Evaluating whether the performance indicators of a spring washer meet the requirements involves examining key dimensions such as material properties, physical performance, anti-loosening capabilities, and environmental adaptability. The evaluation should be based on industry standards, combined with actual test data for a comprehensive judgment. Below are the specific methods and key points for evaluation:
Material Performance Evaluation
The material is the foundation that determines the spring washer's strength, corrosion resistance, and lifespan. The following key indicators need to be verified:
1. Material Composition Testing
Carbon Steel / Alloy Steel: Focus on detecting the content of carbon (C), manganese (Mn), silicon (Si), sulfur (S), phosphorus (P), as well as alloy elements such as nickel (Ni) and chromium (Cr). For example, 65Mn spring steel should contain 0.62%-0.70% C and 0.90%-1.20% Mn.
Stainless Steel: Verify the content of chromium (Cr), nickel (Ni), and molybdenum (Mo). For example, 304 stainless steel should contain 18%-20% Cr and 8%-10.5% Ni, avoiding the use of inferior steel such as 201.
Copper Alloys: Test the content ratio of copper (Cu), zinc (Zn), and tin (Sn). For example, tin bronze should contain 8%-14% Sn.
Testing Method:
Request material certification or spectral analysis reports from the supplier (using X-ray fluorescence spectroscopy for rapid detection).
For high-requirement scenarios (such as aerospace), third-party laboratories can be commissioned for chemical titration or direct-reading spectrometer testing.
2. Hardness Testing
Standard Requirements:
Ordinary carbon steel washers: Hardness typically HRC 28-35 (before surface treatment).
High-strength steel washers (such as 65Mn): After quenching and tempering, hardness should reach HRC 42-48.
Stainless steel washers (304 material): Hardness ≤ HRC 20 (soft state). To increase hardness, special treatments such as cold work hardening to HRC 30-35 are required.
Testing Tools:
Portable Rockwell hardness tester (for batch sampling) or Vickers hardness tester (for thin sheets or precision components).
Sampling Rules:
Randomly select 5-10 pieces per batch, testing hardness at the washer surface or at the cut edge. The tolerance should be ≤ ±3 HRC.
Physical Performance Evaluation
1. Dimensional Accuracy Testing
Main Parameters:
Inner diameter (d1): Should be slightly larger than the bolt diameter (e.g., for an M8 bolt, the inner diameter of the washer should be 8.4-8.6 mm). The tolerance is typically +0.1/-0.05 mm.
Thickness (s): For standard specifications, an M4 washer is 0.8 mm thick, and an M12 washer is 2 mm thick, with a tolerance of ±0.1 mm.
Width (b): Should match the nut size (e.g., for an M10 nut, the washer width should be 16 mm), with a tolerance of ±0.5 mm.
Testing Tools:
Calipers (precision of 0.02 mm) or projectors (for high-precision testing). Measure the inner diameter and thickness of every washer, with at least 20% of the width sampled.
2. Elastic and Fatigue Performance Testing
Elasticity Test:
Compression rebound test: Compress the washer to a standard load (e.g., M10 washer compressed to 800 N), hold for 30 seconds, then release and measure the residual deformation. A good washer should have a residual deformation of ≤ 5% (i.e., compression recovery rate ≥ 95%).
Simple manual test: Press the washer by hand and release it. It should rebound quickly without long-term deformation or cracking.
Fatigue Life Test:
Vibration Test: Simulate real working conditions (such as ISO 10816 vibration standards), fix the washer and bolt assembly on a vibration table, and vibrate at a specified frequency and amplitude (e.g., 50 Hz, amplitude 2 mm). Record the number of cycles until the washer fails. A qualified product should pass at least 100,000 vibration cycles without failure.
Supplier Qualification Verification:
Request third-party test reports focusing on "fatigue limit" and "cyclic life" data.
Anti-Loosening Performance Evaluation
Anti-loosening is the primary function of spring washers, and its ability to maintain locking force under dynamic loads needs to be verified:
1. Preload Force Testing
Testing Method:
Use a torque wrench to tighten the washer and bolt assembly to the standard torque (e.g., for an M10 bolt, torque should be 40 N·m). Measure the preload force using a pressure sensor or strain gauges. The preload force should meet the design requirements (usually 70%-80% of the bolt’s yield strength).
Compare the preload force variation across different batches; the error should be ≤ ±10%.
2. Anti-Loosening Effect Simulation
Vibration Loosening Test:
Refer to ASTM F1519 standard, fix the assembled bolt unit on a vibration test machine, apply axial vibrations (frequency 20-2000 Hz, amplitude 0.15 mm) for 30 minutes, and check the degree of nut loosening. Qualified washers should keep the nut loosening angle ≤ 15°.
Simple Method: Manually strike the assembly to simulate vibration and observe whether the nut becomes visibly loose.
Environmental Adaptability Evaluation
Verify the washer’s resistance to corrosion, high temperatures, and other environmental factors based on the usage scenario:
1. Corrosion Resistance Testing
Salt Spray Test:
Electroplated washers: ≥ 48 hours without red rust.
Hot-dip galvanized washers: ≥ 720 hours without red rust.
Dacromet-coated washers: ≥ 1000 hours without corrosion.
Neutral Salt Spray Test: Perform this test for surface-treated washers (e.g., galvanized, Dacromet) according to ISO 9227.
Moisture and Heat Aging Test:
Place the washer in a humidity chamber (95% humidity, 60°C temperature) for 7 days and observe any signs of rust or oxidation.
2. High-Temperature Performance Testing
Heat Resistance Evaluation:
For high-temperature scenarios (such as engine compartments), heat the washer to its operating temperature (e.g., 200°C), hold for 2 hours, then cool and measure any changes in hardness and elasticity. Hardness decrease should be ≤ 10%, and elasticity recovery rate should be ≥ 90%.
Stainless steel or nickel-based alloy washers need additional verification for high-temperature strength (e.g., tensile strength ≥ 200 MPa at 800°C).
Reference Standards and Acceptance Procedures
1. National Standards Comparison
GB/T 93-1987: "Standard Spring Washers" specifies dimensions, technical requirements, and acceptance rules.
GB/T 859-1987: "Light Spring Washers" for light-load scenarios.
GB/T 7244-1987: "Heavy Spring Washers" for stronger connections.
ISO 7093-1:2000: International standard for metric threaded connections.
2. Acceptance Procedure Recommendations
Initial Sample Validation: New suppliers must provide samples, which will be fully tested according to the above indicators. Once qualified, a "Sample Acceptance Certificate" will be signed.
Batch Sampling: After each batch arrives, sample inspection should be carried out according to GB/T 2828.1 standards (e.g., General Inspection Level II, AQL=1.0), checking dimensions, hardness, elasticity, and other critical items.
Long-Term Quality Monitoring: Regularly (quarterly or semi-annually) commission third-party testing for material, fatigue life, etc., to prevent quality deterioration due to process fluctuations.
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