US2655815A

US2655815A - Belt drive for grind mill roll stands

Info

Publication number: US2655815A
Application number: US211275A
Authority: US
Inventors: Mcclelland Kenneth
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-02-16
Filing date: 1951-02-16
Publication date: 1953-10-20
Anticipated expiration: 1970-10-20

Description

Oct. 20, 1953 K. MGCLELLAND BELT DRIVE FOR GRIND MILL ROLL STANDS 4 Sheets-Sheet 1 Filed Feb. 16, 1951 INVENTOR O 1953 K. MQCLELLAND 5 ,815

BELT DRIVE FOR GRIND MILL ROLL STANDS Filed Feb. 16, 1951 4 Sheets-Sheet 2 Oct. 20, 1953 K. MQCLELLAND 5,

BELT DRIVE FOR GRIND MILL ROLL STANDS Filed Feb. 16, 1951 4 Sheets-Sheet :5

Oct. 20, 1953 K. M CLELLAND BELT DRIVE FOR GRIND MILL ROLL STANDS 4 Sheets-Sheet 4 Filed Feb. 16, 1951 1 N VE NTOR A ORNEY Patented Oct. 20, 1953 UNITED STATES PATENT OFFICE BELT DRIVE FOR GRIND MILL ROLL STANDS Kenneth McClelland, Chicago, Ill.

Application February 16, 1951, Serial No. 211,275

11 Claims. (Cl. 74-24211) This invention relates to grind mill r011 Stands of the type comprising two pairs of belt-driven grinding rolls, each pair of which includes a fast roll and a slow roll, and has a particular reference to improvements in the arrangement of the rolls and the belt drive connections between the drive shafts and the grinding rolls of such stands.

In flour mills, the largest users of roll stands of the type disclosed herein, the maintenance of mill balance or the distribution of the mill stocks according to the distribution of capacity is essential to successful operation, more important even than uninterrupted twenty-four hour operation all week long,

Flour milling is a gradual reduction where each roll stand does a definite type of grinding on a classified stream of stock, the product of that roll stand then passing to certain classification facilities to be reclassified for further grinding. These classifiers also serve to distribute the mill stock, all of one classification going to its assigned roll or rolls.

Unbalance in the flour mill reduces both the percentage of highest'quality flour and the capacity of the mill as a whole. High qualit flour erly adjusted for the type and amount of stock flowing to it and running at normal speed, with normal difference in speed of fast and slow rolls.

The variations in mill balance effected by slipping belts on one roll stand are the variations of the product of that roll stand, which determine the loading of subsequent roll stands. As the roll setting is maintained by stiff spring pressure, appreciable variation of the amount of stock passing through the rolls varies the roll pressure and granulation of that roll stand, changing the loading of other subsequent roll stands. This unbalanced condition is further complicated by the fact that the classification facilities after'each roll stand are limited both as to capacity and range of assortment. If any of these classifiers are either overloaded or underloaded, they may damage the mill stock. Unusual mill stocks fed to a certain classifier Will not be satisfactorily classified.

The control of the milling process is effected by the sampling of the ground product beneath each pair of rolls. As both pairs on the same stand are ordinarily set for the same grind, this sampling includes comparison of the product of the two pairs of rolls.

This sampling process is improved if the rolls are symmetrically placed, that is, either the fast roll or the slow roll is placed to the outside of the roll stand on both sides. The product fans out beneath the pair of rolls, one classification tending to fall beneath the slow roll and another classification tending to fall beneath the fast roll. The sampling door is below and outside the outer roll. If the miller reaches in and takes a sample in the same manner on both sides, he gets the same cross section if the rolls are so symmetrically placed. If they are placed as is now common, one side having the fast roll outside, the other having the slow roll outside, the samples taken in the same manner on the two sides are not alike.

The miller prefers the fast roll outside for facility and safety in replacing scrapers while running. In grinding with smooth rolls, which more than half the roll stands use, scrapers are used to remove the last of the ground stock from the rolls. The slow roll scraper is not absolutely essential, if faulty it can be changed at the end of the week, but the fast roll scraper is required at all times. If the fast roll is outside the replacement of this necessary scraper while running is much simpler, faster and safer than if the fast rolls are inside the slow roll.

Occasionally a roll stand is choked, despite the power applied, either from excessive stock wedging in between the rolls, or filling up because a choke below the stand will not permit the egress of the ground product or the rolls expanding from the heat of rubbing against each other without stock when the flow of stock to the rolls is interrupted. Sometimes the belts will burn off, and occasionally they will kee on driving and start a fire in the stand. If the belts can be made to fly ofi immediately on such overloads and the miller notified by an alarm, the fire hazard, and damage to rolls, bearings and belts will be minimized. The miller cannot always catch these maladjustments immediately because for sixteen of the twenty-four hours there is only one man on the grinding floor and he has many duties elsewhere.

Primarily the object of the invention is to provide, between the drive shaft and the fast and slow rolls of a grind mill roll stand of the type mentioned, novel belt connections which insure maintenance of predetermined speeds of rotation of the fast and slow rolls, and, consequently, constant, uniform grinding actions of the rolls, whereby a maximum amount of high quality flour or other ground product is obtained from any given amount of grain or other material fed between the rolls.

Heretofore, it has been usual in grind mill roll stands of the type mentioned to provide, between the drive shaft and the fast rolls, one belt to drive the fast rolls and, between the drive shaft and the slow rolls, either another belt or a pair of belts and generally a countershaft to control the speed of the slow rolls. In this connection, during grinding, the tendency of the fast rolls is to increase the speeds of the slow rolls to the speeds of the fast rolls, and, hence, to cause the slow rolls to develop power tending to cause them to over-run their speed-retarding drives and to return a certain amount of power. However, according to such usual prior practice the slow roll speed control belt or belts and the countershaft. if used, unnecessarily duplicates the handling of part of the power, using more belting than necessary, with attendant loss of efficiency and added maintenance, and need for attention to the more complex mechanism.

Accordingly, a special object of the present invention is to provide, in a grind mill roll stand of the type mentioned, one belt which connects the drive shaft with the fast roll of one pair and the slow roll of the other pair, and another belt which connects the drive shaft with the remaining fast and slow rolls of the two pairs, whereby both belts are ad antageously edually loaded and both advantageously operate to utilize the power developed in the slow rolls while grinding to help drive the fa t rolls without any supplementary belting or mechani m. Other particular advantages of the present belt drive arrangement as just outlined are that belt ten ions are minimized and that, therefore, narrower and less costly belts may be used than heretofore: that narrower belts conserve valuable space; and that bearing pressures are reduced with con equent reduction in roll stand maintenance costs.

Another special and important obiect of the invention is to associate with the belts of the present belt drive arrangement as outlined, simple, practical means of determining and automatically maintaining proper tensions in the belts such that they are effective to tran mit all necessary power for proper operation of any given roll stand under normal grinding conditions, but are ineffective to tran mit appreciably greater power, whereby they will ride off their pulleys and top operation of the roll stand should they for any rea on become overloaded as, for example, due to iamming of material between the rolls of the roll stand. In this way roll damage is minimized and there practically is eliminated any possibility of damage to the belts or overheating of bearings or the occurrence of a fire due to chokes.

Another ob e t of the invention is to provide a roll arrangement similar on the two sides of the roll stand to facilitate ampling of the ground stock, and as far as possible provide for the fast rolls on the outside to facilitate replacement of the fa t roll scraper.

Another object of the invention is to provide dependab e means for driving the roll stands with the fiat belts with line haft a short center distance from the rolls to make possible the utilization of the shaft floor for other purposes. The roll floor in a flour mill is above a shaft floor almost exclusively devoted to the shafting and pulleys necessary for driving the roll stands.

An additional special and important object of this invention is to provide a construction and arrangement adaptable to existing roll stands in order to make it useful to industry. Roll stands are long lived; probably 75 of those in the country are over thirty years old; a substantial percentage are over fifty years old. Very few flour milling companies can afford the capital investment required to completely replace their r011 stands.

A further object of the invention is to eliminate the tunnel commonly extending through the roll stand to provide for the countershaft controlling the slow rolls. This tunnel bisecting the space for egress of the ground product increases the possibility of choke-up beneath the stand and provides a breeding place for insect infestation.

A still further object of the invention is to provide means whereby a suitable alarm is operated in the event of the development of an abnormal condition in either of the belts of the present belt drive.

With the foregoing and other objects in view, as will become more fully apparent as the nature of the invention is better understood, the same consists in grind mill roll stand arrangement and belt drive connections such as are illustrated by way of example in the accompanying drawings and as will be hereinafter more fully described and claimed.

In the accompanying drawings, wherein like reference characters denote corresponding parts in related views:

Figure 1 is a perspective view illustrating more or less schematically belt drive connections between the drive shaft and the fast and slow rolls of a ring mill roll stand in accordance with one practical embodiment of the invention; and

Figures 2, 3 and 4 are views similar to Figure 1 illustrating belt drive connections in accordance with alternative embodiments of the invention.

Referring to the drawings in detail, it will be observed that, according to each of the different illustrated embodiments of the invention, the grind mill roll stand is of the type comprising two pairs of rolls each pair of which is composed of a fast roll and a slow roll. The rolls are, of course, disposed horizontally and parallel to each other. Preferably, too, they are disposed in a common horizontal plane, although this is not essential. In any event, the two pairs are suitably spaced apart and the rolls of each pair are disposed for grindin cooperation closely adjacent to each other.

Referring now particularly to the embodiment of the invention illustrated in Figure l of the drawings, the two fast rolls are designated as A, A. and their related slow rolls are designated as B, B. In this connection and as will be noted, each fast roll is disposed outwardly with respect to its related slow roll. This, however, although a departure from prior common practice, is preferable but not essential, since the fast rolls may, if desired, be disposed inwardly relative to their related slow rolls, as will later become apparent.

Each of the rolls A and B includes, as usual, a shaft l0 extended on one end to accommodate a pulley, said shaft being journaled in a bearing 1 l suitably mounted upon a frame element I2. whereby the T0115 are mounted for rotation and in proper relationship to each other. In accordance with known practice, suitable provision is made whereby one roll of each pair is adiustable toward and away from its companion roll to vary the fineness of grinding of material fed between the rolls. However, the present invention is not concerned with this and therefore it has not been illustrated.

Below or otherwise suitably located relative to the rolls A and B is a drive shaft, designated as It, which is horizontally or substantially horizontally disposed and which usually extends parallel or substantially parallel to the rolls A and B.

On the shaft ii! of the fast roll A of one pair of the rolls is fixed a pulley it which is disposed at one side of the roll stand. On the shaft ID of the slow roll B of the other pair of rolls is fixed a companion pulley which is disposed at the same side of the roll stand as the pulley I l and in the same plane as the latter. Similar companion pulleys l6 and I? are fixed to the shafts Iii of the other fast and slow rolls, respectively, at the other side of the roll stand.

On the drive shaft it are fixed two pulleys I8 and 9 the former of which is disposed for proper alinement with the pulleys I l and i5 and the latter of which is disposed for proper alinement with the pulleys it and I1.

Engaged with the pulleys l4, l5 and i8 is an endless belt 2!], which extends directly across the pulleys l4 and It, and directly from the outer sides of the latter to the pulley it, while engaged with the pulley it, It and I9 is an endless belt 2! which likewise extends directly across the pulleys it and II and directly from the outer sides of the latter to the pulley it. Thus, the fast roll of one pair and the slow roll of the other pair are connected to the drive shaft it by the belt 23 at one side of the roll stand, and the other fast and slow rolls are connected to the drive shaft I? by the belt 2! at the other side of the roll stand.

Preferably the two drive shaft pulleys It and 19 are of equal diameters; preferably the two fast roll pulleys it and it are of equal diameters; and preferably the two slow roll pulleys I5 and l! are of equal diameters. If so, the slow roll pulleys I5 and i; will, of. course, be of suitably greater diameters than the fast roll pulleys Id and i6, whereby the fast rolls are driven by the shaft It at suitably greater speed than the slow rolls. However, corresponding pulleys of the two sets need not be of equal diameters since desired higher speeds of the fast rolls than the slow rolls may be obtained by otherwise suitably varying the diameters of the respective pulleys. In any event, one of the belts, the belt 20 in the present instance, is crossed so that the rolls of each pair are driven inwardly and downwardly relative to each other.

Suitably cooperating with the belts 2t and 2! is, or are, suitable means for automatically maintaining them under constant, predetermined tensions sufficient to prevent them from slipping relative to their related pulleys under normal load conditions of the roll stand, but insufficient to prevent either of the same from readily slipping oi'f its related pulleys in the event of minor overloading of either pair of rolls.

In the drawings, the belt tensioning means referred to is in the form of a pair of slack take-up pulleys in the event of minor overloading of either pair of rolls. The pulleys 22'*-22 are, of course, engaged with the slack strands of the belts 29 and 2! and may be loaded either by weights 23 or, alternatively, by springs. In either case, their proper loading may be determined by varying the values of the weights 23 or the strengths of the springs, as the case may be during a trial period of grinding operation of the roll stand. Thereafter their loading is constant and is such as to maintain the belts under constant tensions as described under wide range of variation of belt lengths. Alternatively, the drive shaft l3 may be mounted for movement toward and away from the rolls A and B and a weight or weight or a spring or springs may be employed to tend constantly to shift said shaft away from said rolls to maintain the belts 2i) and 2| under constant tensions as aforesaid.

As will be apparent from the foregoing, not only are the belts 2t and 2i maintained under constant tensions such as to insure predetermined speeds of the fast and slow rolls and uniform grinding actions of said rolls with the output of a maximum amount of high quality ground material under normal load conditions of the roll stand, but their loading always is of a minimum value not appreciably in excess of that required to adapt them properly to perform their functions. Hence they may be of minimum widths with the advantages of low cost and conservation of space at either side of the roll stand. In addition, they impose minimum pressures upon the bearings l l and, hence, contribute materially to minimizing maintenance and power costs of the roll stand.

The embodiment of the invention illustrated in Figure 1 of the drawings may be used in any instance where the belts 28 and ii are of lengths such that they will operate satisfactorily when one of them is crossed, and it has the advantage that the slack sides of the belts do not become taut at the instant of startirr of operation of the roll stand as well as the further advantage that the belts exert inward pressures upon the fast roll pulleys with consequent relief of normal grinding pressure on the fast roll bearings ll.

When the roll mill is in operation the fast rolls act through the material being ground to tend to rotate the slow rolls at the same speeds as the fast rolls. Hence, the drive shaft is not required to furnish power directly to the slow rolls to drive them. On the contrary, the slow roll, being driven by the fast roll of its pair, acts through its belt to help drive the fast roll of the other pair. Therefore, the maximum load on each belt is that required to drive its fast roll and the power drawn from the lineshaft the difference between that required by the fast roll and that furnished by the slow roll of the other pair. As this salvage of slow roll power is simple and direct there is minimum loss of power.

Suitable means are provided whereby an alarm is operated in the event of the development of an abnormal condition in either of the belts 28 or 2 i An abnormal condition of either belt may result from an amount of stretch thereof such that its slacl; take-up means has reached the end of its effective range of movement, or from the belt having ridden off its pulleys. in either case, one or the other of the idler pulleys 22 will move to its limit of movement under the influence of its Weight 23, or equivalently, its spring, or the drive shaft it will move to its limit of movement under the influence of its weight or weights or pring or sprin as the casemav be. Ther for such movement of either of the idler pulleys or of said drive shaft, may appropriately be employed for the purpose of operating an alarm. In this connection and as illustrated in the drawings, the pivoted arms 2t upon which the idler pulleys 22 are mounted may each have suitably mounted thereon an electric switch 25 of a type which maintains the circuit of an electric alarm 26 open as long as the arm and the switch are not tilted beyond a predetermined angle, but which serves to close said circuit upon tilting of said arm and said switch beyond said angle. As long as the belts 2i] and 2| are in normal conditions the angles of the arms 23 and of the switches 25 are such that said switches are open. When, however, an abnormal condition of either belt develops, the related arm 2 and switch 25 assume angular positions such that the switch closes the alarm circuit. Accordingly, the alarm is operated when an abnormal condition of either belt develops.

In some instances the drive shaft [3 may be desired so near the grind rolls as to preclude the possibility of using a crossed belt as in the Figure 1 embodiment of the invention. In any such instance most of the various advantages of the belt drive arrangement illustrated in Figure 1 of the drawings may be attained by a belt drive arrangement as illustrated in Figure 2 of the drawings.

In Figure 2 of the drawings the arrangements of the grind rolls and their pulleys and the drive shaft and its pulleys are the same as in the Figure l embodiment of the invention, except that the drive shaft is disposed so near the grind rolls that it is impracticable to use one of the belts crossed as in the Figure l arrangement. Accordingly, the same reference characters as are employed in Figure 1 are employed in Figure 2, with the exponent 2, to designate parts corresponding to parts shown in Figure 1. In other Words, in Figure 2, the fast rolls are designated as A the slow rolls as B the roll shafts as IE the fast and the slow roll pulleys cf the two sets as M I I5 and H respectively, the drive shaft as l3 its pulleys as I3 I9 and the belts as 29 and 2 i At one side of the roll stand of the Figure 2 embodiment of the invention one of the belts has the same arrangement relative to its pulleys as the corresponding belt of the Figure 1 embodiment of the invention. In other words, the belt ZI of Figure 2 has the same arrangement relative to its pulleys :6 I1 and 59 as the corre sponding belt 2! of Figure 1 has relative to its pulleys IS, IT and 19. The other belt, 29 of the Figure 2 embodiment of the invention, instead of being crossed as in the case of the corresponding belt 20 of the Figure 1 form of the invention, and instead of extending directly across the pulleys I4 and !5 as in the case of the belt 23 with respect to the pulleys l4 and I5, extends from the drive shaft pulley A8 to the inner sides of the pulleys I4 and I5 outwardly and downwardly over the latter pulleys past said drive shaft pulley I8 and to and about an idler pulley 22 located at the side of the drive shaft l3 remote from the rolls A and B Thus, the belt 29 connects the fast roll of one pair and the slow roll of the other pair to the lineshaft, the belt 2| connects the remaining fast and slow rolls, and the rolls of each pair are properly driven downwardly and inwardly relative to each other.

The belt 20 has the appearance of the slow roll belt used in the common method of driving properly drive the fast rolls.

8 a roll stand without a countershaft. In that slow roll belt, however, the strand passing beneath the lineshaft is not the slack strand which precludes automatically slack side tension control through the idler pulley beneath the lineshaft, which is made possible in the present drive.

The pulley 22 may be either a slack take-up pulley or simply a fixed idler pulley. If it is a slack take-up pulley, another slack take-up pulley 22 may be provided to cooperate with the slack strand or reach of the belt 2| and both of said slack take-up pulleys 22 may be loaded in the same manner as the slack take-up pulleys 22 of the Figure 1 embodiment of the invention to maintain the belts 2 0 and 2! under constant tensions sufficient to prevent slip of the same relative to their associated pulleys under normal load conditions of the roll stand, but insufficient to prevent the same from readily slipping off their associated pulleys in the event of abnormal load,- ing of the rolls. If, on the other hand, either

pulley

22 or 22 is a fixed idler pulley, the drive shaft I3 may be mounted for adjustment toward and away from the rolls A and B and may be weight or spring loaded to urge it away from said rolls to maintain the belts 20 and 2 I under constant tensions as aforesaid. Moreover, alarm operating means may be associated with either the slack take-up

pulleys

22 or 22 or the drive shaft I3 as the case may be, in the same manner as set forth in connection with the alarm operating means of the Figure 1 embodiment of the invention.

Obviously, the Figure 2 embodiment of the invention has the same advantage as the Figure 1 embodiment of the invention respecting maintenance of predetermined speeds of the fast and the slow rolls; equal loading of the belts; minimum tension in the belts; minimum width belts; conservation of space at the sides of the roll stand; relief on overloads; better sampling of ground stock; ease of replacement of fast roll scrapers etc., but does not have the fast roll bearing pressure on one side so directed as to relieve the grinding pressure.

According to the embodiments of the invention illustrated in Figures 1 and 2 the differences in speed between the fast and the slow rolls is minor and therefore the fast roll pulleys may be amply large to permit the use of belts in the manner shown in said figures. In some instances, however, it may be desirable to have major differences in speed between the fast and the slow rolls. In such instances, the difference in pulley sizes may be of such as not to permit belts to be best used as in the embodiments of the invention illustrated in Figures 1 and 2 because of lack of sufficient wrap of the belts about the fast roll pulleys to In any such instance, the heretofore described general features and advantages of the invention may be attained in embodiments of the invention as illustrated in Figures 3 and 4 of the drawings.

Referring first to Figure 3 of the drawings, it will be observed that the arrangement of the two pairs of grind rolls and the drive shaft is generally the same as in the Figure 1 embodiment of the invention, but that the positions of the rolls of each pair are reversed as compared with the said Figure 1 roll arrangement. That is to say, the fast roll of each pair is disposed inwardly instead of outwardly with respect to its companion slow roll. However, the same elements are involved in the Figure 3 embodiment of the invention as in the Figure l embodiment of the invention. Accordingly, the same reference characters as are employed in Figure 1 are employed in Figure 3, with the exponent 3 to designate parts corresponding to parts shown in Figure 1. Thus, in Figure 3, the fast rolls are designated as A the slow rolls as 13 the roll shafts as H3 the roll pulleys as I4 I5 E6 and IF, the drive shaft as I3 its pulleys as I8 and E9 and the belts as and 2| At each side of the Figure 3 roll stand the related belt, instead of extending directly across the related fast and slow roll pulleys, as in the Figure 1 embodiment of the invention, extends downwardly between said fast and slow roll pulleys and beneath

idler pulleys

22 and 22 on the slack strand located nearer the drive shaft I3 than the fast and the slow roll pulleys, whereby ample wrap of each belt about its related fast roll pulley of comparatively small diameter is attained. Otherwise, the Figure 3 embodiment of the invention is the same, in all essential respects as the Figure 1 embodiment of the invention. That is to say, one of the Figure 3 belts is crossed to provide for downward and inward rotation of the rolls of each pair; the belts are tensionecl to the extent of the belts of the Figures 1 and 2 forms of the invention either by means of the

pulleys

22 or 22 or by means of the drive shaft I3 and alarm operating means either are associated with the pulleys 22* or 22 or with the drive shaft I3 as the case may be, in the manner heretofore described.

The Figure 3 embodiment of the invention is suitable for use in any instance where fast roll pulleys of small diameters are used and where the drive shaft is spaced sufficiently from the grind rolls to permit one of the belts to be crossed. In any instance where fast roll pulleys of small diameters are used and where the drive shaft is disposed so close to the grind rolls as not to permit one of the belts to be crossed, an arrangement of the belts as illustrated in Figure 4 of the drawings may be employed. According to Figure 4 the arrangement of the belts is the same as in Figure 3, except, on the one hand, that neither of the belts is crossed, and except, on the other hand, that one of the drive shaft pulleys, instead of being mounted directly on the drive shaft, is mounted on a countershaft 2'l connected by gears 28 to the drive shaft to insure downward and inward rotation of the rolls of each pair relative to each other.

Since, except for the countershaft 27 and the gears 28, the Figure 4 embodiment of the invention the same in all essential respects as the Figure 3 embodiment of the invention, the same reference characters as are employed in Figure 3 are employed in Figure 4, with the exponent 4, to designate parts corresponding to parts shown in Figure 3.

According to the Figure 4 embodiment of the invention, either the

rollers

22 or 22 may be loaded to tension the

belts

20 and 21 to the extent set forth in connection with the other embodiments of the invention, or, alternatively, the drive shaft I3 and its associated countershaft 27 may be adjustable and may be properly loaded for this purpose. Likewise, alarm operating means may be associated with either the pulleys 22 or the shafts l3 and 27 in the manner set forth in connection with the other embodiments of the invention.

Obviously, the Figures 3 and 4 embodiments of the invention have the same advantages as the Figures 1 and 2 embodiments of the invention respecting maintenance of predetermined speeds of the fast and the slow rolls; equal loading of the belts; minimum tension in the belts; minimum belt widths; conservation of space at the sides of the roll; relief on overloads; better sampling of ground stock but does not have the advantage of ease of replacement of fast roll scrapers, or the fast roll bearing pressure directed so as to release the grinding pressure.

As will be understood, of course, all forms of the present invention contemplate the use of flat belts in order that the belts may readily ride off their pulleys under overload conditions.

From the foregoing description considered in connection with the accompanying drawings, it is believed that the construction and'mode of operation of a grind mill roll stand having belt drives in accordance with any of the different embodiments of the present invention will be clearly understood and its advantages appreciated. It is desired to point out, however, that while only certain specific embodiments of the invention have been illustrated and described, the same is readily capable of other specifically different embodiments within its spirit and scope as defined in the appended claims.

I claim:

1. A grind mill roll stand including, two pairs of rolls each pair comprising a fast roll and a slow roll, like rolls symmetrically placed with respect to the center line of the roll stand; companion roll pulleys one fixed to the fast roll of one pair and one fixed to the slow roll of the other pair at one side of the roll stand, similar companion pulleys fixed to the other fast and slow rolls, respectively, at the other side of the roll stand; a drive shaft having fixed thereto two driving pulleys one alined with the companion roll pulleys at one side of the roll stand and the other alined with the companion roll pulleys at the other side of the roll stand, and an endless belt at each side of the roll stand each engaged over the pulleys of the fast and the slow rolls and the related drive shaft pulleys at its side of the roll stand, the slack side of each belt leading to its related fast roll, and each operable to rotate its related fast and slow rolls in the same direction but oppositely to the direction in which the other fast and slow rolls are rotated by the other belt.

2. A grind mill roll stand including, two pairs of rolls each pair comprising a fast roll and a slow roll, like rolls symmetrically placed with respect to the center line of the roll stand; companion roll pulleys one fixed t0 the fast roll of one pair and one fixed to the slow roll of the other pair at one side of the roll stand, similiar companion pulleys fixed to the other fast and slow rolls, respectively, at the other side of the roll stand, a drive shaft having fixed thereto two driving pulleys one alined with the companion roll pulleys at one side of the roll stand and the other alined with the companion roll pulleys at the other side of the roll stand, an endless belt at each side of the roll stand each engaged over the pulleys of the fast and the slow roll and the related drive shaft pulleys at its side of the roll stand and each operable to rotate its related fast and slow rolls in the same direction but oppositely to the direction in which the other fast and slow rolls are rotated by the other belt, an idler "pulley engaged with the slack side of each belt, and means maintaining a load on each idler pulley to automatically maintain each belt under a constant predetermined slack side tension sufficient to prevent slip of the belt relative to its 3. A grind mill roll stand as set forth in claim 2 in which the fast rolls are disposed outwardly with respect to the slow rolls.

4. A grind mill roll stand as set forth in claim 2 in which each belt extends directly from its related fast roll pulley to its related slow roll pulley.

5. A grind mill roll stand as set forth in claim 2'in which one of the belts is crossed.

6. A grind mill r'oll stand as set forth in claim 2 in which each of the belts extends directly from its related fast roll pulley to its related slow roll pulley and in which one of the belts is crossed.

7. A grind mill roll stand as set forth in claim 2 in which one of the belts extends directly from its related fast roll pulley to its related slow roll pulley, and in which the other belt extends from the related drive shaft pulley to the inner sides of the related fast and slow roll pulleys then over the latter pulleys and then to and about an idler pulley located at the side of the drive shaft remote from the rolls.

8. A grind mill roll stand as set forth in claim 2 including a pair of idler pulleys one associated with the companion fast and slow roll pulleys at one side of the roll stand and the other associated with the companion fast and slow roll pulleys at the other side of the roll stand and each located nearer the drive shaft than the related fast and slow roll pulleys, and in which each belt extends from its related slow roll pulley first about the related idler pulley and then to the related fast roll pulley.

9. A grind mill roll stand as set forth in claim 2 including a pair of idler pulleys one associated with the companion fast and slow roll pulleys at one side of the roll stand and the other associated with the companion fast and slow roll pulleys at the other side of the roll stand each located nearer the drive shaft than the related fast and slow roll pulleys, and in which each belt extends from its related slow roll pulley first about the related idler pulley and then to the related fast roll pulley, and in which one of said belts is crossed.

10. A grind mill roll stand having two pairs of rolls each pair comprising a fast roll and a slow roll, companion roll pulleys one fixed to the fast roll of one pair and on fixed to the slow roll'of the other pair at one side of the roll stand, similar companion pulleys fixed to the other fast and slow rolls, respectively, at the other side of the roll stand, a drive shaft having fixed thereto a drive pulley alined with the companion pulleys at one side of the roll stand, 'a countershaft geared to said drive shaft for reverse rotation relative thereto, a drive pulley fixed to said countershaft and alined with the companion pulleys at the other side of the roll stand, an idler pulley at each side of the roll stand located nearer the drive' shaft than the companion fast and slow roll pulleys, and an endless belt at each side of the roll stand, each belt extending from its related drive pulley to the outer sides of the related fast and slow roll pulleys and from the latter to and about the related idler pulley.

11. A grind mill roll stand having two pairs of rolls each pair comprising a fast roll on the inside and a slow roll on the outside, companion roll pulleys one fixed to the fast roll of one pair and one fixed to the slow roll of the other pair at one side of the roll stand, similar companion pulleys fixed to the other fast and slow rolls, respectively, at the other side of the roll stand, a drive shaft having fixed thereto a drive ulley alined with the companion pulleys at one side of the roll stand, a countershaft geared to said drive shaft for reverse rotation relative thereto, a drive pulley fixed to said countershaft and alined with the companion pulleys at the other side of the roll stand, an idler pulley at each side of the roll stand located nearer the drive shaft than the companion fast and slow roll pulleys, an endless belt at each side of the roll stand, each belt ex- 7 tending from its related drive pulley to the outer sides of the related fast and slow roll pulleys and from the latter to and about the related idler pulley, and means automatically maintaining each belt under a constant predetermined tension sufficient to prevent slip of the same relative to its related pulleys under normal load conditions of the roll stand, but insufficient to prevent the belt from readily slipping off its pulleys in the event of only minor abnormal loading of the roll stand.

KENNETH MCCLELLAND.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 178,063 King -1 May 30, 1876 250,954 Odell Dec. 13, 1881 252,945 Holt Jan. 31, 1882 260,225- Odell June 27, 1882 298,206 Holt May 6, 1684 333,866 Lauholf Jan. 5,1886 334,460 Obenchain Jan. 19, 1886 382,583 Barnard May 8, 1888 385,420 Mawhood July 3', 1888 1,949,119 Gibbs Feb. 27, 1934 2,418,464 Corwin Apr. 8, 1947 FOREIGN PATENTS Number Country Date 11,641 Great Britain 1885 4,011 Great Britain Dec. 18, 1897 32,758 Germany Aug. 31, 1885