Spectacle frames made of NI alloy
BACKGROUND OF THE INVENTION 
     The invention is directed to the use of nickel alloys for spectacle frames and other spectacle parts. 
     Spectacle frames and spectacle parts are prepared and frequently prepared from metals or metal alloys. Thereby, there are used chiefly copper alloys, such as, e.g., tin bronze (CuSn 6, CuSn 8), copper bronze (Cu 82 Ni 2 Sn 5, Zn 11) and German silver or nickel alloys, which alloys are characterized by good workability but have a high susceptability to corrosion so that the spectacle parts made of these materials must be provided with coatings of nobler metals or alloys. However, the use of such clad metals is unsatisfactory since even the smallest pores in the coating of the carrier material permit corrosion and spectacles in use are subject to an abrasive wear, which after some time exposes the non-noble carrier materials. 
     Recently, there have been proposed for spectacle parts nickel-chromium and nickel-chromium-silver alloys (German OS No. 3045334), which are characterized by a good resistance to corrosion but have workability problems. Thus, e.g., a nickel alloy containing 10-15% chromium has only poor machinability since it is inclined to weld to the tool. The machinability can be improved by the addition of about 1% silver to the nickel-chromium but this is purchased at a higher material cost and a difficult working technique. 
     The non-machining shaping with these materials also is difficult since both types of materials (Ni-Cr, Ni-Cr-Ag) show a very steep work hardening characteristic with increasing degree of deformation and thus must be annealed repeatedly. Besides the shaping can be carried out only with special rolls and special drawing nozzles. 
     Alloys which exhibit good resistance to corrosion and good working properties are mentioned in German patent 3340054. They contain as the chief components nickel, copper, and zinc. Because of their high melting points of over 1300° C. and the content of 8-25% of easily vaporizable zinc, the production of these alloys is difficult. 
     Therefore, it was the problem of the present invention to develop nickel alloys for spectacle frames and other spectacle parts, e.g., hinges and screws, which besides good resistance to corrosion and good workability also present the possibility of being produced in a simple manner. 
     SUMMARY OF THE INVENTION 
     This problem was solved according to the invention by using nickel alloys which besides nickel contain as the remainder 5 to 20% copper, 2 to 6% aluminum, 0 to 1% beryllium, and 0 to 0.5% carbon. 
     Preferably, the alloys contain 9 to 14% copper and 2.5 to 5% aluminum. 
     The nickel-copper-aluminum alloys have a very good resistance to corrosion and a very good processability. The optional additives of beryllium and carbon improve the elastic properties of the alloys and cause a displacement of the recrystallization temperature to higher temperatures. 
     The omission of zinc makes the production of these alloys free from problem. 
     The Al content of 0 to 4% mentioned as an additive to nickel-copper-zinc alloys in German patent 3340054 causes an improvement in the elastic properties, but it does not increase the resistance to corrosion of the basic alloy nickel-copper-zinc. 
     However, unexpectedly for the zinc-free alloys in the system nickel-copper aluminum, there is formed an increase in the corrosion resistance with the content of aluminum. Especially at aluminum contents of 2.5 to 5% there are obtained good to very good corrosion resistances. 
    
    
     In the table there are set forth the properties of several known spectacle materials (Examples 4-6) and several alloys according to the invention (Examples 1 to 3). 
     
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                         Stiffening With Cold Forming                     
       Composition (Wt. %)                                                
                         (Hardness Vickers)                               
Example No.                                                               
       Ni Cu Al                                                           
               Additional Material                                        
                         Soft                                             
                            40% Deformation                               
                                     80% Deformation                      
                                              Means of Fabrication        
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1      84.4                                                               
          11.3                                                            
             4.3                                                          
               --        115                                              
                            235      270      meltable in vacuum          
2      84.4                                                               
          11.2                                                            
             4.2                                                          
                0.1 Be   125                                              
                            245      285      meltable in vacuum          
3      85 11.1                                                            
             3.8                                                          
                0.1 C    140                                              
                            265      310      meltable in vacuum          
4      78.5                                                               
          10.6                                                            
             --                                                           
               10.9 Zn   103                                              
                            210      245      only meltable with          
5      78.3                                                               
          10.5                                                            
             0.4                                                          
               10.8 Zn   113                                              
                            220      250      high pressure melting       
6      78.3                                                               
          10.6                                                            
             --                                                           
               10.9 Zn   118                                              
                            230      265      equipment                   
                0.2 Be                                                    
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     The entire disclosure of German priority application No. P3500554.8 is hereby incorporated by reference.