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7HF is an oil based ready to use black ink for wet method magnetic particle testing.
The ink is used in conjunction with suitable magnetising equipment to locate fine surface and slightly subsurface discontinuities in ferrous materials.
Typical defects found include shrink cracks, welding defects, grinding cracks, quenching cracks and fatigue cracks. 7HF gives clear black indications when viewed in daylight.

Composition

7HF consists of a suspension of magnetic particles in a high flash petroleum distillate.

Method of Use

Components should be cleaned prior to testing to provide a suitable test surface.
The Ink can be applied by spraying, immersion or flooding.
The ink must be mixed thoroughly prior to use and must be kept agitated during testing.

Using the wet continuous method, the ink is applied to all surfaces of the component during magnetisation. The indications will be formed during the application of magnetising current. The flow of ink must stop before the magnetising current otherwise there is a risk that the force of the ink application may wash away indications.

Using the wet residual method, the premagnetized part is immersed in the bath, removed, allowed to drain and then inspected. This method is generally less sensitive than the continuous method and is more susceptible to rapid particle depletion and bath contamination.

In situations where the test surface colour is dark, a thin coating of a suitable white contrast paint such as Magnaflux WCP-2, may be applied prior to testing to provide a contrasting background.


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