#41
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new chain, slack
On 12/26/2017 8:42 AM, Emanuel Berg wrote:
Frank Krygowski wrote: If there were nothing to bend the links (as when they wrap or unwrap around the sprockets), then applying and releasing tension would cause essentially no wear at all. To get wear you need relative motion between the parts, as well as some contact pressure. "Relative motion between the parts", yes of course. What do you mean by "contact pressure"? Contact pressure is the force applied between two mechanical pieces divided by the area of contact. For now, I'll postpone discussing the internal geometry of the chain. Let's just look at two steel bars, dimensions 10 mm x 10 mm x 1 m. Place one horizontally on your workbench. Place the second bar on top of the first and perpendicular to it. If you apply any downward force to the bar on top, that force generates pressure on the square centimeter of area in contact. Force divided by area gives you the magnitude of the pressure. E.g., if you have a chain attached to a heavy boulder and drag it back and forth, starting and stopping, isn't there wear when the slack chain turns stiff and pulls the boulder into motion, after which load balances out over all the links and the boulder moves forward in part by its own momentum? If the chain moves (from hanging slack to being nearly straight under tension) and tension is applied, there will be some opportunity for it to wear, although I think the wear would be negligible in this case. If the chain were supported so that it was horizontal and did not move as tension were applied, there would be essentially zero wear. It's easier to visualize a chain hanging vertically and having a load applied and removed. (If you want to do it right, test a length of chain in a Universal Testing Machine. See http://www.instron.us/en-us/products...esting-systems ) Done this way there will be no motion during the application and removal of load, and essentially no wear even if the forces are large. -- - Frank Krygowski |
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#42
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new chain, slack
Frank Krygowski wrote:
Contact pressure is the force applied between two mechanical pieces divided by the area of contact. OK, good. So where is the pressure area? The rollers and the inside/front of the sprocket and chainring teeth? And pressure from pedaling and driving the bike forward? I take it wear is reduced to a huge extent by the sprocket and chainring rotating in the same direction as the pull? Or rather the required pressure is reduced? If the chain moves (from hanging slack to being nearly straight under tension) and tension is applied, there will be some opportunity for it to wear, although I think the wear would be negligible in this case. If the chain were supported so that it was horizontal and did not move as tension were applied, there would be essentially zero wear. It's easier to visualize a chain hanging vertically and having a load applied and removed. (If you want to do it right, test a length of chain in a Universal Testing Machine. See http://www.instron.us/en-us/products...esting-systems ) Done this way there will be no motion during the application and removal of load, and essentially no wear even if the forces are large. OK, cool. -- underground experts united http://user.it.uu.se/~embe8573 |
#43
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new chain, slack
Contact pressure is the force applied
between two mechanical pieces divided by the area of contact. OK, good. So where is the pressure area? The rollers and the inside/front of the sprocket and chainring teeth? Wait, if the preassure area and wear happens at the same place, this doesn't make any sense... If wear happens inside the chain between to links, when does this happen on the chain cycle? When one link is on a teeth pulling the load and another (the link next to it) is "free" pulling the tangled link? Because the chain or pair of two links aren't in a stright line at that point? -- underground experts united http://user.it.uu.se/~embe8573 |
#44
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new chain, slack
On Tuesday, December 26, 2017 at 8:13:38 PM UTC+1, Emanuel Berg wrote:
Contact pressure is the force applied between two mechanical pieces divided by the area of contact. OK, good. So where is the pressure area? The rollers and the inside/front of the sprocket and chainring teeth? Wait, if the preassure area and wear happens at the same place, this doesn't make any sense... If wear happens inside the chain between to links, when does this happen on the chain cycle? When one link is on a teeth pulling the load and another (the link next to it) is "free" pulling the tangled link? Because the chain or pair of two links aren't in a stright line at that point? -- underground experts united http://user.it.uu.se/~embe8573 Jesus Christ... The wear happens at the moment a link leaves the sprocket and when it enters the chainring. At that moment you have a relative movement and tension between the parts that wear. You can push your handpalm on a piece of sandpaper. That doesn't hurts. It hurts when you aren pushing and moving over the sandpaper. Tip; take a chain/link apart and figure out how it works. Lou |
#45
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new chain, slack
Lou wrote:
Jesus Christ... The wear happens at the moment a link leaves the sprocket and when it enters the chainring. At that moment you have a relative movement and tension between the parts that wear. Scales of Set... Right, that's what I said. Except for the chainring which is the analogue situation on the other end. One would think there would be marginally less wear there as there is less "relative movement" due to the larger size, right? -- underground experts united http://user.it.uu.se/~embe8573 |
#46
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new chain, slack
On Sunday, December 24, 2017 at 1:21:47 PM UTC-8, AMuzi wrote:
On 12/24/2017 12:50 PM, Emanuel Berg wrote: Frank Krygowski wrote: OK, but is there a reason why you bring this up in such detail? Yes. I brought it up because you asked. OK, thank you in that case. Your average guy imagines that the chain wears against the teeth. This is not so. The chain roller doesn't turn or wear against the tooth, chain wear is inside the chain. Although I've broken and crushed rollers on a Sedis chain -- super low gear climbing pulling a kid in a trailer. -- Jay Beattie. |
#47
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new chain, slack
jbeattie wrote:
Although I've broken and crushed rollers on a Sedis chain -- super low gear climbing pulling a kid in a trailer. I've broken chains as well but that was before I had this interest, so I didn't examine what piece in particular broke. Darn It was while standing up, climbing, with additional stuff loaded on the bike as well. I suppose this puts extra tention on the chain and it prolongs the situation where wear is the most intense for an individual link or pair of links, because of the surplus load, and "subplus" speed, right? -- underground experts united http://user.it.uu.se/~embe8573 |
#48
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new chain, slack
On 12/27/2017 10:20 PM, jbeattie wrote:
On Sunday, December 24, 2017 at 1:21:47 PM UTC-8, AMuzi wrote: On 12/24/2017 12:50 PM, Emanuel Berg wrote: Frank Krygowski wrote: OK, but is there a reason why you bring this up in such detail? Yes. I brought it up because you asked. OK, thank you in that case. Your average guy imagines that the chain wears against the teeth. This is not so. The chain roller doesn't turn or wear against the tooth, chain wear is inside the chain. Although I've broken and crushed rollers on a Sedis chain -- super low gear climbing pulling a kid in a trailer. Whoa! You're manlier than Joerg! -- - Frank Krygowski |
#49
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new chain, slack
On Thursday, December 28, 2017 at 12:16:43 PM UTC-8, Frank Krygowski wrote:
On 12/27/2017 10:20 PM, jbeattie wrote: On Sunday, December 24, 2017 at 1:21:47 PM UTC-8, AMuzi wrote: On 12/24/2017 12:50 PM, Emanuel Berg wrote: Frank Krygowski wrote: OK, but is there a reason why you bring this up in such detail? Yes. I brought it up because you asked. OK, thank you in that case. Your average guy imagines that the chain wears against the teeth. This is not so. The chain roller doesn't turn or wear against the tooth, chain wear is inside the chain. Although I've broken and crushed rollers on a Sedis chain -- super low gear climbing pulling a kid in a trailer. Whoa! You're manlier than Joerg! Or I got a crappy chain. I think Sedis had a problem with QC for a period of time. I think this was pre-SRAM, but it might have been at that cross-over point. I prefer Shimano (except the lack of a master link) and KMC chains. -- Jay Beattie. |
#50
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new chain, slack
AMuzi wrote:
Overly tight chain will destroy hub and crank bearings before significant chain wear. Today or if it was yesterday I tried this and for sure there was a terrible noise and a totally obnoxious pedaling experience. I hope I didn't take the experiment too far so the bearings will have to be replaced :-$ -- underground experts united http://user.it.uu.se/~embe8573 |
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