WELDING INSTRUMENTS
VALVES
_Tank Valves._--The acetylene tank valve is of the needle type, fitted
with suitable stuffing box nuts and ending in an exposed square shank to
which the special wrench may be fitted when the valve is to be opened or
closed.
The valve used on Linde oxygen cylinders is also a needle type, but of
slightly more complex construction. The body of the valve, which screws
into the top of the cylinder, has an opening below through which the gas
comes from the cylinder, and another opening on the side through which it
issues to the torch line. A needle screws down from above to close this
lower opening. The needle which closes the valve is not connected directly
to the threaded member, but fits loosely into it. The threaded part is
turned by a small hand wheel attached to the upper end. When this hand
wheel is turned to the left, or up, as far as it will go, opening the
valve, a rubber disc is compressed inside of the valve body and this disc
serves to prevent leakage of the gas around the spindle.
The oxygen valve also includes a safety nut having a small hole through it
closed by a fusible metal which melts at 250° Fahrenheit. Melting of this
plug allows the gas to exert its pressure against a thin copper diaphragm,
this diaphragm bursting under the gas pressure and allowing the oxygen to
escape into the air.
The hand wheel and upper end of the valve mechanism are protected during
shipment by a large steel cap which covers them when screwed on to the end
of the cylinder. This cap should always be in place when tanks are received
from the makers or returned to them.
[Illustration: Figure 14.--Regulating Valve]
_Regulating Valves._--While the pressure in the gas containers may be
anything from zero to 1,800 pounds, and will vary as the gas is withdrawn,
the pressure of the gas admitted to the torch must be held steady and at a
definite point. This is accomplished by various forms of automatic
regulating valves, which, while they differ somewhat in details of
construction, all operate on the same principle.
The regulator body (Figure 14) carries a union which attaches to the side
outlet on the oxygen tank valve. The gas passes through this union,
following an opening which leads to a large gauge which registers the
pressure on the oxygen remaining in the tank and also to a very small
opening in the end of a tube. The gas passes through this opening and into
the interior of the regulator body. Inside of the body is a metal or rubber
diaphragm placed so that the pressure of the incoming gas causes it to
bulge slightly. Attached to the diaphragm is a sleeve or an arm tipped
with a small piece of fibre, the fibre being placed so that it is directly
opposite the small hole through which the gas entered the diaphragm
chamber. The slight movement of the diaphragm draws the fibre tightly over
the small opening through which the gas is entering, with the result that
further flow is prevented.
Against the opposite side of the diaphragm is the end of a plunger. This
plunger is pressed against the diaphragm by a coiled spring. The tension on
the coiled spring is controlled by the operator through a threaded spindle
ending in a wing or milled nut on the outside of the regulator body.
Screwing in on the nut causes the tension on the spring to increase, with a
consequent increase of pressure on the side of the diaphragm opposite to
that on which the gas acts. Inasmuch as the gas pressure acted to close the
small gas opening and the spring pressure acts in the opposite direction
from the gas, it will be seen that the spring pressure tends to keep the
valve open.
When the nut is turned way out there is of course, no pressure on the
spring side of the diaphragm and the first gas coming through automatically
closes the opening through which it entered. If now the tension on the
spring be slightly increased, the valve will again open and admit gas until
the pressure of gas within the regulator is just sufficient to overcome the
spring pressure and again close the opening. There will then be a pressure
of gas within the regulator that corresponds to the pressure placed on the
spring by the operator. An opening leads from the regulator interior to the
torch lines so that all gas going to the torches is drawn from the
diaphragm chamber.
Any withdrawal of gas will, of course, lower the pressure of that remaining
inside the regulator. The spring tension, remaining at the point determined
by the operator, will overcome this lessened pressure of the gas, and the
valve will again open and admit enough more gas to bring the pressure back
to the starting point. This action continues as long as the spring tension
remains at this point and as long as any gas is taken from the regulator.
Increasing the spring tension will require a greater gas pressure to close
the valve and the pressure of that in the regulator will be correspondingly
higher.
When the regulator is not being used, the hand nut should be unscrewed
until no tension remains on the spring, thus closing the valve. After the
oxygen tank valve is open, the regulator hand nut is slowly screwed in
until the spring tension is sufficient to give the required pressure in the
torch lines. Another gauge is attached to the regulator so that it
communicates with the interior of the diaphragm chamber, this gauge showing
the gas pressure going to the torch. It is customary to incorporate a
safety valve in the regulator which will blow off at a dangerous pressure.
In regulating valves and tank valves, as well as all other parts with which
the oxygen comes in contact, it is not permissible to use any form of oil
or grease because of danger of ignition and explosion. The mechanism of a
regulator is too delicate to be handled in the ordinary shop and should any
trouble or leakage develop in this part of the equipment it should be sent
to a company familiar with this class of work for the necessary repairs.
Gas must never be admitted to a regulator until the hand nut is all the way
out, because of danger to the regulator itself and to the operator as well.
A regulator can only be properly adjusted when the tank valve and torch
valves are fully opened.
[Illustration: Figure 15.--High and Low Pressure Gauges with Regulator]
Acetylene regulators are used in connection with tanks of compressed gas.
They are built on exactly the same lines as the oxygen regulating valve and
operate in a similar way. One gauge only, the low pressure indicator, is
used for acetylene regulators, although both high and low pressure may be
used if desired. (See Figure 15.)
TORCHES
Flame is always produced by the combustion of a gas with oxygen and in no
other way. When we burn oil or candles or anything else, the material of
the fuel is first turned to a gas by the heat and is then burned by
combining with the oxygen of the air. If more than a normal supply of air
is forced into the flame, a greater heat and more active burning follows.
If the amount of air, and consequently oxygen, is reduced, the flame
becomes smaller and weaker and the combustion is less rapid. A flame may be
easily extinguished by shutting off all of its air supply.
The oxygen of the combustion only forms one-fifth of the total volume of
air; therefore, if we were to supply pure oxygen in place of air, and in
equal volume, the action would be several times as intense. If the oxygen
is mixed with the fuel gas in the proportion that burns to the very best
advantage, the flame is still further strengthened and still more heat is
developed because of the perfect combustion. The greater the amount of fuel
gas that can be burned in a certain space and within a certain time, the
more heat will be developed from that fuel.
The great amount of heat contained in acetylene gas, greater than that
found in any other gaseous fuel, is used by leading this gas to the
oxy-acetylene torch and there combining it with just the right amount of
oxygen to make a flame of the greatest power and heat than can possibly be
produced by any form of combustion of fuels of this kind. The heat
developed by the flame is about 6300° Fahrenheit and easily melts all the
metals, as well as other solids.
Other gases have been and are now being used in the torch. None of them,
however, produce the heat that acetylene does, and therefore the
oxy-acetylene process has proved the most useful of all. Hydrogen was used
for many years before acetylene was introduced in this field. The
oxy-hydrogen flame develops a heat far below that of oxy-acetylene, namely
4500° Fahrenheit. Coal gas, benzine gas, blaugas and others have also been
used in successful applications, but for the present we will deal
exclusively with the acetylene fuel.
It was only with great difficulty that the obstacles in the way of
successfully using acetylene were overcome by the development of
practicable controlling devices and torches, as well as generators. At
present the oxy-acetylene process is the most universally adaptable, and
probably finds the most widely extended field of usefulness of any welding
process.
The theoretical proportion of the gases for perfect combustion is two and
one-half volumes of oxygen to one of acetylene. In practice this proportion
is one and one-eighth or one and one-quarter volumes of oxygen to one
volume of acetylene, so that the cost is considerably reduced below what it
would be if the theoretical quantity were really necessary, as oxygen costs
much more than acetylene in all cases.
While the heat is so intense as to fuse anything brought into the path of
the flame, it is localized in the small "welding cone" at the torch tip so
that the torch is not at all difficult to handle without special protection
except for the eyes, as already noted. The art of successful welding may be
acquired by any operator of average intelligence within a reasonable time
and with some practice. One trouble met with in the adoption of this
process has been that the operation looks so simple and so easy of
performance that unskilled and unprepared persons have been tempted to try
welding, with results that often caused condemnation of the process, when
the real fault lay entirely with the operator.
The form of torch usually employed is from twelve to twenty-four inches
long and is composed of a handle at one end with tubes leading from this
handle to the "welding head" or torch proper. At or near one end of the
handle are adjustable cocks or valves for allowing the gases to flow into
the torch or to prevent them from doing so. These cocks are often used for
regulating the pressure and amount of gas flowing to the welding head, but
are not always constructed for this purpose and should not be so used when
it is possible to secure pressure adjustment at the regulators (Figure 16).
Figure 16 shows three different sizes of torches. The number 5 torch is
designed especially for jewelers' work and thin sheet steel welding. It is
eleven inches in length and weighs nineteen ounces. The tips for the number
10 torch are interchangeable with the number 5. The number 10 torch is
adapted for general use on light and medium heavy work. It has six tips and
its length is sixteen inches, with a weight of twenty-three ounces.
The number 15 torch is designed for heavy work, being twenty-five inches in
length, permitting the operator to stand away from the heat of the metal
being worked. These heavy tips are in two parts, the oxygen check being
renewable.
[Illustration: Figure 16.--Three Sizes of Torches, with Tips]
Figures 17 and 18 show two sizes of another welding torch. Still another
type is shown in Figure 19 with four interchangeable tips, the function of
each being as follows:
No. 1. For heavy castings.
No. 2. Light castings and heavy sheet metal.
No. 3. Light sheet metal.
No. 4. Very light sheet metal and wire.
[Illustration: Figure 17.--Cox Welding Torch (No. 1)]
[Illustration: Figure 18.--Cox Welding Torch (No. 2)]
[Illustration: Figure 19.--Monarch Welding Torch]
At the side of the shut off cock away from the torch handle the gas tubes
end in standard forms of hose nozzles, to which the rubber hose from the
gas supply tanks or generators can be attached. The tubes from the handle
to the head may be entirely separate from each other, or one may be
contained within the other. As a general rule the upper one of two
separate tubes carries the oxygen, while this gas is carried in the inside
tube when they are concentric with each other.
In the welding head is the mixing chamber designed to produce an intimate
mixture of the two gases before they issue from the nozzle to the flame.
The nozzle, or welding tip, of a suitable size are design for the work to
be handled and the pressure of gases being used, is attached to the welding
head and consists essentially of the passage at the outer end of which the
flame appears.
The torch body and tubes are usually made of brass, although copper is
sometimes used. The joint must be very strong, and are usually threaded and
soldered with silver solder. The nozzle proper is made from copper, because
it withstands the heat of the flame better than other less suitable metals.
The torch must be built in such a way that it is not at all liable to come
apart under the influence of high temperatures.
All torches are constructed in such a way that it is impossible for the
gases to mix by any possible chance before they reach the head, and the
amount of gas contained in the head and tip after being mixed is made as
small as possible. In order to prevent the return of the flame through the
acetylene tube under the influence of the high pressure oxygen some form of
back flash preventer is usually incorporated in the torch at or near the
point at which the acetylene enters. This preventer takes the form of some
porous and heat absorbing material, such as aluminum shavings, contained in
a small cavity through which the gas passes on its way to the head.
_High Pressure Torches._--Torches are divided into the same classes as
are the generators; that is, high pressure, medium pressure and low
pressure. As mentioned before, the medium pressure is usually called the
high pressure, because there are very few true high pressure systems in
use, and comparatively speaking the medium pressure type is one of high
pressure.
[Illustration: Figure 20.--High Pressure Torch Head]
With a true high pressure torch (Figure 20) the gases are used at very
nearly equal heads so that the mixing before ignition is a simple matter.
This type admits the oxygen at the inner end of a straight passage leading
to the tip of the nozzle. The acetylene comes into this same passage from
openings at one side and near the inner end. The difference in direction of
the two gases as they enter the passage assists in making a homogeneous
mixture. The construction of this nozzle is perfectly simple and is easily
understood. The true high pressure torch nozzle is only suited for use with
compressed and dissolved acetylene, no other gas being at a sufficient
pressure to make the action necessary in mixing the gases.
_Medium Pressure Torches._--The medium pressure (usually called high
pressure) torch (Figure 21) uses acetylene from a medium pressure generator
or from tanks of compressed gas, but will not take the acetylene from low
pressure generators.
[Illustration: Figure 21.--Medium Pressure Torch Head]
The construction of the mixing chamber and nozzle is very similar to that
of the high pressure torch, the gases entering in the same way and from the
same positions of openings. The pressure of the acetylene is but little
lower than that of the oxygen, and the two gases, meeting at right angles,
form a very intimate mixture at this point of juncture. The mixture in its
proportions of gases depends entirely on the sizes of the oxygen and
acetylene openings into the mixing chamber and on the pressures at which
the gases are admitted. There is a very slight injector action as the fast
moving stream of oxygen tends to draw the acetylene from the side openings
into the chamber, but the operation of the torch does not depend on this
action to any extent.
_Low Pressure Torches._--The low pressure torch (Figure 22) will use
gas from low pressure generators from medium pressure machines or from
tanks in which it has been compressed and dissolved. This type depends for
a perfect mixture of gas upon the principle of the injector just as it is
applied in steam boiler practice.
[Illustration: Figure 22.--Low Pressure Torch with Separate Injector
Nozzle]
The oxygen enters the head at considerable pressure and passes through its
tube to a small jet within the head. The opening of this jet is directly
opposite the end of the opening through the nozzle which forms the mixing
chamber and the path of the gases to the flame. A small distance remains
between the opening from which the oxygen issues and the inner opening into
the mixing passage. The stream of oxygen rushes across this space and
enters the mixing chamber, being driven by its own pressure.
The acetylene enters the head in an annular space surrounding the oxygen
tube. The space between oxygen jet and mixing chamber opening is at one end
of this acetylene space and the stream of oxygen seizes the acetylene and
under the injector action draws it into the mixing chamber, it being
necessary only to have a sufficient supply of acetylene flowing into the
head to allow the oxygen to draw the required proportion for a proper
mixture.
The volume of gas drawn into the mixing chamber depends on the size of the
injector openings and the pressure of the oxygen. In practice the oxygen
pressure is not altered to produce different sized flames, but a new nozzle
is substituted which is designed to give the required flame. Each nozzle
carries its own injector, so that the design is always suited to the
conditions. While torches are made having the injector as a permanent part
of the torch body, the replaceable nozzle is more commonly used because it
makes the one torch suitable for a large range of work and a large number
of different sized flames. With the replaceable head a definite pressure of
oxygen is required for the size being used, this pressure being the one for
which the injector and corresponding mixing chamber were designed in
producing the correct mixture.
_Adjustable Injectors._-Another form of low pressure torch operates on
the injector principle, but the injector itself is a permanent part of the
torch, the nozzle only being changed for different sizes of work and flame.
The injector is placed in or near the handle and its opening is the largest
required by any work that can be handled by this particular torch. The
opening through the tip of the injector through which the oxygen issues on
its way to the mixing chamber may be wholly or partly closed by a needle
valve which may be screwed into the opening or withdrawn from it, according
to the operator's judgment. The needle valve ends in a milled nut outside
the torch handle, this being the adjustment provided for the different
nozzles.
_Torch Construction._--A well designed torch is so designed that the
weight distribution is best for holding it in the proper position for
welding. When a torch is grasped by its handle with the gas hose attached,
it should balance so that it does not feel appreciably heavier on one end
than on the other.
The head and nozzle may be placed so that the flame issues in a line at
right angles with the torch body, or they may be attached at an angle
convenient for the work to be done. The head set at an angle of from 120 to
170 degrees with the body is usually preferred for general work in welding,
while the cutting torch usually has its head at right angles to the body.
Removable nozzles have various size openings through them and the different
sizes are designated by numbers from 1 up. The same number does not always
indicate the same size opening in torches of different makes, nor does it
indicate a nozzle of the same capacity.
The design of the nozzle, the mixing chamber, the injector, when one is
used, and the size of the gas openings must be such that all these things
are suited to each other if a proper mixture of gas is to be secured. Parts
that are not made to work together are unsafe if used because of the danger
of a flash back of the flame into the mixing chamber and gas tubes. It is
well known that flame travels through any inflammable gas at a certain
definite rate of speed, depending on the degree of inflammability of the
gas. The easier and quicker the gas burns, the faster will the flame travel
through it.
If the gas in the nozzle and mixing chamber stood still, the flame would
immediately travel back into these parts and produce an explosion of more
or less violence. The speed with which the gases issue from the nozzle
prevent this from happening because the flame travels back through the gas
at the same speed at which the gas issues from the torch tip. Should the
velocity of the gas be greater than the speed of flame propagation through
it, it will be impossible to keep the flame at the tip, the tendency being
for a space of unburned gas to appear between tip and flame. On the other
hand, should the speed of the flame exceed the velocity with which the gas
comes from the torch there will result a flash back and explosion.
_Care of Torches._--An oxy-acetylene torch is a very delicate and
sensitive device, much more so that appears on the surface. It must be
given equally as good care and attention as any other high-priced piece of
machinery if it is to be maintained in good condition for use.
It requires cleaning of the nozzles at regular intervals if used regularly.
This cleaning is accomplished with a piece of copper or brass wire run
through the opening, and never with any metal such as steel or iron that is
harder than the nozzle itself, because of the danger of changing the size
of the openings. The torch head and nozzle can often be cleaned by allowing
the oxygen to blow through at high pressure without the use of any tools.
In using a torch a deposit of carbon will gradually form inside of the
head, and this deposit will be more rapid if the operator lights the stream
of acetylene before turning any oxygen into the torch. This deposit may be
removed by running kerosene through the nozzle while it is removed from the
torch, setting fire to the kerosene and allowing oxygen to flow through
while the oil is burning.
Should a torch become clogged in the head or tubes, it may usually be
cleaned by removing the oxygen hose from the handle end, closing the
acetylene cock on the torch, placing the end of the oxygen hose over the
opening in the nozzle and turning on the oxygen under pressure to blow the
obstruction back through the passage that it has entered. By opening the
acetylene cock and closing the oxygen cock at the handle, the acetylene
passages may then be cleaned in the same way. Under no conditions should a
torch be taken apart any more than to remove the changeable nozzle, except
in the hands of those experienced in this work.
_Nozzle Sizes._--The size of opening through the nozzle is determined
according to the thickness and kind of metal being handled. The following
sizes are recommended for steel:
Davis-Bournonville. Oxweld Low
Thickness of Metal (Medium Pressure.) Pressure
1/32 Tip No. 1 Head No. 2
1/16 2
5/64 3
3/32 3 4
3/8 4 5
3/16 5 6
1/4 6 7
5/16 7
3/8 8 8
1/2 9 10
5/8 10 12
3/4 11 15
Very heavy 12 15
_Cutting Torches._--Steel may be cut with a jet of oxygen at a rate of
speed greater than in any other practicable way under usual conditions. The
action consists of burning away a thin section of the metal by allowing a
stream of oxygen to flow onto it while the gas is at high pressure and the
metal at a white heat.
[Illustration: Figure 23.--Cutting Torch]
The cutting torch (Figure 23) has the same characteristics as the welding
torch, but has an additional nozzle or means for temporarily using the
welding opening for the high pressure oxygen. The oxygen issues from the
opening while cutting at a pressure of from ten to 100 pounds to the square
inch.
The work is first heated to a white heat by adjusting the torch for a
welding flame. As soon as the metal reaches this temperature, the high
pressure oxygen is turned on to the white-hot portion of the steel. When
the jet of gas strikes the metal it cuts straight through, leaving a very
narrow slot and removing but little metal. Thicknesses of steel up to ten
inches can be economically handled in this way.
The oxygen nozzle is usually arranged so that it is surrounded by a number
of small jets for the heating flame. It will be seen that this arrangement
makes the heating flame always precede the oxygen jet, no matter in which
direction the torch is moved.
The torch is held firmly, either by hand or with the help of special
mechanism for guiding it in the desired path, and is steadily advanced in
the direction it is desired to extend the cut, the rate of advance being
from three inches to two feet per minute through metal from nine inches
down to one-quarter of an inch in thickness.
The following data on cutting is given by the Davis-Bournonville Company:
Cubic
Feet Cost of
Thickness of Gas Inches Gases
of Cutting Heating per Foot Oxygen Cut per per Foot
Steel Oxygen Oxygen of Cut Acetylene Min. of Cut
1/4 10 lbs. 4 lbs. .40 .086 24 $ .013
1/2 20 4 .91 .150 15 .029
3/4 30 4 1.16 .150 15 .036
1 30 4 1.45 .172 12 .045
1 1/2 30 5 2.40 .380 12 .076
2 40 5 2.96 .380 12 .093
4 50 5 9.70 .800 7 .299
6 70 6 21.09 1.50 4 .648
9 100 6 43.20 2.00 3 1.311
_Acetylene-Air Torch._--A form of torch which burns the acetylene after
mixing it with atmospheric air at normal pressure rather than with the
oxygen under higher pressures has been found useful in certain pre-heating,
brazing and similar operations. This torch (Figure 24) is attached by a
rubber gas hose to any compressed acetylene tank and is regulated as to
flame size and temperature by opening or closing the tank valve more or
less.
After attaching the torch to the tank, the gas is turned on very slowly and
is lighted at the torch tip. The adjustment should cause the presence of a
greenish-white cone of flame surrounded by a larger body of burning gas,
the cone starting at the mouth of the torch.
[Illustration: Figure 24.--Acetylene-Air Torch]
By opening the tank valve more, a longer and hotter flame is produced, the
length being regulated by the tank valve also. This torch will give
sufficient heat to melt steel, although not under conditions suited to
welding. Because of the excess of acetylene always present there is no
danger of oxidizing the metal being heated.
The only care required by this torch is to keep the small air passages at
the nozzle clean and free from carbon deposits. The flame should be
extinguished when not in use rather than turned low, because this low flame
rapidly deposits large quantities of soot in the burner.