EP0589901A1

EP0589901A1 - Apparatus for producing tubular unsintered ceramic compacts

Info

Publication number: EP0589901A1
Application number: EP92909586A
Authority: EP
Inventors: Glyn Atherton; John Martin Sutton
Original assignee: Chloride Silent Power Ltd
Current assignee: Chloride Silent Power Ltd
Priority date: 1991-06-12
Filing date: 1992-05-20
Publication date: 1994-04-06
Also published as: IE921887A1; GB9112659D0; EP0518505A1; JPH06507851A; WO1992022407A1

Abstract

Appareil de fabrication de comprimés en céramique non frittés et de forme tubulaire comprenant un mandrin cylindrique ainsi qu'un moyen destiné à façonner le comprimé sur le mandrin. On décrit également un poste de retrait (40) ainsi qu'un moyen de maintien destiné à maintenir le mandrin dans le poste de retrait (40) afin de retirer ledit comprimé (56) du mandrin (19). Le poste de retrait comporte un organe annulaire (60) aligné axialement avec le mandrin (19) lorsqu'il se trouve dans le moyen de maintien ainsi qu'un manchon élastique (66) monté à l'intérieur de l'organe annulaire (60) pour définir une chambre annulaire. Un moyen d'actionnement est agencé pour conférer le mouvement axial à l'élément annulaire (60) ainsi qu'au mandrin (19) l'un par rapport à l'autre entre une position de contact, le mandrin (19) s'étendant dans l'élément annulaire, et une position sans contact, l'élément annulaire (60) étant séparé du mandrin (19). Des moyens de mise sous pression sont prévus pour appliquer sélectivement une pression différentielle entre l'intérieur et l'extérieur de la chambre annulaire (60) de manière à déformer le manchon (66) entre un état serré, dans lequel le manchon peut serrer un comprimé (56) positionné sur le mandrin (19) lorsqu'il se trouve dans ladite position de contact, et un état non serré. Des moyens de commande sont prévus pour commander le fonctionnement du poste de retrait (40). Le moyen d'actionnement permet de déplacer l'élément annulaire (60) ainsi que le mandrin (19) en position de contact, tandis que le moyen de mise sous pression maintient le manchon (66) dans l'état non serré. Le moyen de mise sous pression serre alors le comprimé (56) sur le mandrin (19) et le moyen d'actionnement permet de retirer le comprimé (56) du mandrin (19).Apparatus for manufacturing unsintered, tubular shaped ceramic compacts comprising a cylindrical mandrel and means for forming the compact on the mandrel. Also disclosed is a removal station (40) and holding means for holding the mandrel in the removal station (40) to remove said tablet (56) from the mandrel (19). The removal station includes an annular member (60) axially aligned with the mandrel (19) when in the holding means and an elastic sleeve (66) mounted within the annular member (60 ) to define an annular chamber. An actuating means is arranged to impart axial movement to the annular element (60) as well as to the mandrel (19) with respect to each other between a position of contact, the mandrel (19) extending into the ring member, and a non-contact position, the ring member (60) being separated from the mandrel (19). Pressurizing means are provided for selectively applying a differential pressure between the interior and exterior of the annular chamber (60) so as to deform the sleeve (66) between a clamped state, in which the sleeve can clamp a tablet (56) positioned on the mandrel (19) when in said contact position, and an unclamped condition. Control means are provided for controlling the operation of the withdrawal station (40). The actuating means allows the annular element (60) and the mandrel (19) to be moved into the contact position, while the pressurizing means maintains the sleeve (66) in the untightened state. The pressurizing means then squeezes the tablet (56) onto the chuck (19) and the actuating means removes the tablet (56) from the chuck (19).

Description

"DIAMOND FRAME FOR SAWING BLOCKS OF GRANITE OR OTHER STONE MATERIAL".

* * * *

DESCRIPTION The present invention relates to a diamond frame for sawing blocks of granite or other stone material.

More particularly the present invention relates to a subvertical high speed diamond frame with preformed packs of blades, open bilaterally for simultaneous sawing but with independent feed of blocks of material.

Among the stone materials used by man, granite, in spite of its ready availability in the natural state, is the least used.

Its beauty, resistance to wear and degradation caused by atmospheric and chemical agents, do not suffice to compensate the considerable differences between its processing costs and those of marble.

This difference is further increased by the excellent results in sawing marble which have been achieved using conventional diamond frames for the past 25 years. The hardness of granite emphasises the main defects of current diamond frames, that is to say:

1) bidirectional movement of the blade, which prevents the formation of a shoulder to support the diamond granule which consequently falls rapidly from its alveolus. 2) The blade abrades the material according to the pressure exerted on the material and its speed, which varies sinusoidally.

The blade does not saw at the top and bottom dead centers since it is momentarily at a standstill and, being unable to follow the constant rhythm of the blade-holder square, starts to assume a negative camber.

If, after the movement which follows the halts at the dead centers, this countercamber is not eliminated, or worse still increases, deviations and breakages occur. 3) A blade which never detaches from the material only performs an abrasive action and, in the event of deviations, being in contact along its whole length, manages to straighten with difficulty.

In the European patent no. 0002265, in the name of the same Applicant, a diamond blade frame is described, wherein the blades describe, parallel to each other, an ellipsoid, and the teeth, during their contact with the material, describe an arc of a circle whose length equals the pitch.

In agreement with the abovementioned European patent, the following has been obtained: monodirectional motion; constant speed during contact with the material; detaching from the material at each turn and, in addition to the abrasive action of the teeth, a chiselling action. These blades are however a condition only necessary for sawing granite and nevertheless are not sufficient since, whereas even with types of marble and stone which differ from each other it is possible to adopt identical blades, that is to say with identical binder, concentration, grain size and type of diamond, for the approximately 100 granites processed the situation changes.

The various types of granite have very different hardnesses and can only be sawn with diamond blades of different and adequate features, particularly in order to obtain small thickness slabs from them. With the diamond frames currently known, in which the pack of blades is mounted inside the square, it is not possible to saw economically the approximately one hundred types of granite processed, since the operations to change the pack of blades are long and complex and it would require a store of blades at least equal to the number of the classes, three or five, in which the granites are grouped on the basis of the index of sawabi lity.

The advantages of quality, higher hourly production rate, less scrap and elimination of the abrasive mixture from the sediment, which can be obtained with diamond saws, could not compensate the increased costs of sawing compared to the more traditional grit saws, and the consequent increases in cost between soft and hard granites. The object of the present invention is a diamond frame suitable for sawing blocks of granite, as also other stone material, which functions efficiently and at acceptable costs.

A further object of the invention is a diamond frame which enables the pack of blades to be changed simply and rapidly, in order to adapt them to the features of the material to be processed, thus lowering times and costs of sawing.

In accordance with these objects, the frame according to the invention comprises a mobile blade-holder square, operatively connected to motor means and to motion transmission means via suitable mechanisms capable of driving the same blade-holder square to move with a certain pattern along predetermined paths, and is characterised in that the abovementioned blade-holder square is fitted with bracket means, cantilever mounted in order to support at least one blade in a removable manner. According to a preferred embodiment, the abovementioned bracket means are composed of at least one pair of brackets, a lower and an upper one, cantilever mounted, and at least one bracket is cantilever mounted by means of disengageable constraining means at an adjustable height. Moreover the abovementioned pair of brackets is able to support the abovementioned blades, pre-assembled in a pack, with suitable spacers placed between. Advantageously the abovementioned brackets are cantilever mounted on one or both of the external sides of the blade-holder square and at least the abovementioned upper bracket is fitted with hydraulic tighteners capable of supporting the abovementioned blades pre-assembled in a pack, in order to adjust their traction. The abovementioned brackets are preferably composed of rods and the abovementioned constraining means are formed by tie rods connected to the abovementioned brackets by means of f rst disengageable pins and to the square by means of second pins. The abovementioned constraining means are preferably also formed by third pins suitable for connecting in a disengageable manner at least the abovementioned upper bracket to the abovementioned blade-holder square, the abovementioned second pins also being disengageable.

In a frame structured in this way the pre-assembled pack of blades is changed by simple and rapid operations which enable the times for processing the blocks and hence the costs of products processed in slabs to be reduced considerably.

The characteristic features and advantages of the invention are to be illustrated henceforth with reference to the accompanying figures 1-6, in which a preferred embodiment of the same invention is represented, by way of a non-limiting example, and without observing any real scale due to drawing requi rements.

Fig. 1 is a front schematic view of a frame suitable for sawing granite or other stone material, accomplished according to the invention.

Fig. 2 is a side view, partially sectioned along the trace plane II-II of Fig. 1;

Fig. 3 is a side view on an enlarged scale and partially sectioned along the trace plane III-III of Fig. 1; Fig. 4 is a partial section view along the trace plane IV-IV of Fig. 3;

Fig. 5 is a front schematic view of a system comprising the frame of Fig. 1;

Fig. 6 is a view from above of the system in Fig. 5. In Fig. 1 10 denotes in its entirety a diamond frame suitable for sawing blocks of stone material, particularly blocks of granite, and obtain therefrom slabs of a certain thickness.

The frame 10 comprises a blade holder square, denoted in its entirety by 11, formed by two uprights 12, by two cross members 13, by two lower brackets 14 and by two upper brackets, denoted in their entirety by 15, suitable for supporting in a removable manner two pre-assembled packs of blades, denoted in their entirety by 16. As shown in Fig. 3, the blades, denoted by 26, are provided with teeth 30 formed by diamond concretion and diamond granules embedded therein.

The blade-holder square 11, which in the figures is represented vertically, can be tilted at a certain angle with respect to the vertical line. The lower brackets 14 are formed by rods constrained to the sides 12a of the uprights 12 by means of the disengageable pins 18 and by means of the tie rods 19, which in turn are constrained to the sides of the same uprights by means of the pins 20, and to the abovementioned brackets 14 by means of the disengageable pins 21.

The upper brackets 15 are constrained to the sides 12a of the uprights 12 by means of respective disengageable pins 22 and by means of respective tie rods 23, which in turn are constrained to the sides of the same uprights by means of disengageable pins 24, and to the abovementioned brackets 15 by means of the pins 25, likewise disengageable.

Each pack 16 is formed by a set of blades 26 and by spacers 27, placed between the same blades, as shown in Figs. 3 and 4. The blades and spacers are held tight by the tie rods 28, which are inserted in the holes 29 of the same spacers and are locked by nuts, screwed at their threaded ends.

The spacers 27 are provided with sinusoidally-shaped edges 31, capable of improving contact with the blades and resistance to bending loads. The blades 26 are provided with two slots 33, a lower one and an upper one, which can be seen in Figs. 3 and 4, and likewise the spacers 27 are provided with slots 34, lower and upper, wherein the brackets 14 and 15 are inserted, once they have been released from the tie rods 19 and 23. The brackets 15 are formed by hollow rods 36 fitted with hydraulic tighteners, denoted in their entirety by 37, each of which comprises a piston 38 running, sealed, in a cylinder 39 fixed to the respective rod 36. The pistons 38 can be driven by pressurized oil fed to the same cylinders 39 through fittings 40 by the manifold 41, which can be operatively connected to a source of pressurized oil and to a drain for the same oil, by valve means which can be actuated manually and are not shown since they are known.

The hydraulic tighteners 37 are equal in number to the blades 26 of each pack 16 and are arranged in a row, aligned along a generatrix of the rod 36, at a distance which depends upon the distance between the centres of the same blades of a pack.

When the brackets 14 and 15 are unhooked from the respective tie rods 19 and 23, the packs 16 of blades 26 are fitted onto the same brackets. Subsequently the brackets are once again hooked to the tie rods by means of the pins 21 and 25 and the traction of the individual blades 26 is regulated by means of the hydraulic tighteners 37. The upper brackets 15, together with the respective tie rods

23, can be displaced along the sides 12a of the uprights 12, as shown by dotted lines in Fig. 1, in order to adjust their distance from the Lower brackets 14 as a function of the height of the blades 26; for this purpose the sides of the uprights are fitted with three pairs of flanges provided with holes 42, 43, 44, to two of which, as required, the bracket 15 and the relative tie rod 23 are constrained by means of the pins 22 and

24, so as to be able to arrange the same bracket 15 at a distance from the bracket 14 at the level required for supporting blades having three different working heights, for example 170 cm, 62 cm and 36 cm.

Integral with the uprights 12 of the blade-holder square 11 are four pins, two lower 50 and two upper 51, which connect it to drive mechanisms denoted as a whole by 52 and 53, the type of those which form the object of the European patent no. 0002265 in the name of the same Applicant.

As shown by Figs. 1 and 2, the mechanisms 52 and 53 comprise the connecting rods 54 and 55 to which the abovementioned pins 50 and 51 are rotarily connected, at a predetermined distance from the feet of the same connecting rods. The heads of the connecting rods 54 and 55 are in turn rotarily connected to the crank pins 56 and 57 of flywheels denoted in their entirety by 58 and 59, which are supported for rotation in the frames 60 of a support structure, denoted in its entirety by 49, formed by uprights 45 and 46 and by cross members 47 and 48, suitably accomplished and positioned so as to allow the assembly and movement of the blade-holder square 11. The feet of the same connecting rods 54 and 55 are rotarily connected to the pins 62 and 63 fixed to respective levers 64 and 65, whose ends are in turn rotarily connected to the pins 66 and 67. The pins 66 and 67 are fixed to pairs of rocker arms 68 and 69, in turn hinged in 70 and 71 to the uprights 46 of the support structure 49. The Levers 64 and 65 and the pairs of rocker arms 68 and 69 guide the feet of the connecting rods 54 and 55 to move along predetermined rectilinear and vertical paths.

In the particular case, as shown in Fig. 1, the flywheels 58 and 59 are formed by two half-fLywheels 58a, 58b, and 59a, 59b, and the crank pins 56 and 57 are fixed to the inner walls of the same half-flywheels by an arm preset with respect to the axes of rotation 72 and 73. To the outer walls of the same half-flywheels, by the same arm, are attached the crank pins 74a, 74b and 75a, 75b, to which the heads of the pairs of balancing counterconnecting rods 76a, 76b and 77a, 77b are rotarily connected. The counterconnecting rods, which serve to eliminate the tilting couple, are provided with counterweights 78a, 78b and 79a, 79b, equal to an eighth of the weight of the blade-holder square 11, distanced from the foot of the same counterconnecting rods to the same extent as the pins 50 and 51 from the foot of the respective connecting rods 54 and 55. The feet of the counterconnecting rods are also rotarily connected to the pins 80a, 80b and 81a, 81b, attached to respective levers 82a, 82b and 83a, 83b. The ends of the levers are in turn rotarily connected to the pins 84a, 84b and 85a, 85b attached to pairs of rocker arms 86a, 86b and 87a, 87b, in turn hinged in 88a, 88b and 89a, 89b to the uprights 46 of the support structure 49.

The flywheels 58 and 59 are operatively connected to an electric motor 90 through transmission members denoted in their entirety by 91 and 92. In the specific case the crank pins 74b and 75b are attached eccentrically to auxiliary flywheels 93 and 94, rotarily supported in the uprights 45 by the shafts 95 and 96 coaxial with the flywheels 58 and 59. Cogged pulleys 97 and 98 are integral with the shafts 95 and 96 and driven in rotation, by means of the cogged belts 99 and 100, by the transmission cogged pulleys 101 and 102, integral with the shafts 103 and 104, rotarily supported in the uprights 45 of the structure 49. 105 and 106 denote belt-tightening pulleys, which can be seen in Fig. 2, which enable the tightness of the belts 99 and 100 and the timing between the pulleys 97, 101 and 98, 102, to be regulated according to the invention of the

Italian patent application no. 20565 A/86 in the name of the same Applicant.

Integral with the shafts 103 and 104 are respective cogged pulleys 107, 108, which are driven in rotation by means of the cogged belt 109, by the cogged pulley 110 integral with the driving shaft 111, driven by the electric motor 90.

The electric motor 90 could be replaced by two electric motors which can be energised separately or jointly, to adapt the available power to the work load of the frame 10. As shown in Figs. 5 and 6, arranged on the sides of the frame 10 are the conveyor belts 112, whose function is to push the blocks 113 of stone material to be sawn against the packs 16 of blades 26, and the conveyor belts 114, whose function is to move away from the same packs of blades the slabs 115 of sawn stone material. Two conveyor trolleys 116 and 117, running on tracks 118 and 119, load the blocks to be sawn onto the conveyor belts 112. For this purpose the conveyor trolleys are provided with mobile cross members 120 and 121, capable of raising the block to be sawn and moving it sideways in order to deposit it on the same conveyor belts 112, inserting its own cross members between those of the conveyor belts.

When the electric motor 90 is functioning, the mechanisms 52 and 53 drive the blade-holder square 11, and hence the blades 26 of the packs 16, to perform repeated movements along an elliptical path in which the ratio between the greater axis and the smaller axis depends on the ratio between the stroke of the foot of the connecting rods 54, 55 and the distance of the pins 50, 51 from the same foot of the connecting rods. By performing these movements the two packs 16 of blades 26 are able to saw the blocks 113 of stone material carried by the conveyor belts 112.

A frame of this type is particularly suitable for sawing material of the hardness of granite, due to the fact that the blades, by performing repeated movements along elliptical paths, carry out the sawing with monodirectional movements and with a combined abrasion and chiselling action.

Thus the problems are avoided which, due to the hardness of granite, are found with usual diamond frames, in which the blades move reciprocally along rectilinear paths. In these frames in fact, due to the bidirectional movements of the blades during sawing, the diamond granules of the covering of the blade are subjected to reciprocal stresses which cause the granule to fall from the alveolus, with consequent rapid wear of the blades. The blades abrade the material according to their pressure and their speed, which varies sinusoidal ly. At the top and bottom dead centers the blades are momentarily at a standstill and do not saw, hence while the blade-holder square begins the return stroke, they cannot follow it and begin to assume a negative camber, which causes deviations or breakages if it is not eliminated or even increases in the return stroke. A blade which never detaches from the material and is in contact with the latter for most of its length is only able to straighten with difficulty.

The frame described above represents an optimum solution for sawing granite since it enables the blades to be changed in order to adapt them to the hardness of the material to be sawn in a simple and rapid manner, reaching the blade-holder square 11 from its sides, to replace the pre-assembled packs 16 of blades 26. Generally the approximately one hundred granites processed are divided into five classes on the basis of the index of sawability, which is a function of their hardness. Therefore, in order to saw different types of granite with the frame described, it is sufficient to have packs 16 composed of five different types of blades 26, to each of which correspond diamond teeth of certain characteristics.

In order to change the blades 26 in the square 11, the hydraulic tighteners 37 are released in order to eliminate the traction of the blades, and the pins 21 and 25 are disengaged in order to unhook the tie rods 19 and 23 from the brackets 14 and 15. Then at each bracket 15 a trolley is positioned, provided with an auxiliary bracket which supports the pack 16 of blades 26 to be changed. After having adjusted the position of the brackets 15 along the sides 12a of the uprights 12 in relation to the height of the new blades to be used, the trolley which transports the pack 16 pre-assembled with the new blades 26 is moved towards the square 11. The brackets 14 and 15 are inserted in the slots 33 and 34 of the blades 26 and spacers 27 which form the pack 16, the tie rods 19 and 23 are re-hooked to the brackets, engaging the pins 21 and 25 with the same tie rods and brackets, and the blades 26 of the new pack are put into traction, sending pressurized oil to the hydraulic tighteners 37.

Therefore in short periods of time and by simple operations the square 11 can be equipped and the frame 10 is ready for sawing blocks of granite of different hardness or blocks of different materials into slabs and blocks.

1) Diamond frame for sawing blocks (113) of granite or other stone material and obtain therefrom slabs and blocks, comprising a mobile blade-holder square (11), operatively connected to motor means (90) and to motion transmission means (91, 92) by means of suitable mechanisms (52, 53), capable of driving the same blade-holder square to move with a certain pattern along predetermined paths, characterised in that the abovementioned blade-holder square (11) is provided with bracket means (14, 15) cantilever mounted to support at least one blade (26) in a removable manner.

2) Frame according to claim 1, characterised in that the aforementioned bracket means (14, 15) are composed of at least one pair of brackets, a lower one (14) and an upper one (15), cantilever mounted by disengageable constraining means (19, 21, 23, 25).

3) Frame according to claim 2, characterised in that the above brackets (14, 15) are cantilever mounted at an adjustable height. 4) Frame according to claim 2, characterised in that the abovementioned pair of brackets (14, 15) is able to support the abovementioned blades (26) pre-assembled in a pack (16), with suitable spacers (27) placed between them.

5) Frame according to claims 2 and 3, characterised in that the abovementioned brackets (14, 15) are cantilever mounted on at least one outer side of the abovementioned blade-holder square (11).

6) Frame according to claims 2 and 4, characterised in that at least the abovementioned upper bracket (15) is provided with hydraulic tighteners (37) capable of supporting the abovementioned blades (26) pre-assembled in a pack (16), in such a way as to regulate their traction.

7) Frame according to claim 2, characterised in that the abovementioned brackets (14, 15) are composed of rods. 8) Frame according to claim 2, characterised in that the abovementioned constraining means are formed by tie rods (19, 23) connected to the abovementioned brackets (14, 15) by first disengageable pins (21, 25) and to the same square (11) by means of second pins (20, 24). 9) Frame according to claims 2 and 8, characterised in that the abovementioned constraining means are also formed by third pins (18, 22) suitable for connecting in a disengageable manner at least the abovementioned brackets (14, 15) to the abovementioned blade-holder square (11), the abovementioned second pins (20, 24) also being disengageable.

10) Frame according to claims 1 and 2, characterised in that the abovementioned blade-holder square (11) is formed by two uprights (12), connected by cross members (13) on the outer side (12a) of each of the abovementioned two uprights, it being possible to mount in a cantilever manner a pair of the abovementioned brackets (14, 15) by means of constraining means composed of tie rods (19, 23) connected to the abovementioned brackets (14, 15) by means of first disengageable pins (21, 25) and to one of the abovementioned uprights (12) by means of second pins (20, 24).

11) Frame according to claims 2 and 10, characterised in that the abovementioned constraining means are also composed of third pins (18, 22) suitable for connecting in a disengageable manner at least the abovementioned brackets (14, 15) to the abovementioned blade-holder square (11).

Claims

12) Frame according to claims 2 and 10, characterised in that the abovementioned two uprights (12) are provided with flanges (42, 43, 44) for the attachment of the abovementioned upper bracket (15), placed at a pre-established distance from the abovementioned lower bracket (14).

13) Frame according to claims 1 and 10, characterised in that the abovementioned two uprights (12) of the blade-holder square (11) are constrained by pin means (50, 51) to connecting rod (54, 55) and crank (56, 57) flywheel (58, 59) and balancing counterconnecting rod (76a, 76b, 77a, 77b) mechanisms, operatively connected to at least one electric motor (90) by means of auxiliary flywheels (93, 94) and a cogged pulley transmission (97, 98, 101, 102, 107, 108, 110) and cogged belts (99, 100, 109), the abovementioned mechanisms being able to drive the same blade-holder square (11) to move with repeated movements along elliptical paths.

14) Frame according to claim 13, characterised in that the abovementioned flywheel (58, 59) is composed of two half-flywheels (58a, 58b, 59a, 59b), to whose inner walls is attached a first crank pin (56, 57) connected to the abovementioned connecting rod (54, 55) and to whose outer walls are attached second crank pins (74a, 74b, 75a, 75b) connected to the abovementioned balancing counterconnecting rods (76a, 76b, 77a, 77b), the .abovementioned second crank pins (74b, 75b) also being attached eccentrically to the abovementioned auxiliary flywheels (93, 94).

15) Frame according to claim 13, characterised in that the abovementioned two uprights (12) of the blade-holder square (11) are constrained by four pin means (50, 51) to four connecting rod (54, 55) crank (56, 57) flywheel (58, 59) and balancing counterconnecting rod (76a, 76b, 77a, 77b) mechanisms.

16) Frame according to claim 1, characterised in that each blade (26) is composed of a metal strip of constant section with a cutting edge provided with diamond teeth (30).

17) Frame according to claim 16, characterised in that in proximity of its ends the blade (26) is perforated by two holes (33), perpendicular to said metal strip, for the passage of said bracket means (14, 15), said holes (33) being substantially oval in shape with the longer axis coinciding with the longitudinal axis of the blade (26).

18) Frame according to claim 17, characterised in that each blade (26) is held separately by an adjacent blade (26) by means of spacers (27) placed at the ends of the blades and perforated by oval holes (34) coaxial with those (33) of said blades for the passage of said bracket means (14, 15).

19) Frame according to claim 18, characterised in that each of said spacers (27) has two edges substantially parallel to the Longitudinal axis of the blades (26) and other two edges extending crosswise to said longitudinal axis, at least one (31) of said other edges being of a substantially sinusoidal undulating shape.

20) Frame according to claim 18, characterised in that it comprises a plurality of adjacent blades (26) distanced by said spacers (27) and held in longitudinal traction by respective hydraulic tighteners (38) aligned along one of said bracket means (14, 15).

21) Frame according to claim 20, characterised in that each hydraulic tightener (37) is composed of a piston (38) acting on a portion of the end of the perimetral edge of one of said oval holes (33) of the blade (26) and of a cylinder (39) housed in a transverse seat of one of said bracket means (14, 15).