a minimum flow. Vortex valves per se are well known in many designs or configurations and require no further description. With reference to Figure 3 there is shown schematically one embodiment of the invention. The embodiment shows a stand of a strip mill having a top roll 7 and a bottom roll 8. There is further provided a vortex valve 20 having a primary inlet 21 adapted to receive coolant from a header supply 22 via a primary flow pump 28. The outlet 23 of valve 20 is adapted either to spray directly onto a mill roll 7 or preferably is conducted to a respective spray nozzle 24 directed at roll 7. A second flow 36 of coolant is fed to control inlet 30 of vortex valve 20 by means of pump 29 from a secondary supply reservoir 25 at a flow rate which may be varied by means of a control valve 26 which is electrically or pneumatically operated by a respective feedback control signal 27 from a shape meter (not shown in Figure 3) located downstream of the mill rolls. The shape meter generates a signal 27 indicative of a change in the flatness or stress distribution of rolled strip on a line in the strip rolling direction corresponding with the position of nozzle 24 with respect to the mill roll 7. In use feedback signal 27 operates control valve 26 to increase or decrease control flow from reservoir 25 to " vortex valve control inlet 30. If " the control flow 36 to valve inlet 30 increases, the total flow of coolant from that vortex valve outlet 23 to the mill roll 5 decreases. In a preferred embodiment the control flow coolant at 30 is at a higher temperature than the primary flow coolant at 21. Hot coolant which is spent after cooling the m ll rolls is pumped from sump 40 by a pump 41 through a heat exchanger 31 whereby waste heat is extracted and the resultant cold coolant is returned via line 32 to header supply 22. A fraction of the hot coolant is taken off at 35 between pump 41 and heat exchanger 31, passed through a filter 33 and relieved via line 34 to secondary supply reservoir 25 from which the control flow emanates. Consequently when the control flow into inlet 30 is at a maximum, the flow rate of coolant from outlet 23 is not only at a minimum but is at a maximum temperature, consisting predominantly of hot coolant. As the control flow of the hot fluid into inlet 30 is reduced the flow rate of cold coolant increases, the proportion of hot control flow in the outflowing mixture is reduced and the temperature of the outflow from outlet 23 falls. The system thus utilizes both a change in flow rate, and a change in temperature of the coolant to control the roll temperature. In practice a plurality of nozzles 24 are disposed in a row extending the width of the top roll and/or of the bottom roll. Each nozzle of the plurality is in communication with the outlet 23 of a corresponding one of a plurality of vortex valves 20. The control flow of each vortex valve 20 is varied by means of a corresponding respective control valve 26, or if desired a group of vortex valves 20, may be controlled by a shared control valve 26. More than one nozzle 24 may be fed from a vortex valve. Thus, for example, an upper and corresponding lower roll nozzle 25 may both be fed by one vortex valve outlet 23; or by separate vortex valves controlled by a single control valve 26; or by separate vortex valves 20 each under the control of a respective control valve 26. The control valves may be of an analogue type controlled by signals from a shape meter or similar transducer or may be an of/off valve, the- ratio of "on-time" to "off-time" being influenced by the feed back signals. Similarly, if a transverse ^ temperature distribution for the roll or rolled product is measured, instead of the strip shape, then it may be controlled in a similar manner to that described above for strip shape control. Thus the control signal may be provided by a temperature transducer or other transducers For preference in case of maintenance, and to provide a better environment for the control valves, the on-off control valves are located away from the headers at the side of a mill. A pump provides a high pressure supply of filtered control fluid with a common supply being available to all stands. Typically about 10% of the total coolant flow is used for control. In some instances, for example, if different fluid temperatures are involved, higher control flow fractions may be advantageous. The control signal flows are preferably diverted by flexible armoured hydraulic cables provided with quick release couplings. For preference the connection of fluid control signals to individual vortex valves is accomplished by means of a distribution disc located at one or both ends of each flexible control flow cable. This enables the number of control valves to be minimised. It also allows the number of control signals in the flexible cables to be minimised whilst maintaining a standard design of header in which each vortex valve is individually connected to the distribution disc at the point where the control cable connects to the header. The distribution discs have channels or grooves which provide an arbitrary connection between the inlet control ports and the outlet ports to the vortex valves. Advantages of the system include that a greatly reduced number of control valves is required for a given degree of control since more than one spray nozzle can be controlled by each vortex valve and since less than half the number of control valves is needed in comparison with conventional headers since redundancy is unnecessary. The vortex valves may be adapted for automatic unblocking of valves and nozzles, for example my means of a counter flow and filter system involving the reduction. of the primary supply pressure and increasing the control pressure to maximum. This can cause a reversal of the primary flow and unblocking of the inlet pipe or inlet filters on the primary supply. The system is able to operate with low pressure valves and to use a standardized modular design for all widths of roll. The system has no moving parts and is less susceptible to blockage. A minimum flow is guaranteed under ail normal operating conditions. Surprisingly we have found that when the fluid from outlet 4 of a vortex valve is directed through a "V" slot or similarly shaped nozzle, the emanating spray may be changed from fan-shaped spray envelope to a conical-shaped spray envelope depending on the control flow and other factors. This characteristics is controlled by varying the distance from the point where the outlet flow leaves the conical chamber to the spray nozzle. The longer the distance, the less rotational swirl remains in the flow at the spray nozzle and the less tendency there is to form a conical shape of envelope ("conical spray"). This means that, when the control flow is off, the fluid emerging from the nozzle will have a low angular momentum and little tendency to form a conical spray for the case of a "V" jet. However, when the control flow is applied, the spray characteristic will change to that of a conical spray. This characteristic may be utilized in two ways. Firstly, it may be used to generate conical-shaped sprays without the complexity and blockage tendencies of special-purpose nozzles of conventional design. Secondly, by interposing a plate containing a carefully sized slot, between the nozzle and the roll or workpiece, additional flow rate variations are possible. This is achieved by locating the nozzle close to the vortex chamber exit to maximise the tendency to form a conical spray shape. Therefore, when the control flow is at a maximum, the normally fan-shaped spray which passes through the slot when the control flow is off is converted to a conical spray which impinges on the interposed plate and little, if any, flow goes to the- roll or workpiece. By this means, the effective control range of the roll cooling or lubricating device is effectively increased significantly. With reference to Figure 4 and Figure 5 a shield or plate 40 defining a slotted apperture 42 is shown with impinging sprays from a "V" jet nozzle 41 for the cases of control flow on (Figure 4), and control flow off (Figure 5) . Figure 4 shows how with control flow to valve 20 off a major proportion of the fan-shaped spray passes through slot 42 and impinges on roll 7. In Figure 5, the control flow to valve 20 is "on", the spray is conical and the major proportion of the conical-shaped spray is unable to pass through the narrow rectangular slot 42. The use of conical spray shapes and associated, modified coolant droplet characteristics also alters the heat transfer coefficient between the coolant and the roll and may be used to advantage in particular applications of the technology. Because vortex valves store angular momentum when the control flow is "on" the valve has "inertia" and thus a lower frequency pulse rate may be used when achieving modulated flow with a defined on-time and off-time ratio. Although the invention has herein been described with particular reference to vortex valves, other suitable fluidic valves having an equivalent operation may be substituted therefor. As will be apparent to those skilled in the art from the teaching hereof, the invention may be applied in other embodiments and in other forms without departing from the concept hereof and such embodiments or forms are deemed to be within the scope hereof.

Claims: CLAIMS : 1. a method for controlling the temperature of a tool or workpiece comprising the steps of: (a) providing a first flow of a coolant or lubricant to the primary inlet of a fluidic device; (b) providing a second flow of a coolant or lubricant to the control inlet of a fluidic device; (c) conducting the outflow from an outlet of said fluidic device to said tool or workpiece; and (d) controlling the flow rate of the second flow whereby to control the flow rate of said coolant or lubricant provided to said tool or workpiece. 2. A method according to claim 1 wherein at least a portion of the spent coolant or lubricant after extraction of heat is recycled to the primary inlet. 3. A method according to claim 1 or claim 2 wherein the temperature of the coolant or lubricant provided to the primary inlet differs from that provided to the control inlet. 4. A method according to any one of the preceding claims wherein the fluid supplied to the primary inlet is a coolant or lubricant at a different concentration from the coolant or lubricant fluid supplied to the control inlet. 5. A method according to any one of the preceding claims wherein the fluidic device is a vortex valve. 6. A method according to claim 1 wherein two fluidic devices are used, one of said devices selectively applying lubricant and the other selectively supplying coolant. 7. A method according to any of the preceding claims wherein the tool is the work roll of a rolling mill. 8. A method according to claim 7 wherein the flow rate of the second flow is controlled in response to a signal indicative of a change in the flatness or stress distribution of the workpiece during rolling. 9. A method according to any one of the preceeding claims wherein a fluidic device is controlled to selectively apply lubricant in the vicinity of edges of a workpiece being rolled. 10. A rolling mill for working a rolled product comprising a fluidic device having a primary inlet adapted to receive pressurized fluid from a first supply of coolant or lubricant, means for directing fluid from an outlet of the fluidic device to a roll of the mill and/or the product, means for providing a second flow of pressurized fluid from the same or another supply to a control " flow inlet of the fluidic device whereby to vary the flow of liquid from said device outlet, and means for varying the secondary flow to compensate for variation in a property of the roll or of the rolled product. 11. A rolling mill according to claim 10 wherein the second flow is at a different temperature from the first fluid received at the primary inlet. 12. A rolling mill according to claim 10 wherein the second flow is at a concentration different from the fluid received at the first inlet. 13. A rolling mill according to claim 10 further comprising a shape meter for generating a signal indicative of change in the flatness or stress distribution of rolled strip and a control valve responsive to the signal for varying said secondary flow. 14. A rolling mill according to any one of the preceding claims wherein the fluidic device is a vortex valve 15. A rolling mill comprising a first fluidic device according to claim 10 adapted to supply a coolant and a second fluidic device according to claim 10 for supplying a lubricant. 14. Apparatus substantially as herein described with reference to Figure 3. 15. A method according to claim 5 further comprising the step of directing the outflow through a nozzle and changing the shape of the envelope of spray emanating from the nozzle by changing the control flow. 16. A method according to claim 15 further comprising the step of interposing an appertured shield between the nozzle and the workpiece, the appertured shield permitting a high proportion of the spray to pass the shield at one shape of spray envelope and a lower proportion to pass at another shape of spray envelope. 17. A method substantially as herein described with reference to Figure 3. 18. A method substantially as herein described with reference to Figures 4 and 5. 19. Apparatus substantially as herein described with reference to Figure 3.

Inventors: EDWARDS WILLIAM JOHN, EDWARDS, WILLIAM, JOHN
Applicants: EDWARDS WILLIAM J, EDWARDS, WILLIAM, JOHN
Application year: 1988
Main classification: B21B27
IPC codes: B21B27, B21B37, B21B45, B23Q11, F16N7