NR SA70
Hardness band
SA70 = shore A 70
Stiffer black stock for load-bearing pads, wheel treads and abrasion liners.
Values for the SA70 condition
Other NR grades and fills
NR is listed in 14 conditions; see the grade overview at NR.
Compare all 14 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
NR sponge / closed-cell foam | Blown NR for cushioning, sealing strips and anti-vibration pads where low density beats strength. | — | 2 | 200 | 25 Shore A |
TSR20 / SCR20 raw block rubber | Standard technically specified raw bale traded on SHFE/SICOM — the feedstock grade compounders buy. | — | 3 | 900 | 30 Shore A |
RSS3 ribbed smoked sheet | Visually graded smoked-sheet raw rubber, preferred for truck tire and high-green-strength compounds. | — | 3 | 900 | 32 Shore A |
Flame-retardant NR compound | ATH/halogen-loaded NR for mining conveyor belts, cable jackets and transit parts needing flame/smoke ratings. | — | 12 | 350 | 20 Shore D |
Shore A 90 | Near-rigid rubber for wear plates, mill liners and metal-bonded stiff mounts. | — | 17 | 230 | 38 Shore D |
Shore A 80 | High-modulus stock for bridge bearings, heavy-duty bushings and roll covers. | — | 20 | 350 | 30 Shore D |
Peroxide-cured NR | Choose when low compression set and better heat ageing matter more than tensile/tear. | — | 20 | 500 | 55 Shore A |
Shore A 40 | Soft, highly resilient stock for low-stiffness mounts, diaphragms and soft rollers. | — | 22 | 700 | 40 Shore A |
Synthetic cis-polyisoprene | Protein-free, consistent synthetic equivalent of NR for medical/latex-allergy and clean applications; slightly lower green strength and tear. | — | 22 | 700 | 50 Shore A |
SA70This page Shore A 70 | Stiffer black stock for load-bearing pads, wheel treads and abrasion liners. | — | 23 | 450 | 22 Shore D |
GUMDefault Gum / unfilled NR vulcanizate | Baseline unfilled sulfur-cured NR — highest elongation and resilience, used for rubber bands, gum sheeting, tubing and vibration springs. | — | 24 | 750 | 40 Shore A |
Shore A 50 | Most common sheet/gasket hardness; best balance of tear, resilience and handling. | — | 25 | 620 | 50 Shore A |
Shore A 60 | Standard black-filled engineering grade for mounts, bushings and conveyor covers. | — | 26 | 550 | 15 Shore D |
Ebonite / hard rubber | 30–40 phr sulfur cure giving a rigid, chemically resistant lining material for tank and pipe linings and battery cases. | — | 50 | 5 | 85 Shore D |
What is NR SA70?
NR SA70 is NR heat treated to SA70 — stiffer black stock for load-bearing pads, wheel treads and abrasion liners. NR SA70 has a tensile strength of 23 MPa (3.34 ksi), weaker than 69% of polymer grades. Elongation at break is 450% and the elastic modulus is 0.01 GPa (8.7×10⁻⁴ Msi). NR SA70 has a density of 1.14 g/cm³ (0.0412 lb/in³), lighter than 60% of polymer grades. Its glass-transition temperature is -70°C (-94 °F). GUM is the default condition FabDigit quotes; SA70 is available on request or by drawing note.
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 98% of polymer grades
- Ductile — tolerates forming and impact — 450%, better than 88% of polymer grades
Limitations
- Degrades in UV without stabilisers — 20/100, worse than 88% of polymer grades
- Low stiffness — 0.01 GPa (8.7×10⁻⁴ Msi), worse than 86% of polymer grades
- Difficult to machine — 35/100, worse than 84% of polymer grades
- Absorbs moisture — dry before molding — 1%, worse than 84% of polymer grades
- Hard to polish — 30/100, worse than 82% of polymer grades
NR SA70 properties
Typical room-temperature values for NR SA70; 18 are specific to this condition. Other listed values are NR reference data and may not represent this condition. Bars are the position among polymer grades.
Physical5
NR SA70 has a density of 1.14 g/cm³ (0.0412 lb/in³), lighter than 60% of polymer grades. Its glass-transition temperature is -70°C (-94 °F).
Mechanical10
NR SA70 has a tensile strength of 23 MPa (3.34 ksi), weaker than 69% of polymer grades. Elongation at break is 450% and the elastic modulus is 0.01 GPa (8.7×10⁻⁴ Msi).
Thermal8
NR SA70 is rated for continuous service to 80°C (176 °F). It conducts heat at 0.22 W/m·K (0.127 BTU/hr·ft·°F), better than 60% of polymer grades. Thermal expansion is 220 µm/m·K (122.2 µin/in·°F).
Electrical6
NR SA70 is an electrical insulator with a dielectric strength of 22 kV/mm (558.8 V/mil) and a resistivity of 1,000,000 Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (70/100), worse than 78% of polymer grades. UV resistance is poor.
Sustainability4
Producing a kilogram of NR SA70 takes about 65 MJ of energy and emits 1.9 kg of CO₂ — less than 95% of polymer grades. Typical recycled content is 5%.
Manufacturability6
NR SA70's machinability is fair (35/100, worse than 84% of polymer grades); weldability poor (15/100); formability very good (75/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with NR SA70
Is NR easy to machine?
Cured NR is die-cut, waterjet or abrasive-ground rather than turned; freeze-trim or cryogenic deflashing gives clean edges, and any turning needs razor-sharp tools with water cooling.
Can NR be welded?
Not weldable — parts are joined by uncured splicing plus press vulcanization, or by CR/cyanoacrylate adhesives and hot-bonded metal inserts (Chemlok primer systems).
Can NR be formed, bent or molded?
Mill-mixed or internally mixed then compression, transfer or injection molded and cured 5–20 min at 140–170 °C; watch reversion at high temperature and allow ~2 % mold shrink.
What surface finishes work on NR?
Surfaces replicate the mold; chlorination or plasma treatment reduces tack and friction, and rubber-to-metal bonding is done with two-coat phenolic primer/adhesive during cure.
NR chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| carbon black (N330/N550)0 phr in gum, 30–60 phr in engineering compounds | 0 – 40 | 20 |
| zinc oxidecure activator, ~5 phr | 1.5 – 4 | 3 |
| stearic acidactivator, ~2 phr | 0.5 – 2 | 1.2 |
| sulfur1.5–2.5 phr conventional cure; 30–40 phr for ebonite | 0.5 – 2.5 | 1.5 |
| accelerator (CBS/TBBS/MBTS) | 0.3 – 1.5 | 0.7 |
| antioxidant / antiozonant (TMQ, 6PPD, wa | 0.5 – 3 | 1.5 |
| process oil / plasticizer | 0 – 10 | 3 |
| non-rubber constituents in raw NR (proteTSR20: dirt ≤0.16 %, ash ≤0.8 %, N ≤0.6 %, volatiles ≤0.8 % | 0.2 – 6 | 5 |
| cis-1,4-polyisoprene (NR)≥99.9 % rubber hydrocarbon in raw bale; 45–70 wt% of a typical vulcanizate | ≥ 45 (balance) | — |
NR SA70 — frequently asked
What is NR SA70 used for?
NR SA70 is typically used for tires, vibration mounts, seals, conveyor belts and shoe soles. In short: highest-resilience general elastomer; 750 % elongation at break; poor oil and ozone resistance.
What is the tensile strength of NR SA70?
NR SA70 has a typical tensile strength of 23 MPa (3.34 ksi) — weaker than 69% of polymer grades. Strength varies by condition: see the 14 listed tempers.
Is NR SA70 easy to machine?
Not especially — machinability is rated fair (35/100, worse than 84% of polymer grades). Cured NR is die-cut, waterjet or abrasive-ground rather than turned; freeze-trim or cryogenic deflashing gives clean edges, and any turning needs razor-sharp tools with water cooling.
Can NR SA70 be welded?
Not readily — weldability is rated poor (15/100). Not weldable — parts are joined by uncured splicing plus press vulcanization, or by CR/cyanoacrylate adhesives and hot-bonded metal inserts (Chemlok primer systems).
What surface finishes work on NR SA70?
Surfaces replicate the mold; chlorination or plasma treatment reduces tack and friction, and rubber-to-metal bonding is done with two-coat phenolic primer/adhesive during cure.
Can NR SA70 be formed, bent or molded?
Mill-mixed or internally mixed then compression, transfer or injection molded and cured 5–20 min at 140–170 °C; watch reversion at high temperature and allow ~2 % mold shrink.
What is the maximum service temperature of NR SA70?
NR SA70 is rated for continuous use to about 80°C (176 °F), and briefly to 100°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
Sources
- ASTM D2000 — Classification System for Rubber Products in Automotive Applications — ASTM (2020)
- ASTM D412 / D624 / D395 / D2240 — tensile, tear, compression set, durometer test methods — ASTM (2022)
- ISO 2000 — Rubber, raw natural: guidelines for the specification of technically specified rubber (TSR) — ISO (2020)
- Rubber Technology (Morton, ed.) — Springer (1999)
- Engineering with Rubber: How to Design Rubber Components (Gent, ed.) — Hanser (2012)
- The Vanderbilt Rubber Handbook, 14th ed. — R.T. Vanderbilt Co. (2010)
- Granta/CES elastomer property and eco-property records — natural rubber — Ansys Granta (2023)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.