More On Hash Marks

Q. I read with interest your reply to B.M., concerning the striations he is getting on his parts that are being dipped.

Since he has changed to an air dry enamel, he is using a completely different coating. My first concern would be to look into the flow of the material as it is withdrawn from the dip tank. Perhaps the solvent balance should be adjusted to give better flow. If I remember correctly, the rate of flow should be pretty close to the withdrawal speed of the part from the paint.

Another problem might be pigment float. There may be some incompatibility with one of the pigments and the vehicle causing the separation or float before the film sets up. The longer the film stays wet, the greater the chance for some pigment float to occur.

I would look into the flow and float characteristics of the coating in addition to your comments regarding the inconsistent speed of the conveyor.

As you well know, I look forward to reading your column as soon as my issue arrives. Thank you for the opportunity to recall some of my paint sales knowledge and experiences. S. B.

 

A. Thank you, S. B. You stated the correct rule of thumb for rate of flow vs. withdrawal speed. However, in the present climate of environmental issues, solvent balance adjustment is not as easy as it was in the past. Some of the old standby flow adjusting solvents are not being used.

I’m not sure about pigment float on the surface of an airdrying film causing striations. Instead, the effect should be rather even or perhaps blotchy. In the dip tank, pigment float should be eliminated by tank agitation. Certainly, without proper agitation, there would be pigment float at the dip tank surface which could cause striations when parts are withdrawn using a jerky conveyor.ble primer/surfacer. Although hand sanding is labor intensive, it may be the only way to cover highly textured substrates.