Welding and Cutting Metals

SOLDERING

Common solder is an alloy of one-half lead with one-half tin, and is called

"half and half." Hard solder is made with two-thirds tin and one-third

lead. These alloys, when heated, are used to join surfaces of the same or

dissimilar metals such as copper, brass, lead, galvanized iron, zinc,

tinned plate, etc. These metals are easily joined, but the action of solder

with iron, steel and aluminum is not so satisfactory and requires greater

care and skill.

The solder is caused to make a perfect union with the surfaces treated with

the help of heat from a soldering iron. The soldering iron is made from a

piece of copper, pointed at one end and with the other end attached to an

iron rod and wooden handle. A flux is used to remove impurities from the

joint and allow the solder to secure a firm union with the metal surface.

The iron, and in many cases the work, is heated with a gasoline blow torch,

a small gas furnace, an electric heater or an acetylene and air torch.

The gasoline torch which is most commonly used should be filled two-thirds

full of gasoline through the hole in the bottom, which is closed by a screw

plug. After working the small hand pump for 10 to 20 strokes, hold the palm

of your hand over the end of the large iron tube on top of the torch and

open the gasoline needle valve about a half turn. Hold the torch so that

the liquid runs down into the cup below the tube and fills it. Shut the

gasoline needle valve, wipe the hands dry, and set fire to the fuel in the

cup. Just as the gasoline fire goes out, open the gasoline needle valve

about a half turn and hold a lighted match at the end of the iron tube to

ignite the mixture of vaporized gasoline and air. Open or close the needle

valve to secure a flame about 4 inches long.

On top of the iron tube from which the flame issues there is a rest for

supporting the soldering iron with the copper part in the flame. Place the

iron in the flame and allow it to remain until the copper becomes very hot,

not quite red, but almost so.

A new soldering iron or one that has been misused will have to be "tinned"

before using. To do this, take the iron from the fire while very hot and

rub the tip on some flux or dip it into soldering acid. Then rub the tip of

the iron on a stick of solder or rub the solder on the iron. If the solder

melts off the stick without coating the end of the iron, allow a few drops

to fall on a piece of tin plate, then nil the end of the iron on the tin

plate with considerable force. Alternately rub the iron on the solder and

dip into flux until the tip has a coating of bright solder for about half

an inch from the end. If the iron is in very bad shape, it may be necessary

to scrape or file the end before dipping in the flux for the first time.

After the end of the iron is tinned in this way, replace it on the rest of

the torch so that the tinned point is not directly in the flame, turning

the flame down to accomplish this.

Flux.--The commonest flux, which is called "soldering acid," is made

by placing pieces of zinc in muriatic (hydrochloric) acid contained in a

heavy glass or porcelain dish. There will be bubbles and considerable heat

evolved and zinc should be added until this action ceases and the zinc

remains in the liquid, which is now chloride of zinc.

This soldering acid may be used on any metal to be soldered by applying

with a brush or swab. For electrical work, this acid should be made neutral

by the addition of one part ammonia and one part water to each three parts

of the acid. This neutralized flux will not corrode metal as will the

ordinary acid.

Powdered resin makes a good flux for lead, tin plate, galvanized iron and

aluminum. Tallow, olive oil, beeswax and vaseline are also used for this

purpose. Muriatic acid may be used for zinc or galvanized iron without the

addition of the zinc, as described in making zinc chloride. The addition of

two heaping teaspoonfuls of sal ammoniac to each pint of the chloride of

zinc is sometimes found to improve its action.

Soldering Metal Parts.--All surfaces to be joined should be fitted

to each other as accurately as possible and then thoroughly cleaned with a

file, emery cloth, scratch bush or by dipping in lye. Work may be cleaned

by dipping it into nitric acid which has been diluted with an equal volume

of water. The work should be heated as hot as possible without danger of

melting, as this causes the solder to flow better and secure a much better

hold on the surfaces. Hard solder gives better results than half and half,

but is more difficult to work. It is very important that the soldering iron

be kept at a high heat during all work, otherwise the solder will only

stick to the surfaces and will not join with them.

Sweating is a form of soldering in which the surfaces of the work are first

covered with a thin layer of solder by rubbing them with the hot iron after

it has been dipped in or touched to the soldering stick. These surfaces are

then placed in contact and heated to a point at which the solder melts and

unites. Sweating is much to be preferred to ordinary soldering where the

form of the work permits it. This is the only method which should ever be

used when a fitting is to be placed over the end of a length of tube.

Soldering Holes.--Clean the surfaces for some distance around the

hole until they are bright, and apply flux while holding the hot iron near

the hole. Touch the tip of the iron to some solder until the solder is

picked up on the iron, and then place this solder, which was just picked

up, around the edge of the hole. It will leave the soldering iron and stick

to the metal. Keep adding solder in this way until the hole has been closed

up by working from the edges and building toward the center. After the hole

is closed, apply more flux to the job and smooth over with the hot iron

until there are no rough spots. Should the solder refuse to flow smoothly,

the iron is not hot enough.

Soldering Seams.--Clean back from the seam or split for at least

half an inch all around and then build up the solder in the same way as was

done with the hole. After closing the opening, apply more flux to the work

and run the hot iron lengthwise to smooth the job.

Soldering Wires.--Clean all insulation from the ends to be soldered

and scrape the ends bright. Lay the ends parallel to each other and,

starting at the middle of the cleaned portion, wrap the ends around each

other, one being wrapped to the right, the other to the left. Hold the hot

iron under the twisted joint and apply flux to the wire. Then dip the iron

in the solder and apply to the twisted portion until the spaces between the

wires are filled with solder. Finish by smoothing the joint and cleaning

away all excess metal by rubbing the hot iron lengthwise. The joint should

now be covered with a layer of rubber tape and this covered with a layer of

ordinary friction tape.

Steel and Iron.--Steel surfaces should be cleaned, then covered with

clear muriatic acid. While the acid is on the metal, rub with a stick of

zinc and then tin the surfaces with the hot iron as directed. Cast iron

should be cleaned and dipped in strong lye to remove grease. Wash the lye

away with clean water and cover with muriatic acid as with steel. Then rub

with a piece of zinc and tin the surfaces by using resin as a flux.

It is very difficult to solder aluminum with ordinary solder. A special

aluminum solder should be secured, which is easily applied and makes a

strong joint. Zinc or phosphor tin may be used in place of ordinary solder

to tin the surfaces or to fill small holes or cracks. The aluminum must be

thoroughly heated before attempting to solder and the flux may be either

resin or soldering acid. The aluminum must be thoroughly cleaned with

dilute nitric acid and kept hot while the solder is applied by forcible

rubbing with the hot iron.

BRAZING

This is a process for joining metal parts, very similar to soldering,

except that brass is used to make the joint in place of the lead and zinc

alloys which form solder. Brazing must not be attempted on metals whose

melting point is less than that of sheet brass.

Two pieces of brass to be brazed together are heated to a temperature at

which the brass used in the process will melt and flow between the

surfaces. The brass amalgamates with the surfaces and makes a very strong

and perfect joint, which is far superior to any form of soldering where the

work allows this process to be used, and in many cases is the equal of

welding for the particular field in which it applies.

Brazing Heat and Tools.--The metal commonly used for brazing will

melt at heats between 1350° and 1650° Fahrenheit. To bring the parts to

this temperature, various methods are in use, using solid, liquid or

gaseous fuels. While brazing may be accomplished with the fire of the

blacksmith forge, this method is seldom satisfactory because of the

difficulty of making a sufficiently clean fire with smithing coal, and it

should not be used when anything else is available. Large jobs of brazing

may be handled with a charcoal fire built in the forge, as this fuel

produces a very satisfactory and clean fire. The only objection is in the

difficulty of confining the heat to the desired parts of the work.

The most satisfactory fire is that from a fuel gas torch built for this

work. These torches are simply forms of Bunsen burners, mixing the proper

quantity of air with the gas to bring about a perfect combustion. Hose

lines lead to the mixing tube of the gas torch, one line carrying the gas

and the other air under a moderate pressure. The air line is often

dispensed with, allowing the gas to draw air into the burner on the

injector principle, much the same as with illuminating gas burners for use

with incandescent mantles. Valves are provided with which the operator may

regulate the amount of both gas and air, and ordinarily the quality and

intensity of the flame.

When gas is not available, recourse may be had to the gasoline torch made

for brazing. This torch is built in the same way as the small portable

gasoline torches for soldering operations, with the exception that two

regulating needle valves are incorporated in place of only one.

The torches are carried on a framework, which also supports the work being

handled. Fuel is forced to the torch from a large tank of gasoline into

which air pressure is pumped by hand. The torches are regulated to give

the desired flame by means of the needle valves in much the same way as

with any other form of pressure torch using liquid fuel.

Another very satisfactory form of torch for brazing is the acetylene-air

combination described in the chapter on welding instruments. This torch

gives the correct degree of heat and may be regulated to give a clean and

easily controlled flame.

Regardless of the source of heat, the fire or flame must be adjusted so

that no soot is deposited on the metal surfaces of the work. This can only

be accomplished by supplying the exact amounts of gas and air that will

produce a complete burning of the fuel. With the brazing torches in common

use two heads are furnished, being supplied from the same source of fuel,

but with separate regulating devices. The torches are adjustably mounted in

such a way that the flames may be directed toward each other, heating two

sides of the work at the same time and allowing the pieces to be completely

surrounded with the flame.

Except for the source of heat, but one tool is required for ordinary

brazing operations, this being a spatula formed by flattening one end of a

quarter-inch steel rod. The spatula is used for placing the brazing metal

on the work and for handling the flux that is required in this work as in

all other similar operations.

Spelter.--The metal that is melted into the joint is called spelter.

While this name originally applied to but one particular grade or

composition of metal, common use has extended the meaning until it is

generally applied to all grades.

Spelter is variously composed of alloys containing copper, zinc, tin and

antimony, the mixture employed depending on the work to be done. The

different grades are of varying hardness, the harder kinds melting at

higher temperatures than the soft ones and producing a stronger joint when

used. The reason for not using hard spelter in all cases is the increased

difficulty of working it and the fact that its melting point is so near to

some of the metals brazed that there is great danger of melting the work as

well as the spelter.

The hardest grade of spelter is made from three-fourths copper with

one-fourth zinc and is used for working on malleable and cast iron and for

steel.

This hard spelter melts at about 1650° and is correspondingly difficult to

handle.

A spelter suitable for working with copper is made from equal parts of

copper and zinc, melting at about 1400° Fahrenheit, 500° below the melting

point of the copper itself. A still softer brazing metal is composed of

half copper, three-eighths zinc and one-eighth tin. This grade is used for

fastening brass to iron and copper and for working with large pieces of

brass to brass. For brazing thin sheet brass and light brass castings, a

metal is used which contains two-thirds tin and one-third antimony. The

low melting point of this last composition makes it very easy to work with

and the danger of melting the work is very slight. However, as might be

expected, a comparatively weak joint is secured, which will not stand any

great strain.

All of the above brazing metals are used in powder form so that they may be

applied with the spatula where the joint is exposed on the outside of the

work. In case it is necessary to braze on the inside of a tube or any deep

recess, the spelter may be placed on a flat rod long enough to reach to

the farthest point. By distributing the spelter at the proper points along

the rod it may be placed at the right points by turning the rod over after

inserting into the recess.

Flux.--In order to remove the oxides produced under brazing heat and

to allow the brazing metal to flow freely into place, a flux of some kind

must be used. The commonest flux is simply a pure calcined borax powder,

that is, a borax powder that has been heated until practically all the

water has been driven off.

Calcined borax may also be mixed with about 15 per cent of sal ammoniac to

make a satisfactory fluxing powder. It is absolutely necessary to use flux

of some kind and a part of whatever is used should be made into a paste

with water so that it can be applied to the joint to be brazed before

heating. The remainder of the powder should be kept dry for use during the

operation and after the heat has been applied.

Preparing the Work.--The surfaces to be brazed are first thoroughly

cleaned with files, emery cloth or sand paper. If the work is greasy, it

should be dipped into a bath of lye or hot soda water so that all trace of

oil is removed. The parts are then placed in the relation to each other

that they are to occupy when the work has been completed. The edges to be

joined should make a secure and tight fit, and should match each other at

all points so that the smallest possible space is left between them. This

fit should not be so tight that it is necessary to force the work into

place, neither should it be loose enough to allow any considerable space

between the surfaces. The molten spelter will penetrate between surfaces

that water will flow between when the work and spelter have both been

brought to the proper heat. It is, of course, necessary that the two parts

have a sufficient number of points of contact so that they will remain in

the proper relative position.

The work is placed on the surface of the brazing table in such a position

that the flame from the torches will strike the parts to be heated, and

with the joint in such a position that the melted spelter will flow down

through it and fill every possible part of the space between the surfaces

under the action of gravity. That means that the edge of the joint must be

uppermost and the crack to be filled must not lie horizontal, but at the

greatest slant possible. Better than any degree of slant would be to have

the line of the joint vertical.

The work is braced up or clamped in the proper position before commencing

to braze, and it is best to place fire brick in such positions that it will

be impossible for cooling draughts of air to reach the heated metal should

the flame be removed temporarily during the process. In case there is a

large body of iron, steel or copper to be handled, it is often advisable to

place charcoal around the work, igniting this with the flame of the torch

before starting to braze so that the metal will be maintained at the

correct heat without depending entirely on the torch.

When handling brass pieces having thin sections there is danger of melting

the brass and causing it to flow away from under the flame, with the result

that the work is ruined. If, in the judgment of the workman, this may

happen with the particular job in hand, it is well to build up a mould of

fire clay back of the thin parts or preferably back of the whole piece, so

that the metal will have the necessary support. This mould may be made by

mixing the fire clay into a stiff paste with water and then packing it

against the piece to be supported tightly enough so that the form will be

retained even if the metal softens.

Brazing.--With the work in place, it should be well covered with the

paste of flux and water, then heated until this flux boils up and runs over

the surfaces. Spelter is then placed in such a position that it will run

into the joint and the heat is continued or increased until the spelter

melts and flows in between the two surfaces. The flame should surround the

work during the heating so that outside air is excluded as far as is

possible to prevent excessive oxidization.

When handling brass or copper, the flame should not be directed so that its

center strikes the metal squarely, but so that it glances from one side or

the other. Directing the flame straight against the work is often the cause

of melting the pieces before the operation is completed. When brazing two

different metals, the flame should play only on the one that melts at the

higher temperature, the lower melting part receiving its heat from the

other. This avoids the danger of melting one before the other reaches the

brazing point.

The heat should be continued only long enough to cause the spelter to flow

into place and no longer. Prolonged heating of any metal can do nothing but

oxidize and weaken it, and this practice should be avoided as much as

possible. If the spelter melts into small globules in place of flowing, it

may be caused to spread and run into the joint by lightly tapping the work.

More dry flux may be added with the spatula if the tapping does not produce

the desired result.

Excessive use of flux, especially toward the end of the work, will result

in a very hard surface on all the work, a surface which will be extremely

difficult to finish properly. This trouble will be present to a certain

extent anyway, but it may be lessened by a vigorous scraping with a wire

brush just as soon as the work is removed from the fire. If allowed to cool

before cleaning, the final appearance will not be as good as with the

surplus metal and scale removed immediately upon completing the job.

After the work has been cleaned with the brush it may be allowed to cool

and finished to the desired shape, size and surface by filing and

polishing. When filed, a very thin line of brass should appear where the

crack was at the beginning of the work. If it is desired to avoid a square

shoulder and fill in an angle joint to make it rounding, the filling is

best accomplished by winding a coil of very thin brass wire around the part

of the work that projects and then causing this to flow itself or else

allow the spelter to fill the spaces between the layers of wire. Copper

wire may also be used for this purpose, the spaces being filled with

melted spelter.

THERMIT WELDING

The process of welding which makes use of the great heat produced by oxygen

combining with aluminum is known as the Thermit process and was perfected

by Dr. Hans Goldschmidt. The process, which is controlled by the

Goldschmidt Thermit Company, makes use of a mixture of finely powdered

aluminum with an oxide of iron called by the trade name, Thermit.

The reaction is started with a special ignition powder, such as barium

superoxide and aluminum, and the oxygen from the iron oxide combining with

the aluminum, producing a mass of superheated steel at about 5000 degrees

Fahrenheit. After the reaction, which takes from. 30 seconds to a minute,

the molten metal is drawn from the crucible on to the surfaces to be

joined. Its extreme heat fuses the metal and a perfect joint is the result.

This process is suited for welding iron or steel parts of comparatively

large size.

Preparation.--The parts to be joined are thoroughly cleaned on the

surfaces and for several inches back from the joint, after which they are

supported in place. The surfaces between which the metal will flow are

separated from 1/4 to 1 inch, depending on the size of the parts, but

cutting or drilling part of the metal away. After this separation is made

for allowing the entrance of new metal, the effects of contraction of the

molten steel are cared for by preheating adjacent parts or by forcing the

ends apart with wedges and jacks. The amount of this last separation must

be determined by the shape and proportions of the parts in the same way as

would be done for any other class of welding which heats the parts to a

melting point.

Yellow wax, which has been warmed until plastic, is then placed around the

joint to form a collar, the wax completely filling the space between the

ends and being provided with vent holes by imbedding a piece of stout cord,

which is pulled out after the wax cools.

A retaining mould (Figure 55) made from sheet steel or fire brick is then

placed around the parts. This mould is then filled with a mixture of one

part fire clay, one part ground fire brick and one part fire sand. These

materials are well mixed and moistened with enough water so that they will

pack. This mixture is then placed in the mould, filling the space between

the walls and the wax, and is packed hard with a rammer so that the

material forms a wall several inches thick between any point of the mould

and the wax. The mixture must be placed in the mould in small quantities

and packed tight as the filling progresses.

Image Figure 55.--Thermit Mould Construction

Three or more openings are provided through this moulding material by the

insertion of wood or pipe forms. One of these openings will lead from the

lowest point of the wax pattern and is used for the introduction of the

preheating flame. Another opening leads from the top of the mould into this

preheating gate, opening into the preheating gate at a point about one inch

from the wax pattern. Openings, called risers, are then provided from each

of the high points of the wax pattern to the top of the mould, these risers

ending at the top in a shallow basin. The molten metal comes up into these

risers and cares for contraction of the casting, as well as avoiding

defects in the collar of the weld. After the moulding material is well

packed, these gate patterns are tapped lightly and withdrawn, except in the

case of the metal pipes which are placed at points at which it would be

impossible to withdraw a pattern.

Preheating.--The ends to be welded are brought to a bright red heat

by introducing the flame from a torch through the preheating gate. The

torch must use either gasoline or kerosene, and not crude oil, as the crude

oil deposits too much carbon on the parts. Preheating of other adjacent

parts to care for contraction is done at this time by an additional torch

burner.

The heating flame is started gently at first and gradually increased. The

wax will melt and may be allowed to run out of the preheating gate by

removing the flame at intervals for a few seconds. The heat is continued

until the mould is thoroughly dried and the parts to be joined are brought

to the red heat required. This leaves a mould just the shape of the wax

pattern.

The heating gate should then be plugged with a sand core, iron plug or

piece of fitted fire brick, and backed up with several shovels full of the

moulding mixture, well packed.

Image Figure 56.--Thermit Crucible Plug.

A, Hard burn magnesia stone;

B, Magnesia thimble;

C, Refractory sand;

D, Metal disc;

E, Asbestos washer;

F, Tapping pin

Thermit Metal.--The reaction takes place in a special crucible lined

with magnesia tar, which is baked at a red heat until the tar is driven off

and the magnesia left. This lining should last from twelve to fifteen

reactions. This magnesia lining ends at the bottom of the crucible in a

ring of magnesia stone and this ring carries a magnesia thimble through

which the molten steel passes on its way to the mould. It will usually be

necessary to renew this thimble after each reaction. This lower opening is

closed before filling the crucible with thermit by means of a small disc or

iron carrying a stem, which is called a tapping pin (Figure 56). This pin,

F, is placed in the thimble with the stem extending down through the

opening and exposing about two inches. The top of this pin is covered with

an asbestos, washer, E, then with another iron disc. D, and

finally with a layer of refractory sand. The crucible is tapped by knocking

the stem of the pin upwards with a spade or piece of flat iron about four

feet long.

The charge of thermit is added by placing a few handfuls over the

refractory sand and then pouring in the balance required. The amount of

thermit required is calculated from the wax used. The wax is weighed before

and after filling the entire space that the thermit will occupy.

This does not mean only the wax collar, but the space of the mould with all

gates filled with wax. The number of pounds of wax required for this

filling multiplied by 25 will give the number of pounds of thermit to be

used. To this quantity of thermit should be added I per cent of pure

manganese, 1 per cent nickel thermit and 15 per cent of steel punchings.

It is necessary, when more than 10 pounds of thermit will be used, to mix

steel punchings not exceeding 3/8 inch diameter by 1/8 inch thick with the

powder in order to sufficiently retard the intensity of the reaction.

Half a teaspoonful of ignition powder is placed on top of the thermit

charge and ignited with a storm match or piece of red hot iron. The cover

should be immediately closed on the top of the crucible and the operator

should get away to a safe distance because of the metal that may be thrown

out of the crucible.

After allowing about 30 seconds to a minute for the reaction to take place

and the slag to rise to the top of the crucible, the tapping pin is struck

from below and the molten metal allowed to run into the mould. The mould

should be allowed to remain in place as long as possible, preferably over

night, so as to anneal the steel in the weld, but in no case should it be

disturbed for several hours after pouring. After removing the mould, drill

through the metal left in the riser and gates and knock these sections off.

No part of the collar should be removed unless absolutely necessary.

Welding and Cutting Metals

vineri, 28 martie 2014

OXYGEN PROCESS FOR REMOVAL OF CARBON

SOLDERING, BRAZING AND THERMIT WELDING