Air Carbon-arc Gouging: A Fast and Efficient Way to Get Rid of Metal

In metal working maintenance and repair, it is sometimes required to repair or replace a weld, or remove excess metal from a worn or defective part. A process called air carbon-arc (also known as air arc) gouging, developed in the 1940’s, has become a widely accepted method for metal working. Compared to grinding, chipping, and cutting, air arc gouging provides a much faster, more efficient, and more cost-effective means to remove unwanted metal.

Air carbon-arc gouging differs significantly from oxy-fuel cutting (OFC) and plasma cutting. Air carbon-arc does not require oxidation to maintain the cut and is able to be used on many kinds of metal. Air carbon-arc gouging cuts and removes metal by an electric arc created a carbon or graphite electrode as it is drawn along the target metal. As the arc melts the target metal, a steady, high velocity air stream blows the molten material out of the way. The arc is supported by a constant current power source. A compressed 60 to 100 psi gas source supplies the air stream. A special air arc torch is required, as it not only holds the electrodes, but has unidirectional air ports built in to direct the air stream.

Air carbon-arc gouging will work on any material that will conduct electricity and which can be melted by the electric arc, such as carbon steel, stainless steel, cast irons, and many copper alloys. Metal removal rate is controlled by increasing the gouger’s amperage, slowing down the movement of the electrode, and by the efficiency of the air stream. Most common uses for air arc gouging are cutting, removal of defective welds, removal of bolts, removal of rivets, making holes, and casting finishing.

If you have any questions about air carbon-arc gougers, contact:

AFTEK-EHS Welders
6121 Airways Blvd.
Chattanooga, TN 37421
Phone # 423.424.0515
Fax # 423.424.0518

FM Approved Silicone Rubber Heaters for Tank and Vessel Heating

Silicone rubber electric heating element for tank and vessel heating.

Silicone rubber electric heating elements are well proven, tried and tested flexible heaters for heating plastic or metallic tanks and vessels. Their low mass offers virtually no thermal inertia and within minutes can achieve elevated temperatures. They are generally easy to apply to the surface of tanks, chutes, or hoppers and can be custom designed in virtually any shape, all that is required is a sketch of the heated area and information about the electrical connections.

Silicone rubber electric heating elements are constructed by vulcanizing a nichrome heating element to the silicone rubber layer to produce a homogenous laminate. Two layers of 0.028” thick silicone rubber compound, sheath cured on one side, are calendared with high strength fiberglass mesh and vulcanized together under heat and pressure. This bonding sandwiches the resistance heating element between the two layers. An electric grounding mesh is located on the assembly and a further layer of silicone rubber is applied and vulcanized, making a homogenous assembly.

The heaters are used primarily for metallic and non-metallic tank and vessel heating. Their flexibility, both physically and design-wise, allow the heaters to be used for a wide variety of applications. Silicone rubber heaters are water-resistant and may be used for outdoor or “wet” applications, as long as the thermal insulation or exterior covering over the heaters is weatherproofed.

Silicone rubber heating systems must be correctly temperature controlled. The controls and all electrical components must be approved for the area as classified. All wiring must follow Federal, State and Local codes and be fully compliant with the NEC as it relates to the project. If in doubt, please contact an industrial heating applications expert for assistance.

For more information about silicone rubber tank and vessel heaters visit this link.

Pre Weld and Postweld (PWHT) Heat Treatment Furnaces

Industrial furnaces are used for pre and post-weld heat treating by welders and fabricators to heat-treat weldments or metallic parts. Industries that require these types of furnaces include pressure vessels and piping, storage tanks, building construction, bridge building, offshore platforms, petrochemical plants, power plants, and oil and gas refineries.

By using furnaces for PWHT,  stress introduced by the welding process is reduced and redistributed through the heating, soaking and cooling the weldment/machined surface. This greatly improves the weld properties. PWHT is most times mandatory in order to comply with welding codes and specifications for the welding of carbon steels, stainless/high alloy steels and work hardened steels.

Fairly sophisticated control systems carefully follow mandatory heating and cooling profiles, as outlined by welding code. Control systems with thermocouples that monitor internal furnace temperature, along with weldment part temperature are usually included. These control systems also include the ability to ramp up to temperature and cool off over specified time intervals. Finally, the use of recorders or data loggers is common for quality control documentation.

Additional benefits of pre and post weld heat treating are:

• Improved ductility and/or harness
• Lower risk of brittle fracture
• Improved metallurgical structure
• Reduction in diffusible hydrogen induced cracking 

Most pre or post weld heat treating furnaces are customized in one way or another, whether it size, total BTU output, energy source (electric, gas, oil), control scheme, door configuration, or having the furnace built on wheels or on rails.

Furnaces can be designed permanently, portable, or field erected. By having the furnace local, or right on-site, companies eliminate the need to send parts out and thus save time and costs associated with shipping. Depending on the scope of work, its not uncommon for the investment made in a fabricated furnace to pay off within the first year.

For more information on any custom built pre heat or post weld heat treat furnaces, contact:

Hotfoil-EHS, Inc.
2960 East State Street Ext.
Hamilton, NJ 08619
Phone # 609.588.0900
Fax # 609.588.8333
Email: dap@hotfoilehs.com

Multi-Operator Welding Systems

Multi-operator welding system (Aftek Quad Arc 1200)

There are many different welding processes utilized in the welding industry today. Welding processes include stick arc welding, gas tungsten arc welding (GTAW), flux core arc welding (FCAW), shielded metal arc welding (SMAW), gas metal arc welding (GMAW), and air carbon arc gouging.

Most arc welding operations are performed using direct current from a DC power source an AC power source which has been rectified from AC to DC. Many industries use these welding processes in a wide variety of environments including factories, construction sites, power plant construction, boiler construction and repair, and shipyards.

Multiple operator welding equipment was developed to allow several welding modules to operate from a single common power supply. The power supply typically includes a transformer and rectifier to step down the supply voltage, and then convert the power from AC to DC.

Multi-station welding systems afford a number of advantages the principals of which are a lower initial capital cost, a much lower cost of installation, much lower maintenance cost and less power requirements as compared with single operator equipment. Multi-operator welding systems are practical and efficient as they provide a welding station where each welder has the ability to work. They provide for multiple simultaneous welding projects where workers can work efficiently and meet production deadlines.

The clear advantages of multi-operator welders:

• Improved productivity
• Lower total cost of ownership
• Less equipment to transport
• Reduced maintenance costs
• Noise reduction

Portable Auxiliary Power Boxes (PAPB) for Convenient Source to Run Tools, Save Time, Improve Safety

Portable Auxiliary Power Boxes (PAPB)
30kVA (left) and 15kVA (right)

In many field welding situations simply having convenient access to 120 volt or 240 volt supply power to run auxiliary power tools such as grinders, stud guns, and drills is important. In some situations, bringing power to these locations can difficult or nearly impossible. Worse yet, short-cuts and quick fixes can compromise safety. While its not uncommon to have an available 480 or 575 volt power source, conversion to 120 or 240 volts is a challenge. Simply running extension cords can be impractical or present a safety hazard. What's really needed is a portable power box, with all necessary transformers, circuit protection and safety devices built-in to conveniently convert high voltage to 120/240 volt power.

Internal view of cabling and outlets

A new product by Hotfoil-EHS has been developed for just this situation. Named the PAPB (short for portable auxiliary power box), the new product taps into the available high voltage feed and puts convenient, usable 120/240 volt power right at the worker's location.

The PAPB is designed with small supplementary circuit breakers at each of the outgoing power connections for protection and ease of resetting. The main power supply is also protected by a main circuit breaker.

Transformers made in-house

Portable auxiliary power box's can be custom made and manufactured in virtually any size.  The ones pictured above are relatively small; 15kVA and 30kVA. 

Internal view

All PAPB's are made in the USA with major components being fabricated in-house.  All framework, tubing, sheet metal, transformers, wiring, and assembly is done at Hotfoil-EHS's production facility in Hamilton, NJ.  The units are 100% QC'd and tested  prior to shipping. When the equipment leaves the factory, it is 100% ready to go to work.

For more information, contact:

Hotfoil-EHS, Inc.
2960 East State Street Ext.
Hamilton, NJ 08619
Phone # 609.588.0900
Fax # 609.588.8333
Email: dap@hotfoilehs.com

The TAU: A Perfect Solution for Fast, Strong, and Inexpensive Thermocouple, Stud, and Pin Welidng

Thermocouple attachment unit (TAU) used for creating
thermocouples quickly and inexpensively, plus welding
studs and pins to metal structures.

Are you buying pre-made thermocouples? Do you know how easy it is to make your own? Are you always looking for a fast and easy way to attach studs or pins to a target structure? A thermocouple attachment unit (TAU) is the answer. TAU’s will help you save time and money in the fabrication of welding thermocouples and stud/pin welding.

Thermocouple attachment units (TAUs) are small, self contained spot welders that achieve superior results for welding thermocouple junctions and attachment. They are portable and are easy to use. Also known as thermocouple welders, these units are provide a capacitive discharge (as the energy source) in a compact, self-contained, hand welding unit. They are designed to form very strong, free standing junctions in just seconds using standard thermocouple wire. There's no need for clamping, bracketing or strapping. TAUs provide a direct bonding method for thermocouples, pins and studs that is quick, easy, and low-cost while still providing accurate temperature measurement.

Thermocouple attachment units continue to enhance their power outputs which creates more potential uses for TAUs. Higher power output opens doors to a broader application base. Higher power TAUs can be used to weld thermocouple pairs but also can be used to weld studs, rods and pins to a wide variety of metal structures. For example, a common use for TAU’s is attaching insulation pins to welding insulation blanket support.

An internal power supply constantly recharges an internal battery giving the operator portability in field thermocouple welding. Readily available controls allow for easy adjustment based on wire size and material.

Thermocouple attachment units offer a very convenient and economical method of forming and attaching thermocouple sensing wires, studs, and pins where and when you need them. Models vary based on requirements. Some models accommodate a greater range of wire sizes and materials, handling wire up to 14 gauge and capable of creating weld junctions in under a second. Because the power supply provides a short recharge interval, multiple welds can be done very quickly (4-6 welds per minute).

For more information on thermocouple attachment units, contact:

Hotfoil-EHS
2960 East State Street Ext.
Hamilton, NJ 08619
Phone # 609.588.0900
Fax # 609.588.8333
Email: dap@hotfoilehs.com
www.hotfoilehs.com

Electrostatic Precipitator and Bag House Hopper Heaters Prevent Fly Ash Production Problems

Coal fired power plants must manage fly ash properly.

Coal fired power plants in the United States require the use of electrostatic precipitators or bag houses to filter out very fine fly ash particulate incorporated in the flue gas. The ash is collected as the flue gas passes through filter bags or by large electrodes, and then falls into collection hoppers.

As the hot fly ash cools, condensate on the hopper walls can form. The mixture of dry, sulfur rich fly ash and water is very problematic, so it's very important to keep condensation from forming in the collection hoppers. The mixture of water and fly ash can cause clogging (or “pluggage”) in the throat of the hopper,  and more importantly, the residual sulphur in the flue gas will combine with the condensate to form sulphuric acid. The suluric acid attacks the hopper walls from the inside causing corrosion, weakening the walls and creating significant (and costly) maintenance issues over time.

Fly ash hopper with heaters.

Efficient and continuous fly ash removal is critical for all coal fired power plants. Collection hoppers are an integral part of the removal process. Pluggage or inoperable hoppers are a known issue to engineers and maintenance crews. The constant maintenance and excess of down time seriously hinder a plant’s ability to manage the fly ash production rate. Slower fly ash production means limiting energy production and efficiency. A power plant’s electricity production is directly proportional with its coal combustion rate which, in turn, directly effects the fly ash production rate. Plant maintenance personnel usually attempt to remedy ash system failures in real time by deactivating the affected hopper while continuing to generate power and ash. In some situations (to prevent boilers shutdowns) ash will be dumped on the floor, requiring costly clean up.

The evacuation and management of fly ash is much easier when the ash is kept hot. One of the most common ways to maintain elevated fly ash and hopper temperature are electric hopper heaters attached to the external hopper walls. Hopper heaters play a very important role in the removal of fly ash from precipitators and bag filter hoppers by keeping the hopper temperatures operating above the flue gas acid dew point. The hopper heater’s sole function is to preheat the hopper and the internal environment to prevent the formation of moisture and the resulting clumping of fly ash and development of sulphuric acid.

Flexible heating element used on hopper throat.

Hopper heaters are designed for the dirty, high vibration environment of a power plant. They provide the optimum watt density for proper conduction through the hopper wall and for uniform heating. The are available in square, rectangular, and trapezoidal shapes to accommodate any hopper design. Ancillary flexible heating blankets are available for poke tubes, man-ways, and cylindrical throats.

The use of electric hopper heaters on electrostatic precipitator and bag house fly ash collection systems is a time proven, effective way to prevent condensate formation and the resulting clumping and corrosive acids in hoppers, thus facilitating a better opportunity for uninterrupted fly ash production.

For more information, contact:

Hotfoil-EHS, Inc.
2960 East State Street Ext.
Hamilton, NJ 08619
Phone # 609.588.0900
Fax # 609.588.8333

Email: dap@hotfoilehs.com

www.hotfoilehs.com