HVOF thermal spray uses a fuel (i.e., propylene, hydrogen, propane, kerosene)/oxygen mixture in a combustion chamber. This combustion process melts a metal powder that is continually fed into a gun using a carrier gas (argon) and propels it at high speeds (3,000 - 4,000 ft/sec) towards the surface of the part to be coated. The high speed of the spray produces a coating upon impact that can be used as an alternative to the HCP process. The metal powder is available in many compositions, including: nickel, nichrome, inconel, chrome carbide, and tungsten carbide. Uniform coating thickness of up to 0.250 inches can be achieved.

The only waste stream produced by HVOF is from the capture of the overspray. Current systems use a dry cartridge filter system with an optional high efficiency particulate air (HEPA) filter. Since the overspray contains only the pure metal or alloy, it is feasible to recycle or reclaim this waste stream.

The reduction of hazardous waste helps facilities meet the requirements of waste reduction under RCRA, 40 CFR 262, Appendix, and may also help facilities reduce their generator status and lessen the amount of regulations (i.e., recordkeeping, reporting, inspections, transportation, accumulation time, emergency prevention and preparedness, emergency response) they are required to comply with under RCRA, 40 CFR 262. In addition, since bath solutions are eliminated (i.e., less sulfuric acid and chromic acid) there is less of a chance that the facility would meet any of the reporting thresholds for hazardous substances/chemicals under SARA Title III (40 CFR 300, 355, 370, and 372; and EO 12856). The elimination of hard and decorative chromium electroplating from a facility may also decrease the need for meeting NESHAP requirements under 40 CFR 63.340 - 63.347 and for an air permit under 40 CFR 70 and 40 CFR 71. It should be noted that a new air emission may result from the use of this new technology. Additionally, this technology uses considerably less water than the traditional electroplating operations and as required under EO 12902, Energy Efficiency and Water Conservation at Federal Facilities.

The compliance benefits listed here are only meant to be used as a general guideline and are not meant to be strictly interpreted. Actual compliance benefits will vary depending on the factors involved, e.g. the amount of workload involved.

Consult your local industrial health specialist, your local health and safety personnel, and the appropriate MSDS prior to implementing this technology.

• Surface coating physical properties are at least equal to those of HCP, and often exceed HCP in corrosion protection, abrasive wear resistance, and adhesive wear resistance.
• Multiple choice of coating materials.
• Large volume reduction of hazardous waste and the associated disposal costs.
• Toxic air emissions from HCP bath containers reduced.

• Line-of-sight process, can only coat the external surface of a part, not the inner diameters.
• High capital cost.
• Process must be housed in a full enclosure of sufficient size to process parts that normally utilize HCP.

• Quantity of work to be transferred from HCP.
• Whether a robotic or manual system is used.
• Type of capture system used.
• Availability of space at the facility to house the HVOF enclosure.

The following cost comparison uses figures from Norfolk Naval Shipyard, in Portsmouth, VA.

Assumptions:

• Capital cost plus installation of HVOF equipment, including sound-proof room, diamond-jet system, powder, HEPA filter exhaust system, air compressor, fuel and oxygen gases, and grit blast preparation system is approximately $250,000.
• Metal powder for coating is tungsten or chromium carbide costing $40-65 per pound.
• Current disposal treatment for HCP waste streams is pretreatment at the Industrial Wastewater Treatment Plant (IWTP) costing $50/1000 gallons.
• Chrome plating bath can be reused several times if anodes are replenished.
• Chrome plating bath is 1,000 gallons.
• Bath solution is replaced once a year.
• No disposal costs for overspray during thermal spray procedure; recovered metals are sold to a local refiner.
• Finished product cost is dependent on the number of parts processed and the computed cost for consumables and labor per mil× ft² of coating (1 mil = 0.001 inches).
• Labor includes preparation for thermal spray and spray time (approximately 1.75 hours per part); for hard chrome plating, labor includes time to dip part in chrome bath (approximately 3 hours per part).
• Labor is approximately $17/hour.
• Plating costs, including cleaning, etching, and rinsing, are $250/part.
• The following comparison is based on coating a part 4 inches in diameter and 36 inches long (3.14 sq. ft.) with 8 mil coating.
• Approximately 1,500 parts are coated annually.
• Cost of hazardous waste treatment is $1/gallon.
• System generates 10,000 gallons of rinsewater treated through an IWTP.

Cost Comparison for HVOF vs. HCP Technologies

Economic Analysis Summary

Annual Savings for HVOF: $326,400
Capital Cost for Diversion Equipment/Process: $250,000
payback Period for Investment in Equipment/Process: 9 months

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*There are multiple MSDSs for most NSNs.
The MSDS (if shown above) is only meant to serve as an example.

Praxair TAFA
146 Pembroke Road
Concord,  NH   03301
Phone: (603) 224-9585