MadSci Network: Physics

Re: Willoil orwater reduse friction more between two pieces of wood?

Date: Fri Jan 4 11:53:34 2002
Posted By: Jaime Valencia-Rodríguez, Guest Researcher, Chemical Science and Technology Lab, NIST.
Area of science: Physics
ID: 1008096987.Ph

Dear Anonymous:

Your question, albeit very interesting, is hard to answer due to lack of 
details. In order to answer it properly, it will be necessary to know 
which kind of wood and what type of oil you are intending to use.
Some kinds of wood are very oily and will slide over another similar piece 
of wood even if no additional lubricant is used.
It is also important to note that some oils will become sticky after some 
time or at some temperatures.

I checked the Internet and I found the following information.

There is a very nice website 
containing the following definitions:

LOAD WEAR INDEX (LWI) - measure of the relative ability of a lubricant to 
prevent wear under applied loads; it is calculated from data obtained from 
the Four Ball EP Method. Formerly called mean Hertz load.
LUBRICATION - control of friction and wear by the introduction of a 
friction-reducing film between moving surfaces in contact. The lubricant 
used may be a fluid, solid, or plastic substance. For principles of 
lubrication, see boundary lubrication, full-fluid-film lubrication, ZN/P 
LUBRICATING OIL - compounded or finished oil consisting of base stocks and 
the additives necessary for providing the required performance. 
LUBRICITY - ability of an oil or grease to lubricate; also, called film 
strength. Lubricity can be enhanced by additive treatment. See compounded 
COMPOUNDED OIL - mixture of a petroleum oil with animal or vegetable fat 
or oil. Compounded oils have a strong affinity for metal surfaces; they 
are particularly suitable for wet-steam conditions and for applications 
where lubricity and extra load-carrying ability are needed. They are not 
generally recommended where long-term oxidation stability is required. 
CORROSIVE WEAR - progressive removal of material from rubbing surface 
caused by a combination of chemical attack and mechanical action. 

As an example of the problems found using the inappropriate lubricant, I 
found the following information contained in  foxtail

Mechanical Music Digest™ Archives 
Wooden Crank Rod Lubrication
By Craig Brougher

Bill Finch had a very nice experiment there, concerning crank rod 
elongation.  I have also noticed that maple elongates less, but there are 
different qualities of maple, too.
The self-lubrication of wood comes from its resins liquefying under 
friction heat, and you will then notice a varnish buildup on the cranks 
after awhile.  This is what gets hot in minuscule amounts.  The reason oak 
has less friction but more elongation is probably obvious -- the 
internal "wicking action" of the wood is stronger in oak because of 
the "sinew-like structure of oak with the large pores, but the compression 
of oak is greater because there is less wood contacting the crank, since 
the pores are big and hollow.
However, the reason for the knocking of wooden rods is due to the stopping 
and starting of these pumps, thousands of times a year.  Once the rod 
cools off and the resin gets hard, then you get a tremendous amount of 
wear and tear until the rods get hot again.  (I'm not talking about the 
whole rod -- just a very thin contacting surface, so you can't measure it 
very well.).
The grease must be there, or your orchestration or band organ will 
definitely start knocking again, and you will have to make new rods.
The grease substitutes for wood resins, so, since you are either going to 
use wood resins or grease, you'd better pick a good grease.
A little common sense will tell you that any test run continuously can 
only test the continuous operation factor.  Testing engines that way 
produces absolutely wonderful results, too.  But turning them on and off, 
letting them get cold, and then switching them back on, and you get 
terrible results.  Even changing the speed, changing the loading factor, 
etc. makes enormous differences in your results.  So when this happens all 
the time in band organs, you end up instead looking around for truly great 
In the other hand, using water as a lubricant could be tricky, because dry 
wood could absorb a lot of water (it depends on how dry it is and what 
kind of wood we are considering).
In the nice site natmus we find:

Wood is typical of the water-containing materials. Wood in furniture 
contains roughly ten percent water by weight. The exact water content 
depends on the temperature and humidity of the surrounding air during the 
previous few weeks. The water content matters to conservators because wood 
swells and shrinks at it absorbs and desorbs water. Water is also an 
accelerator of slow decomposition reactions. 
Under what circumstances does wood exchange water with air? 
If we take a five-liter jar we can calculate, by reference to the Mollier 
diagram and the density of air, that the air within it, at room 
temperature, cannot contain more than about a tenth of a gram of water. If 
we now pour in a kilogram of wood chips the bottle will contain about 100 
grams of water, almost entirely in the wood. We can therefore flush the 
jar quickly with dry air and wait to see what happens, knowing that the 
relative change of water content of the wood will be very small indeed. 
In spite of the overwhelming reserve of water in the wood, the air in the 
flask does not become saturated with water but comes to equilibrium, after 
a short time, at about 50% relative humidity. 
A graph of the equilibrium RH of the air in the bottle after equilibration 
with wood pre-adjusted to various water contents (EMC = Equilibrium 
moisture content) looks like this:

The exact curve depends a little on the species of tree, but the shape of 
the curve is always the same.  
The temperature dependence of the water content of wood 
The curve is called the absorption isotherm, a jargon term which means 
that the curve joins a series of measurements made at a constant 
temperature, 15 degrees in this case. 
We can complete the diagram by conducting the same series of measurements 
at various temperatures. The curves lie close together. Usually one can 
ignore the slight temperature dependence of the equilibrium, but there are 
circumstances where it is important: a point I will take up in a later 


Many materials show similar behavior: cotton, linen, wool, silk, silica 
gel and even concrete. 
Because the equilibrium RH depends on the water content of the material, 
almost unaffected by temperature, conservators always refer to the water 
content of air in terms of RH. This is not strictly correct, because RH is 
just a ratio, which can only be converted into water vapor content if the 
temperature is also quoted. It doesn't usually matter but when it does, 
this casual simplification can cause a lot of misunderstanding. 
Furniture is not usually displayed in glass bottles, even in museums. In 
the real world it is the air that controls the water content of the wood, 
because its low water vapor concentration is compensated by the continuous 
flow of fresh air past the object. Although the air is now controlling the 
water content of the wood, the results derived from the sealed jar 
experiments still apply. One must get used to thinking in both ways. 
Occasions when the sealed jar concept applies are quite numerous: packing 
for transport, freezing or heating in a sealed bag to kill bugs, flushing 
bagged objects with nitrogen or carbon dioxide to kill bugs, enclosure in 
a showcase.

In order to prevent water absorption (or water loss), there are several 
treatments based upon the use of different oils. As an example we found 

For hardwood floorings it is recommended that both the second and third 
coats of Haarlem Oil be diluted with 10 - 15% of vegetable turpentine. 
Hardwoods are Eucalyptus, Kwila, Iroko, Rata, Pohutukawa, Oak, Beeeh, etc. 
Oil absorption rates for these woods are lower.

And also (

WIPLAM – is a revolutionary product for applications in the transformer 
industry. It is a homogenous material manufactured from specified species 
of timber. It has exceptional mechanical properties coupled with oil 
absorption characteristics. After vacuum drying and impregnation with 
Pyrochlor or transformer oil, it acquires dielectric properties of 
transformer oil with enhanced mechanical properties.

And finally (

Wolman® RainCoat®
Clear Water Repellent
A totally clear, mildew-resistant, oil-base water repellent that allows 
wood to gray naturally. Protects wood from damage caused by water 
absorption. Deep penetrating oil formula gives wood a rich, attractive 

Some of the natural damage found in very old wood could be avoided, 
according to the following site  oilwrfr.pdf using oil treatment:

Treatments at low temperatures using vegetable oils (120 ?C to 140 ?C) 
avoids splits and reduce tannins leaching.

I hope this helps.


Jaime Valencia

Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-2001. All rights reserved.