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214 trol exercised by an experienced and in- formed personnel throughout the dif- ferent stages, are all of utmost import- ance in the production of tubing of the highest quality to obviate any difficulties _ from splitting, corrosion, and_ pitting. MARINE REVIEW Though more expensive, the best qual- ity of condenser tubing is decidedly the more economical for the hard service of marine use, corrosion particularly quick- ly affecting condenser tubing in this field. The recurring expense due to de- June, 1923 lay, labor, and new tubes, in retubing condensers .where tubes have failed, and of equal importance the service trou- bles resulting from leaky tubes, cer- tainly makes it imperative to seek the best quality condenser tubes obtainable. Rakes Made by Cupping Process MANUFACTURING establish- ment,’ the Scovill Mfg. Co., Waterbury, Conn., founded 121 years ago, is applying to the fullest extent its own long experience in the making of brass products and_ the latest researches of science to the mak- ing of condenser tubes. A thorough study of condenser tube failures was made to avoid mistakes of the past. The microscope is an important fea- ture in the modern method of studying metal failures and as an indicator of proper proportions of the metals in an alloy and the treatment in the processes of manufacture. The surface of the specimen to be inspected or micrographed is highly polished with the finest polish- ing material obtainable and is then treat- ed with a corrosive chemical in order to cut away the surface layer and to reveal its structure. Every change in property of an alloy or metal is accom- panied by a corresponding change in microstructure. The use of the mi- croscope for a proper knowledge of the condition of any metal or alloy, is, there- fore, of prime importance. One view on page 212 shows hard rolled brass worked cold and not heated; another, the same material heated to a moderately high temperature, while a_ third shows complete recrystallization and coarse grain resulting from a bright red heat. Another shows the microstructure of cup drawn admiralty condenser tubing. Uniform recrystallization and extreme- ly fine grain is evident. Failures of Condenser Tubes Splitting or cracking of tubes in a longitudinal direction, known as_ season cracks, and corrosion or pitting are the usual causes for failure of condenser tubes. Taking these in order, season cracks are directly due to improper mill methods in the manufacture of the tubes. Cold working of the metal in the proc- ess of manufacture sets up excessive un- ‘balanced internal strains which cause fine intercrystallization cracks resulting ulti- mately in a split tube. Proper heat treatment after each process in the cold working will definitely overcome this difficulty. Impurities in, small amounts if introduced during melting will some- times segregate in such a way as to cause fracture. An excessive amount of gas is sometimes retained in an alloy during melting and gas pockets are formed which will make trouble later. Corrosion or pitting is in a sense de- cay, nature’s effort to reduce the con- stituents of the alloy into their natural forms, that is into metallic salts or oxides. This tendency is stronger in some alloys than in others and _ conse- quently, to resist corrosion, different al- loys have been tried out. For salt water conditions the admiralty mixture is the best. Using the best alloy, care should be taken to avoid the introduction of dross and dirt and unsoundness in the melting of the metal, and proper treat- ment should be given to produce a fine uniform grain structure. To conform with the recommendations above for superior results, the actual process of manufacture is of great im- portance. At the Scovill plant, the manufacture of seamless tubing requires a complete unit consisting of an up-to- date casting shop, a fully equipped roll- ing mill, powerful cupping and drawing presses, as well as the regular tube mill equipment. Of all alloys developed and proved up to this time, the admiralty mixture (copper 70 per cent, zinc 29 per cent and tin 1 per cent) has proved the best. Great,care is taken to use only the purest materials and the pro- portions are carefully determined by weight. In melting, precautions are taken to prevent an excessive absorption of gases and the loss of too much zinc by vola- tilization. The cast bars are trimmed to remove any unsound metal. Samples from each heat are analyzed for cop- per, lead, tin and iron. Lead and iron exist as impurities and must be kept down to a minimum. Only the metal that conforms to specifications is used. After having milled the surfaces of the cast bars they are rolled to size and cut into large disks. The disks are inspected on flat surfaces and _ edges and are then cupped on a press. The cupping operation is itself a severe test and only sound metal will draw into perfect cups. If the metal is imperfect, the bottom of the cups will show checked or will break through. The interior of the tube by this process is just as clean and smooth as the outside and the gage is uniform. Annealed by heating to a red_ heat to remove the hardness induced by cold working, the process of redrawing is continued’ to a point where a_ great length of cup is produced. The cup is then completed on the draw bench. Every annealing operation is carefully con- trolled by indicating and recording py- rometers and at regular intervals, samples are examined under the microscope to check up the heat treatments. The hard drawn tubes are finally heat treated to produce a fine uniform grain. Finished tubes are straightened, cut to length, in- spected inside and outside and gaged for size and uniformity of thickness. A hydrostatic test of 1000 pounds and an air pressure of 80 pounds is applied to each tube. Compression and flattening tests are also made. The fine, dense structure, and the fact that the metal is in itself. uniform throughout is sought to insure the great- est resistance to corrosion. The tube has rigidity but at the same time is so ductile that it can be flattened upon itself without cracking. It will stand a great degree of expansion and can be twisted without showing strain. The method seeks to eliminate season crack- ing through obtaining a high degree of elasticity and freedom from drawing strain. Extrusion Process Special muntz tubing is manufactured with the same care but by entirely dif- ferent processes. A large billet is cast and trimmed to remove casting de- fects. Sections are cut off and heated to redness and by means of a hydraulic press are extruded .through a die into the form of rods. After inspection, these rods are cut to length and are again heated red hot and then pierced . on a machine, and so made into heavy gaged shells which are then drawn down into tube sizes on the regular draw bench. The double hot working treat- ments are said to impart exceptional physical properties, refining the struc- ture and making it more dense. Fine uniform grain structure nearly identical: with that for the admiralty tubing is ob- tained. ° All physical tests as required for admiralty condenser tubes by the United States navy can readily be met by this special muntz. It has high resist- ance to corrosion but does not equal the admiralty alloy in this respect.