Mineral insulated heating elements with one-wire

Kamet supplies a range of standard individual mineral insulated resistance heating elements.  These are available as one-wire heating elements (our internal reference CVX & BVX heaters) and two-wire heating elements (our internal reference CXX & BXX heaters). On this page we provide information on the one-wire heaters including their properties and possible applications. For the two-wire heater properties, visit this page.

One wire heating elements (CVX & BVX heaters)

Mineral insulated heating elements consisting of one current-carrying conductor, insulated with magnesium oxide (MGO) and protected with a flexible metal sheath that has a minimum bending radius of 2x the outside diameter.

The MI heating elements are supplied with a conductive cold end. This conductive cold end is generally made of material with a much lower resistance value (e.g. copper or nickel). This cold end allows for easy termination. This cold end facilitates straightforward termination, often achieved through the use of metal-to-ceramic connectors. The primary distinction between one-wire and two-wire heating elements lies in their termination requirements: one-wire heating elements necessitate termination at both ends, whereas two-wire heating elements require termination at just one end, thanks to the circuit formed by the two wires.

This cold end has a internal/seamless hot/cold transition. Meaning there is no difference in outer (sheath) diameter where hot and cold elements meet. The sheath is electro-etched where internal hot/cold splices are located.

Due to its high power density, mineral insulated heating elements are suitable for applications where the linear power in the heated zone is high (>100 W/m) and the cold ends can go through insulated walls without the concern of overheating.

Physical properties

  • Sheath: Inconel® 600 standard 304SS, 316SS, or 321SS on request
  • Insulator: ≥99.4% Compacted MgO
  • Hot Wire: Inconel® 600 standard. Nichrome 80/20 on request
  • Cold Wire: Copper

Maximum working temperature

  • Hot Part: 1000⁰C
  • Cold Part: 300⁰C

Tolerances

  • Sheath Diameter: +0/-0.08mm
  • Hot Section Linear Resistance: ±10%
  • Hot Section Length: <1500mm; +0/-10% ≥1500mm; +0/-7%

Usage of MI Heating elements for heating solids or surfaces

When heating liquids, the method involves submerging directly in the liquid that needs to be heated, adhering to a maximum power density of less than 9 W/cm² for standing liquid and not exceeding a maximum temperature of 980°C. It’s important to note that for applications involving fast-moving liquids, the power density can be increased, and one should reach out to Kamet for specialized advice on this matter.

In contrast, when heating gases, the typical approach is to use coils that are commonly inserted inside a tube, allowing the gas to move over these coils, or to use these coils as an oven heating element in harsh environments. The maximum power density for standing air is less than 4.5 W/cm², with the same maximum temperature limit of 980°C.

Similar to the liquid heating application, for situations involving fast-moving gases, an increase in power density is possible, and consulting with Kamet Trading is recommended to obtain appropriate guidance. Based on our experience, one-wire heating elements typically achieve optimal temperature transfer when they are cast onto a metal block through a process known as vacuum brazing. Consequently, they are frequently chosen for such applications. These heating elements are arranged in a meandering pattern on surfaces such as a stainless steel plate, which facilitates uniform heating. More information given in the section below about mounting methods.

Heating in vacuum environments

Radiant heat transfer stands out as a predominant method within vacuum environments. For electric heaters to effectively radiate heat from their surfaces, they need to reach temperatures exceeding 500°C. This process helps concentrate heat in the intended process area while minimizing heat loss to the colder sections of the cable, ushering in an era of enhanced efficiency for radiant vacuum process heating.

The selection of a mounting method is closely tied to the specific heating rate and power requirements of the application. However, operating in a vacuum introduces unique challenges: the vacuum environment functions as a heat trap, keeping heat contained within the heater or the components being heated until radiant temperatures are met.

Additionally, accurately measuring temperatures from the metal surfaces of heaters in a vacuum can prove to be complex. We encourage reaching out for further guidance on these issues. It’s also worth noting that for improvements in longevity or heating uniformity, employing brazing or casting techniques is advisable, even at power densities lower than 4.5 W/cm².

Mounting methods

Heating elements can be mounted onto all kinds of materials. Due to its flexibility, the heaters can be bent in several shapes to transfer heat effectively. The mounting can be done by wrapping the heating element around the object to be heated, but it can also be grooved or brazed onto a surface. The chosen mounting method depends on the desired heating rate and required power. The table below contains information on the parameters of various mounting methods for the mineral insulated heating elements.

Power Density W/cm^2Temperature ⁰CMounting Method
< 3< 980Simple wrap & loose clamping is acceptable
3 – 6< 300Simple wrap & loose clamping is acceptable
3 – 6300 – 600Must be clamped tightly to the object
3 – 6600 – 980Must be partially brazed or cast into the piece to be heated
6 – 15< 980Must be completely soldered, brazed, or cast into the piece to be heated

Kamet’s range of mineral insulated heating elements

  • CVX heaters: One-wire mineral insulated heaters with hot wire of INC600 or Nichrome 80/20 and a copper cold wire. Detailed application guide for CVX.
  • BVX heaters: One-wire mineral insulated heaters with a hot wire of INC600 or Nichrome 80/20 and a nickel cold wire

Why do business with Kamet?

We also offer services through other partner ARi, such as vacuum brazing whereby the heater is cast into the customer’s required material.

Vacuum brazing produces clean, flux-free joints with excellent mechanical strength and resistance to thermal and mechanical stress, which is crucial for the durability of heating elements. The process ensures uniform heating of the assembly, leading to uniform expansion and contraction. This uniformity is beneficial for complex shapes and assemblies, reducing the risk of thermal distortion.

We look forward to hearing from you. Please feel free to contact us with your particular heating needs.


Other products in this category
Cathode heaters for ion thrustersCustom-made heatersMetal-to-ceramic heating connectorsMineral insulated heating elements with two-wiresWafer HeatersMineral insulated microheaters