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.

Ceramic Heater Pads for Weld Preheating and Post Weld Heat Treating

Welding ceramic pad heater
(courtesy of HotfoilEHS)

The goal of preheating and post weld (PWHT) heating is to maintain temperature between weld passes and to uniformly control changes in target temperatures. By properly achieving, maintaining, and then cooling weld temperatures, you lower weld stress, distortion, reduce shrinkage stress and allow unwanted hydrogen to escape.

It is very important to understand the material characteristics of the metals being welded, and know minimum and maximum preheat temperatures, particularly in tempered steels.

For most preheating, post heat treating, and interpass heating, precise temperature control isn't required. Its more important to maintain a minimum temperature, and stay within an acceptable range during the actual welding process, as well as during cool down.

Exceptions are with tempered steels. Tempered steels have already been heat treated at the steel mill and applying too much preheat can alter that tempering. In these cases, proper set point, temperature limiting, and temperature ramp rate of the welded part is critical.

Use of Ceramic Heater Pads

Resistance heating pads are constructed of ceramic beads strung on nichrome wire. These resistance heating elements accurately raise the workpiece temperature to the proper temperature before, during, and after welding, complying with recommended preheat, interpass, and PWHT practices. These semi-flexible ceramic heater pads, with their interlocking beads and high temperature wire, allow for a fit conforming to the shape of the workpiece, and are capable of temperatures up to 1,850 degrees F. Ceramic mat (pad) heaters have an additional benefit in that they don’t have to be moved during welding.

Recorders and controls used for
welding preheat and post heat.

Electronic temperature controllers use several thermocouples spot welded to the workpiece to monitor and regulate the actual part temperature throughout the operation. Many times the electronic controllers have ramping or temperature profiling capabilities, so that heat-up and cool-down can be carefully controlled. Recorders are often used to produce a record of the temperature profiles over time before, during, and after welding. This is important when welding jobs require careful documentation.

An average application is as follows: the heater pad is wrapped around the workpiece, and insulation is applied to the weld joint and the temperature controller is set. Once preheat temperature is achieved, a welder removes the insulation and starts their work. After the weld, the ceramic heaters can be placed over the weld and the controllers can be reset for proper PWHT.

Replacing the Print Head on AH4000 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:

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

Self Regulating Heating Cable

Self regulating heating cable

Self-regulating heating cables automatically adjust their power output to compensate for temperature changes. The outer jacket, braid, and inner jacket provide mechanical, chemical, and electrical protection. The magic happens in the conductive core that surrounds the two parallel conductors. As the ambient temperature drops, the core contracts microscopically, and the number of electrical paths through the core increases, more heat is produced. Conversely, as the ambient temperature rises, the core expands and has fewer electrical paths, and less heat is produced. At a certain temperature, almost all the electrical paths are disrupted and power output is close to zero. A self-regulating heating cable adjusts its power output along its entire length. That's what makes it a safe and reliable solution for many applications.

Self-regulating cable is flexible, and is much easier than constant wattage cable because it can be cut-to-length in the field, terminated, and (if needed) overlapped without fear of burnout. This is very valuable in areas where complex piping systems exist with many valves, tanks and vessels.

As with any heat tracing cable, proper wattage requirements need to be calculated. In order to properly calculate wattage, the following information must be known:

• Pipe size and material
• Insulation type and thickness
• Maintain temperature
• Minimum ambient temperature
• Minimum start-up temperature
• Service voltage
• Chemical environment
• Maximum intermittent exposure temperature
• Electrical area classification

Once this information is known, most manufacturers will have wattage calculators where you can simply use the above data to calculate your requirements.

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

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.

Heat Transfer - The Basics

Industrial hopper heaters are
example of conductive heat transfer.

Heat transfer is the movement of heat from one body or substance to another by radiation, conduction, convection, or a combination of these processes.

When heating a pan of water over a gas flame for example, all three forms a heat transfer are taking place. Heat from the flame radiates in all directions. Conduction takes place with the transfer of heat from the burner to the metal pan. This heat transfer is also responsible for making the handle hot after a period of time. Water is heated by the process up convection which is a circular movement caused by heated water rising and cold water falling.

The process of heat transfer also occurs when an object cools. If a mug of hot coffee is left standing on a cold kitchen countertop, its temperature will gradually decrease as heat is lost. The heat energy dissipates by conduction through the mug to the table top by convection as the liquid rises, cools and sinks, and by the radiation of heat into the surrounding air.

One way to conserve the heat a liquid and prevent heat transfer is to place it in a thermos. The use a vacuum chamber with silvered surfaces, along with low conductive materials, can greatly improve the amount of heat or cold that is lost to the surrounding environment. In between the silvered glass walls up a thermos lies a vacuum. In the case of a hot liquid heat transfer by convection through the vacuum is greatly restricted due to the absence have air molecules necessary to facilitate the transfer of heat. The lack of physical contact between the inside and outside walls of the thermos due to this airless space also greatly inhibits the movement of heat by conduction. Heat loss by radiation is prevented by the silvered walls reflecting radiant energy back into the thermos. Some conduction of heat through the stopper in glass can be expected but this too is limited because they are made of materials with very low conductivity. Thus the temperatures are both hot and cold liquids can be maintained by a properly designed thermos that limits the transfer energy through radiation convection and conduction.

Heat capacity is the amount of heat required to change the temperature of an object or substance by one degree Celsius. The heat capacity of water varies depending on its phase. As solid ice, the heat capacity of water is .5 calories per gram for every one degree Celsius, which means it takes half a calorie to raise the temperature of one gram of ice one degree Celsius.

As a liquid, water heat capacity is one calorie per gram for every one degree Celsius, so it takes one calorie of heat energy to raise one gram of water one degree Celsius.

The processes of phase change between solid, liquid, and gas also require a specific amount of heat energy. The amount of energy required to change a liquid into a solid, or a solid into a liquid, is known as heat of fusion. The amount of heat required to change one gram of ice to water is 80 calories. Similarly the heat vaporization is the energy required to transform a liquid into a gas. It requires 540 calories to change one gram of liquid water into a gas. With these values its easy to calculate exactly how many calories of heat energy are required to transform one gram a ice at absolute zero to steam.

To warm 1 gram of ice from -273 degrees Celsius to 0 degrees celsius would be 273 times .5 gram per calorie or about 140 calories. The phase-change of one gram a ice to liquid water requires 80 calories. Then to heat the water from zero degrees Celsius to 100 degrees Celsius with the heat capacity at one calorie per gram, would require 100 calories. The final phase change it one gram a boiling water to steam would require an additional 540 calories. Adding all of these values together yields 860 calories, the amount of heat energy it takes to transform one gram gram of ice at absolute zero to steam.

Watch this video for an illustration of the above: