Leeb Testing Factors

Factors Influencing the Accuracy and Limitations of Leeb Hardness Testing As with any hardness testing method, whether using a robust bench-top unit or a portable device, improperly prepared samples can lead to significant measurement errors. Ensuring that the sample and test surface meet specific conditions is crucial to obtaining accurate results. If you want to learn more, please visit our website. Sample Suitability: Thin-walled parts like tubing, sheet metal, sheet aluminum, smaller die-cast parts, and machined parts with thin walls and lightweight components are generally not suitable for this testing method. Weight and Rigidity: The sample's weight and rigidity are paramount as the Leeb principle relies on the impact rod's rebound to measure hardness. Inadequate weight or rigidity will result in the sample absorbing much of the impact, leading to inaccurate results: - Sample weight ≥5kg (10lbs), not easily movable, can be directly tested and is considered ideal. - Sample weight 2-5kgs (4-10lbs) should be appropriately clamped in place. - Sample weight 0.05-2kgs (0.1-4lbs) should be coupled with a supporting material before testing. - Sample weight ≤0.05kg (0.1lbs) is inappropriate for use with this tester. Coupling Method: To achieve an effective integrated sample, the test sample's backside should be prepared with a flat, smooth surface making full contact with a supporting object weighing more than 5kg. A little coupling substance, like industrial grease, can be used. Sample Preparation: When preparing the sample, avoid altering it through cold processing (e.g., striking with a hammer, causing work hardening) and thermal processing (e.g., excessive grinding leading to localized heat treatment). Surface Conditions: A flat or planar surface provides the best results. The test surface must be clean, metallic, and free of oxide layers (rust), stains, or paint. Curved Surfaces: If the testing surface is not flat, ensure the curvature radius of the testing surface is larger than 30mm. Select and install an appropriate supporting ring to keep the tester probe as perpendicular as possible. Surface Roughness: The surface roughness at all testing points must be Ra ≤ 1.6. Use appropriate grit wheels (200 for type D or 60 for type G) to achieve the required finish. Impact Devices and Surface Roughness: Types of impact devices: D/D+15/DL, G, C Max surface roughness: 2μm, 7μm, 0.4μm respectively You will get efficient and thoughtful service from AJR. Sample Thickness and Surface Absorption Layer: Samples should be thick enough and have a sufficient surface absorption layer. For the D-type device, sample thickness must be greater than 1" (25mm) if not supported, and the surface absorption layer should not be less than 0.8mm. Impact Devices and Minimum Sample Thickness: Types of impact devices: D/D+15/DL, G, C Minimum sample thickness: 1/8" - .125" (3mm), 3/8" -.387" (10mm), 3/64" -.047" (1mm) respectively Magnetization: A sample should not be magnetized, as the magnetic field will interfere with the impact device's signal, causing inaccurate test results. Temperature: The sample surface temperature should be less than 250°F (120°C). Proximity to Edges: The test location should be a minimum of 5mm (0.2 inches) from the edge of the part, with 10mm (0.5 inches) or greater being recommended. Real-World Use and Observations: When testing on various materials, the results are reproducible across different sample sizes and thicknesses. Small fin parts may require back-up, while larger parts do not. Proper greasing and coupling to the back-up block significantly improve the accuracy of hardness readings. One consideration is whether dirt could enter the dart tube or debris collect on the ball assembly. The unit includes a brush for cleaning, and the dart can be easily removed and cleaned if needed. The device can be positioned in various orientations due to its spring or air gun mechanism, enhancing its versatility in testing massive parts. Surface Finish and Measurements: Surface finish should be around 1.6 micrometers. The device reads Leeb units, Rc, Brinell B, and other units as selectable from the hand-held display menu. Overall, this device appears reliable and precise in its application, offering good build quality and performance. For more details, kindly visit Portable Leeb Hardness Tester.