Ask Dr. Dave

Ask Dr. Dave

In his November 2008 column, Dr. Dave discusses the assembly and sealing of aluminum parts and the proper use of superglues.

Question: We are assembling and sealing some aluminum parts using an RTV silicone and the adhesion values are inconsistent. Can you offer some suggestions to remedy the problem?

Answer: There are several possible reasons for your problem. First, you need to make sure that you are using the best silicone. Some of the modern alcohol-emitting sealants do not give as much adhesion as older acetoxy versions. Talk to your supplier and make sure that adhesion promoters are built into the product, or see if he can supply you with an adhesion-promoting primer. Also, look at the mode of adhesive failure. Are you getting cohesive failure of the silicone and leaving adhesive on both surfaces when the bond fails? If so, then a higher-strength silicone may be the answer. If you are getting adhesive failure to one of the surfaces, the bond should break and leave you with a clean surface. In addition, make sure that the silicone is properly cured to maximize the adhesion. Measure the adhesive strength as function of time. Make sure that there is sufficient ambient humidity to cure the silicone, and also that you are not trying to cure through a large depth, which can take a long time when moisture has to diffuse in from the outside. In my experience, cleanliness and preparation of a surface is usually the key to high and consistent bond strengths. Measure the surface energy of the surface using “dyne solutions” and try cleaning the surface. Usually, appropriate solvents will give a reproducible surface, but corona or plasma treatment can also be effective, although they may be much more expensive.

Question: We use superglues (cyanoacrylates) frequently, but we never seem to be able to keep them from getting on our fingers. How can we keep this from happening?

Answer: I have worked with cyanoacrylates since 1974, and I guarantee that I have stuck my fingers together many more times than you! Obviously, you could wear gloves when handling them, but the real secret is to use modern tools and thickened formulas. The worst possible applicator from a handling point of view is regular liquid superglue in an aluminum tube. This gives good shelf life to the product, but the low viscosity coupled with the lack of “suck back” with the tube virtually guarantees some overflow or drips. If your production is large enough to justify an automatic syringe-type applicator, this should solve the problem. Otherwise, consider using a plastic bottle that will give you some suck-back during dispensing. Some of the modern retail packages really make it easy to dispense the adhesives. Personally, when I use the product at home, I prefer the gelled version. Remember the TV commercial some years ago that talked about "No runs, no drips, no errors"?


Did you enjoy this article? Click here to subscribe to Adhesives & Sealants Industry Magazine.

Recent Articles by Dave Dunn

You must login or register in order to post a comment.



Image Galleries

ASI April 2014 Photo Gallery

Our April 2014 issue is now available!


ExxonMobil Tackifier Expansion

Dwight Tozer, vice president of ExxonMobil’s Adhesion Industry business, discusses the company’s latest tackifier expansion project with Editor-in-Chief Susan Sutton.

More Podcasts

Adhesives & Sealants Industry Magazine

ASI May 2015 cover

2015 May

You won't want to miss our May issue, with a special packaging-focused Adhesives at Work section, as well as coverage of pressure-sensitive adhesives (PSAs), biorenewable feedstocks, and more!

Table Of Contents Subscribe

Better Jobs

Is the economy prompting you to consider leaving your job for a better one?
View Results Poll Archive


Handbook of Sealant Technology

The Handbook of Sealant Technology provides an in-depth examination of sealants, reviewing their historical developments and fundamentals, adhesion theories and properties, and today’s wide range of applications.

More Products

ASI 2014 Buyers GuideASI's Buyers' Guide

Annual purchasing resource for equipment used in the manufacture/formulation of adhesives, sealants, pressure sensitives, tapes and labels and for application of finished adhesives. 


facebook_40px twitter_40  youtube_40pxlinkedin_40 google+ icon ASI 30px

Clear Seas Research

With access to over one million professionals and more than 60 industry-specific publications, Clear Seas Research offers relevant insights from those who know your industry best. Let us customize a market research solution that exceeds your marketing goals.