EP0915747A1

EP0915747A1 - Metal part having external surface with particular profile, polishing method for its production and device for implementing the method

Info

Publication number: EP0915747A1
Application number: EP98928392A
Authority: EP
Inventors: Alain Lienard
Original assignee: Uranie International
Current assignee: Uranie International
Priority date: 1997-06-05
Filing date: 1998-05-29
Publication date: 1999-05-19
Anticipated expiration: 2018-05-29
Also published as: US6736697B2; US20010011001A1; EP0915747B1; WO1998055260A1; ATE210534T1; DE69802892D1; FR2764225A1; DE69802892T2; FR2764225B1; JP2000501345A

Abstract

The invention relates to a circularly-symmetrical metal part (1) having an outer surface (3) which, in axial section, has a general profile made up of a uniform succession of flattened convex arches (4). The invention also relates to a polishing method in which the polishing means move in a tracking motion so as to track the outer surface of the part to be polished, and to apparatus for implementing the polishing method.

Description

Metal part having an external surface having a particular profile, polishing process for its realization and device for implementing the process.

The present invention relates to a metal part ^¬ that of revolution having an external surface having a particular profile. It also relates to a polishing process allowing this particular profile to be obtained and a device for implementing the process.

There are metallic parts of revolution whose external surface has, in an axial section, a profile composed of an irregular succession of projecting edges and hollows. Such metal parts are for example intended to constitute rods of jacks.

In this type of use, in particular for hydraulic cylinders, an important problem resides in the elimination of leaks at the level of the passage hole of the rod in the body of the cylinder. Seals are therefore arranged in the through hole so as to rub on the rod and thus ensure the tightness of the cylinder body. However, the external surface of the metal part forming the rod, having a profile consisting of an irregular succession of projecting edges and hollows, has only a low rate of bearing length. This results in a poor distribution of the contact pressures between the seal and the external surface, and this poor distribution of the contact pressures causes excessive wear of the seals which causes oil leaks. This is particularly detrimental and obliges, to replace the sealing elements, to stop machines whose high cost and intense operating time (often twenty-four hours out of twenty-four) make a shutdown for maintenance extremely expensive.

After a certain time of use of the jack, the external surface of the metal part forming a rod is lapped, so that the rate of bearing length increases, causing less wear on the seals. It is therefore important that the rate of bearing length is maximum for the shortest running-in time. Currently, for a lapping corresponding to a cutting depth (equivalent to leveling an upper part of the profile of the external surface) equal to 40% of the total height of the profile (corresponding to the height of the most protruding edge measured from the lowest trough), the bearing length rate obtained is around 20%. However, for such a bearing length rate, the wear generated remains very high.

In order to reduce the roughness of a surface, it is known, in particular from document JP-A-61 061760, a method of treating a surface consisting in blunting the projecting edges of the surface in order to limit the wear by friction d 'a moving part in relation to this surface. It has also been proposed, in particular in document O-A-95 02486, a method of surface treatment by hard anodization. However, the parts obtained by these methods do not constitute a satisfactory solution to the aforementioned problems.

In addition, the metal part is sometimes subject to ambient conditions (humidity, heat, salt spray, etc.) leading to its oxidation. This oxidation weakens the metal part and can ultimately lead to rupture. To avoid this, the external surface of the metal part is conventionally covered with a layer of stainless chrome. Due to the irregularity of the profile of the external surface, the chromium layer inevitably has zones of small thickness, and in these zones, cracks of small dimension are sufficient to expose the external surface to the ambient environment. This exposure then generates a harmful oxidation of the metal part. An object of the invention is to propose a part metallic whose external surface has a particular profile allowing obtaining a high bearing length rate for a short running-in time.

With a view to achieving this goal, there is provided according to the invention, a metal part of revolution having a longitudinal axis and an external surface having in axial section a general profile composed of a regular succession of flattened convex arches.

Thus, the regular succession of flattened convex arches provides a high bearing length rate before running in, so that this rate is maximum after a very short running time. The contact pressures between the members in relative motion are thus distributed more widely. When the metal part concerned is used as a cylinder rod, the wear of the sealing elements is thereby limited, and the risks of overheating and seizing are minimized. In addition, the hollows separating the flattened arches from each other are regularly distributed along the external surface. These recesses constitute in particular in the case of hydraulic cylinders, oil reserves whose regular succession along the metal part promotes lubrication. Furthermore, such a particular profile allows the deposition of a layer of metallic coating of uniform thickness. Corrosion resistance is thus further improved.

Advantageously, the external surface of the metal part is covered with a layer of metal coating having an external surface also having in axial section a general profile composed of a regular succession of flattened convex arches.

The metal coating layer covering the external surface of the metal part is of constant thickness and provides good protection of the metal part. By its profile which is also in arches flattened convex, the coating layer has a high bearing length ratio before running in, so that the above-mentioned advantages are found for the coated part, with in particular low wear of the sealing elements. Preferably, the shape of the arches and the periodicity of their succession are such that, for Profon ^¬ makers cut between 20% and 50%, the outer surface has a bearing length ratio between 25% and 95%. Advantageously then, the shape of the arches and the periodicity of their succession are such that, for a cutting depth substantially equal to 40%, the external surface has a bearing length ratio of between 40% and 95%. Such values of bearing length ratio at these cutting depths constitute an excellent compromise between limiting the wear of the sealing elements and the sufficient conservation of oil reserves to ensure correct lubrication. They also favor the deposition of a coating layer of constant thickness in the case where the metal part is covered with such a layer, with then an external surface of the part having a particular profile similar in succession of flattened convex arches. . The subject of the invention is also a method of polishing the external surface of a metallic piece of revolution which may include shape defects, comprising the steps of setting the metallic piece in motion relative to a tool and applying the tool on an area of the external surface of this part so that it exerts a force on it, the tool being driven by a movement following the external surface of the metal part in a radial direction essentially normal to this in the application area of the tool, so that the force exerted by the tool on the workpiece remains constant throughout the duration of the polishing whatever the shape defects present on the surface, until a general profile is obtained in axial section in the form of a regular succession of flattened convex arches.

This polishing process thus makes it possible to obtain metal parts having at least one of the preceding characteristics.

Advantageously, the metal part is supported vertically above the tool in a region of the symmetrical external surface of the zone of application of the tool with respect to the longitudinal axis of the metal part.

The invention finally relates to a device for implementing the polishing process having at least one of the aforementioned characteristics, the device comprising means for supporting and setting in motion the workpiece relative to a tool, the tool being mounted on a movable structure in a direction substantially normal to the external surface of the part to be applied by an associated effort cylinder on this surface by exerting a force on it, and a means for controlling the movement of the mobile structure depending on the shape defects of the external surface.

In accordance with a particular embodiment, the tool essentially consists of an abrasive belt passing over a contact wheel and a return roller forming the mobile structure on which said tool is mounted. Preferably then, the axis of the deflection roller is mounted to slide in a vertical plane by means of an associated jack so as to constitute a tensioning roller.

According to another particular characteristic, a shoe is arranged vertically above the tool to support the metal part in a direction substantially normal to the external surface thereof. Advantageously then, the position of the pad is adjustable by means of an associated jack, in a direction substantially normal to the external surface of the part. The wear of the pad can thus be compensated, and the position thereof adapted to different diameters of workpieces to be polished.

Other characteristics and advantages of the invention will emerge on reading the following description of a particular embodiment and non-limiting implementation of the invention. Reference will be made to the appended drawings, among which:

FIG. 1 is a traditional graphic representation of a surface profile of the ordinary type,

FIG. 2 is a partial simplified half-view in axial section of a metal part according to the invention, making it possible to distinguish the particular profile in succession from flattened associated arches,

FIG. 3 is a view similar to FIG. 2 of a metal part according to the invention, covered with a layer of metal coating, the external surface of which also has the particular profile in succession of flattened convex arches, and

- Figure 4 is a partial schematic side view of a device for implementing the polishing process allowing the production of the particular profile of the metal part according to the invention.

It should first of all be recalled the meaning of the terms "depth of cut" and "bearing length ratio" used in the present application within the meaning of the French standard NF-E-05 015.

With reference to FIG. 1, one can see a curve representing the profile P, along an axial section of the external surface of a part of the known type. Profile P here consists of an alternation of projecting edges and hollows, and extends over a measurement length L. A such a curve can be obtained using a roughness meter whose feeler, in contact with the surface, is moved over a length L.

The line of protrusions denoted ls extends tangentially to the highest projecting edge, and the line of depressions denoted it extends tangentially to the lowest trough. The distance separating the line of the projections ls from the line of the hollows le is the maximum height of the profile denoted Rt. The depth of cut c corresponds to a percentage of the maximum height of the profile Rt. The lengths of the material segments measured at a given depth of cut are denoted j _x .

For a given depth of cut c (in%), the bearing length rate Tp (in%) will be given by the formula:

The metal part according to the invention and the means allowing the production of the particular profile of this part will now be described in more detail.

Referring to Figure 2, the metal part according to the invention, generally designated in 1, is a cylindrical section part made of steel and intended in this case, to serve as a cylinder rod. The metal part

1 has a longitudinal axis 2 and an external surface 3.

As shown in FIG. 2, in axial section, and in accordance with a characteristic of the invention, the external surface 3 has a profile consisting of a regular succession of flattened convex arches 4. When this metal part 1 is intended to constitute a cylinder rod, the shape of the flattened convex arches 4 and the periodicity of their succession are advantageously such that the profile of the external surface 3 has a (Tp) ₄₀ of between 40% and 95% . In this way, the (Tp) ₄₀ being greater than 40%, the sealing elements are little worn due to their friction on the external surface 3, and the (Tp) ₄₀ being less than 95%, there remains sufficient hollow denoted 9 between the flattened convex arches 4 to constitute oil reserves in order to ensure correct lubrication of the external surface 3.

FIG. 3 illustrates a variant of the invention. In this figure we can see a metal part 1 similar to that of Figure 2 but whose outer surface 3 is covered with a metallic coating layer 5, for example a layer of chromium. The external surface 3 has a profile in succession of flattened convex arches 4 which then makes it possible to obtain a covering layer 5 of constant thickness, and the external surface 6 of this layer 5 also has a profile consisting of a regular succession flattened convex arches 7. The layer 5 thus protects the metal part 1 against oxidation and constitutes a contact surface, the friction of which, on the sealing elements of the cylinder body, will only cause slight wear of these. Thus, in the variant of Figure 3, the particular profile in succession of flattened arches is present at the outer surface of the coating layer. It is understood that the layer 5 could be a mechanical or other reinforcement layer instead of, or in addition, being a layer of protection against oxidation.

According to a particularly advantageous characteristic of the variant of FIG. 3, the dimensions of the flattened convex arches 7 and the periodicity of their succession are such that the profile of the external surface 6 of layer 5 has a (Tp) ₄₀ of between 40% and 95%.

With reference to FIG. 4, a polishing device for the production of the metal part 1 described above comprises, in a manner known per se, a series of rollers 10 and 11 regularly spaced apart and pivotally mounted on a frame (not shown here) for support the metal part 1 in the manner of a guide V. The rollers 10 and 11 are connected to a motor to drive the metal part 1 in a direction of advance parallel to the longitudinal axis 2 of the part, and in rotation about this same axis.

A polishing means, generally designated at 12, is mounted on the frame directly above the metal part 1 so that it can be applied to the external surface of the metal part in a direction normal to it.

The polishing means 12 comprises a contact wheel 13 and a deflection roller 14 around which is wound an abrasive strip 15 constituting the polishing tool.

The idler roller 14 is mounted to pivot freely around an axis 16 parallel to the direction of advance. In this case, the pin 16 is mounted on the frame to slide in a vertical plane via an associated jack 17, the pin 16 being mounted at the end of the rod of the jack 17, and the body of the cylinder being fixed to a tool holder 30 mounted on the frame. Thanks to this arrangement, the idler roller 14 is in addition a tension roller. The contact wheel 13 is integral with an axis 18 parallel to the direction of advance. The axis 18 is connected to a motor, not shown, to be driven in rotation. The axis 18 is mounted on the frame for sliding along a vertical plane by means of a cutting force cylinder 19. The axis 18 is mounted at the end of the cylinder rod cutting force 19, and the body of this cylinder is fixed to the tool holder 30. The cutting force cylinder 19 is connected to be controlled by a proportional regulator 20 of the cutting force. The wheel 13 and the roller 14, with their associated support members which connect them to the frame, thus form a mobile structure in a direction substantially normal to the part 1.

A shoe 21 is also arranged on the other side of the contact wheel 13 relative to the direction of advance, between two pairs of rollers 10 and 11. The shoe 21 is mounted on the frame to slide in a vertical direction . It is integral with a height adjustment member 22 fixed to the frame. The height adjustment member can be a jack, a slide associated with a locking screw in position, or any other known means. The shoe 21 is in this case made of a plastic material with a low coefficient of friction such as polytetrafluoroethylene. The shoe 21 could also include a pivoting contact member.

In operation, the contact wheel 13 is rotated so as to frictionally drive the abrasive belt 15. The metal part 1 is set in motion relative to the polishing means 12 according to the direction of advance via the motor driving the rollers 10 and 11 in rotation. The abrasive strip 15 is then applied according to a generator of the contact wheel 13 to an area of the external surface 3 of the metal part so as to exert a force on it in a direction normal to this outer surface. This force is exerted by means of the cutting force cylinder 19. ^• The shoe 21 supports the metal part 1 directly above the polishing means 12 in a zone of the external surface symmetrical with the zone d application of the strip relative to the longitudinal axis 2. The metal part 1 generally does not have a perfect geometry, so that it has defects in shape such as ovalization, triangulation ... During conventional polishing using a fixed contact wheel, such defects cause variations in the depth of cut and the cutting force producing an irregular profile of the external surface. The consequence of such defects is to limit the rate of bearing length that can be obtained. When such faults are encountered during polishing with the device according to the invention, these faults exert a resistant force on the strip 15 and the contact wheel 13 tending to move them. The contact wheel 13 thus plays the role of a follower member of the external surface of the metal part. This results in a variation of the fluid pressure in the full section chamber of the cutting force cylinder 19. This pressure variation is immediately detected by the proportional regulator 20 which restores the initial pressure in the full section chamber of the cylinder 19 by exhaust or fueled ^¬, so that the cutting force exerted by it remains constant for the duration of polishing.

One could possibly plan to associate a regulation (not illustrated here) with the jack 17 associated with the roller 14, so that this jack 17 automatically compensates for the displacements of the contact wheel 13 so that the tension of the strip remains constant. This also makes it possible to ensure effective drive of the strip 15 by the contact wheel 13. The shoe 21, by supporting the external surface of the metal part 1, contributes to the constancy of the cutting force by forming a rigid element of feedback of this effort and limiting the deformations of the metal part 1 under the action of the polishing means. The external surface 3 of the metal part 1, once thus polished, can be covered with the coating layer 5.

The external surface 6 of the layer 5 must then in turn be polished in accordance with the polishing process according to the invention.

It is easily understood that the dimensions of the flattened convex arches and the periodicity of their succession can be modified by varying in particular the speed of advance of the metal part and its speed of rotation around the axis of the part. One can quite imagine that this variation is carried out during polishing so that the layer 5 has an external surface having different bearing length ratios.

Of course, the invention is not limited to the embodiment described and it is possible to make variant embodiments without departing from the scope of the invention as defined by the claims.

In particular, although the metal part has been described in relation to a subsequent use as a cylinder rod, its applications are not limited to this use.

In addition, although the polishing device has been described as comprising a proportional cutting force regulator detecting pressure variations, one could alternatively use a shape, optical or mechanical defect detector, disposed upstream of the means of polishing with reference to the direction of travel. The cutting force cylinder would then be connected to this detector by a servo link. Finally, the abrasive belt could be replaced by a grinding wheel whose axis is coupled to the rod of the cutting force cylinder.

Claims

1. A metal revolution part (1) having a longitudinal axis (2) and an outer surface (3), charac ^¬ See in that the outer surface (3) of the workpiece (1) has in axial section a general profile compound of a regular succession of flattened convex arches (4).

2. metallic part of revolution according to claim 1, characterized in that the external surface (3) of the metallic part (1) is covered with a layer of metallic coating (5) having an external surface (6) also having axial section a general profile composed of a regular succession of flattened convex arches (7).

3. metallic piece of revolution according to claim 1 or claim 2, characterized in that the shape of the arches (4, 7) and the periodicity of their succession are such that, for depths of cut (c) between 20% and 50%, the external surface has a bearing length ratio (Tp) of between 25% and 95%.

4. Metallic part of revolution according to claim 3, characterized in that the shape of the arches (4, 7) and the periodicity of their succession are such that, for a cutting depth (c) substantially equal to 40%, the surface external has a bearing length rate (Tp) of between 40% and 95%.

5. A method of polishing the external surface of a metallic piece of revolution which may have shape defects, comprising the steps of setting in motion the metallic piece (1) relative to a tool (15) and applying the tool (15) on an area of the external surface of this part so that it exerts a force on it, characterized in that the tool (15) is driven by a movement following the external surface of the metal part (1) in a radial direction essentially normal to it in the area of application of the tool, so that the force exerted by the tool (15) on the workpiece (1) remains constant throughout the duration of the polishing whatever the shape defects present on the surface, until a profile is obtained general in axial section in the form of a regular succession of flattened convex arches.

6. Polishing method according to claim 5, characterized in that the metal part (1) is supported perpendicular to the tool (15) in a region of the symmetrical external surface of the application area of the tool relative to the longitudinal axis of the metal part.

7. Device for implementing the method of polishing the external surface of a metal part according to claim 5 or claim 6, characterized in that it comprises means (10, 11) for supporting and setting in motion of the part (1) relative to a tool

(15), the tool (15) being mounted on a structure (13, 14) movable in a direction substantially normal to the external surface of the part (1) to be applied by an associated force cylinder (19) on said surface by exerting a force thereon, and a control means moves ^¬ of the movable structure (13, 14) depending on defects in shape of the workpiece surface (1).

8. Device according to claim 7, character ized in that the tool (15) consists essentially of an abrasive strip passing over a contact wheel (13) and a deflection roller (14) forming the movable structure on which is mounted said tool.

9. Device according to claim 8, character ized in that the axis (16) of the idler roller (14) is mounted to slide in a vertical plane by means of an associated jack (17) so as to constitute a tension roller.

10. Device according to one of claims 7 to 9, characterized in that a shoe (21) is arranged at the vertical alignment of the tool (15) to support the metal part (1) in a direction substantially normal to the external surface thereof.

11. Device according to claim 10, charac ^¬ terized in that it comprises means (22) for adjusting the position of the pad (21) in a direction substantially normal to the external surface of the part (1).