Showing posts with label Ceramic Mat Heaters. Show all posts
Showing posts with label Ceramic Mat Heaters. Show all posts

Pre Weld and Post Weld Heat Treatment

Pre Weld and Post Weld Heat Treatment
Welding between insulated heating areas
Heating done by ceramic heaters (pink). 
There are several key reasons why it's important to preheat before welding. First, a preheated part cools more slowly, which slows the overall cooling rate of the welded part. This improves the metallurgical (crystalline) structure and makes it less prone to cracking. Additionally, hydrogen that may be present immediately after a weld is also released more efficiently, which further reduces the possibility cracking. Preheating also mitigates stress from the shrinkage at the weld joint and nearby metal. Finally, pre-heating reduces the possibility of fracture during fabrication due to brittleness.

An industry standard means of accurately managing the pre-heat and post-weld heat treatment is through the use of specialized electric heaters. Electric welding preheaters, known as "ceramic mat heaters", are rugged and flexible heating elements designed so that they conform uniformly around the weld and surrounding area.  Ceramic mat heaters are normally controlled by a power console that uses thermocouples and electronic controllers to regulate, monitor, and many times record, the preheat temperature profile.

ceramic mat heaters on spool piece
Ceramic heaters on spool piece.
Welding codes, gathered from years of rigorously tested data, including metallurgical science, chemical properties of materials, and radiographic analysis, provide specific detail on the minimum preheat temperature, the soak time, and the welding process to be used.

Before deciding to preheat or post heat any welding job, consult with a heat treating expert to make sure proper welding code requirements are being followed.

Ceramic Pre Weld and Post Weld Heaters Get The Heat to the Weldment Efficiently

Ceramic mat heaters
Ceramic mat heaters
The most important feature of a resistance heater is the ability to transfer the heat away from the resistance wire to the outer covering where it can be absorbed by the work piece. Even when accurately controlled, a poorly designed or poorly applied heater can cause the wire temperature to exceed the wires operational limits. Ceramic mat heaters, also known as ceramic pad heaters, are designed to produce more even and efficient heat transfer while maintaining maximum flexibility.

Design:

1) Sintered alumina oxide is formed into shapes and fired at precise temperatures to produce a ceramic insulator with a combination of high dielectric strength and efficient, fast heat transfer. This ceramic is also solid enough to withstand physical shock and resistance to oxidation and corrosion from a broad range of chemicals and atmospheres.

2) An accurately measured length of stranded nickel-chromium wire is precisely wound through the ceramic beads ensuring electrical isolation to produce a compact and flexible resistance heater. Suitable for operation at 2000 deg. F.

3) The resistance wire is then metallurgically bonded to a stranded nickel-copper wire to provide trouble free electrical continuity. The flexible stranded cold junction wire is connected to brass Twistlock connectors fitted with insulated sleeves. The cold junction extension leads are rated for 250 deg. C continuous temperature.

Ceramic mat heaters are efficient, time-tested, and proven heater technology in pre-weld and post weld heating, and are designed for the harsh realities of the welding environment.

For more information, contact:

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

Ceramic Heater Pads for Weld Preheating and Post Weld Heat Treating

welding ceramic pad heater
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.

welding temperature controls
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.

Automatic Heat Treatment Power Consoles

power console
Typical Power Console
(courtesy of HotfoilEHS)
Automatic heat treatment power consoles are used to control various heat treatment processes (i.e. pre-weld, post-weld) by closely controlling the temperature of the item being welded. The power console accurately controls the ramping rate (up and down), the soak temperature, the set point and the time. Power consoles are available from 2 to 24 zones of control. Zone can be used either in the fully automatic or manual mode.

ceramic mat heater
Ceramic Mat Heater
The power console is used to provide power to electric heating elements called ceramic mat heaters. Ceramic mat heaters are constructed of nichrome wire interwoven into ceramic beads which provides electrical insulation and protection. These heaters are quite rugged and conform to curved and irregular shapes.

Thermocouples are used to sense the target temperature and send their signal back to some type of electronic temperature controller, recorder, or combination thereof. The sophistication of the control system can range from simple manual control to fully automatic control with large graphic displays. Recorders are frequently used to document the pre-heat, soak, and post-heat process. Welding integrity depends on precise and accurate control.

Power Console Controller
Recorder used on
welding power console.
Heat treatment power consoles are built on sturdy chassis of steel and depending on ambient conditions, stainless steel. Construction includes wheels and handles for easy relocation and many electrical components for safety and convenience (such as amp meters, indicator lights, cut-off switches, fuses, and alarms).

For more information, contact:

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

Ceramic Mat Heaters for Pre & Post Weld Heat Treating

ceramic mat heater
Ceramic mat heater
for pre and post weld
heat treatment.
Flexible ceramic mat heaters (also known as flexible ceramic pads or FCPs) are designed to provide stress relief for pre and post weld heat treatments for large scale welding requirements, such as those needed for piping fabrication, boilers, pressure vessels, storage tanks, pipeline construction, and mining equipment.

It's very important to pre-heat metal to a specific temperature prior to welding. Pre-heating metals reduces stress in the finished weld,  as well as eliminates moisture and improves the metallic microstructure of the weld material.  For post weld heat treatment (PWHT), use of resistance heaters to apply carefully controlled  cool-down can significantly increase the cross-weld toughness of the heat-affected zone.

Ceramic mat heaters are manufactured using high grade nickel chrome (NiCr) 80/20 wire insulated with interlocking sintered alumina ceramic beads, providing flexibility and convenience for use on curved or flat surfaces. Their design also allows for good contact and high heat transfer. Ceramic mat heaters are intended for repeated use and have considerable mechanical strength and durability. They are capable of achieving temperatures of up to 2050°F.  and are most often are supplied with ceramic insulated leads with either Camlock or Dinse type welder terminations.

The most common voltages used are 40, 60, and 80 volts (as supplied by arc welders) but many custom voltages are available. Special sizes, heating patterns and terminations are also easily accommodated with ceramic mat heaters.

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

Welcome to Our Industrial Heating, Welding and Weld Pre-heating Blog

Hotfoil-EHS is committed to educating and training users of our products, namely electric hopper heating systems, electric pre and post weld heat treating, heat treating furnaces, and multi-operator welding stations.

In future posts, we hope to provide interesting information for a wide variety of applications, performance, and products for the markets we serve.

Here is a breakdown of those markets and products:

HOTFOIL
Coal and Fly Ash Hopper Heaters, Industrial Tank Heaters, Heating Cable, Silicone Heater Blankets, Control Systems.

EHS
Pre & Post Weld Heat Treating Power Consoles, Ceramic Mat Heaters, TAU Units, Temperature Recorders, Cable Sets, Brinell Testers.

AFTEK-EHS
Multi-Operator Power Supplies, Packaged Welding Systems, Single Operator Welders, GRID Systems, Custom Transformers.