Showing posts with label heat treating. Show all posts
Showing posts with label heat treating. Show all posts

Pre Weld and Postweld (PWHT) Heat Treatment Furnaces

pre post weld furnace
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.

pre post weld furnace
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.

pre post weld furnaceAdditional 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 

pre post weld furnaceMost 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.

pre post weld furnaceFurnaces 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

pre post weld furnacepre post weld furnace

Custom Fabricated Gas Trains and Nozzles Capable of 10 Million BTU Output

Gas Trains designed with safety in mind. All gas trains have dual valves on the pilot line and main, low gas pressure switch, high gas pressure switch, and proof of closure.
Fully automatic units are supplied with a 4-20 mA controlled actuator that regulates gas. The control system includes a power-on switch, power-on light, master controller with 4-20mA slave controller, air-on light, gas-on light, ignition-firing light, burner-on light, high-fire light and high-fire switch. Should the limit switch fail system come with a dump button and procedure for clearing the gas out of the lines. Construction is 1.5 inch powered coated tubing.

Other features include:
  • 15HP blower motor than can move up to 2200 cubic feet/minute 
  • Damper with a handle wheel for adjustment 
  • Blower is powder coated for longevity 
  • Starter box incorporates a lockable disconnect 
  • Supplementary circuit breaker 
  • Starter contactor 
  • 750VA transformer 480/120 for power to the train. 
Burners are 316 stainless steel. Three standard sizes: 6-10 million BTU; 3-6 million BTU burner; 1 million BTU burner.

For more information. contact:
Hotfoil-EHS, Inc.
2960 East State Street Ext.
Hamilton, NJ 08619
Phone # 609.588.0900
Fax # 609.588.8333

Transformer Basics

Electric transformer
(courtesy of Aftek EHS)
Transformers are composed of an iron core ring wrapped in coils. One coil is connected to an AC input voltage and is called the primary coil. The other coil is connected to an output circuit with the load resistance, and is called the secondary coil.

The two coils are well insulated from each other and do not form a physical electrical connection. This gives a transformer its unique electricity altering properties. Transformers can either step up or step down a voltage.

In a step down transformer, the number turns in the primary coil is greater than the number of turns in the secondary coil step up transformer the number of turns in the secondary coil is greater than the number of turns in the primary coil. The constantly changing current driven by an alternating voltage source induces a changing magnetic field in the core of the transformer.

The magnetic field created by the alternating current in the primary coil generates the flux in the transformer core. The secondary coil converts the flux back into current flow and produces a voltage at the load, or resistance, in the secondary circuit.

If there are fewer coil turns on the secondary then on the primary, this is called a step down transformer. The resulting voltage in the secondary circuit will be less than the primary.

In this example we have 20 turns on the primary coil and 10 turns on the secondary coil. To determine the decrease in voltage occurring in this step down transformer, we can use a simple ratio formula. This formula simply states that the secondary voltage to primary voltage ratio, is the same as the secondary coil to primary coil turn ratio. Rearranging the formula and then dividing 10 turns by 20 turns, we get .5 multiplied by 120 V. This results in a calculated step down voltage of sixty volts.

HofoilEHS - Your Preferred Source for Pre and Post Weld Heat Treating

HotfoilEHS is a premier manufacturer of pre weld and post weld heat treating equipment. EHS manufactures and sells pre and post-weld heat treating equipment including power consoles, ceramic mat heaters, thermocouple attachment units, pin welders, Brinell testers, Poldi hardness testers, thermocuple wire, insulation, and accessories.

The below video is a little shameless, self promotion.

Power consoles are standardly offered in 6, 9, 12, 18, and 24 zone configurations with a variety of control and recording systems.

Twin heating modules, with and without recorders, and optional ramping controllers are available from EHS.

For special projects, EHS can provide mineral insulated (MI) heating circuits designed into a blanket-type layout, using clips to attach the circuits to a wire mesh in a configured pattern. The circuits are CSA and FM Approved for hazardous and non-hazardous areas.

EHS also offers short or long term rentals on power consoles, temperature recorders, and ceramic mat heaters along with complete support and training services.

EHS engineers, designs, and manufactures proven systems to effectively complete any project more efficiently than competitive systems, while staying within budget. Years of application experience and successful installations have produced thousands of happy customers.

Replacing the Print Head on AH4000 Recorder

AH400 Recorder
AH400 Recorder
The AH4000 multi-channel recorder is used on HotfoilEHS power consoles to monitor and record pre weld, soak, and post weld heat treating. One of the most common questions asked is how to replace the print head.

The video below provides visual, step-by-step instructions.

10 Million BTU Burner for Custom Designed Heat Treating Furnace

Custom heat treating furnaces are designed for the tempering of metals. These furnaces can be electrically heated, or gas heated, depending on the energy source available. Tempering is defined as (from Wikipedia):

"Tempering is a heat treatment technique applied to ferrous alloys, such as steel or cast iron, to achieve greater toughness by decreasing the hardness of the alloy. The reduction in hardness is usually accompanied by an increase in ductility, thereby decreasing the brittleness of the metal. Tempering is usually performed after quenching, which is rapid cooling of the metal to put it in its hardest state. Tempering is accomplished by controlled heating of the quenched work-piece to a temperature below its "lower critical temperature". "

The video below shows the testing of a 10 million BTU ratio air burner designed for a custom heat treating furnace used to pre-stress large metal components prior to welding. Hotfoil-EHS manufactures complete furnace systems using OEM burners and in-house developed control systems.

For more information, contact:

2960 East State Street Ext.
Hamilton, NJ 08619
Phone # 609.588.0900
Fax # 609.588.8333

An Introduction to Thermocouples

Schematic of Type K Thermocouple
(courtesy of Wikipedia)
A thermocouple is a temperature sensor that produces a micro-voltage from a phenomena called the Seebeck Effect. In simple terms, when the junction of two different (dissimilar) metals varies in temperature from a second junction (called the reference junction), a voltage is produced. When the reference junction temperature is known and maintained, the voltage produced by the sensing junction can be measured and directly applied to the change in the sensing junctions' temperature.

Thermocouples are widely used for industrial and commercial temperate control because they are inexpensive, fairly accurate, have a fairly linear temperature-to-signal output curve, come in many “types” (different metal alloys) for many different temperature ranges, and are easily interchangeable. They require no external power to work and can be used in continuous temperature measurement applications from -185 Deg. Celsius (Type T) up to 1700 Deg. Celsius (Type B).

thermocouple attachment unit
Thermocouple attachment unit
For pre-weld heat treatment, Type K thermocouples are generally used. Thermocouples can be directly attached to the workpiece by spot welding the junction of Type K thermocouple wire. The attachment is done with the help of a TAU, or thermocouple attachment devices. Thermocouples are attached so that there is firm contact between the sensing tip and the assembly being heat treated.