Patent Publication Number: US-2022220999-A1

Title: Guiding Member, Mechanical System Comprising Such A Guiding Member, And Method For Producing Such A Guiding Member

Description:
TECHNICAL FIELD 
     The present invention relates to a guiding member, a mechanical system comprising such a guiding member, and a method for producing such a guiding member. 
     The field of the invention is that of mechanical systems operating in oscillation, translation or rotation under high loads and subjected to impacts in an abrasive environment. 
     PRIOR ART 
     Conventionally, such a system comprises a guiding member and a mobile element, as described in document WO 2006087498. 
     By way of example, the system can form a joint for a public work or mining machine, of an agricultural vehicle, of an industrial machine, etc. 
     The rings made of bronze, of composite material or of polymer material have the advantage, when they are subjected to high loads, of being able to accommodate to the geometry of the shaft and thus to reduce normal pressures. The reduction of the factor p.V (product of the diametral pressure p in N/mm 2  and the circumferential speed V in m/s) then leads to a reduction in the wear of the ring. 
     However, their low surface hardness results in a low resistance to abrasive wear. 
     As a result, for applications subjected to high loads and to high abrasion, it is customary to use steels with high mechanical properties (Re&gt;800 MPa) and high hardnesses. These steels are heat-treated and have a bainitic or martensitic structure. 
     However, because of their significant mechanical properties, these rings cannot accommodate bending of axes. This leads to very high localised p.V factors, and therefore to wear and then to jamming. 
     DESCRIPTION OF THE INVENTION 
     The aim of the present invention is to propose an improved guiding member which overcomes the above disadvantages. 
     To this end, the invention relates to a guiding member, comprising a body provided with a bore for mounting a mobile element, the body being made of a metallic material, characterised in that the bore has a surface layer treated against jamming over a diffusion depth of less than or equal to 0.6 mm, the surface layer having a hardness of greater than or equal to 500 Hv1 over a depth of between 5 and 50 μm. 
     Thus, the invention makes it possible to obtain a high performance guiding member in the scope of applications under high loads and impacts in an abrasive environment, with an excellent compromise between resistance to jamming, abrasion resistance and accommodation. The guiding member has high performances, usually obtained with much more expensive categories of steels, as well as longer and deeper surface treatments. The proposed solution is more competitive, with an improved performance/price ratio. 
     According to other advantageous characteristics of the invention, taken individually or in combination:
         The metallic material is a ferrous metal material.   The metallic material is selected from structural steels or low alloy steels.   The metallic material of the body has a yield strength Re of between 200 and 600 MPa.   The metallic material has a yield strength Re of between 300 and 600 MPa.   The metallic material has a yield strength Re of between 400 and 500 MPa.   The surface layer is treated against jamming over a diffusion depth less than or equal to 0.3 mm.   The surface layer has a hardness greater than or equal to 500 Hv1 over a depth of between 25 and 50 μm.   The surface layer has a hardness greater than or equal to 550 Hv1 over a depth of between 5 and 50 μm.   The surface layer has a hardness greater than or equal to 550 Hv1 over a depth of between 25 and 50 μm.       

     The invention also relates to a mechanical system, comprising a guiding member according to one of the preceding claims, and a mobile element arranged in the bore of this guiding member. 
     The invention also relates to a method for producing a guiding member such as described above, said guiding member comprising a body provided with a bore for mounting a mobile element, the method being characterised in that it comprises the following successive steps:
         producing the body from a metallic material;   carrying out a surface treatment of the bore in order to protect the guiding member against jamming, the surface treatment affecting a surface layer of the bore over a diffusion depth less than or equal to 0.6 mm, the surface layer having, after the surface treatment, a hardness greater than or equal to 550 Hv1 over a depth of between 5 and 50 μm.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood from the following description which is given solely by way of non-limiting example and is made with reference to the appended drawings, wherein: 
         FIG. 1  is a longitudinal cross-section of a mechanised system according to the invention, comprising a guiding member according to the invention, and a mobile element. 
         FIG. 2  is an enlarged view of detail II in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 and 2  show a mechanical system  1  according to the invention, comprising a ring  10  according to the invention, and a shaft  20  arranged in the ring  10  along a longitudinal axis X1. 
     The system  1  is designed to withstand high loads and/or impacts in an abrasive environment. The system  1  constitutes, for example, a joint for a public work or mining machine, an agricultural vehicle, an industrial machine for the steel industry, etc. 
     The ring  10  comprises a body  12  and a bore  14  with a cylindrical profile formed in the body  12 . The bore  14  is provided to receive the shaft  20 , mobile in rotation about the axis X1 and/or in translation along the axis X1, according to a continuous or reciprocating movement. The ring  10  constitutes a member for guiding the shaft  20  in rotation and/or translation. 
     The friction interface between the ring  10  and the shaft  20 , more specifically between the bore  14  and the outer surface of the shaft  20 , is preferably lubricated. The bore  14  can be smooth or comprise cavities acting as a lubricant reserve, as described in documents EP 0987456 and WO 2006087498. 
     The body  12  is made of a metallic material having a yield strength Re of between 200 and 600M Pa. Advantageously, the metallic material can be chosen from structural steels or low-alloy steels (comprising at least 95% of iron and carbon). This greatly reduces the cost of producing the ring  10 , while providing several advantages, detailed below. The metallic material has a yield strength Re preferably of between 300 and 600 MPa and even more preferably of between 400 and 500 MPa. 
     By way of non-limiting examples, the material of the body  12  can be chosen from the following metallic materials: 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Tensile yield strength 
                   
               
               
                 Standardised shade 
                 Re (in PMa) 
                 Category 
               
               
                   
               
             
            
               
                 S235 
                 235 
                 Steel for general use 
               
               
                 S335 
                 335 
                 Steel for general use 
               
               
                 E295 
                 295 
                 Machine construction steel 
               
               
                 S355 
                 355 
                 Machine construction steel 
               
               
                 34CrMo4 
                 450 to 600 
                 Low-alloy steel 
               
               
                   
               
            
           
         
       
     
     According to the invention, the bore  14  has a surface layer  16  treated against jamming over a diffusion depth P16 of less than or equal to 0.3 mm. The surface layer  16  has a hardness of greater than or equal to 500 Hv1 over a depth P18 of between 10 and 50 μm. The hardness can be between 500 and 650 Hv1, being preferably greater than 550 Hv1. The depth P18 is preferably between 20 μm and 50 μm. For example, the diffusion depth P16 of the anti-jamming surface treatment applied to the bore  14  can be 0.2 mm, with a hardness equal to 600 Hv1 over a depth P18 of 30 μm. The depths P16 and P18 are not to scale in  FIG. 2  with a view to simplification. 
     Preferably, the anti-jamming treatment is nitriding. 
     If the hardened depth P18 is too low (&lt;10 μm), the wear endurance is too low. If the depth P18 is too great (&gt;50 μm), the surface layer  16  becomes fragile and less resilient, and therefore subject to flaking, and has a smaller capacity for accommodation. 
     The diffusion depth P16 of the anti-jamming surface treatment is limited to 0.3 mm in order to preserve the properties of maximum accommodation. The surface treatment will thus have the advantage of not flaking when it is subjected to compressions of at least 4%. 
     Preferably, the surface layer  16  has a hardness greater than or equal to 500 Hv1, more preferably greater than or equal to 550 Hv1, over a depth P18 of between 25 and 50 μm. A depth of at least 25 μm makes it possible to further increase the service life of the guiding member, by increasing the wear endurance. 
     According to a particular embodiment, the surface layer  16  treated against jamming comprises a combination layer (also called the white layer) at depth P18, and a diffusion layer at depth P16. 
     Preferably, the surface layer  16  treated against jamming also comprises an intermediate layer, located between the combination layer and the diffusion layer. 
     The intermediate layer is preferably located at a depth of between 20 and 50 μm, and more preferably between 25 and 50 μm. A depth P18 of at least 25 μm extends the service life of the intermediate layer, and therefore that of the guiding element as well, by increasing the wear resistance. A depth of 50 μm or less increases the resilience of the intermediate layer, and thus that of the guiding element, improves the accommodation capacity, and limits flaking. 
     The intermediate layer has a hardness greater than or equal to 500 Hv1, preferably greater than or equal to 550 Hv1, over a depth P18 of between 20 and 50 μm, preferably between 25 and 50 μm. 
     The intermediate layer is formed during the treatment against jamming, in particular by nitriding or carbonitriding, when said treatment is carried out at high temperature, i.e. a temperature greater than or equal to 592° C. 
     The temperature of 592° C. delimits the ferritic phase of the austenitic phase in the iron-nitrogen diagram. Above 592° C., a γN phase (nitrogen-enriched austenite) is formed, which corresponds to the intermediate layer described above. 
     Following a post-treatment of the bore  14 , it is possible to check the hardness of the intermediate layer. With a high temperature post-treatment, it is possible to obtain an intermediate layer of high hardness, while with a lower temperature treatment, it is possible to obtain an intermediate layer of lower hardness. Examples of post-treatment which could be used are oxidation, for example by baths of molten salts between 350° C. and 500° C., gas oxidation between 350° C. and 500° C., or oxidation in a brine at boiling point between 120° C. and 160° C. 
     As the metallic materials collapse when they are subjected to loads above their yield strengths, once the accommodation has been carried out, the load resistance of the mechanically stressed zones will be greater. 
     Compared with rings made of metallic materials having significant mechanical properties (Re&gt;600 MPa), the use of a ring  10  made of metallic material having less significant mechanical properties (Re&lt;600 MPa) makes it possible to reduce the normal pressure at the interface between the ring  10  and the shaft  20  by accommodating their facing surfaces, and therefore to reduce the factor p.V, and therefore to reduce wear within the mechanical system  1 . 
     The surface treatment follows the accommodation of the material and provides a high surface hardness, making it possible to have a good abrasion resistance and a jamming resistance. 
     Unexpectedly, the mechanical system  1  is finally more efficient with the ring  10  according to the invention made of material Re&lt;600 MPa than with a ring made of material Re&gt;MPa. 
     Compared with the rings made of composite materials and polymer materials, the ring  10  has better load resistance following work hardening of the surface layer, and better abrasion resistance due to the surface hardness of the surface layer  16  subjected to the surface treatment. 
     Compared with the bronze (125&lt;Re&lt;175 MPa), brass (Re≈180 MPa) and cupro-aluminium rings, the ring  10  has a better abrasion resistance. 
     Compared with the rings made of steel hardened in the mass or superficially (high-frequency induction soaking, cementation), the ring  10  has better resistance to jamming and better capacity to accommodate the load. 
     Compared with the rings having a hard anti-jamming coating applied in the bore (thermal spraying, PVD, chemical Ni, hard Cr, etc.), requiring a material having significant mechanical properties (Re&gt;600 MPa) in order to avoid flaking of the coating subjected to abrasion and to impacts, the ring  10  may be made of a metallic material having less significant mechanical properties (Re&lt;600 MPa), which provides the various advantages presented above. 
     A comparative test is carried out using two mechanical systems, comprising a ring and a shaft that can rotate in the ring for 1000 hours. 
     When the ring is made of steel with Re&gt;600 MPa, the accommodation is insufficient, the loads are poorly distributed, the factor p.V is high at the locations where the loads are maximum, leading to significant wear of the shaft. 
     When the ring  10  is in accordance with the invention, with Re&lt;600 MPa and anti-jamming surface treatment, the accommodation is satisfactory, the loads are better distributed, the factor p.V is limited, and it can be seen that the wear of the shaft  20  is much less than in the case above. 
     It is sought to characterise the ring  10  more specifically by making a cross-section of the body  12  in a radial plane. This makes it possible to show the work hardening of the ring  10  and an increase in its mechanical characteristics. The body  12  has undergone a deformation of 3%, i.e. the diameter of the bore  14  has increased by 3%. The hardness of the body  12 , measured at 0.6 mm from the surface of the deformed bore  14 , goes to 295 Hv0.1 against 265 Hv0.1 before the test, i.e. a tensile yield strength Re going from 850 MPa to 950 MPa. 
     Moreover, the mechanical system  1  may be shaped differently from  FIGS. 1 and 2  without moving away from the scope of the invention. 
     In a variant that is not shown, the system  1  can comprise a guiding member  10  that is different from a ring. 
     According to another variant (not shown), the system  1  can comprise an element  20  different from a shaft, this element  20  being mobile in the member  10  in rotation about the axis X1 and/or in translation along the axis X1. 
     According to another variant (not shown), the member  10  can comprise several bores  14  having a surface layer  16  according to the invention. 
     Furthermore, the technical characteristics of the various embodiments and variants mentioned above can be combined in their entirety or only in part. Thus, the mechanical system  1  and the guiding member  10  can be adapted in terms of cost, functionalities and performance.