Welding Tragedies

Gas Welding Safety

Storage and Handling

• Keep cylinders away from physical damage, heat, and tampering.
• Securely chain equipment to prevent falling.
• Store away from flammable and combustible materials.
• Store extra gas and oxygen cylinders separately.
• Store in an upright position.
• Close cylinder valves before moving.
• Protective caps or regulators should be kept in place.
• Roll cylinders on bottom edges to move—Do not drag.
• Allow very little movement when transporting.

General Gas Welding Safety Tips

• Inspect equipment for leaks at all connections using approved leak-test solution.
• Inspect hoses for leaks and worn places.
• Replace bad hoses.
• Protect hoses and cylinders from sparks, flames and hot metal.
• Use a flint lighter to ignite the flame.
• Stand to the side (away from the regulators) when opening cylinder valves.
• Open cylinder valves very slowly to keep sudden high pressures from exploding the regulators.
• Only open the acetylene cylinder valve 1/4 – 3/4 turn; leave wrench in place so the cylinder can be quickly closed in an emergency.
• Open and light acetylene first, then open and adjust oxygen to a neutral flame.
• Follow the manufacturer's recommendations for shutting off the torch. If the guidelines are not readily available, the common accepted practice is to close the oxygen valve first.
• When finished, close cylinder valves, bleed the lines to take pressure off regulators, neatly coil hoses and replace equipment.
• Have a fire extinguisher easily accessible at the welding site.

Personal Protective Equipment:

• Infrared radiation is a cause of retinal burning and cataracts. Protect your eyes with safety glasses.
• Protect your body from welding spatter and arc flash with protective clothing. Such as:
• Woolen clothing
• Flame-proof apron
• Gloves
• Properly fitted clothing that is not frayed or worn.
• Shirts should have long sleeves.
• Trousers should be straight-legged and covering shoes when arc welding.
• Fire resistant cape or shoulder covers are needed for overhead work.
• Check protective clothing equipment before each use to make sure it is in good condition.
• Keep clothes free of grease and oil.

Proper Ventilation
Be sure there is adequate ventilation available when welding in confined areas or where there are barriers to air movement. Natural drafts, fans and positioning of the head can help keep fumes away from the welder’s face.

Ventilation is sufficient if:

• The room or welding area contains at least 10,000 cubic feet for each welder.
• The ceiling height is not less than 16 feet.
• Cross ventilation is not blocked by partitions, equipment, or other structural barriers.
• Welding is not done in a confined space.

**If these space requirements are not met then the area needs to be equipped with mechanical ventilating equipment that exhausts at least 2000 cfm of air for each welder, except where local exhaust hoods or booths, or air-line respirators are used.

Safety Precautions For Engine Powered Welders

• Always activate in an open well-ventilated area or vent the engine exhaust directly outdoors.
• Never fuel the engine while running or in the occurrence of an open flame.
• Wipe up spilled fuel instantly and wait for fumes to disperse before starting the engine. Never eliminate the radiator pressure cap from liquid cooled engines while they are hot to prevent scalding yourself.
• Stop the engine before performing any preservation or trouble shooting. The explosion system should be disabled to prevent unintentional start of the engine.
• Keep all guards and shields in place.
• Keep hands, hair, and clothing away from moving parts.

FIRST AID

The welding area should always be prepared with a fire blanket and a well stocked first aid kit. It is enviable that one person be trained in first aid to treat the minor injuries that may occur. All injuries, no matter how minor they may seem can become more serious if not properly treated by trained medical personnel.

Personal Protection While Welding

It is necessary that the worker and helpers be properly clothed and protected because of the heat, ultra-violet rays, and sparks, produced by the arc welder. For body protection a pair of fire retardant long sleeved coveralls without manacles is a good choice. Always avoid clothing with tears, snags, rips, or worn spots as these are effortlessly ignited by sparks. The sleeves and collars should be kept buttoned. The hands should be confined with leather gauntlet gloves. A pair o high top leather shoes, rather safety shoes, is good defense for the feet. If low shoes are worn the ankles should be protected by fire opposed to leggings. Eyes should be protected by translucent spectacles if the person wears recommendation glasses or safety glasses if not. A welding helmet or hand shield with filter plate and cover plate is mandatory for eye defense from the harmful rays of the arc. The filter plate should be at least shade for common welding up to 200 amps. However, certain operations such as carbon-arc welding and higher current welding operations need darker shades. Never use a helmet if the riddle plate or cover lens is cracked or broken. A flame-proof skull cap to protect the hair and head as well as hearing shield in noisy situations is recommended.

Plastic throwaway cigarette lighters are very dangerous around heat and fire. It is very imperative that they not be carried in the pockets while welding. Always provide protection to bystanders or other workers by welding inside a appropriately screened area, if possible. If powerless to work inside a screened area then protection to others should be provided by a transferable screen or shield, or by their wearing anti-flash goggles

Setting Up The Welding Machine

• Steel: Use DC straight polarity and an electrode with a red end (2% Thoriated). When welding steel with DC straight polarity make sure the tip is ground to a conical point.
  
  
• Aluminum: Use AC current and an electrode with a green end (100% Tungsten) Ensure that the tip is round properly.
  
  
• Other Material: Consult welding reference or experienced welder.
  
  
• Amperage varies depending on material thickness and type of weld.

Welding Techniques

• Hold torch approximately 75-80 degrees from horizontal and the filler rod 15-20 degrees from horizontal.
  
  
• Hold the tip of the electrode about 1/8” away from piece and press the pedal down until an arc is created between the electrode and work piece.
  
  
• Keep peddle depressed until puddle is created.
  
  
• Ensure the tip of the electrode does not touch the molten weld puddle. This cause electrodes to become contaminated with weld material.
  
  
• After puddle is created use a circular motion or repeated crescent motion to move puddle while adding filler rod.
  
  
• When welding thinner materials a heat sink, consisting of a metal block, can be used to dissipate excess heat. Place this heat sink underneath material when welding.

MIG Aluminum Welding

Welding Hazards

To avoid electric shocks and possible electrocution, personnel should take the following precautions:

• Wear dry, insulated gloves in good condition and protective clothing. (Change as necessary to keep dry)


• Insulate yourself from the workpiece and ground by wearing rubber soled shoes or stand on a dry insulated mat. Do not touch the ground with any other part of your body.


• Use fully insulated electrode holders.


• Do not use worn, damaged, undersized or poorly spliced cables.


• Do not wrap cables carrying current around your body.


• Do not touch an energized electrode with bare hands.


• Turn off all equipment when not in use.


• Use only well maintained equipment. Repair or replace damaged parts before further use.


• Wet working conditions should be avoided. Even a person's perspiration can lower the body's resistance to electrical shock.

The avoidance of electrical shock is largely within the control of the welder. Therefore, it is especially important that the welder be thoroughly trained on safe welding procedures. Safe procedures must be observed at all times when working with equipment having voltages necessary for arc welding. These voltages can be dangerous to life. Even mild shocks can cause involuntary muscular contractions.

The Ternary Gas Plasma Welding Torch

The increase in performance that the Ternary Gas Plasma Welding Torch achieves is attributed to a secondary inert gas acting in conjunction with the primary inert gas to provide a substantially "stiffer" arc from the electrode of the torch than a typical single inert gas provides.

Benefits

• Improves weld quality through a stiffer more controllable arc
• Reduces cost through reduction in weld "cutting" defects
• Reduces welding times
• Narrower weld with greater penetration at any given electrical current setting
• More desirable Heat Affected Zone (HAZ)
• Reduces dependency on operator's skills
• Expands the capabilities for joining thicker materials with relatively low heat inputs.

The Technology

The Ternary-Gas Plasma Arc Welding (TGPAW) torch functions by utilizing three gases: a primary inert plasma gas, a secondary inert plasma gas, and an inert shielding gas. The primary inert plasma gas is directed through the body of the welding torch and out of the body across the tip of a welding electrode disposed at the forward end of the body. The second plasma gas is disposed for flow through a longitudinal bore in the electrode. It is directed through the electrode to co-act with the arc to produce equivalent defect free welds in types and thickness of metals (ferrous and non-ferrous) with less total heat input per inch of weld (i.e. less current/voltage output and/or high travel speeds). The completed weld is narrower with greater penetration at any given electrical current setting, thereby producing a more desirable Heat Affected Zone (HAZ) and greater ultimate tensile strength values. In addition, the secondary inert plasma gas compliments the primary inert gas to provide a "stiffer" arc, less subject to becoming skewed and unequal in dimensional shape. This characteristic aids alleviating weld "cutting" defects caused by an asymmetrical arc and subsequent asymmetrical heating pattern at the weld joint. The secondary plasma gas may be any of the inert gases or semi-reactive gases or a mixture of two or more of these, however the choice is dependent on the material being welded and the results desired. The process can be applied to Direct Current Straight Polarity and Variable Polarity Welding Modes. The third inert plasma gas is "shield" gas that is directed through the torch body for circulating around the head of the torch adjacent to the electrode tip. The following diagram illustrates the Ternary Gas system:

Various Types of Welding

Shielded Metal Arc Welding


Shielded Metal Arc Welding is the most common method of joining metals. “Stick” welding as it is commonly referred, is an arc welding process with the arc between a covered electrode and the weld pool. SMAW uses shielding from the decomposition of the electrode covering, and filler metal from the electrode. Using the SMAW process the welder can rapidly make high quality welds on various types of metals with varying thicknesses in all positions with excellent uniformity.

Gas Metal Arc Welding


Also known as “Mig” welding, this process, because it uses an arc between a continuous filler wire and the weld pool, is extremely fast and economical. GMAW is often used to do production work due to its speed, versatility, and ease of use. The process is used with shielding from an externally supplied gas and is used to weld on a variety of metal thicknesses from thin-gauge metal to heavy plate metal in any position.

Gas Tungsten Arc Welding


Gas Tungsten Arc Welding – Often referred to as “Tig” welding, can be used on almost any metal. An arc between a non-consumable electrode (tungsten) and the weld pool produces high quality welds that require little or no post weld finishing. This process uses a shielding gas to protect the weld pool.

Flux Core Arc Welding



Flux Cored Arc Welding – The flux cored arc welding process is similar to the GMAW process and uses the same type of equipment as GMAW. FCAW also uses an arc between a continuous filler wire and the weld pool. This process is used with shielding gas from a flux contained within the tubular electrode, and can also use an externally supplied gas (dual shield wire).

Air Carbon Arc Gouging

Settings for TIG Welding Stainless Steel

In the TIG (tungsten inert gas) welding process, an essentially non-consumable tungsten electrode is used to provide an electric arc for welding. A sheath of inert gas surrounds the electrode, the arc, and the area to be welded. This gas shielding process prevents any oxidization of the weld and allows for the production of neat, clean welds.

Using plasma arc cutting to clean-cut stainless steel sheet

To clean-cut stainless steel sheet and plate, fabricators first must choose the right CNC cutting equipment and then set the correct process-related variables. Precise machine motion controls, torch-to-material distance control, and the correct plasma and assist gases all are crucial to producing weld-ready plasma-cut edges on all stainless steel thicknesses.

To cut stainless steels and other metals with plasma successfully, fabricators need the following tools:

1. Precision machine motion controls

2. A smooth linear drive system

3. Software controls that automatically compensate and provide proper speed and acceleration and deceleration for various part features

Machine Motion Control

During the plasma cutting process, material is in the molten state inside the kerf zone. Mechanical problems such as motion irregularities cause vibrations, which transfer through the machine axis into the cut edge. These vibrations are solidified into the cut surface and can be easily mistaken for process problems. These motion irregularities and/or vibrations cause a rough-cut surface, nonlinear cut edges, and overall poor cut quality.

Torch Tip-to-Material Distance Control

To initiate the cutting process, a pneumatic probe locates the material position and provides an accurate and repeatable pierce height. After the pierce is made, the plasma arc cutting (PAC) voltage from the plasma power unit is used in a closed-loop process control system to maintain torch-to-material height while cutting.

Automatic voltage control precisely maintains the torch tip-to-material distance. This is vital when processing thin sheet and stainless steel plate.

Plasma Gases

Fabricators can process stainless steel with clean-cut surfaces by using nitrogen or a blend of oxygen and nitrogen as a plasma gas. These plasma gases provide a nonoxidizing plasma arc, which produces a clean-cut edge that is weld-ready without secondary operations.

Nitrogen also increases electrode life by preventing oxide formation on the tip of the halfnium electrode. Halfnium is used as the metallic element in the electrode, which also is compatible with oxygen as a plasma gas for steel cutting.

Pure oxygen is not recommended as a plasma gas for stainless steel cutting because of its oxidizing characteristics, which leave an oxidized, contaminated cut edge.
Compressed air is not used for cutting because it often is contaminated with water, oil, or other contaminants. These contaminants can cause regulator and solenoid valve breakdown, as well as plasma double-arcing.

Assist Gases

The type of stainless steel assist gas (or shield gas) to use varies according to the material thickness and the desired cleanliness of the cut edge. Based on each assist gas type and the material thickness, different conditions and chemical reactions result.

The five main assist gases are:

1. Compressed air.
2. Carbon dioxide.
3. Nitrogen plus hydrogen.
4. Nitrogen plus propane.
5. Nitrogen.

The assist gas serves multiple purposes:

-- It helps to prevent molten pierce metal from coming into contact with the nozzle and shield cap during piercing and cutting.

-- It protects the nozzle and shield cap from double-arcing.

-- It offers a method for high-speed flushing of the kerf during cutting with pure nitrogen.

-- It produces a chemical reaction with hydrocarbons or other reactive gases.

Advanced Piercing Controls

Advanced piercing controls used in clean-cutting stainless steel sheet and plate include:

1. Automatic pilot current control: This sets the proper pilot amperage needed for various cutting conditions and pierce heights. Pilot current relates directly to the plasma gas type, pressure, nozzle size, and piercing height.
As the material thickness increases, higher pierce heights are necessary to prevent shield cap and nozzle damage. This is achieved by using higher pilot current to connect the pilot arc to the workpiece. If pilot currents are set too high, however, premature nozzle or electrode failure can occur if the pilot arc current burns the nozzle.

2. Start gas pressure control: This minimizes the amount of pilot current necessary to generate the pilot arc. The higher the plasma gas pressure setting is, the more pilot current, high frequency, and start voltage are needed to create the pilot.

3. Two-step pierce height control: Piercing is initiated at 0.250 inch or less before the torch retracts to a programmed final height. After the main arc transfer has taken place, the torch automatically rises to the final height, away from pierce splatter, until the piercing is complete. The shield cap and nozzle are protected from damage even when piercing 0.750-inch stainless steel.

Electric welding Accessories

An electrical appliance which—

(a) is for use in the electric arc welding process;

(b) is for connection to single phase low voltage supply;

(c) is fitted with a flexible cord and plug rated at not more than 16 A;

(d) can easily be moved from one place to another while it is connected to supply; and

(e) has, for GMAW (gas metal arc welding), GTAW (gas tungsten arc welding), and FCAW (flux cored arc welding) machines, a 100% output rating not exceeding 65 A. The 100% rating is calculated from the square root of the marked duty cycle expressed in decimal form multiplied by the marked output current associated with the duty cycle in amperes;

but does not include—

(f) an arc welding machine promoted exclusively to industry.
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For spot welding low carbon steel and stainless steel.

Due to the popularity of inexpensive, mass-produced, commercial-grade knives, Damascus steel craft became what many considered a lost art. However, fine quality never really falls out of fashion, and there's no question that Damascus steel is more durable and holds a razor-sharp edge longer than any other steel. Duncan and his colleagues recognized the demand, and they have been largely responsible for bringing Damascus back into vogue.

As the inside of the forge approaches 2,300 degrees, Duncan carefully stacks 10 steel wafers to form a rectangular billet. These wafers are alternating layers of high-carbon and high-nickel steel. He uses an arc welder to attach a steel handle to the rectangle. This also immobilizes the wafers, allowing Duncan to control them during the forging process. Then, like a baker stuffing a loaf of bread dough into an oven, Duncan places the billet into the forge. We pour ourselves a cup of coffee and wait. Within minutes, the billet reaches welding temperature, which is about 2,300 degrees. This is the temperature at which steel molecules separate into a semi-liquid state, allowing them to bond. At this point, the 10 layers will be hot enough to forge into one solid billet.

Duncan removes the billet from the heated forge and puts it under a hydraulic press, which squeezes the layers of steel into one homogeneous mass. He creases the middle of the billet after pressing the layers together and expanding them to the right length. This allows Duncan to fold the billet in half. Now, instead of 10 layers, the billet contains 20 layers. After reheating, he'll fold it again to form 40 layers, then 80, then 160, on up to however many Duncan desires.

Gas Tungsten arc welder

The team’s first experiments examined titanium welds. Titanium is popular in manufacturing because of its corrosion resistance and light weight. Also, titanium has two well-characterized solid-phase transitions at ambient air pressure before it melts. In pure titanium, the alpha phase exists from room temperature to 882°C. At these temperatures, titanium has a hexagonal-close-packed crystalline structure.

Using the experimental setup shown in the figure below, a metal bar rotates under a Gas Tungsten arc, taking 6 minutes for a full revolution. An intense x-ray beam from the synchrotron source passes through a pinhole to allow researchers to resolve features as small as 180 micrometers. During welding, the x-ray beam is aimed at specific points around the heat source. A silicon photodiode linear array detector records the diffraction patterns during the experiment.

Phase mapping experiments performed using the SRXRD method are useful for observing phase changes under quasi-steady-state heating and cooling conditions. The next step was to examine the changes that occur at a single spot as a function of time. Wong developed a time-resolved x-ray diffraction (TRXRD) technique that takes a set of x-ray diffraction patterns at a single location adjacent to or within a stationary spot weld.

When the detector is clocked for durations of tens to hundreds of milliseconds, phase transformation may be observed on a much shorter time scale than is possible with moving welds. Changes in the diffraction pattern show directly how phase changes are taking place as a function of time and temperature. As the temperature goes up and then down, the metal at the weld becomes liquid and then solidifies. With TRXRD, the Livermore team has been able to examine the solidification and subsequent solid-state phase transformations in a number of different materials for the first time.

Welds Take the Heat

When two pieces of material are being welded together, high heat rapidly melts the solid material, which quickly cools and solidifies again as the heat source moves away. Adjacent to the immediate weld area, or fusion zone, is the heat-affected zone (HAZ). As the name HAZ implies, the material there is affected by the high heat of the welding process but does not melt.

Heat causes changes in the material. The three well-known basic phases of a material are gas, liquid, and solid. But for many materials, multiple solid phases exist at various temperatures or at various combinations of temperature and pressure. At sea level—1 atmosphere—plain old H2O may form several kinds of ice, each of which is a different solid phase. Iron undergoes three solid-state phase transformations as its temperature increases from room temperature to 1,535°C, where it melts. Carbon also has several solid phases, including graphite and diamond. No one would confuse graphite and diamond. Each one is still carbon, but their crystal structures are very different.

When a material is welded, its crystalline structure changes. It is these microstructural changes that interest Elmer. They can affect the strength of the material as well as its corrosion resistance, ductility, and mechanical properties. Any or all of the changes could either enhance the quality of the weld or reduce the weld’s integrity. “We want to be able to understand the welding process by modeling it and then predict the changes that will occur,” says Elmer. “But first, we need to gather real experimental data during welding to understand the fundamental properties of the process.”

Advanced Welding Torch

The B&B Precision Machine Variable Polarity Plasma Arc welding torch.

In the course of VPPA development, it became apparent that the technique had broad potential for improving weld reliability and lowering costs not only in NASA work but in many private industry applications. Since there were no suitable commercially available tools for VPPA welding, MSFC expanded the development effort to include a technology transfer project designed to make VPPA available to the private sector.

A key part of this effort was development of a welding torch that would have dual utility, as a component of NASA's External Tank welding system and as a component of derivative systems for commercial applications. MSFC awarded the torch contract to B&B Precision Machine, Owens Cross Road, Alabama. Working in cooperation with MSFC's Materials and Processing Laboratory, B&B developed and patented a Shuttle-use torch that won a 1987 NASA Inventor of the Year Award for Bob Dempsey of B&B, Ernest Bayless and Sam Clark of MSFC.

A small version of the B&B torch is used in commercial sheet metal welding.

The small torch, which has attracted considerable interest in the commercial sector, has the same features and advantages as the original torch, but it fits in approximately half the space. It is in commercial service with Whirlpool Corporation for sheet metal welding of major appliance parts, where the torch's production line dependability is a significant asset. Offering such advantages as multiple cost reductions and eventual reduction of requirements for x-ray inspection of welds, the microprocessor-controlled VPPA system is in use at the plants of such industrial giants as Babcock and Wilcox, Boeing, General Dynamics, Lockheed Martin and McDonnell Douglas. The system and the B&B torch continue to make all the welds in the External Tank and they have been selected as the preferred welding approach for the International Space Station.

Effective control of gas shielded arc welding fume

HSE inspectors have noted that, although Local Exhaust Ventilation (LEV) was often available for controlling exposure to inert gas shielded welding fume, it frequently remained unused, due, partly to claims by welders that the LEV was responsible for removing shielding gas and thereby compromising the quality of the weld. However, there appeared to be few data to substantiate the welders’ claims. HSE commissioned this research project to establish whether efficient welding fume capture could be achieved using LEV whilst, at the same time, maintaining weld metal integrity. The objectives of this research project were to be met in three phases:

• Phase 1 was to provide the information necessary to develop an experimental plan.

• Phase 2 was to determine the maximum cross flow velocity of air that could be tolerated before the onset of weld metal porosity during gas shielded arc welding using parameters defined in Phase 1.

• Phase 3 was to measure capture efficiencies for a range of different LEV hoods positioned at various distances and orientations to the welding arc, whilst monitoring weld metal integrity. An on-gun extraction system was also evaluated. This report gives a brief summary of the work carried out in phase 1 and 2, and details the work carried out in phase 3

The report shows that when using standard welding parameters, satisfactory fume extraction is possible without compromising the weld integrity. The results are confirmed for a number of welding positions and with various extraction hoods in different positions. The results for the on-gun extraction equipment are evaluated against those observed for the stand-alone fume extraction equipment.

This report and the work it describes were funded by the Health and Safety Executive (HSE). The on-gun evaluation study was part funded by Nederman and Abicor-Binzel. Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

KEY POINTS AND SUPPORTING INFORMATION

ARC, TIG, AND MIG WELDING SAFETY:

OBJECTIVE:

Identify and use the safety practices that should be observed when arc welding.

MATERIALS:

AC (alternating current) welder, DC (direct current) welder, AC/DC welder, MIG welder, TIG welder and all accessories.

1. Protect yourself: Wear welding gloves, helmet, leather apron, welding chaps, leather shoes, and eye protection to help prevent weld burns and injury. The welder and all observers must wear welding helmets with the appropriate filter lens strength for the type of welding being done. Arc welding requires a No. 10 to 12 filter lens. MIG welding requires at least a No. 10 shaded lens. TIG welding requires a No. 11 or 12 shaded filter lens.

2. Weld in a well-ventilated area: Welding fumes should be ventilated away from the person welding, not across the welder's face. Remember that shielding gases are asphyxiants, and welding fumes are harmful. Work in well-ventilated areas to prevent suffocation or fume sickness.

3. Never wear synthetic fiber clothing or weld with flammables in your pocket: Synthetic fibers are highly flammable. If ignited by a welding spark, flammable (i.e. matches, butane lighters, fuel sticks, etc.) could cause serious burns. Do not allow bystanders to smoke in the welding area.

4. Avoid electrical shock: Make certain that the electrode holder and all electrical connections and cables are properly insulated. Check to see that the welder is properly grounded. Do not dip the electrode holder in water to cool it because this practice may result in electrical shock. Never weld in damp locations because of the shock hazard. When operating a MIG welder, never touch and electrical connection, bare wire, work, or a machine part which may cause electrical shock. Gloves help to insulate against possible shock.

When TIG welding never touch the tungsten electrode with the filler rod. The tungsten electrode is charged with electric current which may charge the filler rod and shock the person welding. The current potential at the tungsten electrode is at the arc voltage level or higher. A shock from the electrode could be deadly.

5. Wear hearing protection with TIG pulsed power and high current settings:Power pulses cause the arc to emit sound waves. Because the noise produced may be loud at high current pulses, hearing protection should be worn.

6. Adjust the TIG high frequency unit only within the limits recommended by the manufacturer: This will help reduce the possibility of shock and body burns.

7. Protect welding cables: Keep the cables from coming in contact with hot metal and sharp edges. Do not drive over cables. When welding, avoid wrapping electrode cables around your body.

8. Use both hands: reduce fatigue, use both hands for welding.
9. Handle hot metal with pliers or tongs: Submerge hot metal completely in water to prevent steam burns.

10. Do not allow electrode to stick: If the electrode sticks, cut off the switch, allow electrode to cool, and then break it loose with your gloved hand.

11. Prevent burns: Never allow the hot electrode or electrode holder to touch bare skin. Avoid letting the electrode touch the grounded cable. Remove hot metal from the work area when you are finished welding to prevent burns to others.

12. Secure work: Use a welding table with a positioner to hold welds securely in place. Clamps and vises can be used to hold odd-shaped work or field work. Securing work will also prevent injury from accidental dropping of metal on your feet or body.

Cutting a Sprocket with CNC plasma - PlasmaCAM

DISTINGUISHING FEATURES OF THE WELDERS:

The fundamental reason this classification exists is to perform skilled welding work in the fabrication and repair of metal equipment. Welders use acetylene and electrical equipment in the fabricating, heating, welding, cutting, and brazing of ferrous and non-ferrous metals in accordance with standard trade practices. Generally, welding assignments are accompanied by blueprints, sketches, and oral instructions indicating the type of material to be used. Work includes performing mechanical repairs on heavy duty equipment. Work methods or techniques are left to the discretion of the employee, subject to inspection as to the volume of production and quality of workmanship.

ESSENTIAL FUNCTIONS:

• Welds shafts, cams, spindles, hubs, and bushings on automobiles, trucks, trailers, well pumps, booster pumps, etc.;

• Welds a variety of park, playground, and sports equipment and facilities;

• Performs mechanical repairs on heavy duty automotive equipment;

• Performs welding tasks in well fields and water and wastewater treatment plant to ensure water tight integrity;

• Repairs airport hanger doors and performs welding operations on airport automotive equipment;

• Creates and updates written of work accomplished;

• Performs miscellaneous welding work required during the construction and repair of City buildings;

• Welds storm grates and manholes;

• Straightens and rebuilds heavy duty equipment;

• Performs aluminum welding;

• Welds various traffic signal poles and utility poles;

• Welds fire trucks, water tanks, stainless steel, and brass fittings;

• Fabricates various objects from oral instructions;

Required Knowledge, Skills and Abilities:

• The standard tools, materials, motions, and practices of the welding trade.

• Ferrous and non-ferrous metals in relating to welding and brazing.

• Occupational hazards and effective safety precautions of the trade.

• Arc air procedures and equipment

Skill in:

• The use of acetylene and electronic welding equipment (i.e., MIG, TIG, and standard) and other standard tools and equipment related to the trade.

Ability to:

• Read and interpret blueprints and working drawings.

• Plan welding work and make estimates of materials required.

• Make precise arm-hand positioning movements and maintain static arm-hand position.

• Make fine, highly controlled muscular movements to adjust the position of a control mechanism.

• Make skillful, controlled manipulations of small objects.

• Lift arms above shoulder level.

• Work in small, cramped areas.

• Work at heights or depths greater than ten feet

Additional Requirements:

• Some positions will require the performance of other essential and marginal functions depending upon work location, assignment or shift.

• Some positions require the use of personal or City vehicles on City business. Individuals must be physically capable of operating the vehicles safely, possess a valid driver's license and have an acceptable driving record. In addition, individuals may be required to pass an Arizona Department of Transportation physical exam and possess the appropriate commercial driver's license (CDL).

Cutting Machine Conditions

1. Cutting and welding are done by authorized personnel in designated cutting and welding areas to the greatest extend practical.
2. Adequate ventilation is provided for all cutting and welding work.
3. Torches, regulators, pressure reducing valves, and manifolds are Underwriters Laboratory listed or Factory Mutual approved.
4. Oxygen fuel gas systems (e.g., oxygen/acetylene welders) are equipped with listed and/or approved backflow valves and pressure relief devices.
5. Eye protection and protective clothing are worn by all cutters and welders, helpers, and fire watches, as appropriate. Workers adjacent to arc welding areas are protected from the rays by screens or shields.
6. When cutting and welding are done outside of designated areas, the following actions are performed.
7. Permit is completed for each shift.
8. continuous fire watch is maintained, when designated by permit, by trained employees (see employee training, Fire Watch). A fire is attacked only when obviously within the capability of the portable extinguisher.
9. A member of supervision (i.e., craft supervisor) inspects the job site at lest once before the start of each job and at least once every 24 hours until the completion of the job.

1. A craft supervisor determines the best location (s) for the fire watch and verifies that automatic fire protection is in service, that precautions taken are adequate, and that information on the Permit is correct.
2. Combustible materials, equipment, or building surfaces within 20 feet of the work or below the work must be either covered with fire-resistant welding blankets, moved, or wetted down. Openings in ducts, tanks, or other confined spaces within 20 feet of the work are also covered or plugged. Fire-resistant welding blankets are used for electric arc operations instead of wetting the work down.
3. Cutting or welding is prohibited in the following situations.
4. In sprinklered areas while sprinkler protection is out of service.
5. In explosive atmospheres of gases, vapors, or dusts or where explosive atmospheres could develop from residues or accumulations in confined spaces (see item 8).
6. On metal walls, ceilings, or roofs built of combustible sandwich type panel construction or having combustible covering.
7. Confined spaces such as tanks are tested to ensure that the atmosphere is not in excess of 10% of the lower flammable limit prior to cutting or welding in or on the tank. Tests are repeated as conditions warrant, once each shift as a minimum. Mechanical ventilation is continuous when cutting or welding in or on a confined space.
8. When cutting or welding must be done on small tanks, piping, or containers that cannot be entered, they are cleaned, purged, and tested prior to starting the work. For work on combustible liquid or gas piping or tanks, intermittent testing is done during the work and a Job Safety Analysis is provided with the assistance of Fire Protection Engineering.
   

Types of Diesel-Powered Generators

Diesel Emissions and Particulates:

• A commenter questioned whether these generators would be classifiedas heavy-duty diesel-powered equipment.

• This issue is beyond the scope of this rulemaking because it does not address the electrical safety ofgrounding circuits for diesel-powered electrical generators.

• Examples of standards that address the types of diesel generators are Sec.

• Several commenters raised concerns that the proposed rule did not address any limits for diesel emissions and particulates emitted into the mine atmosphere as a health risk to miners.

• One commenter stated that the proposed rule should include carbon monoxide and nitrogen oxide monitoring on the inby equipment operator while the diesel generator was used to take equipment in and out of the mine.

• Another commented that the diesel particulate emitted into the mine atmosphere is detrimental to miner health.

Fire Hazards:

• These issues are beyond the scope of this rulemaking which addresses the electrical safety of grounding circuits for diesel-powered electrical generators.

• These issues are addressed by other standards concerning emissions requirements of diesel-powered generators.

• One commenter stated that diesel-powered generators are fire hazards and could be placed in areas where smoke could overtake the miners.

• Another commented that diesel-powered generators are a fire hazard because the proposed rule failed to require a fire suppression system.

Moving Equipment:

• We disagree with these commenters that the use of diesel-powered electrical generators is a fire hazard.

• We have found that any previous safety concerns such as explosion, fire, and shock hazards initially associated with the use of diesel-powered electrical generators have been sufficiently addressed by advances in technology.

• Rather, we recognize that diesel-powered electrical generator equipment and circuit design improvements in combination with sensitive electrical circuit protections actually reduce fire, explosion, and shock hazards.

• Moreover, during the 13 years these diesel generators have been approved through the use of PFM for use in underground mines, and we have received no reported incidents of mine fires resulting from their use
  

Maintenance of Equipment:

• In addition, these issues are beyond the scope of this rulemaking- electrical safety of grounding circuits for diesel-powered electrical generators, and they are addressed by other existing safety standards.

• For example, Sec. 75.380 (Escapeways; bituminous and lignite mines) requires two separate and distinct escapeways for miners to escape during emergency situations in an underground coal mine, to address any smoke hazard.

• Section 75.1909(j)(3) (Nonpermissible diesel-powered equipment; design and performance requirements) requires an automatic fire suppression system to address fire hazards.

• This fire suppression system for diesel-powered equipment applies to the diesel-powered equipment at issue here.
  

• Finally, all other examination requirements in 30 CFR part 75 for diesel-powered equipment apply.

• In a matter related to fire hazards of diesel-powered generators, we received a comment on safe operating temperatures of equipment being powered by the diesel generators.

DC AC arc Welding Plant

• DC or AC arc welding plant shall be used Instruments, cables and the accessories shall conform to the requirements of the relevant Indian Standards wherever available


• Their capacity shall be adequate for the Welding procedure laid down. All welding plants shall be maintained in good working order.

• The arc shall be struck on the points/crossing and then the electrodes shall be progressively advanced by maintaining the arc using uniform movement.

• Means for measuring the current (tong tester) shall be available in addition to the current setting panel integrated with the welding plant.

• The actual output of welding current may not be equal to the current as set on the control panel in many cases, specially when the plant becomes old.

• The current range as recommended by the manufacturer for the particular brand of electrode selected for welding shall be used.

• All electrical appliances required with the welding plant shall be properly earthed.

• The points and crossings shall be pre-heated by oxyacetylene films to a temperature between 250 degree centigrade to 300 degree centigrade before welding.

• This temperature shall be maintained throughout the welding operation.

• If welding is to be interrupted for some reason, then the portions to be reclaimed subsequently shall be pre-heated again to the above temperature range before welding as continued.

• The pre-heating and inter pass temperature shall be measured either by contact type pyrometer or tempil stick. No post heat-treatment is required after welding.

Tungsten Electrodes in Weldings

We are the leading and specialized manufacturer of tungsten electrodes in China, and our products have a good sale all over the country and a big part been exported to more than 28 countries. For the high quality and reasonable prices and good services, we have built up good reputation among our customers.

Our main products including:
1) Thoriated tungsten electrodes (WT20)
2) Ceriated tungsten electrodes (WC20)
3) Pure tungsten electrodes (WP)
4) Lanthanated tungsten electrodes (WL10, WL15, WL20)
5) Zirconiated tungsten electrodes (WZ3, WZ8)
6) Yttriated tungsten electrodes (WY20)

Shandong Roman Technology & Trade Co., Ltd. covers 30,000 square meters and has a total investment of USD1, 200,000. We have many high level management personnel and professionals engaging in the research, development, and production of welding materials.

Manufacture and deal with tungsten and molybdenum; deal with welding equipment and consumables, rubber and plastic products, construction machinery, general merchandise, costume, textile, household appliances, hardware products, chemically product, communication equipments.

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