Most industries love vapor degreasing with chlorinated solvents. The Kauri-butanol number is usually the main reason given. If we examine how parts are cleaned we can see an even larger reason why they work so well. The Normal Boiling Point (NBP) of chlorinated solvents is much higher than most solvent substitutes available. Why is that important? Vapor degreasing works by condensing the solvent on the part and the liquid solvent dissolves the contaminant and drips off the part. As we condense the solvent, your part heats up until it reaches the vapor temperature. Are you getting enough liquid on your part to dissolve your contaminant with your solvent?

There are three factors to consider. First is the NBP. Second is the size of your part. Third is the latent heat of vaporization (amount of heat associated with the volume of liquid condensed). Let’s compare trichloroethylene (TCE) to fluorinated blends of trans dichloroethylene (Trans), a common substitute being used in vapor degreasers.

The normal boiling point of fluorinated blends range from 109 F to 118 F as compared to TCE at 188 F. The latent heat of vaporization per volume is approximately the same ( 1310 and 1255 Btu/gal respectively). For a part entering a vapor degreaser at room temperature (70 F), the delta temperature between the vapor temperature and the part ranges from 39 to 118 F. This means that 2.5 to 3 times (118/39, 118/48) more liquid condenses on a part in a TCE degreaser.  If regulations allow chlorinated solvents, you may want to use a solvent that delivers more solvent to your part and use a vacuum system. If required, a switch to an unregulated solvent can be done in the future. If you need excellent vapor degreasing with a low boiling solvent, vacuum vapor degreasers can accomplish this with correct design.

In short, not all solvents perform the same even if they are chemically similar. Changing your cleaning chemistry is not as easy as some vendors or regulators would lead you to believe. Talk to us first. We have over 25 years of experience.