446 BELL SYSTEM TECHNICAL JOURNAL 



by powder methods for use as thermocouple elements^. When these are 

 used with nickel wire as the second element, the couples can operate at 

 temperatures up to 1300° (Ni-Mo) and 1400° C. (Ni-W). Ease of prep- 

 aration and not reproducibility of composition was probably the main 

 factor in the fabrication of these two types of thermocouple elements since 

 the compositions reported are in the range where relatively large changes 

 in composition produce little variation in thermoelectric voltage. 



10. Parts for Ordnance 



As has already been mentioned, many powder metal parts are being 

 manufactured for use in equipment of the Armed Services, and, while in 

 some instances the parts are made by powder methods only because of 

 expedience, it should be noted that, in all cases definite specifications must 

 be met before acceptance, and a powder metal part that does not meet 

 the rigid requirements has no more chance of acceptance than has an 

 inferior part made by other methods. 



Among the parts which have been successfully produced are copper and 

 brass rotating bands for projectiles^®. While the cost of the powder 

 metal bands is greater than that of bands made in the normal manner 

 from copper or brass tubing, they compare favorably in actual performance 

 in firing tests both as to behavior on the projectile and wear on the gun 

 barrel. 



Improvement of the strength of porous metal bearings has been a factor 

 in their adoption for use in anti-aircraft guns where they may operate under 

 severe conditions. It has been reported that 100 parts are thus utilized 

 in a single gun installation^^ 



Another item reported to be in production is an iron powder part of an 

 elevating hand mechanism for both the .30 and .50 cahber anti-aircraft 

 machine guns'®. KnurUng of the outer surface of the ring part and the 

 marking off of degrees are performed on the part in a coining blow. 



11. Sintered Iron Parts 



Prior to the wartime demands for sintered iron parts, there had been 

 developed a fairly extensive field for peacetime uses particularly in the 

 automotive industry. Bearings had been manufactured for some time and, 

 following this, production had extended to the fabrication of oil pump 

 gears, door catches, cams, and other parts where very high strength is 

 not essential. In general, these sintered iron parts have mechanical prop- 

 erties similar to those of cast iron, but considerable range in properties 

 may be obtained by proper selection of raw material and treatment. Grad- 



