CONTROL SYSTEM

Abstract: A hydraulic control system for a gyratory crusher with a hydraulically supported main shaft. The inlet line (3) of hydraulic fluid is provided with a pressure relief valve (5), such that when the pressure in the cylinder, e.g. because of a disturbance, exceeds the opening pressure of the relief valve, fluid flows from the cylinder through the pressure relief valve to the lubricating circuit of the crusher. The safety system thus constructed is simple, reliable, and quick.

Description: CONTROL SYSTEM TECHNICAL FIELD The present invention relates to a hydraulic control system of gyratory crushers. The invention relates especially to a safety system for overload situations in such crushers where the main shaft is hydraulically supported by a piston. TECHNICAL BACKGROUND The main shaft of a gyratory crusher is usually hydraulically supported by a piston such that the vertical position of the main shaft can be adjusted. The hydraulic circuit in such crushers is usually also provided with a safety system for overload situations. When a noncrushable particle enters the crusher, the system allows the piston and thereby the main shaft to move downwards and thus let the particle go through the crusher. Thereafter the main shaft must rise to the original position to continue the crushing process. In such known systems there is a pressure relief valve and a pressure accumulator. Pressure accumulators are however quite expensive and they require a relatively large space. They also have to be checked relatively often. DESCRIPTION OF THE INVENTION General description Now a system in accordance with claim 1 has been in¬ vented. Preferable embodiments of the invention are described in the other claims. In the invention it is essential that in an overload situation the pressure relief valve allows the fluid to flow from the cylinder to the lubricating circuit of the crusher, and thus makes the main shaft to move downwards. When, after the disturbance, an automatic control system reacts to this movement and pumps fluid back to the crusher, and thus lifts the main shaft to the pre-determined position. No pressure accumulator and no corresponding hoses are needed. According to a preferable embodiment, the pressure relief valve is integrated to or into the crusher. Detailed description of preferable embodiments In the drawings of the description, - Fig. 1 shows the hydraulic scheme of a system in accordance with the invention, - Fig. 2 shows a partial sectional view of a crusher that can be used in the system of Fig. 1, - Fig. 3 shows a partial sectional view of another crus¬ her. Crusher 1 comprises a frame and therein a main shaft supported through a suitable bearing by a piston movable in a hydraulic cylinder. The main shaft can be kept at a desired position by adjusting the amount of hydraulic fluid in the cylinder. Pressurized fluid is led from pump unit 2 through inlet line 3 into the cylinder to support the piston and thereby the main shaft. The fluid is normally led out from the cylinder through the line 3 and adjusting means of the pump unit into tank 4. The pump unit then takes fluid from the tank. The inlet line 3 is provided with a pressure relief valve 5 integrated to or preferably into the crusher. In case of an overload situation in the crusher, for instance because of an uncrushable particle, overpressure in the cylinder opens the relief valve, and fluid flows from the inlet line through a by-pass line 6 and outlet 7 to return line 8. The crusher is also provided with a setting transducer 9, which detects the change of the main shaft position. When an overload situation is over, the shaft is automatically raised to the original position. The process is controlled by means of control unit 10 connected to the pump unit and to the transducer. Because there is no pressure accumulator, the system is simpler, more compact and easier to assemble than the known systems. Further, when the relief valve is joined without hoses to the crusher, the system response times are very short. This is an important advantage especially in cold climates, where the resistance in hoses is even more signifi¬ cant. In an overload situation there is also no counterpressure to the oil, which further increases the ef- ficiency and reliability of the system. Also the service demand is reduced. The setting transducer 9 may comprise of a toothed rack attached to the piston and of a corresponding gear wheel con- nected to a angle detector. As normally, hydraulic fluid is used here also as a lubricating oil. Fluid is taken from the tank 4 by a lubrication pump unit 11 and led into the crusher lubricating circuit through a lubrication inlet line 12. From the lubricating oil circuit the fluid is returned through the outlet 7 to the return line 8. The pump unit 2, tank 4, and lubrication pump unit 11, are provided with normal auxiliary equipment necessary for reliable operation of such systems. Fig. 2 shows in more detail how the relief valve 5 is mounted into the frame of the crusher. The by-pass line 8 has been made into the frame so as to lead from the valve 5 into the lubrication circuit. In a normal situation the stem of the valve closes the by-pass line. In an overload situation the stem moves backwards and allows fluid to flow into the by-pass line. Alternatively, an external by-pass line can be used. Fig. 2 also shows a cuplike piston 13 surrounding the main shaft 14. In this way the height if the crusher is lower than in conventional crushers with a piston-cylinder pair totally below the main shaft. The present invention can of course be applied also to conventional crushers. Fig. 3 shows an embodiment in which relief valve 5' has been placed in a conventional piston 14 ' . In an overload situation fluid flows from the cylinder through the relief valve into the lubrication circuit.

Claims: CLAIMS 1. A hydraulic control system for a gyratory crusher in which the main shaft of the crusher is supported hydraulically by a piston movable in a cylinder and the crusher is lubrica¬ ted by means of a lubricating circuit, the system comprising - a tank for hydraulic fluid, - a pump unit and inlet lines for leading hydraulic fluid from the tank into the cylinder and into the lubricating circuit, - a return line for leading hydraulic fluid from the cylinder and from the lubricating circuit into the tank, and - a pressure relief valve connected to the inlet line, and a by-pass line connected between the relief valve and lubricating circuit, such that when the pressure in the cylinder exceeds the opening pressure of the relief valve, fluid flows from the cylinder through the relief valve to the lubricating circuit and further to the return line. 2. A system in accordance with claim 1, wherein the pressure relief valve has been integrated to, or preferably into the crusher. 3. A system in accordance with claim 2, wherein the by¬ pass line has been placed in the frame of the crusher. 4. A system in accordance with any of claims 1 - 3, further comprising - a transducer for monitoring the height position of the main shaft in the crusher, and - a control unit connected to the transducer and to the pump unit such that when the pressure in the cylinder is below the opening pressure of the relief valve, the main shaft is automatically kept at a predetermined position.

Inventors: ELORANTA JARMO, RIKKONEN KARI, ELORANTA, JARMO, RIKKONEN, KARI
Applicants: ELORANTA JARMO, NORDBERG LOKOMO OY, RIKKONEN KARI, ELORANTA, JARMO, NORDBERG-LOKOMO OY, RIKKONEN, KARI
Application year: 1995
Main classification: B02C2
IPC codes: B02C2