US2328933A

US2328933A - Salt bath

Info

Publication number: US2328933A
Application number: US420342A
Authority: US
Inventors: Johann S Streicher
Original assignee: American Platinum Works
Current assignee: American Platinum Works
Priority date: 1941-11-25
Filing date: 1941-11-25
Publication date: 1943-09-07
Anticipated expiration: 1960-09-07

Description

Patented Sept. 7, 1943 SALT BATH Johann S. Streicher, Newark, N. J., assignor to The American Platinum Works, Newark, N. J a corporation of New Jersey No Drawing. Application November 25, 1941,

Serial No. 420,342

2 Claims.

. This invention relates to salt bath furnaces and is directed particularly to an improvement in salt baths for salt bath furnaces and the annealing of metals therein.

Salt bath furnaces are used primarily. for the annealing of metals at elevated temperatures. Salt baths as heretofore known usually comprise mixtures embodying one or more of such ingredients as sodium chloride, potassium chloride, soda ash, potash, sodium nitrates, potassium nitrates, cyanides, etc. One well known salt bath comprises, for instance, a mixture of 50% potassium chloride and 5Q% sodium carbonate. Such salt baths produce, however, an alkaline reaction and tend to corrode metals to be annealed and to produce surface conditions on such metals which are detrimental to subsequent soldering or welding operations. Salt baths embodying cyanides produce highly, poisonous fumes and salt baths embodying nitrates and nitrites are highly oxidizing and have only invention to provide a.

develop poisonous fumes in use and which shall not be of oxidizing nature. It is another object of gmy invention to anneal metals in such salt bat i I have found that an excellent salt bath-for salt bath furnaces is produced by an aqueous mixture of boric acid 'and sodium fluoride in the proportions of 55% to 71% boric acid and 45% to 29% sodium fluoride. the mixture which'is exothermic, evolving considerable heat, and produces ahydrated polyboric acid compound, probably tetraboric acid and pentaboric acid, containing water as a constituent thereof. -The compound alsoseems to contain sodium fluoride as a constituent there-- of. When heated "the reacted mixture quickly loses any excess of water, but the water which is A reaction occurs in 40 not only metals as such but also alloys and other contained in the boric acid compoundas a conmass has a. high liquidity and fluidity, a factor of great importance in producing a successful operative salt bath for salt bath furnaces. Likewise, such mass has a low surface tension. The

lidify as a transparent glassy mass and do not.

have a definite melting point.

In the salt bath according to my invention there is produced a weak acid reaction, rather than an alkaline reaction as heretofore, and no corrosion of metals takes place during the annealing. The liquid salt bath according to my invention also has an excellent cleaning effect upon the material annealed therein. Harmful alkaline films are entirely. eliminated and no poisonous fumes are developed. In view of the high liquidity and fluidity of my salt bath mechanical losses in using such bath are kept at a.

minimum. Oxidation or other contamination of the object being annealed is prevented due to the nature of my salt bath composition.

My. salt baths can beutilized in the annealing of ferrous as well as non-ferrous metals and metal compositions and-is suitable for the annealing of brass, copper, aluminum, steel, stainless steel, and other metals of base metal nature as well as in the annealing of precious metals such as silver, gold, platinum, etc. The object to be annealed in my salt baths may be in the form of sheet, wire or any other suitable shape; The

saltbath furnace, containing the molten salt bath according to this invention, may be-operated electrically or-may be fuel fired.

The term metal? as ,herein used shall, include metal compositions or combinations, and the term annealing shall also include any other form of heat treatment.

The hydrated complex polyboric acid compound salt bath is best produced by'flrst mixing together, preferably in a mortar or grinding machine, the sodium ,fluoride'and boric acid in the specified proportions and then. adding the proper amount of water. Thus about 35 to" cc. water may be added to 100 grams mixture according to my invention of sodium fluoride and boric acid to result in the desired hydration. Since boric acid -does not readily wet water, there may be added to. the water a trace of wetting agent. The

liquid crystallizes while evolving heat to result in a hard mass which is then ground into a thin paste. The mass may also be produced by dissolving sodium fluoride in hot water and then adding boric acid, the hydrated complex polyboric acid compound crystallizing after cooling. For

instance, a mixture of commercial boric acid,

dehydrated commercial sodium fluoride, and 750 cc. water containing a trace of Lamepon A as wetting agent, is finely. ground until the mass is transformed into a thick gray liquid which on standing turns itself by crystallization into a white mass which is thenthoroughly ground and thereby transformed into a smooth paste.

The salt bath for salt bath furnaces, according to my invention, may also be produced by ing said metal in a molten salt bath consisting of the reaction product of a mixture of 55% to 71% boric acid and 29% to 45% sodium fluoride.

JOHANN S. STREICHER.