US2135627A - Temperature control for paper mills and the like - Google Patents

Description

Nov. 8, 1938. H, J. SMITH TEMPERATURE CONTROL FOR PAPER MILLS AND THE LIKE Filed June 24, 1955 a Sheets-Sheet 1 INVEN R,

ATTORNEY.

NOV. 8, 1938. H, J, sMlTH 2,135,627

TEMPERATURE CONTROL FOP. PAPER MILLS AND THE LIKE Filed June 24, 1935 3 $heets$heet 2 '3 4g Q .50 a:

a; INVE OR.

ATTORNEY.

Nov. 8, 1938. H, J, TH 2,135,627

TEMPERATURE CONTROL FOR PAPER MILLS AND THE LIKE Filed June 24, 1935 3 Sheets-Sheet 3 1 3 151 v g 424 i 121' 9? l0 7 10 o 0 1 8 I L 409 I I 1&9 110 H OV.A.C.

ATTORNEY.

Patented Nov. a, 1938 ausszr ram-saunas common roa Paras mans also m use I Razor 1. Smith, Longmeadow, Mara, assignor, by

mesne i nments,

to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application June 24-, 1935, Serial No. 28,056

Claim.

This invention relates to temperature control systems, and more particularly toa system for controlling the temperature of the drying rolls in paper mills and the like.

An object of the invention is to provide an automatic control for the moisture content of the sheet which is discharged from the drying rolls of a paper mill.

Another object is to provide an'accurate and automatic system, controlled by variations in the moisture content of the sheet which is received by the drying rolls, for varying the temperature of the rolls so as to discharge the sheet with a uniform moisture content. I

i Another object is to provide a system of the above type which-maybe readily adjusted to accommodate diiferent types of sheet, or stock having different moisture contents.

Another object is to provide .a system of the above type which is adapted to operate in conjunction with present equipment, whereby the cost of installation is reduced to a minimum.

Another object is to provide a system for maintaining the rolls at a predetermined temperature thereby.

Another object is to provide a simple, conven-' lent and dependable device of the type above indicated. v

Other objects will be apparent from the following description. 7

The invention is primarily intended for use in connection with the drying rolls of a paper mill. In such mills the sheet is passed successively over a plurality of rolls which are maintained at suitable temperatures by heating means,- such as steam, and are adapted to discharge the sheet with a predetermined moisture content. A feature of the present invention consists in stills-- ll ing the variations of moisture content of the incoming sheet to control the steam supplied to the rolls in such manner as to compensate for said variations.

In one embodiment, the tension of the incom- 5 ing sheet is used as a measure of the moisture content. A tensionlng roll, such, for example, as a Stickies roll, is held against the incoming sheet in' such manner that the position of the roll is determined by the moisture content of the sheet at any instant. Inasmuch as the tensioning roll accordance with the average moisture content of the sheet over predetermined intervals.

during periods when no sheet is being received In accordance with the present invention, the position of the tensioning roll is translated into movement of a steam supply valve by means of a reversible motor-control unit. In order to provide means for adjusting the "range of control of the motor-control unit in accordance with changes in stock. a second motor-control unit is provided which is operated by a hand control or by an automatic thermostat. The ratio of control eifected by the first and second motor-control units may be varied in order to provide the desired result. The automatic thermostat may be controlled in accordance with the steam condensate temperature at a selected roll, for the purpose of maintaining the temperature of the rolls substantially uniform when the control of the first unit is interrupted, as, for example, in response to a break in the sheet. Means is provided for manually connecting either the hand control or the thermostat into the circuit, as desired.

' Other features of the invention consist in the various details of construction and combination of parts as hereinafter more fully set forth.

The broader aspects of the invention will be better understood by referring to the following description, taken in connection with the accom- D nying drawings in which a preferred embodiment has been disclosed for purposes of illustrationonly.

; In the drawings,

Figure 1 is a ditic view of a temperature-control system embodying the present in-' vention;

Figure 2 is a front elevation of the automatic control switch.

Figure 3 is a side view thereof; I A

' Figure 4 is a detail view of the automatic control mechanism;

Figure 5 is a front elevation of the control panel;

Figure 8 is a wiring diagram showing the 6011-! nections of the signal lights;

Figure 7 is a section of the indicating unit, taken along the'line I---l of Figure 8;

' Figure 8 is a side view of the indicating unit; and

Figure 9 is a wiring diagram showing the connections between the hand control; automatic temperature control and motor-control unit.

In the following description and in the claims, certain specific terms have been used for convenlence in referring to the various details of the invention. These terms, however, are to be interpreted as broadly as the art will permit.

Referring to the drawings more in detail, the invention is shown in Figure l as applied to the drier of a paper mill which comprises a plurality of rolls in over which a sheet H of paper is passed in the usual manner for successively drying the same as it passes over the rolls. The rolls may be heated by steam supplied from a header l2 and fed to the individual rolls l0 by communicatingpipes [3. The condensate from each roll is collected in a well l4 and is removed through a pipe l5 which connects with a drain line it. Steam maybe supplied to the header l2 from a mainl1 having a control valve 20 which may be operated by a lever 2 lin accordance with the automatic control mechanism to be described.

The lever 21 is controlled by a pair of motorcontrol units 25 and 26 having arms 21 and 28 respectively which are connected by links 29 and 30 to a control lever 3|. The control lever 3i is connected to the lever 2| by means of a link 32, the point of connection of the link 32 to the control lever 3i being varied by a slider 33 having a hand set screw 34. By varying the position of the slider 33, the ratio of the control of the motor- control units 25 and 26 may be adjusted. When one of the control units is stationary, the link 29 or so which is connected thereto serves as a fulcrum about which the control lever 3| may pivot in response to movement of the other motor-control unit. In the form disclosed, the motor-control unit 26 operates as a master control for varying the operating range of the valve 20, whereas the motor-control unit 25 operates as an automatic control which is actuated in accordance with the moisture content of the incoming sheet.

The control device for actuating the motorcontrol unit 25 is shown more in detail in Figure 4. It comprises a tensioning roll 33 which is mounted upon an arm 39, pivoted as at 40, and held by a weight 4| against the sheet H of paper which is being supplied to the drying rolls. The arm 39 is connected to a valve 42 which controls the flow of fluid, such as water, through a pipe 43 leading to a cylinder 44. The cylinder 44 is provided with a discharge line 45 regulated by a valve 46. The cylinder 44 carries a piston 41, the position of which is determined by the quantity of fluid within the cylinder.

The piston 41 carries a piston rod 48 which is connected to a belt 49 passing over pulleys 50 and 5| and having stops 52 and 53 adapted to engage the lever 2| for controlling the position of said lever in accordance with the movement of the belt 49. The spacing'between the stops 52 and 53 permits a certain amount of movement of the belt 49 without actuating the lever 2!. Suitable weights 54 and 55 may be associated with the belt 48 for maintaining the same in operating condition and to determine the operating characteristics of the device.

A belt 59 may also be connected to the piston rod 48, as by an arm 50. Said belt 59 may be passed around a pulley GI and thence over a pulley 52 of a control switch 53 which is adapted, by its position, to determine the operating position of the motor-control unit 25. A weight 64 may be hung on the end of the belt 59 to hold the same in frictional engagement with the pulley 52.

The control switch 63 is shown more in detail in Figures 2 and 3 as comprising the pulley 82, over which the belt 59 passes, and a pair of contacts 68 mounted upon a shaft .59 which carries the pulley G2 and turns therewith. The contacts 58 are adapted to alternately engage contacts 1| carried by a contact arm 12 which is supported by a sleeve 13 journalled on the shaft 59. The

contact arm 12 carries a pair of brushes 10 which are electrically connected, respectively, to the contacts 1| and are adapted to engage sets of through to cause rotation of the contact arm 12. Rotation of the pulley 62 in the opposite direction breaks the first-mentioned pair 01 contacts 68 and 1!, closes the other pair of contacts 68 and 1!, and causes rotation of the contact arm 12 in the opposite direction. The contacts 68 and 1| thus constitute reversing contacts to complete a circuit to one or the other of the brushes 10, depending upon the direction of rotation of the pulley 52. The position of the brushes 1!) determines the position of the motor-control unit 25 by a circuit, to be described.

For limiting the movement of the pulley 62, a stop 11 is provided which is adapted to engage the belt 59 when the pulley 82 is moved to either extreme position. A contact 18 may be carried by the stop 11 to engage one of a pair of contacts 19 for closing the circuit to the signal lights, to be described.

The various contacts 14 and 1.5 are connected by a cable (Figure 1) to the motor-controb unit 25 in such manner that the arm 21 of the motor-control unit is caused to take up a position corresponding to the position of the brushes 10 on said contacts.

In the operation of the control device illustrated in Figure 4, the tensioning roll 38 presses against the sheet I l and causes movement of the arm 39, dependent upon the moisture content of the sheet. Innormal operation, the arm 39 is caused-to oscillate in accordance with the instantaneous variations in the sheet. In so doing, it causes the valve 42 to operate in a corresponding manner. If the valve 42 admits water to the cylinder at a rate equal to the rate of discharge of water through the discharge line 45, no movement of the piston 41 will take place. If the valve 42 admits water to the cylinder 44 at a rate in excess of or less than the rate of discharge through the discharge line 45, the water level will rise or fall, respectively, in the cylinder 44 and will cause corresponding movement of the piston 41, which is transmitted by the belt 59 to the control switch 53. The control switch 63 actuates the motor-control unit 25 to progressively open or close the valve 20.

The manner of connection is such that an increase in the moisture content of the sheet II causes the valve 20 to be opened so as to supply additional steam to the rolls 10, whereby the temperature of said rolls is raised an amount adapted to compensate for the extra moisture contained in the incoming sheet. If the moisture content of the incoming sheet decreases, a reverse operation takes place, the piston 41 being raised or lowered in accordance with the average opening of the valve 42 which, in turn, is determined by the average moisture content of the sheet H over a given interval.

The contacts 19 may be connected to heating coils 82 which are associated with thermostatic switches 83. Each switch 83 is adapted to close a contact 84 to a signal light 85 which may be mounted,,for example, on the control panel 86,

as illustrated in Figure 5. The connection is being energized in response to momentary closing of the contacts 19. When the pulley 62 is moved to either of its extreme positions, the stop 11 engages the belt 59 to limit the movement of the pulley. If further movement of the piston 41 takes place, the belt 59 slips about the periphcry of the pulley 62. The stop 11 also provides manual means for adjusting the pulley 62 with respect to the belt 59.

The second motor-control unit 26 may be connected to a hand switch 89 (Figure 1) or to an automatic thermostat 90, both of which may be mounted upon the control panel 86.

The hand switch 89 may be of the type described in my copending application Serial No. 657,237, filed February 17, 1933, for Control by integration. It may comprise, for example, a shaft 9| (Figures 7, 8 and 9). carrying an arm 92 having apair of contacts 93 adapted to engage contacts 94 mounted on a contact arm 95. The contact arm 95 is mounted for rotation on a sleeve 96 which is journalled eccentrically about the shaft 9|. .A control handle 91 may be connected to the shaft 9|. The contact arm 95 carries a pair of brushes 98, 99 which engage sets oi contacts I00, I0! in accordance with the position of the control handle 91. The contacts I00, IOI are connected to the motor-control unit 26 in the manner to be described.

The thermostat 90 may be of the type shown in 0 my Patent No. 1,952,571, dated March 27, 1934.

It may comprise, for example, an arm I 03 pivoted, as at I04, and actuated by any expansible bellows I05 in accordance with the temperature of the fluid therein. A spring I06 may be used to adjust the operating range of the thermostat. The arm I03 carries a pair of contacts I 01 which are adapted to engage contacts I08 carriedon a contact arm I09 which is pivoted, as at H0, to the arm I03. The contact arm I09 carries a pair of brushes III which are adapted to engage sets of contacts II 2 and H3. The contacts I I2 and I I3 may be connected to the motorcontrol unit 26 in the manner to be described, whereby, the motor-control unit may be operated in accordance with the position of the thermostat.

The bellows I05 may be connected by a flexible tube II4 to a bulb II5 which may be mounted in a suitable well in the return condensate line of one of the rolls I0. The thermostat accordingly is responsive to the temperature of the steam condensate in the selected roll I0 and is adapted to actuate the motor-control unit 26 so as to' control the steam supplied to the roll in-a manner adapted to maintain the roll at a predetermined temperature.

In order to indicate to the operator the position of the motor-control unit 26, an indicating unit I20 is provided (Figures 5, '1 and 8) having an indicator I2I moving over a scalell9, calibrated to show the angular position of the arms I20 is illustrated, for example, in Figure 9, In

gear. train I 26 from a pinion I26 carried by a reversible motor I21. A plurality of sets of stationary contacts I28, I29 and a contact I30 are mounted on a support I3I in position to engage the commutator I23 as the commutator is rotated 5 bythe motor I21.

The motor- control units 25 and 26 and the indicating unit I20 maybe of similar construction with the exception of the indicator I2I, which, in the case of the motor- control units 25 and 26, is replaced by the arms 21 and 28. The units may, for example, be of the type described in my copending application, above-mentioned. A suitable control circuit for the indicating unit 16 this figure, the reversible motor I21 is shown as a reversible shaded pole motor having a field winding I32 which may constitute the secondary of the transformer I33, the primary I34 of which may be connected to a source of A. C. supply. The motor is provided with a pair of shading coils I35 which when energized, are adapted to cause rotation of the motor in one direction, and another pair of shading coils I36 which are adapted to cause rotation of the motor in the opposite direction. These coils I35 and I36 may be connected to a double-pole, double-throw switch I31 having a set of poles I38 connected by leads I39 to the contadts 9a of the hand switch 89 and a set of poles I40 connected by leads I to the contacts I01 of the thermostat 90. The contacts I00 of the hand switch 89 and the contacts II2 of the thermostat maybe connected by cables I45 and I46, respectively, to a junction box I41 which is connected by a cable I48 to the contacts I28 of the indicator unit I20. The contacts IOI of the hand switch 89 and the contacts II 3 of the thermostat 90 may be connected by cables I49 and I50, respectively, to a junction box.

I5I which is connected by a cable I52 to the coni tacts I29 of the indicatorunit I20; The contact I30 of the indicator unit I20 is connected by a line I53 to the field winding I32 of the motor I21. The above connections are such that when the switch I31 is in one position, the hand-control switch 89 is connected in the circuit. If then the handle 91 is turned in one direction, for example, in' a counter-clockwise direction, as viewed in Figure 9, the pair of contacts 93 and. 94 at theleft is closed, thereby completing the circuit from I the shading coils I35 through the switch I 31 and one lead I39 to the selected contacts 93 and 94, thence to the brush 98, one of the contacts I 00, through the cables I45 and I48 to one of the contacts I28, thence through the commutator I23, the contact I30 and the return line I 53 to the field winding I32 of the motor I21. The motor is then caused to operate in agiven direction until the circuit is broken. by the commutator I23 leaving the contact I28 which is energized at that moment. If the handle 91 is moved in the opposite direction, the opposite pair of con tacts 93, 94 is closed, thereby completing a circuit through the brush 99, a contact I III, cables I49, I52 to a contact I29 and energizing the op- 5 posite coils I36, which causes a reverse movement of the motor until the commutator I23 breaks contact with the contact I29" which is energized at that moment. The motor I 21 is thus reversibly and progressively operated in ac- (0 cordance with the position of the handle 91. The contacts I28 and I29 may be relatively dis- I placed to provide difierent positions of the motor- I control unit inopening and closing the valve 20.

I When the switch I31 is thrown into the oppo- 76 site position, the hand-control switch 89 is disconnected and the thermostat 90 is connected in the circuit. The control of the motor I21 by the thermostat 96 is then the same as that above described in connection with the hand switch, the motor being reversibly and progressively actuated in response to temperature variations registered by the thermostat 90.

It is to be understood that the connections between the contacts 14 and I5 of the control switch 63, and the motor-control unit 25 are similar to those above described. This connection is illustrated in Figure 1 as comprising a cable connecting the control device 63 with the motor-control unit 25. It is also to be noted that the motor-control unit 26 and the indicating unit I20 are connected in parallel so that the indicator I2I shows at all times the position of the motor-control unit 26. The switch I3! is connected to a junction box I55 which is connected in parallel by cables I56 and I51, respectively, to the motor-control unit 26 and the indicating unit I20. The switch I31 may be operated by a handle I58 mounted upon the control panel 86. The control panel may also carry a suitable temperature recorder I59, a steam pressure recorder I66 and a chart IBI.

In the operation of this system, the handle I58 is normally in a position such that the handcontrol switch 89 is connected in circuit, whereby the position of the motor-control unit 26 and the indicator unit I20 are governed by the position of the handle 91. Assuming a paper having'predetermined characteristics to be passing over the various rolls ID, the tensioning roll 38 will take up a position depending upon the moisture content of the paper, thereby causing the piston 41 and the belts 49 and 59 to take up corresponding positions. The motor-control unit 26 is then actuated by manipulation of the handle 91 so as to bring the lever 2! into engagement with the stop 53 of the belt 49, whereby the control of the steam supply is taken by the belt 49. The stop 'I'I of the control switch 63 is then adjusted to the central position by causing the pulley 62 to slip with respect to the belt 59. Thereafter, the steam supply will be under the control of the tensioning roll 38 and the motor-control unit 25. Said unit operates to produce minor variations in the steam supply in accordance with the instantaneous positions of the control switch 63 caused by changes in the average moisture con tent of the sheet.

If the moisture content of the sheet changes suddenly or becomes such that the control switch 63 is actuated to the limit of its'movement, thereby closing one of the contacts I9, one of the indicating lights on the panel 86 will be energized to indicate to the operator that a change is taking place. If the control device does not soon correct the change, the operator may make suitable manual adjustment of the steam supply by actuation of the handle 91 of the hand switch 89. The hand switch 89 is also used when the stock is changed and to adapt the system for use with different grades of paper.

In the event of a break or between runs when no sheet is passed over the rolls I0, the control device 63 becomes inoperative. It may be desired to maintain the temperature of the rolls I0 substantially constant during this period so that the rolls will be ready for use when a sheet is again supplied thereto. For this purpose, the lever I58 is thrown to the opposite position, thereby disconnecting the hand switch 89 and connecting the thermostat 90 to the motor-control unit 26. The thermostat 90 is adjusted to actuate the motor-control unit 26 so as to maintain the rolls I0 at a predetermined temperature.

When changing from the thermostat control to the hand switch, it is necessary to know the position of the motor-control unit 26 in order to make a corresponding setting of the hand switch. The indicating unit I20 is used for this purpose, since it operates in conjunction with the motorcontrol unit 26 and shows at all times the position thereof. It is obvious, however, that this unit may be omitted if such indication is not required in any particular instance.

It will be noted that the above device is adapted to maintain the drying rolls at suitable temperatures to stabilize the moisture content of the finished sheet. In certain instances, the moisture readings were stabilized with a variation of 0.2%. The device also permits the rapid change-over between different types of stock and eliminates waste due to improperly dried paper or due to breaks which are often caused by faulty drying. The adjustments are such that they may be readily adapted to any desired operating conditions, and the controls are arranged on a panel suited to give a visible record of the operation of the system.

The position-indicating unit I20 shows at all times the position of the motor-control unit 26. After a paper break or on change of orders, the operator sees instantly just where to position the handle 91 to pick up where the thermostat leaves off.

Under the close control herein provided, it is possible to readjust the distribution of heat in the various rolls and to provide for balanced paper shrinkage across the mill, thereby reducing the breaks and improving the general quality of the paper. The ability to maintain a uniform and correct drying roll temperature with proper distribution of the shrinkage across the whole mill permits increasing the speed, and therefore the tonnage, up to the limit of capacity of the mill.

The hand switch 89 may constitute a master control for adjusting the system for different papers. The master control can position the valve in any one of twelve positions. The control switch 63 can position the valve in twenty-six different positions. The relative control can be adjusted by varying the position of the slider 33 on the control lever 3I. It is to be noted, therefore, that an extremely accurate control is effected.

The signal lights 85 may, for example, com- 'prise red and green lights, and are adapted to call the operators attention to the fact that the sheet is too wet or too dry and that connection at the master control is required.

Although a preferred embodiment has been disclosed for purposes of illustration, it is evident that various changes and modifications may be made therein without departing from the scope of the invention, which is to be limited only in accordance with the following claims when interpreted in view of the prior art.

I claim:

1. A temperature-control device for paper mill drying rolls over which a sheet of paper is passed to be dried comprising, in combination, a source of heat supply to said rolls, a valve adapted to control said supply, a pair of reversible motorcontrol units adapted to jointly control the position of said valve, means responsive to variations in tension of the sheet due to variations in moissheet to automatically actuate one ot'said units ture content thereof to actuate one of said units,

'a hand control, means responsive to the roll temperature, and means to actuate the second unit by either said hand-control or said temperatureresponsive means.

2. A temperature-control device for papermill drying rolls over which a sheet of paper is passed to be dried comprising, in combination, a source of heat supply to said rolls, a valve adapted to control said supply, a pair of reversible motorcontrol units adapted to jointly control the position of said valve, means responsive to variations in tension of the sheet due to variations in moisture content thereof to actuate one of said units, a hand control, means responsive to the roll temperature, means to actuate the second unit by either said hand-control or said temperatureresponsive means and an indicator unit adapted to indicate the position of said second unit so as to assist the operator in making manual adjustmentsby said hand control.

3. A device for controlling ,the temperature of drying rolls over which a sheet of paper is passed to be dried, which comprises means responsive to variations in tension of said sheet due to variations in moisture content thereof, a progressive successive multi-step reversible switch actuated by said means, a reversible motor-control unit actuated in accordance with the movement of said switch, a source of heat supply to said rolls, means actuated by said unit to control progressively said supply, means to limit the movement of said switch, a pair of signal circuits, and means operable when the switch remains in its respective limit positions for a, given time to energize said circuits.

4. A device for controlling the temperature of drying rolls over which a sheet of paper is passed to be dried, which comprises means responsive to variations in tension of said sheet due to variations in moisture content thereof, a progressive reversible switch actuated by said means, a' reversible motor-control unit actuated in accordance with the movement of said switch, a source of heat supply to said rolls, means actuated by pair of signal circuits, thermostatic switches to --'progressive reversible control switch actuated by movement of said piston, a reversible motor control unit actuated in accordance with said control switch, a source of heat for said rolls, and means actuated by said motor-control unit to control said source. I

6. A temperature control device for paper mill drying rolls over which a sheet of paper is passed to be dried comprising, in combination, a source of heat supply to said rolls, a valve adapted to control said supply, a pair of motor-control units, a variable ratio linkage connecting said units to said valve wherebythe ratio of control effected by the respective units may be adjusted, means responsive to variations in moisture content of said and a second control means adapted to actuate the other of said units.

7. A temperature-control device for paper mill drying rolls over which a sheet of paper is passed to be dried comprising, in combination, a source of heat supply to said rolls, a valve adapted to control said supply,'a-pair of reversible motorcontrol units adapted to jointly control the position of said valve,'means responsive to variations in tension of the sheet due to variations in moisture content thereof to actuate one of said units, and a second control means adapted to actuate the other of said units.-

8- Atemperature-control device for paper mill drying rolls over which a sheet of paper is passed to be dried comprising, in combination, a source of heat supply to said rolls, a valve adapted to control said supply. a pair of reversible motorcontrol units adapted to jointly control the position of said valve, a progressive reversible switch adapted to controleach of said units, means actuating one of said switches in accordance with the tension of said sheet, and manual means to actuate the other of saidswitches.

9. A temperature-control device for paper mill drying rolls over which a sheet of paper is passed to be dried comprising, in combination, a source of heat supply to said rolls, a valve adapted to control said supply, a pair of reversible motorcontrol units adapted to jointly control the position or said valve, a progressive reversible switch adapted to control eachof said units, means actuating one of said switches in accordance with the tension'of said sheet, and thermostatic means responsive to the roll temperature adapted to actuate the other of said. switches.

10. A temperature control device for paper mill drying rolls over which a sheet of paper is passed to be dried, comprising, in combination, a source of heat supply to said rolls, a valve adapted to control said supply, a lever adapted to control said valve, amember adapted to press against said sheet for tensioning the same, integrating means responsive to the average position of said member over given time intervals, a belt actuated by said integrating means to control said lever between limits, and a motor-control unit adapted to control said lever within said limits, said motor-control unit also being actuated by said integrating device.

11. A temperature control device for paper mill drying rolls over which a sheet of paper is passed to be dried, comprising, in combination, a source of heat supply to said rolls, a valve adapted to controlsaid supply, a lever adapted to control said valve, 9. member adapted to press against said sheet m tensioning thesame, integrating means responsive to theaverage position of said member over given time intervals, a belt actuated by said integrating means to control said lever between limits, a motor-control unit adapted to control said lever within said limits, said motor control unit also being actuated by said integrating device, and a master control adapted'to change the range of control of said motor-control unit.

12; In a paper mill, in combination, a drying roll adapted to receive a sheet ofv paper to be dried, a source of steam supply therefor, a control valve for said steam supply, a pair of motorcontrol units adapted to independently control said valve, means automatically operating one of said units in response to variations in the moisture content of said sheet, and a second control means actuating the other of said units.

13. A device for controlling the temperature of drying rolls over which a sheet of paper is passed to be dried, which comprises a member adapted to press against the sheet for tensioning the same, a fluid cylinder, means responsive to movement of said member to control the supply of fluid to said cylindena piston actuated by said fluid, a source of heat for said rolls, and means actuated in accordance with the position of said piston to control said source for varying the temperature of said rolls so as to compensate for variations in moisture of the incoming sheet.

14. A device for controlling the temperature of drying rolls over which a sheet of paper is passed to be dried, whichcomprises a source of heat for said rolls, a proressive reversible control means for controlling said source, means responsive to variations in the moisture content of the sheet, a belt actuated by said last means, said belt passing over said control means for actuating the same, means to limit the movement of said control means, said belt being adapted to slide thereover when the limit of movement 01 said control means has been reached or to permit adjustment of said control means with respect to said belt.

' RAZOR J. SMITH.

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