Engineering-grade, pressure-sensitive silicone adhesives such as FLEXcon's Densil for brake damping must resist dirt and moisture, temperature extremes, and corrosion by substances such as brake fluid.
Nice article, Ann. I didn't realize the wide range of uses for adhesives. You mention the economic advantages of adhesives in the manufacturing process. I would imagine there is also an economic advantage is the cost of materials. Most mechanical fasteners are probably far more expensive than adhesives.
Interestingly, although cost is always an issue, most vendors mentioned the differences in function and problems to be solved between fasteners and adhesives. And when it came to cost, what most (adhesives) vendors mentioned regarding the cost differentials had to do with lower cost processes for applying adhesives, not a difference in the cost of materials or the items as such.
Ann, thanks for the whirlwind tour through the world of fastening. You covered a lot in this article!
My first reaction when you mentioned a shear strength of 1000 psi for a structural adhesive was that it seemed very small compared to the shear strength of a Grade 8 bolt (around 100,000 psi). Then it occurred to me that, with an adhesive, the load can be spread out over a much larger area.
As a rough approximation, for a structural adhesive with a shear strength of 1000 psi, 7.5 square inches of adhesive should be able to withstand the same load as a 3/8-16 Grade 8 bolt. Neat!
Great overview of adhesives, Ann. I was recently fortunate enough to take a tour of one of the Fabrico facilities, and it's really interesting to see the sophisticated layering process, utilizing adhesives, by which the end products are manufactured and QC's (via machine vision) as they go down the line.
I would think that adhesives offer an advantage in smaller electronics partially because mechanical fasteners can only get so small before they become a manufacturing problem. I would imagine that some of today's razor thin phones would be a good example of this.
Interesting, Ann. It could be that the material costs are small compared to overall costs. If the adhesives are particularly effective, there could be additional savings in quality through the life of the product. That could matter in terms of overall costs.
Dave and Alex, thanks for the feedback. A whirlwind tour it was. Each of these subjects deserves its own feature, and in fact, each will get its own spot at least once again this year. I concentrated on structural solutions since those seem like the toughest area for adhesives to beat fasteners, but they came closer than I'd initially expected. The fact that adhesives spread out the load over a larger area seems to be one of their biggest advantages. Pretty awesome numbers, eh? There's a lot more going on with adhesives, and they've come a lot further, than I would have guessed.
Chuck, that's an intriguing point about adhesives replacing fasteners in ever-shrinking smaller electronics. That's what I would have thought, but it turns out there's a "micro" class of fasteners that are ridiculously small--I don't recall the exact dimensions--and that will be the subject of an upcoming feature this year.
I've experienced the opposite problem. In fact experiencing it now. When attempting to fasten small components with adhesives, there is less margin of error. Less surface area, more opportunity for contaminant, or surface irregularity to confound adhesive. I guess there are some caveats - such as surface preparation, use of cleanroom, etc. Sometimes you simply want there to be a "mechanical" connection.
Ann: We were able to reduce the cost of a small shaft assembly by eliminating machining operations for traditional fasteners by switching to an anaerobic shaft-locker. The resulting bond is stronger than the small 17-7Ph shaft it is used on. Surface prep is critical, dispensing must be done carefully but when done in a controlled environment with fixturing the assembly times can be managed. Life & overstress testing has validated the process and we continue to monitor it as this is new ground for us.
The resulting parts are stronger (no flats for stress raisers), have less vendor issues (deburring on fine ID bores from cross threading or stepped shaft diameters). and take less space (even small fasteners have length requirements that conflict with highly packed components).
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This discussion will examine what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.