US2792132A - Apparatus for heat-treating fluent solids - Google Patents

Description

May 14, 1957 F. D. DE VANEY ET Al- 2,792,132

APPARATUS FOR HEAT-TREATING FLUENT soLIDs 3 Sheets-Sheet l Filed July 17, 1951 V -iim 'lllllllllllllllllllllllllllillll llllll INVENTOR Zw @Uma .BY/WW Wg/WM ATTORNELS May 14, 1957 F, D DE VANEY ETAL 2,792,132

APPARATUS FOR HEAT-TREATING FLUENT soLIDs Filed July 17, 1951 3 Sheets-Sheet 2 /Vorma/ ATTORNEYS May 14, 1957 F. D. DE vANEY ETAL 2,792,132

APPARATUS Foa HEAT-TREATING FLUENT soLIDs Filed July 17, 1951 5 Sheets-Sheet 5 ATTORNEY United States Patent APPARATUS FOR HEAT-TREATING FLUENT SOLIDS Fred D. De Varney, Hibbing, Minn., and Donald Beggs,

Toledo, hio, assignors to Erie Mining Company, Hibbing, Minn., a corporation of Minnesota Application July 17, 1951, Serial No. 237,209

7 Slaims. (Cl. 214-182) The present invention relates to apparatus for continuously laying down small masses, e. g., pellets, of mineral particles, e. g., ore concentrates or fines, onto the stockline of a gravitationally descending charge column within a shaft furnace, wherein the small masses constituting the charge are subjected to a desired heat treatment. The invention is particularly concerned with the provision of improvements in the control of a loader mechanism for continuously laying down relatively fragile pellets of moist mineral particles in a manner to compensate for irregularities in the profile of the stockline, arising from irregularities in the rate of feed to the column and from uneven descent of the column, and to maintain a substantially uniform stockline. The improved control mechanism is applicable generally to furnace loaders which continuously travel over the stockline of the charge either in a rotary manner in the case of a shaft furnace of generally circular cross-section or in a reciprocatory manner in the case of a shaft furnace of generally rectangular cross-section, and will be described, in the following, with particular reference to rotary loaders for pellet-indurating shaft furnaces. It is to be noted, however, that the improvements of the present invention are applicable to any type of shaft furnace, Whether used for pellet-indurating or for some other heating or metallurgical operation, wherein it is desirable or necessary to maintain a uniform stockline without mechanical rabbling.

In most shaft-type furnaces or chambers where a iluent material is charged into the top and discharged from the bottom, the stoclrline profile obtained depends in most part either on the angle of repose of the material or the functioning of some mechanical leveling device such as a rabbling arm. ln the art of indurating pellets of balledup moist particles of mineral solids such as iron ore concentrates neither of the above means can be used because (l) the irregularity of prole represented by an angle of repose amounts to too great a variation in the length f travel of the countercurrent stream of heat-treating gas, and (2) mechanical rabbling would break up the relatively very feeble or fragile pellets or balls. Thus, in charging such pellets to the indurating furnace the same must be dropped-for only a minimum distance-onto the stockline and thereafter not disturbed. The stockline of the pellet-indurating furnace must be relatively uniform for two reasons: Y

(l) The distance that the balls are dropped from the loader must be maintained at a minimum in order to avoid breakage from excessive impact, and

(2) The velocity of gases leaving the stockline must be as uniform as possible over the entire surface, which precludes hills and valleys of any substantial magnitude. With hills and valleys the gas velocity would be greater at the valley than at the peak of the hill. This uniformity of gas flow must be maintained in order to maintain `uniform drying and heat treating of the balls. The problem of maintaining the stockline uniform in an indurating furnace in which the fluent material is 'ne ely dropped onto the stockline and left undisturbed (i. e., not rabbled) deserves consideration and discussion.

2,792,132 Patented May 14, 1957 First assume that the stockline rate of descent is absolutely uniform over the entire surface: now, if the loader deposits 1% more feed continuously in a first area than in a second area, the rst area will in time build up to a ridge with a valley at the second area. In other words, no continuous error in feed can be tolerated, even of small magnitude. Conversely, with an absolute uniformity in feed distribution, no continuous differential in rate of descent of the stockline can be tolerated, in spite of which it is the fact that in the operation of such shafttype furnace, irregularities in the rate of descent invariably occur. From a practical point of view, when dealing with commercial size shaft `furnaces, the following is true:

(a) Any mechanical feeding mechanism will have some error in uniformity of distribution, where material is simply dropped onto the stockline, and

`(b) The stockline descent will always be subject to irregularities.

Thus, with no means for correction, the stockline cannot be maintained desirably uniform.

The expression substantially uniform stockline as used above is intended to describe not only a charge column top surface which lies substantially in a single horizontal plane but also a charge column top surface which is intended to present, in cross-section, any 4other predetermined contour. Thus, said expression is specifically intended to apply to a dimpled stockline, i. e., to a charge column top surface which, in cross-section, is characterized by two similar downwardly converging, merging, convexly arcuate lines. Such dimpled Ycontour is or may be desired in situations where the countercurrent of heating gas is rin its entirety introduced'into the charge column about the periphery of the latter and at a level a considerable distance below the stockline, and it is desirable or necessary that the flow of the heating gas be as uniform as possible throughout the upperpart of the column. In such instances, the contour is dimpled so that the straight line distances from a peripheral gas inlet point to all points on the stockline on the same side of the major vertical axis of the charge column as the column.

The general object of the present invention is to pro-V il vide automatic means for maintaining a substantially uniform stockline by providing correction in accordance with deviations from a normal in order to maintain the deviations at a minimum.

According to the present invention, the novel means for maintaining uniformity of the -stockline comprises, in association ywith the traveling loader mechanism of the sha-ft furnace, a control means responsive to a change in the prole of the stockline for varying the rate of deposit of fluent material by the loader mechanism inversely as the change in elevation of the profile to effect an increase in deposit rate at valleys along said path and a decrease in ldeposit at hills along said path. In its preferred embodiment, the invention comprises, in association with the traveling loader mechanism, a loader carriage mechanism adjacent the top of the shaft furnace, a stockline feeler functioning `to gauge the stockline profile just ahead of the loader mechanism in its path of travel, and carriage drive control mechanism, responsive to said feeler, for varying the -rate of travel of the loader carriage and hence for varying the thickness of the layer of fluent solid masses laid down onto the stockline by the loader. The following comprise the basic elements ofthe apparatus involved:

(l) Shaft furnace into which material is charged at the top and discharged from the bottom;

(2) Loader or feeder for distributing material onto the stockline;

(3) Conveyor for conveying material to the feeder;

(4) Carriage for carrying the loader over its feed path;

(5) Carriage drive for moving the carriage;

(6) Discharge mechanism for discharging material from the furnace;

(7) Discharge mechanism drive for actuating the discharge mechanism;

(8) Stockline feeler for gauging stockline elevation just ahead of the loader in its path of travel; and

(9) Carriage drive control responsive to position of stockline feeler to maintain constant profile of stockline.

In its preferred form, the apparatus also includes a (10) Discharge control responsive to position of stockline feeler to maintain average stockline elevation.

In essence, the functioning of the improved apparatus organization is as follows: the average elevation of the stockline of the charge column is maintained within predetermined normal limits preferably by appropriate adjustment of the discharge rate, and lactual prole irregularities in the stockline are reduced to a minimum by (a) feeling any low or high area ahead of the loader mechanism, and (b) reducing or increasing respectively the rate of travel of the loader carriage in passage of the loader over said area.

The invention will now be described 'with greater particularity with reference to the laccompanying drawing, in which Fig. l is a view in vertical section of an indurating furnace of generally cylindrical construction having a rotatable carriage and loader supported thereby and in which is incorporated one embodiment of the invention;

Fig. 2 is a view of the furnace in part top plan illustrating the essential features of the loader carriage control;

Fig. 3 is a schematic electrical diagram appertaining to the automatic control for the carriage drive motor and furnace discharge motor -according to the preferred em bodiment of the invention as illustrated in Figs. l and 2; and

Fig. 4 is also a schematic electrical diagram for a somewhat modifled embodiment of the invention.

With reference now to the drawings:

=In Fig. 1, a generally cylindrical and vertical, heatinsulated shaft furnace is represented in cross-section at 1. For charging this cylindrical type of furnace, a rotary type of loader or feeder is utilized. The principal components of this loader comprise a horizontal frame or carriage 2 made of structural iron having depending therefrom a circular trackway 3 supported by a plurality of rollers 4 journalled in bearing brackets 5 secured in spaced relation around the furnace on -a horizontal offset portion of the furnace wall just below the furnace mouth. The center of trackway 3 is concentric with the vertical axis x-x of the furnace and hence carriage 2 is revolvable -about the furnace axis. Mounted upon the carriage at one side of the furnace axis x--x is a reciprocating type of conveyor consisting of 'an upper chute 6 anda lower chute 7 connected to a diester type of reciprocating drive designated generally by reference numeral 8. This type of drive obtains its power from an electric motor 9 by a belt and wheel 10 and the rotary input motion is converted into a reciprocating output motion of rod 11 which is coupled by lever 12 and linkage 13 to the upper and lower chutes 6 and 7 in such manner that the chutesrreciprocate simultaneously in opposite directions. Chutes 6 and 7 are arranged one above the other in ya direction generally radial of the furnace axis x-x. With the diester type drive and the chute interlinked as shown, the radially outward stroke of chute 6 and the simultaneous radially inward stroke of chute 7 will be relatively rapid and the reverse strokes will be 4relatively slow. Hence, as the chutes reciprocate, uent solid materials carried to the furnace by an endless conveyor 'belt 14 and dropped onto the inner end of chute 6 will be caused to travel radially outward to the outer end thereof. The material is then transferred t-o the outer end of lower chute 7 and caused to travel radially inward and spill off the side edges thereof onto the stockline 15 of a charge column 16 of similar materials generally filling the furnace.

The upper chute 6 is substantially uniform in width throughout its length yand serves to collocate the material. the lower chute 7 is, however, stepped downwardly in width in the radially inward `direction as seen in Fig. 2 in order to distribute the material uniformly over the stockline as -the carriage 2 rotates. For rotating carriage 2, the latter is provided with a depending ring gear 17 meshed with the gear 18 on the drive shaft of motor 19.

From a metallurgical point of View, furnace 1 correspends generally to that disclosed in U. S. Patent No. 2,533,142, according to which latter the shaft comprises an upper part A communicating with a lower part B, the two parts being so designed and positioned with respect to each other as to provide a passageway therebetween and, as represented at 23 and 24 respectively, lower and upper, annular, plenum spaces immediately adjacent and contiguous with free surfaces of the charge column at the upper end of lower part B and adjacent the lower end of upper part A, respectively. Offset from parts A and B is a chamber 25 providing combustion space D, which communicates with parts A and B at plenum spaces 24 and 23 respectively. In the lower part B of the furnace there is provided an inlet conduit 26 for a forced current of air supplied by pump 27 to be passed upwardly through the material in part B to plenum space 23, thence into and through combustion space D, and finally to plenum space 24 and into and through the material in part A. At 28 is represented a fuel inlet for delivering iuid fuel to the combustion space D for combustion in the air current whereby to thermally enrich the latter prior to its passage through part A.

The pellets of fluent material undergo an indurating process as they descend progressively through the furnace and are finally discharged at the bottom of the furnace by means of a discharge mechanism which, in the form illustrated, is comprised of an endless belt conveyor 30 driven by an electric motor 31.

It has been explained that the principal objective sought by the present invention is the substantially complete elimination of all hills and valleys in the profile of the stockline of the charge column in the furnace. To this end, reference is now made in particular to Figs. 2 and 3. A feeler cup 32, for sensing, i. e., determining the stockline profile is mounted at the outer end of an arm 33 whose inner end is made fast to a rocker shaft 34. Rocker shaft 34 is mounted for rotation in a bracket 35 secured to'the carriage 2. Feeler cup 32 rides by gravity upon the surface of the stockline 15 and is located slightly in advance of the leading side 7a of the tapered discharge chute 7 as viewed in Fig. 2. That is, with rotation of the carriage 2 counterclockwise as indicated in Fig. 2 by the directional arrow, cup 32 occupies a position counterclockwise from the leading side 7a of chute 7 and is used to determine the stockline profile slightly in advance of the rotation of the feeder chutes.

As the feeler cup 32 rides in a circular path over the stockline 15, part of which is shown in development in Fig. 3, it rises and falls according to the hills 15a and valleys 15b in the stockline which represent in a somewhat exaggerated manner the undesirable deviations in the stockline profile from the uniformly even level indicated by the line 15e. The circuit of motor 19 which drives carriage 2 includes a rheostat 36 connected in series therewith from the power line conductors L1 and L2 and mounted within a housing 37 also carried by bracket 35. The position of the rheostat slider 38 on the resistor element 39 at any instant is governed by the essaies instant elevation of feeler cup 32, and the arrangement is such that the portion of resistor 39 in circuit with carriage drive motor 19 increases from normal as feeler cup 32 drops in a valley 15b in the stockline and decreases from normal vas the cup rises over a hill 15a in the stockline. To this end slider 38 can be mounted as shown upon an arm 40 secured to rock shaft 34 such that as arm 33 rises, arm 40 will be lowered, and vice versa. An increase in resistance from the normal setting is effective to slow down the carriage motor drive from its normal rate of about one revolution per minute and hence the immediate result is to deposit the fluent material at a greater than normal rate, per unit of travel, upon this valleyed portion of the stockline. In a similar manner, a decrease in resistance signalled by a rise in cup 32 upon a hill is effective to speed up the carriage drive motor 19 with the result that the fluent material deposited upon the hilled portion will be at a less-thannormal rate. Thus, by slowing down the rate of rotation of the carriage 2 and thereby also the chutes 6 and 7 at any temporary valley in the stockline detected by feeler 32 and conversely increasing the rate of rotation at any temporary hill detected by feeler 32, the general result will be to maintain the stockline at the same level throughout the entire rotational path of the feeder chutes. The control is progressive in character in that the change in speed of the carriage drive motor 19 is proportional to the rise or fall of the feeler cup 32 on the stockline 15.

It will also be observed from Fig. 3 that a mercury type of switch 42 is also included in the control circuit of the motor 31 which drives the discharge conveyor 30 for switching in or out of the motor circuit a control resistor 43 connected in series between the power line, L1, L2 and motor 31. With resistor 43 shunted out of the circuit of motor 31 by closure of the contacts in switch 42, motor 31 will receive a higher operating voltage, the effect of which is to cause it to run faster and hence increase the speed of the discharge conveyor belt 30 which in turn effects a corresponding increase in the rate at which the heat-treated fluent material is discharged from the furnace.

Conversely, with resistor 43 connected in the circuit of motor 31 which is the condition which obtains when the'contacts of switch 42 are open, the operating voltage for the motor is decreased, causing it, and hence also the conveyor belt 30, to decrease in speed and hence effect a decrease in the discharge rate of the fluent material from the furnace. With the rheostat arm 3S at the normal position on resistance 39 as pictured in Fig. 3, the contacts of switch 42 can be closed or open.

Switch 42 is 'also conveniently located within housing 37 and can also be secured to arm 46 on the opposite side of the rock shaft pivot axis 34a from feeler cup 32, As illustrated, the arrangement is such that when the feeler cup 32 rides the stockline at the normal level 15C sought to be maintained, or is above such level, switch 42 will be tipped to such an angle that the mercury 42a therein bridges and closes the circuit at the switch contacts 42b thus shunting out resistor 43 and causing discharge conveyor 30 to operate at its fast rate and withdraw uent material from the furnace at a greater rate than it is being brought to the furnace by conveyor 14. The effect of this will be to slightly lower the general level of the stockline 15. Then when the general level of the stockline has decreased to a point below the normal average, switch 42 is tipped upward to a posi tion wherein the mercury 42a will no longer bridge and close the circuit across the switch contacts 42b. Control resistor 43 is thereby reconnected in the circuit of motor 31 and the latter will run at its slow rate to thereby effect withdrawal of the material from the furnace at a lesser rate than it is being brought to the furnace by conveyor 14. The effect of this will be to raise the average level of the stockline 15 back to at least normal,

6 whereupon the control cycle will be repeated. Thus Yby the hunting type of control wherein the discharge rate of the material from the furnace is cyclically increased and decreased, a generally average elevation of the stockline will be maintained in the furnace. A somewhat similar type of'control for maintaining the average elevation of the stockline is disclosed and claimed in application Serial No. 6,743, tiled February 6, 1948, in the name'of Carl W. Sisco, now Patent No. 2,646,900.

From the foregoing description it should now be clearly apparent that the two motor controls shown in Fig. 3 operate in conjunction with each other, the control for motor 31 serving to maintain an average elevation of -the stockline 15 and the control for motor 19 serving to remove any hills and valleys from the profile of the stockline regardless of its instant average height.

A modified type 4of control over the speed of the carriage drive motor is illustrated in Fig. 4 wherein means are provided for running motor 19 at three speeds, high, normal and low, as distinguished from the rheostat control of Fig. 3 wherein the speed of motor 19 is varied more directly proportionally to the size of the hills and valleys in the stockline prole.

With reference now to Fig. 4, wherein elements which are the same as in Fig. 3 have been assigned the same reference numbers, it v/ill be seen that the circuit from motor 19 Ito the line conductors L1, L2 includes two resistors 44, 45 connected in series therewith, and that control over these resistors which are arranged to be selectively shunted out of the motor circuit is exercised by two mercury switches 46, 47 mounted on arm 41, the resistors 44, 45 and their shunting switches 46, 47 taking the place of the rheostat 36 in the Fig. 2 control. Also mounted on arm 41 is another mercury switch 42 which functions to control the speed of the material discharge device in the same manner as in the Fig. 3 arrangement. Mercury switches 46 and 47 are so adjusted on their supports that the contacts of both will be open whenever the feeler cup 32 'detects a low spot or valley 15b in the stockline profile. Under these conditions both resistors 44, 45 remain in series circuit relation with the carriage drive motor 19 causing the carriage and material loader to rotate at the low speed. When feeler cup 32 rides the stockline at the normal profile as depicted in Fig. 4, switch 46 will remain lopen but switch 47 will be elo-sed, thus shunting out resistor 44 through conductors 4d, 49 and 50 and causing the carriage drive motor 19 to operate at its middle or normal speed. When feeler cup 32 detects a hill 15a in the profile of the stockline as measured along its circular path around the stockline, mercury switch 46 will also close which is effective to shunt out both resistors 44, 4S through conductors 4S, 51 and 52, whereupon carriage drive motor 19 is caused to run at its high speed.

Control over the speed of the material discharge as explained above is effected through mercury switch 42 which operates in the same manner as in the Fig. 3 circuit and preferably the mercury switches 42 and 47 are so adjusted that their contacts close at the s-ame time.

Thus, as long as carriage 2 travels at the normal speed the feeder chute 7 will deposit on the stockline 15 a material layer of norm-al (and uniform) thickness, whereas the chute 7 will deposit a thinner than normal layer when the carriage is traveling at the high speed, and a thicker than normal layer when the carriage is traveling at the low speed. Hence, as long as stockline feeler 32 feels a stockline surface whose levelness is within the limits of normal range, the carriage 2 travels at normal rate causing feeder chute 7 to lay down a pellet layer of normal, uniform thickness. When, however, feeler 32 encounters a stockline surface portion whose height is greater than normal (i. e., hits a high spot in the profile of the stockline), the rate of angular movement of the carriage 2 is increased to high" speed and feeder chute 7 is caused 'to deposit a thinner than normal 'ferred to in the specific disclosure.

'conveyor in its longitudinal travel.

layer of pellets. As soon as feeler 32 passes over the high spot and encounters a stockline surface portion whose height is within the normal range, the rate of movement of carriage 2 is decreased to normal speed, whereupon feed chute 7 is caused to deposit a pellet layer of normal thickness. When feeler 32 encounters a stockline surface portion whose height is less than normal (i. e., hits a low spot in the stockline profile), the rate of movement of carriage 2 is decreased from normal speed to low speed and feeder chute 7 is caused to deposit a thicker than normal layer of pellets on stockline for so long as feeler 32 continues to signal the presence of the low spot, thus tending to correct the low spot, whereafter the rate of movement of carriage 2 is advanced to normal speed and feeder chute 7 of the loader is caused to deposit a pellet layer of normal thickness.

By thus controlling and varying the speed of travel of the loader carriage 2, the relative thickness of the pellet layer laid down on the stockline 15 is m-ade self-compensating to the end that hills and valleys will be eliminated from the stockline prole practically as fast as they start to appear.

Conventional slip rings and brushes are utilized for connecting switch 42 and rheostat 36 according to the Fig. 3 arrangement or the switches 42, 46 and 47 according to the Fig. 4 arrangement into their respective control circuits for thev loader carriage drive motor 19 and the material discharge drive motor 31; the brushes 53 are carried by and rotate with the carriage 2, and the slip rings 54 on which the brushes ride are arranged one above the other and are secured about the periphery of the furnace 1.

It is to be noted that the principle of stockline profile control inherent in the two specific embodiments above described in Figs. 3 and 4 can be applied equally as well to a rectangular furnace as to the cylindrical furnace re For example, the simplest way to feed a rectangular furnace is to use a belt conveyor carried by a reciprocating carriage so that the point of discharge of the belt conveyor is caused to travel generally longitudinally back and forth over the stockline. The average stockline elevation is maintained normal by regulating the relative furnace discharge rate to feed rate, in a manner similar to that above disclosed. The actual deviations from normal in stockline profile can be maintained at a minimum by regulating the speed of travel of the ltraveling carriage whereby the belt conveyor feeder, driven at a constant speed, deposits more or less material in low or high spots. The stockline feeler is arranged to determine the stockline elevation just ahead or in the vicinity of the point of feed of the belt In certain possible paths of feed travel over the stockline, two feelers may be required due to direction reversal of the traveling carriage.

It is to be noted that levelling out of the hills and valleys in the stockline is effected by varying the speed of travel of the traveling carriage without regard to the rate at which the pellets are delivered to the point of discharge from the carriage by the feeder conveyor 14, This condition cannot be otherwise for the pellets must be carried along by conveyor 14 from their source, namely the balling drum, at whatever rate they are discharged from the drum. The reason for this stems for the fragile nature of the pellets as they leave the drum which makes it impossible to deliver them to some intermediate storage point from the drum and from wherever they could be carried as needed to the furnace by the feeder 14. Consequently, it would not be practical to effect levelling of the stockline by keeping the speed of the carriage constant and adjusting the rate of delivery of the pellets to the carriage from the feed conveyor 14.

Moreover, in certain applications of the invention where no control over the discharge rate may be required it is obvious that this component of the organization, namely the variable drive for the discharge device 30, 30 can be omitted.

In conclusion we desire it to be understood that the various embodiments of our invention as described and illustrated are to be considered as typical rather than exhaustive of the structural variation possible within bounds of our invention and that in accordance therewith, various other arrangements may be developed without, however, departing from the spirit and scope of our invention as defined in the appended claims.

We claim:

l. In a shaft furnace whereinto fluent solid material is fed at the top and wherefrom heat-treated fluent solid fmaterial is discharged from a lower part thereof, and

wherein an average stockline elevation is maintained, the combination of a loader for distributing a layer 0f fluent solid material in a path over the stockline, a carriage for transporting the loader over said path, a variable speed drive mechanism for propelling the carriage along said path at variable speed, a determining device for determining the profile of the stockline along said path of said loader, said profile-determining device including a mechanical feeler device riding in surface contact with said stockline in the path of said loader and sensing deviations in stockline height above and below such average stockline elevation, and means controlled by said feeler device for automatically varying the speed of said drive mechanism whereby to move the loader at a higher than normal rate of speed when the same is feeding to an area of the stockline which is above average height and to move the loader at a lower than normal rate of speed when the same is feeding to an area of the stockline which is below the average height.

2. The invention as defined in claim l wherein said variable speed drive mechanism includes an electric motor and a speed changing element connected in circuit therewith and controlled by said stockline profile determining device.

3. The invention as defined in claim 2 wherein said speed changing element is constituted by a rheostat the slider arm of which is controlled by said stockline profile determining device.

` 4. The invention as defined in claim l wherein said variable speed drive mechanism includes an electric motor and speed changing elements selectively connectable in circuit therewith by said stockline profile determining device to effect stepped changes in the motor speed.

5. The invention as defined in claim 4 and wherein said speed changing elements are selectively connected in circuit with said motor by switches controlled by said stockline profile determining device.

6. The invention as defined in claim 1 wherein the fiuent solid material is withdrawn from said furnace by an electrical discharge device operable at different speedsI and the speed of operation thereof is controlled by switch' means actuated by said stockline profile determining device.

7. The invention as defined in claim l wherein said stockline profile determining means is constituted by a mechanical feeler device riding in surface contact with said stockline at one end of a crank arm, the other end of said arm being secured to a rock shaft, and the drive means for said carriage is constituted by an electric motor having a speed control therefor actuated by said rock shaft in accordance with the angular displacement thereof.

References Cited in the file of this patent UNITED STATES PATENTS Y 1,666,027 Beaumont Apr. l0, 1928 1,961,893 Wadman et al lune 5, 1934 2,030,448 Hardgrove Feb'. 11, 1936 2,219,954 Geiger et al. Oct. 29, 1940 2,277,879 Ness et al. Mar. 31, 1942 2,636,606 Dunasky et al. Apr. 28, 1953

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