Maximizing Outsole Longevity: Evaluating Rubber Compounds Under The ASTM D1630 NBS Abrasion Method

For heavy-duty work boots, military footwear, and industrial safety shoes, the outsole is the first point of contact against rough concrete, steel grating, gravel, and chemical-soaked factory floors. When an outsole wears down prematurely, the tread pattern loses its slip-resistant channeling, midsole cushioning becomes exposed, and the footwear fails its intended service life.

For rubber compounders and footwear buyers sourcing for the North American market, verifying outsole durability requires more than a simple hardness check. ASTM D1630 (Standard Test Method for Rubber Property—Abrasion Resistance (Footwear Abrader)), commonly known across the industry as the NBS Abrasion Test, remains the primary benchmark for quantifying the wear life of vulcanized rubber, thermoplastic elastomers (TPE), and polyurethane (PU) sole materials using specialized rubber and plastic testing machines.

Understanding the Mechanics of ASTM D1630 (NBS Abrasion)

Unlike rotary drum abraders such as the DIN Abrasion Resistance Testing Machine (Model GW-008)—where a cylindrical sample traverses along a rotating drum—the NBS Rubber Abrasion Testing Machine (Model GW-006) utilizes a triple-station configuration that simultaneously subjects three square test specimens to direct rotational friction against standardized silicon carbide abrasive paper.

+------------------------------------------------------------------------------------------+
|                       ASTM D1630 (NBS ABRASION) DIAGNOSTIC WORKFLOW                      |
+------------------------------------------------------------------------------------------+
|  [Step 1: Calibration Run]   --->  Run 3 SRM Reference Compound blocks for 2.54 mm wear  |
|  [Step 2: Sample Mounting]   --->  Mount 25.4 x 25.4 mm test outsole specimens on arms   |
|  [Step 3: Loaded Abrasion]   --->  Apply 22.2 N (5 lbf) deadweight load at 45 ± 5 rpm    |
|  [Step 4: Index Calculation] --->  Compute NBS Abrasion Index (%) vs. Reference Standard |
+------------------------------------------------------------------------------------------+

During operation:

1. Uniform Rotational Contact: Three cylindrical drums (150 mm diameter) wrapped with 40-grit silicon carbide abrasive paper rotate at a controlled speed of 45 ± 5 rpm.

2. Independent Lever Loading: Each test specimen is mounted onto a pivoted lever arm and pressed directly against the abrasive drum under a constant static load of 22.2 N (5 lbf).

3. Continuous Debris Removal: A built-in compressed air or vacuum suction manifold continuously clears abraded rubber dust from the garnet track. Without active dust extraction, melted or powdered rubber clogs the abrasive grit, artificially inflating the revolution count and invalidating the test result.

4. Precision Dial Gauge Monitoring: Each station is equipped with a dedicated 0.01 mm dial indicator positioned over the lever arm. The test runs until the specimen loses exactly 2.54 mm (0.100 in.) of vertical thickness, at which point the revolution counter logs the exact cycle total.

Calculating the NBS Abrasion Index

Because abrasive paper wears down slightly with each run and varies marginally across production lots, ASTM D1630 does not rely on raw revolution counts alone. Instead, it normalizes results against a certified Standard Reference Compound (SRM):

$$\text{Abrasion Index (\%)} = \left( \frac{R_1}{R_2} \right) \times 100$$

• $R_1$: The average number of drum revolutions required to abrade 2.54 mm of the test specimen.

• $R_2$: The average number of drum revolutions required to abrade 2.54 mm of the reference compound (averaged from calibration runs performed immediately before and after the test sample).

What do the numbers mean for footwear sourcing?

• An NBS Index above 100% indicates the outsole compound offers higher abrasion resistance than the standard reference rubber.

• Commercial work boots and industrial safety footwear typically require an NBS Index ranging from 120% to 200+%, whereas high-specification military or logging footwear contracts often mandate even higher thresholds.

Critical Equipment Specifications for Repeatable Lab Results

To eliminate operator variance and ensure factory lab results align with third-party commercial inspection bodies, the footwear abrasion tester must maintain strict mechanical tolerances:

Common Pitfalls in Outsole Compound Production

When footwear factories rely solely on raw material supplier certificates rather than testing finished outsoles in-house, three manufacturing issues frequently slip through quality control:

1. Under-Vulcanization (Cure State Drift): If press platen temperatures drop or molding cycle times are shortened to boost daily output, cross-link density in nitrile (NBR) or styrene-butadiene (SBR) rubber drops sharply. Monitoring rubber curing curves beforehand with a No Rotor Vulkameter Rheometer (Model GW-220) helps prevent under-cured batches from losing 30% to 40% of their NBS abrasion index.

2. Excessive Regrind or Filler Loading: Adding high ratios of calcium carbonate or recycled rubber regrind lowers compound cost, but severely degrades tear and abrasion resistance. Pairing abrasion checks with a Digital Universal Tensile Testing Machine for Rubber Materials immediately exposes low tensile and tear strength caused by filler overloading.

3. Surface Skin vs. Core Density & Flex Cracking: In microcellular polyurethane (PU) and EVA/rubber soles, molding skin thickness can mask an overly porous core. Because ASTM D1630 abrades 2.54 mm deep into the specimen, it exposes subsurface foaming defects—which should also be cross-verified for cut growth using the GW-003 Outsoles Flexing Testing Machine.

Upgrade Your Footwear & Rubber Testing Laboratory

At Great Win Instrument Co., Ltd., we manufacture robust, standards-compliant physical testing instruments for rubber compounders, outsole factories, and global footwear brands. Our GW-006 NBS Rubber Abrasion Testing Machine and complete line of abrasion test equipment are engineered for continuous laboratory operation, providing accurate, repeatable ASTM D1630 verification on every production batch.

Contact Our Engineering Team

For technical datasheets, calibration support, or a formal quotation on outsole and whole-shoe testing machinery:

• Official Website: https://www.greatwin-test.com/

• Technical Inquiries: Vincent-zhong@greatwin-test.com

• WhatsApp / Direct Support: +86 13296639265