In the evaluation of material surface properties, scratch resistance and mar resistance are important indicators of a material's ability to withstand damage. The Multi Finger Scratch Mar Tester is a precision testing device specifically designed to evaluate a material's sensitivity to scratches, abrasions, scuffs, and other physical damage. It has been widely used in material research, quality control, and standard testing, making it a typical instrument in material surface performance testing systems.
The Multi Finger Scratch Mar Tester is a testing device used for qualitative and quantitative evaluation of a material’s resistance to scratches and abrasions. Often referred to as a "five-finger" or "five-arm" scratch and mar tester, this instrument was originally developed based on automotive industry surface durability testing standards. It is used to assess the resistance of various materials—especially plastics, coatings, and soft metals—to damage caused by sharp objects.
The instrument employs multiple independent load arms (“finger-like” scratch arms) that apply standardized forces to the material surface using different loads and contact tools. This simulates potential real-world scratches or abrasions, allowing evaluation of a material's relative damage resistance. Test results are useful for material formulation, coating evaluation, and product design optimization.
The basic working principle of the Multi Finger Scratch Mar Tester is to simulate the contact damage of external sharp objects on a material surface. Multiple load fingers apply constant loads on the sample surface via a movable platform, producing scratches or abrasions. This enables observation and measurement of the material’s resistance to such damage.
Sample Loading and Motion Platform
The instrument usually features a pneumatically driven movable platform. The sample is fixed on the platform, which moves linearly during testing. Platform speed can be adjusted via air pressure control, allowing single or repeated scratch tests.
Multi-Finger Mechanism and Load Settings
A support structure holds five independent spline-shaft fingers evenly distributed above the platform. Each load arm maintains a constant vertical load on the sample. Load weights typically range from 2N to 20N, and can be adjusted according to material characteristics and testing standards. By changing the load weights, testers can vary the force applied by each scratch finger, assessing scratch resistance under different load conditions. Some systems also support precision light loads (e.g., 0.6N) or heavier loads (up to 25N) for more comprehensive analysis.
Replaceable Scratch and Mar Probes
Each load finger has a replaceable probe at its contact point. Common configurations include a 1.0mm diameter hemispherical probe for fine scratches and a 7.0mm hemispherical probe for mar testing. Probes are made of high-hardness materials (e.g., tungsten carbide) to ensure repeatable and stable scratch conditions. Alternative probe geometries, such as conical carbide or diamond tips, may be used for detailed evaluation of different surfaces and material structures.
The testing procedure is systematic and includes the following steps:
Sample Preparation and Fixation
The test sample is fixed flat and securely on the pneumatic platform. Clamps or alignment devices may be used to prevent shifting or warping. Sample thickness typically should not exceed ~22mm, but the floating load arms allow testing of slightly curved or uneven surfaces.
Load and Probe Selection
Choose appropriate probe type and load weight based on the material and testing objectives. Multiple load arms can be set with different forces to cover light scratches and more severe mar conditions.
Start Test
The platform moves the sample linearly under the five probe zones, producing a series of scratches or mar marks on the surface. Speed is controlled via air pressure to ensure consistent testing.
Result Evaluation and Analysis
After testing, results can be analyzed using various methods:
Visual Inspection: Evaluate scratch visibility under standard lighting, typically rated 1 (no visible scratches) to 5 (severe scratches).
Geometric Measurement: Measure scratch width and depth using optical microscopes or micrometers for quantitative data.
Image Analysis: Use imaging techniques or scanning microscopes to assess scratch morphology and defects for higher precision.
Analysis should include detailed descriptions of surface morphology changes, material deformation, and color changes, providing insight into material performance under stress.
Pneumatic or Servo Motion Platform
Secures and moves the sample, allowing continuous linear movement under multiple probes. Speed and pass count are controllable for repeated testing.
Multi-Finger Load Mechanism
Five independent spline-shaft load arms with adjustable weights, floating design ensures proper contact even on uneven surfaces.
Probes and Optional Tools
Includes standard scratch and mar probes, with optional conical or diamond tips for specific material testing needs.
Control Unit and Timer
Equipped with control knobs and timing devices to regulate test pace and record durations for standardized testing.
The Multi Finger Scratch Mar Tester has practical applications across multiple industries:
Automotive Industry
Used for testing scratch resistance of interior components, trims, and plastic panels, aligning with automotive material surface standards.
Plastic Material Testing
Common for injection-molded parts, engineering plastics, and polymers to validate material formulation and manufacturing processes.
Coatings and Decorative Materials
Evaluates the durability of surface coatings like powder coatings or spray paints against everyday scuffs and scratches.
Soft Metals and Hard Materials
Assesses potential surface damage for soft metals, rubber, and linoleum under different load conditions.
Multi-Load Parallel Assessment: Multiple load arms apply different forces simultaneously for rapid, multi-condition testing.
Wide Applicability: Suitable for plastics, coatings, soft metals, and more.
Ease of Operation: Pneumatic control and standardized weights simplify setup and repeatability.
Considerations
Ensure sample surfaces are clean and flat.
Select load and probe according to material characteristics and applicable industry standards.
Combine visual, optical, and image analysis methods for comprehensive evaluation.
Maintain stable testing environments to avoid interference affecting scratch morphology.
Follow relevant national or industry standards for different test types.
The Multi Finger Scratch Mar Tester is a professional device for evaluating surface scratch and mar resistance. Using five load arms and replaceable probes, it allows testing under varied loads and contact conditions. This method is flexible, simple, and suitable for a wide range of materials, making it essential for material research, quality control, and product development. Combining qualitative and quantitative analysis provides scientific guidance for material design, process improvement, and performance optimization.
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