Hi Sachin
your query almost answers itself; the "laws of friction" are only an
approximation to what happens in practice. They are useful in many
circumstances, but ignore factors such as heat dissipation, gross
deformation and many other effects.
For example, fast cars have wider tyres for more grip. If the coefficient of
friction was a constant then there would be no point as narrow tyres would
produce the same lateral resistance.
Two pieces of very clean very flat steel will actually bond together,
producing a friction coefficient orders of magnitude higher than the
coefficient normally given, even when the reaction is negative.
A sewing pin resting head down on a block of teflon will have a much lower
coefficient than the same pin point down.
The reasons for the above are fairly self evident, but make the point that
values for friction coefficients should be treated with caution and used
only within the stated range of application .
In the case you state a reasonable load on a 100X100mm teflon block would
squash flat a 1X1mm block to the point where it would fail to support the
reaction.
Cheers
Steve McKenzie
-----Original Message-----
From: Sachin_Bapat@ril.com [mailto:Sachin_Bapat@ril.com]
Sent: Thursday, September 26, 2002 4:08 PM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] PTFE plate
Importance: High
Graphite plate on SS plate, are good option for reducing friction for temperatures more than 200 deg C , but they have one problem their bonding with metal palte is very sensitive to loading & it often crushes under huge loading so better to check loading at the point of support before using them.
QUERY -If we go through "laws of friction" we find that friction at a point
is independent of area of contact ,so my PTFE plate of dimension 1X1 mm2
should be as effective as 100X 100 mm2 plate , even then the manufactures
mention some specific
dimensions of PTFE plate , why is it so ?
Regards
Sachin
Geoff Stone DD&D Australia <blenrayaust@yahoo.co.uk> on 09/24/2002 05:22:15 AM
Please respond to PipingDesign@yahoogroups.com
To: PipingDesign@yahoogroups.com
cc:
Subject: Re: [PipingDesign] PTFE plate
Suggest you visit the Lisega website, www.lisega.com.de and download LICAD.
Get
the local representative to bring you the 2010 catalogue. You could
similarly
download Witch from Carpenter and Paterson.
These companies specialise in pipe supports where thermal expansion occurs. Better to buy from experienced companies than from "backyarders" as you get engineering support.
Do a quick risk assessment on a home made solution versus one from an
internationally recognised company.
--- SubrataP_Saha@ril.com wrote:
<HR>
<html><body>
<tt>
<BR>
Graphite Plate on polished SS mating surface can be used.<BR>
The other means of reducing friction are polished SS to SS contact
surfaces<BR>
, rollers (varied opinion on their performance), PTFE for lower<BR>
temperatures. Whenever possible it is better to design the system so
that<BR>
friction isn't a problem. Also spring hangers may be used.<BR>
<BR>
Thanks<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
"Hossein Ahmadi" <h.ahmadi@nargan.com> on 09/23/2002
02:06:23
PM<BR>
<BR>
Please respond to PipingDesign@yahoogroups.com<BR>
<BR>
To: <PipingDesign@yahoogroups.com><BR>
cc:<BR>
Subject: [PipingDesign] PTFE plate<BR>
<BR>
<BR>
Dear Group Members<BR>
<BR>
I will appreciate if you answer following question :<BR>
If temperature of pipe be ~500 C(930 F),can I use PTFE plate<BR>
under 4" shoe support ?<BR>
If no, what do you recommend?<BR>
Is there any general rule for PTFE plate or another material selection
to<BR>
reduce friction factor ?<BR>
Best regards<BR>
Hosein<BR>
<BR>
<BR>
<BR>
[Non-text portions of this message have been removed]<BR>
<BR>
<BR>
<BR>
<BR>
Texas Flange - a good source for information on industrial flanges, all<BR>
they ask is for referrals for designs they help with.<BR>
877-610-8924.<BR>
www.texasflange.com<BR>
=====================================================<BR>unsubscribe: PipingDesign-unsubscribe@yahoogroups.com<BR>
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Texas Flange - a good source for information on industrial flanges, all
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877-610-8924.<BR>
www.texasflange.com<BR>
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Texas Flange - a good source for information on industrial flanges, all
they ask is for referrals for designs they help with.
877-610-8924.
www.texasflange.com
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
Texas Flange - a good source for information on industrial flanges, all they
ask is for referrals for designs they help with.
877-610-8924.
www.texasflange.com
Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
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