Archive for June, 2013

Good oxy-fuel operators know that safety depends on proper and responsible use of oxy-fuel equipment. Safety has been a central principal at Victor for 100 years. In fact, one of its early innovations was a safer regulator because founder L.W. Stettner had lost an eye in an industrial accident and wanted to prevent that from happening to others. In that spirit, here are a few oxy-fuel safety tips that may prevent accidents from occurring in the first place:

Cylinder-Safetycropped

Fire triangle:

The foundation for all oxy-fuel processes is the “Triangle of Combustion” or “Fire Triangle”. Combustion requires three elements: fuel, oxygen and heat. Operators must control each of these elements, which is why safety starts with a clean work area, free from combustibles.

Oxy-fuel processes produce flames, sparks and a small amount of infrared rays. Eye protection options include a face shield, goggles or safety glasses, all with the appropriate shade lens. If operators use a face shield, they must also wear safety glasses underneath.

For operators that work in street clothes, choose tightly woven fabrics made from natural fibers. Wool is naturally flame retardant, and blue jeans, denim and cotton duck are also good choices. Wearing a lab coat or welding jacket (or at least sleeves) is a good idea; heavy-duty applications often require leather chaps and spats. Button shirt collars and sleeves, and don’t cuff pant legs, as they provide a perfect area to catch sparks and slag.

 

Cylinder identification and handling:

Operators commonly assume cylinder colour indicates a specific gas. Unfortunately, distributors and gas suppliers can paint their cylinders any colour they want. To identify a T cylinder’s contents, read the label. If a cylinder doesn’t have a label, don’t use it.

All cylinders have a United Nations (UN) gas identification marking on their label. Common ID numbers include UN 1072 for oxygen, UN 1001 for acetylene, UN 1978 for propane and UN 1077 for propylene.

When moving cylinders, secure them with a strap or chain and install cylinder caps. Victor engineers understand that an improperly secured cylinder creates a hazardous situation. EDGE regulators feature SLAM (Shock Limitation and Absorp- tion Mechanism) technology. This three-stage “crumple zone” is built into the adjusting knob to help protect against serious cylinder damage in the event of a fall.

 

Gases in the work area:

Oxygen is the source for many gas-related accidents, and a primary culprit is using oxygen in place of compressed air, such as to blow dust off clothing or work areas.

The most widely used fuel gas is acetylene. Other fuels are commonly referred to as “alternate fuels.” These include LP gases (propane, propylene and butane) and compressed gases such as natural gas and methane.

Acetylene cylinders contain a porous mass saturated with liquid acetone. The acetylene gas is then pumped into the cylinder, absorbed into the acetone and released as it is used. Because of its nature, always use and store the acetylene cylinder in an upright position, and never use acetylene above 15 lbs. pressure. Acetylene has a tendency to disassociate above 15 PSI, which can cause a chemical reaction.

Acetylene withdraw rate is critical: never withdraw more than 1/7th of the cylinder volume per hour. For example, if a particular cylinder held 280 cubic feet, dividing that by 7 yields 40 usable cubic feet per hour of gas.

 

Equipment set-up – regulators:

Because different gases have different volume and pressure requirements, manufacturers engineer regulators for specific gases. Victor regulators are colour-coded and labeled for easy identification, such as green for oxygen and red for acetylene.

Pure oxygen can reduce the kindling temperature of petroleum-based lubricants to room temperature, leading to violent combustion. As such, the first safety check is to inspect regulator valves, threads and seats and ensure they are free of oil. Parts contaminated with oil or grease should be inspected and cleaned by qualified service personnel.

 

Equipment set-up – hoses:

There are three grades of hose. Use R and RM grade for acetylene. T grade hose may be used with any fuel gas and is the only grade allowable for alternate fuels. The acetylene hose, which is typically red, has a groove across one nut, which indicates a left-hand thread. The oxygen hose, which is typically green, will not have a groove, indicating that it’s a right-hand thread. Before attaching the hose, inspect it for oil, grease and cracks.

After attaching, remove potential contaminants by purging the hose. To purge a hose, adjust the regulator knob to about 5 PSI and allow gas to flow for a few seconds. Depending on the length of hose, that time may vary. Back out the adjusting knob after allowing adequate flow and repeat the process for the other hose.

 

Torch inspection:

Most torches come in two sections, the torch handle and various attachments for heating, cutting and welding. Before using an attachment, check its cone end and be sure the two O-rings are neither missing nor damaged. Repair them or replace them if necessary. On a cutting attachment, check the seating end for the tip. Dents or scratches here could lead to a leak and promote an accident.

Before connecting any attachment to the torch, inspect the seating area of the torch handle and the thread assembly. When attaching them, hand-tighten only. Using a wrench will damage the O-rings.

Next, inspect the cutting or heating tip to ensure the holes are free of debris. On a cutting tip, check the seating end for scratches or dents. To properly secure a cutting tip, which is a metal-to-metal seal, tighten it with a wrench. Before cutting, make sure the cutting oxygen lever moves freely.

 

Leak test:

After connecting the attachments and tips, operators need to check the entire system for leaks. The steps to perform a leak test are as follows:

Completely back out the regulator adjusting mechanism. Open the cylinder gas valve slowly until the high pressure gauge reading stabilizes, then shut off the cylinder valve. Monitor the gauge for any pressure drop, which would indicate a leak of the high pressure side of the system. If no leak is evident, open the cylinder valve and adjust the oxygen regulator to deliver 20 PSI.

Repeat the process with the fuel gas valve and regulator, but be sure to adjust the fuel gas regulator to deliver about 10 PSI. Close both the oxygen and fuel cylinder valves. Turn the adjusting screw or knob counterclockwise one-half turn. Observe the gauges on both regulators for a few minutes. If the gauge readings do not change, then the system is leak tight.

Open the cylinder valves again. Any movement of the needles indicates a possible leak. If a leak is observed, stop. Do not use leaking equipment. Check all the connections. If the leak can’t be found, have the equipment inspected by a qualified technician.

Purging the torch:

Torches also need to be purged to eliminate the possibility of gases mixing prematurely, which could lead to a flashback, or worse. To start, open the oxygen valve on the torch handle all the way. With a cutting attachment, also open the preheat oxygen valve. Depress the cutting lever for three to five seconds. Shut the oxygen valves and repeat the process for the fuel side. This is also a good time to recheck the regulators to make sure they maintained set pressure.

 

Shut down:

Regardless of fuel gas used, always shut down the oxygen first and the fuel last. This technique leak checks both valves every time the torch is shut down. A snap or a pop indicates a leaking oxygen valve, while a small flame at the end of the tip indicates a fuel gas leak.

To shut down the entire system, start by closing both cylinder valves. Next, release the pressure inside the system by opening the oxygen valve on the torch until pressure decays; do the same with the fuel gas valve. Next, release the tension on the regulator by turning the knob or screws counterclockwise until they move freely. Check the regulators to be sure they indicate zero pressure in the system.

Always follow the proper shutdown procedures when finished cutting, even if it’s just for a lunch break. Never leave oxy-fuel systems pressurized while unattended. A leaking torch or hose could cause a pool of gas to build up (such as inside a barrel), creating a serious hazard.

 

Leader, participant guidelines:

By following these guidelines, operators minimize the possibility of an accident and make the environment safe for those around them. To support training efforts, Victor offers a DVD featuring a 36-minute Oxy-Fuel Safety Video in English or Spanish and extensive supplemental documents. These documents include checklists for many of the best practices discussed in this article, a 65-page Leader’s Guide on how to conduct a successful seminar and a Participant’s Guide with training materials and quizzes to assess knowledge absorption.

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How fast can you cut an I-beam? Watch as these instructors and students try their hand with a Victor Journeyman torch at the Victor Technologies display at SkillsUSA 2013.

As we continue the celebration of Victor’s 100th Anniversary, we held a cutting contest while exhibiting at Skills USA, Kasas City. Each entrant was equipped with a Victor Journeyman cutting torch and an “I” beam to test their skills.

Michcel Tracz, Jr., Platt Technical High School, Milford, CT, took first place in Victor Technologies’ oxy-acetylene cutting contest at SkillsUSA 2013. Michcel’s winning time of 44.4 seconds beat the next competitor by 5.1 seconds. Victor Technologies district manager Kevin Showers, shown observing, noted that Michcel’s torch angle enabled gravity to help the slag run clear of the cutting path and reduce his cutting time. Michcel won a Victor Medalists 250 cutting system for demonstrating his skill, as did the second and third place winners.

Michcel Tracz, Jr., Platt Technical High School, Milford, CT, took first place in Victor Technologies’ oxy-acetylene cutting contest at SkillsUSA 2013. Michcel’s winning time of 44.4 seconds beat the next competitor by 5.1 seconds. Victor Technologies district manager Kevin Showers, shown observing, noted that Michcel’s torch angle enabled gravity to help the slag run clear of the cutting path and reduce his cutting time. Michcel won a Victor Medalists 250 cutting system for demonstrating his skill, as did the second and third place winners.

Victor Technologies International, Inc. 40 minutes ago Randy Murphy, an instructor at Traviss Career Center in Lakeland, FL., took second place with a time of 49.5 seconds.

Victor Technologies International, Inc.
40 minutes ago
Randy Murphy, an instructor at Traviss Career Center in Lakeland, FL., took second place with a time of 49.5 seconds.

Caption: Caleb Stroud of North Central Kansas Technical College, Beloit, KS., took third with a time of 50.2 seconds.

Caption: Caleb Stroud of North Central Kansas Technical College, Beloit, KS., took third with a time of 50.2 seconds.

With Skills USA in full swing on Tuesday, we had a great time letting students and welders alike try out some of the cutting, gas control & specialty welding equipment we had on display. The Fabricator 211i, the latest in the line of 3-in-1 multi-process welding systems was a huge hit! Take a peek!

“All it takes is one time” welding with the Tweco Fusion MIG gun and you can see the difference!

Gene’s Paint & Body Shop of Denton, Texas, performs collision repair work, and it also specializes in emergency vehicle repair. Welder Brent Culley has more than 25 of experience, including oilfield work. We asked Brent to put the Tweco Fusion MIG with Tweco Velocity consumables to the test, and he reports they delivered better performance and longer consumables life.

When you need to cut through anything – and we mean ANYTHING – quickly and do it in the field, consider Arcair’s SLICE Exothermic Cutting System.

This video explains how the system works and demonstrates its capabilities by cutting through a standard railroad tie in just one rod.

 

By Nakhleh Hussary, Ph.D., David Pryor

When purchasing a new automated cutting table or retrofitting an existing one, which process is best–oxyfuel or plasma? The nature of the application and cutting process both play a role.

Plasma or oxyfuel? - TheFabricator.com

Which process will ultimately yield the lowest cost per cut—oxyfuel or plasma—after all variables are considered? The basic nature of each process immediately dictates some choices when you are purchasing a new automated cutting table or retrofitting an existing one.

In automated oxyfuel cutting, a fuel gas (typically natural gas) heats the metal to its kindling temperature, where a high-pressure stream of pure oxygen rapidly oxidizes and blows away the metal. This process works with carbon steel because iron oxide melts at a lower temperature than steel. Oxyfuel does not work with aluminum because aluminum oxide melts at a higher temperature, and it won’t work with stainless steel because it doesn’t oxidize.

Conversely, the high-precision plasma process works with any electrically conductive material, making it suitable for cutting steel, stainless steel, and aluminum. It heats a gas (usually oxygen, nitrogen, or hydrogen) to an extremely high temperature and ionizes it so that it becomes electrically conductive, allowing the electric arc to transfer to the workpiece. The arc’s heat melts the workpiece, and the force of the plasma and shielding gases blows away the molten metal to cut the workpiece.

Understanding Cost Factors

Assuming costs for the cutting table, controller, and gantry are similar for both processes, the key factors influencing the acquisition and operation of a cutting table are summarized in Figure 1. At first glance, you might think that many factors seem to favor the oxyfuel process, which is why it has been the preferred cutting process of many fabricators for decades. But thanks to the extremely fast piercing and cutting speeds of modern high-precision plasma systems, the choice has become much less clear-cut (so to speak), especially on material less than 1.5 in. thick.

Plasma or oxyfuel? - TheFabricator.com

Figure 3When multiple oxyfuel torches can cut in parallel, cut costs per foot decrease significantly. Photo courtesy of C&G Systems Corp.

Low-cost Oxyfuel

Oxyfuel cutting requires very little capital to implement and operate. A machine torch setup (including hoses, manifolds, and required accessories) costs about $3,000, and a multiple-torch setup can still cost less than $10,000. A cutting tip costs approximately $25 and will last for about 100 hours of cutting. Most automated systems use natural gas because, at least in North America, the cost is nearly free at $0.0001 per cubic foot. Oxygen, the single largest operating cost for the oxyfuel process, runs at about $0.010 per cubic foot. A high-precision automated system also uses oxygen for the plasma gas when cutting mild steel, but at lower volumes.

Once installed, an oxyfuel system operates almost maintenance-free. Other than changing consumables, the torch, gas distribution, and manifold system are extremely robust.

Oxyfuel’s primary limitation is its relatively slow piercing and cutting speeds. As Figure 2 shows, the torch may cut up to 30 inches per minute (IPM) on thin material, but the speed levels out around 15 IPM on material 2 in. and thicker.

In metal 0.25 to 1.5 in. thick, slow cutting speeds drive up the cut cost per foot. However, at thicknesses of 2 in. and greater, the plasma process no longer has a speed advantage.

Oxyfuel also provides an advantage when the same pattern can be cut in parallel, which enables using multiple oxyfuel torches (see Figure 3). In fact, up to eight torches on the same gantry is relatively common. Note that if the part requires multiple pierces, or if a limited part run can’t justify adding more torches, the advantage may tip back to plasma.

Plasma or oxyfuel? - TheFabricator.comFigure 5With a few turns, this cartridge with 100-amp consumables can be replaced with a cartridge for cutting at 400 amps.

High-speed Plasma

An automated high-precision plasma system costs an average of 10 times more than an oxyfuel system. Its torch consumables cost more too—about $45 for an electrode tip and shield cap—and the electrode may last for only two shifts, depending on the application.

However, the speed of plasma cutting gives it a pronounced economic advantage. Equipment manufacturers have developed 400-amp plasma systems that increase travel speed on medium-thickness material and remain competitive with oxyfuel on steel up to 2 in. thick (see Figure 4). For example, they can cut 1-in.-thick mild steel at more than 80 IPM, while oxyfuel cuts at less than 20 IPM. On thinner materials, the speed advantage is even more significant, with plasma cutting 0.5-in.-thick steel at 150 IPM. The cost per foot is about $0.045 for plasma and $0.210 for oxyfuel.

Applications involving part nests and workpieces requiring multiple pierces also are more suitable for the plasma process because the plate does not require preheating, as it does with oxyfuel. Plasma can pierce 1.25-in.-thick steel in about 1.5 seconds, whereas oxyfuel takes about 20 seconds.

In places with high labor rates, including the U.S., Canada, and Europe, obtaining fast cutting speeds and cycle times is critical for profitable plasma operation. As a result of higher-capacity and higher-speed systems, plasma now is commonly found in heavy equipment, pressure vessel, ship, rail, and other fabrication operations that previously were the domain of oxyfuel cutting.

Plasma or oxyfuel? - TheFabricator.comFigure 6In about 20 minutes, a technician can install an inverter block to increase this plasma unit’s capacity up to 400 amps.

Some fabricators are using plasma to bevel pipe, as new torch configurations provide better joint access. Still, for cutting heavy steel used for infrastructure, offshore oil rigs, and mining equipment applications and for cutting pipe in the field, oxyfuel continues to offer attractive cost benefits.

Thickness Flexibility

Optimizing cut performance, speed, and quality with either process requires changing consumables and process variables. With oxyfuel, it’s a matter of selecting the right tip and adjusting gas flow rates accordingly. With plasma, cutting different material thicknesses requires changing torch consumables. In this case, consider systems with consumables cartridges that offer a keyless/no-tool change function, as it will reduce change time to about 30 seconds (see Figure 5).

Traditionally, fabricators were somewhat boxed in when they purchased a plasma system. If they had a 300-amp system for cutting but wanted to cut 1- or 1.5-in.-thick steel at faster speeds, the best alternative was to purchase a new 400-amp system.

To address this, the next generation of plasma systems uses an inverter block design that enables end users to add more inverter blocks in 100-amp increments (see Figure 6). A field technician can perform the upgrade in about 20 minutes. The flexibility of adding more output power eliminates the dilemma of investing in too little or too much capacity.

Plasma or oxyfuel? - TheFabricator.comFigure 7To have the right capability, many fabricators opt to equip their gantry with both plasma and oxyfuel torches. Photo courtesy of C&G Systems Corp.

Setup Factors

With plasma, optimizing torch height during arc start and setting height after piercing greatly extends consumables life and is critical for lowering cut cost. Further, the CNCs for plasma systems have numerous capabilities (such as nesting programs that reduce the number of pierces and cutting routines that produce bolt-ready holes) to lower cutting costs.

Plasma or oxyfuel? - TheFabricator.comFigure 8This high-precision plasma system cut demonstrates a 0.5-degree bevel on 0.25-in. mild steel.

Finally, the standard configuration for modern CNCs lets them manage up to four oxyfuel torches and two plasma torches on the same gantry. Even if you plan to use the plasma process most of the time, you can choose to equip tables with at least one oxyfuel torch for those instances when you run into thicker steel (see Figure 7). Adding an oxyfuel torch to a plasma system may add less than 10 percent to the total cost, and it can provide a good payback when it’s needed.

Cut Quality

Oxyfuel cuts with a 0-degree bevel. However, the swirl of the plasma gas inherently creates a bevel on one side of the cut. High-precision plasma cuts with a 0- to 2-degree bevel (see Figure 8), and thinner material is actually harder to cut.

Note that an oxyfuel cut will have a heat-affected zone (HAZ) that is five to 10 times larger than a plasma cut. And regardless of the cutting process, weld procedure requirements often dictate mechanical removal of the HAZ. Ask for cut samples and discuss the situation with your equipment provider.

For a common point of reference, following are the widely accepted characteristics of a precision-cut surface:

  • Square face, perpendicularity (less than 3-degree bevel).
  • Smooth, with nearly vertical drag lines.
  • Little to no oxides.
  • Little to no dross; what dross is present should be easy to remove.
  • Minimal HAZ and recast layer (remelted metal deposited on cut edges).
  • Good mechanical properties in welded components.

It boils down to quality and cost. Which process you choose will depend on what technology can send the part to the next production step with the least amount of postcut cleaning and at the lowest cost per cut.

Opportunities in Plasma Marking

Plasma or oxyfuel? - TheFabricator.com

High-precision plasma systems using argon or nitrogen for the plasma gas can produce a clean, clear, easily readable line. This is called plasma marking. Fabricators increasingly use this process to distinguish similar components (such as left and right sides) and to permanently identify components.

Plasma marking uses the same power sources, controls, and consumables used in plasma cutting, enabling fast changeover between the two. Marking and cutting on the same table also eliminates the material handling time and costs associated with marking parts in a secondary operation.

Plasma marking can use 5 to 30 amps of current, depending on the particular material and depth of mark desired. To create a mark at lower amperages, the plasma arc creates surface discoloration caused by the deposited heat flux. This type of marking modifies only the top surface layer; the arc vaporizes a very small amount of material (if any), which may be desirable in applications where fabricators want to paint over or otherwise obscure the marking.

At higher amperages, the plasma arc melts or vaporizes a slightly larger amount of material to create an indelible mark. By varying process parameters, fabricators can control the depth and width of the mark. Some might, for example, want a mark to show through a heavy coat of paint or epoxy or after years of exposure in a corrosive environment. Plasma marking can also create dimples that facilitate drill starts or punching.