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