Quick question. Does glass-filled nylon have good bearing properties? I
would have expected its bearing properties to be poor, because wear
would essentially cause particles of sand to break off, but I have been
told otherwise. The product in consideration is a ground nylon piston in
a reamed brass cylinder. A little lubrication, but not a lot. Anyone know?

Many thanks,

Chris

Christopher Tidy wrote:
Quick question. Does glass-filled nylon have good bearing properties? I
would have expected its bearing properties to be poor, because wear
would essentially cause particles of sand to break off, but I have been
told otherwise. The product in consideration is a ground nylon piston in
a reamed brass cylinder. A little lubrication, but not a lot. Anyone know?

Incidentally, I should add, this is a reverse-engineering situation. I'm
trying to figure out what material a defunct company used. The plastic
layer is transparent with a yellowish tint.

Chris

On Sun, 31 Jul 2011 01:57:57 +0000, Christopher Tidy
wrote:

Quick question. Does glass-filled nylon have good bearing properties? I
would have expected its bearing properties to be poor, because wear
would essentially cause particles of sand to break off, but I have been
told otherwise. The product in consideration is a ground nylon piston in
a reamed brass cylinder. A little lubrication, but not a lot. Anyone know?

Many thanks,

Chris

If its not dynamically loaded..should work fine. If its loaded...it wont
last as long as other better Stuff will.


--
Maxim 12: A soft answer turneth away wrath.
Once wrath is looking the other way, shoot it in the head.

On 31/07/2011 03:07, Christopher Tidy wrote:
Christopher Tidy wrote:
Quick question. Does glass-filled nylon have good bearing properties?
I would have expected its bearing properties to be poor, because wear
would essentially cause particles of sand to break off, but I have
been told otherwise. The product in consideration is a ground nylon
piston in a reamed brass cylinder. A little lubrication, but not a
lot. Anyone know?

Incidentally, I should add, this is a reverse-engineering situation. I'm
trying to figure out what material a defunct company used. The plastic
layer is transparent with a yellowish tint.

Chris

How long is a piece of string? A few more details about the application
would help, dimensions / load / pressure / sliding speed / how many
cycles or how far do you need it to slide? Do you want the cheapest
solution, or is it an expensive bit of kit that you don't mind spending
money on?

Transparent doesn't sound like glass filled nylon, more like acrylic,
polycarbonate, perhaps epoxy?

Glass filled nylon is cheap, readily available, easy to machine. There
are also nylons which contain some oil to make them more self-lubricating.

PTFE is pretty good, though not so strong. Fabric reinforced phenolic is
strong, but less happy at combination of high load and sliding speed.
Polyimide (e.g. Vespel) is the Rolls Royce material for many
applications, but not cheap.

Gunner Asch wrote:

If its not dynamically loaded..should work fine. If its loaded...it wont
last as long as other better Stuff will.

Thanks for the thoughts. It's a piston in a miniature air pump. Here's a
picture. The plastic layer is over the knurling you can see:
http://www.mythic-beasts.com/~cdt22/pump_piston.jpg

I had wondered about oil-filled nylon. It's definitely not epoxy as I've
been told it was thermally moulded.

Chris

On Mon, 01 Aug 2011 02:20:10 +0000, Christopher Tidy
wrote:

Gunner Asch wrote:

If its not dynamically loaded..should work fine. If its loaded...it wont
last as long as other better Stuff will.

Thanks for the thoughts. It's a piston in a miniature air pump. Here's a
picture. The plastic layer is over the knurling you can see:
http://www.mythic-beasts.com/~cdt22/pump_piston.jpg

I had wondered about oil-filled nylon. It's definitely not epoxy as I've
been told it was thermally moulded.

Chris


That piston shouldnt be loaded so it should work for quite a while.
Nylon makes poor rollers for heavy stuff, but not bad for that sort of
thing

Gunner

--
"The danger to America is not Barack Obama but a citizenry
capable of entrusting a man like him with the Presidency.
It will be far easier to limit and undo the follies of an
Obama presidency than to restore the necessary common sense
and good judgment to a depraved electorate willing to have
such a man for their? president.. Blaming the prince of the
fools should not blind anyone to the vast confederacy of
fools that made him their prince".

On Sun, 31 Jul 2011 20:00:56 -0700, Gunner Asch
wrote:

On Mon, 01 Aug 2011 02:20:10 +0000, Christopher Tidy
wrote:

Gunner Asch wrote:

If its not dynamically loaded..should work fine. If its loaded...it wont
last as long as other better Stuff will.

Thanks for the thoughts. It's a piston in a miniature air pump. Here's a
picture. The plastic layer is over the knurling you can see:
http://www.mythic-beasts.com/~cdt22/pump_piston.jpg

I had wondered about oil-filled nylon. It's definitely not epoxy as I've
been told it was thermally moulded.

Chris


That piston shouldnt be loaded so it should work for quite a while.
Nylon makes poor rollers for heavy stuff, but not bad for that sort of
thing

Gunner
The only issue I can see with Nylon in that application is Nylon is
Hygroscopic - it attracts and absorbs moisture to some degree - so
make sure you provide ADEQUATE clearance for expansion. Glas filled
should wear very well in that application - just make sure cooling is
adequate as well as the clearance.

"Christopher Tidy" wrote in message
...
Gunner Asch wrote:

If its not dynamically loaded..should work fine. If its loaded...it wont
last as long as other better Stuff will.

Thanks for the thoughts. It's a piston in a miniature air pump. Here's a
picture. The plastic layer is over the knurling you can see:
http://www.mythic-beasts.com/~cdt22/pump_piston.jpg

I had wondered about oil-filled nylon. It's definitely not epoxy as I've
been told it was thermally moulded.

Chris


It is too clear to be filled with anything. It could be nylon, polycarbonate
or even low density polyethylene. If you can do destructive testing,
strong acids will eat nylon, and ketones (lacquer thinner) will eat
polycarbonate. Polyethylene will be more resistant to both, but it is not
compatible with mineral oil.

anorton wrote:

"Christopher Tidy" wrote in message
...
Gunner Asch wrote:

If its not dynamically loaded..should work fine. If its loaded...it
wont
last as long as other better Stuff will.

Thanks for the thoughts. It's a piston in a miniature air pump.
Here's a picture. The plastic layer is over the knurling you can see:
http://www.mythic-beasts.com/~cdt22/pump_piston.jpg

I had wondered about oil-filled nylon. It's definitely not epoxy as
I've been told it was thermally moulded.

Chris


It is too clear to be filled with anything. It could be nylon,
polycarbonate or even low density polyethylene. If you can do
destructive testing, strong acids will eat nylon, and ketones
(lacquer thinner) will eat polycarbonate. Polyethylene will be more
resistant to both, but it is not compatible with mineral oil.
There are some easier tests for basic plastic types and more detail can
probably be found on the net. 3 of the basic ones I remember are nylon
when burned smells like burning hair, polypropylene and polyethylene
smell like a burning candle but one floats in water though I can't
remember which one, it'll be the less dense one anyway. There are a
number of other simple tests like these to help narrow down the basic
stuff.

On Mon, 01 Aug 2011 10:08:01 +0100, David Billington wrote:
anorton wrote:
"Christopher Tidy" cdt22... wrote ...
Gunner Asch wrote:
If its not dynamically loaded..should work fine. If its loaded
...it wont last as long as other better Stuff will.

Thanks for the thoughts. It's a piston in a miniature air pump. Here's
a picture. The plastic layer is over the knurling you can see:
http://www.mythic-beasts.com/~cdt22/pump_piston.jpg

I had wondered about oil-filled nylon. It's definitely not epoxy
as I've been told it was thermally moulded.

It is too clear to be filled with anything. It could be nylon,
polycarbonate or even low density polyethylene. If you can do
destructive testing, strong acids will eat nylon, and ketones (lacquer
thinner) will eat polycarbonate. Polyethylene will be more resistant to
both, but it is not compatible with mineral oil.
There are some easier tests for basic plastic types and more detail can
probably be found on the net. 3 of the basic ones I remember are nylon
when burned smells like burning hair, polypropylene and polyethylene
smell like a burning candle but one floats in water though I can't
remember which one, it'll be the less dense one anyway. There are a
number of other simple tests like these to help narrow down the basic
stuff.

I've seen the following chart several places, but most clearly at:
http://www.consultekusa.com/pdf/Tech%20Resources/New%20ID%20chart%20.pdf
The tests are destructive but can be done with slivers of plastic, via
techniques as at http://www.chymist.com/Polymer%20Identification.pdf.
(On my system, that page didn't display in browser until after I used
wget http://www.chymist.com/Polymer%20Identification.pdf
to fetch it.) It may be that traces of oil on the plastic will
interfere with flame-based and density-based tests given in those
references.

If OP (C.D.T.) hadn't been told that the piston cover "was thermally
moulded", I'd have thought it could have been made by sliding a
short length of vinyl tubing over a knurled brass part.

--
jiw

wrote:

The only issue I can see with Nylon in that application is Nylon is
Hygroscopic - it attracts and absorbs moisture to some degree - so
make sure you provide ADEQUATE clearance for expansion. Glas filled
should wear very well in that application - just make sure cooling is
adequate as well as the clearance.

I have actually been told that this proved to be a problem at times. I'm
trying to trace the history of this product, and have been told various
things about the plastic: that it was thermally moulded, that it was
special nylon with a low coefficient of friction, that it was
hygroscopic, and lastly that it was glass-filled nylon. I've been told
these things by different people, and am trying to figure out the truth.
The glass-filled nylon part I had doubts about.

Thanks for the thoughts.

Chris

On Monday, August 1, 2011 10:22:23 PM UTC-4, Christopher Tidy wrote:
wrote:
[about a plastic piston]

I have actually been told ... that it was thermally moulded, that it was
special nylon with a low coefficient of friction, that it was
hygroscopic, and lastly that it was glass-filled nylon.

Well, 'nylon' means polyamide plastic, glass-filled means it was
probably thermally molded to a precise size (that's the benefit of the glass
filler, that the size is stable).

I suppose you could burn a sliver to see if it has the ammonia-like
smell of polyamide. It's more likely that a low-friction plastic
(Delrin aka acetal) would be used, rather than polyamide, for a sliding part.