Cleaning and Evaluating Drawdown Rods

Question: We use your wire-wound draw down bars here, and have a couple of questions on their care, and how to evaluate their condition. First, please let us know the recommended care and cleaning instructions. Would blasting with baking soda be safe and effective? Second, what is the best way to determine their overall condition?

Answer: Thanks for the question. The most important factor in keeping Mayer rods clean is to use an appropriate solvent immediately after every use. For non-aggressive, low viscosity fluids, simply wiping with a solvent-wetted soft, lint-free cloth may be all that is needed. In other cases, solvent immersion in an ultrasonic cleaning tank, along with brisk scrubbing with a very fine bristle brass brush, may be required. Please keep in mind that this abrasive method may cause burrs on the wire, which will affect subsequent coating performance.

It is important that the final rinse or wipe be done with a liquid such as water or high purity isopropyl alcohol, which will not leave a residue on the surface.

Once cleaned, it is imperative that metering rods be thoroughly dried before re-use, or the residual solvent may interact with the wet film coating when next used. Please note that compressed air – a fast, non-contact drying technique – generally contains trace amounts of oil, and should not be employed.

I don’t necessarily recommend blasting them with baking soda – or any other media – as even with stainless steel there is a potential for some degree of etching, which one would expect would be most pronounced at the “high” spots on the wire winding. This would reduce the area between the windings, with a concommitant reduction of coating thickness. However, if other methods have proven unsatisfactory, I suppose it would be worth a try, especially if the coating formulation is acidic. I would certainly want to check the resulting wet film thickness and finish after trying this! Other than those potential effects, the worst that is likely to happen is that the wire loses its weld or simply breaks and unwinds. If you try this, start with the largest wire sizes first.

As to evaluation of the rod’s condition, precise measurement of the wet film thickness applied would be most important . Evaluating the surface finish quality of the dried (or cured) coating would also be important. If you have a good microscope, that would be an effective inspection tool in this case.

Finally, as the cost of replacement rods is relatively modest, if there is any doubt about quality, it is probably best to simply replace the rods, rather than putting too much time and effort into trying to maintain them forever.

Published by

Russ Smith

Russ Smith formed Diversified Enterprises - the first business to focus specifically on applications of the dyne test - in 1986, and has served as President of the company ever since. He has over 30 years of experience in the fields of surface treatment and analysis, and deals with technical inquiries from customers worldwide on a daily basis. Russ is a member of ASTM, the Society of Plastics Engineers, the American Chemical Society, the American Society for Quality, the American Association for the Advancement of Science, and TAPPI.

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