Hardening foil

The hardening film is suitable for workpieces that can be packaged with little air. It is made of heat-resistant steel and prevents your workpieces from scaling during the hardening process. It is suitable for both small and large workpieces. By tightly wrapping the workpiece, only a small amount of residual oxygen remains inside the hardening film, which is completely consumed during the hardening process. The workpiece can also remain in the hardening film for quenching and tempering.

Practical tip
Wrap the workpiece in a layer of newspaper before hardening. This ensures that no oxygen remains inside the hardening film.

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Product features at a glance

  • Foil with a thickness of only 0.05 mm, but extremely stable

  • Can be used for all temperatures from 400 °C to 1200 °C

  • Easy to pack

  • After heating, a vacuum atmosphere forms in the container, resulting in a bright and super-hard workpiece that is free from decarburization

  • Another advantage is the short delay during heating and quenching, which results in high dimensional accuracy

  • The workpiece is also protected on the way from the oven to the quenching bath

  • The hardening film is suitable for all types and sizes of workpieces

  • Slight discoloration may occur on the workpieces after hardening, but this is insignificant

  • The film is also available in other forms (hardening envelopes, hardening tins)

Available accessories

  • Roller tongs, fitted with plastic rollers
  • Folding wrench incl. turning handle

Available sizes

Use of the hardening foil

 

PREPARATION

The hardening film can be cut to size using standard household scissors.
The corresponding piece of hardening film is cut so that the entire component is covered and the hardening film also protrudes by at least 75 mm. Caution! The film has sharp edges. We recommend wearing protective gloves to avoid cuts!

The hardening film is then spread out on a flat, smooth surface and the component to be hardened is placed in the middle. The hardening film is then carefully pulled upwards at the sides to create a loose package. Make absolutely sure that the hardening film is not damaged by sharp edges or protruding corners. Folding the overhanging part several times will gradually create a tight seal.

For smaller components, it often makes sense to make a pocket from the hardening film. The workpieces are placed inside, the air is pressed out as far as possible and the pocket is then closed by folding the still open upper part several times.
Alternatively, prefabricated hardening envelopes and hardening boxes in various sizes are available from Arnold Schröder Industrieöfen GmbH.

HARDENING

The finished package can now be placed in the oven, which has previously been preheated to hardening temperature. It is not necessary to preheat the component slowly, as the hardening film forms a small protection against thermal shocks on the surface of the workpiece.

The heating time of the workpieces may be extended by a few minutes due to the hardening film. If necessary, the hardening temperature should be increased by 30-50 °C to compensate for the insulating effect of the film.

At the end of the holding time, the entire package can be removed from the oven. Caution! The film may be brittle due to the heat treatment and can be easily damaged.

Quenching

If the hardened material needs to be cooled very quickly, a more intensive coolant than usual should be used to compensate for the insulating properties of the hardening film. For example, it can be useful to quench air hardener in oil and oil hardener in water. Normally, the hardening film delays the quenching process sufficiently to prevent cracks in the component. If there is a risk of cracking due to the component, the package should be removed from the coolant before it has cooled down completely.

After quenching, the hardened parts are removed from the packaging, e.g. by cutting it open with scissors. Correctly treated workpieces are clean and no surface post-treatment should be necessary. Discoloration on components is usually caused by leaks during the cooling process. However, these discolorations often have little or no effect on the hardened components.

Due to the insulating effect of the hardening film, it may be necessary to remove the film before quenching in very special cases – especially with very small components that are in pockets in the oven.

Tempering
Air quenchers can remain in the pack for tempering, while components hardened in oil should be unpacked before tempering.

VENTILATION

Hardening film packs expand and contract as a result of the trapped air and the changing temperatures during use. Particularly with very large components, a large amount of trapped air can expand the hardening film to such an extent that the hardening film tears at the edges. This can be remedied by simple ventilation.

The hardening film pack is prepared as usual. However, a small opening of approx. 6-7 mm diameter is left at one corner. This allows the air to escape during heating and prevents major stresses in the pack. As soon as the pack has reached the hardening temperature, the air hole is closed using tongs.

At very high curing temperatures from approx. 1150 °C, the film may stick to the workpiece during curing. This problem can be largely avoided by venting. However, in this case the vent hole should remain open during the entire holding time and only be closed immediately before quenching

Annealing
The protective properties of hardening film can also be put to excellent use during annealing.

Hints

At very high temperatures, a double layer of hardening film may be useful in exceptional cases to ensure that the workpiece is sufficiently protected. In this case, a further extension of the heating time should be planned.

Adding a small piece of titanium (e.g. a thin strip of sheet metal) to the packaging very often improves the process and often results in a completely oxidation-free surface. This is particularly recommended for very precise and sensitive workpieces. Alternatively, the addition of a piece of newspaper or neutral annealing carbon is also suitable.

The hardening film not only reduces oxidation, but also prevents oil stains on the workpiece due to quenching.

The use of the hardening film at temperatures above 1200 °C is not recommended.