Feb 5 2009
During thermal spray operations excess heat deposition and high temperatures can cause residual stresses, cracking and impaired adhesion between coating and substrate. Linde North America has developed a carbon dioxide (CO2)-based cooling system that minimizes the overheating risk and enhances the quality of the thermal spray process.
Linde North America is a member of The Linde Group, a world-leading gases and engineering company. The company’s new LINSPRAY® CO2 cooling technology significantly reduces cooling time in the thermal spray process, maintains the correct temperature and minimizes the risk of overheating. This is especially important when working on parts with thin walls or with heat-sensitive substrate materials such as titanium, magnesium and aluminum.
Conventional cooling blows compressed air through nozzles directed at the part to reduce temperatures and minimize overheating risks – a method that’s very inefficient, says Joe Berkmanns, manufacturing segment manager, Linde North America.
“While some believe this method is inexpensive because air is free, the indirect costs can often be quite high. When using air, cooling does not occur quickly enough in many cases, and cooling breaks must be programmed into the process. This places the spray gun in a parked position, wastes fuel and spray metal powder and results in a throughput reduction,” Berkmanns said.
“CO2 is the most effective dry cooling agent because it forms snow with a high latent heat of sublimation at -78 degrees C. Also, the CO2 storage and delivery can be tailored to the customer’s exact requirements. For example, for customers who use thermal spraying only occasionally, such as job shops doing re-work maintenance, liquid CO2 can easily be stored in a few high pressure cylinders. Users with more frequent cooling needs – such as full-blown parts manufacturing operations – can store CO2 in larger cryogenic vessels,” Berkmanns said.
In either case, special, Linde-designed nozzles convert the CO2 to snow and enable uniform, directed and continuous cooling results without any clogging, which can result in surface inconsistencies. The nozzle is designed to produce the highest amount of CO2 snow, while optimizing cooling by minimizing the amount of CO2 gas produced.