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Scientific American Supplement, No. 415, December 15, 1883 online

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To use the apparatus in connection with the table: Find the length of
the desired oval in the first column of the table, and the width most
nearly corresponding to that desired in the third column. The
corresponding number in the middle column tells which hole the needle
must be passed through. The tack D, _around_ which the string must pass,
is so placed that the total length of the string AD + DC, or its equal
AE + EC, shall equal the greater diameter of the ellipse. In the figure
it is placed 6½ inches from A, and 1½ inches from C, making the total
length of string 8 inches. The oval described will then be 8 inches long
and 6¼ inches wide.

The above table will be found equally useful in describing ovals by
fastening the ends of the string to the drawing as is recommended in all
the text books on the subject. On the other hand, the instrument may be
set "by guess" when no particular accuracy is required.

* * * * *




THE MANUFACTURE OF CHARCOAL IN KILNS.


The manufacture of charcoal in kilns was declared many years ago, after
a series of experiments made in poorly constructed furnaces, to be
unprofitable, and the subject is dismissed by most writers with the
remark, that in order to use the method economically the products of
distillation, both liquid and gaseous, must be collected. T. Egleston,
Ph.D., of the School of Mines, New York, has read a paper on the subject
before the American Institute of Mining Engineers, from which we extract
as follows: As there are many SILVER DISTRICTS IN THE WEST where coke
cannot be had at such a price as will allow of its being used, and where
the ores are of such a nature that wood cannot be used in a
reverberatory furnace, the most economical method of making charcoal is
an important question.

Kilns for the manufacture of charcoal are made of almost any shape and
size, determined in most cases by the fancy of the builder or by the
necessities of the shape of the ground selected. They do not differ from
each other in any principle of manufacture, nor does there seem to be
any appreciable difference in the quality of the fuel they produce, when
the process is conducted with equal care in the different varieties; but
there is a considerable difference in the yield and in the cost of the
process in favor of small over large kilns. The different varieties have
come into and gone out of use mainly on account of the cost of
construction and of repairs. The object of a kiln is to replace the
cover of a meiler by a permanent structure. Intermediate between the
meiler and the kiln is the Foucauld system, the object of which is to
replace the cover by a structure more or less permanent, which has all
the disadvantages of both systems, with no advantages peculiar to
itself.

The kilns which are used may be divided into the rectangular, the round,
and the conical, but the first two seem to be disappearing before the
last, which is as readily built and much more easily managed.


ALL VARIETIES OF KILNS

Are usually built of red brick, or, rarely, of brick and stone together.
Occasionally, refractory brick is used, but it is not necessary. The
foundations are usually made of stone. There are several precautions
necessary in constructing the walls. The brick should be sufficiently
hard to resist the fire, and should therefore be tested before using. It
is an unnecessary expense to use either second or third quality
fire-brick. As the pyroligneous acid which results from the distillation
of the wood attacks lime mortar, it is best to lay up the brick with
fire-clay mortar, to which a little salt has been added; sometimes loam
mixed with coal-tar, to which a little salt is also added, is used. As
the principal office of this mortar is to fill the joints, special care
must be taken in laying the bricks that every joint is broken, and
frequent headers put in to tie the bricks together. It is especially
necessary that all the joints should be carefully filled, as any small
open spaces would admit air, and would materially decrease the yield of
the kiln. The floor of the kiln was formerly made of two rows of brick
set edgewise and carefully laid, but latterly it is found to be best
made of clay. Any material, however, that will pack hard may be used. It
must be well beaten down with paving mauls. The center must be about six
inches higher than the sides, which are brought up to the bottom of the
lower vents. Most kilns are carefully pointed, and are then painted on
the outside with a wash of clay suspended in water, and covered with a
coating of coal-tar, which makes them waterproof, and does not require
to be renewed for several years.

[Illustration: RECTANGULAR KILNS FOR THE MANUFACTURE OF CHARCOAL.]

The kilns were formerly roofed over with rough boards to protect the
masonry from the weather, but as no special advantage was found to
result from so doing, since of late years they have been made
water-proof, the practice has been discontinued.

The wood used is cut about one and a fifth meters long. The diameter is
not considered of much importance, except in so far as it is desirable
to have it as nearly uniform as possible. When most of the wood is
small, and only a small part of it is large, the large pieces are
usually split, to make it pack well. It has been found most satisfactory
to have three rows of vents around the kiln, which should be provided
with a cast-iron frame reaching to the inside of the furnace. The vents
near the ground are generally five inches high - the size of two
bricks - and four inches wide - the width of one - and the holes are closed
by inserting one or two bricks in them. They are usually the size of one
brick, and larger on the outside than on the inside. These holes are
usually from 0.45 m. to 0.60 m. apart vertically, and from 0.80 m. to
0.90 m. apart horizontally. The lower vents start on the second row of
the brickwork above the foundation, and are placed on the level with the
floor, so that the fire can draw to the bottom. There is sometimes an
additional opening near the top to allow of the rapid escape of the
smoke and gas at the time of firing, which is then closed, and kept
closed until the kiln is discharged. This applies mostly to the best
types of conical kilns. In the circular and conical ones the top
charging door is sometimes used for this purpose. Hard and soft woods
are burned indifferently in the kilns. Hard-wood coal weighs more than
soft, and the hard variety of charcoal is usually preferred for blast
furnaces, and for such purposes there is an advantage of fully 33-1/3
per cent. or even more in using hard woods. For the direct process in
the bloomaries, soft-wood charcoal is preferred. It is found that it is
not usually advantageous to build kilns of over 160 to 180 cubic meters
in capacity. Larger furnaces have been used, and give as good a yield,
but they are much more cumbersome to manage. The largest yield got from
kilns is from 50 to 60 bushels for hard wood to 50 for soft wood. The
average yield, however, is about 45 bushels. In meilers, two and a half
to three cords of wood are required for 100 bushels, or 30 to 40 bushels
to the cord. The kiln charcoal is very large, so that the loss in fine
coal is very much diminished. The pieces usually come out the whole
size, and sometimes the whole length of the wood.

The rectangular kilns were those which were formerly exclusively in use.
They are generally built to contain from 30 to 90 cords of wood. The
usual sizes are given in the table below:

1 2 3 4
Length 50 40 40 48
Width 12 15 14 17
Height 12 15 18 18
Capacity, in cords 55 70 75 90

1 and 2. Used in New England. 3. Type of those used in Mexico. 4. Kiln
at Lauton, Mich.

The arch is usually an arc of a circle. A kiln of the size of No. 4, as
constructed at the Michigan Central Iron Works, with a good burn, will
yield 4,000 bushels of charcoal.

The vertical walls in the best constructions are 12 to 13 feet high, and
1-½ brick thick, containing from 20 to 52 bricks to the cubic foot of
wall. To insure sufficient strength to resist the expansion and
contraction due to the heating and cooling, they should be provided with
buttresses which are 1 brick thick and 2 wide, as at Wassaic, New York;
but many of them are built without them, as at Lauton, Michigan, as
shown in the engraving. In both cases they are supported with strong
braces, from 3 to 4 feet apart, made of round or hewn wood, or of cast
iron, which are buried in the ground below, and are tied above and below
with iron rods, as in the engraving, and the lower end passing beneath
the floor of the kiln. When made of wood they are usually 8 inches
square or round, or sometimes by 8 inches placed edgewise. They are
sometimes tied at the top with wooden braces of the same size, which are
securely fastened by iron rods running through the corners, as shown.
When a number of kilns are built together, as at the Michigan Central
Iron Works, at Lauton, Michigan, shown in the plan view, only the end
kilns are braced in this way. The intermediate ones are supported below
by wooden braces, securely fastened at the bottom. The roof is always
arched, is one brick, or eight inches, thick, and is laid in headers,
fourteen being used in each superficial foot. Many of the kilns have in
the center a round hole, from sixteen to eighteen inches in diameter,
which is closed by a cast iron plate. It requires from 35 M. to 40 M.
brick for a kiln of 45 cords, and 60 M. to 65 M. for one of 90 cords.

* * * * *

The belief that population in the West Indies is stationary is so far
from accurate that, as Sir Anthony Musgrave points out, it is increasing
more rapidly than the population of the United Kingdom. The statistics
of population show an increase of 16 per cent. on the last decennial
period, while the increase in the United Kingdom in the ten years
preceding the last census was under 11 per cent. This increase appears
to be general, and is only slightly influenced by immigration. "The
population of the West Indies," adds Sir A. Musgrave, "is now greater
than that of any of the larger Australian colonies, and three times that
of New Zealand."

* * * * *




HEAT DEVELOPED IN FORGING.


M. Tresca has lately presented to the Academy of Sciences some very
interesting experiments on the development and distribution of heat
produced by a blow of the steam hammer in the process of forging. The
method used was as follows: The bar was carefully polished on both
sides, and this polished part covered with a thin layer of wax. It was
then placed on an anvil and struck by a monkey of known weight, P,
falling from a height, H. The faces of the monkey and anvil were exactly
alike, and care was taken that the whole work, T = PH, should be
expended upon the bar. A single blow was enough to melt the wax over a
certain zone; and this indicated clearly how much of the lateral faces
had been raised by the shock to the temperature of melting wax. The form
of this melted part could be made to differ considerably, but
approximated to that of an equilateral hyperbola. Let A be the area of
this zone, b the width of the bar, d the density, C the heat capacity,
and t-t0 the excess of temperature of melting wax over the temperature
of the air. Then, assuming that the area, A, is the base of a horizontal
prism, which is everywhere heated to the temperature, t, the heating
effect produced will be expressed by

Ab x d x C(t-t0)

Multiplying this by 425, or Joule's equivalent for the metrical system,
the energy developed in heat is given by

T1 = 425 AbdC(t-t0).

Dividing T1 by T, we obtain the ratio which the energy developed in heat
bears to the total energy of the blow.

With regard to the form of the zone of melting, it was found always to
extend round the edges of the indent produced in the bar by the blow. We
are speaking for the present of cases where the faces of the monkey and
anvil were sharp. On the sides of the bar the zone took the form of a
sort of cross with curved arms, the arms being thinner or thicker
according to the greater or less energy of the shock. These forms are
shown in Figs. 1 to 6. It will be seen that these zones correspond to
the zones of greatest sliding in the deformation of a bar forged with a
sharp edged hammer, showing in fact that it is the mechanical work done
in this sliding which is afterward transformed into heat.

[Illustration]

With regard to the ratio, above mentioned, between the heat developed
and the energy of the blow, it is very much greater than had been
expected when the other sources of loss were taken into consideration.
In some cases it reached 80 per cent., and in a table given the limits
vary for an iron bar between 68.4 per cent. with an energy of 40
kilogram-meters, and 83.6 per cent. with an energy of 90
kilogram-meters. With copper the energy is nearly constant at 70 per
cent. It will be seen that the proportion is less when the energy is
less, and it also diminishes with the section of the bar. This is no
doubt due to the fact that the heat is then conducted away more rapidly.
On the whole, the results are summed up by M. Tresca as follows:

(1) The development of heat depends on the form of the faces and the
energy of the blow.

(2) In the case of faces with sharp edges, the process described allows
this heat to be clearly indicated.

(3) The development of heat is greatest where the shearing of the
material is strongest. This shearing is therefore the mechanical cause
which produces the heating effect.

(4) With a blow of sufficient energy and a bar of sufficient size, about
80 per cent. of the energy reappears in the heat.

(5) The figures formed by the melted wax give a sort of diagram, showing
the distribution of the heat and the character of the deformation in the
bar.

(6) Where the energy is small the calculation of the percentage is not
reliable.

So far we have spoken only of cases where the anvil and monkey have
sharp faces. Where the faces are rounded the phenomena are somewhat
different. Figs. 7 to 12 give the area of melted wax in the case of bars
struck with blows gradually increasing in energy. It will be seen that,
instead of commencing at the edges of the indent, the fusion begins near
the middle, and appears in small triangular figures, which gradually
increase in width and depth until at last they meet at the apex, as in
Fig. 12. The explanation is that with the rounded edges the compression
at first takes place only in the outer layers of the bar, the inner
remaining comparatively unaffected. Hence the development of heat is
concentrated on these outer layers, so long as the blows are moderate in
intensity. The same thing had already been remarked in cases of holes
punched with a rounded punch, where the burr, when examined, was found
to have suffered the greatest compression just below the punch. With
regard to the percentage of energy developed as heat, it was about the
same as in the previous experiments, reaching in one case, with an iron
bar and with an energy of 110 kilogram-meters, the exceedingly high
figure of 91 per cent. With copper, the same figure varied between 50
and 60 per cent. - _Iron_.

* * * * *




A NOVEL PROPELLER ENGINE.

By Prof. C.W. MacCord.


The accompanying engravings illustrate the arrangement of a propeller
engine of 20 inch bore and 22 inch stroke, whose cylinder and valve gear
were recently designed by the writer, and are in process of construction
by Messrs. Valk & Murdoch, of Charleston, S.C.

In the principal features of the engine, taken as a whole, as will be
perceived, there is no new departure. The main slide valve, following
nearly full stroke, is of the ordinary form, and reversed by a shifting
link actuated by two eccentrics, in the usual manner; and the expansion
valves are of the well known Meyer type, consisting of two plates on the
back of the main valve, driven by a third eccentric, and connected by a
right and left handed screw, the turning of which alters the distance
between the plates and the point of cutting off.

The details of this mechanism, however, present several novel features,
of which the following description will be understood by reference to
the detached cuts, which are drawn upon a larger scale than the general
plan shown in Figs. 1 and 2.

[Illustration: Figs. 1-2 IMPROVED STEAM ENGINE. - BY PROF MACCORD.]

The first of these relates to the arrangement of the right and left
handed screw, above mentioned, and of the device by which it is rotated.

Usually, the threads, both right handed and left handed, are cut upon
the cut-off valve stem itself, which must be so connected with the
eccentric rod as to admit of being turned; and in most cases the valve
stem extends through both ends of the steam chest, so that it must both
slide endwise and turn upon its axis in two stuffing boxes, necessarily
of comparatively large size.

All this involves considerable friction, and in the engine under
consideration an attempt has been made to reduce the amount of this
friction, and to make the whole of this part of the gear neater and more
compact, in the following manner:

Two small valve stems are used, which are connected at their lower ends
by a crosstail actuated directly by the eccentric rod, and at their
upper ends by a transverse yoke. This yoke, filling snugly between two
collars formed upon a sleeve which it embraces, imparts a longitudinal
motion to the latter, while at the same time leaving it free to rotate.

This sleeve has cut upon it the right and left handed screws for
adjusting the cut-off valves; and it slides freely upon a central
spindle which has no longitudinal motion, but, projecting through the
upper end of the valve chest, can be turned at pleasure by means of a
bevel wheel and pinion. The rotation of the spindle is communicated to
the sleeve by means of two steel keys fixed in the body of the latter
and projecting inwardly so as to slide in corresponding longitudinal
grooves in the spindle.

Thus the point of cutting off is varied at will while the engine is
running, by means of the hand wheel on the horizontal axis of the bevel
pinion, and a small worm on the same axis turns the index, which points
out upon the dial the distance followed. These details are shown in
Figs. 3, 4, and 5; in further explanation of which it may be added that
Fig. 3 is a front view of the valve chest and its contents, the cover,
and also the balance plate for relieving the pressure on the back of the
main valve (in the arrangement of which there is nothing new), being
removed in order to show the valve stems, transverse yoke, sleeve, and
spindle above described. Fig. 4 is a longitudinal section, and Fig. 5 is
a transverse section, the right hand side showing the cylinder cut by a
plane through the middle of the exhaust port, the left hand side being a
section by a plane above, for the purpose of exhibiting more clearly the
manner in which the steam is admitted to the valve chest; the latter
having no pipes for this service, the steam enters below the valve, at
each end of the chest, just as it escapes in the center.

The second noteworthy feature consists in this: that the cut-off
eccentric is not keyed fast, as is customary when valve gear of this
kind is employed, but is loose upon the shaft, the angular position in
relation to the crank being changed when the engine is reversed; two
strong lugs are bolted on the shaft, one driving the eccentric in one
direction, the other in the opposite, by acting against the reverse
faces of a projection from the side of The eccentric pulley.

The loose eccentric is of course a familiar arrangement in connection
with poppet valves, as well as for the purpose of reversing an engine
when driving a single slide valve. Its use in connection with the Meyer
cut-off valves, however, is believed to be new; and the reason for its
employment will be understood by the aid of Fig. 6.

For the purposes of this explanation we may neglect the angular
vibrations of the connecting rod and eccentric rod, considering them
both as of infinite length. Let O be the center of the shaft; let L O M
represent the face of the main valve seat, in which is shown the port
leading to the cylinder; and let A be the edge of the main valve, at the
beginning of a stroke of the piston. It will then be apparent that the
center of the eccentric must at that instant be at the point, C, if the
engine turn to the left, as shown by the arrow, and at G, if the
rotation be in the opposite direction; C and G then may be taken as the
centers of the "go-ahead" and the "backing" eccentrics respectively,
which operate the main valve through the intervention of the link.

Now, in each revolution of the engine, the cut-off eccentric in effect
revolves in the same direction about the center of the main eccentric.
Consequently, we may let R C S, parallel to L O M, represent the face of
the cut-off valve seat, or, in other words, the back of the main valve,
in which the port, C N, corresponds to one of those shown in Fig. 4; and
the motion of the cut-off valve over this seat will be precisely, the
same as though it were driven directly by an eccentric revolving around
the center, C.

In determining the position of this eccentric, we proceed upon the
assumption that the best results will be effected by such an arrangement
that when cutting off at the earliest point required, the cut-off valve
shall, at the instant of closing the port, be moving over it at its
highest speed. And this requires that the center of the eccentric shall
at the instant in question lie in the vertical line through C.

[Illustration: Figs. 3-12 IMPROVED STEAM ENGINE. - BY PROF MACCORD.]

Next, the least distance to be followed being assigned, the angle
through which the crank will turn while the piston is traveling that
distance is readily found; then, drawing an indefinite line C T, making
with the vertical line, G O, an angle, G C T. equal to the one thus
determined, any point upon that line may be assumed as the position of
the required center of the cut-off eccentric, at the beginning of the
stroke.

But again, in order that the cut-off may operate in the same manner when
backing as when going ahead, this eccentric must be symmetrically
situated with respect to both C and G; and since L O M bisects and is
perpendicular to G C, it follows that if the cut-off eccentric be fixed
on the shaft, its center must be located at H, the intersection of C T
with L M. This would require the edge of the cut-off valve at the given
instant to be at Q, perpendicularly over H; and the travel over the main
valve would be equal to twice C H, the virtual lever arm of the
eccentric, the actual traverse in the valve chest being twice O H, the
real eccentricity.

This being clearly excessive, let us next see what will occur if the
lever arm, CH, be reduced as in the diagram to CK. The edge of the
cut-off valve will then be at N; it instantly begins to close the port.
CN, but not so rapidly as the main valve opens the port, AB.

The former motion increases in rapidity, while the latter decreases;
therefore at some point they will become equal in velocity, and the
openings of the two ports will be the same; and the question is, Will
this maximum effective port area give a sufficient supply of steam?

This diagram is the same as the one actually used in the engine under
consideration, in which it was required to follow a minimum distance of
5 inches in the stroke of 22. Under these conditions it is found that
the actual port opening for that point of cutting off is three-fifths of
that allowed when following full stroke, whereas the speed of the piston
at the time when this maximum opening occurs is less than half its
greatest speed.

This, it would seem, is ample; but we now find the eccentric, K, no
longer in the right position for backing; when the engine is reversed it
ought to be at, P, the angle, POL, being equal to the angle, KOL. By
leaving it free, therefore, to move upon the shaft, by the means above
described, through the angle, KOP, the desired object is accomplished.
The real eccentricity is now reduced in the proportion of OK to OH,
while the lengths of the cut-off valves, and what is equally important,
their travel over the back of the main valve, are reduced in the


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Online LibraryVariousScientific American Supplement, No. 415, December 15, 1883 → online text (page 3 of 9)