NEWS EDITION
S E P T E M B E R 20, 1935 Thursday, Friday,
October 10 October 11
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October 14
Wednesday, October 16 Thursday, October 17 Saturday, Monday,
October 19 October 21
Wednesday, October 23 Friday, Monday, Tuesday,
October 25 October 28 October 29
Colorado Section Sigma Xi, Lara mie, Wyo. Northwestern Utah Section Southern Califor nia Section California Section University of Ne vada Oregon Section Puget Sound Sec tion Washington-Id ah ο Border Section Montana Section Minnesota Section Northeast Wiscon sin Section
T h e t o u r was arranged by t h e secretary of t h e Local Section Officers group.
Silver Solders for Chemical Plant C. H . S. T u p h o l m e 6, H a m i l t o n G a r d e n s , N . W . 8, London, England N V I E W of t h e fact t h a t t h e price of silver has fallen t o an extent which m a k e s t h e metal a practical proposition for chemical plant, a n increasing n u m b e r of British chemical plant makers a r e a d o p t i n g silver solders for constructionT w o of the chief characteristics of silver solders are t h e relatively low t e m p e r a t u r e s a t which they melt, a n d their remarkable fluidity when molten. T h e melting points of t h e silver solders chiefly in use range from 670° to 850° C , whereas the melting points of the brazing brasses range from 870° to 1150° C. A fact which c o m m a n d s t h e closest a t t e n t i o n is t h e difference of approximately 200° C. which occurs be tween t h e lowest melting point of the silver solder group a n d the lowest melting point of t h e brazing brasses group, and t h e dif ference of 300° C. which occurs between t h e highest melting point of the two groups. T h e greater fusibility of t h e silver sol ders is not accompanied by a n y d i m i n u tion of those i m p o r t a n t properties on which t h e value of a t r u e solder depends a n d t h e use of silver solders is, therefore, specially recommended in all cases where t h e higher t e m p e r a t u r e s required to melt brazing brasses tend to produce " g r a i n g r o w t h " to t h e d e t r i m e n t of the m e t a l which is being jointed. T h e free-flowing a n d penetrating quali ties of silver solders greatly assist t h e production of strong, ductile joints. I n t h e cast condition t h e tensile strength of silver solders varies from a b o u t 15 t o 30 t o n s per square inch, mainly depending upon t h e constitution of t h e alloy. T h e s t r e n g t h of t h e joint, however, is also d e p e n d e n t upon m a n y variable factors, t h e effect of which can be accurately d e t e r mined only b y testing under actual w o r k ing conditions, which procedure is recom mended wherever possible. I t is generally acknowledged t h a t b y using t h e correct grade of silver solder with proper brazing technic, the resultant joint can frequently be m a d e equally strong a s t h e metal to which t h e solder is applied. Silver solders, being more malleable a n d ductile and having m u c h higher tensile strength than brazing brasses, will m a k e b e t t e r joints with greater resistance t o shock and vibration. These silver solders used in conjunction with brass, bronze, copper, nickel, a n d nickel alloys, such as monel, have been subjected to laboratory tests in dilute solutions of sulfuric, hydrochloric, a n d acetic acids, dilute ammonia, and 0.1 Ν salt solution. As a result of these t e s t s it
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has been shown t h a t silver solders are superior t o brazing brasses in their resistance t o corrosion—an i m p o r t a n t con sideration when corrosion-resistant metals a r e employed. This fact has led t o a m u c h 'wider application of silver solders in firstclass work. T h e physical properties of silver solders permit these alloys t o be produced in t h e form m o s t convenient for economical use in t h e workshop— t h e r e is no waste. W h e t h e r supplied in sheet, strip, wire, or filings, it is necessary t o use only t h e m i n i m u m q u a n t i t y of silver solder t o secure maximum strength a t t h e point of application. T h e flux usually employed with silver solders is borax, which melts readily and is perfectly fluid at 760° C ; it may be used as a s a t u r a t e d solution in water, or m a y be m a d e into a suitable paste by mixing with water or alcohol. Borax is eminently satisfactory for use with cop per, brass, a n d the various bronzes. In engineering practice a mixture of b o r a x a n d boric acid is sometimes pre ferred for iron, steel, nickel, a n d nickel alloys. T h e addition of boric acid t e n d s t o reduce t h e fluidity and swelling of t h e b o r a x a t t h e higher t e m p e r a t u r e required for t h e jointing of these metals. Special fluxes are supplied for use with stainless steel and other alloys containing c h r o m i u m . I n these instances t h e refrac t o r y oxides formed during the soldering operation are not readily dissolved in o r d i n a r y borax, and it is, therefore, im p o r t a n t to use the special mixtures recom m e n d e d to insure t h e proper wetting of t h e surface b y the solder. Silver solders find increasing applica tion for m a k i n g strong, ductile joints on brass of all compositions. In many cases silver solders have entirely superseded o r d i n a r y brazing alloys, especially where experience has shown t h a t damage d u e t o o v e r h e a t i n g t h e metal can be avoided b y using the correct grade of silver solder with a relatively low flow point. Copper is second only t o silver in h e a t conductivity, and although the relatively hi^h melting point of copper permits t h e use of all grades of silver solder, it is de sirable to use a high-grade solder with a low flow point in order to prevent deterio ration of t h e copper b y overheating. This precaution is doubly necessary when sec tions of t h i n tubing are involved. For this purpose an alloy with a flow point of 670° C. is eminently satisfactory. Highgrade silver solders a r e also recommended to p r o d u c e strong ductile joints on sheet, rod, or tube, where subsequent cold work is introduced. In all cases due care m u s t be exercised, both in the choice of solder and t h e control of t e m p e r a t u r e during t h e soldering operation, t o avoid local over h e a t i n g a n d consequent grain growth. T h e s e high-class engineering alloys h a v e wide application for a variety of industrial purposes, a n d a r e largely used where durability, strength, and corrosionresistance are the main considerations. Silver solders are also being used ex tensively in marine engineering. T u r b i n e manufacture, where great strength a n d resistance to corrosion are vital factors, is dependent upon silver solder for fixing t h e blades in position. Increasing instances of t h e application of silver solders a r e found in t h e manufacture of dyeing a n d bleaching machinery, hospital fittings, a n d other equipment where monel metal is employed. B y virtue of their high tensile strength and corrosion-resisting properties silver solders find increasing application with nickel a n d nickel alloys. One alloy is used extensively on nickel in t h e construc tion of dairy equipment a n d plant for t h e preparation of food products, where r e sistance t o corrosion is t h e important fac
377 tor. Other solders an» in increasing de m a n d for a wide variety of industrial pur poses where tensile strength is the main consideration. To insure perfect joints due care must be exercised to prevent oxidation of the m e t a l during the soldering operation. T h e successful jointing of cupronickel and nickel alloys of the monel metal type de pends on the careful control of the tem peratures during the brazing operation. These alloys should not be heated above 790° C , since higher temperatures tend to produce a coarse structure in the metal with consequent poor workini; properties. Silver solders of all grades are used ex tensively on t h e various qualities of nickel silver. Where applicable, high-grade silver solders are finding increasing favor for the various stainless steel alloys, the necessary control of temperature being more readily effected b y use of these jointing materials t h a n by ordinary brazing brass. T h e successful soldering of stainless steels (containing chromium in varying proportions) depends to a great extent on t h e a d e q u a t e protection of the surface dur ing t h e soldering operation. Careful regu lation of the t e m p e r a t u r e , which m u s t be maintained a s low as possible, is neces sary to p r e v e n t t h e formation of a refrac tory oxide. Silver solders are used extensively for m a k i n g strong, ductile joints on wrought iron, carbon, and mild steels, where strength and ductility a r e of p a r a m o u n t importance. T h e best known e x a m p l e of t h e application of silver solders to this p a r t i c u l a r range of alloys is the joining of steel b a n d saws, for which purpose silver solder is employed exclusively, in order to produce strong ductile joints, capable of w i t h s t a n d i n g the heavy stresses to which b a n d saws a r e subjected under ordinary working conditions. T h e introduction of a new brazing alloy known a s Sil-Fos containing silver, is claimed to insure greater efficiency and economy in many brazing and jointing operations. Sil-Fos is very free flowing, p e n e t r a t e s quickly a n d alloys with ad jacent metal, making strong, sound joints. Unlike ordinary brazing brasses, which melt a t temperatures ranging from 870° to 1150°, Sil-Fos melts readily a t 710° C. S o y B e a n A c r e a g e in U . S. T i m e s T h a t of 1907
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H E soy bean, brought here from the T Orient a n d improved year after year, has become a n i m p o r t a n t American crop. T h e acreage h a s increased from 50,000 acres in 1907 t o more than 5,000,000acres in 1935. T h i s year American farmers planted 5,463,000 acres for soy beans grown alone— almost a third more acreage t h a n in 1934. T h e r e was also a large acreage grown with corn and other crops for forage. The seed harvest in 1934 amounted to 17,762,000 bushels, which was about 6,000,000 bushels more than in 1933 seed yield. Soy bean growing h a s spread t o 27 States, and to determine which varieties are most suitable to varying climatic and soil conditions, the U. S. Department of Agriculture is continuing its experiments. A t o t a l of 6,906,000 bushels, or a b o u t 40 per cent of the 1934 seed crop, was used from October 1, 1934, t o June 30, 1935, in the manufacture of s o y bean oil and meal for making a variety of com mercial products. Chemists have found more t h a n 300 widely assorted uses for t h e soy bean. Factories in t h e United States used 20,907,000 pounds of soy bean oil in 1934. A b o u t half—10,451,000 pounds — w e n t into the making of paint and varnish.
