Plug Welding

Plug welding is an alternative to spot welding used by vehicle manufacturers where there is insufficient access for a spot welder. For DIY car restoration it's generally used instead of spot welding on panels flanges that would have originally been spot welded.

Plug welding

Start off by drilling 7.5mm holes in the front sheet of metal at a spacing of normally 25mm to 40mm (or whatever the original spot weld spacing was). Then clamp this sheet onto the back sheet.

7.5mm is a reasonably good hole size for 0.8 or 1.0mm sheet. Thicker sheet might require a slightly larger hole size. Try a little test piece out like this one before welding a whole sill onto a car and check the weld has penetrated through both sheets.

Welding through the hole

Position the welding torch with the wire in the center of the hole contacting the back sheet of metal. It is important to arc against this back sheet rather than on the edge of the hole, otherwise the weld might not penetrate into the back sheet. The torch should ideally be pointing directly into the hole rather than at the angle in the photograph.

Start welding in this position and don't move the welder until the hole is almost full of weld. Then move the welder outwards in ever increasing circles until the weld is completed.

The completed welds

If the sheets are the same thickness then the power setting used for plug welding would be the same as you would use for 1.5 times the thickness of one of the sheets. Plug welding can be seen in action on the Aston Martin sills page.

Weld penetration

This is the sort of penetration you would expect from a plug weld. The

molten pool is just breaking out of the reverse of the back sheet.

The heat marks indicate the weld has arced against the back sheet rather than at the side of the hole. If you don't get these marks then consider a little seam welding just to be sure.

Plug welding clamp

There is a special clamp designed for plug welding that makes life really easy. The parts you see in the photograph are attached to a normal mole grip. This clamp came in a se

t of three random welding clamps all of which are extremely useful.

The clamp holds together the flanges and there is space in the middle for the torch to weld the plug weld. The rear face of the clamp is offset so it can fit over flanges.

MIG Spot Welding

One alternative to plug welding is "MIG spot welding". It is similar to plug welding, although a hole is not drilled in the front sheet of metal. Instead the power of the MIG is relied upon to fully melt the top sheet and penetrate into the back sheet.

This technique would require less preparation work than plug welding, but the two sheets need to be in tight contact and high amps used to complete the weld or else the weld could be very weak. Plug welding is a much more suitable technique for all but the most experienced welders.

Final disinfection

The filtered water goes through one last step, secondary disinfection, to provide continuous disinfection when it is delivered to water users. Our treatment plants use chlorine and chloramine to kill any bacteria or viruses that may be present in the pipes from our plant to your tap. Chloramine is a combined chlorine and ammonia compound used to disinfect potable water.

Chlorine was first successfully used as a disinfectant for water in 1908. Chlorine disinfection has just about wiped out water-borne diseases such as cholera and typhoid in the United States. The science of water treatment has progressed so far that detection and control of contaminants in water have reduced health hazards to nearly zero.

Holding ponds where mud settles

After the water is treated, it flows through the pipelines all across the Santa Clara Valley. Your water retailer takes it from here and distributes the water.

The mud press: solids waste stream
Mud from the bottom of the clarifiers flows into the holding ponds where it settles and thickens to approximately 4 to 5 percent of solids in the water.

The mud is then pumped into a mixing tank where anionic polymer is added to cause it to coagulate or separate from the water as it is pumped onto the belt press.

Mud pumped onto a belt press

The mud is spread out on the top belt and channeled back and forth by plastic blades to allow most of the water to drain through the belts (meshed nets). The mud is then dropped onto the lower belt and sandwiched between the upper belt as it moves through a series of rollers, which squeezes out even more water.

The belt press process

The mud cake is scraped off the belt and drops onto a conveyor and deposited in an outside holding area where it is periodically hauled off to a landfill.

Filtration

Next, the water is filtered to remove microscopic particles. Rinconada has six filters each capable of filtering 16.7 million gallons of water per day. Each filtration tank is 13 feet deep and 77 feet long, about half the length of an Olympic-sized swimming pool.

At the bottom of each filter are layers of coarse sand (6 inches), fine sand (18 inches), and anthracite goal (1 foot). As the water seeps down the layers of sand and coal, tiny particles as small as one micron are left behind.

Each of our plants will use granular activated carbon, or GAC, in the future instead of anthracite coal. GAC, the same type of material used in many home filtration systems, removes tiny particles and also chemical compounds that affect the water’s taste and odor.

Just like any home water filtration system, these filters get dirty and must be maintained. To keep them functional, they have to be washed periodically. The process, called "backwashing," involves several steps. First, the filter is taken off line and the water is drained down to the filter bed. Then, the air wash cycle is started which pushes air up through the filter bed causing the filter bed to appear to boil. This breaks up the compacted filter bed and forces the accumulated particles into suspension. The air wash cycle lasts for about three minutes.

After the air wash cycle stops, the backwash cycle starts with water flowing up through the filter bed. Most of the accumulated particles are flushed out. This cycle continues until the backwash water looks clean. The filter is then refilled with water and put back on-line. The backwash water flows into the recovery ponds where the solids in the washwater settle out and the water is pumped back to the beginning of the process to be treated again.

At the Santa Teresa plant (starting in the spring 2006), the waste backwash water enters a mini-treatment plant to pre-clean it before it is pumped back to the starting point again. This will further reduce the possibility of parasites like giardia and cryptosporidium cycling back to the main treatment process. The other two plants may have this capability in the future.

Ozone disinfection

Starting in the spring of 2006, new ozone systems will be in place at Penitencia and Santa Teresa water treatment plants. Ozone is a powerful disinfectant, minimizes harmful disinfection byproducts and removes unpleasant odors and tastes.

The first step in ozone disinfection is to generate ozone gas. Liquid oxygen is transported to the plant and stored for use. It is then vaporized into oxygen gas. When electric currents are applied to a flow of oxygen gas, some oxygen molecules (O2) are split and bond to other oxygen molecules to form ozone molecules (O3).

Next, water that has finished the flocculation process is piped into the ozone contactor basins. Ozone is bubbled up through the water. Water typically will spend 15

Ozone generation

minutes in this system, traveling up and down a series of columns to maximize the contact with the ozone gas.

The newly ozone treated water then moves on through the pipes to the next step, filtration.

Meanwhile, the ozone that was used in the process is converted back into harmless oxygen and released into the atmosphere.

Removing solids

At our Rinconada Water Treatment Plant, we remove the suspended solids in large tanks called clarifiers, the largest feature at the plant. Each tank is approximately 20 feet deep and 117 feet square. Clarifiers at Rinconada Water Treatment Plant

We add special chemicals--such as aluminum sulfate--to the

water that enters the clarifier. These chemicals, called coagulants, cause the solid particles to clump together. This process is called flocculation.

Eventually, the clumps form a "sludge blanket." The solid clumps are far heavier than the water, so the blanket sinks to the bottom. As it does, the blanket works like a finely-meshed net to catch other smaller particles.

The water at the top of the tank, now free of solids, overflows to the gutter-like spokes you see radiating from the center of the tanks in the picture above.

Rakes slowly rotate along the bottom of the clarifier. They scrape the settled sludge at the bottom of the tank into the center where it is removed periodically through pipes that run under the clarifiers.

Historical Theories on Corrosion by UR Evans

Corrosion in an aqueous environment and in an atmospheric environment is an electrochemical process because corrosion involves the transfer of electrons between a metal surface and an aqueous electrolyte solution. It results from the overwhelming tendency of metals to react electrochemically with oxygen, water, and other substances in the aqueous environment. In this context, the term anode is used to describe that portion of the metal surface that is actually corroding while the term cathode is used to describe the metal surface that consumes the electrons produced by the corrosion reaction. (reference)

An electrochemical reaction is defined as a chemical reaction involving the transfer of electrons. It is also a chemical reaction which involves oxidation and reduction. Since metallic corrosion is almost always an electrochemical process, it is important to understand the basic nature of electrochemical reactions. The discoveries that gradually evolved in modern corrosion science have, in fact, played an important role in the development of a multitude of technologies we are enjoying today. These principles are illustrated with the use of a Daniell cell in which copper and zinc metals are immersed in solutions of their respective sulfates. The Daniell cell was the first truly practical and reliable electric battery that supported many nineteenth century electrical innovations such as the telegraph.

The fact that corrosion consists of at least one oxidation and one reduction reaction is not always as obvious as it is in batteries. The two reactions are often combined on a single piece of metal as illustrated schematically here for a piece of steel and in the following Figure for a piece of zinc immersed in an acidic solution.

Electrochemical reactions occurring during the corrosion of zinc in air-free hydrochloric acid

In this Figure, a piece of zinc immersed in hydrochloric acid solution is undergoing corrosion. At some point on the surface, zinc is transformed to zinc ions, according to equation. This reaction produces electrons and these pass through the solid conducting metal to other sites on the metal surface where hydrogen ions are reduced to hydrogen gas according to equation.

These equations illustrate the nature of an electrochemical reaction for zinc. During such a reaction, electrons are transferred, or, viewing it another way, an oxidation process occurs together with a reduction process. The overall corrosion processes are summarized in the following equation:

Briefly then, for corrosion to occur there must be a formation of ions and release of electrons at an anodic surface where oxidation or deterioration of the metal occurs. There must be a simultaneous acceptance at the cathodic surface of the electrons generated at the anode. This acceptance of electrons can take the form of neutralization of positive hydrogen ions, or the formation of negative ions. The anodic and cathodic reactions must go on at the same time and at equivalent rates. However, corrosion occurs only at the areas that serve as anodes.

Corrosion in Neutral or Alkaline Environments

The corrosion of metals can also occur in fresh water, seawater, salt solutions, and alkaline or basic media. In almost all of these environments, corrosion occurs importantly only if dissolved oxygen is also present. Water solutions rapidly dissolve oxygen from the air, and this is the source of the oxygen required in the corrosion process. The most familiar corrosion of this type is the rusting of iron when exposed to a moist atmosphere.

In this equation, iron combines with water and oxygen to produce an insoluble reddish-brown corrosion product that falls out of the solution, as shown by the downward pointing arrow.

During rusting in the atmosphere, there is an opportunity for drying, and this ferric hydroxide dehydrates and forms the familiar red-brown ferric oxide (rust) or Fe₂O₃, as shown below:

Similar reactions occur when zinc is exposed to water or moist air followed by natural drying.

The resulting zinc oxide is the whitish deposit seen on galvanized pails, rain gutters, and imperfectly chrome-plated bathroom faucets. It also familiarly called 'white rust' a non-protective and even destructive form of corrosion that attacks incompletely passivated galvanized steel material or galvanized components subjected to marine atmospheres.

White rust on seaside road railing

As discussed previously, the iron that took part in the reaction with hydrochloric acid in had a valence of 2, whereas the iron that takes part in the reaction shown in the previous equation has a valence of 3. The clue to this lies in the examination of the equation for the corrosion product Fe(OH)₃. Note that water ionized into H⁺ and OH^-. It is further known that hydrogen ion has a valence of 1 (it has only one electron to lose). It would require three hydrogen ions with the corresponding three positive charges to combine with the three OH^- ions held by the iron. It can thus be concluded that the iron ion must have been Fe³⁺ or a ferric ion.

Also note that there is no oxidation or reduction (electron transfer) during either reaction. In both cases the valences of the elements on the left of each reaction remain what it is on the right. The valences of iron, zinc, hydrogen, and oxygen elements remain unchanged throughout the course of these reactions, and it is consequently not possible to divide these reactions into individual oxidation and reduction reactions.

Types of Flames Welding

(1) General. There are three basic flame types: neutral (balanced), excess acetylene (carburizing), and excess oxygen (oxidizing). They are shown in figure 11-2.

(a) The neutral flame has a one-to-one ratio of acetylene and oxygen. It obtains additional oxygen from the air and provides complete combustion. It is generally preferred for welding. The neutral flame has a clear, well-defined, or luminous cone indicating that combustion is complete.

(b) The carburizing flame has excess acetylene, the inner cone has a feathery edge extending beyond it. This white feather is called the acetylene feather. If the acetylene feather is twice as long as the inner cone it is known as a 2X flame, which is a way of expressing the amount of excess acetylene. The carburizing flame may add carbon to the weld metal.

(c) The oxidizing flame, which has an excess of oxygen, has a shorter envelope and a small pointed white cone. The reduction in length of the inner core is a measure of excess oxygen. This flame tends to oxidize the weld metal and is used only for welding specific metals.

(2) Neutral flame.

(a) The welding flame should be adjusted to neutral before either the carburizing or oxidizing flame mixture is set. There are two clearly defined zones in the neutral flame. The inner zone consists of a luminous cone that is bluish-white. Surrounding this is a light blue flame envelope or sheath. This neutral flame is obtained by starting with an excess acetylene flame in which there is a "feather" extension of the inner cone. When the flow of acetylene is decreased or the flow of oxygen increased the feather will tend to disappear. The neutral flame begins when the feather disappears.

(b) The neutral or balanced flame is obtained when the mixed torch gas consists of approximately one volume of oxygen and one volume of acetylene. It is obtained by gradually opening the oxygen valve to shorten the acetylene flame until a clearly defined inner cone is visible. For a strictly neutral flame, no whitish streamers should be present at the end of the cone. In some cases, it is desirable to leave a slight acetylene streamer or "feather" 1/16 to 1/8 in. (1.6 to 3.2 mm) long at the end of the cone to ensure that the flame is not oxidizing. This flame adjustment is used for most welding operations and for preheating during cutting operations. When welding steel with this flame, the molten metal puddle is quiet and clear. The metal flows easily without boiling, foaming, or sparking.

(c) In the neutral flame, the temperature at the inner cone tip is approximately 5850°F (3232°C), while at the end of the outer sheath or envelope the temperature drops to approximately 2300°F (1260°C). This variation within the flame permits some temperature control when making a weld. The position of the flame to the molten puddle can be changed, and the heat controlled in this manner.

(3) Reducing or carburizing flame.

(a) The reducing or carburizing flame is obtained when slightly less than one volume of oxygen is mixed with one volume of acetylene. This flame is obtained by first adjusting to neutral and then slowly opening the acetylene valve until an acetylene streamer or "feather" is at the end of the inner cone. The length of this excess streamer indicates the degree of flame carburization. For most welding operations, this streamer should be no more than half the length of the inner cone.

(b) The reducing or carburizing flame can always be recognized by the presence of three distinct flame zones. There is a clearly defined bluish-white inner cone, white intermediate cone indicating the amount of excess acetylene, and a light blue outer flare envelope. This type of flare burns with a coarse rushing sound. It has a temperature of approximately 5700°F (3149°C) at the inner cone tips.

(c) When a strongly carburizing flame is used for welding, the metal boils and is not clear. The steel, which is absorbing carbon from the flame, gives off heat. This causes the metal to boil. When cold, the weld has the properties of high carbon steel, being brittle and subject to cracking.

(d) A slight feather flame of acetylene is sometimes used for back-hand welding. A carburizing flame is advantageous for welding high carbon steel and hard facing such nonferrous alloys as nickel and Monel. When used in silver solder and soft solder operations, only the intermediate and outer flame cones are used. They impart a low temperature soaking heat to the parts being soldered.

(4) Oxidizing flame.

(a) The oxidizing flame is produced when slightly more than one volume of oxygen is mixed with one volume of acetylene. To obtain this type of flame, the torch should first be adjusted to a neutral flame. The flow of oxygen is then increased until the inner cone is shortened to about one-tenth of its original length. When the flame is properly adjusted, the inner cone is pointed and slightly purple. An oxidizing flame can also be recognized by its distinct hissing sound. The temperature of this flame is approximately 6300°F (3482°C) at the inner cone tip.

(b) When applied to steel, an oxidizing flame causes the molten metal to foam and give off sparks. This indicates that the excess oxygen is combining with the steel and burning it. An oxidizing flame should not be used for welding steel because the deposited metal will be porous, oxidized, and brittle. This flame will ruin most metals and should be avoided, except as noted in (c) below.

(c) A slightly oxidizing flame is used in torch brazing of steel and cast iron. A stronger oxidizing flame is used in the welding of brass or bronze.

(d) In most cases, the amount of excess oxygen used in this flame must be determined by observing the action of the flame on the molten metal.

(5) MAPP gas flames.

(a) The heat transfer properties of primary and secondary flames differ for different fuel gases. MAPP gas has a high heat release in the primary flame, and a high heat release in the secondary. Propylene is intermediate between propane and MAPP gas. Heating values of fuel gases are shown in table 11-3.

(b) The coupling distance between the work and the flame is not nearly as critical with MAPP gas as it is with other fuels.

(c) Adjusting a MAPP gas flame. Flame adjustment is the most important factor for successful welding or brazing with MAPP gas. As with any other fuel gas, there are three basic MAPP gas flames: carburizing, neutral, and oxidizing (fig. 11-3).

1. A carburizing flame looks much the same with MAPP gas or acetylene. It has a yellow feather on the end of the primary cone. Carburizing flames are obtained with MAPP gas when oxyfuel ratios are around 2.2:1 or lower. Slightly carburizing or "reducing" flames are used to weld or braze easily oxidized alloys such as aluminum.

2. As oxygen is increased, or the fuel is turned down, the carburizing feather pulls off and disappears. When the feather disappears, the oxyfuel ratio is about 2.3:1. The inner flame is a very deep blue. This is the neutral MAPP gas flame for welding, shown in figure 11-3. The flame remains neutral up to about 2.5:1 oxygen-to-fuel ratio.

3. Increasing the oxygen flame produces a lighter blue flame, a longer inner cone, and a louder burning sound. This is an oxidizing MAPP gas flare. An operator experience with acetylene will immediately adjust the MAPP gas flame to look like the short, intense blue flame typical of the neutral acetylene flame setting. What will be produced, however, is a typical oxidizing MAPP gas flame. With certain exceptions such as welding or brazing copper and copper alloys, an oxidizing flame is the worst possible flame setting, whatever the fuel gas used. The neutral flame is the principle setting for welding or brazing steel. A neutral MAPP gas flame has a primary flame cone abut 1-1/2 to 2 times as long as the primary acetylene flame cone.

OXYGEN FUEL GAS WELDING PROCEDURES

Section I. WELDING PROCESSES AND TECHNIQUES

GENERAL GAS WELDING PROCDURES

a. General.

(1) Oxyfuel gas welding (OEW) is a group of welding processes which join metals by heating with a fuel gas flame or flares with or without the application of pressure and with or without the use of filler metal. OFW includes any welding operation that makes use of a fuel gas combined with oxygen as a heating medium. The process involves the melting of the base metal and a filler metal, if used, by means of the flame produced at the tip of a welding torch. Fuel gas and oxygen are mixed in the proper proportions in a mixing chamber which may be part of the welding tip assembly. Molten metal from the plate edges and filler metal, if used, intermix in a common molten pool. Upon cooling, they coalesce to form a continuous piece.

(2) There are three major processes within this group: oxyacetylene welding, oxyhydrogen welding, and pressure gas welding. There is one process of minor industrial significance, known as air acetylene welding, in which heat is obtained from the combustion of acetylene with air. Welding with methylacetone-propadiene gas (MAPP gas) is also an oxyfuel procedure.

b. Advantages.

(1) One advantage of this welding process is the control a welder can exercise over the rate of heat input, the temperature of the weld zone, and the oxidizing or reducing potential of the welding atmosphere.

(2) Weld bead size and shape and weld puddle viscosity are also controlled in the welding process because the filler metal is added independently of the welding heat source.

(3) OFW is ideally suited to the welding of thin sheet, tubes, and small diameter pipe. It is also used for repair welding. Thick section welds, except for repair work, are not economical.

c. Equipment.

(1) The equipment used in OFW is low in cost, usually portable, and versatile enough to be used for a variety of related operations, such as bending and straightening, preheating, postheating, surface, braze welding, and torch brazing. With relatively simple changes in equipment, manual and mechanized oxygen cutting operations can be performed. Metals normally welded with the oxyfuel process include steels, especially low alloy steels, and most nonferrous metals. The process is generally not used for welding refractory or reactive metals.

d. Gases.

(1) Commercial fuel gases have one common property: they all require oxygen to support combustion. To be suitable for welding operations, a fuel gas, when burned with oxygen, must have the following:

(a) High flame temperature.

(b) High rate of flame propagation.

(c) Adequate heat content.

(d) Minimum chemical reaction of the flame with base and filler metals.

(2) Among the commercially available fuel gases, acetylene most closely meets all these requirements. Other gases, fuel such as MAPP gas, propylene, propane, natural gas, and proprietary gases based on these, have sufficiently high flame temperatures but exhibit low flame propagation rates. These gas flames are excessively oxidizing at oxygen-to-fuel gas ratios high enough to produce usable heat transfer rates. Flame holding devices, such as counterbores on the tips, are necessary for stable operation and good heat transfer, even at the higher ratios. These gases, however, are used for oxygen cutting. They are also used for torch brazing, soldering, and many other operations where the demands upon the flame characteristics and heat transfer rates are not the same as those for welding.

e. Base Metal Preparation.

(1) Dirt, oil, and oxides can cause incomplete fusion, slag inclusions, and porosity in the weld. Contaminants must be removed along the joint and sides of the base metal.

(2) The root opening for a given thickness of metal should permit the gap to be bridged without difficulty, yet it should be large enough to permit full penetration. Specifications for root openings should be followed exactly.

(3) The thickness of the base metal at the joint determines the type of edge preparation for welding. Thin sheet metal is easily melted completely by the flame. Thus, edges with square faces can be butted-together and welded. This type of joint is limited to material under 3/16 in. (4.8 mm) in thickness. For thicknesses of 3/16 to 1/4 in. (4.8 to 6.4 mm), a slight root opening or groove is necessary for complete penetration, but filler metal must be added to compensate for the opening.

(4) Joint edges 1/4 in. (6.4 mm) and thicker should be beveled. Beveled edges at the joint provide a groove for better penetration and fusion at the sides. The angle of bevel for oxyacetylene welding varies from 35 to 45 degrees, which is equivalent to a variation in the included angle of the joint from 70 to 90 degrees, depending upon the application. A root face 1/16 in. (1.6 mm) wide is normal, but feather edges are sometimes used. Plate thicknesses 3/4 in. (19 mm) and above are double beveled when welding can be done from both sides. The root face can vary from 0 to 1/8 in. (0 to 3.2 mm). Beveling both sides reduces the amount of filler metal required by approximately one-half. Gas consumption per unit length of weld is also reduced.

(5) A square groove edge preparation is the easiest to obtain. This edge can be machined, chipped, ground, or oxygen cut. The thin oxide coating on oxygen-cut surface does not have to be removed, because it is not detrimental to the welding operation or to the quality of the joint. A bevel angle can be oxygen cut.

f. Multiple Layer Welding.

(1) Multiple layer welding is used when maximum ductility of a steel weld in the as-welded or stress-relieved condition is desired, or when several layers are required in welding thick metal. Multiple layer welding is done by depositing filler metal in successive passes along the joint until it is filled. Since the area covered with each pass is small, the weld puddle is reduced in size. This procedure enables the welder to obtain complete joint penetration without excessive penetration and overheating while the first few passes are being deposited. The smaller puddle is more easily controlled. The welder can avoid oxides, slag inclusions, and incomplete fusion with the base metal.

(2) Grain refinement in the underlying passes as they are reheated increases ductility in the deposited steel. The final layer will not have this refinement unless an extra pass is added and removed or the torch is passed over the joint to bring the last deposit up to normalizing temperature.

g. Weld Quality.

(1) The appearance of a weld does not necessarily indicate its quality. Visual examination of the underside of a weld will determine whether there is complete penetration or whether there are excessive globules of metal. Inadequate joint penetration may be due to insufficient beveling of the edges, too wide a root face, too great a welding speed, or poor torch and welding rod manipulation.

(2) Oversized and undersized welds can be observed readily. Weld gauges are available to determine whether a weld has excessive or insufficient reinforcement. Undercut or overlap at the sides of the welds can usually be detected by visual inspection.

(3) Although other discontinuities, such as incomplete fusion, porosity, and cracking may or may not be apparent, excessive grain growth or the presence of hard spots cannot be determined visually. Incomplete fusion may be caused by insufficient heating of the base metal, too rapid travel, or gas or dirt inclusions. Porosity is a result of entrapped gases, usually carbon monoxide, which may be avoided by more careful flame manipulation and adequate fluxing where needed. Hard spots and cracking are a result of metallurgical characteristics of the weldment.

h. Welding With Other Fuel Gases.

(1) Principles of operation.

(a) Hydrocarbon gases, such as propane, butane, city gas, and natural gas, are not suitable for welding ferrous materials due to their oxidizing characteristics. In some instances, many nonferrous and ferrous metals can be braze welded with care taken in the adjustment of flare and the use of flux. It is important to use tips designed for the fuel gas being employed. These gases are extensively used for brazing and soldering operations, utilizing both mechanized and manual methods.

(b) These fuel gases have relatively low flame propagation rates, with the exception of some manufactured city gases containing considerable amounts of hydrogen. When standard welding tips are used, the maximum flame velocity is so 1ow that it interferes seriously with heat transfer from the flame to the work. The highest flame temperatures of the gases are obtained at high oxygen-to-fuel gas ratios. These ratios produce highly oxidizing flames, which prevent the satisfactory welding of most metals.

(c) Tips should be used having flame-holding devices, such as skirts, counterbores, and holder flames, to permit higher gas velocities before they leave the tip. This makes it possible to use these fuel gases for many heating applications with excellent heat transfer efficiency.

(d) Air contains approximately 80 percent nitrogen by volume. This does not support combustion. Fuel gases burned with air, therefore, produce lower flame temperatures than those burned with oxygen. The total heat content is also lower. The air-fuel gas flame is suitable only for welding light sections of lead and for light brazing and soldering operations.

(2) Equipment.

(a) Standard oxyacetylene equipment, with the exception of torch tips and regulators, can be used to distribute and bum these gases. Special regulators may be obtained, and heating and cutting tips are available. City gas and natural gas are supplied by pipelines; propane and butane are stored in cylinders or delivered in liquid form to storage tanks on the user's property.

(b) The torches for use with air-fuel gas generally are designed to aspirate the proper quantity of air from the atmosphere to provide combustion. The fuel gas flows through the torch at a supply pressure of 2 to 40 psig and serves to aspirate the air. For light work, fuel gas usually is supplied from a small cylinder that is easily transportable.

(c) The plumbing, refrigeration, and electrical trades use propane in small cylinders for many heating and soldering applications. The propane flows through the torch at a supply pressure from 3 to 60 psig and serves to aspirate the air. The torches are used for soldering electrical connections, the joints in copper pipelines, and light brazing jobs.

(3) Applications.

Air-fuel gas is used for welding lead up to approximately 1/4 in. (6.4 mm) in thickness. The greatest field of application in the plumbing and electrical industry. The process is used extensively for soldering copper tubing.