WO2012013836A2

WO2012013836A2 - Gas spring with pivoting cover

Info

Publication number: WO2012013836A2
Application number: PCT/ES2010/070800
Authority: WO
Inventors: Gabriel Jarava Melgarejo; Oscar Alejos; Félix ESTIRADO
Original assignee: Azol-Gas, S. L.
Priority date: 2010-07-26
Filing date: 2010-12-03
Publication date: 2012-02-02
Also published as: ES2351837A1; WO2012013836A3; ES2351837B1

Abstract

The invention relates to a gas spring (1) with a pivoting cover (4) for absorbing non-axial loads, thus preventing the stress resulting from said loads from causing failures and reducing the working life of the spring (1). The cover (4) is divided into a fixed external portion (4a) that is rigidly secured to the body (2), and a pivoting internal portion (4b) having a hole over which the shaft (3) slides, the two portions (4a, 4b) being connected via an at least partially spherical contact surface, such that the pivoting internal portion (4b) is orientable. The spring (1) also comprises an additional O-ring seal (5) between the fixed external portion (4a) and the pivoting internal portion (4b) of the cover (4) for preventing gas leaks. The end of the shaft (3) also has a sliding element (7) that can move radially to absorb horizontal movements.

Description

GAS SPRING WITH SWING COVER

OBJECTIVE OF THE INVENTION The object of the present invention is a gas spring provided with a tilting cover designed to absorb non-axial loads, thus preventing the stresses caused by said loads from causing breakdowns and reducing the life of the gas spring. BACKGROUND OF THE INVENTION

A gas spring is essentially formed by a movable rod along the inner chamber of a hollow cylindrical body, being also provided with a cover to prevent the gas from escaping at the end through which the rod is introduced. Thanks to the presence of a gas confined inside said chamber, the rod acts as a spring or spring: when, starting from a certain resting position, a force pushes the rod into the chamber, the gas is compressed and opposes a growing force with displacement; when the force on the rod ceases, the pressure of the gas returns the rod to its resting position. Current gas springs are normally prepared to work in the axial direction, that is, in the direction of the shaft of the rod and the cylindrical chamber. To do this, they are provided with a flat surface at the end of the rod on which the thrust surface rests. If this thrust surface is not perfectly perpendicular to the axis of the spring, the contact between the two surfaces is made on an edge of the rod, producing a torque that is detrimental to the correct operation of the spring. Gas springs have been used for some time in different industries as elastic force limitation elements, for example in presses in sheet metal stamping processes.

A drawback of current gas springs is that, as a result of the specific configuration and operation characteristics of a particular installation, or of the mounting conditions of the spring itself, vibrations or lateral stresses sometimes occur at points concrete of the rod stroke, causing the gas spring not to work exactly aligned in the direction of its axis. Any component of stress outside the shaft, in turn, causes friction, heat generation and even wear of the pressed area.

Gas springs are constructed by assembling machined parts in lathes, which largely ensures that their configuration is concentric and that the support surfaces are perpendicular to the axis of the part. In general, gas springs do not pose misalignment problems with respect to their work axis and the value of static misalignment does not exceed one tenth of a degree. In dynamic, the error is even smaller because the axis in its movement causes both the axis and the top cover to be arranged in the direction of movement. On the other hand, an installed gas spring rests on two surfaces that theoretically are parallel but may have small deviations. For example, in the case of gas springs installed in a press, it can generally be accepted that the surfaces of the press are sufficiently parallel, but it is another factor to be taken into account in the total composition. Additionally, a coarse finish can also influence the quality of the gas spring seat on said surfaces. Note also that the gas spring is a very elongated element in relation to its base, and therefore a small deviation in its seat can make the oscillation at its upper end be a few millimeters.

As a result of the combination of all these elements, misalignments sometimes occur that can cause the following effects:

- Increased support of the rod on the guiding elements.

- Different distribution of stress on the seal.

- The upper cover is forced to be oriented according to the working direction of the rod.

- Metal-metal contact between cover and stem. As a result, more heat is generated, which in turn causes the gaskets to work closer to their thermal limit or even exceed it, and that the guiding elements wear out through the pressure zone and become produced Metal-to-metal contacts, which can fire small particles of steel or chips that scratch the joints, causing gas leaks. The ultimate consequence is the occurrence of breakdowns and the decrease in the life of gas springs.

To solve these problems, a proposed solution has been to provide the upper end of the rod with a spherical shape in order to minimize the effect of the torque on the rod. However, this option causes the appearance in the generatrix opposite to the contact point of a higher load than in the rest of the rod surface, so that the problem is not completely resolved.

In addition to the above in a die, lateral movements also occur due to the construction of the die itself and the aforementioned inclination of the support surfaces. In the case of horizontal movements by the construction of the die, these are due to the fact that there are situations in which it is necessary to build a floating treadmill or elements not perfectly guided in the direction of movement of the press, which due to the work they do, they can move horizontally a small distance while the press descends. Although the support surface of the gas spring is perfectly horizontal and parallel to the base of the press, if the element on which the axis of the gas spring is supported moves horizontally to one side, this will cause lateral stress on the gas spring that will make the guiding elements have to work considerably, even exceeding their maximum effort limit. The gas spring will tend to maintain its verticality, since the support surfaces are horizontal and parallel, but will transmit the lateral stress to the gas spring. In the case of inclination of the support surface, the lateral movements are due to the fact that one or both surfaces on which the gas spring is supported while the die is closed are inclined. Because the movement of the press is always vertical, if the gas spring is being compressed with a slight degree of inclination, there will be a displacement on the surface of contact with the die that will cause a lateral load. The forces involved in the gas spring generate a reaction in the components involved in the process that can cause permanent deformation of the guiding elements and a greater inclination to compensate for that effort.

DESCRIPTION OF THE INVENTION

The proposed solution consists in having the upper cover and rod assembly oriented at all times perpendicularly to the thrust surface so that no overstress occurs. To do this, the lid is basically divided into two portions, an external potion fixed to the cylindrical body and an inner portion provided with the hole into which the rod slides, the inner portion being configured to allow rotational or tilting movements relative to the cylindrical body . Thus, when the surface on which the rod rests is not perfectly perpendicular to the axis of the spring, the tilting inner portion rotates or tilts to align with said surface.

Therefore, the gas spring with a tilting lid of the invention comprises a hollow cylindrical body that is closed at one end and along whose inner chamber a rod slides. The open end of said cylindrical body is closed by the rod and by an approximately cylindrical shaped lid. The particularity of the cover of the invention is that it is divided into a fixed outer portion integral with the cylindrical body and a tilting inner portion provided with a hole through which the rod slides, both portions being joined by means of a contact surface at least partially spherical that allows the inner tilting portion to be orientable. Thus, when the surface on which the rod end rests is not completely perpendicular to the axis of the spring, the portion tilting interior rotates relative to the fixed outer portion until the rod is perfectly aligned with said surface, avoiding unwanted friction with the guide elements of the spring. The spring further comprises an additional O-ring disposed between the fixed portion and the tilting portion of the lid, which prevents gas from escaping from the chamber during oscillations of the tilting inner portion of the lid.

According to a preferred embodiment of the invention, the spring also comprises an elastic ring located in the lower part of the cover to hold the inner tilting portion, thus preventing it from falling into the gas spring when the gas is evacuated from the chamber.

BRIEF DESCRIPTION OF THE FIGURES Fig. 1 shows a gas spring according to the prior art where the effects of non-linear loads with the axis are shown.

Fig. 2 shows a known solution to the problem of non-collinear loads with the shaft.

Fig. 3 shows a preferred embodiment of the gas spring of the present invention.

Fig. 4 shows a preferred embodiment in which the gas spring also has a sliding stop.

PREFERRED EMBODIMENT OF THE INVENTION

First, a conventional gas spring (100) depicted in Fig. 1 is described. It can be seen that it is formed by a cylindrical body (102) into which a rod (103) slides, the inner chamber of the cylindrical body (102) filled with a gas. When the gas is confined inside the chamber, the compression and expansion of the gas when the rod (103) descends or rises causes the spring (100) to behave as a dock. Fig. 1 also shows the different elements arranged between the body (102) and the rod (103) to achieve adequate sealing of the assembly, as well as adequate guidance of the rod (103). In particular, the cover (104) is provided, provided with a groove that houses an outer O-ring (105) to prevent gas leaks and other inner housing in which an inner bushing (106) is arranged. There is also a scraper (107), a protector (108), a ring (109) and the gasket (1 10). All these elements and their functions are known in the prior art. Thus, if the gas spring (100) of Fig. 1 rests on a thrust surface that is not perpendicular to its axis, as shown in the upper area of the figure, a torque is produced which it causes friction near the generatrix of the rod opposite the point of contact with said thrust surface.

Fig. 2 shows another example of spring (200) according to the prior art where similar reference numbers have been used to refer to parts equivalent to those of Fig. 1. This spring (200) has a rounded upper end surface (203) to better accommodate thrust surfaces that are not perfectly perpendicular to the spring axis (200). This solution, however, does not prevent the appearance of excessive loads on the stem generatrix (203) opposite the thrust point, as represented by an arrow. Fig. 3 shows a spring (1) according to the invention where the hollow cylindrical body (2), the rod (3) and the cover (4) can be seen. As mentioned hereinbefore, in this example the cover (4) is formed by two differentiated portions: a fixed portion (4a) and a tilting portion (4b). It can be seen in Fig. 3 how the fixed portion (4a) has an approximately cylindrical shape in its lower part, while at the top it has a concave spherical shape that is complemented by the convex spherical shape of the upper part of the tilting portion (4b). This configuration allows the tilting portion (4b) to rotate or tilt in relation to the fixed portion (4a), which is, in turn, fixed to the outer cylindrical body (2). That way, when a Thrust surface not completely perpendicular to the rod (3) exerts a load on the spring (1), the tilting body (4b) rotates, sliding on the fixed body (4a), until it reaches a position where said thrust surface is perfectly seated on the surface of the upper end of the stem (3).

To prevent gas losses during the tilting movements, the spring (1) comprises an additional O-ring (5) between the fixed portion (4a) and the movable portion (4b). In addition, the spring (1) of this example incorporates an elastic ring to prevent the tilting portion (4b) of the cover (4) from falling into the chamber in case the gas is evacuated.

An example of embodiment of the gas spring that solves the problem derived from lateral movements is shown in Fig. 4. For this, the end of the rod (3) of the gas spring (1) comprises a housing in which a sliding element (7) is arranged which is configured so as to have radial displacement capacity with respect to the rod (3) of the spring of gas (1). Thus, by contacting, for example, with an inclined surface that can move laterally to the rod (3), the sliding element (7) would move laterally with respect to the rod (3), but would not transmit this effort to the gas spring (1 ) absorbing it.

An exemplary embodiment is shown in Fig. 4 in which the sliding element (7) and the cover (4) are combined, although the sliding element (7) can be incorporated into the gas spring without the said tilting cover (4) ). In the exemplary embodiment shown, the sliding element (7) has a cylindrical shape and is located in a cylindrical housing of the end part of the stem (3) of the spring (1). Finally, between the sliding support (7) and the inner wall of the housing thereof (7) at the end of the rod (3) there is a damping means. This buffer means can be oil, for which the sliding support (7) would include a gasket (8) that centers the sliding support (7) and prevents the oil from escaping. Therefore, a gas spring that incorporates both the tilting cover (4) and the sliding support (7) manages to absorb any difference in the supports or in the movement of the die, thus achieving a longer life of the spring of gas (1).

Claims

1. Gas spring (1) with a tilting lid, comprising a hollow cylindrical body (2) closed at one end along whose inner chamber a rod (3) slides, and the open end of said body (2) being closed ) by the rod (3) and by an approximately cylindrical cover (4), characterized in that the cover (4) is divided into a fixed outer portion (4a) integral with the body (2) and a tilting inner portion (4b) provided with a hole on which the rod (3) slides, both portions (4a, 4b) being joined by a contact surface at least partially spherical, so that the tilting inner portion (4b) is orientable, and also comprises a joint O-ring (5) arranged between the fixed outer portion (4a) and the tilting inner portion (4b) of the lid (4) to prevent gas leakage.

2. Gas spring (1) according to claim 1, characterized in that it further comprises an elastic ring (6) located in the lower area of the cover (4).

3. Gas spring (1) according to any one of the preceding claims, characterized in that the end of the rod (3) comprises a housing in which a sliding element (7) is inserted which is configured so as to have displacement capability radial with respect to the rod (3) of the gas spring (1).

4. Gas spring (1) according to claim 3, characterized in that the sliding element (7) has a cylindrical shape.

5. Gas spring (1) according to claim 3 or 4, characterized in that it comprises a damping means between the sliding support (7) and the internal wall of the housing thereof (7) at the end of the rod.

6. Gas spring (1) according to claim 5, characterized in that the buffer means is oil.