November 29, 2023

Immersion heaters guide

I – Introduction

This year, Cougar Electronics had the pleasure of announcing its partnership with Atherm, as presented in the article “Partnership with ATHERM“. Today, we introduce a product from Atherm that we are delighted to distribute throughout North America: the immersion heaters. Developed over 30 years through continuous feedback, we are excited to present these devices. Immersion heaters are electric heating devices submerged in molten light metals, aluminum, and zinc. They are used for temperature maintenance, temperature increase in baths, and also for metal melting. This article aims to present the composition of immersion heaters, their operating principle, and the various applications they have been implemented in.

II – Composition of Immersion Heaters

II. 1 – Components

Visually, immersion heaters can be divided into two distinct parts. The lower part consists of a tubular ceramic section, and the upper part comprises a flange, an extension, and a metal compartment. The ceramic sheath in the lower part contains an electric resistance inserted into an electrical insulator, responsible for heating the immersion heater. It also houses a thermocouple for temperature monitoring to prevent overheating. To connect the electric resistance to the upper part of the immersion heater, current leads are used. In the upper part, there is a terminal block for electrical cable connection or a quick connector. The thermocouple is also connected to a plug on the side of the immersion heater head. The flange allows fixing the immersion heater to the furnace lid or walls.

Figure 1: The parts

II. 2 – Information

Immersion heaters have a serial number and an identification plate, which provide all the necessary information about the immersion heater. Atherm can retrieve the manufacturing and testing data for each of its products using the serial number.

Figure 2: Information plate

The information on the identification plate includes:

  • Model
  • Serial number
  • Voltage
  • Type of current
  • Power
  • Heating lenght
Figure 3 : Identification Number

The serial number is also affixed to the head and extension of the immersion heaters.

III – Operating Principle

III. 1 – Overview

Immersion heaters are electrical devices immersed in molten light metals, used for temperature maintenance, temperature increase, or metal melting. The following applications of these devices are numerous and will be presented.

III. 2 – Positioning and Fixation

Immersion heaters can be installed vertically on furnace lids, inclined, or horizontally on furnace walls.

Figure 4: Installation position in the furnace

 To fix them, they need to be screwed via the fixing flange onto the furnace lid or walls, using the mounting brackets provided by the furnace manufacturer.

Figure 5: Mounting

III. 3 – Commissioning

Immersion heaters can be commissioned in two ways. In a furnace containing molten metal, they can be immersed directly or filled with molten metal after installation. In both cases, precautions should be taken to avoid damaging the ceramic sheath. The thermocouple’s temperature should not exceed the metal’s temperature, and the difference should not exceed 300°C (540°F) between the metal and the thermocouple.

Figure 6: Temperature information

For commissioning in a full furnace, immersion heaters need to be preheated to meet the aforementioned conditions. Placing them above the bath will increase their temperature.

Figure 7: Installation on removable lid

For commissioning in an empty furnace, immersion heaters also need to be preheated before filling the furnace with liquid metal.

Figure 8: Installation in an empty furnace

III. 4 – Control Mode

Immersion heaters are regulated using a dedicated power cabinet, as shown in the diagram below.

Figure 9: Regulation

Recommendations for regulation using immersion heaters are provided later.

IV – Applications of Immersion Heaters

Today, immersion heaters have found applications in several lightweight metal foundry processes. We will present a dozen of these applications, but we would be delighted to develop immersion heaters for new applications that suit your needs.

IV. 1 – Holding Furnace

This holding furnace consists of two chambers, each holding 3.5 tons of metal, maintained at a specific temperature. For this application, 2 sets of 3 immersion heaters (totaling 6) with a diameter of 55mm and a power of 40kW each, and a sheath length of 1320mm are used. The immersion heaters have a lifespan of over 2 and a half years and are controlled by a dedicated control cabinet.

Figure 10: Picture/schematic of a holding furnace

IV. 2 – Melting Furnace

This application involves a large industrial melting furnace, where aluminum is melted using immersion heaters from solid aluminum. The required temperature to maintain during the melting process is 750°C. For this purpose, 13 immersion heaters with a diameter of Ø32mm, each with a power of 13kW, are used. This innovative electric melting furnace saves energy compared to other solutions. Our recent installation requests require higher power capacities. The immersion heaters used have diameters of 55mm and 75mm with extended sheaths. These installations can reach installed power capacities in the megawatt range.

Figure 11: Melting furnace

IV. 3 – Dynamic Heating Crucible

In this application, there are specific requirements:

  • 400kg of liquid aluminum
  • 4 immersion heaters with a diameter of Ø28mm, each with a power of 15kW
  • Temperature increase from 750°C to 800°C in 10 minutes
  • A cover position sensor capable of stopping the power
  • Dedicated control power cabinet
  • Ensuring the quality of the aluminum
Figure 12: Crucible and his control cabinet

IV. 4 – Filtration Unit

The aluminum flow rate for this filtration unit is 4 tons per hour, and the objective is to maintain and increase the temperature. Three horizontal immersion heaters, each with a power of 9kW, are used to address the mechanical and thermal challenges of the installation.

Figure 13: Filtration unit

IV. 5 – Furnaces with Low Bath Level

Furnaces with low bath levels are equipped with horizontal immersion heaters mounted on the furnace walls.

Figure 14: installation in a low bath level furnace

IV. 6 – Transfer Ladle

The features of the transfer ladle equipped with immersion heaters are:

  • 1200kg of aluminum in the ladle
  • Loss of temperature during transfer from furnace to ladle and ladle to mold. Preheating is required before pouring into a mold.
  • Ensuring the quality of the aluminum
  • A well-insulated cover with three Ø28mm immersion heaters, each with a power of 15kW
  • Temperature increase from 700°C to 760°C in 6 minutes
Figure 15: Transfer ladle

IV. 7 – Maintaining Temperature in Road Transport Ladles

This road transport ladle requires a temperature increase of 10°C per hour up to 830°C. It is equipped with three Ø32mm immersion heaters, each with a length of 1400mm and a power of 15kW.

Figure 16: Road transport ladle

IV. 8 – Replacement of Roof Heating Elements with Immersion Heaters

This application involves:

  • High dynamics
  • Homogeneous temperature
  • 40% reduced energy consumption
  • Six immersion heaters, each with a power of 15kW
  • No degradation of aluminum quality, no corundum
Figure 17: Retrofit

IV. 9 – Retrofitting a Degassing Unit

For this retrofit, inefficient and costly graphite heating blocks are replaced with efficient immersion heaters. Rotors causing high temperature losses and excessive aluminum vortex are eliminated, reducing the risk of chloride and other additive contamination. One Ø55mm immersion heater per chamber is added as a permanent solution, offering efficiency, cost-effectiveness, and thermal dynamics.

Figure 18: Degassing unit

IV. 10 – Temperature Maintenance During Maintenance

In this case, immersion heaters are used for maintenance of 28 45kW vault furnaces with corundum. The aluminum temperature is maintained at 665°C, and if it drops to 630°C, 4 hours of reheating are required before restarting production. A mobile “heating” station is used:

  • One Ø32mm immersion heater and one Ø55mm immersion heater, each with a power of 12.5kW
  • Saves 2 hours on the maintenance of 28 furnaces, twice a month.
Figure 19: Maintenance immersion heater

IV. 11 – Maintaining Aluminum Temperature in Chutes

Immersion heaters can also be used in specific conditions, such as pouring aluminum into chutes. The restricted space and low bath level are addressed by using horizontal immersion heaters, enabling smooth pouring without aluminum solidification.

Figure 20: Chutes

IV. 12 – Continuous Casting

For continuous casting, specialized immersion heaters pins and dedicated preheating furnaces are designed to ensure the immersion heaters are ready for use upon installation.

Figure 21: Heating pin / Preheating furnace/ Installation

V – Sizing

To meet the requirements of these applications, several parameters need consideration.

V. 1 – Required Power

To determine the necessary power, the function and temperature of the bath where the immersion heaters will operate must be known. Dynamic losses of the furnace must also be considered to ensure sufficient power to compensate for them. With this information, the total required power for the application can be determined, followed by the selection of the appropriate number and dimensions of immersion heaters.

V. 2 – Installation Space

Respecting the spacing between immersion heaters and their surroundings is essential. Additionally, the available depth of the metal bath needs to be taken into account. These factors will influence the choice of immersion heaters for your specific application.

Immersion heater positionMinimum distance to be respected
a [mm]b [mm]c [mm]d [mm]
Vertical (figure 1)5010050
Tilted (figure 2)5010050100
Horizontal (figure 3)10010050100
Figure 22: Placement of the immersion heaters in the furnaces

a: distance between the top of the heating length and the bath level.

b: distance between the sheath or the heating length and the furnace wall.

c: distance between the end of the sheath and the bottom of the tank or the walls.

d: distance between the sheath or the heating length and the furnace wall.

The distance between immersion heaters must also be taken into account; it must be greater than 100mm.

Figure 23: Distance in between two heaters

V. 3 – Current Dimensions of Our Immersion Heaters

Currently, our immersion heaters come in the following range, based on our years of experience:

Sheath diameter [mm]Sheath diameter [inch]Minimum sheath length [mm]Maximum sheath length [mm]Minimum sheath length [inch]Maximum sheath length [inch]Maximum Power [W]
281.1700145027.5657.0915
321.26 25
552.17135053.15 50
752.95 70
Figure 24: Table of the dimensions

If these dimensions do not meet your application requirements, please feel free to contact us, Cougar Electronics and Atherm can study your configuration and adapt our products accordingly.

VI – Usage Advice

VI. 1 – Handling

Immersion heaters must not be handled when they are still hot. When handling them, use gloves and hold them by the designated areas. Care should be taken not to rotate the immersion heater head or cause any impact to the sheath, as it could lead to cracks and breakage upon the next use.

Figure 25: Handling instruction

VI. 2 – Maintenance

Cleaning operations depend on the quality of the aluminum. If the aluminum quality is sufficient, there may be no need for cleaning operations. A filter can be installed upstream to clean it regularly. If furnace maintenance allows cleaning of the immersion heaters within 30 minutes, a careful cleaning of the sheaths can be performed with the appropriate tools, as demonstrated in the procedure provided. It is necessary to pay attention to the sheath temperature to avoid a too large difference with that of the tool.

Figure 26: Maintenance instruction

VII – Advantages

Our conductive immersion heater technology stands out for its ability to achieve remarkable power densities. This feature holds particular significance in the light metal industry. By opting for direct heating at the core of the metal, we ensure obtaining optimal metallurgical quality. Through this method, issues of overheating and oxidation become a thing of the past, guaranteeing unparalleled metal purity. Furthermore, our precise temperature control proves to be a pivotal factor in producing superior quality cast parts. Fluctuations are minimized, and variations are kept within a range of +/-2°C (+/-3.6°F), resulting in exceptional outcomes.

One of the substantial advantages of our approach is also the significant extension of refractory material lifespan. The precision of our heating technology alleviates stress on refractories, thus prolonging their durability. From a broader perspective, the economic impact of this extended lifespan translates into substantial savings for our clients. Additionally, thanks to targeted heating and precise regulation, we take pride in contributing to a notable reduction in maintenance operations. Lastly, it’s crucial to underline that our approach also leads to substantial metal savings, a crucial factor in the light metal industry where every ounce counts.

In addition to these benefits, it’s worth noting that our technology boasts minimal thermal losses. For every kilowatt (kW) of electrical power input, an equivalent kilowatt (kW) of thermal power is generated due to the efficiency of our design. Thanks to its conductive technology, our immersion heater demonstrates exceptional performance in dynamic heating scenarios, further enhancing productivity gains. This, combined with the quality improvements in the cast parts, results in an overall boost in productivity.

In summary, our commitment to thermal excellence and metal quality is reflected in every aspect of our heating technology within the light metal industry.

VIII – New technology: Dual

We are pleased to introduce you to the new product, which is the Dual immersion heater. Its external appearance remains very similar to traditional immersion heaters, but its functionalities have been improved. It still has a traditional heating mode that allows it to heat within lightweight metals. However, it is now possible to perform preheating of furnaces using this immersion heater. In fact, it is capable of heating in the air to carry out this action. This heating mode can also be used when the level of the metal bath is too low. In this case, the immersion heater heats both in the low level of metal and in the air.

Figure 27: Dual immersion heater

IX – Conclusion

In conclusion, immersion heaters are a remarkable innovation in the light metal industry, offering efficient, precise, and energy-saving electric heating solutions. With their ingenious design, these devices immersed in molten metals maintain, increase temperature, and melt metals with high efficiency.

The composition of immersion heaters, with their ceramic sheath containing an electric resistance and a thermocouple, ensures precise regulation and prevents overheating, leading to improved aluminum quality and extended furnace refractory lifespan.

Their versatility is highlighted by their applications, ranging from holding and melting furnaces to transfer ladles and filtration units. Immersion heaters have proven essential for maintaining temperature in chutes and ensuring rapid and uniform heating in continuous casting processes.

Besides their technical performance, immersion heaters offer significant economic and environmental benefits. Their energy efficiency leads to cost savings in production and reduced environmental impact by minimizing energy consumption and waste from impurities.

In conclusion, Atherm’s immersion heaters, developed through 30 years of experience and continuous improvement, have revolutionized the light metal industry with superior performance, precise regulation, and substantial economic advantages. Their ability to address various applications and adapt to specific customer needs ensures their crucial role in light metal production processes.

If you would like to learn more about our immersion heaters or discuss a specific application, please do not hesitate to contact us. We are eager to collaborate with you to find the best electric heating solution that meets your needs and enhances the efficiency of your industrial operations.

Thank you for considering our immersion heaters, and we look forward to the opportunity to work with you.

Sincerely, Cougar Electronics

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