JLB wrote:
> David Martin wrote:
>>
>>> 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?
Obviously more carefully than you.
> 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.
Oh, very funny. Now, your starter for ten is to find *any* mention of
the load being significant in abrasive wear on that page. The three
significant factors listed are:
Particle size, particle hardness and particle density. No mention of
load at all except obliquely as 'load-bearing surface'.
Now, returning to figure 1. Which mode of wear is most significant by
several orders of magnitude. Why, it is abrasion!
>>> 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?
because the cites you gave do not indicate load as significant in
abrasive wear, and abrasive wear is indicated as the major component of
wear.
> 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.
fair enough, and load will be a factor in this. Still with a potential
of several orders of magnitude less than dirt though.
>
>>
>>
>>> 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.
>
>
Not the same at all. Given the option of reducing load or reducing
contaminants in the lubrication, it appears from the cites you ahve
given that far more can be done to reduce wear by reducing the contaminants.
>
>>
>> Which is the most important factor for bicycle chains, load or dirt?
>
>
> This is not the question being addressed.
Yes it is. The arguement was over whether it was increased load or
increased dirt that was primarily responsible for shortening the lives
of cycle chains.
> 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.
We are arguing cross purposes here. I am obviously using a different
meaning of significant to you.
You are using significant in the strict sense of 'has to be present'.
I am using it in the sense of 'changes in this parameter are most
closely related to changes in the effect under study'
Think of my version of significant as 'principal component'.
And so, the arguement can be rephrased as:
Dirt is the prinicpal component affecting chain wear. Load is a minor
but necessary component.
...d
