Tyre technology and rubber product manufacture

Polymer / Plastics / Rubber Technology (B.Tech) · Polymer processing · free study notes for exams, placements and interviews

In short

Tyre technology is the design, compounding, assembly and vulcanisation of a composite of rubber compounds, textile and steel cord into a pressure vessel that carries load, transmits traction and braking, absorbs road shock and steers a vehicle. The same compounding and curing science makes hoses, belts, seals, gloves, footwear, anti-vibration mounts and rubber linings. It is examined in polymer processing and rubber technology papers (compound recipes in phr, cure kinetics from rheometer curves, tyre construction, defects) and in GATE-level questions on vulcanisation and filler reinforcement. India is the world's largest natural rubber-consuming tyre market after China, and MRF, Apollo, JK Tyre, CEAT, BKT, TVS Srichakra, Bridgestone India and Yokohama India recruit heavily for mixing, building, curing, quality and R&D roles. Tyres carry mandatory BIS certification under the pneumatic tyres and tubes Quality Control Order, and performance (rolling resistance, wet grip, rolling sound) is governed through AIS-142 under the CMVR.

Explained

Rubbers and compounding ingredients

Natural rubber (NR, cis-1,4-polyisoprene): high green strength, strain-crystallising, best tear and fatigue resistance, low heat build-up — backbone of truck tyre treads, carcass and bead compounds. Indian grades: ribbed smoked sheets RSS 1-5 (visual grading) and technically specified ISNR 3L/5/10/20 (ash, dirt, volatile matter, plasticity retention index); regulated by the Rubber Board, Kottayam under the Rubber Act, 1947.
SBR: emulsion (E-SBR 1502, 1712 oil-extended) and solution S-SBR with controlled vinyl/styrene for silica treads — good wet grip and abrasion, poorer tear than NR.
BR (polybutadiene, high-cis): lowest Tg, outstanding abrasion and resilience, poor wet grip and processing — always blended (NR/BR, SBR/BR) in treads and sidewalls.
IIR/halobutyl (CIIR, BIIR): lowest gas permeability and high damping — tubeless innerliner, inner tubes, curing bladders. EPDM: weather and ozone resistance — profiles, hoses, roofing. CR (neoprene): oil/flame resistance. NBR: oil seals. Silicone/FKM: high-temperature seals.
Fillers: carbon black by ASTM designation Nxyz — N = normal curing, first digit = particle-size/surface-area class; N110 (SAF), N220 (ISAF), N330 (HAF) for treads, N550/N660 for carcass, sidewall and extruded goods. Smaller particle = higher surface area = more reinforcement, higher hysteresis and viscosity. Structure measured by DBP absorption, surface area by iodine/N₂ (BET).
Precipitated silica + bis-triethoxysilylpropyl tetrasulphide (TESPT) silane: "green tyre" tread — cuts rolling resistance while keeping wet grip, because silica-silane networks have low hysteresis at 60 °C (rolling) and high at 0 °C (wet grip).
Plasticisers/process oils: TDAE and MES oils have replaced highly aromatic (DAE) oils because of PAH limits in export markets; naphthenic/paraffinic oils and ester plasticisers elsewhere.
Curatives: sulphur (insoluble sulphur in treads to avoid bloom), activators ZnO + stearic acid, accelerators — thiazoles (MBT, MBTS), sulphenamides (CBS, TBBS — delayed action, safe processing), thiurams (TMTD) and guanidines (DPG) as secondary boosters, dithiocarbamates (ultra-fast, latex).
Protective agents: antioxidants/antiozonants 6PPD, TMQ; microcrystalline wax; prevulcanisation inhibitor (PVI, CTP) to extend scorch safety; peptisers; tackifying and reinforcing resins; cobalt salts and resorcinol-formaldehyde-silica (RFS) for steel-cord adhesion; RFL dip for textile cord.
Recipes are written in phr — parts by weight per 100 parts rubber — so the polymer is always 100 regardless of batch size.

Vulcanisation: chemistry, systems and kinetics

Vulcanisation converts a plastic, soluble, tacky mass into an elastic insoluble network by sulphur crosslinks between allylic carbons; modulus, resilience, set resistance and solvent resistance rise, hysteresis and permanent flow fall.
Cure systems by sulphur-to-accelerator ratio: *conventional (CV)* S 2.0-2.5 phr, acc 0.5-0.6 — polysulphidic links, excellent flex fatigue, poor heat/reversion resistance; *semi-EV*; *efficient (EV)* S 0.3-0.5, acc 2.5-5 — mono/disulphidic links, good heat ageing and low set, poorer fatigue. Sulphur donors (DTDM, TMTD) replace part of the free sulphur.
Non-sulphur cures: peroxide (EPDM, EVA, silicone — C-C links, best heat ageing, no scorch delay), resin cure (butyl bladders), metal oxide (ZnO/MgO for CR), radiation and moisture/condensation (silicone RTV).
Rheometer (MDR/ODR) curve gives ML (minimum torque, processing viscosity), ts1/ts2 (scorch safety), t50, t90 (optimum cure ≈ 90% of torque rise), MH, and the plateau shape — reversion (NR at high temperature, polysulphide breakdown), plateau (EV, peroxide) or marching modulus (silica, BR-rich).
Cure is a thermally activated reaction (Ea ≈ 80-105 kJ/mol), so cure time roughly halves per 10 °C rise (Q₁₀ ≈ 2) and thick articles are controlled by heat conduction — time scales with thickness squared, which is why truck tyres cure for 40-60 min and passenger tyres for 10-15 min.
Scorch = premature crosslinking during mixing/extrusion; prevented by dumping productive-stage stock below about 105-110 °C, delayed-action accelerators and PVI.

Mixing, shaping and semi-finished components

Mastication (NR only): shear in a mixer or mill breaks chains, drops Mooney viscosity to a processable level; peptisers assist.
Internal mixer (tangential Banbury or intermeshing), 100-400 L chamber, fill factor 0.65-0.75, ram pressure 0.4-0.8 MPa, rotor 20-60 rpm. Non-productive/masterbatch stage: polymer, filler, oil, ZnO, stearic acid, antidegradants — dumped at 150-165 °C to complete filler dispersion and silica silanisation. Remill if needed. Productive/final stage: sulphur and accelerators at low speed, dumped below ~105 °C.
Specific mixing energy (kWh/kg) and dump temperature are the control variables; dispersion checked by dispergrader, Mooney and rheometer on every batch.
Dump mill / twin-screw sheeter → sheet or strip → batch-off with antitack dip and cooling festoon.
Extrusion: hot-feed or cold-feed, vented extruders; quadruplex/triplex heads co-extrude tread cap, base, wing and sidewall in one profile; profiles, hose tubes, bead apex and innerliner by extrusion or calendering.
Calendering: 3- or 4-roll, inverted-L or Z; topping/skim-coating textile or steel cord fabric on both sides, plus friction calendering; roll-bending and crown correct deflection.
Bead: high-tensile brass-coated steel wire, rubber-coated, wound into a hexagonal/round bundle and wrapped; apex (bead filler) is a hard extruded triangle.
Cutting/bias-cutting of plies to the required cord angle; steel belt plies cut at 18-25° to the circumference.

Tyre construction, building and curing

Components: tread (cap/base), sidewall, carcass (body) plies, steel belts, belt edge cover/cap ply (nylon or aramid for high speed), bead bundle + apex, chafer, innerliner (halobutyl), squeegee/insulation gum, shoulder wedge.
Bias (diagonal): plies at 30-40° to centre-line, crossed; carcass and tread move together — high rolling resistance, more heat, poorer handling; still used in some agricultural, OTR and two-wheeler sizes. Belted bias adds a breaker. Radial: carcass cords at ~90° (radial) with a stiff, low-angle belt — flexible sidewall, rigid tread, lower rolling resistance, longer tread life, better grip and comfort; dominant in passenger and now truck (TBR) fitment in India.
Tyre building: Stage 1 on a collapsible drum — innerliner, squeegee, carcass ply, bead set, ply turn-up (bladder), chafer and sidewalls → carcass band. Stage 2 — belts and tread assembled on a shaping drum, carcass inflated into the belt package, stitched down → green (uncured) tyre, lubricant sprayed inside/out.
Curing: green tyre loaded into a two-piece or segmented mould in a Bag-O-Matic/bladder press; the butyl bladder is filled with steam, hot water or nitrogen at 15-25 bar to force the green tyre into the mould and transfer heat from inside, while platens/dome heat the mould to 150-175 °C. Mould vents and sipes form the tread pattern and sidewall markings. Nylon-carcass tyres go for post-cure inflation (PCI) to prevent flat-spotting as the cords cool under tension.
Finishing and inspection: trimming of vent spews, visual, X-ray or shearography for cord/belt defects, dynamic balance and tyre uniformity (radial/lateral force variation, conicity), barcode/TIN marking.
Sidewall marking example 205/55 R16 91V: 205 = section width mm, 55 = aspect ratio %, R = radial, 16 = rim diameter inch, 91 = load index (615 kg), V = speed symbol (240 km/h); plus M+S, tubeless, TIN/week-year of manufacture, ISI mark and licence number.
The "magic triangle": rolling resistance, wet grip and tread wear trade off against each other; silica-silane treads and functionalised S-SBR break the compromise partly.

Other rubber products and their processes

Hoses: mandrel-built or mandrel-free — extruded inner tube, braided/spiralled/knitted textile or wire reinforcement, extruded cover, lead-sheath or wrapped cure in autoclave/steam, then stripping.
Belts: V-belts (cord-reinforced, compression-moulded), conveyor belts (multi-ply or steel-cord, built up and press-cured in long flat-bed vulcanisers), timing belts (polyurethane/HNBR).
Moulded goods: compression moulding (cheapest, most flash), transfer moulding (pot and plunger, better for inserts), rubber injection moulding (cold runner, barrel at 70-100 °C, mould 180-200 °C, fastest cycle, least waste) — O-rings, bushes, engine mounts, boots. Shrinkage allowance about 1.5-2.5% (≈2% for NR); flash grooves, spew lines, vents and cryogenic deflashing are design considerations.
Latex products: centrifuged 60% DRC latex, compounded with dispersions; coagulant dipping on formers for gloves, condoms and balloons, then leaching, beading, vulcanising and chlorination/powder-free coating; foam by Dunlop or Talalay process; dipped threads and adhesives.
Retreading: buffing, skiving, cementing, then precured tread strip with cushion gum cured in a chamber (cold-cure, ~100-110 °C) or a mould (hot-cure). Important in Indian truck fleets; BIS has standards for retreaded tyres and precured tread rubber.
Rubber lining, rollers, anti-vibration mounts, footwear (DIP/direct injection, moulded soles) and rubber-to-metal bonding with phenolic/Chemlok primers.

Testing, standards and Indian regulation

Raw/compound tests: Mooney viscosity ML(1+4)100 °C, plasticity retention index (PRI) for NR, Garvey die extrudability, Mooney scorch, MDR cure curve, specific gravity, dispersion rating.
Vulcanisate tests (IS 3400 series, methods of test for vulcanised rubbers; ASTM D412/D624/D2240/D5963): tensile strength, modulus at 100/300%, elongation at break, tear, hardness (Shore A / IRHD), rebound resilience, DIN or Akron abrasion, compression set, heat build-up (Goodrich flexometer), air-oven and ozone ageing, swelling in oil, low-temperature brittleness, tan δ by DMA.
Tyre tests under CMVR/AIS: plunger energy (strength), bead unseating, endurance load/speed, high-speed performance, tubeless air retention, and rolling resistance measured per the ISO 28580 method.
Indian regulation: pneumatic tyres and tubes for automotive vehicles are under a BIS Quality Control Order — ISI marking is compulsory for the covered categories. Product standards include IS 15633 (passenger car tyres), IS 15636 (commercial vehicle tyres) and IS 15627 (two- and three-wheeler tyres); confirm the current amendment/edition before quoting, as these are revised often. Construction/performance requirements for type approval come through AIS-142, which sets rolling resistance coefficient, wet grip index and rolling sound limits, implemented in stages by CMVR amendment — treat the staged dates as category-specific. Import of new pneumatic tyres has been placed under the restricted list by DGFT (licence required).
Environment and safety: waste tyres are covered by extended producer responsibility under the Hazardous and Other Wastes (Management and Transboundary Movement) Rules as amended, with producer and recycler registration and EPR certificates on the CPCB portal; tyre pyrolysis units need CPCB/SPCB consent under the Air and Water Acts. Factory health and safety (rubber dust and fumes, nitrosamines from thiuram/dithiocarbamate accelerators, press guarding, noise) is now governed by the OSH&WC Code, 2020, in force with the four Labour Codes from 21 November 2025. GST on tyres is 18% under the 5/18/40 slab structure effective 22 September 2025; natural rubber attracts a lower slab — verify the current HSN rate.

Key points

phr - parts per hundred rubber; every ingredient is dosed against 100 parts of polymer, so recipes scale to any batch size.
Vulcanisation - sulphur (or peroxide/resin/metal oxide) crosslinking that makes rubber elastic, insoluble and set-resistant.
Cure system choice - CV gives fatigue life, EV gives heat-ageing resistance and low set; semi-EV balances the two.
Activator pair - ZnO + stearic acid forms the zinc-accelerator complex; without it sulphur cures are slow and inefficient.
ts2 and t90 - scorch safety and optimum cure time from the rheometer; CRI = 100/(t90 − ts2).
Reversion - loss of crosslinks in NR on overcure; marching modulus - continued rise in silica/BR stocks.
Carbon black Nxyz - N = normal cure, first digit = particle size class; finer black = more reinforcement, more hysteresis.
Silica + silane tread - lowers rolling resistance at equal wet grip; needs a high dump temperature for silanisation.
Halobutyl innerliner - lowest air permeability; makes the tubeless tyre possible and holds inflation pressure.
Two-stage mixing - masterbatch dumped at 150-165 °C, curatives added below ~105 °C to avoid scorch.
Radial vs bias - radial carcass at 90° plus a stiff belt gives lower rolling resistance, longer wear and better handling.
Green tyre - the uncured assembly from the building machine, cured in a bladder press at 150-175 °C and 15-25 bar.
PCI - post-cure inflation keeps nylon cords in tension while cooling, preventing flat-spotting.
Tyre marking - 205/55 R16 91V = width/aspect/radial/rim inch/load index/speed symbol.
Magic triangle - rolling resistance, wet grip and abrasion resistance trade off; compounding tries to break the trade-off.
Cure time scaling - halves per 10 °C (Q₁₀ ≈ 2) and rises with the square of article thickness.
Mandatory BIS certification - automotive tyres and tubes carry the ISI mark under the applicable Quality Control Order; AIS-142 governs rolling resistance, wet grip and noise.
Waste tyre EPR - producers and recyclers register with CPCB under the hazardous and other wastes rules as amended.

Formulas and examples

Compound specific gravity: SG = Σ(phr)ᵢ / Σ(phrᵢ / SGᵢ) — phr in parts by mass, SGᵢ the ingredient specific gravity (dimensionless).
Mixer batch mass: m = V_chamber × f × SG — V in litres, f = fill factor (0.65-0.75), SG in kg/L → m in kg.
Ingredient weight: wᵢ = m × phrᵢ / Σphr (kg).
Compound cost: ₹/kg = Σ(phrᵢ × rateᵢ) / Σphrᵢ — rate in ₹/kg.
Cure rate index: CRI = 100 / (t90 − ts2) — t in minutes, CRI in min⁻¹.
Temperature scaling (rule of thumb): t₂ = t₁ × Q^{(T₁−T₂)/10}, Q ≈ 2, T in °C.
Arrhenius form: ln(t₁/t₂) = (Ea/R)(1/T₁ − 1/T₂) — T in K, R = 8.314 J/mol·K, Ea in J/mol.
Heat-conduction scaling: cure time ∝ L²/α — L = half-thickness (m), α = thermal diffusivity (≈1.1 × 10⁻⁷ m²/s for rubber).
Tyre outer diameter: OD = rim dia + 2 × (section width × aspect ratio/100); 1 inch = 25.4 mm.
Revolutions per km: N = 1000 / (loaded rolling circumference in m); LRC ≈ 0.96-0.97 × π × OD.
Rolling resistance: F_r = C_rr × F_z; power P = F_r × v — F in N, F_z = vertical load (N), v in m/s, P in W.
Abrasion loss (volume): ΔV = Δm / ρ — mm³ per standard test run; abrasion resistance index = reference loss/sample loss.
Press capacity: tyres/day = 1440 × cavities / cycle time (min).

Example 1 — Recipe, specific gravity, batch weight and cost. Tread masterbatch: NR 100 (SG 0.93), N330 50 (1.80), ZnO 5 (5.60), stearic acid 2 (0.92), TDAE oil 5 (0.95), 6PPD 2 (1.00), sulphur 2.5 (2.07), CBS 1 (1.27). Σphr = 167.5. Volumes (cm³ per 167.5 g): 107.53 + 27.78 + 0.89 + 2.17 + 5.26 + 2.00 + 1.21 + 0.79 = 147.63. SG = 167.5/147.63 = 1.135. Batch in a 250 L mixer at f = 0.70: m = 250 × 0.70 × 1.135 = 198.6 kg. NR charge = 198.6 × 100/167.5 = 118.6 kg; N330 = 59.3 kg; sulphur = 198.6 × 2.5/167.5 = 2.96 kg. Cost at illustrative rates (₹/kg): NR 170, N330 95, ZnO 290, stearic 130, oil 75, 6PPD 450, S 45, CBS 520 → Σ(phr × rate) = 17,000 + 4,750 + 1,450 + 260 + 375 + 900 + 112.5 + 520 = ₹25,367.5 → ₹151.4 per kg of compound (rates fluctuate; use current purchase prices).

Example 2 — Cure kinetics. MDR at 150 °C gives ts2 = 3.5 min, t90 = 12.0 min. CRI = 100/(12.0 − 3.5) = 11.8 min⁻¹. Q₁₀ = 2 rule at 160 °C: t90 = 12.0 × 2⁻¹ = 6.0 min. Arrhenius with Ea = 90 kJ/mol: (90,000/8.314)(1/423.15 − 1/433.15) = 10,825 × 5.456 × 10⁻⁵ = 0.591 → ratio e^0.591 = 1.805 → t90 = 12.0/1.805 = 6.65 min. The Q₁₀ rule is about 10% optimistic here, so press time is set from the Arrhenius value plus a heat-up allowance.

Example 3 — Tyre geometry. 205/55 R16 91V: section height = 205 × 0.55 = 112.75 mm; rim = 16 × 25.4 = 406.4 mm. OD = 406.4 + 2 × 112.75 = 631.9 mm; free circumference = π × 0.6319 = 1.985 m. Loaded rolling circumference ≈ 0.97 × 1.985 = 1.926 m → N = 1000/1.926 = 519 rev/km. Load index 91 = 615 kg per tyre → four tyres carry 2,460 kg; speed symbol V = 240 km/h.

Example 4 — Rolling resistance and fuel. Car of 1,400 kg, load shared equally, at 100 km/h (27.78 m/s). F_z total = 1400 × 9.81 = 13,734 N. Tyre A, C_rr = 0.0095: F_r = 130.5 N → P = 130.5 × 27.78 = 3.63 kW. Tyre B, C_rr = 0.0120: F_r = 164.8 N → P = 4.58 kW. Extra work of B over 100 km = (164.8 − 130.5) × 10⁵ = 3.43 MJ at the wheels; at 30% tank-to-wheel efficiency that is 11.4 MJ of fuel; petrol ≈ 32.4 MJ/L → about 0.35 L per 100 km — the basis of rolling-resistance labelling under AIS-142.

Example 5 — Press and extruder capacity. PCR cure 11 min + 1 min load/unload = 12 min cycle, twin-cavity press: 1440 × 2/12 = 240 tyres/press/day; for 6,000 tyres/day, 6000/240 = 25 presses. Tread extrusion: cross-section 2,400 mm² = 24 cm², SG 1.15 → 24 × 100 × 1.15 = 2,760 g/m = 2.76 kg/m; tread length 1.99 m → 5.49 kg/tyre. A quadruplex line at 1,200 kg/h feeds 1200/5.49 = 218 treads/h ≈ 5,240/day — one line supports the 6,000/day plant only with an extra shift or a second line.

Feature	Bias (diagonal)	Radial
Carcass cord angle	30-40° crossed plies	~90° radial
Belt	None (or breaker)	Steel belts at 18-25°
Rolling resistance	High	20-30% lower
Tread life, heat build-up	Lower life, more heat	Longer life, cooler
Ride and handling	Stiff sidewall, poorer cornering	Flexible sidewall, better grip
Retreadability, cost	Cheaper to build	Costlier, better casing life
Typical Indian use	Some farm, OTR, small two-wheeler sizes	Cars, TBR, most new fitment

Cure system	S : accelerator	Crosslink type	Strength
Conventional (CV)	2.0-2.5 : 0.5	Mainly polysulphidic	Best flex fatigue, high tear
Semi-EV	1.0-1.7 : 1.0-1.5	Mixed	Balanced
Efficient (EV)	0.3-0.5 : 2.5-5	Mono/disulphidic	Best heat ageing, low set
Peroxide	—	C-C	No reversion, poor fatigue

Where it is used

Tyre plants: MRF, Apollo, JK Tyre, CEAT, BKT, TVS Srichakra, Bridgestone and Yokohama India — roles in mixing room, building, curing, tyre engineering, compound R&D, process and quality.
Auto component rubber: hoses, weatherstrips, engine mounts, boots and seals for Maruti Suzuki, Tata Motors, Mahindra and the two-wheeler makers; suppliers such as Anand/Gabriel, Sundaram, Rubber Products Ltd.
Industrial rubber goods: conveyor and V-belts, rubber-lined pipes and tanks, pump liners and screens for cement, mining, steel and fertiliser plants.
Latex and consumer goods: examination and surgical gloves, condoms, balloons, foam mattresses, footwear soles (Kerala and Tamil Nadu latex clusters, HLL Lifecare).
Testing and certification: IRMRA Thane, ARAI/ICAT and BIS-recognised labs for IS/AIS tyre testing, and tyre type approval work.
Recycling and reclaim: retreading shops, crumb rubber and reclaim rubber units, tyre pyrolysis plants operating under CPCB EPR registration.

Interview questions

Q: Why is sulphur added in the final mixing stage and not with the filler? A: The masterbatch stage reaches 150-165 °C, where sulphur and accelerator would start crosslinking (scorch); curatives are added at low speed and dumped below about 105 °C.
Q: What does t90 mean and why is press time not equal to t90? A: t90 is the time to reach 90% of the torque rise at the test temperature in a thin rheometer sample; a thick tyre needs extra time for heat to conduct inward, so press time includes a heat-up allowance and is checked by cure-state measurements on sections.
Q: Difference between reversion and marching modulus? A: Reversion is a fall in torque/modulus on overcure from polysulphide breakdown (typical of NR at high temperature); marching modulus is a continuing rise, common in silica-filled and BR-rich stocks.
Q: Why is halobutyl used for the innerliner? A: Butyl's isobutylene backbone has very low gas permeability; halogenation lets it co-cure and bond to the unsaturated carcass rubber.
Q: Why does a radial tyre have lower rolling resistance? A: The radial carcass and stiff low-angle belt let the sidewall flex without flexing the tread, so less rubber is cyclically deformed and less energy is lost as hysteresis heat.
Q: How does silica with silane reduce rolling resistance without losing wet grip? A: The silane couples silica to the polymer, reducing filler-filler friction and hysteresis at rolling frequencies (around 60 °C) while retaining high loss at the low-temperature/high-frequency range that governs wet grip.
Q: What is the role of ZnO and stearic acid? A: They activate the accelerator by forming a soluble zinc-accelerator complex that makes sulphur crosslinking faster and more efficient.
Q: Why is post-cure inflation used? A: Nylon carcass cords shrink on cooling; holding the tyre inflated while it cools prevents flat-spotting and dimensional distortion.
Q: What causes blisters or porosity in a cured moulded part? A: Trapped air or moisture and undercure near the centre; remedies are better venting, mould design and preforms, drying the compound, higher cure pressure and correct cure time.
Q: Read 185/65 R15 88T. A: Section width 185 mm, aspect ratio 65%, radial construction, 15-inch rim, load index 88 (560 kg), speed symbol T (190 km/h).
Q: Which approvals must an Indian tyre carry before sale? A: BIS certification (ISI mark) under the pneumatic tyres and tubes Quality Control Order for the covered categories, plus CMVR type approval, with rolling resistance, wet grip and rolling sound limits applied through AIS-142.
Q: Why is NR preferred for truck tyre treads and BR avoided alone? A: NR strain-crystallises, giving high tear strength, low heat build-up and cut/chip resistance needed under heavy loads; BR has superb abrasion but poor wet grip, tear and processing, so it is only blended.

Common mistakes

Treating phr as a percentage — in the example above 50 phr carbon black is 29.9% of the compound, not 50%.
Using the Q₁₀ ≈ 2 rule as exact, or applying a thin-sample t90 directly as the press time for a thick article.
Mixing up the carbon black code: the first digit is the particle-size/surface-area class, not the loading, and N stands for normal-curing, not a number.
Saying "more crosslinks always means better properties" — tensile and tear peak at an optimum crosslink density and fall with overcure.
Confusing scorch time (processing safety) with cure time, or claiming that a faster accelerator improves both.
Calculating tyre diameter from the aspect ratio as if it were the whole tyre height, or forgetting to convert the rim size from inches.
Quoting withdrawn or superseded IS numbers and old emission/labelling dates; standards for tyres are revised frequently and AIS-142 applies in category-wise stages.