Grinding burn test

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Grinding burn is a test method to avoid failures caused by defects in the grinding of gears.

Reason for the exam

For the production of very precise surfaces on gear flanks, the profile is used as a manufacturing method loops used. In the grinding process, unfavorable process management (e.g. excessive feed, excessive contact pressure) can lead to more or less large zones of local overheating. Local overheating can cause tempering processes or re-hardening zones, which can later lead to premature failures.

history

In 1963, the American Gear Manufacturer's Association AGMA established a procedure for grinding burn testing. The American military also standardized a procedure for “temper etch inspection” based on surface etching with nitric acid. In Europe, the process was only used later.

Test procedure

Nital etching

Laminar pearlite in a eutectic (0.8% carbon) steel after annealing , made visible by nital etching

Nital etching: Nital etching is one of the oldest and still frequently used test methods for assessing the edge zone quality of hard-finished components. The grinding burn test on the workpieces is carried out in accordance with the ANSI / AGMA standard 2007 or ISO standard 14104 by etching in an immersion bath. It is the dominant non-destructive grinding burn test in practice, both in production and in research - a very reliable method of detecting grinding burn . The zones of the workpieces affected by grinding burns take on a dark color after the process has been carried out.

Barkhausen noise

Barkhausen noise: When a piece of steel is magnetized by an external alternating field, the change in magnetic flux follows a hysteresis loop. At first glance, the curve appears to be smooth, but on closer inspection it turns out that it actually consists of incremental changes (jumps). If a coil is placed near the surface of the workpiece, a pulse-like signal is generated in the coil. Such impulses generated in solid material form a noise-like signal with a broad spectrum, the so-called "Barkhausen noise". The microstructure of a component and the residual stresses on its surface can be evaluated by measuring the intensity of the Barkhausen noise. Voltage increases the intensity of the Barkhausen noise ( magnetic Barkhausen effect ) and pressure decreases it. The greater the hardness, the lower the measured noise signal.

Surface crack inspection

Surface crack testing (fluxing): Surface crack testing using the magnetic powder method is possible with all ferromagnetic materials whose conductivity is> 100 μ. Cracks are detected on the surface, the ratio of width - depth - length ≥ 1 - 10 - 100. The material to be tested is magnetized. The resulting field lines run parallel to the surface. Cross-running cracks generate a magnetic stray field. Magnetic poles are formed, which attract the magnetic powder distributed on the surface. Parallel cracks are not recognized.

Norms

  • ANSI / AGMA 2007-C00 Surface Temper Etch Inspection After Grinding
  • MIL-STD-867 Temper Etch Inspection
  • ISO14104 gears - grinding burn test

literature

  • Sauer, WJ: Thermal Aspects of Grinding. Dissertation, Carnegie-Mellon University Pittsburg 1971
  • Wobker, H.-G .; Spintig, W .; Brandt, D .: Edge zone changes during the machining of hardened materials. HTM 50, 1995/5, S276-281

Web links

Individual evidence

  1. ↑ Schleifprofi.com: Nital etching [1]
  2. ↑ Schleifprofi.com: Barkhausen noise [2]
  3. ↑ Schleifprofi.com: Fluxing [3]