U.S. patent number 3,813,215 [Application Number 05/383,682] was granted by the patent office on 1974-05-28 for subjecting samples to elevated temperature.
This patent grant is currently assigned to Electrothermal Engineering Limited. Invention is credited to Henry Arthur John Ward.
United States Patent |
3,813,215 |
Ward |
May 28, 1974 |
SUBJECTING SAMPLES TO ELEVATED TEMPERATURE
Abstract
There is disclosed apparatus for use in subjecting samples to
elevated temperature. The apparatus includes first chambers for
receiving samples, part of each of the first chambers being within
a second chamber which is out of communication with the first
chambers and there being a third chamber which communicates by way
of entrance openings with the first chambers, each first chamber
having an exit opening, there being air in all the first, second
and third chambers, an air inlet to the third chamber and means for
heating the air. In use of the apparatus, heated air passes from
the third chamber by way of the entrance openings into the first
chambers, past the samples and out of the first chambers by way of
the exit openings and heated air in the second chamber is in
contact with the walls of the first chambers and heats them.
Inventors: |
Ward; Henry Arthur John (Essex,
EN) |
Assignee: |
Electrothermal Engineering
Limited (London, EN)
|
Family
ID: |
10391663 |
Appl.
No.: |
05/383,682 |
Filed: |
July 30, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Aug 7, 1972 [GB] |
|
|
36846/72 |
|
Current U.S.
Class: |
432/226; 432/5;
432/231 |
Current CPC
Class: |
B01L
7/02 (20130101); G01N 17/00 (20130101) |
Current International
Class: |
B01L
7/02 (20060101); B01L 7/00 (20060101); G01N
17/00 (20060101); F27b 005/02 () |
Field of
Search: |
;432/1,5,219,220,225,226,231 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Camby; John J.
Attorney, Agent or Firm: Finnegan, Henderson, Farabow and
Garrett
Claims
I claim:
1. Apparatus for use in subjecting a sample to elevated
temperature, including:
a. first wall means, defining a first chamber for receiving a
sample and having an entrance opening and an exit opening,
b. second wall means, defining (i) a second chamber within which
part of said first wall means is disposed and which does not
communicate with said first chamber and (ii) a third chamber which
communicates by way of said entrance opening with said first
chamber, there being air in all three chambers,
c. an air inlet to said third chamber and
d. means for heating the air, whereby heated air can pass, in use
of the apparatus, from said third chamber by way of said entrance
opening into said first chamber, past the sample and out of said
first chamber by way of said exit opening and heated air in said
second chamber is in contact with said first wall means and heats
it.
2. Apparatus according to claim 1, including:
a. at least one heater in said second chamber for heating the air
in that chamber and
b. an air inlet duct to said third chamber running through said
second chamber for preheating the air supplied to said third
chamber by heat exchange with the air in said second chamber.
3. Apparatus according to claim 1, including a plurality of such
first wall means, each defining a respective first chamber for
receiving a sample and having a respective entrance opening and a
respective exit opening, the first chambers being spaced apart so
that their entrance openings, by way of which they communicate with
said third chamber, can receive from that chamber air at
substantially equal temperature.
4. Apparatus according to claim 2, including a plurality of such
first wall means, each defining a respective first chamber for
receiving a sample and having a respective entrance opening and a
respective exit opening, the first chambers being spaced apart so
that their entrance openings, by way of which they communicate with
said third chamber, can receive from that chamber air at
substantially equal temperature.
5. Apparatus according to claim 4, wherein said air inlet duct
extends across said third chamber and has formed in it holes of
varying size distributed along it so that air can escape into said
third chamber in a substantially uniform manner.
6. Apparatus according to claim 5, wherein said air inlet duct is
of serpentine form.
7. Apparatus according to claim 5, including a grid between said
holes and the said entrance openings.
8. Apparatus according to claim 1, wherein the first chamber has in
it carrying means for carrying a sample.
Description
BACKGROUND OF THE INVENTION
This invention relates to subjecting samples to elevated
temperature, for example for carrying out an accelerated aging test
on a sample.
One form of accelerated aging test of, for example, a sample of
rubber or plastics material consists in subjecting a test sample to
controlled deterioration by air at elevated temperature and at
atmospheric pressure, after which one or more physical properties
of the sample is or are measured and compared with a corresponding
property or properties of a similar sample which has not been so
heated.
For the heating of test samples, two types of ovens including
chambers for receiving samples have been proposed. One is an oven
incorporating a heated oil bath for heating the chambers and the
other an oven incorporating a heated block of solid material which
receives the chambers for heating them. The former usually has the
disadvantages of being too limited in temperature and cumbersome,
and the latter usually has the disadvantages of being cumbersome
and suffering from inherent temperature gradient problems.
THE INVENTION
The object of the invention is to provide apparatus for use in
subjecting a sample to elevated temperature including a chamber for
receiving such a sample, in which heated air is used for heating
the chamber.
According to the invention there is provided apparatus for use in
subjecting a sample to elevated temperature, including:
A. FIRST WALL MEANS, DEFINING A FIRST CHAMBER FOR RECEIVING A
SAMPLE AND HAVING AN ENTRANCE OPENING AND AN EXIT OPENING,
B. SECOND WALL MEANS, DEFINING (I) A SECOND CHAMBER WITHIN WHICH
PART OF SAID FIRST WALL MEANS IS DISPOSED AND WHICH IS OUT OF
COMMUNICATION WITH SAID FIRST CHAMBER AND (II) A THIRD CHAMBER
WHICH COMMUNICATES BY WAY OF SAID ENTRANCE OPENING WITH SAID FIRST
CHAMBER, THERE BEING AIR IN ALL THREE CHAMBERS,
C. AN AIR INLET TO SAID THIRD CHAMBER AND
D. MEANS FOR HEATING THE AIR, WHEREBY HEATED AIR CAN PASS, IN USE
OF THE APPARATUS, FROM SAID THIRD CHAMBER BY WAY OF SAID ENTRANCE
OPENING INTO SAID FIRST CHAMBER, PAST THE SAMPLE AND OUT OF SAID
FIRST CHAMBER BY WAY OF SAID EXIT OPENING AND HEATED AIR IN SAID
SECOND CHAMBER IS IN CONTACT WITH SAID FIRST WALL MEANS AND HEATS
IT.
The testing could be an artificial aging test.
There could be at least one heater in said second chamber for
heating the air in that chamber and/or at least one heater in said
third chamber for heating the air in that chamber, but it is
preferred to have at least one heater in said second chamber for
heating the air in that chamber and an air inlet duct to said third
chamber running through said second chamber for preheating the air
supplied to said third chamber by heat exchange with the air in
said second chamber (the air supplied to said third chamber not
being further heated whilst in said third chamber). There may be a
plurality of such first wall means, each defining a respective
first chamber for receiving a sample and having a respective
entrance opening and a respective exit opening, in which case they
(the first chambers) are all spaced apart so that their entrance
openings, by way of which they communicate with said third chamber,
can receive from that chamber air at substantially equal
temperature. This may be achieved by having the above-mentioned air
inlet duct extend across said third chamber, for example in
serpentine form, and formed with holes of varying size distributed
along it so that air can escape into said third chamber in a
substantially uniform manner. It helps to provide a grid, for
example of wire, between these holes and said entrance
openings.
An example in accordance with the invention is described below with
reference to the accompanying drawings, in which:
FIG. 1 shows a diagrammatic sectional plan view of apparatus for
use in testing samples at elevated temperature,
FIG. 2 shows a sectional side view of the apparatus,
FIG. 3 shows a detail of part of the apparatus,
FIG. 4 shows a detail of part of what is shown in FIG. 2,
FIG. 5 shows in greater detail means forming one of the first
chambers and its associated parts, including sample carrying
means,
FIG. 6 a shows the sample carrying means per se and FIG. 6 b an end
view of part of the sample carrying means, and
FIGS. 7 a and 7 c show different devices that can be used with a
thermometer in the apparatus, FIG. 7b showing the manner of using
one of them.
In the example, twenty thick-walled vertical aluminum tubes 1 of
constant circular cross-section are used to hold samples of rubber
or plastics material to be subjected to an accelerated aging test.
Each tube is at least 30 cm. long and is dimensioned in accordance
with British Standard Specification No. 903 Part 19 (1956). At the
top of each tube is a tube extension 2 made of
polytetrafluoroethylene and to that is attached a top cap 3 of
polytetrafluoroethylene from which, in all cases except one, a
conventional sample carrier depends, this being capable of carrying
samples of material spaced apart along the tube and out of contact
with the wall of the tube. Each tube provides a chamber 4 and most
of each of them is within a chamber 5 formed by an oblong aluminum
tank having walls 6, this being within another tank made of mild
steel and having side walls 7 and a bottom wall 7a, there being
glass wool or other heat-insulating material 8 of two inches
thickness between the two tanks. The tank having walls 6 and the
tank having side walls 7 and bottom wall 7a are secured to a square
wooden frame 9 in a manner to be described below, a mild steel
intermediate plate 10 being provided with glass wool or other
heat-insulating material 11 of two inches thickness between it and
the uppermost wall 6. The tank having walls 6 has a partition 12
extending across it so that the tank forms another chamber 13. The
chambers 4 do not communicate with the chamber 5, but their lower
ends open into the chamber 13. In this chamber there is a
serpentine pipe 14 and between this and the lower ends of the
chambers 4 there is a steel wire mesh 15. Cold air is drawn in from
outside the apparatus and supplied by means of a diaphragm pump 16
and it flows through a tube in the chamber 5 in which it is heated,
this tube having two serpentine portions 17 as shown in FIG. 3
(which for simplicity shows no other details of the apparatus other
than the tank having walls 6) at opposite sides of the chamber and
a straight portion 18 interconnecting them. Then the heated air
flows from the tube in the chamber 5 into the pipe 14 in the
chamber 13. This pipe is closed at its downstream end and has holes
of varying size distributed along it so that it distributes the
heated air substantially uniformly over the chamber 13, 14a in FIG.
1 showing path of the pipe 14. The heated air flows through the
wire mesh 15, which increases the uniformity of its distribution,
into the lower ends of the chambers 4. It flows upwardly over the
samples and out through small vent holes (see FIGS. 5 and 6 a ) in
the top caps 3 to atmosphere.
In the chamber 5, at opposite sides of it, there are two panel-type
electric heaters 19, consisting of a wire mesh heater sandwiched
between two sheets of asbestos, which are heated to incandescence
but heat the air, which is trapped, in the chamber 5. There is heat
exchange between this air and the air in the tube having the parts
17 and 18 and the air in the chamber 13 has in consequence
substantially the same temperature as that in the chamber 5.
There is a mild steel casing having side walls 20 and a bottom wall
20a in which is disposed the tank having side walls 7 and bottom
wall 7a, and spaced from it by at least one inch, this containing,
outside the latter tank, the diaphragm pump 16 and an electric
motor for driving it, and an electric motor 21 which drives a fan
22 inside the chamber 5 and which distributes substantially
uniformly the air in the chamber so that it is all substantially at
the same temperature. Heat sinks of aluminum are fixed to the
stator of the motor 21 and the motor which drives the diaphragm
pump 16, to keep the bearings cool and prevent seizing up.
Attached to the side walls 20 of the outer mild steel casing is a
mild steel panel 24 having an opening which carries a bracket 27
around its inside edge which is screwed by wood screws to the
wooden frame 9 (see FIG. 4). The inner tank having walls 6 is
carried by the wooden frame 9 by means of stainless steel L-shaped
brackets 23, the latter being fixed by wood screws to the frame 9
and bolted via flanges to the tank, the wood screws also fixing the
walls 7 to the frame 9. The brackets 23 provide a long heat path
between the walls 6 and the frame 9. On the inner side of the frame
9 a square bracket 26 of U-shaped cross-section is fixed by wood
screws, and bolted to the lower flange of the bracket 26 is the
intermediate plate 10 and bolted to the upper flange is a Duralumin
facia panel 25 through which the tops of the extensions 2 extend.
There is a one inch air gap between the facia panel 25 and the
intermediate plate 10.
Referring to FIGS. 5, 6 a and 6b, each top cap 3 (having a vent
hole 28) carries a stainless steel rod 29 to which are fixed up to
five clips 30 (three only being shown) for carrying respective
samples to be heated, and at the opposite end of the rod 29 is
fixed an apertured aluminum catcher plate 31 (shown in end view in
FIG. 6b) for preventing samples falling from the clips into the
chamber 13. The tubes 1 should not be made of or contain copper or
copper alloy, except perhaps if they are clad with appropriate
material, for example by being chromium or cadmium plated. Sealing
rings (not shown) of a silastomer surround the tubes 1 where they
pass through the partition 12.
The temperature in the chamber 5 is monitored by a variable-setting
mercury-type contact thermometer 32 which includes a tungsten
electrode which can be adjusted in position so that contact between
it and the mercury occurs when the air temperature in the chamber
is 70.degree., 100.degree., 125.degree., 150.degree., 175.degree.,
200.degree. or 250.degree.C. When contact is made a signal supplied
by way of a cable 33 and a jack plug 34, which engages in a socket
not shown, ensures that no current can be supplied to the heaters
19 and when contact is broken it is arranged that current can be
supplied to them, so that the temperature in the chamber 5 is
maintained substantially at the value set at the contact
thermometer. When the jack plug is not in its socket, current
cannot be supplied to the heaters. The contact thermometer 32,
cable 33 and jack plug 34 can be removed for transit of the
apparatus.
The chamber 4 which does not contain a sample carrier instead
contains the lower end of a thermometer which projects through the
top cap 3 of that chamber.
In use of the apparatus, samples are held by the clips 30, a
flowmeter in the apparatus measures the rate of supply of air to
the tube having the parts 17 and 18 and a valve controlled by the
flowmeter ensures that the rate of supply of air per hour is equal
to the number of chambers 4 times the volume of each chamber times
a factor not less than three and not more than ten. The samples are
subjected to a constant elevated temperature and substantially
atmospheric pressure for an appropriate time and then one or more
of their physical properties is or are measured and compared with a
corresponding property or corresponding properties of similar
samples which have not been heated.
Another electric motor drives a fan, which cools the space, which
contains this motor and fan, between the tank having the side walls
7 and the casing having side walls 20, which is formed with louvres
for the inlet and outlet of cooling air.
Control of the heating by the heaters 19 is effected by altering,
by turning a heat control knob, the ratio between "on" and "off"
periods of a substantially sinusoidal current which is supplied to
the heaters when the contact thermometer allows it, switching on
and off being effected when the voltage passes through zero. The
heat control knob and the flowmeter are situated on a control panel
accessible at the outside of the apparatus and on this panel there
are also a lamp for indicating whether or not current is being
supplied to the heaters and another lamp for indicating whether or
not the mains are switched on, switching on being effected by a
master switch on the control panel which, when open, disconnects
all the electrical apparatus from the mains.
In addition, there is a safety thermostat which will switch off the
supply to the heaters in the event of the temperature in the
chamber 5 rising to, say, 10.degree.C. above that set on the
contact thermometer, due to a failure.
The contact thermometer 32 has its stem, projecting below the scale
and into the chamber 5 and including a mercury filled bulb,
surrounded by one or the other of two so-called "calibration
tubes", one for use when the temperature within the tubes 1 is to
be 125.degree.C. or lower and the other when this temperature is to
be above 125.degree.C. The tubes are made of chromium-plated brass
and have a wall thickness of 1/16 inch. The first is shown in FIGS.
7 a and 7b and has a screw-thread 35 at its upper end which is
screwed into the contact thermometer housing 36 (see FIG. 7 b). At
its lower end the tube has two diametrically opposite sets each of
three holes and two diametrically opposite sets each of two holes,
all the holes being 3/8 inch in diameter and passing right through
the wall of the tube. The stem, made of glass, of the thermometer
is shown at 37 and the mercury bulb at 38. The second tube differs
from the first in that it has, as shown in FIG. 7 c, two
diametrically opposite rows each of eight holes and two
diametrically opposite rows each of six holes, all the holes
passing right through the wall of the tube and all being 3/8 inch
in diameter except the lowest two of the eight-holed rows, which
are 1/4 inch in diameter.
In each case the tube is shown from one side; its appearance from
the opposite side is the same. The "calibration tubes" ensure that
when the temperature of the chamber 5 is rising, the reading of the
contact thermometer lags the actual temperature in the chamber 5.
The arrangements of holes in the tubes are chosen to ensure
substantial equality between the temperature within the tubes 1 and
the temperature in the chamber 5 and to ensure that this
temperature is about equal to that set on the contact
thermometer.
* * * * *