Engineering Solid Tire Compound Design: Tread, Middle, and Base Compounds

Engineering Solid Tire Compound Design: Tread, Middle, and Base Compounds

Engineering solid tires are used in mines, construction sites, and other harsh environments where punctures, chunking, and blowouts are common. This article presents a three-compound formulation (tread / middle / base) using NR/SBR/BR blends with N326/N550/VN3 silica, meeting GB/T 10824-2008 for 12.00-20 solid tires.

Keywords: solid tire; engineering tire; tread compound; NR/SBR/BR; N326; silica; Si-69; anti-reversion agent; chunk resistance; cut resistance

Why Solid Tires?

In mining and construction environments, pneumatic tires suffer puncture damage, chunking, and bead blows — often leading to catastrophic failure. Engineering solid tires offer excellent puncture resistance and large abrasion volume. Because they are non-pneumatic, a severe puncture cannot cause a blowout, protecting vehicle operators.

Engineering vehicles operate in small-radius loops on rough terrain under heavy load. Beyond puncture damage, the tire generates significant compressive fatigue heat. Adding 20–30% compensated carbon black (relative to total CB) improves tear resistance and cut-growth resistance. When using silica, the bifunctional silane coupling agent Si-69 reacts with silica surface hydroxyl groups, converting silica from hydrophilic to hydrophobic and improving rubber compatibility.

Raw Materials and Formulation

Polymers: NR STR20, BR9000, SBR1502. Fillers: N326, N660 carbon black, VN3 silica. Chemicals: phenolic reinforcing resin, anti-tear resin SL-6903, silane Si-69, anti-reversion agent PK-900.

Three-Compound Formulation (phr)

Material Tread Middle Base
NR 80 65 70
SBR1502 10 — 30
BR9000 10 35 —
N326 37 48 —
N660 — — 60
Silica (VN3) 25 15 15
Zinc oxide 5 7 10
Stearic acid 2 2 2
RD antioxidant 2 2 2
4020 2 1.5 1.5
Si-69 coupling agent — 1.5 1.5
Anti-tear resin 2.5 — —
Sulfur 1.8 1.6 1.6
Accelerator 1.6 1.6 1.6
PK-900 anti-reversion 0.5 — 0.5

Mixing Process

Tread Compound — Low-Temperature Continuous Line (GK305)

Polymer + fine ingredients (anti-tear resin, ZnO, stearic acid, antioxidants, PK-900) → ram up 20s at 55 rpm → add silica, carbon black, Si-69 → ram down → dump at 135°C → slow to 25 rpm → ram down → dump at 150°C → sheet into rings → add pre-dispersed scorch retarder (2 min) → add pre-dispersed sulfur (2 min) → add accelerator (3 min) → sheet and cool.

Middle and Base Compounds — Two-Stage on F270

First stage (40 rpm): polymer + ZnO/stearic/antioxidants → ram 40s → add silica, CB, Si-69 → ram → 120°C ram up 10s → ram → dump at 145°C, rest 8h.

Second stage (20 rpm): masterbatch + sulfur/accelerator → ram 90s → ram up 10s → ram → dump at 105°C.

Key Results — Laboratory Recipe (small-scale)

Property Tread (60 min cure) Middle (60 min) Base (60 min)
M100% (MPa) 3.4 4.1 9.8
M300% (MPa) 11.8 15.6 —
Tensile strength (MPa) 24.8 21.9 14.6
Elongation at break (%) 532 501 183
Tear strength (kN/m) 101.2 50.2 41.3
Shore A hardness 70 65 88
Rebound (%) 50 55.8 32
Akron abrasion (cm³) 0.226 — —
Heat buildup — center (°C) 49.7 43.2 —
Heat buildup — bottom (°C) 10.6 12.0 —

Production-Scale Results (large batch)

Large-batch data matched small-batch results closely. Because low-temperature mixing was used, tensile strength was slightly better and dispersion grade improved (grade 5–6). Low-temperature mixing significantly reduces silica agglomeration in high-silica formulations.

Finished Tire Performance (12.00-20/8.0)

Property Tread — Measured Tread — GB/T 10824 Base — Measured Base — Standard
Tensile strength (MPa) 24.1 ≥18 14.1 ≥13
Elongation at break (%) 512 ≥450 179 —
Shore A hardness 69 67±5 89 85±5
Rebound (%) 49.6 — 32.5 —
Akron abrasion (cm³) 0.232 ≤0.6 — —

All properties exceed GB/T 10824-2008 requirements. Tensile strength and abrasion resistance far exceed the standard, extending service life in harsh mining/construction environments.

Formulation Rationale

  • N326 instead of N220 in the tread: higher tensile, elongation, and tear strength; lower heat buildup; better endurance and longer service life.
  • Si-69 coupling agent bridges silica surface to polymer, creating more filler-polymer bonds, reinforcing modulus and tensile strength, and improving abrasion.
  • Higher ZnO in middle compound (7 phr vs 5 in tread): reduces the temperature difference between surface and center during fatigue, extending tire life.
  • PK-900 anti-reversion agent in tread and base: prevents reversion during long cures (60–100 min) at 145°C.
  • Three-compound design (tread/middle/base): the middle compound provides low heat buildup and good buffering, lowering overall tire operating temperature vs. conventional two-compound solid tires.

Conclusion

The series includes 12.00-20, 11.00-20, and 10.00-20 small-to-medium engineering solid tires. They offer excellent abrasion resistance and superior chunk/cut resistance. The added middle compound layer (low heat buildup, good buffering) reduces overall operating temperature compared to standard solid tires, extending service life.

/0 Comments/by

Natural Rubber Compound Formulation Design: Vulcanization, Fillers & Protection

Natural Rubber Compound Formulation Design: A Practical Guide

Natural rubber (NR) is an unsaturated, crystallizable diene rubber with excellent elasticity, high mechanical strength, and superior processing characteristics. It is the oldest and most widely used rubber type. This guide covers the four core formulation systems: vulcanization, reinforcement/filling, protection, and plasticization.

Keywords: natural rubber; NR; compound formulation; vulcanization system; sulfur cure; carbon black; antioxidant; plasticizer; rubber recipe design

1. Vulcanization System

Curing agents suitable for natural rubber include sulfur, selenium, tellurium; sulfur donors; organic peroxides; ester-type; and quinone-type curing systems. The choice depends on the required product properties.

Sulfur vulcanization systems vary by the ratio of accelerator to sulfur, producing three characteristic systems:

Conventional Sulfur Cure (High Sulfur / Low Accelerator)

Uses high sulfur and low accelerator. Crosslinks are predominantly polysulfidic bonds. The uncured compound has good general physical-mechanical properties: high strength, good elasticity, high abrasion resistance, and low cost. However, heat resistance and aging resistance are poor, and reversion during cure is significant. Because NR has high unsaturation, sulfur loading can be higher than in synthetic rubber — typically 2–3 phr (commonly 1.75–2.75 phr) for soft rubber products. Accelerator loading is below 1 phr.

Common accelerators: M, DM, CZ, NOBS, D, TT. They can be used alone or in combinations such as DM, D/TS, D/DM, M/H, M/TT, M/TS, CZ/TT, DM/D/H, DM/M/TT, DM/TT, CZ/DM, NOBS/DM.

Semi-Efficient Cure (semi-EV)

Intermediate between conventional and efficient cure. Uses medium sulfur loading (1–1.7 phr) with accelerator. Crosslinks contain both polysulfidic and mono/disulfidic bonds. The vulcanizate combines heat resistance, fatigue resistance, and reversion resistance — widely used. Typical recipes: S/NS (1.5/1.5), S/NS/DTDM (1.5/0.6/0.6).

Efficient Cure (EV)

Low sulfur / high accelerator ratio, producing mainly mono- and disulfidic crosslinks with excellent heat aging and reversion resistance, but lower tensile strength and dynamic fatigue resistance.

Effect of Sulfur Loading on NR Vulcanizate Properties

Sulfur (phr) 1.0 1.5 2.0 2.5 3.0 3.5 4.0
M300% (MPa) 6.4 7.3 8.0 9.1 10.0 11.5 12.8
Tensile strength (MPa) 26.0 28.3 29.6 31.5 31.1 31.1 31.6
Elongation at break (%) 670 672 660 660 670 670 660
Permanent set (%) 23 29 34 34 42 42 46
Shore A hardness 57 60 64 64 68 68 69

Accelerator: DM 0.5 phr + M 0.5 phr.

Other Cure Systems

  • Ester-type (urethane) cure: Addition products of diisocyanates (TDI, MDI) and p-nitrosophenol. Provides good reversion resistance, heat resistance, and aging resistance. Improves adhesion to cords, fabrics, and steel.
  • Maleimide cure: High-temperature cure system with excellent reversion resistance, thermal stability, low compression set, and good glass-fiber adhesion. Most effective: N,N’-m-phenylene dimaleimide and 4,4′-dithiodiphenyl maleimide.
  • Organic peroxide cure: DCP (dicumyl peroxide) at 2–4 phr forms C-C crosslinks. Provides excellent thermal stability, heat aging, low creep, low compression set, and good dynamic properties. Fast cure speed, high crosslink efficiency.

Sulfur cures typically use zinc oxide 2–5 phr and stearic acid 1–3 phr as activators.

2. Reinforcement and Filling System

Porous powder quartz (natural amorphous silica) improves physical properties with high fineness, high activity, and low specific gravity. It can partially replace carbon black and silica to reduce cost.

Carbon Black Selection

Requirement Recommended Carbon Black
High abrasion resistance N110 (SAF), N220 (ISAF), N330 (HAF)
High tear resistance Channel black best
Lower strength, high elasticity, good processing N550 (FEF), N660 (GPF), N770 (SRF)

When selecting carbon black, consider particle size, structure, surface activity, and pH. pH affects cure speed — adjust the cure system accordingly. For furnace blacks, use delayed-action accelerators in moderate dosage.

Light-Colored Compounds

For light or bright-colored products, use precipitated silica, highly dispersible silica, or ultra-fine porous quartz. When using precipitated silica, add organo-activators such as diethylene glycol (DEG), glycerin, ethanolamine, or polyvinyl alcohol at 5–10% of silica loading to adjust cure speed.

For maximum tensile strength, filler loading of 40–45 phr is optimal; excessive loading reduces strength. For low-strength, low-cost products, add clay or CaCO3 to reduce rubber content.

3. Protection System

Because NR is unsaturated, it readily reacts with oxygen and ozone, causing aging. Heat, light, flexing, and metal ions (manganese, copper) accelerate degradation. Antioxidants must be selected based on actual service conditions:

  • General antioxidants: D, A, DNP, 4010, 4010NA, AW, MB, SP, SP-C, RD
  • Can be used alone or in combinations
  • For light-colored products, choose non-staining antioxidants

4. Plasticizing / Softening System

Physical Plasticizers

Used for processing benefits: tackiness, softness, easier mixing/calendering/extrusion, and hardness adjustment. Common types: pine tar and solid coumarone-indene resin at 4–5 phr; petroleum-based softeners at 5–15 phr.

Chemical Plasticizers (Peptizers)

Smoked sheet and crepe natural rubber have high Mooney viscosity, making mastication difficult. Traditional addition of accelerators M and DM is not effective. Chemical peptizers improve mastication efficiency and shorten cycle time. Common peptizers for NR: SJ-103 (works on both open mills and internal mixers) and 12-I (internal mixer only), at 0.1–0.3 phr.

Summary

Natural rubber formulation design balances four systems:

  1. Vulcanization: Choose conventional / semi-EV / EV based on heat aging vs. strength trade-off; sulfur loading directly modulates M300, hardness, and permanent set.
  2. Reinforcement: Match carbon black grade to abrasion/tear/elasticity needs; use silica for light colors; 40–45 phr for maximum strength.
  3. Protection: Select antioxidants based on aging environment; use non-staining grades for light colors.
  4. Plasticization: Physical softeners for processing; chemical peptizers for high-Mooney NR mastication.
/0 Comments/by

Four SSBR Grades in High-Performance Tire Tread: Comparative Study

Four SSBR Grades in High-Performance Tire Tread Compounds: A Comparative Study

This study compares four solution styrene-butadiene rubber (SSBR) grades (SOL5251H, SOL5360H, SOL5271H, SOL6440H from Kumho Petrochemical) in high-dispersible silica-filled tread compounds, evaluating processing, cure, mechanical properties, wet grip, rolling resistance, and wear.

Keywords: SSBR; solution SBR; high-performance tire; tread compound; wet grip; rolling resistance; silica; Payne effect

Introduction

Modern high-performance tires are judged on three core metrics: wet grip, rolling resistance, and wear. Each wet grip grade improvement shortens braking distance by 3–5 m; each rolling resistance grade improvement saves ~17 L gasoline per tire per 50,000 km (~68 L per vehicle). BR has low hysteresis and good wear but poor wet grip; NR has high strength but inadequate wet grip. SSBR offers controllable microstructure — styrene and vinyl content can be tuned independently. Higher vinyl content raises Tg for better wet grip without the heat buildup caused by high styrene. Narrow molecular weight distribution means fewer low-molecular-weight chains and lower hysteresis, making SSBR the preferred matrix for high-performance treads.

Experimental

Materials

Material Grade Supplier
SSBR (dual-end modified, non-oil-extended) SOL5251H Kumho Petrochem
SSBR (dual-end modified, non-oil-extended) SOL5360H Kumho Petrochem
SSBR (dual-end modified, non-oil-extended) SOL5271H Kumho Petrochem
SSBR (single-end modified, 37.5 phr treated distillate aromatic extract oil) SOL6440H Kumho Petrochem
High-dispersion silica HD165MP Fujian Zhengsheng

Formulation (phr): SSBR 100; silica 80; silane coupling agent 12.8; naphthenic oil 37.5; activator 5; antioxidant 3; sulfur 1.5; accelerator 4.

Mixing: Two-stage. First stage: 90 rpm, 60°C cooling, dump at 150°C. Second stage: 40 rpm, add sulfur + accelerator, dump ≤105°C. Cure: 161°C, 20 min (2 mm sheets / DIN abrasion), 30 min (mechanical specimens).

Results and Discussion

Raw Polymer Properties

Property 5251H 5360H 5271H 6440H
Styrene content 0.210 0.285 0.210 0.355
Vinyl (1,2-butadiene) content 0.43 0.41 0.50 0.26
Tg (°C) -30 -21 -24 -26
Mw (×10⁴) 47.9 43.8 45.3 110.9
PDI (Mw/Mn) 1.54 1.41 1.35 2.29

5360H has elevated styrene (higher Tg). 5271H keeps styrene at 5251H level but greatly increases vinyl. 6440H has the highest styrene and lowest vinyl, with very high Mw (1.1 million) and broader PDI — high green strength but harder processing. 5251H/5360H/5271H have narrow PDI, favoring low hysteresis.

Cure Characteristics

Property 5251H 5360H 5271H 6440H
Mooney ML(1+4)@100°C 73 73 76 88
Scorch t5 @127°C (min) 26.6 21.1 23.1 18.6
Fmax-FL (dN·m) 13.2 13.2 13.4 14.6

6440H has the highest Mooney viscosity (from massive molecular chain entanglement), shortest scorch time (narrower processing window), and highest crosslink density.

Physical Mechanical Properties

Property 5251H 5360H 5271H 6440H
Shore A hardness 59 59 58 62
M300% (MPa) 15.0 16.9 16.6 14.5
Tensile strength (MPa) 19.2 18.9 18.1 23.2
Elongation at break (%) 357 327 313 429
Tear strength (kN/m) 33 30 29 43
Rebound (%) 39 26 30 25
DIN abrasion index (higher=better) 149 125 139 141

6440H has the highest hardness, tensile, and tear strength due to ultra-high molecular weight. Compared to 5251H, 5360H and 5271H show higher M300 but lower rebound and wear — chain stiffness increases. 6440H’s single-end modification gives weaker filler-rubber interaction (lower M300 than 5271H) but its massive Mw delivers the best strength.

Dynamic Mechanical Properties

Property 5251H 5360H 5271H 6440H
Cured Tg (°C) -17 -9 -12 -12
tanδ @ 0°C (wet grip index) 0.555 0.902 0.755 0.722
tanδ @ 60°C (RR index) 0.088 0.093 0.091 0.101
Compression heat buildup (°C) 20.1 18.3 19.0 21.5
ΔG’ Payne effect (kPa) 557 535 440 1152

Wet grip ranking: 5360H > 5271H > 6440H > 5251H. Styrene content contributes more to 0°C tanδ than vinyl at similar Tg.

Rolling resistance: 5251H is best (lowest 60°C tanδ). Both higher styrene and higher vinyl slightly increase 60°C tanδ. Despite same raw Tg, 6440H has significantly higher RR than 5271H due to its strong filler network (Payne effect ΔG’ = 1152 kPa, more than double the others).

Conclusions

  1. SSBR5251H: Lowest Mooney, best processability; highest rebound and DIN wear; lowest rolling resistance; lowest Tg means weaker wet grip. Best for low-RR-oriented tread compounds.
  2. SSBR5360H: High styrene; processability similar to 5251H; higher M300, slightly lower wear; dramatically higher 0°C tanδ (best wet grip), with only modest RR penalty. Best for high-wet-grip treads.
  3. SSBR5271H: High-vinyl dual-end modified; higher M300, slightly lower wear; combines good wet grip with low rolling resistance — the balanced all-rounder.
  4. SSBR6440H: Ultra-high molecular weight, highest Mooney, shortest scorch, narrowest processing window; best tensile and tear strength, decent wear; same raw Tg as 5271H but strong Payne effect (poor silica dispersion) means higher RR and heat buildup.

 

/0 Comments/by