Oil Resistant Conveyor Belt: NBR Grades, Applications & How to Choose the Right Belt

2026-03-23 10:36:02

oil resistant conveyor belt: NBR Grades, Applications & How to Choose the Right Belt

Oil is one of the most destructive substances a rubber conveyor belt can encounter. When standard rubber contacts petroleum oils, animal fats, or vegetable oils, the rubber matrix absorbs the oil and swells — sometimes expanding in volume by 30% or more. This swelling softens the cover, destroys the bonding between plies, causes the belt to track erratically, and leads to rapid structural failure.

The oil resistant Conveyor Belt is specifically engineered to resist this degradation. Using oil-compatible rubber compounds — primarily Nitrile Butadiene Rubber (NBR) — these belts maintain their physical properties, dimensional stability, and service life even under sustained oil contact.

This guide explains how oil resistant belts work, the grading system used to classify them, which industries rely on them, and how to select the right specification from a qualified oil resistant conveyor belt supplier.

How Oil Damages Standard Rubber Conveyor Belts

To understand why oil resistant belts are necessary, it helps to understand the failure mechanism in standard rubber when oil is present.

Natural rubber (NR) and styrene-butadiene rubber (SBR) — the most common compounds in standard conveyor belt covers — have a non-polar polymer structure. Oil is also non-polar. Following the fundamental chemistry principle that "like dissolves like," oil molecules penetrate and are absorbed into the rubber polymer chains, causing:

• Volume swell: The belt cover expands, becoming soft and spongy. This uneven swelling causes the belt to cup, bow, or twist, making tracking impossible.

• Tensile strength loss: Oil-swollen rubber loses much of its structural integrity. Impact resistance drops dramatically.

• Ply delamination: Oil migrating through the cover eventually attacks the adhesive bonds between the cover and carcass, causing layers to separate.

• Accelerated wear: A softened, oil-saturated cover wears far more rapidly than normal rubber, even under moderate abrasion loads.

In food processing, chemical plants, oil sand operations, and similar environments, a standard belt can fail within days or weeks of first contact with oily materials. The correct oil resistant belt in the same application may run for two to four years.

Oil Resistance Grades: MOR vs. SOR

Oil resistant conveyor belts are classified into two standard grades based on the degree of oil resistance required. The most widely referenced standard is ISO 340 alongside DIN 22102 and GB/T 7984.

MOR — Moderate Oil Resistance

• Compound base: NBR blend or modified SBR with oil-resistant additives

• Volume swell limit: Maximum 12% volume increase after 72-hour immersion in reference oil at 70°C (per ISO standard testing)

• Suitable for: Materials with incidental or moderate oil contact — greasy bulk solids, oily seeds and grains, slightly oiled mechanical parts

SOR — Strong Oil Resistance

• Compound base: High-NBR content compound (typically 30–50% acrylonitrile content)

• Volume swell limit: Maximum 6% volume increase under the same test conditions

• Suitable for: Direct and sustained contact with petroleum oils, heavy greases, cutting fluids, fish meal and animal fats, oil-contaminated ores

Which Grade Do You Need?

Situation

Rule of thumb: When in doubt between MOR and SOR, specify SOR. The cost difference is modest; the performance difference in demanding applications is significant.

NBR: The Key Compound in Oil Resistant Belts

Nitrile Butadiene Rubber (NBR) is the foundation material for all serious oil resistant conveyor belt applications. Its oil resistance comes from the presence of polar acrylonitrile groups in the polymer chain, which repel non-polar oil molecules rather than absorbing them.

Acrylonitrile Content and Performance

The oil resistance of NBR increases with higher acrylonitrile (ACN) content:

ACN Content

Important trade-off: Higher ACN content improves oil resistance but reduces low-temperature flexibility. For applications in cold climates or refrigerated environments, confirm that the specified compound remains flexible at your lowest operating temperature.

What NBR Does Not Resist

It is equally important to understand the limitations of NBR compound:

• Heat resistance: Standard NBR begins to degrade above 100°C. For combined oil and high-temperature applications, a special HNBR (hydrogenated NBR) or ACM compound may be required — consult your manufacturer.

• Strong acids and bases: NBR has limited resistance to concentrated acids or alkaline solutions. For oil plus chemical applications, confirm compatibility.

• Aromatic hydrocarbons: Benzene, toluene, and similar aromatic solvents cause significant swelling even in high-ACN NBR. For aromatic solvent environments, a different compound class is needed.

Carcass Selection for Oil Resistant Belts

The oil resistant rubber cover protects the carcass from direct oil contact, but oil migration through damaged areas or via the belt edges can still affect carcass performance. Consider the following:

Polyester (EP) fabric carcass: The standard choice for most oil resistant applications. Polyester itself has good resistance to oil and most chemicals, and its low elongation minimizes belt tension variation.

Nylon (NN) carcass: Suitable for shorter, higher-impact applications. Nylon is also reasonably oil-resistant, though its higher elongation requires more active take-up maintenance.

Edge sealing: In oil-saturated environments, specify that the belt edges are sealed with oil-resistant compound to prevent capillary migration of oil into the carcass along the cut edge. This is especially important in immersive or splash-intensive applications.

Cover thickness: Thicker covers extend the time before oil can migrate to the carcass after surface damage. A minimum of 4–6 mm top cover is typical for SOR grade applications; 6–8 mm is recommended for heavy oil contact environments.

Key Industries and Applications

Food Processing

One of the largest application sectors for oil resistant belts globally. Animal fats, cooking oils, fish oil, and meat processing by-products all attack standard rubber rapidly. Key requirements in food processing:

• SOR grade compound

• Food-safe certification: The rubber compound must comply with food contact regulations (e.g., FDA 21 CFR, EU Regulation 10/2011, or equivalent) — not all NBR compounds are food-safe; confirm this explicitly with your supplier

• Good cleanability — smooth cover surface, no surface cracks that harbor bacteria

• Resistance to cleaning chemicals (caustic wash solutions used in food plants)

Oil Sands and Mining

Oil sands operations in Canada, Venezuela, and elsewhere present one of the most demanding environments for conveyor belts — highly abrasive tar-saturated ore at elevated temperatures. Requirements:

• SOR grade with high abrasion resistance

• Often combined with heat resistance (warm oil sands extraction process)

• Heavy covers (8–12 mm top cover typical) to handle sharp aggregate in the ore matrix

Chemical Industry

Conveying petroleum-based chemicals, waxes, rubber crumb, and polymer granules often involves sustained oil and solvent contact. Confirm the specific chemical compatibility of the NBR compound with your materials before specifying.

Automotive Manufacturing

Assembly line conveyors transporting oiled components, stampings, and machined parts require MOR or SOR grade belts depending on the degree of oil contamination.

Fertilizer and Agriculture

Some fertilizer raw materials and processed organic products contain natural oils and fats that attack standard rubber over time. MOR grade belts are typically sufficient for most fertilizer applications.

Installation and Maintenance Considerations

Splice selection: Oil resistant belts must use vulcanized splices with oil-resistant splice compound. Standard NR/SBR splice kits are chemically incompatible with NBR belt compounds — using them results in splice failure within weeks. Always specify NBR-compatible splice kits and confirm with your supplier.

Belt cleaning: Effective belt cleaning is especially important in oil-contaminated environments. Oil-soaked carry-back material is highly adhesive and can build up rapidly under the belt, on idlers, and on the structure, creating fire hazards and causing tracking problems. Install appropriate belt cleaners and ensure they are maintained.

Storage: Unused NBR belt rolls should be stored away from petroleum products, solvents, and ozone-generating equipment. NBR has good ozone resistance, but prolonged storage in contaminated environments can degrade the surface. Store rolls upright or on proper rack supports to avoid flat-spotting.

Frequently Asked Questions

Can I use an oil resistant belt for general (non-oily) applications? Yes, technically — an SOR belt will function perfectly well on a dry aggregate conveyor. However, the cost premium over a standard belt is rarely justified unless there is genuine oil contact. NBR compound also has somewhat lower abrasion resistance than premium SBR/NR abrasion-grade compounds, so for highly abrasive dry material with no oil, a standard abrasion-grade belt may actually outlast an oil resistant belt.

How do I know if my current belt is failing due to oil damage? Key signs: belt cover becomes soft and swollen (presses in easily with a finger, does not spring back), belt edges begin to curl or cup, unusual tracking problems that cannot be corrected by standard adjustments, and rapid delamination of the top cover. If you observe these symptoms, have the belt compound tested — or simply switch to the appropriate oil resistant grade.

What is the difference between an oil resistant belt and a chemical resistant belt? Oil resistant belts (NBR compound) are optimized for petroleum oils, fats, and greases. Chemical resistant belts use different compound bases — such as CR, EPDM, or CSM — for resistance to acids, alkalis, and specific solvents. Some specialty compounds offer both oil and chemical resistance simultaneously, but always confirm compatibility with your specific materials.

Can oil resistant belts operate outdoors? Standard NBR has moderate ozone and UV resistance — acceptable for most outdoor applications. For long-term outdoor exposure in high-UV environments, specify a belt with an ozone and weather-resistant outer compound, or inquire about HNBR compound options which offer improved weathering resistance.

Conclusion

Selecting the correct oil resistant conveyor belt requires more than just ordering a "NBR belt." Specifying the right ACN content for your oil type, confirming food-grade compliance if required, matching the carcass to your load conditions, and ensuring splice compatibility with NBR compound are all critical steps that determine whether your belt lasts for years or fails in months.

As an experienced oil resistant conveyor belt supplier, we manufacture MOR and SOR grade belts to DIN 22102 and ISO 340 standards, with food-grade compound options available. Our technical team is ready to help you specify the optimal belt for your exact application.

Contact us today with your material data and conveyor specifications to receive a tailored recommendation and competitive quotation.