GB789899A - Improvements in or relating to pulverizing mill and process of pulverizing material - Google Patents

Abstract

789,899. Grinding apparatus. HARDINGE CO., Inc. Sept 12, 1955 [Sept. 30. 1954], No. 26003/55. Class 59 A grinding mill comprises a base member 30, Fig. 3, which is rotatable about a vertical axis, at least one rolling element 34 which is supported above the base member so that its peripheral surface cooperates with the surface of the latter member to pulverize material between the two surfaces, fluid pressure holding and shockabsorbing means connected to the rolling member so as to permit the latter yieldably to move away from the base member to accommodate variations in the thickness of material between them and selectively-settable control means for the fluid pressure means operable to maintain substantially uniform predetermined pressure upon the rolling element during the pulverizing operation regardless of the thickness of the material between the two members. In the mill shown in Figs. 2 and 3, two rollers 34 are disposed in edge relation on the upper face of a grinding ring 30 on a disc 28 rotated from a motor 32 through a gear reduction unit. Each roller is rotatably mounted on a shaft 40 carried by a pivoted arm 36, and cross members 42 on the two arms are connected by two piston- and-cylinder devices 44, 46 disposed on opposite sides of the mill. Hydraulic or pneumatic pressure from a pump or compressor 52 is applied to both these devices through an adjustable pressure-regulating valve 56 and pipe 58 so that the rollers are urged towards the disc. A valve 60 arranged in the pipe 58 provides for the relief of excess pressure in the cylinders 46 as a result of the rollers rising because, for example, the depth of material on the ring increases; the valve 60 either constantly bleeds a small amount of fluid from the pipe 58 or can be set to relieve pressure in excess of that provided by the valve 56. Increases of pressure in the cylinders 46 caused by sudden increase of fluid or the presence of tramp metal beneath the rollers are absorbed by the action of the valve 60 and also by the compressibility of the pressure fluid when the latter is pneumatic. A shock-absorbing spring 130, Fig. 8, may also be interposed, between the piston rod of each device 44 and the corresponding arm 36 to take up such sudden shocks. The system for operating the devices 44 may be combined hydraulic and pneumatic, air for applying the pressure to the devices 44 being supplied from a reservoir 134, Fig. 9, which is maintained under compression by hydraulic fluid supplied thereto by a pump 138 from a reservoir 136 through a pressure-regulating valve 140. The pump delivers fluid at a pressure exceeding the maximum setting of the valve, and a compression dome 149 is associated with the valve to maintain the excess pressure supply until this is reduced to that for which the valve is set; the pump motor is controlled by a switch 147 which operates automatically to start and stop the motor at lower and upper pressure limits. A bleeder valve 150 is provided in a conduit 148 connecting the reservoirs 134, 136. The system shown in Fig. 9 may be modified to work only with pneumatic fluid in which case the reservoirs 134 136 are dispensed with and the pump 138 could draw from the atmosphere. The mill shown in Figs. 2 and 3 is enclosed in a casing 12 comprising a feed inlet 18. discharge outlets 28 for unusable material, and inlet 76 for the passage of air or other gas which flows upwardly around the disc 30 so as to entrain the comminuted material and pass it to a rotary classifier from which the fine particles pass out through a conduit 16 and the coarse particles drop back into the mill. Surrounding the ring 30 is a dam 70, Fig. 5, which is adjustable vertically so that, by varying its position relatively to the rollers, it determines the angle at which the crushed material leaves the ring and intersects the upward gaseous streams so as to affect the quantity and particle size of the material entrained. In the modification shown in Fig. 6, each of three rollers 92 co-operating with a grinding ring 90 on the sloping side of a rotary bowl 88 is rotatably supported by a pivoted bearing sleeve 96 having an extension 100 by means of which a piston- and-cylinder device 102 urges the roller towards the ring. Hydraulic or pneumatic pressure supplied to the cylinders 102 is controlled by pressure regulating and exhaust valves 56, 60 as described above. A similar pressure control is provided for a mill in which balls 112, Fig. 7, co-operating with a rotating disc 110 are urged downwardly by a ring 114 which is placed under pressure by a number of piston-andcylinder devices 120. In. operating any of the above described mills, the regulating valve 56 is first adjusted to provide for pressure at less than the normal operating pressure, material is then fed to the rotating ring, disc or bowl while the fluid pressure is increased and the rate of feed adjusted, and finally the fluid pressure is adjusted to work uniformly at that necessary to produce the desired range of sizes of the product.