FR2464427A1 - Axial overload protection for forging press etc. - has shaft cone shrunk in conical ring bore, cone angles less than static friction angle - Google Patents

Abstract

The mechanical overload protection is for a rolling mill, a press, or a forging machine etc. in which an axial force is transmitted many times. The axial force is transmitted via a conical shaft end (1) which is shrunk into a conical bore in a ring (2). The two cones have approximately equal cone angle which is smaller than the limit angle whose tangent equals the coefficient of static friction. The fit of the cones is pref. such that fracture of the ring occurs at the same time as the static friction resistance is exceeded.

Description

The present invention relates to a mechanical safety device against overloads for rolling mill, press, forging machine and similar machine with high load frequency, in which the pressure is transmitted by means of a conical pin and a surrounding ring said post along its axis.

Mechanical safety devices for rolling mills are already known which are in the form of breakable containers (see German patent 1 101 328) as well as in the form of conical studs enclosed in split sockets the elements of which are held together by strips (see in particular German patent 51 978), which break during the appearance of overloads and consequently free up empty space, so that the various elements of the installations are protected against damage.

Safety devices transmitting pressure have the disadvantage that, during frequent efforts, as is the case in rolling mills or forging machines, they break prematurely by fatigue and must be changed frequently or else only break for a load so heavy that the machine parts can no longer be protected.

In tensile stresses, it is known to combat this drawback by high prestressing of the safety elements and therefore to bring together a small breaking margin re (a breaking load can be obtained of approximately 1.2 times the usual nominal load ) with a long service life under a minimum load.

The object of the present invention is a mechanical safety device making it possible to avoid the drawbacks of the mechanical safety of rolling mills, so as to allow the transmission of a pressure less than or at most equal to the nominal load, the rupture however occurring from suddenly during a light overload compared to the nominal load.

To this end, according to the invention, the mechanical safety device against overloads for rolling mill, press, forging machine and similar machines with high load frequency, in which the pressure is transmitted by means of a tenon and d 'a ring surrounding said post along its axis, is remarkable in that the post and the annular body are provided with conical surfaces respectively outer and inner, the angles of said surfaces being substantially equal and in both cases less than the angle friction limit, said post and said annular body being adjusted and connected to each other by shrinking.

Preferably, the adjustment of the two parts is such that when the breaking load is exceeded, the adhesion between these two parts and the transmissible force of the annular body are exceeded simultaneously. The outer face of this annular body can be cylindrical.

According to the invention, for the mechanical safety device, a hardened post is chosen and an advantageously brittle body, which is hooped on the post to be able to transmit a longitudinal pressure, the force on one of the front faces passing through the post and the force on the other front face passing through the ring.

The figures of the appended drawing will make it clear how the invention can be implemented.

Figure 1 shows a device according to the invention, comprising a cylindrical outer surface, and a clearance path outside the safety device.

Figure 2 shows a safety device according to the invention provided with a conical outer surface and having a free space in its interior.

As shown in Figure 1, the hardened post 1 has a conical surface whose inclination relative to the longitudinal axis is smaller than the limit angle of friction. This hardened post 1 is hooped in an annular body 2 provided with a conical inner surface of equal or similar inclination, the hooping being such that without external loads (for example applied by the rolling mill) the ring is located under a pre- high stress.

When a pressure is applied, the thrust force is modified in the hooping, without causing relative sliding, as long as the pressure is less than the nominal load pre-determined by the choice of dimensions, of the material of the ring 2 and hooping. When the force exceeds the nominal load up to the breaking load, an abrupt axial movement occurs between the post 1 and the ring 2, this sliding causing the breakage of the ring 2 and therefore the interruption of the transmission. forces.

The breaking load is, by the choice of materials and dimensions as well as by the hooping, kept within narrow limits, so that when obtaining the breaking load the ratio of the force of the thrust compared to the pressure force between the tenon 1 and the ring 2 exceeds the coefficient of friction and at the same time the effort that can be supported by the ring is displaced. It is therefore advantageous to use a healthy material and a low ratio between the outside and inside diameters of the ring.

 During the manufacture of the safety device according to the invention, it is advantageous that the ratio between the outside and inside diameters is kept constant for all the sections, as is the intensity of the hooping for these diameters. This means that the outer surface of the ring is also conical and that the angle of the post 1 is, before it is trapped by the hooping, slightly larger than the angle of the ring 2 before hooping.

Claims (2)

1- Mechanical safety device against overloads for rolling mill, press, forging machine and similar machines with high load frequency, in which the pressure is transmitted by means of a tenon and a ring surrounding said tenon along of its axis, characterized in that the tenon (1) and the annular body (2) are provided with conical surfaces respectively exterior and interior, the angles of said surfaces being substantially equal and in both cases, less than the limit angle of friction, said post and said ring being adjusted and connected to each other by shrinking 2- Device according to claim 1, characterized in that the adjustment of the post and the annular body is such that, when the breaking load, the adhesion between these two elements and the force that can be supported by the ring are exceeded simultaneously. 3- Device according to any one of claims 1 or 2, characterized in that the outer surface of the annular body is conical.