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     Heat Treatment Salt Bath Image credit: Wallwork HT

 

Heat Treatment Salts

 

Hubbard-Hall manufactures molten heat treatment or heat treating salts to serve both the metal treating and rubber curing industries. These molten salts are manufactured using raw materials with the highest purity. Hubbard-Hall's molten heat treat salts are found widely used in the treatment of metal for the following purposes: hardening, annealing, tempering and isothermal quenching.

 

Hardening and quenching in molten salt baths offer the following benefits over other hardening and quenching methods:

  • Requires less floor space
  • Faster heating cycles
  • Scale free parts
  • No pitting
  • Reduced part distortion
  • Elimination of quench cracks
  • Easily washed 

How Heat Treatment Salts Work

 

Heat treatment salts are melted in a salt bath furnace or system to form a molten salt bath. Parts are dipped into the molten salt to clean, descale, anneal, temper, quench, cure, nitride, carburize, carbonitride, case harden or coat. Operating temperatures or working temperature ranges of molten salt baths range from under 200 to over 2000° F. Some heat treatment salts are used inside sealed pack, which are then heated in a furnace to perform a pack carburizing process. The large mass of the molten salt provides a very uniform heat source, which assures parts are exposed to the same thermal profile within a batch or across a large part. Molten salts are also useful in removing oxides and scales from metal without attacking the base metal, which allows molten descaling salt baths to replace dangerous mineral acid solutions in some applications.

 

An animated look at heat treatment salt cleaning.

 

               Desludging a black oxide bath Video credit: Heatbath Corp.

 

Heat Treatment Salts' Components

 

Heat Treatment salts are made of inorganic compounds such as blends of several different salts to provide the desired melting point and working range and chemical characteristics. For example, potassium nitrate and sodium nitrate salts are used in aluminum solution treating. Cyanide salts are used in carburizing, casing or case hardening. Neutral salts usually consist of a blend of chlorides and/or carbonates for use in steel annealing, austenitizing, hardening, tempering and brazing. Molten salts for descaling have high alkalinity. Oxidizing molten salts are used for stripping or removal of coatings, lubricants, polymer layers and other organics.

 

Choosing Heat Treatment Salts

 

Heat treatment salts are selected based on their working temperature range and melting point as well as the specific process for which the salt composition has been designed. For this process, a production or metallurgical engineer specifying the product will make his/her selection based on the thermal processing equipment in their plant or plant designs.

 

Neutral Salts

Designed to provide excellent fluidity and great stability, Hubbard-Hall's neutral heat treatment salts are formulated with a balanced mixture of chlorides. The neutral salts highlighted in this section include only one non-barium product (neutral salt B). Selection of neutral salts is generally based on operating range.

 

Quenching and Tempering Salts

This line of heat treatment salts is composed of nitrate-nitrite salts for use as steel tempering or quenching media. All are completely water soluble, easily washed and have similar high-transfer rates and heat capacity.

 

Rubber Curing Salts

Rubber curing heat treatment salts are a high purity, eutectic mixture of nitrate and nitrite salts. They are formulated specifically for curing extruded rubber profiles at the lowest possible temperature ranges. All chemicals used in these rubber curing salts are water-soluble and do not form any insolubles. Therefore, the solidified salt is easily removed from the surface in a hot water spray rinsing station at the end of the trough just after emerging from the salt trough.

 

Solution Heat Treating/Annealing of Aluminum

Molten heat treatment salts provide the high degree of temperature uniformity required for the satisfactory heat treatment of aluminum alloys. Hubbard-Hall's aluminum heat treatment salts are free flowing and high purity products.

 

Descaling Salts

Molten descaling salts can be used to remove oxide scales from both ferrous and non-ferrous metals. Molten descaling salts have the ability to produce clean scale free surfaces that are free of base metal loss, pitting or etching.

 

Common Heat Treatment Salt Types

  • Annealing Salt
  • Black Oxide Salt
  • Brazing Salt/Braze Aid
  • Carbonitriding Salt
  • Carburizing Salt
  • Cleaning Salt
  • Coating/Deposition Salt
  • Descaling Salt
  • Heat Transfer Salt
  • Lubricant/Coating Removal Salt
  • Neutral Salt
  • Nitriding Salt
  • Pack Carburizing/Treatment
  • Quench and Temper Salt
  • Rubber Cure Salt
  • Smelting/Alloying Salt (Floating Covers)
  • Soldering Salt
  • Solution Treating Salt
  • Stripping Salt

Hubbard-Hall Heat Treatment Salts Melting Points

 

Type Product Melting Point Working Range
Neutral Salt Neutral Salt B 1200º F  1300º - 1700º F
Hardening Neutral Salt C 850º F  950º - 1600º F
  Neutral Salt H 1200º F  1300º - 1900º F
  Neutral Salt HH 1600 º F  1700º - 2400º F
Tempering Quick Cure 275 275º F  300º - 1000º F
Rubber Curing Quick Cure 300 310 º F  380º - 1000º F
  Quick Cure 420 420º F  500º - 1100º F
Austempering Quick Cure 275 75º F   300º - 1000º F
Martemping & Isothermal Quenching Quick Cure 420 420º F  500º - 1100º F
Solution Heat Annealing of Aluminum Quick Cure 420 420º F  500º - 1100º F
Descaling of Titanium Quick Descale TI    

                                           Table credit: Hubbard-Hall

 

 Heat Treating Products

 

Aluminum Salt Bath Brazing Heatbath®/Park Metallurgical aluminum brazing salts offer outstanding characteristics such as superior fluidity, high stability, ease of cleaning and minimal sludge.
Aluminum Solution Heat Treating Aluminum solution treating is commonly conducted in molten nitrate baths in the 850-1050 deg F range. Maintenance of neutrality to avoid attack on aluminum is critical. Heatbath®/Park Metallurgical nitrate salts are formulated for maximum purity and neutrality for use in aluminum solution treating.
Carbon Products Heatbath®/Park Metallurgical carbon products are used primarily as floating covers and as neutral packing media for annealing tool steels.
Carburizing Uniform carbon case depths, ranging from a few thousandths to over 0.100 inches, are produced rapidly and economically by Heatbath®/Park Metallurgical's carburizing products. Our product line is the industry's most complete and diverse. These standard industry products are designed for deep and shallow case and high and low dragout operations. Plus, these easy maintenance salts provide for high quality, uniform shop production.
Also, there are the carbon-atmosphere-producing liquids using the drip method in place of the expensive and high maintenance endothermic and exothermic atmosphere producing generators for atmosphere carburizing.
Cleaning and Descaling Salts This family of compounds covers the full range of any heat treater's cleaning and descaling needs.
High Speed Hardening Salts For hardening all types of high speed steels (HSS) including molybdenum, molybdenum-tungsten and cobalt. Large numbers of tools may be safely hardened in a comparatively short time with a high speed steel salt bath set-up. These salts are designed for the proper heat treatment of HSS by balancing the composition in such a way as to insure as neutral a bath as practical, minimize dragout or carry-over and promote easy cleaning. HSS tools can be treated rapidly and uniformly without oxidation, decarburization or pitting. Accurate and uniform temperature control is possible and distortion is reduced to a minimum. #90 Casing Salt is available for casing HSS tools to prolong their life and improve their cutting ability.
Liquid Nitriding Very hard and wear resistant surfaces are produced on a wide variety of steels and cast irons. The relatively low temperatures used permit casing of previously hardened steels or cast irons with little or no loss of core hardness and minimum dimensional change.
Neutral Salts Neutral Salts are balanced mixtures of chlorides designed to provide neutrality, excellent fluidity and great stability. Their melting points and working ranges have been designed to furnish neutral salt baths for heat treating from 850-2400 deg F.
Pack Carburizing Compounds One of the oldest heat treating processes, pack carburizing, is still used because it requires relatively simple and inexpensive equipment. It can be used in either batch or continuous type furnaces to produce deep cases both efficiently and economically. Parts are surrounded by the pack carburizer, sealed in steel containers and heated in an air furnace to operating temperature.
Quenching and Tempering Salts Group I quench salts are composed of nitrate/nitrite salts for use as steel tempering or quenching media. All are completely water soluble, easily washed and have similar high heat transfer rates and heat capacity. Group I quench salts come standard in a powder form with pink dye (for identification purposes) and organic anticake. They are also available without dye and anticake in a briquette form under the Heatbath®/Park Metallurgical trade name PARKETTES. Group II salts are neutral salts of the chloride family that operate in the higher temperature ranges. They are completely water soluble, thermally stable and highly fluid. They are more hygroscopic than Group I but more stable and non-oxidizing.
Rubber Cure Salts

A family of salts specially formulated for use in rubber curing. Most of Heatbath®/Park Metallurgical's rubber cure products are nitrate/nitrite salts. However, we also offer a Nitrite-free alternative for those who are concerned with the possible formation of nitrosamines. With our rubber cure salts, no reaction with surfaces of extruded or molded rubber parts will occur below 500 deg F in the normal cure times. All salts are completely water soluble and are easily washed from parts. All products are available in a predominantly free flowing form, a crystalline form with an anti-caking agent, or in a briquette form available under the trade name PARKETTES.

                                                             Table credit: Heatbath Corp.

 

Heat Treatment Salt Specifications

 

Primary Specifications

  • Working or operating temperature range

  • Melting point

Secondary Specifications

  • Density

  • Specific heat

Available Heat Treatment Salt Features

  • Barium Free
  • Cyanide Free

 

Resources

 

Hubbard-Hall

 

WallWork Heat Treatment

 

Kolene Corp.

 

Heatbath Corp./Park Metallurgical  

 

 

 

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