Adhesive and sealant troubleshooting tips from Dr. Dave Dunn.

Question: What is the difference between flow-in bonding and weld-through bonding?

Answer: The “weld-through” process is generally accepted as the most economical and effective bonding procedure these days. Weld bonding is commonly used in the automotive industry, at both the OEM level and in body repair. The technique provides the combined benefits of welded joints and adhesively bonded joints. Adhesives used in this application are usually filled with metallic powders to make them electrically conductive.

The term “flow-in” describes bonding processes in which a joint is welded before an adhesive is allowed to flow into the joint. The “weld-through” process involves applying the adhesive first and then welding through the uncured or fully cured adhesive - a common practice in repair procedures. (It is worth mentioning that “flow-in” is sometimes erroneously used to describe processes in which an adhesive is applied and then welded in the liquid state before it has cured.)

Question: I am a re-manufacturer of diesel fuel-injection parts. I am currently experiencing a leakage problem in one of my products, an aluminum casting that contains an aluminum sleeve. I have used epoxy, anaerobic adhesives, flange sealants, press fits and .002” clearance, and yet I still have problems. Can you suggest a remedy?

Answer: It seems to me that you may have an inherent porosity problem with your aluminum castings. Have you considered getting them impregnated with either an anaerobic or heat-cured acrylic sealant prior to applying your adhesive/sealant? These impregnation sealants will fill any porosity in the castings to prevent gas or fluid leaks.