Patent Publication Number: US-5290627-A

Title: Friction material for operating in oil

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to friction materials utilized for wet brake, wet clutch, power shift clutch, power take-off clutch, transmission, etc. for industrial machine vehicles, construction machine vehicles and cars, which are excellent in the wear resistance particularly under the conditions of high-speed and high-pressure applied and in moisture-containing oil. 
     With conventional paper-like friction materials for operating in oil, the wear is significant under the conditions of high-speed and high-pressure applied and further chipping and peeling-off generate on braking, hence the limit of use conditions has been at low level. Moreover, even if they may be used without problems in a new oil at the beginning of use, a phenomenon of abnormally increased wear occurs when moisture is incorporated into oil due to some external reason, formation of dew, or the like. 
     As a result of extensive investigations in view of this situation, friction materials for operating in oil having excellent wear resistance under the conditions of high-speed and high-pressure applied and in moisture-containing oil have been developed by the invention. 
     SUMMARY OF THE INVENTION 
     One of the inventive paper-like friction materials for operating in oil is characterized by containing 5 to 70 wt. % of fibrillated ramie fibers with a freeness of 400 to 700 ml. 
     Moreover, other one of the inventive friction materials is characterized by containing 5 to 70 wt. % of fibrillated ramie fibers with a freeness of 400 to 700 ml and further containing cotton pulp and/or aramid fibers such as KEVLAR (E.I. Du-Pont). 
     DETAILED DESCRIPTION OF THE INVENTION 
     Since such fibrillated ramie fibers (hemp pulp) with a high value of freeness have characteristics of low contraction on drying and high tensile strength, a smooth product with low dimensional change, thus low strain on producing friction material can be obtained, with which the wear resistance is high and the chipping, peeling-off, etc. are hard to occur. 
     Moreover, since the tensile strength in water is superior to that of wood pulp or cotton pulp, the generation of abnormal wear when using particularly in moisture-containing oil can be prevented. 
     The freeness of fibrillated ramie fibers to be used is set on 400 to 700 ml as described above, but fibers adjusted to 500 to 600 ml are more preferable. 
     And, for the inventive friction materials, following formulating compositions are suitable. 
     
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Formulating composition                                                   
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Fibrillated ramie fibers                                                  
                      5-70 wt. %                                          
Cotton pulp           0-65 wt. %                                          
Friction dust         3-10 wt. %                                          
Rouge                 1-10 wt. %                                          
Graphite              1-10 wt. %                                          
Rubber latex          1-10 wt. %                                          
Diatomaceous earth    10-30 wt. %                                         
Aramid fibers         0-30 wt. %                                          
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     A paper-like sheet is made with such formulating composition. After liquid phenolic resin was impregnated into this sheet at a content of 20 to 30 wt. % and dried, the sheet is die-cut to a fixed ring shape. Then, this is thrown into a hot press mold and thermally molded for 2 minutes at a temperature of 170 ° C. and under a pressure of 150 kg/cm 2  to finish to a fixed thickness and density. Next, after the heat treatment for 2 hours at 160 ° C., said ring-shaped sheets are adhered onto both sides of steel plate and groove machining is made on inner faces of this steel plate to give a product of friction material. Besides, at this time, simultaneous implementation of simultaneous mold is more advantageous from the aspects of cost, adhesive strength and dimensional accuracy (variation in thickness). 
    
    
     In following, examples of the invention will be illustrated. 
     EXAMPLE 
     From the paper-like sheets with formulating proportions as shown in Table 1, the inventive friction materials and a comparative friction material were made according to the method aforementioned. 
     
                       TABLE 1                                                     
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              Inventive Inventive Comparative                             
Formulating component                                                     
              friction  friction  friction                                
(wt. %)       material 1                                                  
                        material 2                                        
                                  material 3                              
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Fibrillated ramie                                                         
              60        30        --                                      
fibers                                                                    
Cotton pulp   --        25        60                                      
Friction dust 5         5         5                                       
Rouge         5         5         5                                       
Graphite      3         3         3                                       
Rubber latex  2         2         2                                       
Diatomaceous earth                                                        
              25        25        25                                      
Kevlar (aramid fibers)                                                    
              --        5         --                                      
Resin content 25        25        25                                      
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     With two sheets of each said friction material, test of frictional performance was carried out with wet dynamometer (inertia type) using an oil: Transmission oil #80 (J-20A), oil temperature: 80° to 120° C. and mating friction material: AISI 1045 and further under conditions shown in Table 2, The results are put down in Table 2. 
     
                       TABLE 2                                                     
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              Inventive Inventive Comparative                             
              friction  friction  friction                                
Item          material 1                                                  
                        material 2                                        
                                  material 3                              
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Test conditions                                                           
Test size     173φ ×                                            
                        Same as   Same as                                 
              143φ ×                                            
                        left      left                                    
              4.7t                                                        
Inertial moment (kgms.sup.2)                                              
              0.3       Same as   Same as                                 
                        left      left                                    
Number of revolutions                                                     
              1800      Same as   Same as                                 
(rpm)                   left      left                                    
Pressure (kg/cm.sup.2)                                                    
              30        Same as   Same as                                 
                        left      left                                    
Test results                                                              
Incorporation level of                                                    
              0      1      0    1    0    1                              
water in oil (%)                                                          
Wear level after 1000                                                     
              0.02   0.02   0.02 0.03 0.06 0.13                           
brakings (mm)                                                             
Wear level after 10000                                                    
              0.07   0.08   0.08 0.10 --   --                             
brakings (mm)                                                             
Chipping and peeling-off                                                  
              No     No     No   No   Yes  Yes                            
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     According to Table 2, both of the inventive friction materials 1 and 2 show lower wear level and further less increase in wear level even when water is incorporated into oil, compared with comparative friction material 3 not containing fibrillated ramie fibers. In addition, with the inventive friction materials, no chipping and peeling-off generated. 
     As described, in accordance with the inventive friction materials, conspicuous effects are exerted in that excellent wear resistance can be obtained even under severe conditions of high-speed and high-pressure applied and further even in oil incorporated with water, and others.