David Martin said:JLB said:David Martin said:On 16/12/04 12:57 am, in article [email hidden],
"JLB" <[email hidden]> wrote:
>David Martin wrote:
>
>>On 16/12/04 12:03 am, in article [email hidden],
>>"JLB" <[email hidden]> wrote:
>>
>>>Dave Kahn wrote:
>>>
>>>>On Wed, 15 Dec 2004 17:13:49 +0000, JLB <[email hidden]>
>>>>wrote:
>>>>
>>>>>Your statement "I still don't believe that load is a significant
>>>>>factor in chain wear" suggests you refuse to accept basic mechanical
>>>>>engineering knowledge.
Quoted message said:>>>>It might suggest that except for the fact that you conveniently cut
>>>>four words from the end of my statement. What I actually said was, "I
>>>>still don't believe that load is a significant factor in chain wear in
>>>>normal bicycle riding."
Quoted message said:>>>Fine. Put it back in. And explain what the difference is between a
>>>bicycle chain in normal bicycle riding and a mechanical system of
>>>components subject to conventional well-known tribological wear
>>>mechanisms. If you can't, you are still pissing into the wind.
Quoted message said:>>The arguement is not over whether load is a factor, it clearly is, but over
>>the significance of the load.
Quoted message said:>The original statement said load was not significant, which is absurd.
>You have changed the debate.
It is not a change in the debate. Load having no effect is very different to
load having a significant role.
Which bit of "I still don't believe that load is a significant factor in
chain wear in normal bicycle riding." are you struggling with? Either
load is significant, in which case the belief is wrong, or load is
insignificant, in which case the belief is right.
Quoted message said:Significant in this case is relative to other factors.
No it is not. No load = no wear. Nothing in the relevant statement talks
about relevant to other factors, and even if it did it would be wrong,
because those other factors cannot produce any wear in the absence of
load. Load is necessary before there can be any wear and wear rates
increase as load increases. How can that not be significant?
If dirt relates to
Quoted message said:chain wear very well, but load poorly (evne though in the controlled
environment when the other factors are constant there is a clear linear
relationship) the load is not a *significant* factor.
See subsequent cites.
Quoted message said:>>Which variable would have most effect on the chain wear rate? High load or
>>high dirt?
This is not the question. Dirt matters. However, it is absurd to suggest
that load is insignificant because load is necessary before there can be
any wear and wear rates increase as load increases.
Quoted message said:>The chain will wear if there is load even with no dirt whatsoever,
>because the lubrication of a bicycle chain will in practice not be
>perfect. Whenever the steel components make contact and there is any
>normal force there will be wear. The wear will produce particles that
>will themselves accelerate the rate of wear.
Of course it will. This misses the point though. The point is how fast this
occurs and whether external dirt is significant in dramatically accelerating
the process.
This is not the question. Th point is it is absurd to suggest that load
is insignificant because load is necessary before there can be any wear
and wear rates increase as load increases
Let me phrase that differently. A change in load may be insignificant in
respect to a change in maintenance and cleanliness of the chain.
The age of the rider is, by your arguement, also significant because with no
rider there is no wear. Silly arguement.
Are you being deliberately dim, or deliberately silly?
It does not matter what the source of the load is. Could be this rider,
another rider, bike chain test machine, anything at all; but still it
follows that no load = no wear; and increase in load = increase in wear.
The whole debate hinges on whether
Quoted message said:variations in load are better predictors for variations in chain wear than
variations in chain cleanliness.
No. The statement was "I still don't believe that load is a significant
factor in chain wear in normal bicycle riding." Show me the bit of that
statement that says anything about "better predictors". Explain how the
load can be other than significant.
Quoted message said:
Quoted message said:Quoted message said:>>At which point we gather lots of data and start to evaluate them with
>>respect to wear rate.
Tribologists have been doing this for quite a while. It is one of the
reasons we can be confident load is significant because it is necessary
for there to be load before there can be any wear and wear rates
increase as load increases
indeed they do. And the relationship is extremely well modelled if you keep
conditions constant (ie same amount of dirt, lubrication etc.)
Quoted message said:Quoted message said:>>If you ignore the dirt on the chain, what is the correlation between load
>>and wear? (R = x)
Quoted message said:>>If you ignore the load on the chain, what is the correlation between dirt
>>and wear? (R = y)
Quoted message said:>There might even be a point where there is so much dirt it decreases the
>rate of wear by providing a better spread of load and therefore lower
>stresses across the chain components.
Indeed. We can all speculate. Easy to do in the absence of data. (how many
angels on the head of that pin?)
See the cites and note how load is included in every one as a
significant factor.
Remember: the debate is whether it is reasonable to believe load is not
significant.
but they all refer to the same system. Taking a population of cyclists, will
load be a significant predictor of chain wear? Will dirt be a significant
predictor of chain wear? WIll lubrication be a significant predictor of
chain wear?
Why don't you find out if you want to know? What is indisputable is that
load is significant.
Quoted message said:Quoted message said:Some cites
http://www.whitfordww.com/design/wear.html
http://www.tribology-abc.com/abc/wear.htm
http://www.machinerylubrication.com/article_detail.asp?articleid=468&relatedbo
okgroup=WearDebris
It's all good stuff. For example, on the machinerylubrication webpage,
Fig. 1 is a handy summary of the recognised wear mechanisms and how
they are influenced by certain variables. Note that one parameter is
hardness/load.
It is indeed for fatigue and adhesion modes of wear. It is not mentioned for
abrasive wear, wheras teh main focus of the abrasive wear is the nature and
size of contaminant particles in teh lubricant, ie the dirt.
Did you actually look? There is extensive mention of abrasion. The
specific Fig. 1 that I referred to is a summary of four wear mechanisms,
the first one being "abrasion"; this figure is followed be a whole
section of discussion of abrasion. You might not have spotted it because
it was disguised under the misleading heading "abrasion", which could
have put you off the scent, before you reached Figure 2, which is
described on the page as "Nominal Wear Factors for Abrasive Wear", so
how would anybody realise that had anything to do with abrasive wear?
Apart from that though, and of course corrosion, which is also there,
you almost have a point.
Quoted message said:Quoted message said:Wear is slower with harder materials; wear is faster with
increased load. Then note that the horizontal axis is logarithmic, which
is a hint that the rate at which wear increases can be quite dramatic.
Indeed. And in the situations described, ie a bicycle chain, the wear mode
is most likely to be abrasive or corrosive. It is far less likely to be
adhesive.
And this relates to the question of whether load is significant how?
Also, why rule out adhesive wear? Whenever the lubrication fails to
prevent direct contact of the chain components under load, adhesive wear
will occur. Given how bicycle chains are used and lubricated this is
entirely predictable. This is described in the first cite.
Quoted message said:Quoted message said:However, even if it is merely linear, there is no shadow or scintilla of
doubt that load is significant because it is necessary for there to be
load before there can be any wear and wear rates increase as load increases.
It is about realtive rates of increase. If <handwave> wear increases
linearly with load, but abrasion increases exponentially, load will not be
significant compared to changes in the nature of the dirt in the
lubricant</handwave>
Even if your handwave was true concerning the relationship of wear to
the various factors the conclusion would still be false. It is as absurd
as arguing that for a simple DC circuit where you are interested in the
amount of current you can declare that voltage matters but resistance is
simply not significant.
Quoted message said:Which is the most important factor for bicycle chains, load or dirt?
This is not the question being addressed. Load is significant. It is
necessary for there to be load before there can be any wear and wear
rates increase as load increases. That's not merely significant, it's
fundamental. There's no point in even thinking about understanding wear
unless you are going to allow the significance of load.
--
Joe * If I cannot be free I'll be cheap
