BACKGROUND OF THE INVENTION The object of the present invention is a system for tightening tie rods of a press. STATE OF THE ART

As is known, the press is a machine that exerts a preset pressure on a material to perform a set operation, which can be punching, drawing, moulding, forging or other things.

The carrying structure of a press substantially provides a base with supporting plane of the material, a head and a frame consisting of two or four columns that connect the head to the supporting base.

Along the columns a ram moves with reciprocating movement to and from the supporting plane, driven by a mechanical or hydraulic means fixed to the head. The ram carries the tools or the moulds for processing and at the moment of pressing acts on the supporting plane and reacts on the head; the forces in action and the reactions are thus all closed within the press.

To join the base, the head and the columns, tie rods are used, each of which is received inside a respective column. The ends of each tie rod are threaded and one of the tie rods (19) is at the base whereas the other is at the head. On the two ends two respective nuts are tightened, one of which acts on the base whereas the other acts on the head to fix the various parts together.

Tightening the nuts of the tie rods is a very important operation, both in the assembly step and in the step of periodical checking of the press, as the tie rods have to be preloaded correctly so that the press does not suffer deformation during pressing at the compression force for which the press is calibrated. The tie rods are tightened manually by torque wrenches.

Using torque wrenches requires the tie rods to protrude from the structure of the press to be able to access the nuts for manual tightening. This entails an increase in overall dimensions of the press of a certain amount.

It should be added that these torque wrenches are also bulky and are moreover costly.

OBJECT OF THE INVENTION

The object of the present invention is to propose a system for tightening tie rods of a press that is able to solve the aforesaid problems.

SHORT DESCRIPTION OF THE INVENTION

This object is achieved by a system for tightening tie rods of a press according to claim 1.

SHORT DESCRIPTION OF THE DRAWINGS

In order to understand better the invention, a description is set out below of an embodiment thereof by way of non-limiting example, illustrated in the attached drawings, in which:

fig. l is a perspective view of a press with tie rods that uses a system for tightening according to the invention;

fig.2 is a partially sectioned perspective view of the press of fig. l ;

fig.3 is a frontal section view of the press of fig. l ;

fig.4 is a partially sectioned perspective view of a detail of the press of fig. l ;

fig.5 is a partially sectioned raised view of a device used on the press of fig. l ;

fig.6 is a top section view of the device of fig.5.

DETAILED DESCRIPTION OF THE INVENTION With reference to figs 1, 2, the illustrated press, indicated generally by 10, has a carrying structure that provides substantially a base 11, a head 12 and a frame consisting of four columns 13 that connect the head 12 to the base 11. The base 11 is provided with a plane 14 on which the material to be processed rests.

To the columns 13 guides 15 are fixed along which a ram 16 runs that is driven by reciprocating motion to and from the supporting plane 14. As illustrated in fig.3, the ram 16 is driven by a hydraulic cylinder 17, fitted in the head 12, provided internally with a piston 18 that is connected to the ram 16 and moves with a reciprocating motion by fluid thrust.

On the ram 16 the tools or moulds are fitted for processing. During pressing, the ram 16 acts on the supporting plane 14 and reacts on the head 12.

With reference to figs 1, 2, 4, to join the base 11, the head 12 and the columns 13, four tie rods 19 are provided, each of which runs inside a respective column 13. Each tie rod 19 has two threaded ends 20, one of which, a lower threaded end, is at the base 11 whereas the other, the upper threaded end, is at the head 12 (fig. 4). On each end 20 a respective internally threaded toothed wheel 21 is screwed. In the base 11 and in the head 12 recesses 22 are obtained, each of which receives a respective toothed wheel 21. The toothed wheel 21 locks axially against a wall of the recess 22 with the interposition of a washer 23. For the regulation of the tie rods 19, with the press 10 a mechanical device 24 for reducing the operating force is associated, which is drivable manually from the exterior, intended to be coupled with the toothed wheels 21, which is visible in detail in figs 5,6. The device 24 provides a support bracket 25 that enables the device 24 to be fixed, by suitable screws 26, to the body of the press 10 at a toothed wheel 21. On the bracket 25 a kinematic chain is anchored that consists of a rack 27, which engages with the toothed wheel 21 inside the recess 22, a long screw 28, which is integral with the rack 27, and a nut 29 which is tightened on the screw 28. For fixing to the rack 27, as illustrated in fig. 6, an end part 30 of the screw 28 is screwed in a threaded hole 31 and is locked by a nut 32, tightened on the screw 28 and fastened against the rack 27. An end portion 33 of the screw 28 traverses the bracket 25 and the nut 29 screwing on this end portion 33 comes to lock axially against the bracket 25 with the interposition of a washer 34, outside the press 10.

The tie rods 19 are tightened in the following manner according to a preset preload. First, manual tightening is performed with a low load by means of a tool, visible in figs 1-3 and indicated with 35, that provides a grip with at the end an internally toothed rim that is intended to engage with the toothed wheel 21. Once the toothed rim has engaged the toothed wheel 21 the toothed rim is rotated manually by the grip to carry out low-load tightening. A toothed wheel 21 of a tie rod 19 acts on the base 11 whereas the other toothed wheel 21 acts on the head 12 to tighten the various parts.

Subsequently, the device 24 is fitted at the toothed wheel 21 subjected to the aforesaid first tightening, such that the rack 27 engages with the toothed wheel 21. In this case tightening is carried out with a heavy load by rotating the nut 29 with a normal wrench. As the nut 29 is locked axially against the bracket 25, the rotation of the nut 29 involves the axial movement of the screw 28 and thus of the rack 27 that causes a rotation of the toothed wheel 21 so as to tighten the corresponding tie rod 19.

And it is thus continued for each toothed wheel 21 of the press 10 until all the tie rods 19 have been preloaded correctly. After tightening the tie rods 19, the device 24 for reducing the operating force is dismantled from the press 10. The mechanical double demultiplication given by the coupling between the toothed wheel 21 and rack 27 and by the coupling between the screw 28 and nut 29 permits the operator to exert with little operating force great tightening force on the tie rod 19. The described and illustrated system for tightening the tie rods 19 does not entail significant increases in overall dimension because the tightening toothed wheels 21 are received in the recesses 22 of the base 11 and of the head 12 and the device 24 for reducing the operating force is removed from the press 10 once the tie rods 19 are tightened.

The tightening equipment is cheaper because it consists of just a few low-cost mechanical elements.

It is clear that variations on and/or additions to what has been disclosed and illustrated are possible.

The components of the mechanical device for reducing the operating force can be replaced by other mechanical components reducing operating force in an equivalent manner, that are able to engage the toothed wheel of the tie rod.

Also several force-reducing devices can be used that are applied to the press to accelerate tightening of the tie rods.

In a less cheap embodiment, a force-reducing device may be provided for each toothed wheel of each tie rod. In this case the device is fixed to the body of the press and is not dismantled once tightening has been carried out. The system for tightening seen can be applied to any type of press that has tie rods.