Many processing steps apply heat to the workpiece. This can affect dimensions and material structure.
Cooling time is required to exclude the possibility of overheating. The cooling window can be reduced if carbon dioxide (CO2) snow or liquid nitrogen are used as cooling agents.
It takes between 0.5 and 1.0 litres of liquid nitrogen per kilogram of metal to reduce the temperature from +20°C to -196°C. Liquid nitrogen must be handled like boiling water because of the risk of cryogenic burns.
CO2 ice/snow (dry ice)
It takes about 0.2 kilos of dry ice per kilogram of metal to reduce the temperature by 98°C. Dry ice can be sprayed or applied as pellets.
LINSPRAY® carbon dioxide (CO2) cooling solutions
LINSPRAY® carbon dioxide (CO2) cooling solutions avoid the problem of overheating by effectively cooling the work piece around the flame. CO2 is fed from a pressure vessel at a low (18 bar) or high pressure (56 bar). Normally, a tank is used to supply these cooling applications, but small-volume or occasional users may find cylinder bundles (56 bar) adequate.
Our CO2 thermal spraying cooling solutions are an ideal application to support the thermal spraying processes on temperature-sensitive substrate materials such as Carbon Fibre Re-enforced Plastic (CFRP), Titanium, Aluminium and Magnesium, thin-walled components, components with poor thermal conductivity, oxide-sensitive spray materials and products with different heat expansion rates.
Compared with other cooling methods using air or nitrogen, CO2 is a highly effective cooling medium. Although nitrogen has an extremely low temperature (–195°C), this cooling power cannot be applied effectively as there is no direct contact between the liquid nitrogen and the component to be cooled.
BOC CO2 snow particles are propelled directly onto the surface, thus penetrating the insulation layer. On contact with the surface, the CO2 snow sublimates (i.e. changes from a solid to a gas state), thus releasing maximum cooling power.
The speed and performance benefits of CO2 snow open up new applications for thermal spraying. To maximise the efficiency and performance gains of CO2 cooling, we complement our gas and service offering with custom-developed hardware and nozzles. These sophisticated, commercially viable devices bring our customers the added bonus of ease of use.
BOC Cooling Nozzles
BOC nozzles feature a pre-chamber at the mouth end, where liquid CO2 is expanded via a calibrated slit nozzle. The patented design of this pre-chamber ensures extremely effective expansion. The precision-manufactured mouth opening ensures an exact, turbulence-free jet shape and avoids nozzle blockage. The proportion of CO2 snow in the cooling jet disappears after it hits the substrate surface, resulting in optimum heat removal.
To suit individual needs, we have developed different nozzle models for a fanned or focused effect. These nozzles also come in different sizes to enable operators to tailor cooling power to individual application requirements. Cooling power can only be adjusted by means of the nozzle as liquid CO2 is always supplied at a constant pressure.
CO2 cooling for thermal spraying provides the following benefits:
Fast-acting, effective cooling power
Custom-designed hardware and nozzles
Focused or fanned effect
Ease of use.
Watch our CO2 cooling solutions for Thermal Spraying video to find out more.
If you are unable to view this video, please visit the BOC YouTube channel to view it at www.youtube.com/watch?v=p6I8R6Tchl4