GB2116072A - Roller mills - Google Patents

Abstract

A roller mill for fine comminution of minerals and aggregates in the production of sands and grits, has a pair of rollers (2,3), counter-rotatable about parallel horizontal shafts. The nip (S) between the rollers (2,3) is set according to the desired grain. A high-pressure hand pump (14), and two fixed hydraulic cylinders (10) control two rods (6), which determine the position of a bearing support 4 for the movable roller 3. Two diaphragm type hydraulic accumulators (18), filled with high-pressure nitrogen and inserted into the hydraulic circuit, permit the movable cylinder (3) to move immediately away from the stationary cylinder (2), in the event of uncrushable materials (iron or other) entering the nip. <IMAGE>

Description

SPECIFICATION Cylinder mill with hydraulic control and safety A cylinder mill is a well-known machine which has been used for many years for grinding minerals and aggregates. The most common type of cylinder mill consists of two cylinders mounted on shafts supported at their ends through four bearings of a suitable type. One of the cylinders is stationary and the two bearings thereof are rigidly connected to the machine's bedplate. The bearings of the other cylinder slide on guides of a suitable type made on the body of the machine and are pushed, by means of th rust springs and screws, against stationary pawls having a thickness which varies according to the required gauge of mineral and aggregate particles.

This type of construction and of regulation presents many disadvantages among which the more significant are the following: - the regulation, which is a laborious process, can be performed only when the machine is at standstill; - the calibration of the forcing pressure of the contrast springs is difficult; - the movable cylinder tends to jerk and vibrate which makes the machine noisy, and gives the requirement of considerable foundations; - the connection and fastening elements frequently loosen and break; - owing to all the abovementioned reasons, the machine must work at a low rotating speed of the cylinders, with resultant low production.

All these reasons as above mentioned have caused this type of machine to be gradually neglected in the course of the last years, favouring instead other types of mills.

The abovementioned disadvantages are eliminated by the use of the present invention which provides that the movable cylinder is mounted on a body which can osciallate around a joint relative the bedplate itself. The oscillating motion of this movable cylinder and the relative motion of approaching and moving away from the stationary cylinder preferably obtained through two hydraulic cylinders operated by means of a high-pressure hand pump: these cylinders, through two sturdy stay-rods, control the oscillating body supporting the movable cylinder.Two diaphragm-type hydraulic accumulators, filled with high-pressure nitrogen and connected in the hydraulic circuit, ensure a safe construction as they permit the movable cylinder to move away should the oil pressure into the hydraulic circuit casually increase beyond the predetermined value, for instance due to the introduction between the two cylinders of uncrushable materials (iron or other), so that the uncrushable materials can escape from the machine without any damage to the machine whatsoever. When the overload has passed, the cylinders go automatically back to give the predetermined port setting.

This permits regulation of the port with the machine in operation, as well as the realization of a quite rigid unit able to eliminate any vibration, jerks and noises.

Very high operating speeds can thus be attained with the relative high values of specific production.

An embodiment of the mill according to the invention is illustrated in one of its realizations in the enclosed drawing of which the single Figure, Figure 1 shows a diagrammatic side view of the mill complete with the movable cylinder control hyd raulic equipment.

Referring to the drawing, the machine consists of a bedplate or body 1 to which bearings of the stationary cylinder 2 are fastened.

Articulated joints 5 are also fitted on this body: movable body 4 is articulated on them and to it the bearings of movable cylinder 3 are fastened.

Regulation of guage "S" is set through two stay-rods 6 fastened at one end to the oscillating body 4 by means of articulated joints 7 and connected at the other end, through two spherical thrust bearings 8, to pistons 9 of two hydraulic cylinders 10, the latter being fastened to body 1 of the machine.

The pressure chambers of the two cylinders 10 are connected by suitable piping to two hydraulic accumulator chambers, of the diaphragm type, 18, preloaded with high-pressure nitrogen. Two unidirectional throttling valves 19 are also installed in this piping. The piping continues beyond the two accumulators interconnecting them.

The hydraulic system includes devices which permit the regulation of the volume of oil introduced into the two cylinders, and as a consequence permit variation in the port between the grinding cylinders.

These devices comprise a tank 11 for the hydraulic oil, complete with fillercap 12 for charging the tank with oil, filter and with level gauge unit 13. The tank 11 is directly connected with a high-pressure hand pump 14 complete with bypass cock 15.

The delivery piping of the pump has a glycerine gauge 16 and a cut off cock 17 and is inserted in the piping interconnecting the two accumulators 18.

As clearly shown in Figure 1,theoil pressure inside cylinders 10 is generated solely by the thrust against the movavble cylinder 3 of the material being crushed between the cylinders which tries to enlarge port "S" between the cylinders; under normal working conditions cock 17 is closed and therefore oil does not have any possibility of flowing out of cylinders 10 to tank 11. It can only flow into the diaphragm-type hydraulic accumulator chambers 18, but in order to do this it is necessary that pressure inside cylinders 10 should increase to values higher than that of the nitrogen with which the abovementioned chambers 18 have been filled.

As a consequence, in normal conditions, port"S" remains unalterable and the material is crushed until it can pass through this discharge port.

Should some steel pieces or other uncrushable matter enter by chance between the two cylinders, the thrust exerted against the movable cylinder increases the pressure of the oil contained within the cylinders 10 to values which are higher than the nitrogen calibration values of accumulators 18.

Oil will then reflow rapidly from cylinders 10 to accumulators 18 going through valve 19 in the direction in which flow is allowed at the maximum delivery.

The volume of oil which can reflow into accumulators 18 is such as to allow a considerable separating of the two cylinders 2 and 3, and therefore the uncrushable matter shall go out from the machine without any damage to the machine whatsoever, when the cause of the overpressure in the hydraulic circuit will thus be stopped. Nitrogen compressed in the two accumulators 18 will then compel oil to flow back towards cylinders 10 to bring backgauge to the predetermined values. In orderto avoid water hammer, the reflowing of oil takes place by degrees or in other controlled position. This operating condition is ensured by the unidirectional throttling valve 19, suitably cailbrated.In order to determine gauge "S", a contrast stay-rod 20, connected to articulated joints 4 through the spheric seat nut 22 with the interposition of a rubber spring packet, has been provided. In order to vary the port (for instance, for decreasing the port), the following procedure is adopted: First of all, the spherical seat nut 22 is unloosened until sufficient decompression of the spring rubber bodies packet 21 takes place. Bypass cock 15 is then closed in order to avoid reflowing of oil to the tank and subsequently cock 17 is opened and, through the hand-pump 14, the quantity of oil sufficient for reducing the port to the required value is introduced into the hydraulic circuit and into the two cylinders 10.

Lastly, the spherical seat nut 22 is screwed on until packet 21 is precompressed slightly. Finally cock 17 is closed.

In order to increase the port opening the following procedure is adopted: Cutoff cock 17 is opened. Then open bypass cock 15 is opened thus permitting the reflowing to tank 11 of oil from cylinder 10 until the reqired port is reached. Cock 15 is then blocked followed cock 17.

Lastly, the mechanical clearances shall be compensated by operating on the spherical seat nut 22 of the contrast stay-rod 20 until an adequate precompression of the packet of spring bodies 21 is reached.

As clearly appears from the above description, both the regulation of the port and the hydraulic safety are ensured by means of a simple and highly reliable devices, The result is a machine which is capable of operating at high rates of specific production, and of ensuring high yields while scarcely necessitating of maintenance operations.

Claims (5)

1. A cylinder mill comprising two cylinders dis pcsed with their axes horizontal, one cylinder being mounted on stationary bearings on the -edplate of the machine and the other cylinder being mounted on portable body means so that it is movable towards and away from the stationary cylinder to vary the grinding space between the cylinders, and inciuding adjustable hydraulically operated means for pivoting the body means to give the required relative positioning of the cylinders and hydraulic safety device permitting the cylinders to separate in the event of an uncrushable obstruction lodging between the cylinders.

2. A cylinder mill according to claim 1, wherein the hydraulically operated means inciudes two hydraulic cylinders respectively connected to two stays connected to the body means and common hydraulic piping supplying both cylinders through a lock, a high pressure pump fitted with a by pass cock, a guage and an oil tank.

3. A cylinder mill according to claim 2, wherein the hydraulic safety device comprises two accumulators of the diaphragm type filled with a gas such as nitrogen and connected through two unidirectional throttling valves to the hydraulic feeding circuit of the two cylinders.

4. A cylinder mill according to any preceding claim including a contrast stay-rod operating on the body means through articulated joints and a rubber spring packet.

5. A cylinder mill substantially as hereinbefore described with reference to the accompanying drawing.