Improvements in Pyrometers.
Year: 1893

page_text: COMPLETE SPECIFICATION.
Improvements in Pyrometers.
A communication from EDWARD BROWN, of 3617, Powelton Avenue, Philadelphia,
County of Philadelphia, State of Pennsylvania, United States of America,
Mechanical Engineer.
I, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
Chartered Patent Agent, do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:-
This invention relates to the construction of pyrometers which have a long
expansion stem projecting into the medium, the temperature of which is to be
indicated, which stem is secured to a case containing the multiplying mechanism,
pointer and dial.
To give sufficient rigidity and strength, this style of stem pyrometer is made
with somewhat heavy or thick walls; and especially is this necessary when the
pyrometer is employed to indicate the temperature of gases above red heat; a red
heat being very destructive in its oxidizing effect upon the metals which are most
easily available, and the stem in a few weeks or months becomes bent or eaten
Again this
away, or the structure of the material entirely altered and useless.
style of pyrometer as heretofore made is only accurate when the stem as a whole
has been inserted in the heated medium a sufficient time to acquire a uniform
temperature throughout its parts which takes from ten to twenty minutes, too long
a time to be spared by a workman, and consequently the pyrometer is only used as
a fixed or stationary pyrometer.
In the invention now to be described, this stem pyrometer is made to indicate
accurately in one minute or less the temperature of red hot gases or fluids.
This is done by making the stem substantially in two parts; the lower end of
very thin sheet metal tubing connected firmly to a much heavier and thicker pipe.
Within this composite stem, and at the bottom is the heavy and slow-expanding
rod of infusible material, and upon this rests a rod of metal which communicates
with the indicating mechanism and pointer.
The
When in use this thin sheet metal tube is rapidly heated and communicates its
expansion to the pointer before the heat has had time to produce much effect in
raising the temperature of the other and heavier part of the stem. The instru-
ment can at once be withdrawn after the trial, thus prolonging its durability;
and not only is it made more durable but the same metals can thus be used to
indicate higher temperatures than heretofore; and metals almost infusible are
thus made available for indicating temperatures much above white heat.
inside rod, which communicates between the lower end of the stem and the
indicating mechanism, is also made of composite metals having a greater expan-
sion than the outside tube, which thereby permits the insertion of the stem to
varying depths without altering its indication. This rapid expansion principle is
also carried out by placing the thin expanding bar within a non-expanding frame.
By this means my correspondent is able to introduce into the centre of a heating
furnace at a white heat, a strip of platinum or other refractory metal, and
measure in a few seconds the motion due to its expansion, before the heavy
metal frame has received sufficient heat to materially expand it and affect the
indication.
Features in this invention different from any previous invention are these; the
expansion bar and the slow-expanding frame or fulcrum to which it is attached
may be of different materials or may both be of the same material, such as iron.
The mechanism in the head is so adjusted as to show the temperature when the

page_text: expansion bar first arrives at its full or nearly full maximum heat, for it is
evident that, should the strip and slow-expanding bar be of the same materials
and the stem be kept in the heat until it is all evenly heated, the pointer must
return again to the temperature at which it originally started. By this inven-
tion a smaller quantity of metal such as platinum is able to be used; and the
white-hot temperature of a heating furnace indicated in a few seconds and without
injury to the metals employed.
In the accompanying drawings
Fig. 1 is a general view of the pyrometer as a whole.
Fig. 2 shows the same inserted by the attendant workman into a heating or
annealing oven.
Fig. 3 shows a vertical section through the stem with the expansion tube outside.
Fig. 4 is especially to show the composite interior connecting rod of the stem.
Fig. 5 is a modified forin showing the thin expansion rod within the non-
expanding bar.
Fig. 6 is a section through the same.
Fig. 7 is a section on line X Y.
Fig. 8 shows the interior mechanism of the pyrometer head.
In Fig. 1 is shown the case or head A having a dial and a pointer V which
is actuated by the difference in expansion in the parts of the stem. B is a
socket uniting the head to the stem. R the thin expansion tube, coupled to the
lower end of the stem. The stem shown in Figure 3 is constructed of a heavy
iron pipe C to give strength and rigidity when inserted three or four feet
into a red hot furnace. The lower end of this pipe is faced and screwed
to fit the coupling K³ similarly to what is known as a union joint. R is the
expansion tube of thin sheet metal, as iron or platinum, a flange ¹ is turned
on its top edge by which the tube is coupled to the heavy pipe C. When this
tube is very thin it is slipped over the reduced end C¹ of the pipe C as shown,
and secured by screws, to give additional rigidity to the joint. In the lower
end of the expansion tube is fitted the plug S. This plug is countersunk inside,
to receive centrally the bar M of iron, plumbago ware, fire-brick, or similar
infusible material, which is called the slow-expanding bar. Upon this bar rests
the iron rod D, the upper end of which communicates through the spring pin W
with the mechanism in the head A, and any motion due to the difference in
expansion of the parts of this composite stem is communicated to the pointer.
d2 are discs or buttons for preventing the rod D bending within C.
In Figure 2 is shown the instrument as used in a heating oven T, the tempe-
rature of which may be white-hot. The wall in this case is from 18 inches to
20 inches thick, and white hot on its inside edge and several hundred degrees
Fahrenheit cooler on the outside. To prevent the pipe C being heated or
affected by this high temperature of the oven, or wall, it is made heavy and
encased in another tube E and the space between the two at N is filled in with
asbestos paper wrapped around the pipe C. To protect the thin expansion
tube R when not in use a sliding case H is placed outside the tube E.
The instrument operates in this way. When inserted into gases at a white
heat the expansion tube R being very thin, about No. 27 wire gauge, acquires
the full temperature of the oven in one minute or less, the pointer V becoming
stationary or receding and indicating the temperature on the dial, quite definitely
to a practiced eve. As however some heat is slowly penetrating to the pipe C
and bar M the pointer will not long remain stationary but fluctuate until the
stem is heated all through evenly.
That the indication of the pointer may be more correct than if the inside
rod D in Fig. 4 be made of the same material as the outside tube, the bottom
end p is made of brass, which expands more than the outside tube C of iron,
also other pieces p² of brass are placed in the same iron rod, the effect of which
when properly proportioned in length is to make the pyrometer to indicate more
promptly and to cause the pyrometer not to vary under the same temperature,

page_text: whatever depth the stem may be inserted or whatever the temperature of the
furnace wall. The effect of this construction is such that the expansion tube R
will indicate the temperature due to its elongation in less than one minute, at
which time the heat begins to elongate the lower end of rod D more than the
pipe which causes the pointer to recede ten or twenty degrees, from the
maximum indicating precisely the temperature reached. L Fig. is a movable
flange adjustable by screws --this flange serves to close the aperture into the
oven or furnace and prevent an influx of cold air.
When the tube R has a different rate of expansion per degree of heat, from that
of the bar M-this same stem see Fig. 4 may be left in the heat until it is all
evenly heated, in which case the mechanism in the head is adjusted to suit. The
mechanism within the head is shown in Fig. 8. D' is the toothed segment gearing
into the pinion do which carries the pointer V. On this segment is hinged the
adjusting arm C. A pin c connects the arm C with the link c² which in turn is
connected with the sliding rod K (see Fig. 6) within the stem. A stud c³ projects
from the segment, through which stud the screw c¹ passes, and presses against the
arm C. A spring keeps the arm in contact with the screw. An opening is
made in the case at C through which is inserted a screw driver to turn the screw c
and by this the radius or distance of the pin from the pivot of D₁ is regulated
without removing the glass, pointer, or dial. The arm C is secured permanently
by the set screw c'. The pyrometer head carrying this mechanism is secured to the
stem by the coupling B. In Figs. 5 and 6 the same general principle is carried
out, viz. a thin expansion rod is placed within the heavy slow-expansion frame.
The stem shown in Fig. 6 is constructed of a heavy pipe M² to give strength
and rigidity when inserted through a two-feet wall into a red-hot furnace. The
lower end of this pipe is screwed into a cross bar D'. Into this cross-bar is
screwed one or more heavy iron rods G, and at the other end of these rods
is secured the cross bar H by means of nuts 3. Within this rectangular frame
is suspended the expansion bar E2, by means of the eye bolts / h². The
upper eye bolt connects the bar with the sliding rod K, upon this rod are
buttons K which steady the rod centrally, making a light rod with very little
friction. The upper end of this rod is attached to the link e² and by this means
the expansion of the bar E2 is communicated to the mechanism in the head and
thence to the pointer V. A strip of wire may be used in place of rod K. To
give additional strength and rigidity the thin expansion bar E2 is made angular or
convex as shown in Fig. 7. The expansion bar is kept under tension by the
spring S2. By making the expansion bar E2 heavier and placing the spring S
on the opposite side of the quadrant the mechanism may be used to compress the
bar instead of having it under tension.
To maintain greater accuracy in the instrument the iron rods G are covered
with asbestos, and outside this is placed an iron tube el. The tube M² is also
covered with asbestos paper, and another heavy tube m' placed outside it. The
effect of this is such, that in fifteen seconds the expansion bar E2 may be heated to
the full temperature of the furnace, perhaps 2000 degrees, Fahrenheit, in which
time the rods G will acquire very little heat, probably not over 100 degrees, and
the tube M still less heat. The tubes e' are of such a thickness as to acquire a
temperature intermediate between the expansion bar E² and rods G thus preventing
the cooling effect of the rods G upon the expansion bar E².
To prevent the access of cold air to the furnace a sliding collar N² is placed
upon the stem, upon the face of the collar is secured an elastic disc (Fig. 5).
This collar is secured at any position on the stem by a set screw. The operation
of the pyrometer is in this manner;-
The pyrometer having been introduced into the furnace, as shown in Fig. 2 the
expansion bar is heated to the full temperature of the furnace (we will suppose
2000 degrees) in fifteen seconds;-at which time the heat has penetrated to the
rods G which begin to expand, and thereby return the pointer V gradually back to
its starting point,

page_text: The arm C of the mechanism is so adjusted in this case, that the pointer
indicates 2000° which is its maximum position before it begins to return.
The pyrometer works well with only one rod G and the bottom cross bar H';
though two rods G are used the better to protect the expansion bar from injury.
The principle of construction being to introduce into the furnace a relatively very
light or thin expansion bar of highly refractory metal which shall be exposed to
and which shall acquire the full temperature of the furnace, and indicate it before
the heavy frame or stem which carries it is materially elongated by the heat.
Having now particularly described and ascertained the nature of the said inven-
tion, as communicated to me by my foreign correspondent, and in what manner
the same is to be performed, I declare that what I claim is,―
1. A pyrometer stem the lower end of which carries a very thin expansion strip
of metal freely exposed to the heat in close proximity to a heavy and slow expanding
bar in combination with a connecting rod communicating the difference of motion of
the aforesaid parts to mechanism so adjusted as to indicate the correct temperature
when the pointer first becomes nearly stationary substantially as and for the
purpose herein described.
2. In a pyrometer the combination of the heavy pipe C the thin expansion
tube R separable from but secured rigidly thereto the interior slow-expanding
bar M the rod D communicating with the mechanism within the head A which is
adjusted to indicate the correct temperature when the pointer first arrives at a
nearly stationary position.
3. In a pyrometer stem the combination of the pipe C the thin expansion tube R
the coupling K³ the slow-expanding bar M the rod D (which at its lower end p¹
elongates per degree of heat more than the pipe C) to operate the pointer V as
herein described.
4. In a pyrometer stem adapted to be inserted in a heated medium the combina-
tion of a heavy pipe C protected from the access of heat by the casing E the thin
metal expansion tube R separable from but secured rigidly thereto the non-
expanding bar M and an inside rod for communicating the expansion of the tube R
to the pointer.
5. In a pyrometer stem the combination of the pipe C the thin metal expansion
tube R flange coupling K the slow expanding bar M the rod D communicating
with the pointer V as herein described.
6. The combination in a pyrometer stem of the outside pipe C and the inside
composite connecting rod D in which are pieces p² to adjust the expansion of the
rod D relatively to the pipe C as herein described.
7. In a pyrometer the combination of the head A carrying the indicating
mechanism the heavy pipe M2 the thin expansion bar E² secured within the
frame D' G H and the rod K which communicates the expansion of the said bar
to the indicating mechanism.
8. In a pyrometer the combination of the expansion strip E2 pivotted within the
frame at the end of the pipe M2 mechanism within the case A connected with the
said strip and adjusted to indicate the correct temperature when the pointer V
first arrives at its maximum position.
9. In a pyrometer stem the combination of the heavy pipe M2 the sliding rod K
the outside case m¹ the expansion strip E' within the frame D' G H and one or
more outside tubes e'.
10. In a pyrometer stem the combination of the convex expansion strip E
pivotted at h¹ to the frame H G D' and the sliding rod K by which the expansion
of the said strip is communicated to the mechanism within the head A.
11. In a pyrometer stem the combination of the expansion strip E of very light
weight relatively to the frame D7 G H which carries it the pipe M2 and sliding
rod K operating substantially as described.
12. The sliding collar N with elastic face n' upon the pyrometer stem m² as
herein described.

page_text: 13 The adjusting mechanism within the case A consisting of a pinion dª a
toothed segment D' carrying the adjusting arm C8 the screw c¹ the spring
case A and opening in the said case.
Dated this 29th day of March 1893.
the
W. P. THOMPSON & BOULT,
Of London, Liverpool, Manchester, and Nottingham,
Agents for the Applicant.