Hi John:
> the largest size listed in the table is 1.00mm minimum metal thickness,
> 2.00mm maxhole dia., and 3.00mm minimum center-center hole spacing. If my
> metal thickness was greater (1.27mm), and my center-center hole spacing was
> 4.75mm, could I not go to a larger hole (3.175 - .125")?
The basic requirement is found in Annex A.5, Hot Flaming
Oil Test.
Table 15 lists a set of hole diameters and center-to-center
distances between holes as a function of metal thickness.
These combinations are such that hot flaming oil will
extinguish when passing through the holes.
The oil does not burn at room temperature. It must be
heated before it will ignite. The burning oil is poured
onto the perferated sheet metal.
The combination of hole diameter, center-to-center spacing,
and metal thickness combine to cool the oil and exclude
oxygen when the oil passes through the oil such that the
oil that passes through the holes ceases to flame.
The extinguishing process is twofold:
1) The bottom surface of the oil film is cooled by the
available metal surface. The top surface of the oil
is heated by the flames and continues to burn.
2) As the oil passes through the hole, the hole actually
fills with oil such that oxygen does not pass through
the hole and thereby does not support combustion to the
cooled oil that passes through holes.
So, the thicker the metal, the more cooling.
The larger the hole, the more likely the flame will follow
the oil through the hole.
2 mm is about the largest diameter hole that will not allow
the flame to pass through. So, you will need to rely on
cooling alone. The hole-to-hole spacing and the metal
thickness will have to cool the oil below ignition
temperature as it falls through the hole. Not likely, in
my opinion.
The only way to know for sure is to perform the test.
The test is easily performed in a fume hood with tools
readily available from a grocery store or kitchen specialty
shop. A metal ladle with a metal handle. For some ladles,
you will need to bend the handle to make it do this job.
I use the largest aluminum foil roasting pan to catch the
oil. I use a small aluminum cake pan (inverted) or
equivalent to place the cheesecloth on.
The height of the ladle above the specimen is critical and
must be maintained constant. I use a rest for the ladle
handle positioned so that the ladle is at the correct
height.
The rate of pour is also critical. You will need to
practice your timing of the pour to get the rate correct.
You'll need someone to help by giving you a countdown as
you pour (you can't watch a clock and pour at the same
time!).
I use putty to make a dam to prevent the oil from going
over the edge of the specimen. Put the dam at the edge
of the specimen so the oil spreads over the specimen, and
does not concentrate at the holes.
The oil is standard diesel or household heating oil.
You may need a fire extinguisher to extinguish the fire
in the roasting pan.
The test is flaky, and not super-repeatable. The pass
criterion is two passes in succession. (All non-passes
are treated as practice tests.) It takes good technique
(constant pour rate, and constant height) to get a pass.
Best regards,
Rich
---------
This message is coming from the emc-pstc discussion list.
To cancel your subscription, send mail to [email protected]
with the single line: "unsubscribe emc-pstc" (without the
quotes). For help, send mail to [email protected],
[email protected], [email protected], or
[email protected] (the list administrators).
