Ask the Expert Question-and-Answer Archive

by Ron Joseph

October, 2002

Spray Application of High Viscosity Oils

Q. I would like to spray the 1500 cSt kinematic viscosity oil with 2 cc/s flow rate. Is it possible with airless method? If it's possible, could you give some suggestions?

A. Thank you for your question. In general, airless spray guns can spray high viscosity fluids, even in the high viscosity range that you mentioned in your email, namely 1,500 c.St. I have checked with a representative from Graco who confirmed this, but he mentioned that your desired flow rate is very low for the tip sizes that are offered by Graco. The two major companies that I am aware of who sell airless spray equipment are Graco www.graco.com, and www.nordson.com/pdf/literature

You might need to send a sample of the oil to one of these vendors so that they can select the appropriate tip size for you. Remember that when you design the tip for an airless gun you must specify not only the fluid flow rate but also the fan width and the distance from the tip to the part you are coating. In other words, you might specify a 2" fan width at 4" distance.

Alternatively, you might need to have an engineer who is knowledgeable on atomization design a special tip for your specific application.

Follow-up reply: You might need to ask a mechanical engineer to design a special nozzle for you in which he can size the orifice of the tip to give you the desired flow rate. You can purchase an airless pump that can deliver pressure from 1,000 psig to 3,000 psig. It might take some trial and error on behalf of the engineer before you have exactly the size tip that you need.

Nordson makes specialized tips for many different applications, including adhesives which have high viscosities. I'm sure that they will be able to give you better advice than I can.