Fillerless welded chain
FIELD OF THE INVENTION 
     This invention relates to a roller chain and in particular to an improved roller chain having substantially increased tensile and fatigue strength created by connecting the individual link plates to the respective bushes by means of a fillerless fusion weld created by electron beam or laser welding. 
     BACKGROUND OF THE INVENTION 
     Conventional steel roller and conveyor-chains are made by alternately joining together an inner link subassembly comprising an inner link plate and a bush pressed therein and an outer link subassembly comprising an outer link plate and a pin pressed therein. When these chains are subjected to tensile load, bending and shearing stresses are exerted on the pin and bush, while tensile stress is applied on the link plates. Particularly, the perforated portion of the link plates where the pin or bush is inserted yields under such tensile stress, thereby giving rise to plastic deformation. Because of this, the engaging force between the outer link plate and the pin and the inner link plate and the bush is reduced, and engagement therebetween is liable to be loosened. Such reduction in engaging force and loose engagement lower the durability of the chain and cause such damages as fatigue and wear rupture of the link plates, pin and bush. To improve the fatigue strength (dynamic strength) of a chain, the following mechanical measures are generally taken: 
     1. Improvement of paralleledness and machining accuracy of the perforated portion of the link plate. 
     2. Chamfering of the hole in the link plate. 
     3. Increase of engaging force between the link plate and the pin or bush through the increase of interference therebetween. 
     4. Pre-exertion of residual compressive stress on the perforated portion of the link plate. 
     Despite the adoption of these methods, the dynamic performance of the chain is reduced in actual use by the loosening of engagement under the influence of thermal stress occurring under the actual operating condition, atmosphere in use, suitability of machine work, and other factors. Therefore, these are not the perfect measures to improve fatigue strength. 
     In an effort to improve the dynamic strength of conventional steel roller chains, the link plates have often been welded to the respective pins and bushes by welding techniques utilizing a filler material, such as the well-known arc-welding technique. However, the resulting chains produced using filler-type welds between the link plates and the respective pins or bushes have not provided any significant increase in the strength and durability of the chain, particularly as regards the dynamic or fatigue strength characteristics. 
     Accordingly, the object of the present invention is to provide a substantially improved roller chain which utilizes a fillerless fusion weld between the link plate and the respective pins or bushes, which fillerless weld results in the chain having substantially increased dynamic strength characteristics. 
     Specifically, the present invention proposes to render the inner link plates and the bushes, and the outer link plates and the pins, into a complete integral body by welding their total engaged surfaces together by means of a precision welding technique, specifically electron beam welding, or laser welding, thereby providing a fillerless fusion weld along the total engaged surfaces of the respective elements while producing extremely little deformation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view illustrating three links of a chain constructed according to the present invention. 
     FIG. 2 is a cross-section view taken along the line II--II of FIG. 1. 
     FIG. 3 is a fragmentary cross-sectional view illustrating an arc-welded inner link assembly which was utilized for experimental test purposes. 
     FIG. 4 is a fragmentary cross-sectional view illustrating an electron-beam welded inner link assembly according to the present invention, as used for experimental test purposes. 
     FIG. 5 is a fragmentary cross-sectional view of an electron-beam welded outer link assembly according to the present invention, as utilized for experimental tests. 
     FIG. 6 is a perspective view of an arc-welded inner link assembly prior to experimental testing. 
     FIG. 7 is a perspective view of an electron beam welded inner link assembly according to the present invention, prior to experimental testing thereof. 
     FIG. 8 is a side view illustrating the electron beam weld created between the bush and pin and the respective link plates, in accordance with the present invention. 
     FIG. 9 illustrates four chain samples which were experimentally tested, Chain No. 1 being a conventional engaged-type chain, Chain No. 2 being an arc-welded chain, and Chain No. 3 and 4 being electron beam welded chains according to the present invention. 
     FIG. 10 is a side view of the engaged type chain (Chain No. 1) illustrating the fracture which occurred in the bush link plates when the chain was experimentally subjected to tensile testing. 
     FIG. 11 is a perspective view of the arc-welded chain (Chain No. 2) and illustrating the fracture which occurred in the bush link plates after subjecting the chain to experimental tensile testing. 
     FIG. 12 is a perspective view of an electron beam welded (Chain No. 3) and illustrating the fracture which occurred in the pin link plate upon subjecting the chain to experimental tensile testing. 
     FIG. 13 is a perspective view of an electron beam welded chain (Chain No. 4) and illustrating the fracture which occurred in one of the pins upon subject the chain to experimental tensile testing. 
     FIG. 14 is a further perspective view of the chain illustrated in FIG. 13 but with one of the pin side plates removed to more clearly illustrate the fracture of the pin. 
     FIG. 15 is a plot illustrating the experimental tensile rupture strength versus the chain pitch. 
     FIG. 16 is a plot illustrating the experimental chain fatigue strength versus chain pitch. 
     FIG. 17 is a plot illustrating the conventional fatigue characteristic curve of an electron beam welded chain (Chain No. 4) according to the present invention in contrast to an arc-welded chain. 
     FIG. 18 is a plot illustrating the relationship between the mean static tensile rupture strength versus the fatigue limit for the different types and sizes of chains. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1 and 2, reference numerals 1 through 4 designate an outer link plate, an inner link plate, a pin and a bush, respectively. The entire circumference of a portion at which said outer link plate 1 and pin 3 are engaged with each other is precision welded, as shown by A and A&#39;, and the same is the case with the engaged portion of said inner link plate 2 and bush 4, as shown by B and B&#39;. However, the pin 3 and the bush 4 are not necessarily welded at both ends. Instead they may be welded at only one end, with the other end being left just engaged so far as suitable arrangements are furnished to keep a balance between the welded and the engaged portions. Otherwise, either of said pins 3 or bushes 4 may be welded, with the remainder being just engaged. 
     Welding is performed from outside the link plate. The weld must be as thick as or thicker than the full thickness of the link plate, so that the entire engaged surface (both axially and circumferentially) of the engaged portions are perfectly joined by a fillerless fusion weld. With respect to such welding of the engaged portions of the inner and outer links, the problem of welding depth at the engaged portions and the heat treatment specifications for the part thus welded requires particular attention from a performance viewpoint. As machined parts (that is pins, bushes and link plates) are assembled into inner and outer link subassemblies. Then said link subassemblies are combined into one piece by welding the entire circumference of the engaged portions by a precision welding method. After this, heat treatment (such as hardening, tempering or isothermal transformation heat treatment) is given to improve the welded structure. By this means, the most stabilized quality and other excellent characteristics are obtained. 
     According to this invention, the outer link plates and the pins, and the inner link plates and the bushes, are perfectly fixed at both ends instead of being simply supported at both ends. The result is that both the inner and outer links are imparted with higher rigidity, provided with greater effective cross-sectional area at their ring-shaped portion, and kept free from loose engagement. By the accumulation of such effects, the static and dynamic strength of the chain is increased remarkably. In the case of bushed chains with the engaged portion of their inner link plates and bushes being electron beam welded, the static tensile rupture strength and fatigue strength are from 1.42 and 1.95 times greater than those of unwelded chains. With electron beam welded bushed chains are made up of link plates, bushes and pins, the inside and outside diameters of a bush and the diameter of a pin can be increased to a suitable extent as compared with ordinary roller chains of the same chain pitch, resulting in greater static tensile rupture strength and fatigue strength (up to about twice as great). This makes it possible to design a compact chain transmission system. 
     With regard to wear life, the possibility to increase the radius of curvature of the contact surface of the pin and bush results in increasing effective bearing area and decreasing surface pressure. This improves the bearing performance, which in turn improves the wear life of the chain. With the conventional chains comprising the combination of the inner link plate and the bush and the outer link plate and the pin, there is a general tendency to attempt to improve their durability by increasing the engaging force by increasing the interference therebetween. This however deforms the inside of the bush. To be more precise, the inside of the bush becomes barrel-shaped on engagement with the link plate, and this tendency to deformation increases with increasing interference. This reduces its contact with the pin to a linear contact only at both ends, thereby rendering it impossible to make effective use of the bearing area. This results in an increase in the initial wear elongation of the chain. 
     On the other hand, with the electron beam welded chains of the present invention, the inner link plate and the bush are engaged with each other by light interference fit or some other means like that. As compared with the engaged-type chains having bushes of the same inside diameter and pins of the same outside diameter, the inside of the electron beam welded chain bush is much less liable to become barrel-shaped. Besides, welding strain also is very limited. All this makes the effective bearing area large. Consequently, the electron beam welded chains suffer from little initial wear elongation, and therefore acquire greatly extended service life. 
     Finally, corrosion, heat (characteristics at high temperature) and atmosphere resistance of the electron beam welded chains of the present invention will be discussed. Corrosion, oxidation and stress corrosion cracking of the engaged portions under various atmospheres, creep rupture of the link plate starting from the engaged portions at high temperatures, reduction in durability of the chain due to relaxation of stress etc., and rupture of the chain, which are commonly the case with the conventional steel-made engaged-type chains, are reduced. In addition, this invention permits integral combination of different materials best suited to the intended application and the condition of use. For these reasons, the above-mentioned resistances are greatly improved. All this makes the electron beam welded chains suitable to such applications where low speed and large load are involved, where heat and corrosion resistance are needed, where water treatment is intended, and where durability and resistance to various atmospheres are required. Furthermore, the chains can be made more compact. They are also applicable as offset and other similar chains. 
     Referring again to FIGS. 1 and 2, the inner link subassembly which is formed by the two bushes 4 and the two inner side plates 2 are welded into one piece, with the fillerless welds B and B&#39; extending throughout the complete width of the side plates 2 so as to create the desired joining of the bushes and side plates throughout the complete engaging areas thereof. This results in a maximum joining between the individual pieces due to the use of electron beam welding. 
     In a similar manner, the outer link subassembly is formed into one piece by welding the two pins 3 to the two outer side plates 1 so as to create the fillerless welding regions A and A&#39;. These welding regions extend throughout the complete width of the side plates 1 so as to optimize both the engaging and the welded area between the plates and the pins. 
     As illustrated in FIG. 2, the use of electron beam welding for joining the bushes and pins to the respective link plates permits the use of link plates which are substantially flat and of substantially uniform thickness. Further, use of electron beam welding permits the ends of the pins and bushes to terminate substantially flush with the outer surfaces of the respective link plates, and the weld areas themselves terminate substantially flush with the outer surfaces of the link plates. 
     The substantial and unexpected improvement in both the static and dynamic strength, that is tensile and fatigue strength, which results from using electron beam welding for forming a chain according to the present invention, in contrast to the much lower static and dynamic strength which exists in conventional engaged type chains and arc-welded chains, will now be explained in detail with reference to accompanying Tables I and II and in conjunction with FIGS. 3-18. These tables and figures graphically depict and illustrate a lengthy and complex experimental evaluation which was conducted on the present invention. 
     A number of different chain samples were both statically and dynamically tested to demonstrate the substantial improvement in both the tensile and fatigue strengths which result when a roller chain is electron beam welded according to the present invention. The first chain sample designated No. 1 comprises a conventional engaged-type chain, whereas the second chain sample designated No. 2 involves an arc-welded chain wherein the bushes were connected to the respective side plates by a conventional filler-type weld. The third sample designated No. 3 utilized electron beam welding according to the present invention, which electron beam welding, existed at all of the connections between the bushes and respective side plates, and some of the connections between the pins and respective side plates. Sample No. 4 was also an electron beam welded chain according to the present invention and represents a desirable embodiment, and in the sample the bushes were all electron beam welded to the respective side plates. Samples No. 3 and 4, since they both utilize electron beam welding, but were of slightly different welded structure in terms of the actual welding connections involved, have been referred to as the A-type and B-type chains, respectively. 
     Referring to Table I, same presents therein a listing of the dimensions and heat treatment specifications of the individual parts for the chain samples No. 1-4. All of the chain samples were of the same size, that is a chain pitch of 50.80 mm (equivalent to A.N.S.I. designation No. 160), and all chain samples were of high strength steel. 
     FIGS. 3-5 illustrate therein the specific configuration used for the samples according to the experimental test program. FIG. 3 specifically illustrates therein the structure of the arc-welded bush link subassembly incorporated into sample No. 2, whereas FIG. 4 illustrates the electron beam welded bush link subassembly as incorporated into samples 3 and 4. FIG. 5 illustrates the electron beam welded pin link subassembly as incorporated into Sample No. 3. 
     FIGS. 6 and 7 are comparative photographic representations of the appearance and shape of the bush link subassembly produced by arc welding and electron beam welding, respectively. As is readily apparent from these illustrations, the electron beam welded bush link subassembly (FIG. 7) of the present invention (which bush link subassembly corresponds to both A-type and B-type chains) has a substantially greater commercial value than the arc-welded bush link subassembly of FIG. 6, since the electron beam welded bush link subassembly has substantially improved accuracy and higher quality workmanship. 
     FIG. 8 is a photographic representation of the appearance and shape of the electron beam welded bush link subassembly and pin link subassembly according to sample No. 3 (A-type), and again illustrates the substantially improved accuracy and workmanship which results from using electron beam welding. 
     Referring now to Table II, same lists therein the details of the test procedures and also the results of the breaking experiments performed on chain samples No. 1-4 as listed in Table I. 
     Table II compares the mean value of the tensile rupture strength for the different chain samples. The arc-welded chain (sample No. 2) showed a rupture strength 1.24 times greater than that of the No. 1 chain, with rupture in the arc-welded chain occurring in the welded portion of the bush link subassembly. In contrast, the B-type chain (sample No. 4) according to the present invention had a rupture strength which was 1.63 times greater than the rupture strength of the No. 1 chain. Thus, the B-type chain of the present invention showed a 63 percent increase in tensile strength in comparison to a conventional engaged type chain (sample No. 1), whereas the B-type chains of the present invention also showed a 31 percent increase in tensile rupture strength in contrast to an arc-welded chain (sample No. 2). The electron beam welded chain, and specifically the B-type chain, thus exhibited a rather large increase in strength. Further, in the B-type chain (sample No. 4), the rupture did not occur at the bush link subassembly, such as in the engaged and arc-welded samples, but rather the rupture in the B-type chain occurred due to a failure of one of the pins. This thus indicates that the weakness of the engaged-type and arc-welded chains, which weakness occurs in the bush link assembly, has been totally overcome when utilizing an electron beam welded B-type chain of the present invention since the failure now occurs in a totally different element, namely the pin. Since the pin itself can be provided with greater strength if desired by appropriate material selection and/or heat treatment, it thus becomes apparent that a chain utilizing electron beam welding according to the present invention (such as a B-type chain) can thus be provided with even greater rupture strength if desired. Further, in the B-type chain sample, the thickness of the pin link plate was slightly greater than the thickness of the bush link plates in order to balance the strength of the individual parts. 
     Referring to FIG. 10, same is a photograph of the No. 1 chain after rupture thereof during experimental tensile testing thereof. This photograph illustrates that the rupture occurs in the link plates associated with the bush link subassembly. In a similar manner, FIG. 11 is a photograph of the arc-welded chain (sample No. 2) after same had been ruptured during tensile rupture testing. FIG. 11 illustrates that the arc-welded chain, like the engaged chain, ruptures due to a failure in the vicinity of the weld between the bush and the respective link plates. 
     On the other hand, FIGS. 13 and 14 are photographs of chain sample No. 4 (the B-type chain) which was constructed utilizing electron beam welding according to the present invention. FIGS. 13 and 14 indicate that the rupture in this chain sample occurred due to a shear fracture of one of the pins. No failure or noticeable weakness is exhibited adjacent any of the welded connections in the bush link subassembly. 
     FIG. 12 is a photograph of sample No. 3 (A-type) and illustrates that the rupture in this case took place in one of the link plates associated with the pin link subassembly, and specifically the rupture occurred in the region between the link plate and pin which were engaged but not welded together. 
     Thus, as is believed apparent from the above discussion with reference to the accompanying figures, causing each of the bush link and pin link subassemblies to be formed into an integral one-piece body by fusing their total engaged surfaces together by a precision welding method, such as electron beam welding, drastically increases the tensile strength of a chain made up of such parts. 
     Referring to FIG. 15, same is a graphical comparison, based on the experimental values, of the relationship between the chain pitch and the mean tensile rupture strengths for a B-type chain according to the present invention and a conventional engaged-type roller chain conforming to the A.N.S.I. standards. As understood from this comparison, the rupture strength of a B-type chain is comparable to that of a roller chain which is two sizes larger. 
     FIG. 16 comprises, based on experimental values, the relationships between the chain pitch and the fatigue limit for a B-type chain according to the present invention and a conventional engaged-type roller chain. As is evidence from this figure, the fatigue limit of the B-type chain is comparable to that of a roller chain which is three or four sizes larger. 
     FIG. 17 illustrates the characteristic fatigue curve (normally referred to as an S-N curve) for the B-type chain of the present invention and an arc-welded chain of the same size. The curves in FIG. 17 are plotted based on experimental results. As the curves of FIG. 17 illustrate, the fatigue limit for a B-type chain according to the present invention is more than two times greater than that of an arc-welded chain of the same size. 
     FIG. 17 also indicates that the B-type chain of the present invention results in a greatly increased life in comparison to an arc-welded chain of the same size when operating within the low-cycle fatigue limit. For example, as noted in FIG. 17, when an arc-welded chain is operated repetitively under a load of 10,000 kilograms, it will have a life of 10 4   cycles prior to fatigue failure. On the other hand, the same size B-type chain when operating repetitively under a load of 10,000 kilograms will have a life of 5 × 10 5  cycles prior to fatigue failure. The fatigue life of the B-type chain of the present invention, in contrast to the same sized arc-welded chain, is thus approximately 50 times of the arc-welded chain when operating within the low-cycle fatigue limit. Needless to say, this represents a very substantial and unexpected improvement when operating under conditions of this type. 
     Referring now to FIG. 18, same compares the relationships between the rupture strengths and the fatigue strengths (or the fatigue limit) for the B-type chain of the present invention and a conventional engaged-type roller chain conforming to the A.N.S.I. standards. This figure also illustrates thereon the relationship of the tested arc-welded chain in contrast to the tested samples of the engaged-type and B-type chains. 
     As FIG. 18 indicates, the tensile rupture strength of the arc-welded chain (size No. 160) is comparable to that of a B-type chain which is one size smaller (Size. No. 140 having a chain pitch of 44.45 mm). Further, the fatigue limit of the arc-welded chain of Size No. 160 is comparable to the fatigue limit of a B-type chain of Size No. 100 (chain pitch = 31.75 mm), which B-type chain is three sizes smaller than the arc-welded chain. 
     Thus, compared with an arc-welded chain of the same size, the B-type chain according to the present invention results in an increase in the rupture strength of greater than 30 percent and results in a fatigue limit which is more than two times greater than that of the same size arc-welded chain. 
     In a similar manner, when comparing the B-type chain of the present invention to a conventional engaged-type roller chain, the B-type chain of the present invention results in a rupture strength comparable to that of a roller chain which is two sizes larger and the B-type chain results in a fatigue limit which is comparable to that of a roller chain which is three to four sizes larger. 
     While the experimental comparison set forth above could have been extended to chains having the bushes and/or pins braised to the link plates, nevertheless such tests were not conducted since it is well known that such braised connections are obviously inferior in strength to the connections produced utilizing arc-welding. Further, high frequency welding techniques are disadvantageous since they result in undesirable defects, such as excessive deformation of the chain. 
     Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention. 
     
                                           Table I                                 
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DIMENSIONS AND HEAT TREATMENT OF INDIVIDUAL PARTS OF CHAINS TESTED        
                 No. 1      No. 2      No. 3       No. 4                  
                 Engaged-type                                             
                            Arc-Welded Chain                              
                                       Electron Beam Welded               
                                                   Electron Beam Welded   
                 Chain                 Chain       Chain                  
                                       A-Type      B-Type                 
__________________________________________________________________________
Chain Pitch      50.80      50.80      50.80       50.80                  
      Pin Diameter                                                        
                 16.70      16.70      16.70       16.70                  
      Bush Outside                                                        
                 28.58      28.58      28.58       28.58                  
Dimension                                                                 
      Diameter                                                            
of    Pin  Thickness                                                      
                 6.4        6.4        6.4         8.0                    
      Link                                                                
Parts Plate                                                               
           Width 41.6       48.2       48.2        48.2                   
(mm)  Bush Thickness                                                      
                 6.4        6.4        6.4         6.4                    
      Link                                                                
      Plate                                                               
           Width 48.2       48.2       48.2        48.2                   
      Bush Link In-                                                       
                 31.75      31.75      31.75       31.75                  
      side Width                                                          
Material                                                                  
        Pin      SAE 4340   SAE 4340   SAE 4340    SAE 4340               
of      Bush     SAE 4135   SAE 4135   SAE 4135    SAE 4135               
Parts Pin Link Plate                                                      
                 SAE 4135   SAE 4135   SAE 4135    SAE 4135               
      Bush Link Plate                                                     
                 SAE 4135   SAE 4135   SAE 4135    SAE 4135               
           Harden-                                                        
                 860°C-20 minutes                                  
                            860°C-20 minutes                       
                                       860°C-20 minutes            
                                                   860°C-20        
                                                   minutes                
           ing   Oil Quenched                                             
                            Oil Quenched                                  
                                       Oil Quenched                       
                                                   Oil Quenched           
      Pin                                                                 
           Temper-                                                        
                 200°C-180 minutes                                 
                            200°C-180 minutes                      
                                       200°C-180                   
                                                   200°C-180       
                                                   minutes                
           ing   Air Cooled Air Cooled Air Cooled  Air Cooled             
           Harden-                                                        
                 870°C-20 minutes                                  
                                       870°C-20 minutes            
           ing   Oil Quenched          Oil Quenched                       
      Bush                                                                
           Temper-                                                        
                 430°C-180 minutes                                 
                                       200°C-180 minutes           
Welding    ing   Air Cooled            Air Cooled                         
           Harden-                                                        
                 870°C-20 minutes                                  
                            870°C-20 minutes                       
                                       870°C-20 minutes            
                                                   870°C-20        
                                                   minutes                
and   Pin  ing   Oil Quenched                                             
                            Oil Quenched                                  
                                       Oil Quenched                       
                                                   Oil Quenched           
      Link Temper-                                                        
                 430°C-180 minutes                                 
                            430°C-180 minutes                      
                                       430°C-180                   
                                                   430°C-180       
                                                   minutes                
Heat  Plate                                                               
           ing   Air Cooled Air Cooled Air Cooled  Air Cooled             
Treatment                                                                 
           Harden-                                                        
                 870°-20 minutes                                   
                                       870°C-20 minutes            
of    Bush ing   Oil Quenched          Oil Quenched                       
      Link Temper-                                                        
                 430°C-180 minutes                                 
                                       430°C-180 minutes           
Parts Plate                                                               
           ing   Air Cooled            Air Cooled                         
                                       After assembling pins              
                                       and pin link plates                
                                       into a pin-link sub-               
      Bush                             assembly, following                
                                       the above heat treat-              
           Weld-                       ments, the entire                  
      Link ing                         portions where the                 
      Plate                            pins and pin link                  
                                       plates were engaged                
      Sub-                             were fused together                
      assembly                         by electron-beam-                  
                                       welding.                           
           Temper-                     200°C-180 minutes           
           ing                         Air Cooled (to re-                 
           After                       move welding strain                
           Welding                                                        
                            After assembling                              
                                       After assembling                   
                                                   After assembling       
                            edge-prepared bushes                          
                                       bushes and bush link               
                                                   bushes and bush link   
                            and bush link plates                          
                                       plates into a bush-                
                                                   plates into a bush-    
                            into a bush-link sub-                         
                                       link subassembly,                  
                                                   link subassembly, the  
                            assembly, all of the                          
                                       following the above                
                                                   entire portions where  
      Bush                  edge-prepared port-                           
                                       heat treatments,                   
                                                   the bushes and bush    
           Welding          ions were arc-welded,                         
                                       entire portions                    
                                                   link plates were en-   
      Link                  using Type MA-96                              
                                       where the bushes                   
                                                   gaged were fused to-   
                            welding rod for SAE                           
                                       and bush link plates               
                                                   gether by electron-    
Welding                                                                   
      Plate                 4135 made by Kobe                             
                                       were engaged were                  
                                                   beam-welding to make   
                            Steel, Ltd.                                   
                                       fused together by                  
                                                   a one-piece bush       
                                                   link.                  
and   Sub-                             electron-beam-                     
                                                   Welding depth          
                                                   ≧Bush           
      assem-                           welding. Welding                   
                                                   link plate thickness.  
Heat  bly                              depth = Bush link                  
                                       plate thickness.                   
Treat-     Harden-          870°C-30 minutes                       
                                                   870°C-30        
                                                   minutes                
ment       ing after        Oil quenched           Oil Quenched           
of         welding                                                        
           Tempering        430°C-180 minutes                      
                                       200°C-180                   
                                                   430°C-180       
                                                   minutes                
Parts      after            Air Cooled Air Cooled (to re-                 
                                                   Air Cooled             
           welding                     move welding strain)               
      Pin        Rc 52-54   Rc 52-53   Rc 52-53    Rc 52-53               
Hardness                                                                  
of    Bush       Rc 42-43   Rc 42-43   Rc 50-51    Rc 42-43               
Parts Pin Link Plate                                                      
                 HB 388˜401                                         
                            HB 388˜401                              
                                       HB 388˜401                   
                                                   HB 388˜401       
      Bush Link Plate                                                     
                 HB 388˜401                                         
                            HB 388˜401                              
                                       HB 388˜401                   
                                                   HB 388˜401       
__________________________________________________________________________
 ##SPC1##
 
    
     
         __________________________________________________________________________
             1 28,200    35,000     42,500     46,300                     
             2 28,400    35,300     42,500     46,400                     
     Experimental                                                         
             3 28,600    35,500     42,600     46,500                     
Tensile                                                                   
     Valves  4 28,700    35,600     42,800     46,500                     
Rupture      5 28,700    35,800     43,100     46,800                     
Strength                                                                  
     Statistical                                                          
             x 28,520    35,440     42,700     46,500                     
(Kg) Valves  R 500       800        600        500                        
             σ                                                      
               194       273        255        167                        
               All in the per-                                            
                         All in the welded                                
                                    All in the perfor-                    
     Breaking  forated portion                                            
                         portion of the bush-                             
                                    ated portion in the                   
               of the bush link                                           
                         link subassembly,                                
                                    pin link plate, but                   
     Position  plate (See FIG.                                            
                         but closer to the                                
                                    closer to where the                   
                                               The pin (See FIGS.         
               10)       perforated portion                               
                                    pin is engaged (see                   
                                               13 and 14).                
                         of the bush link                                 
                                    FIG. 12).                             
                         plate (see FIG. 11).                             
                                    12).                                  
     Compared with                                                        
Mean Claim No. 1                                                          
               1.00      1.24       1.50       1.63                       
     Compared with                                                        
Strength                                                                  
     Claim No. 2                                                          
               0.80      1.00       1.20       1.31                       
     Compared with                                                        
Ratio                                                                     
     Claim No. 3                                                          
               0.67      0.83       1.00       1.09                       
     Compared with                                                        
     Claim No. 4                                                          
               0.61      0.76       0.92       1.00                       
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