Protection tube

Protection tube


HER6 and HER7 protection tubes are made of high-performance ceramic. Technical ceramic is known to be especially hard-wearing and is extremely corrosion and heat resistant. However, in many cases their fragility prevents their widespread acceptance in practice. This relatively new ceramic is especially well-suited for applications that call for a combination of strength, resistance to wear, and mechanical and thermal shock resistance. HER6 and HER7 ceramic is resistant to molten non-ferric metals. This factor, together with a combination of extremely high tensile and bending strength up to 1250°C and excellent heat conductivity, results in the following advantages:
• Long service lives in non-ferric metal smelting (1st choice for aluminium)
• No build-up of deposits of metal or cinders on the protection tube
• No contamination of the liquid metal; excellent heat conductivity
• High degree of mechanical strength and gas-tightness all the way into the high temperature range

Features of the HER7 material

HER7 has been especially designed to withstand great stress under the most difficult conditions. HER7 thermocouple protection tubes are intended for use in places where the emphasis is on maximum resilience to abrasion and outstanding thermal shock resistance. We thus find a unique combination of the highest degree of robustness and hardness in this material. HER7 can be used with temperatures up to 1300°C on a permanent basis, and is resistant to temperatures of up to 1600°C for short periods.


HERTH elektrische Temperaturgeber GmbH offers a 1-year guarantee from the delivery date for material and production damage of thermocouple protection tubes made of HER6/HER7 in their use in aluminium smelting in your works, provided that

1. the damage has not been caused by human error, incorrect use, misuse or negligence after delivery;
2. the product is only used as a thermocouple protection tube and in accordance with the afore-mentioned preventive measures;
3. notification of the type of defect is made within 10 days after the discovery of said defect and the protection tube is sent back to us for inspection;
4. the product has not been repaired or altered in any way.

Instructions for use for HER6-/HER7 protection tubes


1. In general, HER6/HER7 protection tubes are markedly resistant, but like all ceramic materials have little or no flexibility and should therefore be cleaned and installed without being subjected to shocks or impacts.
Please never:

• remove clinker residues with a hammer or work on the tube with a hammer for any other purposes;
• install the tube in a (too narrow) holder; we also deliver appropriate adapters;
• allow the tube to fall to the ground or overturn; always lay or place it on an even surface.

2. Pre-heating

• HER6/HER7 protection tubes have good thermo-shock resistance, so it is not necessary to pre-heat them during applications up to approx. 800° C. We do however recommend putting the tube in the furnace chamber for a short time, before it is immersed.
•  Pre-heating is necessary for applications over 800° C. For this purpose, one should not use any open flames, but instead bring the tube to the desired temperature by hanging it up in the furnace chamber or by using a special pre-heating apparatus. The temperature of the tube should always be below the melt temperature!

3. Cleaning by flame cleaning

In individual cases, it can become necessary to remove impurities or soiling. One should thereby proceed as follows:
• The dismantled tube should be hung up in a vertical position
• Use a large gas welding nozzle with a neutral flame
• Take care to keep moving the flame to and fro on the protection tube, in order to avoid overheating it at specific points.
We urgently recommend ventilating the area during the cleaning process! Allow the tube to cool down to room temperature after cleaning without any additional cooling aids. Flame cleaning carried out in this way will not damage the tube.