GB2626587A

GB2626587A - Tensioning arrangement and system for a crushing apparatus

Info

Publication number: GB2626587A
Application number: GB2301202.4A
Authority: GB
Inventors: Douglas Robert
Original assignee: Northern Crusher Spares Ltd
Current assignee: Northern Crusher Spares Ltd
Priority date: 2023-01-27
Filing date: 2023-01-27
Publication date: 2024-07-31
Anticipated expiration: 2043-01-27
Also published as: GB202301202D0; GB2626587B

Abstract

A tensioning arrangement 20 suitable for the adjustment rod 21 of a crushing apparatus 1, such as a jaw or impact crusher. The tensioning arrangement comprises a coil spring 22 in co-operation with a hollow bore hydraulic cylinder 23, the body of the hydraulic cylinder 23 is located substantially within the bore of the coil spring 22. The coil spring 22 may be a helical spring, the adjustment rod 23 may be a draw back or tension rod of a jaw or impact crusher, configured for maintaining a constant spring compression or spring length. The hollow bore hydraulic cylinder may comprise a body, tubular ram, and one or more hydraulic ports for fluid connection. There may be a locating tube. A method of using the tensioning arrangement is disclosed.

Description

TENSIONING ARRANGEMENT AND SYSTEM FOR A CRUSHING APPARATUS

Field of the Invention

The present invention relates to a tensioning arrangement for a crushing apparatus adjustment rod.

Background to the Invention

In materials handing industries, for example quarrying and recycling, it is often necessary to reduce the size of oversize particles, such a large rocks and stones. To achieve this, various types of crushing devices have been developed. One such crushing device is commonly known as a jaw crusher, an example of which is disclosed in US4165044A. In a jaw crusher rocks and the likes are fed into a V-shaped chamber defined by a stationary plate on one side and a moving plate on the other. Material entering the chamber is crushed between the moving plate and the stationary plate. As the moving plate cycles towards and away from the stationary plate the lower end of the chamber opens allowing the material to gradually fall further through the chamber for further crushing before finally exiting the bottom of the chamber on an open stroke. By adjusting the spacing of the moving plate from the stationary plate, which is effected by a toggle plate extending between the moving plate and a fixed position known as a toggle beam or toggle wedge on the crusher body or frame, the final size or grade of the crushed material can be adjusted. To retain the ends of the toggle plate within their seated position at the lower end of the moving plate and at the toggle beam respectively, adjustment rod and spring assemblies are provided whereby each adjustment rod, in the form of tension rod, has a hexagonal nut which cooperates with the spring to adjust the spring compression and thus the tension the adjustment rod. A similar adjustment rod, spring and locking nut arrangement is also employed with impact crushers for adjusting the spacing the spacing between an impact rotor and an impact apron.

The present invention provides an improved arrangement for adjusting the spring compression of a crusher apparatus

Summary of the Invention

In a first aspect of the invention there is provided a tensioning arrangement for a crusher adjustment rod, the arrangement comprising a coil spring in cooperation with a hollow bore hydraulic cylinder.

Optionally, the coil spring is a helical spring.

Optionally, the adjustment rod is a draw back or tension rod of a jaw crusher.

Optionally, the adjustment rod is the adjustment rod of an impact crusher.

Optionally, the tensioning arrangement is configured for maintaining a substantially constant spring compression or spring length.

Optionally, the hollow bore hydraulic cylinder comprises a body, a tubular ram and one or more hydraulic ports for fluid connection to a suitable hydraulic system configured to effect operation of said hydraulic cylinder.

Optionally, the spring and hollow bore hydraulic cylinder are arranged in a substantially concentric assembly.

Optionally, the hollow bore hydraulic cylinder body is located substantially within the bore of the spring.

Optionally, the body of the hollow bore hydraulic cylinder is maintained in axial alignment with the spring by means of a locating tube.

Optionally, the locating tube acts intermediate the spring and the hollow bore hydraulic cylinder.

Optionally, the spring and the hollow bore hydraulic cylinder are arranged to cooperate with an adjustment rod of a crusher, the adjustment rod being axially movable through the respective centre bores of said spring and hydraulic cylinder.

Optionally, the tensioning arrangement comprises a means to connect the hollow bore hydraulic cylinder to the adjustment rod.

Optionally, the means to connect the hollow bore hydraulic cylinder to the adjustment rod comprises a lock nut arrangement.

Optionally, the lock nut is in communication with a bracket arrangement.

Optionally, the lock nut and bracket arrangement provides a means for manual adjustment of the spring's compression.

Optionally, locating tube comprises a cylindrical body having an annular base plate at one end and an outwardlardly extending flange at an opposing end, the cylindrical body being adapted to slidably receive the body of the hollow bore hydraulic cylinder.

Optionally, the outer diameter of the locating tube cylindrical body is less than the inner diameter of the spring such that the body of location tube fits within the bore of the spring with a clearance.

Optionally, the outwardlardly extending flange of the locating tube is configured for seating upon an uppermost coil of the spring.

Optionally, the hollow bore hydraulic cylinder comprises a tubular ram comprising an annular end configured to abut the base plate of the locating tube.

Optionally, the annular end of tubular ram is positioned in substantially concentric alignment with the bore of the base plate which it surrounds when in abutting engagement with said base plate.

Optionally, the locating tube is operatively intermediate the hollow bore hydraulic cylinder and the spring.

Optionally, the hollow bore hydraulic cylinder and the locating tube provide an interface for connection of the adjustment rod to the spring.

Optionally, adjustment of spring compression can be effected by operation of the hollow bore hydraulic cylinder.

Optionally, adjustment of spring compression is configured for automatic adjustment by means of operation of the hollow bore hydraulic cylinder.

Optionally, adjustment of spring compression is configured for manual adjustment by means of the lock nut and bracket arrangement.

It will be understood that the tensioning arrangement in accordance with the invention is not limited to use with jaw or impact crushers, but is suitable for use with other crusher types.

In a second aspect of the invention, there is provided a crusher apparatus comprising a tensioning arrangement in accordance with the first aspect of the invention.

Optionally, the crusher apparatus is an impact crusher Optionally, the crusher apparatus is a jaw crusher.

Optionally, the tensioning arrangement provides a draw back system for the jaw crusher.

Optionally, jaw crusher comprises: a frame/body; a swinging jaw; a fixed jaw; an adjustment rod; a wedge beam; and a toggle plate; wherein the adjustment rod is a tension rod, and wherein the tensioning arrangement is affixed to the wedge beam, optionally via a bracket, and wherein the tension rod is pivotably connected to the rear of the swinging jaw and is arranged to extend axially through the respective centre bores of the spring and the bore of the hollow bore hydraulic cylinder.

In a further aspect of the invention there is provided a draw back system for a jaw crusher, the draw back system comprising a tensioning arrangement in accordance with the first aspect of the invention, and a hydraulic control system, wherein the hydraulic control system is configured to operate the hollow bore hydraulic cylinder of the tensioning arrangement to extend and/or contract to adjust the length of the spring of said draw back arrangement.

Optionally, adjustment of the length of the spring comprises maintaining a constant spring compression.

In a still further aspect of the invention there is provided a method of use of the tensioning arrangement in accordance with any of the preceding aspects of the invention, the method comprising the steps of connecting the hollow bore hydraulic cylinder of the tensioning arrangement to an hydraulic control system; and operating the hydraulic control system to operate the hollow bore hydraulic cylinder to extend and/or contract to adjust the length of the spring of the tensioning arrangement.

Optionally, operation of the hydraulic control system to operate the hollow bore hydraulic cylinder to adjust the length of the spring of the draw back arrangement is active so that the spring is maintained at a desired length.

The various aspects of the present invention can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one aspect can typically be combined alone or together with other features in different aspects of the invention. Any subject matter described in this specification can be combined with any other subject matter in the specification.

Various aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary aspects and implementations. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the scope of the present invention. Accordingly, each example herein should be understood to have broad application, and is meant to illustrate one possible way of carrying out the invention, without intending to suggest that the scope of this disclosure, including the claims, is limited to that example. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. In particular, unless otherwise stated, dimensions and numerical values included herein are presented as examples illustrating one possible aspect of the claimed subject matter, without limiting the disclosure to the particular dimensions or values recited. All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa.

Language such as "including", "comprising", "having", "containing", or "involving" and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Thus, throughout the specification and claims unless the context requires otherwise, the word "comprise" or variations thereof such as "comprises" or "comprising" will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, the words "typically" or "optionally" are to be understood as being intended to indicate optional or non-essential features of the invention which are present in certain examples but which can be omitted in others without departing from the scope of the invention.

Brief Description of the Drawings

The present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which: Figure 1 is an exemplary schematic showing an exemplary jaw crusher apparatus incorporating a tensioning arrangement in accordance with the invention; Figure 2 is a plan view of the apparatus of Figure 1; Figure 3 is a cross section view of the apparatus of Figure 2; Figures 4a and 4b are cross section views of the jaw crusher apparatus showing the tensioning arrangement in exemplary first and second positions, respectively; Figure 5 is a detailed cross section view of the tension rod assembly; Figure 6 is a perspective view of Figure 5; Figure 7a is an exemplary schematic showing an impact crusher; and Figure 7b is an exemplary schematic showing an impact crusher incorporating a tensioning arrangement in accordance with the invention.

B

Detailed Description

With reference to Figures 1 and 2 there is shown an exemplary jaw crusher apparatus comprising a main frame 1 having side walls 2 secured thereto in parallel spaced relation to provide a housing for a stationary jaw die 3 and a movable jaw die 4. The stationary jaw die 3 is rigidly secured to the main frame in a suitable manner for example by means of bolts 5. The movable jaw die 4 is secured to a swinging jaw frame 6 that is suspended at its upper end from an eccentric shaft 7. The eccentric shaft 7 is driven by flywheels 8 and a suitable drive motor (not shown).

Adjacent its lower end, the swinging jaw frame 6 is rockably fulcrumed upon a toggle plate 9 that extends between the rear of the swinging jaw frame 6 and a toggle or wedge beam 10 disposed towards the rear of the main frame 1 to which the wedge beam is affixed Adjustment of the position of wedge beam 10, for example by means of adjustment cylinder 11 (Figures 3, 4a and 4b), controls the crusher's jaw gap, i.e. the spacing between the stationary and swinging jaws.

With reference to Figure 3, the opposing sides of the toggle plate 9 are mounted upon toggle seats 91 and 92 provided at the lower end of the swinging jaw frame 6 and at the forward end of the wedge beam 10, respectively. The toggle plate 9 is retained between the swinging jaw frame 6 and the wedge beam 10 by means of a tensioning arrangement 20 in accordance with a first aspect of the invention.

It should be understood that one or more tensioning arrangements 20 in accordance with the invention may be provided on a crushing apparatus, however in the following description a single tensioning arrangement is described in isolation.

By means of tensioning arrangement 20, toggle plate 9 is compressed between the swinging jaw frame 6 and the main body of the apparatus. This arrangement ensures that any point on the swinging jaw frame 6 moves in an elliptical orbit. Through this movement of the swinging jaw frame, both pressure and friction forces are applied to the material passing between stationary jaw die 3 and movable jaw die 4. This motion is also useful as it assists in pushing the material through the crushing chamber defined by stationary jaw die 3 and movable jaw die 4.

As shown in Figures 3 to 6, in examples, a tensioning arrangement 20 comprises a spring 22 arranged to cooperate with a hollow bore hydraulic cylinder 23. The spring 22 and hollow bore hydraulic cylinder are arranged in turn to cooperate with an adjustment rod 21. Adjustment rod 21 is optionally a tension rod.

In this manner the tensioning arrangement operates to provide a draw back system for the jaw crusher.

Optionally, spring 22 is a compression spring. In the art, tension rods are commonly referred to as pull back or draw back rods.

Hollow bore hydraulic cylinder 23 comprises a body 231, a tubular ram 232 and one or more hydraulic ports 233 configured for fluid connection to a suitable hydraulic system configured to effect operation of said hydraulic cylinder.

Hollow bore hydraulic cylinder 23 is configured so that hydraulic pressure tends to extend the ram to counter the tendency of the spring 22 to push the ram to a retracted position. Hollow bore hydraulic cylinder 23 may be a single acting cylinder or optionally a double acting cylinder configured to operate as a single acting cylinder. Hollow bore hydraulic cylinders are alternatively referred to as hollow rod hydraulic cylinders or centre hole hydraulic cylinders.

Adjustment rod 21 is pivotally secured at one end to a pivot point 61 provided at the rear of the swinging jaw frame 6. The free end of the adjustment rod extends axially through the bore of spring 22 and through the centre of hollow bore hydraulic cylinder 23, the body 231 of which extends substantially into the open bore of spring 22 as described below. Adjustment rod is free to reciprocate through the bores of spring 22 and hydraulic cylinder 23. Adjustment rod 21 is secured to the body 231 of hollow bore hydraulic cylinder 23 by means of a lock nut arrangement 25 proximate the location where said rod exits the hydraulic cylinder.

As shown in detail in Figures 4a to 6, at its base 221, spring 22 is mountable to a bracket 24 which connects to wedge beam 10. The base of spring 221 may be mounted to bracket 24 via a spring seat or cup 222. Brackets 24 and spring seats 222 of this type are commonly found on jaw crushers having conventional spring and tension rod draw back systems and so the draw back apparatus and system of the present invention is particularly adapted for retrofitting to such jaw crushers in place of conventional spring and tension rod draw back systems.

Detail of the location of the hollow bore hydraulic cylinder 23 within the bore of spring 22 is shown in Figures 4a to 6.

With specific reference to Figures 5 and 6, the body 231 of the hollow bore hydraulic cylinder 23 is maintained in axial alignment within the spring 22 by means of a locating tube 26.

Locating tube 26 comprises a cylindrical body 261 having an annular base plate 262 at one end and an outwardlardly extending flange 263 at its opposing end. The outer diameter of locating tube 26 is slightly less than the inner diameter of spring 22 such that the body 261 and base plate 262 of location tube 26 fits within the bore of the spring with a small clearance. When fitted within the bore of spring 22, the outwardlardly extending flange 262 of the locating tube 26 seats or rests upon the uppermost coil of the spring 22.

The inner diameter of cylindrical body 261 is slightly greater than the outer diameter of the hollow bore hydraulic cylinder body 231 such that the cylindrical body 261 being adapted to slidably receive the hollow bore hydraulic cylinder.

As shown in Figures 4a to 6, the annular end of tubular ram 232 is configured to abut base plate 262 of locating tube 26. When in abutting engagement with base plate 262, the annular end of tubular ram 232 is positioned in substantially concentric alignment with the bore of the base plate which it surrounds.

Together with the hollow bore hydraulic cylinder 23, the locating tube 26 provides the interface which connects adjustment rod 21 to spring 22. Locating tube 26 also prevents spring 22 buckling Adjustment of spring 22 compression may be effected by lock nut arrangement 25 and/or by operation of hollow bore hydraulic cylinder 23. In this manner spring compression can be adjusted manually, or automatically via an associated hydraulic control system, for example the hydraulic system of a crusher apparatus.

Operation of the hydraulic cylinder 23 forces ram 232 in the direction of base plate 262, with the resulting reactive force causing hydraulic cylinder body 261 to move in the opposite direction thereby allowing adjustment rod 21 to extend further through spring 22 as shown in Figure 4b. Conversely, reduction of the hydraulic pressure in the hydraulic cylinder 23 allows the force of spring 22 to cause the ram 232 to retract into the body of the hydraulic cylinder as shown in Figure 4a. In Figure 3, the ram 232 is shown extended to an intermediate position. Through constant modulation of the hydraulic cylinder's extension 23 in response the motion of the adjustment rod 21 and/or the force of spring 22, the length of spring 22 can be maintained at a set or desired length, Lspring, as shown in Figure 4a.

Through control of the operation of hollow bored hydraulic cylinder 23, constant varying pressure applied to the tensioning (i.e. draw back) system 20 maintains the spring at a set or constant length as the adjustment rod 21 reciprocates as shown in Figures 4a and 4b, which in turn maintains a compressive force between the swinging jaw 6 and wedge beam via the toggle plate 9. This can be achieved for example by means of a high and low limit control system of the hydraulic system, whereby hydraulic pressure in the cylinder 23 can be continually adjusted to control the extension and contraction of the ram 232 relative the cylinder body 231 in response to the motion of the adjustment rod 21.

As the spring 22 and tension rod 21 assembly is carried entirely by the wedge beam 10 and swinging jaw frame 6, this assembly moves with said wedge beam and swinging jaw frame 6 as adjustments are effected.

With reference to the drawings, operation of a crushing apparatus comprising the tensioning arrangement 20 of the invention is briefly described as follows. To enhance the clarity of the drawings, hydraulic connection of the hydraulic cylinder 23 to a hydraulic control system is shown referenced in Figure 6 only.

As flywheels 8 (Figures 1 to 3) are driven, for example but not limited to, at approximately 300 rpm, pivot point 61 at the ear of the swinging jaw frame 61 moves through an elliptical, i.e. non-linear / non circular, motion relative to its speed of rotation and in geometrical relation to the toggle plate 9 connections. By means of tensioning arrangement 20, tension is applied to pull the swinging jaw 61 rearwards thereby holding the toggle plate 9 in a state of compression between the swinging jaw 61 and wedge beam 10.

As pivot point 61 of swinging jaw 6 moves in its elliptical path, exemplary adjustment rod 21 reciprocates within the confines of spring 22 as shown by way of example in Figures 4a and 4b, in which Figure 4a shows the rod 21 at an exemplary minimum throw and Figure 4b shows rod 21 at an exemplary maximum throw. In Figure 3, rod 21 is shown at an intermediate throw.

It should be noted that the dimensions shown in Figures 4a and 4b are by way of example only, and are not to be construed as limiting, but rather are for illustrative purposes and for aid of understanding.

As rod 21 reciprocates, spring 22 has a tendency to extend and compress.

Advantageously however, application of actively varying hydraulic pressure enables the ram 232 of hydraulic cylinder 23 to actively extend and contract so that spring 22 is maintained to at a set or desired length, Lspring.

Advantageously, the tensioning arrangement of the present invention can be adjusted to enable use with any jaw crushing chamber.

Advantageously, the tensioning arrangement of the present invention is adapted for direct replacement of conventional spring and tension rod draw back systems on existing jaw crushers.

As noted above, adjustment of the position of wedge beam 10, for example by means of adjustment cylinder 11, controls the jaw gap, i.e. the spacing between the stationary and swinging jaws. When the wedge beam position is adjusted in this way, in order to maintain the togged plate in correct compression the spring length must be adjusted in turn to compensate. In a conventional apparatus, this is done manually by tightening or loosening the locking nut arrangement on the tension rod.

Advantageously however, the tensioning arrangement of the present invention enables automatic hydraulic adjustment of the spring length and so the present invention provides easier operator control with improved health and safety as the need for an operator to manually adjust the spring length is obviated. This means that crushing machinery can be operated remotely, without the requirement for on-site personnel. As a locking nut arrangement is retained, the draw back arrangement can also be adjusted manually if required.

In the foregoing, exemplary use of the tensioning arrangement of the invention with a jaw crusher has been described however it should understood that a tensioning arrangement in accordance with the present invention is not limited to use with jaw crushers, but is suitable for use with other crusher types, for example, but not limited to, impact crushers, as shown by way of example in Figure 7.

In Figure 7a there is shown a schematic diagram of the main components of an exemplary impact crusher 70 of a type well known in the art comprising an inlet opening 71, and outlet opening 72, an impact rotor 73 and a plurality of impact aprons or curtains 74. Each impact apron or curtain 74 is pivoted at one end and is connected to an adjustment arrangement 75.

To break down material introduced to the impact crusher 70, it is hit by hammers 731 provided on rotating impact rotor 73 and is thrown against impact aprons 74.

Adjustment of the spacing of an end of each impact apron from the impact rotor 72 is controlled by adjustment arrangement 75, which comprises an adjustment rod 76 pivotally extending from the rear of the impact apron 74 and axially through the bore of a spring 22. Springs 22 are located externally of the crushing chamber. Springs 22 are pre-tensioned by between compression plates 77, 78. The degree of pre-tensioning is adjusted by tightening or loosening a lock nut arrangement 25 provided on adjustment rod 76. Adjustment of the spring tension is made to adjust the degree of smoothening of the forces exerted during normal crusher operation.

With reference to Figure 7b, there is shown a schematic diagram of an impact crusher comprising a tensioning arrangement in accordance with the present invention, the tensioning arrangement comprising a spring 22, a hollow bore hydraulic cylinder 23, lock nut arrangement 25, locating tube 26, and a spring seat 222 substantially as described above in relation to the those of the tensioning arrangement of Figures 1 to 6, wherein the spring 22 and hollow bore hydraulic cylinder 23 etc. are arranged to cooperate with adjustment rod 76. In this manner spring 22 tension, and thus the spacing of an end of an impact apron 74 from the impact rotor 72 can be adjusted manually, or automatically via an associated hydraulic control system, for example the hydraulic system of the crusher apparatus.

Advantageously, use of the present invention enables automatic hydraulic adjustment of the spring tension of an impact crusher and so provides easier operator control with improved health and safety as the need for an operator to manually adjust the spring tension is obviated. This means that such crushing machinery can be operated remotely, without the requirement for on-site personnel. As a locking nut arrangement is retained, spring tension can also be adjusted manually if required.

Advantageously, the adjustment arrangement of the present invention is adapted for direct replacement of conventional spring tension adjustment arrangements on existing impact crushers.

It will be appreciated that features of the various embodiments described above may be combined, where appropriate, with the other embodiments and/or aspects of the invention to form novel and inventive aspects in their own right.

Whilst specific examples of the present invention have been described above, it will be appreciated that modifications are possible within the scope of the present invention as defined in the appended claims.

Claims

Claims 1. A tensioning arrangement for a crusher adjustment rod, the arrangement comprising a coil spring in cooperation with a hollow bore hydraulic cylinder.
2. A tensioning arrangement as claimed in claim 1, wherein the coil spring is a helical spring.
3. A tensioning arrangement as claimed in claim 1 or claim 2, wherein the adjustment rod is a draw back or tension rod of a jaw crusher.
4. A tensioning arrangement as claimed in claim 1, or claim 2, wherein the adjustment rod is the adjustment rod of an impact crusher.
5. A tensioning arrangement as claimed in any preceding claim, wherein the tensioning arrangement is configured for maintaining a substantially constant spring compression or spring length.
6. A tensioning arrangement as claimed in any preceding claim, wherein the hollow bore hydraulic cylinder comprises a body, a tubular ram and one or more hydraulic ports for fluid connection to a suitable hydraulic system.
7. A tensioning arrangement as claimed in any preceding claim, wherein the hollow bore hydraulic cylinder body is located substantially within the bore of the spring.
8. A tensioning arrangement as claimed in any preceding claim, wherein the spring and hollow bore hydraulic cylinder are arranged in a substantially concentric assembly.
9. A tensioning arrangement as claimed in any preceding claim, wherein the body of the hollow bore hydraulic cylinder is maintained in axial alignment with the spring by means of a locating tube.
10. A tensioning arrangement as claimed in claim 9, wherein the locating tube comprises a cylindrical body having an annular base plate at one end and an outwardlardly extending flange at an opposing end, the cylindrical body being adapted to slidably receive the body of the hollow bore hydraulic cylinder, and the outwardlardly extending flange being configured for seating upon an uppermost coil of the spring.
11. A tensioning arrangement as claimed in any preceding claim, wherein the spring and the hollow bore hydraulic cylinder are arranged to cooperate with an adjustment rod of a crusher, the adjustment rod being axially movable through the respective centre bores of said spring and hydraulic cylinder.
12. A tensioning arrangement as claimed in any preceding claim, further comprising a means to connect the hollow bore hydraulic cylinder to the adjustment rod, optionally wherein the means comprises a lock nut and bracket arrangement.
13. A tensioning arrangement as claimed in any one of claims 10 to 12, wherein the hollow bore hydraulic cylinder comprises a tubular ram comprising an annular end configured to abut the base plate of the locating tube.
14. A tensioning arrangement as claimed in any one of claims 10 to 13, wherein the locating tube is operatively intermediate the hollow bore hydraulic cylinder and the spring.
15. A tensioning arrangement as claimed in any preceding claim, wherein operation of the hollow bore hydraulic cylinder effects adjustment of the spring's compression, optionally wherein adjustment of spring compression is configured for automatic adjustment by means of operation of said hollow bore hydraulic cylinder.
16. A crusher apparatus comprising a tensioning arrangement as claimed in any one of claims 1 to 15.
17. A crusher apparatus as claimed in claim 16, wherein the crusher apparatus is a jaw crusher.
18. A crusher apparatus as claimed in claim 16, wherein the crusher apparatus is an impact crusher.
19. A crusher apparatus as claimed in claim 17, wherein the tensioning arrangement is configured as a draw back system for the jaw crusher.
20. A crusher apparatus as claimed in claim 19, wherein the jaw crusher comprises: a frame/body; a swinging jaw; a fixed jaw; an adjustment rod; a wedge beam; and a toggle plate; wherein the adjustment rod is a tension rod, and wherein the tensioning arrangement is affixed to the wedge beam, optionally via a bracket, and wherein the tension rod is pivotably connected to the rear of the swinging jaw and is arranged to extend axially through the respective centre bores of the spring and the bore of the hollow bore hydraulic cylinder.
21. A draw back system for a jaw crusher, the draw back system comprising a tensioning arrangement as claimed in any one of claims 1 to 15, and a hydraulic control system, wherein the hydraulic control system is configured to operate the hollow bore hydraulic cylinder of the tensioning arrangement to extend and/or contract to adjust the length of the spring of said draw back arrangement.
22. A draw back system as claimed in claim 21, wherein adjustment of the length of the spring comprises maintaining a constant spring compression.
23. A method of use of a tensioning arrangement as claimed in any one of claims 1 to 15, comprising the steps of: connecting the hollow bore hydraulic cylinder of the tensioning arrangement to an hydraulic control system; and operating the hydraulic control system to operate the hollow bore hydraulic cylinder to extend and/or contract to adjust the length of the spring of the tensioning arrangement.
24. A method of use of a tensioning arrangement as claimed in claim 23, wherein operation of the hydraulic control system to operate the hollow bore hydraulic cylinder to adjust the length of the spring of the draw back arrangement is active so that the spring is maintained at a desired length.