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Earlier this year I was contacted by an inventor inquiring whether I might be interested in finding applications for a proprietary thread form he had developed. It’s claimed benefit was high-strength, self-locking and self-sealing connections. I declined the invitation, explaining that sales representation of fastening products wasn’t really the company’s focus. The inventor, Dale Van Corr, said he understood but still offered to send me some prototype samples so he could get my impressions of his idea. I agreed, and shortly a box of male/female pairs of rapid prototype samples arrived (Figure 1 shows two of them).
While the configuration and application objective was varied, the fundamental attributes were theoretical 100% thread contact and an axially tapered thread form that fixed how far the thread could be advanced (Figure 2). Dale explained that its origin was an offshoot of a patented conical gear profile he had developed. These gears could be incorporated in a transmission with unique properties. My initial reaction of these threads was that they were a good example of the wide range of geometry that can be conceived when creative and inquisitive minds are paired with the amazing computing power that we all have at our fingertips. Of course whether there were any commercially viable applications for this exercise was another matter. There are obviously practical hurdles; the viability of generating the geometry cost-effectively, the performance implications that thread contact will not actually be 100%, whether they really seal or lock better and with more strength than existing solutions, among them.
While Dale was thinking in terms of all the potential applications of his threads, I simply looked at whether there was any benefit of their use in a threaded fastener (Figure 3). And as such the wave thread, at least in theory, solves the two most vexing problems with the application of bolted joints; how much rotation (tightening) gives the best performance, and how to minimize the potential for vibration loosening. Regarding the first issue, the wave thread has an obvious limitation relative to the standard 60° thread form. The axially tapered shape results in a fixed grip length when used as a threaded fastener. That is, each bolt can only be used in a joint of a specific thickness. While this feature has the implementation challenge of essentially closing off the entire market for standard threaded fasteners, it does have a distinct and powerful advantage. If the height of the joint stack can be well controlled, elongation (and therefore clamp load) can be controlled with the simplest wrench, as bottoming the threads will result in a sudden and obvious spike in resistance. Yes, for high loads and short grip lengths holding the tolerance on stack height could get expensive, but again this is not a wide-ranging solution. Recent editions of our Arch Advisor newsletter have devoted significant time to the problem of threaded fastener loosening. The characteristic of the traditional thread form that contributes most to loosening, thread gaps that allow relative movement, are eliminated in the Wave Thread. Additional possible benefits to weigh against the implementation challenges are:
Increased thread contact area reducing clamp load relaxation due to localized thread yield.
The ability to level the axial distribution of thread stress by varying thread taper and amplitude. Because they would be almost certainly cut rather than headed/rolled product, the cross section of the threads relative to the shank can be optimized.
In summary, I was curious enough about how a concept like this would perform that I offered to conduct some basic comparative testing for Dale at no cost if the test samples were of geometry, materials and production processes reasonably representative of final intent, and if we could publish those results. While Dale agreed, he doesn’t have the FEA resources to optimize his geometry. He has however developed software to translate the geometry into FEA-compatible file formats. If there are readers who are interested in contacting Dale Van Cor about providing these analysis services or to generally discuss Wave Threads, he can be reached at (603) 239-4433 or email@example.com. Dale has provided a more detailed description of his threads in this attachment: Wave Thread: Strength through Geometry.
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