Torlon Grades: 4203 vs 4301 vs 4540 — PV Value Picker

Three grades cover the commercial Torlon stock-shape offering. The differences are not cosmetic — each grade targets a distinct performance axis, and selecting the wrong one can result in premature wear failure, unnecessary cost, or loss of regulatory compliance. This page compares Torlon 4203, 4301, and 4540 across all relevant axes and provides a decision framework for common applications.

At a glance:

• 4203: unfilled, maximum strength, best electrical insulation, only grade with FDA option
• 4301: PTFE + graphite filled, dramatically lower wear rate, moderate strength reduction
• 4540: optimized for highest PV (pressure × velocity) limit — the bearing-grade ceiling
• All three grades require post-cure; confirm cure status before accepting stock
• Filled grades (4301, 4540) are electrically conductive — do not use for insulation
• 4203 provides broadest size availability; 4540 may require extended lead time

Grade-by-Grade Overview

Torlon 4203 — General Purpose Unfilled

Torlon 4203 is the baseline grade. It contains no fillers, so it delivers:

• The highest tensile strength of any Torlon grade: 21,000 psi
• The highest compressive strength: 36,000 psi
• The best electrical insulation: volume resistivity 7 × 10¹⁶ Ω·cm
• The only route to FDA-compliant Torlon for incidental food contact applications

In structural roles — precision machine components, electrical stand-offs, aerospace bushings where a thin oil mist is present, fixtures — 4203 is the right choice. Its dry-running friction coefficient is higher than the filled grades (0.35–0.45 vs steel), and its wear rate without lubrication is substantially worse, so it should not be used in true dry-sliding bearing applications.

Best for: Structural components, electrical insulators, semiconductor tooling (no metallic filler contamination), FDA-regulated food/pharma environments, precision fixtures.

Torlon 4301 — PTFE/Graphite Filled (Low Wear)

Torlon 4301 contains 3% PTFE and 15% graphite by weight. These solid lubricants reduce the friction coefficient by roughly 70% relative to 4203 and reduce wear rate to approximately 5% of the unfilled grade. The mechanism is transfer film formation: on first contact, a thin layer of graphite and PTFE is deposited on the metal mating surface, creating a lubricious interface that persists across millions of sliding cycles.

The practical effect:

• Dry CoF against steel: 0.10–0.15
• PV limit (dry): approximately 35,000 psi·fpm
• Wear rate at rated PV: very low — typically >10,000 hours of bearing life in industrial service

Tensile strength drops to 17,000 psi (vs. 21,000 for 4203), and the material becomes electrically conductive through the graphite phase. Flexural modulus is marginally lower (690,000 psi). These are acceptable tradeoffs for sliding-contact applications.

Best for: Dry-running sleeve bearings, flange bearings, thrust washers (moderate load), compressor rider bands, bushing applications without external lubrication.

Torlon 4540 — High Load-Bearing

Torlon 4540 is formulated specifically to maximize the PV limit — the combination of contact pressure and sliding velocity the material can sustain before tribological failure. Graphite content is higher than 4301, and the filler package is engineered for load transfer rather than pure friction reduction.

Key metrics:

• PV limit: 50,000+ psi·fpm (dry running against steel)
• This exceeds Torlon 4301 by approximately 40% and virgin PEEK by more than 3×
• Tensile strength: 15,500 psi (lower than 4301, furthest from 4203)
• Flexural modulus: 800,000 psi (highest of the three — the graphite filler stiffens the matrix)
• Friction coefficient: 0.10–0.18 depending on PV and surface finish

4540 is specified when 4301 is the right category of material but the load or velocity exceeds 4301's PV envelope. The strength reduction means 4540 is not appropriate for highly stressed structural members, but in tribological applications the filler enables performance unavailable elsewhere in the thermoplastic category.

Best for: High-load compressor valve seats, high-PV thrust washers, reciprocating seals in heavy-duty equipment, any dry bearing where PV exceeds 35,000 psi·fpm.

Full Property Comparison

PV Picker: Which Grade Do You Need?

The decision tree below covers the most common selection scenarios.

Step 1: Is electrical insulation required?

If yes, specify 4203 regardless of load. Graphite-filled grades are conductive and cannot be used where dielectric performance matters.

Step 2: Is FDA or USP compliance required?

If yes, specify 4203 FDA grade. Only the unfilled grade is available with the necessary regulatory formulation. See the Torlon FDA page for specifics.

Step 3: Is this a dry-running sliding contact application?

If yes, proceed to Step 4. If no (lubricated bearing, structural component, fixture), specify 4203 for maximum strength.

Step 4: Calculate PV = (Contact Pressure in psi) × (Sliding Velocity in fpm)

For the 4301/4540 boundary zone (30,000–40,000 psi·fpm), default to 4540 if operating temperature is also high (>350°F) or if duty cycle is continuous rather than intermittent.

Step 5: Confirm mating surface hardness

Torlon filled grades require a hardened mating surface. For PV above 20,000 psi·fpm:

• Steel: ≥ 45 HRC (60 HRC preferred)
• Surface finish: Ra ≤ 16 μin ground preferred; ≤ 32 μin acceptable

Grade Availability in Stock Shapes

For detailed size tables, tolerances, and standard stock availability, see the Torlon specifications page.

For cost context: 4203 and 4301 are similarly priced per pound. 4540, being a specialty formulation with limited converter availability, typically runs 10–20% higher than 4301 for equivalent sizes.

Summary Recommendation by End Use

More related guides

Cross-cluster suggestions to help shoppers and engineers explore adjacent topics:

Applications

• Bushings Bearings
• Aerospace Interior

Industries

• Aerospace
• Oil Gas

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