Patent Publication Number: US-5298336-A

Title: Multilayer composite sliding material having excellent seizure resistance property

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a composite sliding material suitably applicable to a bush, a washer and the like in an automobile, an industrial machine, an agricultural machine and the like, and particularly to a composite sliding material having excellent seizure resistance property in a boundary lubrication state under severe lubrication conditions, as compared with conventional materials. 
     2. Description of the Related Art 
     A sintered copper alloy such as bronze, lead bronze, graphite-containing bronze or the like is mainly used for the bush, the washer or the like. Such an alloy exhibits the sliding ability in its own way under the conditions of use in which lubricant oil is present. 
     However, the alloy is particularly inferior in its seizure resistance property and thus does not exhibits a satisfactory sliding ability in a boundary lubrication region. 
     Although the bronze, lead bronze or graphite-containing bronze is generally widely used as a material having excellent seizure resistance property, there is a demand for a sliding material having more excellent seizure resistance property than that of a conventional material with a recent increase in the performance of an internal combustion engine. 
     SUMMARY OF THE INVENTION 
     The present invention has been designed under the above technical background, and a primary object of the present invention is to provide a sliding material in which the seizure resistance property under boundary lubrication conditions is improved. 
     In order to achieve the object, the present invention provides a multilayer composite sliding material with excellent seizure resistance property comprising a steel plate or a steel plate having surfaces plated with copper; a bond layer having a thickness of 0.05 to 0.5 mm, which is formed on the steel plate and made of a sintered powder material consisting of, by weight, 5 to 16% of tin, 0 to 15% of lead, 0 to 0.5% of phosphorus and balance essentially copper; and an alloy having a thickness of 0.1 to 1.0 mm, which is formed on the surface of the bond layer and made of a sintered powder material consisting of, by weight, 5 to 16% of tin, 1 to 12% of MoS 2  and balance essentially copper. 
     In a preferred form of the multilayer composite sliding material, the alloy layer may contain MoS 2  powder each particle of which is coated with copper or nickel. 
     In another preferred form of the multilayer composite sliding material, the alloy layer may contain not more than 20% of lead. 
     In a further preferred form of the multilayer composite sliding material, the alloy layer may contain not more than 1% of phosphorus. 
     In a still further preferred form of the multilayer composite sliding material, the alloy layer may contain 12% by weight or less of nickel. 
     A description will now be made of the reasons for limiting the composition of the sliding material and the function thereof. 
     (1) Tin: 5 to 16% by weight 
     Tin is alloyed with copper to increase the strength of the matrix. With less than 5%, the material has insufficient strength and poor wear resistance. With over 16% by weight, the alloy becomes brittle. 
     (2) MoS 2  : 1 to 12% by weight 
     MoS 2  functions as a component having the self lubricating ability in a state of metal contact wherein no lubricant oil film is formed. With less than 1%, the lubricating function is insufficient. With over 12%, the alloy strength significantly deteriorate. 
     (3) Lead: not more than 20% by weight 
     Lead functions as a soft component and has an effect on the lubricating ability, and when lubricant oil is present, lead functions as a component having good affinity for oil and has an effect on the lubricating ability. With over 20%, since the alloy strength deteriorates, the material is unsuitable as a sliding material. 
     (4) Phosphorus: not more than 1% by weight 
     Not more than 1% of phosphorus is added in order to improve the wear resistance and sintering property of the material. With over 1%, the toughness among the mechanical properties deteriorates. 
     (5) Nickel: not more than 12% 
     Nickel is contained in the alloy as a coating material for particles of the MoS 2  powder below, and can be added in an amount of 12% in accordance with the amount of MoS 2  added. It also dissolves in copper matrix and improves mechanical properties of the alloy. 
     The MoS 2  powder each paraticle of which is coated with copper or nickel is used in order to increase bonding strength of the sintered substance itself and causing MoS 2  particles to be uniformly dispersed in matrix of the sintered alloy layer. 
     (6) Bond layer 
     The bond layer improves bonding strength between the steel plate and the alloy layer. The bond layer preferably consists of 5 to 16% of tin, 0 to 15% of lead, 0 to 0.5% of phosphorus and balance essentially copper in order to provide the bond layer with higher strength than that of the alloy layer. 
     Although the thickness of the bond layer is preferably as small as possible, it is preferably 0.05 to 0.5 mm in light of a way of powder putting on the steel backing plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a graph showing results of a comparison seizure-test of the invention materials and conventional materials. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Experiment 
     (1) A copper alloy powder having a grain size of 100 μm and consisting of 11% of tin, 4% of lead, 0.3% of phosphorus and balance essentially copper was uniformly put on a steel plate (JIS SPCC) having a thickness of 1.00 mm, a width 120 mm and a copper plated layer of about 10 μm thick on the surface thereof. The alloy powder was then sintered by heating in an atmosphere of hydrogen in a furnace at 700° to 900° C. for 10 to 30 minutes to provide a bond layer. 
     Each of alloy powders shown in Table 1 was further uniformly put on the bond layer and was then sintered by heating in an atmosphere of hydrogen in a furnace at 700° to 900° C. for 10 to 30 minutes to obtain a composite material. The composite material was then rolled and subjected to re-sintering treatment by holding in an atmosphere of hydrogen at 700° to 900° C. for 10 to 30 minutes to obtain a material of the present invention (Samples No. 2 and 4). The bond layer had a thickness of 0.2 mm, and the alloy layer had a thickness of 0.5 mm. The mechanical properties of the composite sliding materials obtained are shown in Table 2, results of seizure tests are shown in FIG. 1, and test conditions are shown in Table 3. 
     (2) Sliding materials (Samples No. 1, 3 and 5 to 10) were obtained by the same method as that employed in above Experiment item 1 with the exception that MoS 2  powder, each particle of which was previously coated with copper by a conventional electroplating method and is shown in Table 1, was used. Similarly, MoS 2  powder each particle of which was previously coated with nickel was used to obtain a material of the present invention (Sample No. 11). 
     Mechanical properties of the materials obtained are shown in Table 2, results of the seizure test is shown in FIG. 1, and the test conditions are shown in Table 3. 
     (3) Comparative materials were formed by the following method: 
     Each of the alloy powders (grain size; 150 μm) shown in Table 1 was uniformly put on a steel plate (JIS SPCC) having a copper plated layer of about 10 μm thick on the surface thereof, a thickness of 1.2 mm and a width of 120 mm. The alloy powder was then sintered by heating in an atmosphere of hydrogen in a furnace at 700° to 900° C. for 10 to 30 minutes to obtain a composite material. The thus-obtained composite material was then rolled and subjected to re-sintering treatment under the same conditions as those of the above sintering to obtain conventional materials (Samples No. 12 to 14). The alloy layer had a thickness of 0.5 mm. Mechanical properties of the materials are shown in Table 2, results of the seizure test are shown in FIG. 1, and the test conditions are shown in Table 3. 
     Evaluation of Test Results 
     Sample No. 12 of a conventional material and Sample No. 9 of this invention material, both of which had a similar composition, were compared by the seizure test. The results of the test shown in FIG. 1 reveal that Sample No. 9 containing 8% of MoS 2  exhibits a maximum surface pressure without higher by 100 Kgf/cm 2  than that of Sample No. 12 and thus has excellent seizure resistance property. Comarison between conventional Sample No. 13 and invention Sample No. 10 reveals that the addition of 2% of MoS 2  increases the maximum surface pressure seizure of invention Sample No. 10 by 50 Kgf/cm 2  and improves the seizure resistance property. 
     As will be apparent from the above, the addition of MoS 2  to the copper alloy in the copper alloy layer of the multilayer composite sliding material of the present invention improves the seizure resistance property, as compared with conventional sintered alloys such as bronze, lead bronze, graphite-containing bronze and the like. 
     
                                           TABLE 1                                 
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    Example                                                               
         Chemical Composition (wt %)                                      
Type                                                                      
    No.  Cu   Sn Pb                                                       
                   Ni MoS.sub.2                                           
                          Cr                                              
                            P   Note                                      
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A   1    balance                                                          
              10 --                                                       
                   -- 4   --                                              
                            --  MoS.sub.2 with                            
                                Cu coating                                
    2    &#34;    10 --                                                       
                   -- 4   --                                              
                            --  MoS.sub.2 without                         
                                Cu coating                                
    3    &#34;     9 --                                                       
                   -- 8   --                                              
                            --  MoS.sub.2 with                            
                                Cu coating                                
    4    &#34;     9 --                                                       
                   -- 8   --                                              
                            --  MoS.sub.2 without                         
                                Cu coating                                
    5    &#34;     9 --                                                       
                   -- 12  --                                              
                            --  MoS.sub.2 with                            
                                Cu coating                                
    6    &#34;    10 --                                                       
                   -- 6   --                                              
                            0.2 MoS.sub.2 with                            
                                Cu coating                                
    7    &#34;    10 --                                                       
                   -- 12  --                                              
                            0.2 MoS.sub.2 with                            
                                Cu coating                                
    8    &#34;     9  4                                                       
                   -- 8   --                                              
                            0.2 MoS.sub.2 with                            
                                Cu coating                                
    9    &#34;    10 10                                                       
                   -- 8   --                                              
                            0.05                                          
                                MoS.sub.2 with                            
                                Cu coating                                
    10   &#34;     5 20                                                       
                   -- 2   --                                              
                            0.02                                          
                                MoS.sub.2 with                            
                                Cu coating                                
    11   &#34;     5 20                                                       
                   5  5   --                                              
                            --  MoS.sub.2 with                            
                                Ni coating                                
B   12   &#34;    10 10                                                       
                   -- --  --                                              
                            0.05                                          
                                no bond                                   
                                layer                                     
    13   &#34;     3 23                                                       
                   -- --  --                                              
                            0.02                                          
                                no bond                                   
                                layer                                     
    14   &#34;    10 --                                                       
                   -- --  4 --  no bond                                   
                                layer                                     
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 A: Invention Sample                                                      
 B: Conventional Sample                                                   
 
    
     
                       TABLE 2                                                     
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          Mechanical Properties                                           
                                  Bonding strength                        
                Hardness          between bond                            
                of alloy  Tensile layer and alloy                         
      Example   layer     strength                                        
                                  layer                                   
Type  No.       (Hv5)     (N/mm.sup.2)                                    
                                  (N/mm.sup.2)                            
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A     1         90        200     165                                     
      2         80        180     120                                     
      3         85        140     107                                     
      4         75        120     72                                      
      5         77         92     50                                      
      6         82        191     125                                     
      7         80        122     83                                      
      8         78         78     59                                      
      9         75         78     59                                      
      10        50         98     69                                      
      11        50         88     62                                      
B     12        73        235     176                                     
      13        48        137     108                                     
      14        57        108     88                                      
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 A: Invention Sample                                                      
 B: Conventional Sample                                                   
 
    
     Note: Since Samples No. 12 to 14 had no bond layer, the bonding strength is shown by a numerical value of bonding strength between the copper-plated steel plate and the alloy layer. 
     
                       TABLE 3                                                     
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Item           Conditions                                                 
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Bearing Size   Internal diameter 20 × width 20 ×              
               thickness 1.5 mm                                           
Revolution of Shaft                                                       
               1000 rpm                                                   
Peripheral Velocity                                                       
               2.0 m/sec                                                  
of Shaft                                                                  
Clearance      0.025-0.070 mm                                             
Lubricant oil  SAE #10                                                    
Oil Feed Rate  2 ml/min                                                   
Shaft Material JIS S55C                                                   
Shaft Surface  1.0 μm Rmax                                             
Roughness                                                                 
Shaft Hardness 670 Hv 10                                                  
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Evaluation Way                                                            
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When the back surface of the sample bearing is heated                     
to 100° C. of temperature by friction, the state is                
considered as seizure, and comparison is made on the                      
basis of load at seizure.                                                 
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