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Posted by on June 12, 2009, 10:07 am
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> The chain mfrs list the maximum allowable tension for low speed
> drives, but I don't recall ever seeing tabulated values for the
> "stretchiness" of chain. It'd be easy enough to estimate by treating
> the sideplates as a solid strip.
I wonder if this is a valid model
>In other words, if you had an imaginary chain made of steel with
>infinite yield strength, 1.5 million pounds would stretch a length of
>#40 chain to twice its original length. In other, other words, a 100
>inch length of real #40 chain will stretch about .007" under a 100#
>load.
Specifically, I would expect that play in the plain bearing between
the
links would add up to more than .007
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Posted by Ned Simmons on June 12, 2009, 10:21 am
Please log in for more thread options On Fri, 12 Jun 2009 07:07:43 -0700 (PDT), cs_posting@hotmail.com
wrote:
>
>> The chain mfrs list the maximum allowable tension for low speed
>> drives, but I don't recall ever seeing tabulated values for the
>> "stretchiness" of chain. It'd be easy enough to estimate by treating
>> the sideplates as a solid strip.
>
>I wonder if this is a valid model
Why wouldn't it be adequate for an estimate? I'd be surprised if you
couldn't get within 20% of the real value with a little care.
>
>>In other words, if you had an imaginary chain made of steel with
>>infinite yield strength, 1.5 million pounds would stretch a length of
>>#40 chain to twice its original length. In other, other words, a 100
>>inch length of real #40 chain will stretch about .007" under a 100#
>>load.
>
>Specifically, I would expect that play in the plain bearing between
>the
>links would add up to more than .007
That's a different issue than the elastic behavior of the chain.
Presumably the chain would be pre-tensioned to eliminate the play.
--
Ned Simmons
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Posted by on June 12, 2009, 11:19 am
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> >Specifically, I would expect that play in the plain bearing between
> >the
> >links would add up to more than .007
>
> That's a different issue than the elastic behavior of the chain.
> Presumably the chain would be pre-tensioned to eliminate the play.
I would expect the elongation due to bearing play to be at least
somewhat
load dependent. I would not be surprised if this overshadows what
you
calculate from the solid elasticity model. But I could well be wrong.
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Posted by Ned Simmons on June 12, 2009, 2:22 pm
Please log in for more thread options On Fri, 12 Jun 2009 08:19:30 -0700 (PDT), cs_posting@hotmail.com
wrote:
>
>> >Specifically, I would expect that play in the plain bearing between
>> >the
>> >links would add up to more than .007
>>
>> That's a different issue than the elastic behavior of the chain.
>> Presumably the chain would be pre-tensioned to eliminate the play.
>
>I would expect the elongation due to bearing play to be at least
>somewhat
>load dependent. I would not be surprised if this overshadows what
>you
>calculate from the solid elasticity model. But I could well be wrong.
I can see how pin clearance in the sideplates would cause some bending
of the plate around the hole, which would not be accounted for by my
approximation, but it would be an elastic effect. An extreme example
would be regular lifting chain. In that case there's clearly a
significant bending component in the curved segment of the loop. I
guess the question is, how big is this effect with a close fitting
pin? My gut sense is that it'll be pretty small, but I'll wait 'til
someone runs an FEA on it before I dig my heels in. <g>
--
Ned Simmons
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Posted by newshound on June 12, 2009, 4:54 pm
Please log in for more thread options
>
>> The chain mfrs list the maximum allowable tension for low speed
>> drives, but I don't recall ever seeing tabulated values for the
>> "stretchiness" of chain. It'd be easy enough to estimate by treating
>> the sideplates as a solid strip.
>
> I wonder if this is a valid model
>
>>In other words, if you had an imaginary chain made of steel with
>>infinite yield strength, 1.5 million pounds would stretch a length of
>>#40 chain to twice its original length. In other, other words, a 100
>>inch length of real #40 chain will stretch about .007" under a 100#
>>load.
>
> Specifically, I would expect that play in the plain bearing between
> the
> links would add up to more than .007
But the OP will be pretensioning the chain to eliminate backlash, surely?
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> drives, but I don't recall ever seeing tabulated values for the
> "stretchiness" of chain. It'd be easy enough to estimate by treating
> the sideplates as a solid strip.