OPERATION
(=29=) In oxy-acetylene welding there are two gases used, as the name
would indicate, namely, oxygen and acetylene. The first is used to
intensify the flame and can in nowise be likened to the inflammable
nature of the second. There is a great deal of oxygen present in the
air we breathe. It is an odorless, tasteless, and colorless gas, as
most of us are aware. In the commercial world oxygen is manufactured
by the decomposition of water into its elements, oxygen and hydrogen,
by the electrolytic process or is taken from the air by a reduction
process and is stored in steel-drawn cylinders. These cylinders are
drawn out of one piece of steel and are of considerable thickness
throughout, having absolutely no seams, welded or otherwise. There is
no filler nor absorbent used on the inside of these cylinders, as pure
oxygen under pressure is not considered dangerous. The standardized
sized oxygen cylinder is one which contains 200 cubic feet of gas fully
charged. Oxygen is compressed in these cylinders at a pressure of 1800
pounds, at normal temperature, and this pressure does not vary to any
great extent with change in temperature (as shown by table on page 29).
There is attached to the tip of the steel cylinder, or “bottle,” as
some workers call it, a double seating valve which has one seat operate
when the cylinder is closed, and the other when the cylinder is wide
open. A regulator is attached to this valve when working.
[Illustration: FIG. 17.--Sectional View of Oxygen Cylinder without
Valve.]
[Illustration:
(_Courtesy of the Linde Air Products Co._)
FIG. 18.--A Standard 200-foot Oxygen Cylinder.]
[Illustration: TABLE SHOWING THE DIFFERENT PRESSURES OF OXYGEN--AT
VARIOUS TEMPERATURES
-----+-------++-----+-------++-----+-------++-----+-------
Temp.| Press.||Temp.| Press.||Temp.| Press.||Temp.| Press.
Deg.|Lb. Per|| Deg.|Lb. Per|| Deg.|Lb. Per|| Deg.|Lb. Per
Fahr.| Deg. ||Fahr.| Deg. ||Fahr.| Deg. ||Fahr.| Deg.
-----+-------++-----+-------++-----+-------++-----+-------
0 | 1568 || 25 | 1654 || 50 | 1739 || 75 | 1824
1 | 1572 || 26 | 1657 || 51 | 1743 || 76 | 1828
2 | 1575 || 27 | 1660 || 52 | 1746 || 77 | 1831
3 | 1579 || 28 | 1664 || 53 | 1749 || 78 | 1835
4 | 1582 || 29 | 1667 || 54 | 1753 || 79 | 1838
5 | 1585 || 30 | 1671 || 55 | 1756 || 80 | 1842
6 | 1589 || 31 | 1674 || 56 | 1760 || 81 | 1845
7 | 1592 || 32 | 1678 || 57 | 1763 || 82 | 1848
8 | 1596 || 33 | 1681 || 58 | 1766 || 83 | 1852
9 | 1599 || 34 | 1684 || 59 | 1770 || 84 | 1855
10 | 1603 || 35 | 1688 || 60 | 1773 || 85 | 1859
11 | 1606 || 36 | 1691 || 61 | 1777 || 86 | 1862
12 | 1609 || 37 | 1695 || 62 | 1780 || 87 | 1865
13 | 1613 || 38 | 1698 || 63 | 1784 || 88 | 1869
14 | 1616 || 39 | 1701 || 64 | 1787 || 89 | 1872
15 | 1620 || 40 | 1705 || 65 | 1790 || 90 | 1876
16 | 1623 || 41 | 1708 || 66 | 1794 || 91 | 1879
17 | 1626 || 42 | 1712 || 67 | 1797 || 92 | 1883
18 | 1630 || 43 | 1715 || 68 | 1800 || 93 | 1886
19 | 1633 || 44 | 1719 || 69 | 1803 || 94 | 1889
20 | 1637 || 45 | 1722 || 70 | 1807 || 95 | 1893
21 | 1640 || 46 | 1725 || 71 | 1811 || 96 | 1895
22 | 1643 || 47 | 1729 || 72 | 1814 || 97 | 1900
23 | 1647 || 48 | 1732 || 73 | 1818 || 98 | 1903
24 | 1650 || 49 | 1736 || 74 | 1821 || 99 | 1906
| || | || | || 100 | 1910
-----+-------++-----+-------++-----+-------++-----+-------
FIG. 19.]
(=30=) Acetylene is the fuel gas, and is one of the greatest containers
of heat known. Burning in a free state, its carbon content is so rich
that complete combustion is impossible, and stringy black particles
will be noticed floating through the air. In order to fully combust
this gas, oxygen is introduced under pressure and a temperature of
over 6000 degrees Fahrenheit is obtained. (Acetylene contains about
five times as many B. T. U.’s (British Thermal Units) as hydrogen.)
This gas, unlike oxygen, becomes very dangerous when in a free state
it is subjected to an excessive pressure. The slightest jar may cause
its disintegration and a violent explosion follows. On account of
this danger, acetylene is not stored in a free state; neither is it
subjected to very high pressures. Its cylinders are put out by various
manufacturers to comply with the laws and regulations of the Interstate
Commerce Commission. Some of these cylinders have been welded, but the
most modern method is to make them of one piece of drawn steel. They
are then filled with an absorbent of some kind to take up the gas and
prevent any portion of it being left in a free state. Acetone is the
popular absorbent, and is a liquid capable of absorbing twenty-five
times its own volume of acetylene gas at normal pressure. The filling
material varies with each of the manufacturers, but charcoal, asbestos
and mineral wool are in very common use. Acetylene is obtained from
calcium carbide brought in contact with water, or vice versa, and is
compressed and then stored in the cylinders at a pressure varying from
150 to 250 pounds. When fully charged this pressure will vary almost
directly with any change of temperature. Acetylene cylinders for
welding are available in 100, 200, 225, and 300 cubic foot sizes.
[Illustration: FIG. 20.--A Generator for Producing Acetylene under
Pressure.]
(=31=) In setting up apparatus for the first time, the regulator
containing the 3000-pound gauge is attached to the taller of the
cylinders, which holds the oxygen gas, and the other regulator is
fastened to the shorter cylinder. The hoses, which should be cleared of
all powder or scale on their interior, are then added. The black hose
should connect the oxygen regulator to the torch valve, marked “OX”
and the red hose, the acetylene regulator to the torch valve stamped
“AC.” In attaching regulators to full cylinders the “cross-bar” on the
regulator should always be turned out, that is to the left, until it
turns freely, to insure all pressure being released from the diaphragm,
before the cylinder pressure is turned on. Another precaution that
should be observed is the “cracking” of the cylinder valves, before
attaching the regulator, in order to blow out any dirt or foreign
particles that may be lodged there, otherwise they will be carried into
the regulator seat, or lodged in some small passage, which will impair
the working of the apparatus. Then too, if no truck or clamping device
has been provided, both the oxygen and acetylene cylinders should be
securely clamped or wired together, a rule which should be insisted
upon at all times, whether in a job shop, manufacturing concern, or
training school, or any place where top-heavy oxygen cylinders are
being used. No particular harm results if these cylinders are turned
over, which is very easily done on account of their rounded base, if no
regulator is attached, but very frequently regulators are attached and
the hose connecting the same to torch is found in the operator’s way.
The slightest pull or tripping on this hose will upset the cylinder,
usually demolishing the regulator and expensive gauges and at times
causing much confusion among the workmen, on account of the loud
hissing noise given off by the escaping gas. Always secure the drums or
the cylinders in a safe manner.
(=32=) In turning on the gas, the oxygen valve is opened wide until
seated and the acetylene valve is only partially opened. Often the
question is raised as to where the operator should stand, especially
when dealing with high-pressure oxygen. It is recommended that
the operator should =stand= at the side and towards the rear when
performing this operation, for sometimes an unreliable gauge may be
attached, which if bursting, would send the glass into the operator’s
face.
[Illustration: FIG. 21.--Acetylene Flame Blowing away from Tip.]
[Illustration: FIG. 22.--Addition of Oxygen to Acetylene Flame.]
[Illustration: FIG. 23.--More Oxygen Pressure Applied. Flame Contains
Slight Excess of Acetylene, and is Known as “Carbonizing.”]
[Illustration: FIG. 24.--“Neutral” Flame. Correct Proportions of Oxygen
and Acetylene Gases.]
[Illustration: FIG. 25.--“Oxidizing” Flame. Too much Oxygen Present.]
(=33=) As soon as an operator has gas pressure in his regulators,
he begins wondering how much pressure should be placed on his
line, that is, the portion between the regulator and the torch. Of
course, this depends upon the size of the tip, but the operator
should have some means of approximating this pressure without going
to his manufacturer’s chart every time. A neutral flame, that is,
theoretically equal parts of oxygen and acetylene, is desired for
welding. Now in lighting, the flame should stand away from the tip a
slight distance, in torches other than the low-pressure type, while in
these there will only be a good full flame issue from the tip. Enough
oxygen must be in evidence to bring this acetylene flame down to the
neutral point. If not enough pressure is used, this result cannot
be obtained, and of course, more pressure must be introduced. It is
better to have too much pressure than not enough on the line, for the
operator may use his torch valve to again regulate this pressure and
is always sure of enough gas. Theoretically, all adjustments should be
made at the regulator, but in practice this is very seldom carried out.
The accompanying cuts will illustrate the five conditions which every
welder should be familiar with, in the flame adjustment. Fig. 21 shows
the acetylene turned on full; no oxygen has as yet been introduced. The
flame has a yellow appearance and is very rich in carbon, as can be
seen by the soot given off. In Fig. 22 we see the oxygen being turned
on; the yellow flame (_A_) is gradually giving way to a white part at
(_B_). In this condition we say that a feather flame exists. Fig. 23
shows slightly more oxygen pressure. In Fig. 24 we have the neutral
flame, which can be readily recognized on account of its bluish white
color and well-defined outline, appearing like the end of an unused
piece of chalk, only, of course, much smaller. In Fig. 25 can be seen
an excess or too much pressure of oxygen. It will be noticed that the
neutral flame assumes a more bluish color, is a little pointed, and a
very noticeable hissing sound is in evidence. This is what is called
an oxidizing flame and will be again referred to. Too much oxygen is
used. Operators who attempt to turn on the oxygen first and then light
it, will find that it does not burn, and their efforts will be useless.
In picking up a torch for the first time, any operator can turn on one
valve and detect by the odor of the gas, whether it is oxygen or the
fuel gas, and can light it in accordance. Some operators, however,
attempt to turn on a little of each gas and light. This is not to
be recommended, for flashbacks may occur. When the welder accustoms
himself to turning on enough pressure to accommodate whatever sized
tip he may have, he will find that there is no great need for paying
attention to the pressure gauges on his regulators except to check up
on the full drums of oxygen, and to tell whether he has enough gas left
to complete a certain piece of work.
(=34=) A neutral flame is theoretically composed of equal parts of
oxygen and acetylene ignited, but this ratio is very seldom worked
out in practice. There is usually an excess of oxygen in evidence.
A neutral flame is generally spoken of as being over 6000 degrees
Fahrenheit, and this does not vary with the different sized tips as
most welders think. Of course there are different quantities of heat
between a very small tip and a large sized one, but the temperature of
the flame is the same.
(=35=) If too much acetylene gas is used, a feather flame such as was
seen in Fig. 23 will appear. This has a carbonizing effect on the weld,
for it introduces carbon and causes the weld to become very brittle.
(=36=) If too much oxygen gas is used, the effect shown in Fig. 25
will take place, and the weld will have oxygen introduced, which is a
very detrimental feature, and is particularly noticeable in working on
steel, for it raises a white foam over the surface of the melted metal,
which sometimes is worked right into the weld itself. An experienced
welder will always know just what kind of a flame action he is
obtaining on his weld, not because he takes the flame away every time
he wishes to look at it, but he can tell by the action of his metal
exactly the nature of his flame.
(=37=) Infra-red (heat) and ultra-violet (light) rays present to a
small extent in the neutral flame are injurious to the naked eye.
Colored glasses or goggles are used to shield the eyes when working
with this flame. Too dark a glass should not be used, as it will cause
a strain upon the eyes more injurious than the flame. Exposed metal
frames should be avoided too, as they hold the heat and burn the
operator.
[Illustration:
(_Courtesy of the Chicago Eye Shield Co._)
FIG. 26.--A Spectacle Made for Welders, having a Frame of Fiber and
Arranged so that Lenses may be Replaced.]
[Illustration:
(_Courtesy of the Chicago Eye Shield Co._)
FIG. 27.--Showing Cover Glass which Protects the Colored Lens and the
Replaceable Features of a Modern Goggle.]
(=38=) To shut off the apparatus for several hours or so, it is best
to relieve all pressure from the lines, such as hose and so forth, and
to do this close both tank valves; open the torch valves; release the
tension on the regulator, by screwing the “cross-bar” to the left,
and finally, close the torch valves. It is quite necessary that
these torch valves closed, for quite frequently, if a small tip is in
the torch and an excess of oxygen pressure comes through the line,
when both torch valves are open, much of the oxygen may back up the
acetylene line and cause a serious flashback when lighting up. This can
be avoided by keeping both torch valves closed when not in use.
(=39=) If a valve on an empty acetylene cylinder is left open the
acetylene gas will escape, and mixing with the air, which is a
supporter of combustion, a very inflammable mixture will be formed. If
any fire is present, such as might be smouldering in a forge, possibly
not used for several hours or so, or a match lighted, or a flame
started in any way, an explosion is likely to occur. When an acetylene
cylinder is exhausted, as far as possible, in a moderately high
atmospheric temperature, then shut off for a while and the temperature
drops, air will be drawn into the vacuum thus formed when the valve is
again opened. In this manner an explosive mixture forms in an empty
acetylene cylinder and is certainly to be avoided. Care should be
taken, especially in winter, to guard against such occurrences, as in
some outlying shops a decided change in temperature takes place between
closing time and starting up time the following morning. Acetylene
tanks should always be securely closed when empty, not only for the
above reasons but insomuch that each contains acetone, which is likely
to escape if the tank is thrown around. Acetone is very costly and used
extensively in the manufacture of smokeless powder, so that at times it
is hard to replenish.
(=40=) Oxygen has an affinity for oils and greases, and should not be
allowed to come in contact with them, especially in confined places,
as a spontaneous combustion may result. Oils and greases should never
be used around oxy-acetylene welding apparatus and on nearly every
apparatus on the market the words “Use no oil,” will be found. Despite
this precaution, however, many times ignorant operators will be found
squirting oil into the holes around the regulator cap, and through the
gauges, in order, as they say, to allow them to work easier. This use
of oil should be discouraged, and the sooner the better.