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)

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)

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)

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.