US1333659A - Grinder for the production of wood-pulp - Google Patents

Description

E. HUTCHINS.

GRINDER FOR THE PRODUCTION 0F WOOD PULPI4 APPLICATION FILED NPV. 30,1918.

1,333,659. Patented Mar. 16,1920.

.6 SHEETS-SHEET I.

E. HUTCHINS.

GRINDER FOR THE PRODUCTION 0F WOOD PULP.

APPLzCATloN FILED N0v.3o,1918.

6 SHEETS-SHEET 2.

l ENTOR M mma,

BY @MM ATTORNEYJ' Patented Mar. 16,1920.

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Y l ///V/@`c//// Iz lo? psoe 4 E. HUTCHINS. GmNnER Fon THE PRonucnoN 4oF woon PULP.

APPLICATION FILED NOV. 30, |918.

l/////// /W//////V// INVENTOR 5W im lfymfww ATTORNEYJ' E. HUTCHINS.

GRINDER FOR THE PRODUCTKON 0F WOOD PULP.

APPLICATION mio 1,333,659. "0V 3 m Patented Mar.16,1920.

6 SHEETS-SHEET 5.

E. HUTCHINS. GRINDER FOR THE PRODUCTION 0F WOD PULP.

APPLICATION FILED NDV- 30, |918.

Patented Mar. 16, 1920.

6 SHE N i INVENTOI? l dam/u( /MM 4STA'ES PATENT OFFICE.

EDWARD HUTCHINS, OF NEW YORK, N. Y., ASSIGNOR T0 INTERNATIONAL PAPER COMPANY, A CORPORATION OF NEW YORK.

GRINDER FOR THE PRODUCTION OF WOOD-PULP.

Specification of Letters Patent.

Patented Mar.16,192o.

Application led November 30, 1918. Serial No. 264,779.

To all 'whom t may concern Be it known that I, EDWARD I-IU'rcI-IINs, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Grinders for the Production of Wood-Pulp, of which the following is a specification, reference being had therein to the accompanying drawings.

This invention relates to vcertainnew and useful improvements in wood grinding mechanism for the production of wood pulp, more particularly for use in the manufacture of paper, such mechanism embodying a grinder, usually in the form of a rotary grindstone, against which the wood held in the pockets in a suitable housing or frame, is forced by power pistons.

In the operation of wood grinders of this type, a number of pockets is provided for the wood,'which in the grinding operation bears with considerable pressure against the periphery of the stone at different points in its circumference, such pressure of the wood acting with a braking effect on the stone and insuring such rate of speed of rotation as. to produce the most effective grinding action and the most economical application of the driving power. When, however, the wood in one of the pockets is completely ground and the pocket is to be furnished with a fresh supply, the pressure on the stone at this point is relieved, and consequently the total braking action on the stone is reduced, with the result that the stone will speed up. This action is very objectionable by reason of the waste of power, the ineffective grinding action on the wood in the pocket or pockets remaining in operation, and for other reasons unnecessary to enumerate.

rlhe present invention aims to obviate this objectionable action, and it consists broadly in means for increasing the pressure on the wood in one pocket, when the pressure on the wood in another pocket is relieved.

In machines of the type above mentioned, the pressure on the wood is applied by means of pressure devices or elements usually in the form of shoes, to which are connected power pistons operating in power cylinders, to which cylinders, pressure fluid under grinding pressure is admitted to one side of the pistons to advance the same in the grinding action, and to which cylinders., 5 pressure fluid under backing-off pressure is admitted to the opposite sides of the pis- -tons to retract the same when the grinding main cylinders and pistons, and an inter- 7` mediate auxiliary cylinder and piston, all of which pistons for a given pocket are connected with the pressure device therein, and I provide valve mechanisms for controlling the admission of pressure fluid to the sev- 7` eral cylinders, the valve mechanisms for the auxiliary cylinders being of such form and construction that normally they will cut off the pressure to the auxiliary cylinders,

which cylinders, under normal conditions 8* with the wood being ground in all the pockets, will be free from pressure, and their pistons consequently exerting no pressure on the pressure devices; and I provide connections between the valve mechanisms of the 8 auxiliary cylinders, of such form and construction that when one of the auxiliary valves is operated, as when the wood in its pocket is all ground and the grinding pressure is out off and the pistons are re- 94 tracted, pressure will be admitted to the auxiliary cylinders of the pockets remaining in operation, thus adding` to the pressure on the wood inv those pockets, a degree of pressure corresponding to that cut off 9 from the empty pocket. As a result, the total pressure acting on the stone maintained and the latter will be prevented from speeding up.

In the accompanying drawings I have l( illustrated my invention as applied to a grinding mechanism, in which three pockets are provided for holding the wood to be ground, the operation of any one of the three auxiliary valves, admitting pressure fiuid to l( the other two auxiliary cylinders of the other pockets, so that the additional pressure imposed on the wood in these two pockets will compensate for and equal that of the two main cylinders in the empty pocket. But it will be manifest that the invention is applicable as well to cases wherein but two wood holding pockets are employed, each provided with one main cylinder and one auxiliary cylinder, in which case the additional pressure imposed on the operative pocket by the action of the auxiliary valve of the empty pocket, will compensate for and equal that of the single main cylinder of the empty pocket.

Referring to the drawings:

Figure l is a transverse sectional view of a wood grinding mechanism having my invention embodied therein, parts being shown in elevation.

Fig. 2 is a longitudinal sectional view of the same, with parts in elevation.

Fig. 3 is a horizontal section through one of the auxiliary valves and adjacent portion of its associated auxiliary cylinder, the section being taken on the line 3-3 of Fig. 2.

Fig. 4 is a section through the same on the line 4*.4 of Fig. 3.

Fig. 5 is a similar section on the lines of Figs. 2, 3 and 4.

Fig. 5a is a horizontal section through one of the main valves on the line .5a-5 of Fig. 2.

Fig. 6 is a diagrammatic view showing the several sets of power cylinders for actuating the pressure devices, the connections to the cylinders for the pressure fluid supply, and the valve mechanisms for controlling said supply, the parts being shown in normal grinding position with all the pressure devices acting on the wood.

Fig. 7 is a similar view showing the pressure device of the central pocket retracted and inactive, and its auxiliary valve adjusted to supply additional pressure to the auxiliary cylinders of the other pressure devices.

Fig. 8 is a longitudinal section through one of the main valves in modified form, for controlling the pressure fluid from a single source of supply, for 'both advancing and retracting the piston.

Fig. 9 is a similar view of one of the auxiliary valves, in modified form, for controlling the pressure fluid from a single source of supply.

Referring to the drawing, A designates a frame or housing in which is mounted a rotary power shaft B having fixed to it a grindstone C. Bolted to the housing are a number of pockets for holding the wood to be ground, there being, in the present instance, three of these pockets D, E and F, as usual. The pockets are open at one end for the reception of the wood and are provided with sliding doors or gates d, for closing the open ends. In each of the pockets is a pressure device or element, preferably in the form of two pressure shoes G, to act on the wood and force the same against the stone, which pressure shoes are flexibly connected together by means of a connecting member in the form of a bar G pivoted as at g to heads g2 extending upwardly from the pressure shoes. Two outer piston rods H and an intermediate piston rod vI are pivoted at their lower ends, as at h, to the connecting bar, and have fixed to their upper ends, power pistons H1, I1, and H1, respectively, the outer pistons H1 sliding in main power cylinders H2, and the intermediate piston I1 sliding in an auxiliary power cylinder I2. These cylinders are bolted to the upper ends of the pocket, it being understood that there is a similar equipment for each of the three pockets.

As a result of the flexible connection of the two pressure shoes by the connecting bar, and the connection of the power pistons to this bar, the pressure on the wood will be exerted uniformly and evenly at both ends, the slices being permitted to adjust themselves to the wood and produce a uniform and equalized contact between the wood and periphery of the stone, notwithstanding the unevenness of the wood.

As shown more particularly in Figs. 2 and 5a, each main cylinder H2 has applied to it a main valve casing J provided with an annular port y', adapted to communicate with a port jl extending longitudinally through the wall. of the cylinder and opening into its upper end on the upper side of the piston, through which ports the pressure fluid is admitted to the cylinder for producing the grinding pressure on the piston and consequently on the pressure device. Similarly', each main valve casing is provided with a second annular port je which is adapted to communicate with a port j* extending longitudinally in the wall of the cylinder and opening into its lower end on the lower side of the piston, and through the ports j and j" the pressure fluid is admitted for producing the backing-off pressure on the piston to retractthe same and consequently the pressure devices, when the wood is completely ground and a fresh' supply is to be placed in the pocket. Branch pipes K lead from the ports j of the several main cylinders of the three pockets to a distributing pipe K, connected to a suitable source of pressure fluid supply for producing the grinding7 pressure; and branch pipes L lead from the ports of the several main cylinders of the three pockets, to a distributing pipe L connected to a suitable source of pressure fluid supply for furnishing backing-off pressure. Also each main valve casing communicates at one end with a branch exhaust pipe M, which pipes of the several casings lead to a main exhaust pipe M. The valve casings J are further provided each with a by-pass port j, which leads from one end of the casing to the other and which is adapted, as will be presently described, to be placed into communication with the up-per end of the main cylinder, so that the exhaust may pass therefrom when the pistons move up in retracting the shoes.

In each of the valve casings J a slide valve N is mounted which is provided with three spaced heads n, al and n2 and intermediate reduced portions or annular cavities n.3 and n4, the form and construction of these parts and their relations to the several ports in the valve casing being such that 'when the valve is moved to the lefthand end, as shown in Figs. 5a and 6, communication will be established between the grinding pressure fluid supply and the upper end of the cylinder through the ports j and jl and valve cavity to force the pistons down and apply grinding pressure to the shoes, and communication between the backing-off pressure fluid supply and lower end of the cylinders lwill be cut ofi' by the valve head '11.2, and communication to the said lower end will be established with the exhaust port in the end of the casing, whereby the exhaust from the cylinder will pass out through exhaust pipe M. When, however, the valve is moved to the right, as shown in the middle of Fig. 7, the grinding pressure will be cut off from the upper end of the cylinder by valve head a and said end will be placed in communication with the by-pass to permit the exhaust from this end of the cylinder to pass to exhaust pipe M, and communication will be established between the backing-off pressure and the lower end of the cylinder by the ports and j* and valve cavity at whereby the pistons will be moved up and retract the shoes, as shown in Fig, 7.

It will be understood that there are three pairs of these main valve casings and main valves, one pair for each pocket, and I propose to arrange for the operation of the. valves of a pair in unison, one pair independently of the other, so that the pressure device of each pocket may be operated independently of the others. To effect this object, each valve has connected with it a stem 77,5 which extends outwardly through the end of the casing, the stems of a pair being connected with a reciprocating bar a, pivoted at one end to an operating lever nl, which in turn is pivoted between its ends to the frame Z, as at as, and provided with a handle n for operating it. By the operation of this lever, both valves will be shifted in unison in the respective casings, it being understood that there is a similar operating mechanism for the pairs of valves of the other main cylinders.

In the operation of the mechanism so far described, by the actuation of the hand levers a? the pressure devices in the several pockets may be independently controlled, and may be caused to advance and force the wood against the periphery of the grindstone, or may be retracted, when the grinding operation in a pocket is completed and a fresh supply of wood is to be placed in the pocket, these actions being effected by admitting the fluid pressure medium to one end or the other of the main cylinders by means of the several main valves.

The several auxiliary cylinders and pistons before alluded to are designed to cooperate with the main cylinders and are normally inactive, that is, when the wood is being ground in all of the pockets and is subjected to the pressure of all of the main power pistons, but when the grinding pressure in any pocket is relieved and the pressure device in that pocket retracted,` as when the wood in the pocket is completely ground and a. new supply is to be furnished, the pressure fluid under grinding pressure will be automatically admitted to the auxiliary cylinders of the pockets remaining in action, and the wood in these pockets will be subjected to additional pressure, in degrec equal to that which was cut off from the empty pocket. Consequently the total pressure of the wood on the stone will be maintained, notwithstanding the reduction of pressure in the empty pocket, and therefore speeding up of the stone will be prevented.

In accomplishing this action of' the parts, each auxiliary power cylinder has applied to it an auxiliary valve casing O containing an auxiliary slide valve l?, and as these parts are the same for the three auxiliary cylinders, a desciption of one set will suffice. T he valve casing, as shown more particularly in Figs. l and 5, is fixed tothe side of the cylinder and is provided with internal annular ports o, ol, 02, 03, 04, and 05, and with a by-pass port 0G extending longitudinally in the wall ot the casing and communieating at its ends respectively with the ends of the casing to permit the unimpeded movement of the valve. The port 08 communi- Cates with a port Q extending in the wall of the cylinder and opening into its upper end at the upper side of the piston, and through these ports the pressurel fluid medium is admitted for producing grinding pressure on the piston. Port 01 communicates with a port Q1, which extends in a wall of the cylinder Iand opens into its lower end at the under side of the piston, the backing off pressure fluid being admitted to the cylinder through these ports from, the port 0 to retract the piston, which ports o of the several casings receive their supply of backing` off pressure fluid through branch pipes O2 which lead to and connect with the main distributing pipe L1, before alluded to.

Port o2 is connected with a branch exhaust pipe R and is situated between ports 01 and 03, and is adapted by the movement of the valve P, as will be presently described, to be placed into communication with either of the ports 01 or o2 to permit either end of the cylinder to be exhausted, the several branch exhaust pipes R being connected with the main exhaust pipe M1 before alluded to. The ports o* in the several auxiliary valve casings are connected respectively together by means of branch pipes S which lead to a connecting pipe S1; and ports 05 in the several casings communicate with branch pipes S2 which lead to and connect with the main distributing' pipe K1, lbefore alluded to, for supplying the grinding pressure.

The auxiliary slide valve P is formed with four heads 79, 721, 792, 793, and with intervening annular cavities 774, 795, 79, the relations of the heads and cavities, to the several ports being such that when the several auxiliary valves are adjusted to the lefthand end of the casing, as shown in Fig. 6, both the backing off pressure fluid and the grinding pressure fluid will be eut offl from the several auxiliary cylinders, and these cylinders will be rendered inactive. In this position of the valves, the grinding pressure fluid admitted to the valve casings by the branch pipes S2 will be blocked by the heads 793 of the valves, While the backing off pressure fluid from the branch pipes O2 will be blocked by the heads 7U- and 791 of the valves, the upper ends of the cylinders will coimnunicate with the connecting pipes S through ports o3 and 0l and valve cavity 77, and the lower ends of the cylinders will connnimicate with the branch exhaust pipes' R through ports o1 and 02 and valve cavity 79:". This is the normal condition of the parts with the main cylinders and pistons in the several pockets active and supplying pressure to the respective -pressure shoes. AWhen, however, the auxiliary valve of any one of the pockets is thrown to the right, as shown in Figs. 3, i and 7, the pressure fluid medium entering through pipe S2 will pass into the valve cavity 79 and thence out through branch pipe S to connecting pipe S1, and through the connecting pipe it will pass to the other two auxiliary valve casings, and flowing into the valve cavities 7) therein will enter the upper ends of the two auxiliary cylinders. In this position of the auxiliary valve of the particular pocket, backing off pressure fluid is admitted to the lower end of the auxiliary cylinder through ports o, o1 and valve cavity 774, and the upper end of the cylinder is placed in communication with the exhaust through ports Q, o2, and 03 and valve cavity It is seen, therefore, that in the normal grinding operation, with all of the main pistons in operation in the several pockets and applying grinding pressure to the wood therein, the several auxiliary pistons are inactive, but when any one of the auxiliary valves is operated when the wood in its pocket is all ground, it will act to admit grinding pressure fluid to the other two auxiliary cylinders remaining in action to increase the grinding pressure on the wood in these pockets.

The respective auxiliary valves are adapted to be operated in cordination with their associated main valves, so that when the main valves of a pocket are operated to cut off the grinding pressure fluid and retract the pressure shoes, the auxiliary valve of that pocket will be also operated to admit grinding pressure fluid to the auxiliary cylinders of the other two pockets remaining in action. To effect this action, the auxiliary valves are each provided with a valve stem T, which stems extend outwardly through the ends of the casings and are Connected respectively with arms t, which arms in turn are connected with the several reciprocating bars n befo-re alluded to. As a result of this connection of the stems of the auxiliary valves with the operating mechanism of the associated main valves, when any one of the hand levers a7 is operated in one direction to shift the main valves to the right'from the position shown in Fig. 6 to that shown in Fig. 7 the auxiliary valve will be likewise shifted, with the result that grinding pressure fluid will be cut off' from the main cylinders, and backing off pressure fluid admitted to retract the pressure shoes, while at the same time grinding pressure fl-uid will be admitted to the auxiliary cylinders of the other two pockets remaining in action; and when the lever is operated in the other direction, the three valves of that pocket will be restored to their former positions, thereby cutting off pressure to all of the auxiliary cylinders, and again admitting grinding pressure fluid to the main cylinder of the particular pocket to cause the main piston to resume grinding pressure on the new supply of wood. It will be understood that the three valves of a given set are operated in cordination with each other as described, and the valves of one set are operated independently of those of the other sets, so that the pressure devices of the dierent pockets may be controlled independently of each other to enable the empty pocket to be refilled without disturbing the grinding action taking place in the other pockets.

The diagrammatic view of Fig. 6 shows the mechanism under normal operating conditions, that is, with the three pockets supplied with wood and acted on by the pressure devices in the pockets, and the various valves adjusted to the left, thereby supplying grinding pressure to the several pairs llO of main cylinders, and cutting oil both grinding and backing off pressure to the several auxiliary cylinders, with the result that the pressure of the main pistons will be applied to the wood and the latter will be forced into grinding relation to the periphery of the grindstone. Assume now that the grinding operation on the woodis completed in the central pocket first. The operator actua-tes the hand lever a? connected with the several valves of this pocket and shifts the valves to the right as shown in Fig. 7. By this actuation of the main valves, grinding pressure is cut oli from the main cylinders and backing off pressure admitted to retract the pistons and connected pressure device, so that a new supply of wood may be inserted in the empty pocket. Simultaneously with this actuation of the main valves, t-he auxiliary valve of this pocket is operated and shifted to the right, whereby grinding pressure is admitted through the connecting pipe S1 to the two inactive auxiliary cylinders of the two pockets remaining in action, thereby imposing on the wood in each of these pockets, additional pressure, in the aggregate corresponding to that which was before actin@ in the empty pocket. When the empty poc zet has been furnished with a new supply of wood, the hand lever a7 thereof is shifted to its former position, thereby restoring the several valves to their former positions, with the result that the backing off pressure will be cut off from the main cylinders of the empty pocket, grinding pressure will be admitted thereto, and grinding pressure cut offI 'from the auxiliary cylinder of this pocket and also from the two auxiliary cylinders of' the other pockets. The mechanism is now again in its normal operative condition, and when the grinding is completed in any one of the other pockets, the valves of that pocket are manipulated in the same way to retract the pressure device and supply additional pressure to the auxiliary cylinders of the pockets remaining in action.

Due to the fact that in the descent of the main pistons in the normal operation of the mechanism, the auxiliary pistons are carried down with them, and due to the fact that in the normal operation of the parts, the pressure fluid, usually water, is cut off from the auxiliary cylinders, unless some means are provided to prevent it, the auxiliary cylinders above their pistons will be insuffi ciently supplied with water, and conseu quently the pressure admitted to them will not act promptly on the operation of the auxiliary valves. In order to meet this contingency and insure that the auxiliary cylinders will always be completely lilled with water, I provide a communicating connection. U between the pipe S1 and the exhaust pipe M1, as shown more particularly in Figs. 2, 6 and 7. This connection is in the form of a pipe containing a check valve u which opens in a direction toward the pipe S1 so as to permit water to flow into said pipe and thence into the auxiliary valve casings and finally into the upper ends of the auxiliary cylinders, when the pistons 0f the latter descend. This check valve closes the connecting pipe U against the escape of water therethrough to the exhaust pipe, so that when the pressure fluid is admitted to the auxiliary cylinders through the connecting pipe S2, it will be prevented from escaping into the exhaust pipe and will exert its pressure on the auxiliary pistons.

In the particular form of mechanism hercinbefore described, and illustrated in the accompanying drawings as embodying my invention, the pressure Huid is taken from two distinct sources, and conducted to the cylinders through two distinct pipe connections, one pressure being for the purpose of' advancing the pistons for applying grinding pressure to the wood, and the other for the purpose of retracting or backing off 2 the pistons. The employment of two such pressures possesses advantages, mainly in the respect of the more even grinding pressure which is attainable, lbut the advantages of my invention may be realized by employing but a single source of pressure fluid and applying the same to the cylinders so as to operate the pistons both to advance them for the grinding operation, and retract or back off the same. The only change necessary'in the apparatus to bring about this result is in the speciiic form of the controlling valves for the main cylinders and the auxiliary cylinders respectively. This is illustrated in Figs. 8 and 9 of the drawings, wherein it will be seen that the main valve casing J1, illustrated particularly in Fig. S, has three annular ports J2, J 3 and J 4, and a by-pass port J 5, which latter communicates at its ends with the two ends respectively oi' the valve casing. The port J2 communicates with the upper end of the main cyl-A inder, and the port J 4 communicates with the lower end of the same. The port J3 communicates with a single source of' fluid pressure supply through a pipe K2, and the end of the valve casing communicates with the exhaust through the pipe l 2. The valve N1 has two valve heads N2 and N3, and an intermediate cavity N4; and when adjusted to the left, as shown in Fig. 8, for the grinding operation, pressure is admitted to the upper end of the cylinder through port J3, valve cavity N4, and port J2, the lower end of the cylinder being opened to the exhaust through port J 4 and exhaust pipe M2. lVhen now the piston is to be retracted so as to back ofi" 2 the pressure device from the wood, the valve is shifted to the right, with the result that pressure will be admitted to the lower end of the cylinder through port J3, valve cavity N4 and port JG, and the upper end of the cylinder will be opened to the exhaust through port J2, by-pass J5, and exhaust pipe h/ 2.

It is seen, therefore, that a single fluid pressure supply entering the valve casing through pipe K2, is utilized both for apply ing grinding pressure to the pistons to advance the pressure devices against the wood, and for applying backing ofi pressure to the pistons to retract the pressure devices when the wood in a pocket is completely ground.

In the modified form of auxiliary' valve casing and valve shown in Fig. 9, the valve casing O1 is provided with the annular ports O2, O3, O4, O5, OG, and with the by-pass port O7, which latter communicates with the ends of the casing and with the port O2, and which by-pass port receives the pressure fluid from a single source through pipe S3. The ports P of the several auxiliary valves are connected together by branch pipes S4 and a connecting pipe, similar to the branch pipe S and to the connecting pipe Sl of the mechanism lirst described, while port O* is connected with exhaust branch pipe R1. Port O3 communicates with the lower end of the auxiliary cylinder, and port O5 communicates with the upper end of the same. The auxiliary valve P3 is provided with three valve heads P4, P5, P, and with intervening valve cavities P7 and PS. In the normal grinding operation with all of the main pistons under grinding pressure, the several auxiliary valves are adjusted to the lefthand end of the casings, with the result that pressure fluid entering the casings through the pipes S3 will be blocked in each casing at the lefthand end by valve head P, and will be blocked at the right by valve head P6, so that the several auxiliary pistons will be inactive and free from pressure. In this position of the valves, however, port O will communicate with the upper end of the cylinder through valve cavity PS and the lower end of the cylinder will communicate with the exhaust through port O3, valve cavity PT and port Ot, so that all of the auxiliary cylinders are ready to receive grinding pressure whenever the auxiliary valve or any particular one of' the auxiliary cylinders is operated when its pocket becomes empty. In such an event, the auxiliary valve of that pocket is adjusted to the right to the position shown in Fig. 9, without, of course, disturbing the other auxiliary valves of the pockets remaining in action, the result being that the pressure fluid entering the by-pass port will pass to the lower end of the cylinder by port- ()2, valve cavity P7 and port O3 and will exert backing oft' pressure on the pistou.

The pressure fluid will also pass from the by-pass port to port O6, and thence to the other auxiliary cylinders by branch pipes S4, and the connecting pipe leading to the other auxiliary valve easings. Also in this position of the valve, the upper end of the auxiliary cylinder is opened to the exhaust through the port Ot, valve cavity P8 and port O5, thereby permitting the upper end of the cylinder to exhaust as the piston is moved up by the pressure acting on the other side.

It will be understood that these two modified forms of main and auxiliary valves of the several pockets will be connected up similar to the connection of the form of valves first described, the only difference being that there is a single connection to each valve casing for furnishing the pressure fluid, instead of' two separate connections to each casing as first described.

It will be noted from the description above given that the fluid pressure medium is under a constant initial pressure, and that the increase of pressure to which the pressure devices in the respective pockets is subjected, is obtained not by varying the initial pressure or the pressure medium, but by admitting saidinedium to an additional or auxiliary pressure cylinder. In other words, the same pressure medium is caused to act on an increased pressure area with which each pressure device is provided, which area is constituted by the piston of the additional or auxiliary cylinder in each pocket, thereby imposing greater pressure on the pressure device or shoe, and consequently greater pressure on the wood against which the shoe acts.

In the foregoing description and accompanying drawings I have set liorth my invention in the particular detailed form and construction which I prefer to adopt, but it will be understood that these details may be variously changed and modified without departing from the spirit of the invention, and further it will be understood that the invention is not to be limited to any particular form or construction of the parts, except in so far as such limitations are specified in the claims.

Having thus described my invention, what I claim is:

l. In a wood grinding machine, the combination of a grinder, a plurality of means for holding the wood to be ground at different points on the grinder, a pressure de- Vice operable on the wood in each holding means, a fluid pressure medium under constant initial pressure acting on said pressure devices to cause them to normally force the wood against the grinder under grinding pressure, and means for controlling said fluid pressure medium, said controlling means acting, when operated to relieve the pressure of the pressure device in one active holding means, to automatically increase the pressure of another pressure device in another active holding means without varying the initial pressure of the fluid pressure medium.

2. In a wood grinding machine, the combination of a grinder, a plurality of pockets for holding the wood to be ground at different points on the grinder, a pressure device operable on the wood' in each pocket and each pressure device provided with a non mally active pressure surface and with a normally inactive pressure surface, a fluid pressure medium acting on the active pressure surfaces and acting t-o normally force the wood in the several pockets against the grinder under grinding pressure, and controlling means for the fluid pressure medium, acting when operated to relieve the pressure in one active pocket, to automatically admit the fluid pressure medium to the inactive pressure surface of the pressure device of the other active pocket, and thereby increase the pressure on the wood in that pocket.

3. In a wood grinding mechanism, the combination of a grinder, a plurality of pockets to hold the wood to be ground, a pressure element in each pocket to act on the wood therein, a plurality of cylinders for each pocket and pistons in said cylinders connected with each pressure element, means for supplying pressure fluid to the cylinders, valve mechanisms for controlling the admission of the pressure fluid to advance the piston and retract the same, said valve mechanisms being operable independently of each other to admit pressure to one of the cylinders of one set to advance its piston, when the valve mechanism of another set is operated to admit pressure to a cylinder of that set to retract its piston.

4L. In a wood grinding mechanism, the combination of a grinder, a plurality of pockets to hold the wood to be ground, a pressure element in each pocket to act yon the wood therein, a plurality of cylinders, and pistons in said cylinders connected with each pressure element, connections for supplying pressure fluid to the opposite sides of the pistons respectively, to advance and retract the same, and valve mechanisms in said connections to control the pressure to the cylinders, the said valve mechanisms being operable independently of each other to admit pressure to one of the cylinders of one set to advance its piston, when the valve mechanism of that set is actuated to admit pressure to the cylinders of the other set to retract their pistons; whereby the pressure on the Wood by the pressure element of one pocket will be increased, when the pressure element of the other pocket is retracted.

5. Ina wood grinding mechanism, the

combinatioon ofa grinder, a plurality of pockets to hold the wood to be ground, a pressure element in each pocket to act on the wood therein, a main cylinder and an auxiliary cylinder, and pistons in said cylinders connected with each pressure element, connections for supplying pressure fluid to the opposite sides of' the pistons of each cylinder to advance and retract the same, and valve mechanisms in said connections to control the admission of pressure to the cylinders, said valve mechanisms normally cutting off the pressure to the auxiliary cylinders, and being operable independently of each other to admit pressure to the auxiliary cylinder of one set to advance its piston,

when the valve mechanism of another set is actuated t0 admit pressure. to the cylinders of that set to retract their pistons; whereby the pressure of the pressure element on the wood in one pocket will 'be increased, when the pressure element of the other pocket is retracted.

6. In a wood grinding mechanism, the combination of a grinder, a plurality of pockets associated with the grinder to hold the wood to be ground, pressure shoes in each pocket to act on the wood, a connecting member flexibly connecting together the pressure shoes of each pocket, two main cylinders andan intermediate auxiliary cylinder, and `pistons in said cylinders connected to each connecting member, connections for supplying pressure fluid to the opposite sides of the respective pistons to advance and retract the same, and valve mechanisms in said connections, said valve mechanisms normally cutting off the pressure to they auxiliary cylinders and being operable to admit pressure to the auxiliary cylinder of one set to advance its piston, when the mechanism is actuated to admit pressure to the cylinders of the other set to retract their pistons.,

7. In a wood grinding mechanism, the combination of a grinder, a plurality of pockets associated with the same for hol ding the wood to be ground, pressure elements in the respective pockets to act on the wood therein, a main cylinder and an auxiliary cylinder, and pistons in said cylinders connected with each pressure element, two sources of pressure fluid supply for furnishing grinding pressure and backing off pressures, and auxiliary valves in the confrom said sources of supply to the opposite sides of the pistons respectively to advance and retract the same, main valves in the connections from the sources of pressure to the respective main cylinders to control said pressures, and auxiliary valves in the connections from the sources ofr pressure to the auxiliary cylinders, said auxiliary valves normally cutting ofi" pressure to the auxiliary cylinders, and the auxiliary valve of one auxiliary cylinder being operable, when actuated to admit backing off pressure to that cylinder, to admit grinding pressure to the other auxiliary cylinder'.

S. In a wood grinding mechanism, the combination of a grinder, a plurality of pockets associated with the grinder for holding the wood to be ground, pressure elements in the respective pockets to act on the wood therein, a main cylinder and an auxiliary cylinder, and pistons in said cylinders connected with each pressure element, two sources of pressure fluid supply for furnishing' grinding pressure Vand backing ofi' pressure to the several cylinders, connections from said sources of pressure to the opposite sides of the pistons respectively, to advance and retract the same, main valves in the connections from the sources of pressure to the respective main cylinders to control said pressures, auxiliary valve casings in the connections from the sources of pressure to the auxiliary cylinders, said casings communieating with each other, auxiliary valves in the respective casings normally cutting ofl' pressure to the auxiliary cylinders and controlling the communication ot' the auxiliary valve casings with each other, and connections between the main and auxiliary valves of each set; whereby when the several valves of one set are operated to admit backing off pressure to the main cylinders of that set, the auxiliary valve of that set will be operated to admit grinding pressure to th r auxiliary cylinder of the other set.

9. In a wood grinding mechanism, the combination of a grinder, a plurality of pockets associated therewith for holding the wood to be ground, pressure elements in the respective pockets to act on the wood therein, a main cylinder and an auxiliary cylinder, and pistons in said cylinders connected with each pressure element, a source of.' pressure Huid supply for Jfurnishing grinding pressure to the several cylinders, and inde.- pendently operable means for controlling the pressure to said cylinders, said means normally cutting ofl` pressure to the auxiliary cylinders, and each of said means being operable, when actuated to cut off grind-- ing pressure to its main cylinder, to admit grinding pressure to the other auxiliary cylinder.

l0. In a wood grinding` mechanism, the combination of a grinder', a plurality of pockets associated therewith for holding the wood to be ground, pressure elements in the respective pockets to act on the wood therein, a main cylinder and an auxiliary cylinder, and pistons in said cylinders connected with each pressure element, a source of grinding pressure fluid connected withv tion between said casings, independently movable valves therein, a communicating connection between each casing and its associated cylinder, and communicating connections between the source of pressure and the respective casings, said valves normally cutting off pressure to the respective cylinders, and each valve acting when moved, to admit pressure to the other auxiliary cylinder.

1l. In a. wood grinding mechanism, the combination of a grinder, a plurality of pockets associated therewith for holding the wood to be ground, a pressure element in each pocket to act on the wood therein, a ina-in cylinder and an auxiliary cylinder, and pistons in said cylinders connected with each pressure element, a source of pressure fluid supply connected with the respective cylinders, means for controlling the admission of pressure to the main cylinders, and two valve mechanisms in the connections between the source of' pressure and the auxiliary cylinders, said valve mechanisms normally cutting oi'f the pressure to the auxiliary cylinders, and each mechanism 4being operable when actuated, to admit pressure to the other auxiliary cylinder.

1Q. In a wood grinding machine, the combination of a grinder, a pocket associated therewith for holding the wood to be ground, a plurality of pressure shoes adapted to act on the wood in said pocket, a. member connecting said shoes flexibly together, two main power cylinders, pistons therein connected with said connecting member respectively adjacent its opposite ends, an intermediate auxiliary power cylinder, and a piston thereinl connected with said connecting member between the points of connection of the other pistons therewith.

13. In a wood grinding mechanism, the combination of a grinder, a pocket associated therewith for -holding the wood to be ground` two pressure shoes in said pocket adapted to act on the wood therein, a connecting member pivoted to said shoes, a plurality of power cylinders, and pistons in said vcylinders pivoted to said connecting member.

la. In a wood grinding mechanism, the combination of a grinder, a pocket associated therewith to hold the wood to be ground, a pressure device in the pocket to act on the wood, a main power cylinder, a piston therein connected with the pressure device and normally active to apply pressure to said device, an auxiliary power cylinder, a piston therein connected with the pressure device and normally inactive to apply pressure, and means for admitting fluid under pressure to the auxiliary cylinder to apply additional pressure to said pressure device.

l5. In a wood grinding mechanism, the combination of a grinder, a pocket assooiated therewith to hold the wood to be ground, two pressure shoes in the pocket adapted to act on the wood therein, e oonnecting member pivoted to said shoes, two main power cylinders, power pistons therein pivoted to the connecting member und normally active to apply pressure to the shoes,

en intermediate auxiliary power cylinder, and t pressure piston therein pivoted to the Connecting member and normally inactive. 10

In testimony whereof I have affixed my signature hereto.

EDARD HUTCHINS.

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