US2655060A - Hydraulic driving means for winding and rolling machines - Google Patents

Description

Oct. 13, l953 A. SPENCER ETAL HYDRAULIC DRIVING MEANS FOR WINDING AND ROLLING MACHINES 3 Sheets-Sheet l Filed March 3, 1948 mO-A I /NVENTUQ ARTHUR sPENc'R um Oct. 13, 1953 A SPENCER ETAL 2,655,06()

HYDRAULIC DRIVING MEANS FOR WINDING AND ROLLING MACHINES Filed March 3, 1948 5 Sheets-Sheet 2 Oct. 13, 1953 A. SPENCER ET AL 2,655,060

HYDRAULIC DRIVING MEANS FOR WINDING AND ROLLING MACHINES Filed March 5, 1948 5 Sheets-Sheet 3 FIGB.

ARTHUR x ENMWJW' E W17 Wi w AGENTS Patented Oct. 13, 1953 HYDRAULIC DRIVING MEANS FOR VVINDING AND ROLLING MACHINES Arthur Spencer and John Hewitt, London, England, assignors to Vickers-Armstrongs Limited, London, England, a British company Application March 3, 1948, Serial No. 12,848 In Great Britain March 19, 1947 4 Claims.

This invention relates to hydraulic rolling machines for rolling metal and metal alloy strips or stock by feeding the material between rolls from one drum to another, the material being drawn between the rolls of the mill when passing from one drum to the other, so that in one direction of operation one of the said drums acts as a coller-on drum and the other as a'coilingoff drum. An object of the present invention is to provide a reversible mill for rolling metal strips or stock having a hydraulic pump serving a motor for each drum and providing independent hydraulic drive therefor so that it is possible to operate any single drive to facilitate threading in of the work.

Another object of the present invention is to ensure maintenance of the operative pressure across each pump and motor and the compensation for changes in diameter of the coil buildup to be made by adjusting the hydraulic unit.

Another object of the present invention is to provide a mill in which the pressure on the work is governed by a servo unit and thereby obviate the disadvantages of relying upon lease Valves for this purpose.

Another object of the present invention is to provide in conjunction with a reversible hydraulic rolling mill means which responds accurately to a signal from the pressure side across each pump and associated motor to correct the strokes iof the motors to maintain in such motors a constant pressure and in which the said means has a derivative control which reduces any tendency for the hydraulic pressure to surge f and further acts on the strokes ofithe motors stroke of the i pressure rey y tratmg embodiments thereof, and wherein:

strip adjusts itself automatically to the process by reason of the fact that the torque cannot be applied until there is a re-action of the process.

VA still further object of the present invention is to provide a reversible rolling mill in which,

in addition to the means driving the rolls there drums can act as a `(miler-,011 andthe other as r to said drum and to maintain a substantially constant horse power in the motor driving said drum.

In addition to the foregoing, an object of the present invention is to control the stroke of the hydraulic motors positively by a pair of hydraulic fluid pressure actuated drivers having a source of operative fluid pressure distinct from that in the closed circuits of the pumps and motors. That is to say, there is a positive duid pressure actuation of the drivers varying the strokes of the motors both for increasing and decreasing the strokes of the motors.

In orderA that the invention may be clearly understood and readily carried into effect diagrammatic drawings are appended hereto illusl Figure 1 is a diagrammatic view showing a mill with three hydraulic drives to (a) rolls, (b) coiling-oif drum, (c) culling-on drum. Each drive consists of a hydraulic pump and motor the hydraulicpumps being driven by electric motors or any other prime movers. This gure also shows a` modified method of obtaining the desired correction for change in tension in the strip when a highly sensitive response to change is necessary. 4 Figure 2 is a diagrammatic view showing the complete hydraulic circuits of one arrangement of control unit for obtaining the control of the hydraulic motor horse power in the coiling drums.

Figures Band 4 are detail views showing a modification of the phase advance or error-derivative part of the appliance.

Referringto Figure 1 of the -drawings showing a milljoperat-ed vby hydraulics. there are shown three hydraulic drives each hydraulic system consists of a variable stroke pump feeding a hydraulic motor. In this case the three hydraulic pumps as shown are driven by two electric motors, one motor |00 driving the pump for the main mill drive and the other motor H3 fitted with shaft extensions at both ends driving the two pumps operating the coiling on and coiling off drives, but may be driven by a single motor through gears or by any other'form of prime mover.

The pump for the roll drive has a variable stroke and controls the speed of the hydraulic motor |02 which has a fixed stroke. The coiling drum pumps |03 and |03 also have variable stroke, these are coupled together with the stroke of the milll pump |0| through shafts and gears |04, |05, |06 and |01 to handwheel |08 so that the delivery of all three pumps have the same ratio at all speeds of the mill. The hydraulic motors |09 and |09' for. both-fthe. drums ||0 and ||0 have variable stroke. The strokes of the hydraulic motors |09 and |09 are positioned by control units ||0a; andi- M205 through linkages |20, |2|, |22 and i233 or IH", |20, |2|', |22', |23. Assume the strip oro-thermaterial being dealt with is passing from; leitiftoright of the mill as depicted in Fig.. 1'. Drum.V ||0 coiling ofi and drum ||0' is coiling-on. When rolling heavy gauge metal and under like conditions in which there is not likely to be any appreciable change in the high pressures required to operate thev motors |09! and' |08 orl in which the change in such pressures willV not produce any greatl change in the: eiiect; in the; heavy gauge metal, the controI-units Hita and ||0b aret connected to the pressurei system through pipes ||2 and |12". However, when dealing with quite thin gauge metal strip,V e.. gf. of a foil-like natu-re, and other materials which are very susceptibley to change in tensioni. it is desirable to connect theV control units: ||0 and ||0b to a constant pressure source which feeds the units at pressures controlledby the tension in the material, as hereinafter describedf with. reference to the devices A and? I3` of ligure. l, The pipes connected to the units H0@ and'. Hb.- in this case are indicated at |'|2a and H22. Handwheels ||3 and H3" are for setting theA spring which will determine the operating pressure in the pipes ||4 and'r |I`||'l between the hydraulic pumps |03 and |03 and hydraulic motors |09 and |09. The pipes IM, I-M, H5', H15", ||6 and IIB connect the hydraulic pumps (0|, |03 and |03 to the hydraulic motors |02, |09 and |09'.

The foregoing describes the arrangement of a reversing mill where each coiling drum reverses its operation, i. e. from of coiling to on coiling or on coiling to off coiling according to the direction of the strip passing through the rolls The horse power input to coiling motors |09 and |09 will depend upon the speed of the strip and the tension in the strip which is equivalent to the quantity of fluid and pressure circulating through the motors |09 and |09. Therefore since the quantity of iluid can be made to vary as the strip speed, by virtue of the fact that the handwheel |08 controls simultaneously the stroke mechanism of the three pumps |0|, |03 and 03', a control of pressure in the coiling motor system will give a control of tension in the strip.

The control units ||0u and ||0b are-designed to give a constant pressure in the pipes ||4 and ||4 feeding the motors |09 and |09.vsee description of Figure 2. When the pressure in the coiling-on motor |09 risesV due -to thej increase of coil diameter, the control 0b'w ill move lever to increas the stroke of thermo,- tor |09' and give out a greater torque at a slower speed, until the pressure has been restored to the predetrmined setting to suit the required tension.

Meanwhile, the coiling-off control unit ||0u i operates in the opposite direction. The coilingoff drum ||0 has to give a resistance to thev pull of the rolls and for this drive the hy-v draulic motor |09 is being driven by the rolls' via the strip and drum ||0. Therefore part of the power is regenerated back into the electric motor IH' as the, 'hydraulic4 motor |09 is acting as a pump and the hydraulic pump |03 is acting as a xed stroke motor. When the drum diameter is reduced by the uncoiling of the. strip., the. pressure .in pipe ||4 tends to increase, because owing to the increase in speed the motor |09 is delivering a greater quantity of iluid thanv thatI corresponding to the capacity and speed of pump |03 and in this case control unit ||0ay will decrease the stroke of motor |09 scrthatv the; pressure is maintained at the higher drumspeeds It will be seen that the control ||0a operates inareverse direction when uncoiling, i. e. the pressure increase, in this case in pipe ||4, tends to, decrease-the stroke. The aforesaid couplings betwecnthe control', umts 10a and H012 have reversing linkages with the appropriate mo.- tors operated byfhandlevers; Il!! and; H9! which4 have to be.L changed, at; the end of the. pass for the next. pass; toi be. taken in the reverse; direction. For example... the hand leverv H9' by moving frame |20 determines. whether control unit shaft. |24 moves stroke.' lever in clockwise or anti-clockwise direction e. the posi-tion ofj the block |23 Iirli the' slot Off trame |20 determines whether the: pulir-push movement, 0f the control box shaft |21' is; operating through link |22 or |12| to. top or bottom of; lever It will be obvious that the above considerations apply' whelemateril, Such. aS Strip Q1? Wire is beingv pulled through rolls'v or dies by the coiling on drum from the coiling ofi` drum Without an intermediate. drive.. In such a case the wholel power is. provided by the coiling on. drive the coiling off drive providing back tension as required.V The apparatus employed is the same as that describedv and depicted in Figure 1 with the deletion of main drive Dump |0| and hydraulic motor |102.

Referring to Figure. 2 ofthe drawings the aforesaid hydraulic. power unit can be regarded as the; hydraulic. motor |09" aforesaid in which the stroke of the. pistons operating in the cylinders is adjusted by controlling theA lever ofthe stroke control or tilting member from the control unit ||0b which embodies servo means responsive to differences in tension and/or rate of travel of the material from the supply source to the take-up means, the hydraulic motor being connected to a pump'l03 driven at. a pre,-l determined speed. The motor |09' is preferae bly of the swash plate type.

The servo device aforesaid embodies a sliding type of pilot valve t operated olf a system or linkage and controlling the admission of pressure fluid to a cylinder 5 accommodating a piston S having a ypush-pull connection |24 to the actuating lever of the tilting plate of the motor |09' the piston rod 8 extending through both ends of the cylinder, the end remote from the motor sliding in a cylindrical chamber 9 acting as a dash-pot device and accommodating midway between its ends a needle type bleed valve I0 together with means (hereinafter described) for ladjusting the reaction of the dash-pot to the 'movement of the piston, the arrangement being 'such that when the piston 0 is moved to adjust vthe tilt of the plate of the motor |09 suction or '-P1'05ure according to the direction of movement of the piston 6 is created in the dash-pot 9, and the piston I I of the dash-pot is moved against the influence of a leaf spring l2 further into or away from the cylinder, the dash-pot piston being connected by a link I 3a 4to the leaf spring I2, which link is connected about midway between its ends to one end of a relatively perpendicular lever I4, e. g. as shown, its upper end, which by reason of the traction of the dash-pot piston, applies through the medium of a connecting rod I5, sliding movement to the pilot valve. The lower end of this lever I4 turns about the upper end of a further lever I6 controlled through the medium of a rod I1 from a iiexible diaphragm I8 supported at its perimeter in a pocket I9 in such manner that variations in pressure in the pocket will produce a movement of the aforesaid rod I'I and consequently adjustment of the lever I6 by reason of the pivotal connection I5' of the rod I'I to the lever I5. The lever I6 actuated olf the diaphragm can, for the purpose of designation be regarded as the diaphragm actuated lever, the rst mentioned lever which is connected to the pilot valve being suitably designated as the dash-pot actuated lever.

The diaphragm I8 with its pocket I9 forms part of a stabilising device comprising an outer housing or block 29 within which slides a cylindrical inner block 2| having a quite restricted movement relatively to the outer block and being damped by a dash-pot 22 in one end of the outer block, the piston 23 of this dash-pot being formed cn the end of a rod 24 remote from the inner block and carrying between its ends a doublepiston type of valve 25 operating in a chamber 25 fed by a conduit 26 leading from the aforesaid pocket I9 and having a port 2'I to exhaust, this pocket I9 also communicating with a bore 28 in the end of the aforesaid outer block remote from the end containing the dash-pot, this bore receiving a double-piston type of valve 29 connected by a rod 39 and link 39' to the upper end of a further lever 3l the fulcrum 32 of which is midway between its ends, the lower end of this third lever being connected by a link 33 to an abutment member 34 `of a spring 35 of a pressure measuring device, comprising the plunger 36 carried by the abutment 34 and operating within a cylinder 3l, which when rolling heavy gauge metal as mentioned hereinbefore, can be connected by a conduit I I2 to the feed line I I4 from the pump HB3 to the motor H39.

However, when winding or rolling the thin gauge materials, such as metal foil, or even plastic materials having a relatively high yield to tension in which relatively low pressures are employed it is necessary to connect the conduit I I2 to a source of pressure independent of the feed line IM', and in which the pressure applied to the cylinder 3'! is controlled from the tension of the material being wound on to or off from the drum H9. Hence, in Figure l there is shown at A and B iioating bearings 80 and 89' for the drums II9 and lili', each bearing being fixed to a plunger 8l operating in a cylinder 82 to which is connected a pipe 83 connected to the pressure side of a constant capacity pump (not shown). rlhe pressure from this pump is fed into the cylinder 3l via line IIZb (or Ila) and as the tension in the drum H9 builds up against the -pressure in the cylinder 82 a release port 84 leading iby line 95 to a tank in the circuit of the latter mentioned pump is gradually throttled down, and the resulting pressure obtained by this throttling down is fed into line II2b to the cylinder 31 and the tilt of the lever III' thereby constantly adjusted to take care of any tendency for the tension in the material to change.

The said bore 23 accommodating the latter mentioned d-ouble piston type of valve 29 communicates with the inlet 4 of the cylinder 4a of the aforesaid pilot valve via a pipe line 49 leading from the discharge 4 I of a gear pump 4I (driven from an electric motor 42) and a branch line 49a. This motor 42 would normally be a fractional horsepower motor.

An adjusting screw 58 is provided to enable the loading of the spring 35 to be varied, the screw 5B being operated via worm gear 59 driven from a tension adjustment shaft 59, and the aforesaid spring 35 is interposed between the said abutment 34 and one end of a housing 43 and connected by suitable remote control means, e. g. a cam or link and lever 44 and shaft 45, to a tension indicator 46 to indicate the pre-setting load on the spring. The shaft 42 on the aforesaid low horsepower electric motor 42 to the gear pump 4I has a gear connection 42a to a shaft 41 driving an eccentric 48 operating a longitudinal rod 49, the end of which remote from the eccentric is connected to the lower end lof a link 59 pivoted at its upper end to a fixed pivotal point 5I thus providing a dither mechanism to keep the whole of the mechanism of the control apparatus alive and thus remove static friction. This ensures that the pilot Valve 4 will accurately return to its closed position when no pressure error exists, and will thereby eliminate any tendency for the tilt control piston 6 to creep due to the pressure iiuid .being admitted through the pilot valve 4 to one side of the tilt control cylinder 5. This dither on the pilot valve also enables the control to respond to very small sustained variations in pressure in the pump and motor circuit. Alternately, this dither may be effected hydraulically by introducing pulsations into the chamber 9.

To enable the pilot valve 4 to be centered accuH rately in its valve block when the links 3 I, I6 and I4 are in the neutral position the leaf spring I2 is xed to a short cranked extension 6 I of a lever .6I operated off an adjuster screw 62.

The position of the fulcrum 32 of the third mentioned, or lower end lever 3l i. e, of the lever connected to the abutment of the spring 35 of the pressure measuring device, is adjustable so that the movement of the pilot valve l for a given Variation in pressure due to the load reaction to the hydraulic motor |09' circuit can be varied on test to ascertain the most suitable rate of response of angle of the lever Ill', i. e. of tilt. In this connection such fulcrum, which as aforesaid is between the ends of this lever, is connected by a bracket 34 and a push-pull rod 32a to a remote control adjuster 52, this adjuster thereby adjusting the position of the fulcrum 32 of the lever 3| which connects the piston 35 to the aforesaid stabilising device.

The aforesaid double piston type of valve 29 of the stabilising device has its rod 33 prolonged into the inner or sliding block of the stabilising device to carry at its end remote from the double piston type valve a further similar type of valve 53. In operation the aforesaid gear pump et supplies the bores 28 and 25 of the two double piston type valves 29 and 25 respectively with fluid at a constant pressure, the fluid passing through the rst mentioned double piston valve bore 28 and a port I9 leading to the pocket Iii containing the diaphragm I8, from whence it passes via 'the .conduit 26 to the bore 25 of the outer block of the stabilising device and from whence the fluid passes via outlet `21 to exhaust.

The double piston valve 29 connected to the upper end of the lower lever 3| of the first mentioned three levers and the double piston valve 53 in the sliding block are pre-set so that when the said three levers I4, S and 3| are in the neutral position the port I9 communicating with the said pocket I9 and the outlet port 21 in the outer block of the stabilising device are of the same area and half open as shown, consequently the pressure drop through each is the same. By this means the diaphragm in the pocket is initially deflected under a pressure of half the supply pressure.

Any movement of the aforesaid double piston type of valve 29 connected to the levers i6 and 3i changes the `area of the port I9 leading to the pocket and at the same time opens two ports 54 and 55 in, and communicating with, opposite ends of a chamber 55 receiving the sliding block 2|, these two ports being otherwise covered by the piston elements of the double piston valve in the sliding block as shown. The opening of either one of these two ports 54, 55 allows pressure fluid to act on the end of the sliding block coinmunieating with the appropriate port, so that the block will then move in the same direction of movement as the valve until the two ports 51E, 55 are closed and the outlet 21 in the outer block is the same area as the port I9 communicating with the diaphragm pocket I6. Owing to the aforesaid dash-pot 22 in one end of the outer block controlling the speed of movement of the double piston valve piston controlling the said exhaust 21, there is a time lag between the changing of the area of the port I9' communi eating with the pocket |9and the equating of the areas of this latter port I9 and the said outlet port 21. This time lag can be adjusted by means of a dash-pot adjuster comprising a screw actuated conical valve 51 establishing communication between the dash-pot 22 and a source of supply of fluid.

The foregoing describes the general arrangement of the control gear, and it will be appreciated that in operation when, e. g. as aforesaid, the apparatus is adapted to the winding, rolling or feeding of materials which are very susceptible i to the influence of changes in tension, having regard to the fact that the variable rate spring takes care of changes in tension build-up in the strip material, i. e. changes in load on the means driven by the hydraulic motor |59 (or |59), by responding to such changes so as to vary the setting of the lever III', the effective horsepower input to the hydraulic motor |69 is maintained at a predetermined value depending upon the tension required in the material and its velocity, e. g. in the feeding of strip metal from rolls to a take-up drum.

To maintain the said pressure constant, any error in pressure is as already described, utilised to move the tilt of the plate of the motor |69 in such a direction as will restore the pressure to its predetermined value. The control comes into the category of a rst derivative of error control, i. e. the movement of said pilot Valve 1 controlling the admission of pressure fluid to the cylinder 5, is proportional to the error plus a function of the rate of changes of error. For

example, Ylet the error in the pressure be P then the input to the pilot valve will be K( f (P) -I'- =pressure error:

rate of change of pressure error The rst portion of this expression is obtained by means of the pressure measuring device 36 which is set before starting to roll the strip, by means of the tension adjustment shaft 60, so that when the tension in the strip is set at the required value, the pressure in the pump and motor system balance 'against the said spring 35 whereby the said three levers I4, I6 and 3| are held in the in-line or neutral position, the pilot valve 4 is closed, and there is no movement of the tilt control piston 6. Any variation in this tension produces a variation in strip horsepower and in pressure in the motor circuit and consequently the said three levers move from the neutral position, the pilot valve 4 opens, and the tilt control piston 6 moves to adjust the speed of the motor. Variable rate springs can be used in order that a giveni variation in pressure between the pump and `motor produces the maximum rate of change of the speed of the hydraulic motor and its associated drum.

The -second portion of the expression fldt is obtained from the aforesaid stabilising device. It is assumed that the double `piston valves 25 and 53 in the said bore of the outer block 20 and in the sliding block 2| are suddenly moved in the direction of the arrow A, there is a sudden reduction of the area of the port I9 leading to the diaphragm pocket I9, whereas the adjustment of the area of the said outlet port 21 is retarded. This will cause a greater pressure drop through the port I9 than through the outlet port 21, with a consequent reduction in pressure in the said pocket I9, and hence the diaphragm will push out the rod I1 connecting it to the intermediate one I6 of the three levers.

A reversal of the movement of piston valves 28 and 53 will result in this rod I1 and lever I6 being pulled in.

This displacement of the rod I1 is proportional to the rate of change of error, since the pressure drop in the pocket is proportional to the difference in area of the pocket port I9 and outlet port 21 and the slower the movement of the double piston valve 2B the closer the double piston valve 25 connected to the sliding block 2| follows the valve 29, and the area of opening the said exhaust port 21 follows the area of opening of the port I9 connecting with the pocket I9. Variations in response of the sliding block can be effected by adjustment of the valve Arising out of the foregoing, as the area of the outlet port 21 approaches the area of the diaphragm pocket port I9', the pressure drop through the exhaust port 21 approaches the pressure through the diaphragm pocket I9 and. consequently the displacement of the rod I1 connected to the diaphragm is gradually reduced until the area of the outlet port 21 equals the area of the diaphragm pocket port I9 whence the diaphragm is returned to its initial position.

Now assume that there is a rise in tension in the strip above the predetermined value. This will create a rise in pressure in the conduit II2 (or I|2b) and the resultant movement of the piston 36 in the pressure measuring device will be in a direction of the arrow B, the lever 3l turning about its fulcrum 32 and the coupled double piston valves 29, 53 of the stabilising device will move inwards. The intermediate lever l 6 of the said three levers will consequently turn about the pivot I6 on the rod connected to the diaphragm, and the lower end pivot I4 of the upper lever I4 will move out. At the same time the diaphragm rod Il will move out owing to a reduction of pressure in the said pocket as previously indicated, the intermediate lever i6 will pivot about its lower end lBa and its movement will be increased. This latter additional movement due to the movement of the diaphragm rod il is gradually removed as indicated in the preceding paragraph. 'I'he upper lever I4 of the three leversI will pivot about its upper end |4a and the pilot valve I4 will open in the direction of the arrow C. Pressure iiuid will then be admitted behind the tilt control piston 6 and the tilt of the motor plate will be increased and the speed of the winding drum reduced.

When the tilt control piston 6 moves, it will create a suction in its associated dash-pot 9, and the piston l l therein acting against the leafspring i2, will be drawn further into the cylinder. The upper lever I4 will pivot about its lower end and the pilot valve 4 will begin to close. The suction created in this dash-pot 9 will draw fluid through the adjustable needle valve lil of the dash-pot, and opposing the leaf spring l2 tends to close the valve 4 so that when the pressure in the main system is restored the rate of the piston 6 has been retarded and approaches its new position simultaneously with the restoration of the pressure in the system. This action is continuous While the tilt control piston d is moving, and tends to restrict the rate of change of tilt or acceleration of the drum, smoothing the operation of the control and reducing any tendency for the tilt lever lll to overshoot the required position. The amount of restriction to the rate of change of tilt to give the most stable condition is obtained by means of the dash-pot adjuster l0.

If the pressure in the pump-motor circuit falls, a reversal of the above sequence of events takes place, until the pressure returns to the normal value and the said three coupled levers are again in their neutral positions.

When it is desired to regulate the take-up of the fed material in synchronism with the processing of the material in such manner that if the feed or processing stops, the material can be fed over or through a feeler in the form of a lever, and for a photo-electric cell device or other means for measuring catenary, and the lever, or its equivalent connected through the medium of a mechanical, hydraulic or electric linkage, so that the rise and fall of the lever, or the effect of the change of catenary, i. e. the displacement of the strip material relatively to the light source of a photo-electric cell is transmitted to the lever 3| instead of to the cylinder 3l and spring 35 to obtain a control of the hydraulic drive.

In the embodiment shown in Figure 3 the lever 3l is connected at its upper end to a piston 29h so that this piston moves at a velocity proportional to the rate of change of error, resulting in oil being pressed out of or drawn in via the adjustable orice 'I0 giving a pressure in the port lli depending upon the rate of displacement of the piston 29h and adjustment of area of the orice lil, which pressure reacts on piston I8b in cylinder 12 against the appropriate one of a 10 pair of balanced springs 'H giving a movement to the rod il proportionate to this pressure. Thus the displacement of the piston I8b and lever point IB therefore depend upon the velocity of the piston 29h. The broken line parts (Fig. 4) show the effect on the lever assembly, a term being added into the system. The addition of this term, or this additive motion has a damping eiect on the system.

The foregoing stabilising means is an appreciably simplified alternative to the stabilising means Ypreviously described, the unit being submerged in oil, so that when the error signal has a velocity to the right in the diagram oil is sucked into the cylinder 'I3 and the piston |819 moves to the left. By providing an adjustable orice l0 the ratio between the deflection of the piston |82: and the velocity of the piston 29h can be regulated.

It will be appreciated that the present invention is applicable also to the automatic control in quantity output of a pump so as to obtain a uniform pressure in lines to a number of apparatus fed by the pump, and in which the number of apparatus in use at a time is subject to variations e. g. in a works or aircraft where one pump is common to a plurality of hydraulic duid pressure actuated apparatus. In such an arn rangement changes in the number of apparatus being fed by the pump will change the pressure in the pump discharge side unless provision is made to adjust, e. g. the stroke and consequently quantity output of the pump automatically according to the changes in reaction due to increase or decrease in number of apparatus being served. Hence, by controlling the pressure in the line 38 to the cylinder 3l via means responding to the reaction in the supply line from the pump, the necessary changes in quantity of iiuid flowing per given unit of time from the pump can be eiected so as to obtain constant pressure to the apparatus in use.

We claim:

l. A reversible rolling mill, comprising rolls for rolling the material, a power unit driving the rolls, a pair of hydraulic pumps, a prime mover driving said pumps, and a pair of variable stroke hydraulic motors, a closed hydraulic circuit across each pump and its associated motor in the form of a supply conduit and a return conduit across each pump and its associated motor, a pair of drums one driven by one of said motors and the other by the remaining motor, said drums each serving alternately to coil-oil and coil-on the material being rolled, so that as one acts as a coiler-on, the other acts as a coller-off and vice versa and the coiler-off drum transmits the tension in the material across it and the rolls to its motor to feed back part of the power generated to the said prime mover, means to change the direction of drive to said drums to reverse the direction of feed of the material between the rolls, iiuid pressure actuated means to increase the stroke of the coiling-on drum motor as the coil diameter increases so as to increase the torque applied to said drum and to maintain a substantially constant horsepower in the motor driving said drum, a pair of hydraulic iluid pressure actuated drivers having a source of operau tive fluid pressure distinct from that in the aforesaid pump-motor circuits and connected to the stroke varying means of the two motors to posi-n tively actuate the stroke varying means both for increasing and decreasing the motor stroke, a v alye with each -saidf -driver controlling lthe flow Ofznplessure Huid tositsassoeiateddriver both as I'Qgalfdiireton anda eiective pressure, `means receiving a controlling.- signal Y from'- l they supply conduit, of eachl pumpw-andmotor regulating the position of each said valve to control the direction and extent of displacement of each said driver so as to give a mo'tor stroke changing response to the `reaction ee'ct inthehydrauliccir cuite of the :assooiatedzpump and motor due to the change in tension in .the materialilbeing?*fed` through the roilsndrthfe changein build-up of thematerial-being woundfon the ceiling-up drum and the'reduc'tion finmaterial being coiled-offthe 05h61'drum?` if. :1:: 311.. :5, it; r

, 2. Arolling mill according to claim 1 including in addition a` pumrrfee'dingza motor( driving thev rolls, thezmotordrivingthe rolling means havinganormally `ixed stroke, and I"means common td all of said pumps tc"y adjust the pumps so that at least the two pumps driving the two drum motors l canfhavezthefsame hydraulicfoutput,` and the due` to the'reajction of the strip material, servo Y means; receivingan operating` signal from said 12 latter means and adapted to control the extentv o'f 'displacement of"'said'vellve to Vcon'iplete the connectioribf thesaid cylinder to the' source of hydraulic fflu'd 'pressure and thereby to maintain a substantially @constant 'horsepower' output o'fV the associated"motor` du'e to the adjustment of the stroke controller, and 'a fluid pressure 'd-is' placedflm'emberoperatively'connected to the valve andfrespon'di'ng tomate of.' change ofthe load on` themotor jto introduce a compensating move; m'ent into'th said-valve means'.

"4;*1'Alrolling mill' accoding'to claim l wherein sadm'eans'adapted'to" b"e pre-set to respond 'toa predetermined *load on" the motor is"`a"spring leaded' member displace'able"against'the in'ueiice off its -spring 'by 'the "influence ofhydraulic pres? sure infin-efsupply4 side-er the associated meter.'

JOHN Hnwrr'r."

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