Very comprehensive overview on the current state of fasteners, Ann. I'm curious at something you said at the end that design for disassembly was not really a big trend any more. That surprises me given all the requirements and focus on sustainability and environmental concerns. isn't design for disassembly part of that march to green design?
New European safety standards mandate captive fasteners on machinery guarding. Fasteners similar to those described in this article will make meeting the standard easier.
The intent of the standard is to make reinstalling covers an easy, no-thought-required task. Non-captive fasteners are easily lost in maintenance evolutions, so putting the guard back on means finding new screws, or making due with one less. Eventually, the guard is held with just a single fastener and doesn't really do its job of guarding very well that way.
Fastener technology has evolved greatly in the application of the use of different building materials. MDF has worked its way into wood working and the production of the "knock-down" self assembly furniture. Previously, you were a the mercy of very coarse threaded lag screws that you hoped would not strip out when it was assembled. Advent of new cam lock studs has definitely opened up the use of MDF for multiple applications.
The basic purpose of fasteners is to break down items into makeable parts and allow for maintenance/adjustment/modifications/storage. The elimination of fasteners is a very valuable part of a design as well.
But the trend is to demand more and more of our fasteners for economic reasons so the design effort has shifted more to the fastener systems themselves.
This environmental treatises of fasteners is timely, Ann.
For military hardware it is usually a requirement to use replacable thread inserts. I've had to put in a few my self and have a couple done for me. I'm aware of the new type that uses standard drill sizes but have as yet to use it. Ok it was developed ~20 years ago. I pretty much always use a torque wrench for Al. And critical Fe parts even the oil drain pan since I've had a couple of problems. And at least one time the torque wrench was the problem not feeling and hearing click. Now I also have an in-lb wrench that I love.
We did use fasteners similar to the "plus-Tite" for installing deveopmental crash sensors inprototype vehicles, because self-tapping screws of any variety are not sufficient. They are one version, there are several slightly different types, The main benefits are much stronger multiple thread engagement and greater reliability, followed by prevention of thread stripping. The fact that some of these threaded inserts are good for extended teperatures is an added benefit as well.
Beth, the statement was a more specific one, about the fact that there are requirements for and limitations on design for disassembly, specifically with regard to fasteners. As TJ points out, these are issues regarding captive and non-captive fasteners.
while adhesives can be superior in some respects, when they are mixed with plastics or other materials, such as MDF or wood products, it makes it a lot harder, if not impossible, to recycle those materials.
wbswenberg, thanks for the input on military hardware and their fastener requirements, and William, thanks for your input on the plus-Tite fastener types. Mil requirements are definitely in a different class.
This is an excellent article and one that "covers a lot of bases".Mechanical fasteners, plus welding and brazing, were just about the only method of "sticking things together" when I spent my time at the university.For the past five (5) years, I have specified adhesives; i.e. acrylics, silicones, hot melt, etc that have actually replaced mechanical fasteners.Quite frankly, I was absolutely amazed to find acceptable performance for a great number of assemblies.Adhesives are not suited for many application where significant tensile and shear stresses are encountered but they are certainly adequate for some jobs where the overriding goal is merely adhesion.I attended a conference in Chicago some months ago in which one subject was the Boeing Dreamliner and was surprised to find most of the skin was adhered to the inner frame with adhesives.