US3314615A

US3314615A - Pulpwood grinder control

Info

Publication number: US3314615A
Application number: US361344A
Authority: US
Inventors: John L Hill
Original assignee: Boise Cascade Corp
Current assignee: Officemax Inc
Priority date: 1964-04-21
Filing date: 1964-04-21
Publication date: 1967-04-18
Anticipated expiration: 1984-04-18

Description

April 18, 1967 H|LL 3,314,615

PULPWOOD GRINDER CONTROL Filed April 21, 1964 5 Sheets-Sheet l INVENTOR. JQHN L. HlLL April 18, 1967 J. L. HILL 3,314,615

PULPWOOD GRINDER CONTROL Filed April 21, 1964 3 Sheets-Sheet 2 as I 36 FIG. 2

INVENTOR. JOHN L. Hl ILL April 18, 1967 J. L. HILL 3,314,615

PULPWOOD GRINDER CONTROL Filed April 21, 1964 3 Sheets-Sheet 5 INVENTOR. JOHN L. H ILL United States Patent 3,314,615 PULPWOOD GRINDER CONTROL John L. Hill, Fort Frances, Ontario, Canada, assignor to Boise Cascade Corporation, Boise, Idaho, at corporation of Delaware.

Filed Apr. 21, 1964, Ser. No. 361,344 3 Claims. (Cl. 241--34) This invention relates generally to pulpwood grinding apparatus, and more particularly to grinding apparatus including control means for effecting a substantially constant rate of pulpwood feed relative to the grinding stone surface.

Mechanical or groundwood pulp is produced by pressing a peeled or barked pulpwood log against the surface of a revolving stone, the rotating axis of the stone being substantially parallel with the fiber direction of the log. The .usual arrangement of pulp grinding devices involves a synchronous grinding motor carrying a pair of grinding wheels at either end, and mounted in pockets, each grinding wheel or stone having a magazine on at least either side adapted to receive logs. A pressure cylinder is mounted in conjunction with each magazine having a pressure foot which is activated thereby and forces the logs against the grinding wheel. The system employed for actuating the hydraulic pressure cylinders in the conventional arrangement includes a reservoir of water and a pump which provides pressure water from the reservoir, which passes through a governor.

The principal variables in mechanical pulping are stone surface, stone speed, grinding pressure, power input, energy consumption, production, temperature of grinding, consistency of grinding, freeness and strength of pulp, and Wood variables. There is a definite relationship between pulp properties, such as freeness and strength and grinding characteristics such as energy consumption and production.

Modern practice in groundwood operation is to operate at increasingly higher surface speeds, higher pressures, and with longer wood. The principal types of grinders may be considered pocket, chain and ring. With any of these types of grinders a great deal of difliculty has been experienced in maintaining proper and substantially uni form freeness. This in part is due to maintaining a con stant load on the drive motor. This method of control is insensitive to the grinding rate.

An object of this invention is to provide a substantially constant and controllable grinding rate per square inch of wood in contact with the grinding surface.

A further object of the invention is to provide a control unit comprised of a plurality of interoperatively'related valve means designed to control one pressure cylinder and employing low pressure fluid for initial control of the pressure foot piston of the pressure cylinder which the control unit serves in its advancing and retiring movement.

A still further object of the invention is to provide a control unit as before which includes means whereby high-pressure fluid may be applied to drive the pressure foot under load.

With these and other objects in view the invention generally relates to a method and apparatus for controlling power applied to the means for forcing pulpwood against a motor driven grindstone.

FIGURE 1 is a diagrammatic view of a control unit in relation to a grinding unit;

FIGURE 2 is a sectional side elevation view of a pocket grinder;

FIGURE 3 is an enlarged side elevational view of a control unit; and

FIGURE 4 is an enlarged section view of control unit shaft.

Referring to the drawings in detail indicates a grind- 3,314,615 Patented Apr. 18, 1967 stone driven by a suitable means (not shown). Pulpwood 12 is forced against the revolving surface of the grind stone by pressure foot 14 which is attached to piston rod 20 of cylinder 22 in which is movable mounted piston 24. Extending from the pressure foot is an extension member 16 to which is attached a cable or line 48. The pressure foot 14 is caused to retract by forcing low pressure fluid such as water to the left hand side of cylinder 22 via conduit 31, valve 30 and conduit 26, the fluid in the right hand side of the cylinder being returned to sump via conduit 36, proportioning valve 38, valve 42 and

conduits

44 and 43. During this retraction of the piston,

valves

28, 32 and 40 are closed. After the pulpwood 12 is inserted in the pocket,

valves

30 and 42 are closed and valve 28 is opened, whereupon low pressure fluid is supplied to the right hand side of the cylinder via conduit 31,

valves

32, 40 and 38, and conduit 36, the left hand side of the cylinder being connected with sump via conduit 26, valve 28 and conduits 46 and 43. During the initial movement of the pressure foot in the forward direction low pressure fluid (for example water at p.s.i.) is admitted through valves 32, 4t) and 38 to the cylinder 22. The fluid flow is controlled by valve 38 which in turn is controlled by pressure transmitted controller 35 which senses the fluid pressure in the cylinder 22, and as the pressure builds up cuts the flow of fluid supply by activating proportioning valve 38. When an adjustable predetermined pressure is obtained controller 35 causes valve 38 to close and holds valve 38 closed until the pressure in the cylinder drops to an adjustable and predetermined value. On closure of valve 33 valve 78 opens admitting high pressure fluid (for example water under 400 p.s.i.) from conduit 76 as controlled by the opening of valve 74 which is operable by grinder control mech-' anism hereinafter to be described.

It is to be understood that the controls for rate oof pulpwood feed to the grinder stone surface may take various forms. The rate of pulpwood feed to the stone surface is selected and maintained by comparing the rate of ram movement with a reference speed standard, in the drawing a synchronous motor.

The reference speed standard may take many forms other. than that disclosed in the drawings. As an example a suitably designed, alternating or direct current motor supplied from a constant potential source could be used. If such a motor was connected to a constant potential source .through a voltage divider potentiometer then a range of reference speeds could be obtained. This arrangement would take the place of the stepped cone pulley.

Instead of measuring the ram rate of travel directly as shown in the drawings the measure of the water flow rate into cylinder 22 could be employed as a measure of the ram speed. If the rate of flow into cyllinder 22 was employed a flow meter would be incorporated in the system between the cylinder 22 and the high pressure supply. Where a flow meter was employed the rate of flow signal from the flow meter would activate a pneumatic controller. Such controller would control a proportioning valve in the high pressure water supply conduit to the cylinder 22. Employing this arrangement whenever the flow deviated from the controller set point the controller would activate the proportioning valve to restore flow rate to the proper value. The activating of the pneumatic controller can be accomplished by the use of a signal from an electrical generator driven from the ram 14.

From the foregoing it can be seen that the basis sensing device for the grinder control must sense either (1) rate of mechanical motion, (2) fluid displacement, or (3) pulp stock characteristics.

A synchronous motor 58 has its shaft 52 pivoted on bearings 54 and 56. Mounted on motor shaft extension is stepped cone pulley 50. Attached to motor 58 is frame member 68 which is connected to a suitable controller 62 by means of rod or linkage 66. The controller 62 activates valve 74 to proportionally control the fluid fiow to ram cylinder 22 and thus maintain a substantially constant ram speed. A cable 48 is attached to the ram 14 and is passed over the stepped pulley 58, the free end of the cable 18 being secured to a weight 60.

In FIGURE 3 is shown an enlarged view of the synchronous motor 58 and controller 62. The motor 58 is restrained by

members

82 and 84 whereby the motor housing can move. The movement of motor housing is controlled by

stops

86 and 90 that are mounted in

supports

82 and 84 and are secured in the desired position by

nuts

88 and 92.

In FIGURE 4 is shown an enlarged sectional view of the motor and pulley shaft. The motor 58 has a shaft 52 coupled with an intermediate shaft 51 by coupling means 94. Shaft 51 is supported by bearings 95, the pulley 50 being rotatably mounted on the shaft. A slip clutch 96 serves to transmit torque between the pulley and the shaft 51. One purpose of the clutch is to permit normal torque to be transmitted and still allows the members to slip in relation to each other during the period when the ram is retracting and/ or filling under low pressure fluid supply. The tension on spring 98 is adjustable and maintained in the predetermined position by lock nuts 100. The number of grooves on the pulley may vary, and the larger the number of grooves, the greater is the range of ram speed that may be controlled.

The speed of travel of the ram 14 is transmitted through cable 48 which drives the stepped cone pulley 50 at the same rotational speed as the shaft of motor 58. The motor frame will be in motion when there is a difference in speed of rotation between the motor shaft and the cone pulley. The differential effect causes the synchronous motor frame to move within the limits defined by

stops

86 and 90. The movement of the motor frame is proportional to the angular difference between the synchronous motor shaft speed and the speed imposed by therotational speed of the cone pulley. The motor frame through

linkage

68, 66, and 64 transmits its movement to controller 62 which activates valve 74 to proportionally control the flow of fluid to the ram cylinder 22 and thus maintains constant ram speed.

The important step of the process is to control the "grinding rate per unit of wood in contact with the grinding surface. Controlling the rate of feed to the stone surface reduces up to 50% in freeness variations. At the same time the pulp strength is increased about and the fine screen rejects are lowered as much as 10%.

What is claimed is:

1. In a wood grinding apparatus including a rotating grinding stone and a pocket for receiving the wood to be ground, the invention which comprises a pressure foot for pressing the wood into contact with the grinding stone;

4, piston and cylinder motor means for actuating said pressure foot; a low pressure fluid source; a high pressure fluid source; alternately operable first and second means for connecting said low pressure and high pressure fluid sources, respectively, with said motor means to actuate said pressure foot in the wood pressing direction, said second means including a control valve; controller means for operating said control valve to establish a predetermined rate of movement of said pressure foot in the wood pressing direction; and controller operating means responsive to a deviation in the rate of movement of said pressure foot from said predetermined value for operating said controller means and said control valve to return the rate of movement of said pressure foot to said predetermined value. 2. In a wood grinder having a rotatable grinding stone, a pocket to receive wood to be ground, a pressure foot for pressing said wood into contact with said grinding stone, and a fluid actuated power unit for actuating said pressure foot, the invention which comprises a first source of fluid under pressure connected to said power unit, a second source of fluid under higher pressure connected to said power unit, a valve for controlling the supply of fluid under pressure from said second source to said power unit, and means for advancing said pressure foot at a constant rate during grinding, comprising a stepped cone pulley, means for operatively connecting the said pulley to said pressure foot, a synchronous motor connected to said stepped cone pulley, and means connecting said motor to said valve.

3. In a wood grinder having a rotatable grinding stone, a pocket to receive wood to be ground, a pressure foot for-pressing wood into grinding contact with said grinding stone, and a double acting hydraulic cylinder and piston power unit for activating said pressure foot, the invention which comprises a first source of fluid under pressure connected to said cylinder, a second source of fluid under higher pressure than said first source connected to said cylinder, a valve for controlling the supply of fluid from said second source to said cylinder, a synchronous motor operatively connected to said valve, a stepped cone pulley connected to said motor, and a cable attached to said pressure foot and passing over said stepped pulley.

References Cited by the Examiner UNITED STATES PATENTS 1,766,548 6/1930 Schnitzer 241-34 X 2,545,260 3/1951 Cole 241-34 X 2,965,315 12/1960 Lyall 241--34 WILLIAM W. DYER, 1a., Primary Examiner.

H. F. PEPPER, Assistant Examiner.

Claims

1. IN A WOOD GRINDING APPARATUS INCLUDING A ROTATING GRINDING STONE AND A POCKET FOR RECEIVING THE WOOD TO BE GROUND, THE INVENTION WHICH COMPRISES A PRESSURE FOOT FOR PRESSING THE WOOD INTO CONTACT WITH THE GRINDING STONE; PISTON AND CYLINDER MOTOR MEANS FOR ACTUATING SAID PRESSURE FOOT; A LOW PRESSURE FLUID SOURCE; A HIGH PRESSURE FLUID SOURCE; ALTERNATELY OPERABLE FIRST AND SECOND MEANS FOR CONNECTING SAID LOW PRESSURE AND HIGH PRESSURE FLUID SOURCES, RESPECTIVELY, WITH SAID MOTOR MEANS TO ACTUATE SAID PRESSURE FOOT IN THE WOOD PRESSING DIRECTION, SAID SECOND MEANS INCLUDING A CONTROL VALVE; CONTROLLER MEANS FOR OPERATING SAID CONTROL VALVE TO ESTABLISH A PREDETERMINED RATE OF MOVEMENT OF SAID PRESSURE FOOT IN THE WOOD PRESSING DIRECTION; AND CONTROLLER OPERATING MEANS RESPONSIVE TO A DEVIATION IN THE RATE OF MOVEMENT OF SAID PRESSURE FOOT FROM SAID PREDETERMINED VALUE FOR OPERATING SAID CONTROLLER MEANS AND SAID CONTROL VALVE TO RETURN THE RATE OF MOVEMENT OF SAID PRESSURE FOOT TO SAID PREDETERMINED VALUE.