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Oxy Acetylene Welding and Cutting

H >> Harold P. Manly >> Oxy Acetylene Welding and Cutting




This diaphragm is carried so that the pressure within the generator acts
on one side while a spring, whose tension is under the control of the
operator, acts on the other side. The diaphragm is connected to the brake
and locking device on the motor in such a way that increasing the tension
on the spring presses the diaphragm and moves a rod that releases the brake
and starts the feed. The gas pressure, increasing with the continuation of
carbide feed, acts on the other side and finally overcomes the pressure of
the spring tension, moving the control rod the other way and stopping the
motor and carbide feed. This spring tension is adjusted and checked with
the help of a pressure gauge attached to the generating chamber.

_Gravity Feed._--This type of feed differs from the foregoing in that
the carbide is simply released and is allowed to fall into the water
without being forced to do so. Any form of valve that is sufficiently
powerful in action to close with the carbide passing through is used and is
operated by the power secured from the rise and fall of the gas holder
bell. When this valve is first opened the carbide runs into the water until
sufficient pressure and volume of gas is generated to raise the bell. This
movement operates the arm attached to the carbide shut off valve and slowly
closes it. A fall of the bell occasioned by gas being withdrawn again opens
the valve and more gas is generated.

_Mechanical Feed._--The previously described methods of feeding
carbide to the water have all been automatic in action and do not depend
on the operator for their proper action.

Some types of large generating plants have a power-driven feed, the power
usually being from some kind of motor other than one operated by a weight,
such as a water motor, for instance. This motor is started and stopped by
the operator when, in his judgment, more gas is wanted or enough has been
generated. This type of machine, often called a "non-automatic generator,"
is suitable for large installations and is attached to a gas holder of
sufficient size to hold a day's supply of acetylene. The generator can then
be operated until a quantity of gas has been made that will fill the large
holder, or gasometer, and then allowed to remain idle for some time.

_Gas Holders._--The commonest type of gas container is that known as a
gasometer. This consists of a circular tank partly filled with water, into
which is lowered another circular tank, inverted, which is made enough
smaller in diameter than the first one so that three-quarters of an inch is
left between them. This upper and inverted portion, called the bell,
receives the gas from the generator and rises or falls in the bath of water
provided in the lower tank as a greater or less amount of gas is contained
in it.

These holders are made large enough so that they will provide a means of
caring for any after generation and so that they maintain a steady and even
flow. The generator, however, must be of a capacity great enough so that
the gas holder will not be drawn on for part of the supply with all torches
in operation. That is, the holder must not be depended on for a reserve
supply.

The bell of the holder is made so that when full of gas its lower edge is
still under a depth of at least nine inches of water in the lower tank. Any
further rise beyond this point should always release the gas, or at least
part of it, to the escape pipe so that the gas will under no circumstances
be forced into the room from, between the bell and tank. The bell is guided
in its rise and fall by vertical rods so that it will not wedge at any
point in its travel.

A condensing chamber to receive the water which condenses from the
acetylene gas in the holder is usually placed under this part and is
provided with a drain so that this water of condensation may be easily
removed.

_Filtering._--A small chamber containing some closely packed but
porous material such as felt is placed in the pipe leading to the torch
lines. As the acetylene gas passes through this filter the particles of
lime dust and other impurities are extracted from it so that danger of
clogging the torch openings is avoided as much as possible.

The gas is also filtered to a large extent by its passage through the water
in the generating chamber, this filtering or "scrubbing" often being
facilitated by the form of piping through which the gas must pass from the
generating chamber into the holder. If the gas passes out of a number of
small openings when going into the holder the small bubbles give a better
washing than large ones would.

_Piping._--Connections from generators to service pipes should
preferably be made with right and left couplings or long thread nipples
with lock nuts. If unions are used, they should be of a type that does not
require gaskets. The piping should be carried and supported so that any
moisture condensing in the lines will drain back toward the generator and
where low points occur they should be drained through tees leading into
drip cups which are permanently closed with screw caps or plugs. No pet
cocks should be used for this purpose.

For the feed pipes to the torch lines the following pipe sizes are
recommended.

3/8 inch pipe. 26 feet long. 2 cubic feet per hour.
1/2 inch pipe. 30 feet long. 4 cubic feet per hour.
3/4 inch pipe. 50 feet long. 15 cubic feet per hour.
1 inch pipe. 70 feet long. 27 cubic feet per hour.
1-1/4 inch pipe. 100 feet long. 50 cubic feet per hour.
1-1/2 inch pipe. 150 feet long. 65 cubic feet per hour.
2 inch pipe. 200 feet long. 125 cubic feet per hour.
2-1/2 inch pipe. 300 feet long. 190 cubic feet per hour.
3 inch pipe. 450 feet long. 335 cubic feet per hour.

When drainage is possible into a sewer, the generator should not be
connected directly into the sewer but should first discharge into an open
receptacle, which may in turn be connected to the sewer.

No valves or pet cocks should open into the generator room or any other
room when it would be possible, by opening them for draining purposes, to
allow any escape of gas. Any condensation must be removed without the use
of valves or other working parts, being drained into closed receptacles. It
should be needless to say that all the piping for gas must be perfectly
tight at every point in its length.

_Safety Devices._--Good generators are built in such a way that the
operator must follow the proper order of operation in charging and cleaning
as well as in all other necessary care. It has been mentioned that the gas
pressure is released or shut off before it is possible to fill the water
compartment, and this same idea is carried further in making the generator
inoperative and free from gas pressure before opening the residue drain of
the carbide filling opening on top of the hopper. Some machines are made so
that they automatically cease to generate should there be a sudden and
abnormal withdrawal of gas such as would be caused by a bad leak. This
method of adding safety by automatic means and interlocking parts may be
carried to any extent that seems desirable or necessary to the maker.

All generators should be provided with escape or relief pipes of large size
which lead to the open air. These pipes are carried so that condensation
will drain back toward the generator and after being led out of the
building to a point at least twelve feet above ground, they end in a
protecting hood so that no rain or solid matter can find its way into them.
Any escape of gas which might ordinarily pass into the generator room is
led into these escape pipes, all parts of the system being connected with
the pipe so that the gas will find this way out.

Safety blow off valves are provided so that any excess gas which cannot be
contained by the gas holder may be allowed to escape without causing an
undue rise in pressure. This valve also allows the escape of pressure above
that for which the generator was designed. Gas released in this way passes
into the escape pipe just described.

Inasmuch as the pressure of the oxygen is much greater than that of the
acetylene when used in the torch, it will be seen that anything that caused
the torch outlet to become closed would allow the oxygen to force the
acetylene back into the generator and the oxygen would follow it, making a
very explosive mixture. This return of the gas is prevented by a hydraulic
safety valve or back pressure valve, as it is often called.

Mechanical check valves have been found unsuitable for this use and those
which employ water as a seal are now required by the insurance rules. The
valve itself (Figure 13) consists of a large cylinder containing water to a
certain depth, which is indicated on the valve body. Two pipes come into
the upper end of this cylinder and lead down into the water, one being
longer than the other. The shorter pipe leads to the escape pipe mentioned
above, while the longer one comes from the generator. The upper end of the
cylinder has an opening to which is attached the pipe leading to the
torches.

[Illustration: Figure 13.--Hydraulic Back-Pressure Valve.
_A_, Acetylene supply line;
_B_, Vent pipe;
_C_, Water filling plug;
_D_, Acetylene service cock;
_E_, Plug to gauge height of water;
_F_, Gas openings under water;
_G_, Return pipe for sealing water;
_H_, Tube to carry gas below water line;
_I_, Tube to carry gas to escape pipe;
_J_, Gas chamber;
_K_, Plug in upper gas chamber;
_L_, High water level;
_M_, Opening through which water returns;
_O_, Bottom clean out casting]

The gas coming from the generator through the longer pipe passes out of the
lower end of the pipe which is under water and bubbles up through the water
to the space in the top of the cylinder. From there the gas goes to the
pipe leading to the torches. The shorter pipe is closed by the depth of
water so that the gas does not escape to the relief pipe. As long as the
gas flows in the normal direction as described there will be no escape to
the air. Should the gas in the torch line return into the hydraulic valve
its pressure will lower the level of water in the cylinder by forcing some
of the liquid up into the two pipes. As the level of the water lowers, the
shorter pipe will be uncovered first, and as this is the pipe leading to
the open air the gas will be allowed to escape, while the pipe leading back
to the generator is still closed by the water seal. As soon as this reverse
flow ceases, the water will again resume its level and the action will
continue. Because of the small amount of water blown out of the escape pipe
each time the valve is called upon to perform this duty, it is necessary to
see that the correct water level is always maintained.

While there are modifications of this construction, the same principle is
used in all types. The pressure escape valve is often attached to this
hydraulic valve body.

_Construction Details._--Flexible tubing (except at torches), swing
pipe joints, springs, mechanical check valves, chains, pulleys and lead or
fusible piping should never be used on acetylene apparatus except where the
failure of those parts will not affect the safety of the machine or permit,
either directly or indirectly, the escape of gas into a room. Floats should
not be used except where failure will only render the machine inoperative.

It should be said that the National Board of Fire Underwriters have
established an inspection service for acetylene generators and any
apparatus which bears their label, stating that that particular model and
type has been passed, is safe to use. This service is for the best
interests of all concerned and looks toward the prevention of accidents.
Such inspection is a very important and desirable feature of any outfit and
should be insisted upon.

_Location of Generators._--Generators should preferably be placed
outside of insured buildings and in properly constructed generator houses.
The operating mechanism should have ample room to work in and there should
be room enough for the attendant to reach the various parts and perform the
required duties without hindrance or the need of artificial light. They
should also be protected from tampering by unauthorized persons.

Generator houses should not be within five feet of any opening into, nor
have any opening toward, any adjacent building, and should be kept under
lock and key. The size of the house should be no greater than called for by
the requirements mentioned above and it should be well ventilated.

The foundation for the generator itself should be of brick, stone, concrete
or iron, if possible. If of wood, they should be extra heavy, located in a
dry place and open to circulation of air. A board platform is not
satisfactory, but the foundation should be of heavy planking or timber to
make a firm base and so that the air can circulate around the wood.

The generator should stand level and no strain should be placed on any of
the pipes or connections or any parts of the generator proper.




CHAPTER IV

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)]

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