NBR (nitrile butadiene rubber) abrasion resistance testing evaluates the wear durability of one of the most widely used oil-resistant synthetic rubbers in seals, hoses, gaskets, and industrial components. This article provides a professional overview of NBR abrasion test samples, testing items, internationally recognized methods such as ISO 4649, ASTM D5963, and DIN 53516, and the practical applications that depend on accurate wear performance data.
Technical Overview
Nitrile butadiene rubber (NBR) is a copolymer of acrylonitrile and butadiene, valued primarily for its excellent resistance to oils, fuels, and hydraulic fluids. Beyond oil resistance, NBR also delivers good tensile strength, tear resistance, and abrasion resistance, which makes it a preferred material for dynamic components such as oil seals, O-rings, hydraulic hose covers, conveyor belt scrapers, and printing rolls. Because many NBR parts operate under continuous sliding, rolling, or rubbing contact, abrasion resistance is one of the most critical performance indicators in material qualification and quality control.
Abrasion in rubber is a complex process involving cutting, tearing, fatigue, and material removal caused by friction against a counter-surface or abrasive medium. The wear behavior of NBR depends on multiple formulation and processing factors, including acrylonitrile content, type and loading of reinforcing fillers such as carbon black, crosslink density, cure system, and the degree of dispersion achieved during mixing. Laboratory abrasion testing provides a standardized, repeatable way to quantify wear resistance through parameters such as relative volume loss and abrasion resistance index, allowing engineers to compare compounds, verify supplier consistency, and predict product service life.
Testing Samples
Standard Molded Test Pieces
For drum-type abrasion tests such as ISO 4649 and ASTM D5963, the standard specimen is a cylindrical disc typically 16 mm in diameter and at least 6 mm thick. These specimens are usually cut from vulcanized rubber sheets with a thickness of approximately 6 to 8 mm, using a rotary cutter to ensure clean, perpendicular edges. Standard test pieces guarantee uniform geometry so that results from different laboratories remain comparable.
Finished Product Specimens
Specimens may also be taken directly from finished products such as seals, hose covers, rollers, or belting. Where the product geometry does not permit a full-size disc, smaller samples can be tested provided they can be securely clamped and present a flat test surface. Testing on actual product material is useful for incoming inspection, failure analysis, and verification that processing conditions have not degraded the intended wear performance.
Compound Development Plaques
During formulation development, cured plaques of trial NBR compounds are molded under controlled time, temperature, and pressure. These plaques allow systematic evaluation of how variables such as carbon black type, filler loading, plasticizer content, and acrylonitrile level influence abrasion resistance, enabling formulation optimization before production scale-up.
Testing Items
A comprehensive NBR abrasion resistance evaluation typically includes the following measured and calculated items:
- Relative volume loss (RVL), expressed in mm³, representing the volume of rubber worn away under defined test conditions
- Abrasion resistance index (ARI), the ratio of the volume loss of a standard reference compound to that of the test compound, expressed as a percentage
- Mass loss of the specimen before and after the abrasion cycle, measured with a precision balance
- Specific abrasion rate normalized against applied force and sliding distance for comparison across test conditions
- Surface morphology assessment of the worn track, including patterns of ridging, cracking, or smearing that reveal the dominant wear mechanism
- Comparative testing against reference compounds or competitor materials for benchmarking purposes
Additional supporting measurements, such as hardness (Shore A), density, tensile strength, and elongation at break, are often performed alongside abrasion testing because wear behavior correlates strongly with these fundamental properties.
Testing Methods
Rotating Cylindrical Drum Method (DIN Abrasion)
The most widely used method for NBR is the rotating cylindrical drum test described in ISO 4649, DIN 53516, and ASTM D5963. A cylindrical specimen is pressed against the surface of a rotating drum covered with a specified abrasive cloth, typically a 60-grit garnet paper, with a force of 10 N. The specimen traverses along the drum for a defined abrasion path length of 40 m, either remaining in a fixed orientation or rotating about its own axis during the test. The mass loss is converted to volume loss using the measured density of the rubber, and the relative volume loss is calculated and reported in mm³. Lower volume loss values indicate better abrasion resistance. Calibration using standard reference compounds is required to verify the aggressiveness of the abrasive sheet and ensure valid comparisons between test runs.
Akron Abrasion Method
The Akron abrasion test subjects a rubber disc to rubbing contact against an abrasive wheel mounted at a small angle, producing a combination of rolling and sliding friction. The specimen weight loss over a specified number of revolutions is measured and converted to volume loss. This method is particularly relevant for components such as tire treads and heavy-duty conveyor components that experience combined rolling and sliding wear.
Taber Rotary Platform Method
In the Taber method, a flat disc-shaped specimen is mounted on a rotating platform and abraded by a pair of weighted abrasive wheels. The test is common for rubber sheets, flooring, coatings, and finished surface layers. Results are reported as weight loss per specified number of cycles or as a wear index, and the method offers flexibility in wheel type and applied load to simulate different service conditions.
Pico and Footwear Abrader Methods
The Pico abrasion method (ASTM D2228) uses tungsten carbide knives to abrade the rubber surface under controlled loads, and is well suited to evaluating highly wear-resistant compounds with high filler loadings. For NBR-based soling and footwear applications, the NBS footwear abrader method (ASTM D1630) measures wear against a standardized abrasive drum and is widely referenced in shoe sole specifications.
Test Condition Control
Regardless of the method selected, several conditions must be strictly controlled to obtain reliable data:
- Specimen conditioning at 23 ± 2 °C and 50 ± 5% relative humidity for a minimum of 16 hours before testing
- Verification and replacement of abrasive media at prescribed intervals, since worn abrasive surfaces reduce cutting efficiency and distort results
- Clean removal of loose debris from the specimen before weighing, without disturbing the worn surface
- Accurate density determination for correct conversion of mass loss to volume loss
- Performance of replicate tests, typically three specimens per material, with results averaged and outliers investigated
Applications
Abrasion resistance testing of NBR supports material selection and quality assurance across a broad range of industries:
- Oil seals, rotary shaft seals, and bearing seals where worn lip surfaces lead directly to leakage and equipment failure
- Hydraulic hoses and fuel lines whose outer covers must resist rubbing, flexing, and contact with adjacent structures
- Conveyor belts, scraper blades, and skirt liners used in mining, aggregate, and bulk material handling
- Printing and industrial rubber rolls that must maintain precise surface geometry under continuous contact
- Footwear components, anti-slip soles, and protective linings requiring documented wear durability
- Automotive components including bushings, grommets, diaphragms, and CV joint boots exposed to abrasive road environments
- Gloves and protective equipment where coating durability affects both service life and user safety
By quantifying wear performance against recognized international standards, manufacturers can set objective acceptance criteria, support product certifications, reduce field failures, and substantiate marketing claims regarding product durability.
FAQ
What is considered a good abrasion resistance value for NBR?
For general-purpose NBR compounds tested under the DIN/ISO 4649 drum method, relative volume loss values commonly fall in the range of 60 to 200 mm³. High-quality, carbon black reinforced NBR can achieve values below 100 mm³, indicating excellent wear resistance. Acceptance limits should always be defined relative to the specific standard, abrasive conditions, and application requirements, since values are not directly transferable between different test methods.
How does acrylonitrile content affect NBR abrasion resistance?
In general, increasing acrylonitrile content improves hardness, tensile strength, and oil resistance, which often enhances abrasion resistance, while lower acrylonitrile grades provide better low-temperature flexibility. The effect is formulation-dependent, and filler type and loading usually exert an even stronger influence on wear performance than acrylonitrile level, which is why empirical testing is essential for compound optimization.
Which abrasion test standard should be chosen for NBR products?
The rotating drum method (ISO 4649, DIN 53516, ASTM D5963, or the equivalent GB/T 9867) is the default choice for most molded and extruded NBR components because of its broad international acceptance and extensive comparative database. Taber testing is preferred for flat sheet materials and surface coatings, while Akron, Pico, or footwear abrader methods are selected for specific product classes such as heavy-duty treads, high-durability compounds, or soling materials.
How are mass loss and volume loss related in the test report?
The specimen is weighed before and after abrasion to determine mass loss. This value is divided by the measured density of the rubber to obtain volume loss, which is the reported parameter because it eliminates the influence of compound density differences. The abrasion resistance index is then calculated as the volume loss of the standard reference rubber divided by that of the test rubber, multiplied by 100.
What sample dimensions and quantities are required?
For the drum method, cylindrical specimens of 16 mm diameter and at least 6 mm thickness are standard, with a minimum of three specimens recommended per material to assess variability. Thinner products may be bonded to a rigid backing or tested with adjusted procedures, provided the total specimen height remains within the instrument specification. Testing laboratories should always confirm feasibility when submitting finished parts rather than standard sheets.