Join Date: Feb 2012
Location: New Orleans Louisiana
Thanked 38 Times in 36 Posts
Rep Power: 3
Re: Chain Plate Replacement
We make a lot of chainplates, and I have a good deal of experience with them. But as I frequently mention I am not a designer, and have no engineering degree, so the best I can do is point people to the answers, and help them find the right experts.
316 stainless is so much weaker than titanium, there really is an issue of overbuilding. While we do our best to drive the prices down, the raw material cost still adds up, and so if a NA can redesign (this is normally just a resizing issue) a chainplate and shave more than half the material from the part, well that is often worth more than his bill.
As an example:
The yield strength of 316 stainless is 32,000psi. While the yield for G5 titanium is 128,000psi. What this means is that a 1" cross section stainless bar will distort at the same point that a 32/128= 1/4" sectional area titanium bar will distort. So you build in a massive amount of additional strength. Combine this with the fact that most chainplates are so overbuild in the first place and you can realistically see titanium chainplates that are 20 times stronger than they need to be.
So how strong should a chainplate be? Well ONLY a NA can tell you, but a good place to start is with the size of your shrouds, since they transmit the load the chainplates need to carry. If we said someone has 1/2" shrouds with a breaking strength of 19,000 pounds, then chainplates any stronger than this are redundant because the wire will break first. Which would put us in the range of a 1/8" sectional area titanium plate. Of course this makes the rest of the system hard to work with, so in reality you have to upsize the titanium a little to fit tangs and bolt holes.
So why do designers overbuild chainplates in the first place? The simple answer is that they know that localized corrosion is the single biggest cause of chainplate failure, and the only way to delay it is by making the plates much larger than need be. This is called corrosion allowance, and is a good engineering tool. However, since titanium doesn't need a corrosion allowance when used for chainplates, there is no need to maintain these massive corrosion allowances.