What is good solvent degreasing practice- part 1
Believe it or not, a good solvent degreasing practice starts when you modify your stock metal, be it machining, forming stamping, blanking etc. That’s because the old adage rubbish in, gets rubbish outs takes centre stage. It’s not the metals, but the machining fluids are sometimes incompatible with solvent degreasing processes that cause problems further along the manufacturing process.
Many of these problems occur in sealed solvent degreasing systems, which is a real shame because when optimised, they are the most straightforward systems to live with day-to-day. I have 20 years of experience selling, operating, programming and servicing sealed solvent degreasers and that experience has shown many problems are avoidable. Here in part one of “what is good solvent degreasing practice” I talk about foaming, a condition that can affect machine performance and part quality.
Foaming solvent in the vapour generator. It’s actually the oils washed off during degreasing that foam, not the solvent, and it generally occurs when there’s a pressure change in the vapour generator. This is because sealed solvent degreasing systems run under vacuum, so, for chlorinated solvents, this is in the range of 600-900mbar, whereas flammables like hydrocarbons or modified alcohols run at 80-120mbar. Foaming occurs when the vapour degreasing valve between the work chamber and vapour generator opens to allow the vapour degreasing step to take place. It also happens when the valve between the vapour generator and heat exchangers opens, allowing solvent vapour to enter heat exchangers for recycling. As the valve opens, there’s a pressure change as the pressure in the two vessels balance. It’s this change that causes the foaming to occur.
Think unscrewing the lid on a fizzy drink!
Foaming is a problem because:-
- Foaming oil can be transported to the heat exchangers that convert vapour back to a liquid enabling continuous distillation (recycling) when not vapour degreasing.
- The heat exchangers become contaminated with chilled viscous oil that remains in the heat exchanger, eventually blocking the narrow galleries. They will need replacing at some expense.
- The solvent vapour contains foaming oil. During the vapour degreasing phase, foaming oil is redeposited onto the parts it was just removed from, leaving them spotted with oily marks.
- Solvent samples taken for titration testing will become discoloured. Instead of being Gin clear, the liquid will take on a pale white wine to a muddy brown colour depending on foaming severity.
Resolving this particular problem requires an oil producer with experience in both camps, metal processing and metal cleaning. The Oest Group has this experience and has produced a range of cutting and forming oils with the unique feature of being highly compatible with solvent degreasing systems. The Oest Solvent Care – OSC® is a technically superior range of additives that eliminate foaming and many other chemistry problems seen in sealed solvent degreasing systems. Why not contact us or look out for part two to find out what else Oest’s OSC® can do for your business?