Prior art The reciprocating motion of the crushing jaws of a jaw crusher results in breaking of the material that has been fed between the jaws for crushing. The motion is generated by means of an eccentric and a so-called pendulum. The jaw crushers are usually divided into two groups according to their operating principle: so-called single toggle jaw crushers and so-called double toggle jaw crushers.

The purpose of the toggle plate is to maintain the distance between the bearing point of the pendulum of the crusher and the bearing point of the rear end of the crusher. Thus, the press force exerted on the toggle plate varies considerably during operation of the crusher.

During idle operation of the crusher, there are moments when the force exerted by the spring of the tension rod and the gravity component parallel to the toggle plate are the only forces acting on the toggle plate. When the gap of the crusher is full of stones, the toggle plate takes the entire crushing force of the lower part of the pendulum.

The press force exerted on the toggle plate depends strongly on the physical properties of the material fed into the crusher. As far as different kinds of mineral materials are concerned, these properties are nearly always easy to predict. When crushing rock, for example, it is relatively easy to estimate the force required for the crushing of the rock in advance and thus also the press force exerted on the toggle plate. This information is used when dimensioning the strength of the crusher parts in the design phase of the crusher.

Jaw crushers, which traditionally have been used mainly for crushing rock, are now used for crushing many other kinds of materials. Today, a typical application of the jaw crusher is the so-called recycle crushing, in which a jaw crusher is used for crushing demolition

waste of various kinds for the purpose of utilising the waste. A typical demolition waste material of this kind is the concrete used in buildings. As far as crushing is concerned, concrete is a problematic material in the respect that concrete structures usually contain different kinds of reinforcements composed of ferrous metals whose size and shape are impossible to determine when viewing the piece of concrete to be crushed from the outside. A considerably stronger force is required for crushing these, or for getting more disintegrated material than the one resulting from the setting of the crusher, than for crushing the concrete itself. Thus, if the crushing of rock and the crushing of recycled material are compared, it is much more difficult in the latter case to predict the strength of the forces acting on the crusher.

Usually the toggle plate, which has a simple and cheap structure, is intentionally dimensioned to form the weakest part of the crusher. The purpose of the design is that the toggle plate yields when a piece difficult to crush enters the gap of the crusher, as a result of which the setting of the crusher increases and the uncrushed piece falls through the gap without breaking the more expensive parts of the crusher, such as the body, eccentric shaft or bearings.

A crusher thus designed has the problem that the yielding of the toggle plate is usually not immediately noticed as the uncrushed piece passes through the crusher. It is typical that the uncrushed piece passing through the crusher gap first makes the toggle plate buckle, causing a very small deformation. In this case, it is often possible to use the crusher for crushing even for several hours before the material of the toggle plate eventually fails and the toggle plate is finally destroyed. After such a long period of time it may not be possible to evaluate the reason for toggle failure: the uncrushed piece that caused the damage is already buried deep in the pile of crushed material, or has possibly even been transported away from the crushing site. Although in this case, the toggle plate breaks exactly in the way it was planned, the failure may come as a complete surprise to the crusher operator: if the operator at the very moment the toggle plate buckled would be alerted of the upcoming toggle plate failure, the operator could take immediate action to find out what made the toggle plate buckle and to prevent it from happening again. Furthermore, the operator of

the crusher could get a spare toggle plate in good time and prepare for a change of toggle plate at a suitable moment during operation.

A breaking switch arranged in connection with a jaw crusher toggle plate and designed to be included in the control circuit of the drive motor of the crusher is known from German patent DE 601 522. The breaking switch is supposed to stop the crusher at the very moment the elongation or the deflection of the switch exceeds the tensile strength thereof. No information is obtained on whether there have been deformations before this, and the crusher stops immediately if the switch is activated.

Description of the invention The method according to claim 1 has now been invented for monitoring the load exerted on a jaw crusher. The characteristics of the jaw crusher according to the invention are set forth in claim 10. In the invention, the deformation of the toggle plate is utilised in the load monitoring. Preferably, an electric alarm system circuit can be closed or opened by the deformation.

The invention makes it possible to warn the crusher operator, at the very moment the toggle plate buckles, of the coming toggle plate failure. The crusher operator can therefore immediately take action to find out why the toggle plate buckled. Consequently, it may in certain situations be possible to prevent the replacement toggle plate from buckling by selecting the feed material more carefully.

Furthermore, the operator of the crusher can take measures in good time for getting a spare toggle plate. It may also be possible for the operator to schedule the change of toggle plate for the most opportune moment during operation.

If the invention is also used for monitoring the elastic deformations of the toggle plate, the operator can easily control the crushing process in such a way that the load on the crusher is the highest possible but still safe for the crusher. The operator can thus maximise the production capacity of crushed material without fear of breaking the crusher.

Brief description of the drawing The invention and the details thereof will be described in more detail with reference to the accompanying drawing wherein Figure 1 is a schematic view of the operating principle of a single toggle jaw crusher, Figure 2 is a vertical sectional view of a single toggle jaw crusher, Figure 3 is a schematic view of a double toggle jaw crusher, Figure 4 shows a toggle plate used in an arrangement according to the invention viewed from the side and in its normal state, Figure 5 shows the same arrangement viewed from above the toggle plate, Figure 6 is a similar view but taken from the end of the toggle plate, Figure 7 is a similar view as Figure 4 but shows the toggle plate in a buckled state, Figure 8 shows a toggle plate used in another embodiment of the invention viewed from the side and in its normal state, Figure 9 shows the toggle plate of Figure 8 in a buckled state, and Figure 10 shows a detail of Figure 8 on a larger scale.

Embodiments of the invention Figures 1 and 2 show a jaw crusher whose main parts are a frame, a pendulum and an eccentric shaft. Today, the frame is usually composed of a front end 1, of a rear end 2 and of two cheek plates 3 that are removably attached to each other. The pendulum 4 is mounted inside the frame in such a way that it is suspended from the upper edge of the frame, from an eccentric shaft 5 mounted in a bore extending through the upper end of the pendulum.

The eccentric shaft 5 is supported in bearings both in the frame and in the pendulum 4. The eccentric shaft is eccentric in such a way that the axis of the shaft part located inside the crusher frame begins to rotate about the axis of the shaft part located outside the frame when the eccentric shaft is rotated by the shaft part located outside the crusher frame. Correspondingly, this rotational motion of the shaft part occurring in the bore of the

pendulum makes the upper end of the pendulum rotate about the axis of shaft part extending to the outside of the crusher frame.

The distance between a given bearing point of the lower end of the pendulum 4 and the corresponding bearing point supported by the rear end 2 of the crusher is fixed by means of a toggle plate 6 and a tension rod 7. The rotational motion of the upper end of the pendulum is thus transferred to the lower end of the pendulum with the result that each point of the surface of a replaceable, movable crushing jaw 8 fixed to the pendulum begins to move back and forth, toward the front end of the crusher and away therefrom. A fixed, replaceable crushing jaw 9 is mounted to the front end 1 of the crusher. The reciprocating motion of the movable crushing jaw and of the fixed crushing jaw with respect to each other causes breakage of the feed material fed between the crushing jaws.

The crushing operation is optimised by changing: -the speed of rotation of the eccentric shaft -the eccentricity of the eccentric shaft -the distance between the lower ends of the crushing jaws (the setting of the crusher) -the angle between the crushing jaws -the position of the bearing point of the rear end of crusher with respect to the rear end -the position of the bearing point of the pendulum of the crusher with respect to the pendulum.

Some of these variables are fixed already in the design phase of the crusher. Others may be adjusted by the crusher operator during operation.

The setting of the crusher is a crusher feature that typically is adjusted when the crusher is in use. The setting of the crusher is usually adjusted by moving the bearing point of the rear end 2 of the crusher, which supports the toggle plate 6 of the crusher, with respect to the rear end of the crusher. The setting of the crusher shown in the example can be reduced, for example, by inserting removable spacer plates 10 between the rear end of the crusher and the toggle plate bearing 11 supported by it. Correspondingly, the setting is increased by removing these adjusting plates.

Further, one of the features of the crusher shown in the example is the possibility of decreasing the setting by pushing adjusting wedges 12,13, tapering in the lateral direction of the crusher and mounted crosswise with respect to each other, toward one another so that their overlap increases. Correspondingly, the setting is increased by pulling the wedges apart so as to decrease their overlap.

The purpose of the tension rod 7 and of the tension rod spring 14 is to exert a press force on the toggle plate 6 in all situations and thereby to hold the toggle plate ends firmly against the toggle plate bearing 11 supported by the rear end and against the toggle plate bearing 15 supported by the pendulum, and thus to prevent the toggle plate from falling from its position. The compression of the tension rod spring 14 can be adjusted by means of a thread located at the end of the tension rod, a tension rod bearing 16 and an adjusting nut 17 intended for the tension rod spring. The compression of the spring is fixed at a desired value by means of a locking nut 18 intended for the adjusting nut of the tension rod spring. The compression of the spring has to be adjustable to keep the tensile stress of the tension rod within the permissible range when the distance between the lower end of the pendulum and the rear end of the crusher changes when the setting of the crusher is adjusted.

In the double toggle jaw crusher shown in Figure 3, the pendulum 4 is mounted on bearings on its centre shaft 19, at the upper edge of the crusher frame. An eccentric shaft 5 drives a pitman 20, supported at its lower end by bearings between two toggle plates 6,6'. One toggle plate 6'is supported, at the other end thereof, in bearings in the rear end 2 of the crusher. The other toggle plate 6 is supported, at its other end, in bearings in the pendulum 4. When the eccentric shaft 5 rotates, the toggle plate bearing points situated on the pitman side move up and down with respect to the crusher frame, with the result that the toggle plates make the lower end of the pendulum move perpendicularly toward the front end of the crusher and away therefrom.

Figures 4 to 7 show an arrangement according to the invention to warn the operator of the crusher of that the toggle plate is going to become damaged. Figure 4 shows the

arrangement viewed from the side of the toggle plate 6. A sensor comprising a sensor body 21,21'is fixed to the toggle plate. The sensor body supports a sensor wire 22,22'at a given, predetermined distance from the toggle plate. The sensor wire is part of an electrical circuit that is insulated from the conducting toggle plate 6. The crusher frame connects the toggle plate electrically to earth. The section of sensor wire located in the open space defined by the sensor body and the toggle plate is uninsulated, the sensor body being isolated from the wire.

Figures 5 and 6 show the same arrangement viewed from above the toggle plate 6 and from the end of the toggle plate, respectively.

Figures 4 to 6 show the toggle plate in its normal state.

Figure 7 show the toggle plate 6 and the toggle plate load monitoring arrangement in a situation in which the toggle plate is buckled. The toggle plate has bent in such a way that the sensor wire 22 touches the toggle plate and causes contact between the toggle plate and the sensor wire. Thus, the uninsulated sensor wire allows the current running through it dissipate to ground through the toggle plate. The current in the electrical circuit changes, which can be observed with an appropriate monitoring arrangement. In the simplest form the monitoring arrangement is, for example, a signal light arranged in the electrical circuit of the sensor wire. Alternatively it can be an automatic multi-function alarm or control system 23 that can be used, for example, to control the feeding device that feeds the crusher or the crusher itself.

Figures 8 to 10 show an alternative embodiment wherein the sensor body 21, in addition to the sensor wire 22 registering toggle plate buckling, comprises other sensor wires 24,25, 26 at varying, predetermined distances from the surface of the toggle plate 6. These sensor wires make it possible to monitor the load exerted on the toggle plate in a situation in which the toggle plate bends only a little, within the range of elasticity, and in which no plastic, toggle-breaking deformation has occurred yet. Furthermore, different kinds of monitoring arrangements can be coupled to the electrical circuits of the sensor wires monitoring the elastic deformations of the toggle plate.

The embodiments described above are not restrictive in character but various modifications can be made to the invention without departing from the scope of the invention as defined by the appended claims.

The direction of the current in the electrical circuit of the monitoring arrangement is not fixed in any particular way. The contact between the sensor wire and the toggle plate can either open or close the electrical circuit of the monitoring arrangement, depending on the construction.

Alternatively, the arrangement can be designed in such a way that a separate, rigid conductor piece that accurately follows the toggle plate deformations and is disposed in the same electrical circuit as the toggle plate, is fixed to the sensor body or to the toggle plate. In such a construction, a deformation of the toggle plate causes a corresponding deformation in the conductor piece, which in turn causes a contact between the conductor piece and the sensor wire.

The sensor wire does not have to have any particular shape in cross-section. The sensor wire can be a single wire or it can be composed of a multi-core conductor material.

The toggle plate deformation monitoring can also be carried out by fixing a strain gauge of the type used in various strength measurements to the surface of the toggle plate. However, this solution has the disadvantage that a strain gauge always generates a very weak voltage, which is why an amplifier of some sort has to be included in the electrical circuit monitoring the load exerted on the toggle plate. Such a solution is very expensive compared with the one described above.

The deformations of the toggle plate can also be monitored by providing limit switches at various positions. However, a drawback when using limit switches is their difficulty of location: the toggle plate moves quickly back and forth with respect to the crusher frame in a normal crushing situation. Besides, the position of the toggle plate with respect to the crusher frame changes every time the setting of the crusher is adjusted, which is why the position of the limit switches also has to be changed when the setting is adjusted.