Read Ebook: The Art of Lead Burning A practical treatise explaining the apparatus and processes. by Fay C H

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Different lead burners have different views on this subject. Some prefer the bellows, with a contained air holder; some the air holder built like a gasometer, while others use an air holder similar to the generator in construction. These all have their advantages. For my part, I own and use all three.

The advantage of the bellows is that it can be easily transported and does the work perfectly, but it requires constant pumping, which soon tires the helper, and for that reason could not be used on jobs requiring more than four or five hours' labor.

The gasometer style of air holder is the easiest to use, if one does not employ a helper and has a large amount of work to do. The pressure can be regulated to suit the work by placing one or more weights upon it until the desired pressure is obtained. It does not require pumping up more than three or four times a day, which is its principal virtue. It is a perfect shop apparatus. Its disadvantage is that it requires a large quantity of water to fill it, which is not always available, and when full it is so heavy that it requires a truck to move it around.

Air Holder No. 1.

The beginner will notice in Fig. 10 that this air holder is so constructed that it gets its air pressure direct from the head of water, and also that this pressure can be varied by making the connecting piece of pipe longer or shorter, as may be desired. Of course, the pressure will vary slightly as the water descends into the air chamber, but not enough to make it objectionable, as it will be the helper's duty to watch the water line and renew pumping as often as the water falls below a certain point.

Air Holder No. 2.

On the inside of this tank and into these couplings screw two pieces of 3/8 -inch pipe 4 inches long with elbows pointing straight up. Into these elbows screw two pieces of 3/8 -inch pipe long enough to come flush with the top of the tank F. On the outside of the tank and into the 3/8 -inch couplings screw two 3/8 -inch nipples 2 inches long, and on these nipples screw two 3/8 -inch hose end gas cocks.

Now, with the same sized sheet iron, make another tank 2 inches smaller in diameter than the first tank. This should have a flat bottom, and be wired as previously described. Then take four strips of sheet iron 30 inches long and 2 inches wide, and form each into V shape lengthwise. Lay off the circumference of this tank in four equal spaces. One side of the V-shaped pieces should then be soldered on at each space. The other side should be left loose to allow for adjustment. These pieces form the guides to the upper tank and prevent it from tipping sideways and binding. Two of the guides are shown in the illustration, Fig. 11.

The lower tank should now be filled about one-third full of water. The upper tank should then be inverted and placed in it. The air pump must then be connected to one of the 3/8 -inch cocks with a short piece of hose, and the air should be pumped into it until the upper tank rises to its highest level.

The pressure in this form of air holder must be regulated by weights, and to secure 1 pound of pressure it is necessary to place weights equal to 1 pound for every inch in area contained in the opening in the upper tank. Two drop handles, such as are used on heavy milk cans, should be riveted and soldered on the sides of the tank to facilitate moving it about.

Air Holder No. 3.

Fig. 12 is a cut of a bellows with a contained air holder. It is not practical to try to make this article, as it can be purchased from any plumbing supply house and is not expensive. It is used principally by dentists, but it is also used in laboratories to supply air to the compound blow pipe. It consists of a small bellows held from the floor on iron legs, with a spring inside the bellows to hold them open, and has a rubber bag fastened to the under side to hold a small supply of air. The rubber bag is incased in a string net to prevent it from becoming inflated too much and bursting. This bag serves to equalize the pressure. The size known as No. 10 A will supply 75 cubic feet per hour at a pressure of 1 1/2 pounds to the square inch, which is sufficient for lead as heavy as 24 pounds. For the light weight leads the pressure can be reduced by pumping lightly and not filling the bag more than half full.

Any of the three described air blast arrangements will answer the purpose, so it is immaterial which is used, and it is left to the discretion of the beginner to obtain whichever is the most convenient.

The Blow Pipe.

Next comes the blow pipe. The only practical compound blow pipe on the market is shown in Fig. 13, and is known as Walmsley's. This is a modification of the Bunsen burner, and consists of a bent blow pipe with the air tube in the center, as shown in Fig. 14. It is a perfect working blow pipe in every respect, and I should advise every one interested in the work to purchase one. For while seams cannot be burned with it in any other position than horizontal, it will be found useful in lengthening traps or lead bends, for which purpose it is well adapted and can be put into instant use, thereby saving its cost many times over in wiping solders.

Burning with Illuminating Gas.

With illuminating gas it is only necessary to connect the gas jet to the compound blow pipe with the hose and regulate the supply of gas with the gas cock. The air inlet is then connected to the air holder, or air may be supplied with the mouth, but good results are not obtained with the mouth, as only a good blow pipe solderer can keep up the blast necessary. To burn the seams use the same flux and follow directions given for gasoline gas.

Making the Gasoline Gas for Burning the Generator.

To operate this device the air should be turned on the gasoline and lighted at the jet. The air should then be admitted gradually until the flame is brought to the proper size and condition, indicated by its being blue and pointed. If too much gas is admitted the flame will be yellow and will blacken the work by depositing a coat of soot on it. If too much air is admitted the flame will be ragged and noisy, and the temperature will be too low to heat the metal. The flame is at its best heat when it burns with a pale blue color which does not show any yellow streaks.

Before attempting to burn the generator the beginner should practice on pieces of sheet lead. It is next to impossible to burn seams in any other position than horizontal with this flame, as it rapidly oxidizes the lead, and in spite of all precaution the lead will become unmanageable in upright seams, so that the beginner would waste time in practicing on seams in any other position than horizontal. If directions have been followed in cutting the lead for the generator the seams will occur only in that position.

To burn the generator the seams should be shaved clean, both on the under and upper sides, for a distance of 1/8 inch, making a seam 1/4 inch wide, taking care to have the lead seams lie close to each other, for, if they do not, this flame will cause the edges of the lead to spread away from each other and leave a hole that is difficult to patch.

Now apply the flux with a small brush. When the flame is in working order bring it quickly to bear on the end of the seam nearest you to be burned. When it starts to fuse draw the flame as quickly away, always drawing it to one side, and from the upper to the lower sheet. The melted drop will follow the flame and unite with the melted drop on the lower sheet.

It is necessary to have the shave hook near at hand, so that, in case of oxidizing when fusing, the melted drop can be broken up and allowed to flow in place.

With a little practice and patience the generator can be burned all right in this manner. This gas is perfectly safe and can be handled with impunity. This method would, of course, be impracticable to use on a job of any size, but I have used it several times where nothing else could be obtained, and have always had very good success with it.

We now assume that the generator is charged and the rest of the apparatus is finished and ready for use, so we will proceed to connect it up ready for a trial.

Testing the Apparatus.

It is necessary to test the generator for leaks, as a small blow hole may sometimes be left in some of the seams or the cocks or cleaning screws become defective.

To do this, first close the gas cock on the top of the gas chamber and make up the cleaning and charging screws, which must be set on a bed of soft putty. Then fill the acid chamber full of hot water, first measuring the water so as to ascertain just how much solution is required in proportion to the amount of water, as it takes the same quantity at all times. Allow it to stand for a few moments, then mark the water line with a pencil or nail, when it should be left standing for an hour. The water should stay at the mark indicated for an indefinite time. If it sinks during this test it shows that there is a leak in the generator and it must be located and repaired.

To locate the leak the gas cock should be opened and the water allowed to run into the gas chamber. If this does not show the leak, force the water back into the acid chamber, which is done by attaching the air pump to the gas cock. Then taking a piece of soap and making a stiff lather, daub it over the cocks and cleaning and charging screw. When the leak is found the escaping air will cause bubbles to be blown. If the leak does not become apparent after the above process, the side boards of the generator should be taken off and the operation repeated on the seams.

Under no circumstances must the apparatus be left until there is absolutely no doubt as to its being perfectly tight, as a slight leak would be likely to cause a disastrous explosion and injure or probably blind the operator. Flying vitriol is not a very pleasant thing to get in one's eyes.

The reason that the air pressure should not be heavier than the gas pressure is that if the air were the stronger there would be danger of the air working back into the gas tube and causing an explosion in the tubes; consequently it is well to note this point carefully. Many lead burners will say that the pressure of air is of no consequence, and all that is required is a sufficient supply; but my experience and experiments have convinced me that when the pressures of air and gas are nearly equal the best results are obtained.

The Mixing Fork and Blow Pipe.

The mixing fork and blow pipe can be made in any plumbing shop and should be made of the smallest size pipe available.

After making sure that the generator is perfectly tight we will proceed to charge it. After removing the 4-inch charging screw take 15 pounds of commercial spelter, which has been broken up with a hammer into pieces about 2 inches square, and place this in the gas chamber, distributing it as evenly as possible over the perforated bottom. This is done so that the zinc will expose all the surface possible to the action of the acid, and must be observed in order to obtain the best results. Do not put any pieces of spelter into the generator that are small enough to drop through the perforated bottom, for if they do they will be likely to generate gas, which will give overpressure and blow gas out through the acid chamber. This can do no harm unless close to a light, but it is very annoying to have acid blown all over the generator. The charging and cleaning screws must be screwed up tight. After closing the gas cock on the generator take the quantity of water that was found to be necessary when testing the apparatus, and pour this into the acid chamber.

Mark the water line and watch it for a few moments to make sure that everything is tight. Then take of sulphuric acid a quantity equal to one-seventh of the water used, and pour that into the water in the acid chamber. It will diffuse itself through the water and thoroughly mix. Experience has taught me that acid mixed in any proportion stronger than seven parts of water to one part of acid does not act as quickly as when mixed in the proportion mentioned. The reason for this is that the strong acid simply coats the zinc with a deposit or scum of sulphate of zinc, which is soluble in water, but is not soluble in acid. Therefore, if the acid is diluted with water to the above mentioned proportion the water readily dissolves the sulphate and allows the acid to act freely on the zinc.

Automatic Action of the Generator.

This gas, by reason of its lightness, will rise to the surface of the acid, and as pressure increases it will force the acid back up through the acid supply pipe into the acid chamber, until the acid falls below the perforated bottom. When the acid and zinc cease to come in contact with each other the generation of gas stops until gas is used, which relieves the pressure; then more acid descends, and as it comes in contact with the zinc more gas is generated, replacing that which has been used. This action makes the generator automatic, unless clogging with sulphate of zinc takes place. This may happen at any time if the apparatus is not cleaned after each day's use.

Cleaning the Generator.

To clean the generator in this case attach the air pump to the gas cock on the generator and force the acid up into the acid chamber by pumping air slowly into the gas chamber until the acid rises to the proper hight in the acid chamber, where it can be held by forcing a long wooden plug into the acid supply pipe. The pumping must cease when the acid rises to the proper level, or the excess pressure of air will work up through the supply pipe and cause a blow of acid.

The charging screw can then be removed and the zinc taken out and washed in hot water. Remove the clean out screw and run one or two pails of hot water through the gas chamber. This will remove the deposits of sulphate paste. The zinc can then be replaced, the screws tightened and the acid released again. Be sure and exhaust the air in the gas chamber, as previously described, by letting the air spurt out of the gas cock before connecting it to the scrubbing cup. Care must be taken not to have any lights near the generator when blowing out this mixture of gas and air, as it is very explosive.

The apparatus will never clog if cleaned after each day's work, which should always be done. The tubes should be removed and hung up over night to dry. The acid, if not spent, can be dipped out of the acid chamber and placed in jugs. The generator can then be carried to a drain and filled with hot water, which should be allowed to flow out through the cleaning screw. This will clean the zinc and wash out all the sulphate deposit. The screws may then be tightened and the apparatus left ready for the next day's use.

Fire Trap and Scrubbing Cup.

One of the most essential parts of a lead burning apparatus is a reliable fire trap and scrubbing cup. This trap reduces to a minimum the danger from explosion caused by neglecting to free the gas from air. Its use as a scrubbing cup is also of infinite value.

The action of the vitriol on the zinc produces a violent ebullition, and a small quantity of the acid is carried in the form of spray from the generator to the tubes, and, unless caught and removed, will frequently get into the blow pipe tip and extinguish the flame, making it necessary to remove the hose and hang it up to drain and dry, which oftentimes causes waste of time and annoyance.

To prove the above assertion we will refer to Professor Marsh, who demonstrated the ability of hydrogen to carry arsenic in the following manner: If a solution containing arsenic be added to a solution of sulphuric acid and zinc, the resulting hydrogen will, upon ignition, deposit a ring of metallic arsenic upon any cold surface that the flame be directed upon.

It will be seen from the above that it is imperative that the operator use a scrubbing cup and see that it is properly filled with a solution of blue vitriol. The ordinary impurities of hydrogen generated in this manner are sulphur and carbon, which should be removed if possible.

The actual use of the scrubbing cup is to catch the above mentioned spray and precipitate to some extent all other impurities contained in the gas, and produce gas sufficiently pure for lead burning.

Directions for Making the Cup.

Regulating Volume and Pressure.

The outer flame will change to a bluish color. Its temperature is low, and its effect on the lead is to coat the metal with a heavy blue oxide, under which the lead runs but does not unite. To demonstrate this, bring the point of the inner or nonoxidizing flame to bear on a piece of sheet lead. It will fuse bright and clean and will have a circle of gray oxide around it. Then quickly remove the flame and the spot will remain bright. Now, again bring the flame to bear on the same piece of lead, keeping the point of the inner flame at least 3/4 inch away from the lead. It will melt and flow together, but will be covered with a coat of gray oxide and the union will not be perfect. Slowly withdraw the flame, and before the flame is entirely removed the spot will be heavily coated with a thick blue oxide, under which the lead will not unite. C, in Fig. 21, shows the appearance of the flame when too much air has been admitted and it is on the point of going out from lack of gas.

It must be remembered to always turn on and light the gas before admitting any air, and when through with the flame the air must be turned off first, then the gas. If this operation is reversed an explosive mixture of gas and air would form in the tube and would spoil the tube, if nothing worse.

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