D
Dellortoman1
Guest
<DIV> <P>More on chains:</P> <P><o
> </o></P> <P>I got carried away with triplex chains in my diatribe a few postings back, and forgot to address the issue of triplex vs simplex, which was the original question!</P> <P><o> </o></P> <P>There seems to be a general opinion that two simplex chains have a similar rating to the original triplex. I think this is a misconception. </P> <P>Firstly, it simply isn?t true. If you look at any chain rating tables, for similar chain construction, a Triplex has 2.5 times the rating of a simplex. </P> <P>Secondly, when using two chains on a pair of sprockets that are fixed together, you can?t simply multiply the load rating of a single chain by two. The reason for this is that no two chains are exactly the same, even if they are cut from the same stock. Engineering tolerances are such that there will be minor differences from link to link, so there may be a slight difference in length between two similar chains. There may also be slight machining irregularities in the sprockets. These differences will be very small, but enough to mean that one chain will be tighter than the other (and not always the same chain as they move around the sprockets). Roller chains have very little stretch so even a slight difference in dimension will mean one chain is significantly more loaded than the other. Therefore engineers must use a de-rating factor for multiple chains. Without looking it up, I think it?s about 1.6 for two chains. That means two single chains in parallel only have 1.6 times the rating of a single chain. As the chains wear, the differences between them will become greater, and the rating factor will reduce to the point that the two chains are not much better than one. Using separate chain tensioners will help, but it?s not an ideal solution.</P> <P><o> </o></P> <P>You may think this is all a bit pedantic, but look back at Bruce?s post (No. 5). He had first-hand experience of this very problem. When you have one chain tighter than the other, they are both worse off. The tight one may fail because of too great a load, and the loose one may fail because of the shock loads imposed by it flapping about.</P> <P><o> </o></P> <P>Also, this goes a long way to answering Brad?s question in the last paragraph of his post (No. 7). Putting a triplex chain back onto sprockets that were previously running two simplex is asking for trouble because the centre sprockets will be less worn-out. So the centre row of the triplex will be tighter (and therefore more highly loaded) than the outside rows. Uneven load distribution will shorten the chain?s already limited life. I guess the bottom line here is that if you decide to go with two simplex chains, make it a permanent change ? don?t go back to triplex without replacing the sprockets.<o></o></P> <P><o> </o></P> <P>Cheers,</P> <P><st1lace w:st="on">Cam</st1lace></P></DIV>
> </o></P> <P>I got carried away with triplex chains in my diatribe a few postings back, and forgot to address the issue of triplex vs simplex, which was the original question!</P> <P><o> </o></P> <P>There seems to be a general opinion that two simplex chains have a similar rating to the original triplex. I think this is a misconception. </P> <P>Firstly, it simply isn?t true. If you look at any chain rating tables, for similar chain construction, a Triplex has 2.5 times the rating of a simplex. </P> <P>Secondly, when using two chains on a pair of sprockets that are fixed together, you can?t simply multiply the load rating of a single chain by two. The reason for this is that no two chains are exactly the same, even if they are cut from the same stock. Engineering tolerances are such that there will be minor differences from link to link, so there may be a slight difference in length between two similar chains. There may also be slight machining irregularities in the sprockets. These differences will be very small, but enough to mean that one chain will be tighter than the other (and not always the same chain as they move around the sprockets). Roller chains have very little stretch so even a slight difference in dimension will mean one chain is significantly more loaded than the other. Therefore engineers must use a de-rating factor for multiple chains. Without looking it up, I think it?s about 1.6 for two chains. That means two single chains in parallel only have 1.6 times the rating of a single chain. As the chains wear, the differences between them will become greater, and the rating factor will reduce to the point that the two chains are not much better than one. Using separate chain tensioners will help, but it?s not an ideal solution.</P> <P><o> </o></P> <P>You may think this is all a bit pedantic, but look back at Bruce?s post (No. 5). He had first-hand experience of this very problem. When you have one chain tighter than the other, they are both worse off. The tight one may fail because of too great a load, and the loose one may fail because of the shock loads imposed by it flapping about.</P> <P><o> </o></P> <P>Also, this goes a long way to answering Brad?s question in the last paragraph of his post (No. 7). Putting a triplex chain back onto sprockets that were previously running two simplex is asking for trouble because the centre sprockets will be less worn-out. So the centre row of the triplex will be tighter (and therefore more highly loaded) than the outside rows. Uneven load distribution will shorten the chain?s already limited life. I guess the bottom line here is that if you decide to go with two simplex chains, make it a permanent change ? don?t go back to triplex without replacing the sprockets.<o></o></P> <P><o> </o></P> <P>Cheers,</P> <P><st1lace w:st="on">Cam</st1lace></P></DIV>