FR2591703A1 - Method for adjusting sets of sealing rings and tool kit for that purpose - Google Patents

Abstract

The invention relates to a method of adjusting a set of a sealing ring on a piston. According to the invention, strips 12 of various thicknesses are formed from bearing ring material, the strips of a material of a chosen thickness are cut to a length suitable for the diameter of the piston 1 and this length is used to replace a thinner bearing ring. The invention applies especially to sets of sealing rings forming a fluid seal between a cylinder and an axially movable member.

Description

 The present invention relates to seal ring assemblies which form a fluid seal between a cylinder and an axially movable member such as a piston, and it relates more particularly to the maintenance of the seal while the cylinder s 'use. Such seal ring assemblies include both one or more seal ring members and one or more support ring members.

 The internal surface of the cylinder is subject to wear and degradation; it is possible to repair the damaged surface by re-boring the cylinder, with a concomitant increase in the diameter of the cylinder. This is typically of the order of 0.5 mm in diameter (0.25 mm in radius). Current sealing rings can take account of an increase in this diameter up to approximately 1 mm, but the present support rings have a more restricted range, usually less than 0.5 mm, otherwise the support clearances. become excessive.

 It is not economical to produce new support rings or a complete piston by molding or machining for each cylinder size.

As a result, the cylinders are not usually re-bored but are discarded.

 The present invention provides a method of adjusting an assembly of a sealing ring which consists in forming bands of crown material of different thicknesses, preferably "pultrusion", and in cutting the bands to a length appropriate to a particular piston diameter; such strips of suitable thickness are used to replace the thinner support rings when the cylinder has been reamed. The original support crowns were also preferably produced in the same way. The "pultrusion" of the support material can be done by the process described in EP-A-0056689, the disclosure of which is incorporated herein by reference.

 The invention also provides a kit for adjusting a set of a sealing ring in a cylinder and for adjusting it after re-boring, comprising a group of bearing crown material with a radial thickness different from that of the bearing crown (s) in the original assembly but each compatible with another or more other rings or crowns of the sealing assembly. Preferably, all of the support crowns are split crowns formed by pultrusion.

The invention will be better understood and other objects, characteristics, details and advantages thereof will appear more clearly during the explanatory description which follows, made with reference to the appended schematic drawings given solely by way of example illustrating a mode and in which
- Figures la and lb are sectional views, along a radius, of a piston and a cylinder representing them before and after re-boring the cylinder and replacing the support ring, respectively; and
- Figure 2 is a perspective view of a split support ring.

 In FIG. 1a, a piston 1 operates in a cylinder 2 which, at the origin, was of a certain radius with respect to the axis 3, therefore its wall was at 4.

 The piston 1 is a piston in two parts being, for example, split at 5 to allow the initial adaptation of a set of a sealing ring generally indicated at 6. This comprises a sealing ring 7, support rings 8, 9 to prevent lateral extrusion of the sealing ring 7 and also a support ring 10. The support ring must resist lateral movement of the piston in the cylinder. It can originally be split or unsplit.

 After wear or digging of the cylinder 2, it is re-bored, which increases its diameter, therefore its wall is now at 11, FIG. Digging may particularly occur after use at very high pressures, for example in hydraulic mine props, in particular due to the contaminants in the hydraulic fluid.

 Since the sealing ring 7 is comparatively elastic, it can accommodate re-boring, but the essentially non-elastic support ring 10 cannot do so without excessive play, at least if the increase in diameter during re-boring exceeds approximately 0.5 mm. .

 The present invention compensates for this and allows continuous use of the assembly by providing a replacement support crown 12 with a thickness greater than that of the crown 10. A thickness greater than 0.25 mm will allow a re-bored cylinder whose increase diameter was 0.5 mm; support crowns of progressively increasing thickness can be provided so that successive reamings of a given cylinder are possible.

 It should be noted that within the capacity limits of the sealing ring 7, only the support rings must be removed from the piston 1 and replaced. Of course, the replacement crowns are fully compatible with the other elements of the assembly. They may have been supplied with the entire original sealing ring.

 A particularly preferred material for the sealing ring is the material obtained by "pultrusion" described and claimed in European patent 56689, but other materials can be used.

 In all cases, it is best to cut the crown material to length on the spot and adapt it as a split crown to avoid the need to disassemble the piston. The material 12 is simply cut to length as can be seen in FIG. 2, its ends 13 having a transverse or oblique configuration for the abutment, or almost, during an adaptation in the assembly 6.

Claims (4)

 1. Method for adjusting an assembly of a sealing ring on a piston, characterized in that it consists in forming strips of a crown material of support of different thicknesses and in cutting the strips of a material of a thickness chosen at a length appropriate to the diameter of the piston, and to use said length to replace a support crown of lesser thickness.  2. Method according to claim 1, characterized in that the aforementioned bands were formed by "pultrusion".  3. Method according to any one of claims 1 or 2, characterized in that the diameter of a cylinder in which the piston must operate has been increased by re-boring, the increment in thickness of the crown having to compensate for said increase.  4. Kit of parts for the adjustment of a set of a sealing ring in a piston and a cylinder after an increase in the diameter of the latter, characterized in that it comprises a group of a material (12) bearing crown of a radial thickness different from that of the bearing crown (s) (10), but each being compatible with the other ring (s) or crowns (7, 8, 9) of the assembly sealing.