Does your shop heat treat and then finish parts? If so, read on to find out about a process that can replace standard quenching fluids in various heat treating processes.
Thermadep quenching enamels can provide not only the final step in a heat treat process but also an attractive finish coat. Developed in 1992, the process deposits a cohesive film on the surface of hot parts submerged in the coating material.
The resulting film can air dry to touch in 1-5 min after removal from the quench tank, depending on part mass, removal temperature and retained heat in the parts. Parts can often be immediately handled or packaged for shipment, although baking will result in formation of an even harder, more durable film, according to Egyptian Coatings (Franklin, TN).
The company says Thermadep is well suited to the manufacture of many types of heat treated metal products including agricultural ground engagement tools, fasteners, mattresses and bedding, springs, gears and similar components, hand tools and machined parts.
According to Egyptian Coatings, which markets the process, Thermadep can be extremely easy to use. Hot parts are submerged in a temperature-controlled, water-reducible polymer bath for 5-50 sec depending upon part mass, the removal temperature needed for proper drying, and desired film thickness.
Parts can be placed in the bath over a wide temperature range from 300-850°F. The coating can penetrate scale and rust, so parts normally do not need to be cleaned or pretreated unless they have an oil coating on them that is not removed during the preheating or heat treatment process. Typical applications for the process include finishing of castings, forgings and other heat treated parts that require temporary coating protection.
Egyptian Coatings says Thermadep is also environmentally friendly and safe for workers. All the materials are waterborne, and most have very low VOC content—typically 0.10-0.9 lb/gal. Dried films usually contain no hazardous materials, so the process can displace oiling, painting or plating for parts that will be handled later.
Baths are also said to be easy to control. Users normally need to maintain a slightly alkaline pH of 8.0-9.0, and monitor the solids content of the bath. In normal operation, pH tends to drop based on basic resin chemistry, tank throughput and temperature. Routine pH analysis, coupled with small and frequent additions of fresh quench bath concentrate, are usually sufficient to maintain pH. Correction, if necessary, can be accomplished using small ammonia additions.
Egyptian Coatings says the process typically provides a uniform, low-gloss finish that resists runs, sags, blisters and other surface imperfections. Most baths have been used to produce a low-gloss black finish, but a wide color palette also includes silver, gold, transparent and clears. The company says it has done work developing a color coding system that enables quick identification of specific springs.
The Thermadep process also offers additional properties, the company says. Corrosion resistance can vary according to the heat treat methods and temperatures used, as well as substrate composition and mass. Egyptian Coatings says Thermadep-treated parts can withstand 24 hr of salt-spray exposure according to ASTM B 117, but notes that actual exterior exposure of coated parts has demonstrated a higher level of protection. In one case, sweeps and ground engagement tools for the agriculture industry showed only minimal corrosion after more than two years of exposure to the elements.
After air drying for seven days, parts coated with a 1-mil thickness have also repeatedly demonstrated at least 200-300 hr of protection in humidity testing, according to ASTM D 2247. Other testing once again indicated that much greater protection was possible, with 3 × 5/8-inch bolts displaying more than 1752 hr of protection with only minimal deterioration.
Egyptian Coatings says parts can also conform to General Motors (Allison Transmission) specification TMS 26915 for exposure to transmission fluid. After a 72-hr immersion in various transmission fluids at 250°F, springs coated with SQW-L50 showed no softening, loss of adhesion or discoloration.
