Torlon PAI Specifications — Sheet, Rod & Tube Sizes

Torlon polyamide-imide stock shapes are produced in three forms — sheet, rod, and tube — across a range of sizes that spans small precision parts to large structural billets. Understanding the dimensional offering, standard tolerances, and post-cure requirements before ordering is essential: Torlon is expensive, lead times on non-standard sizes can be substantial, and dimensional allowances for post-cure shrinkage must be built into machining planning.

At a glance:

• Sheet: 12″ × 24″ (small format) through 24″ × 48″ (full format), thickness 1/4″ – 4″
• Rod: 1/4″ to 8″ diameter, standard lengths 12″, 24″, and 36″
• Tube: available to order for most OD/ID combinations; confirm availability before designing
• Post-cure mandatory: all shapes require a multi-week heat treatment cycle before full properties are achieved
• ASTM D5204 is the applicable standard for PAI molded shapes
• Grade availability varies: 4203 and 4301 are most commonly stocked; 4540 and tube typically require ordering

Sheet Specifications

Standard Sheet Sizes

Sheet Tolerances

Torlon sheet is compression-molded; thickness tolerances are wider than extruded materials:

Width and length tolerances on standard sheet: ± 1/8″. Sheet surfaces exhibit molded skin; if optical flatness is required, plan a skim cut on both faces.

Rod Specifications

Standard Rod Sizes and Lengths

Rod Tolerances

Torlon rod is turned from molded blanks or produced by injection/compression molding into rod tooling. Standard diameter tolerances:

Straightness: maximum bow 0.010″ per foot for diameters up to 2″; contact supplier for larger diameters.

Tube Specifications

Torlon tube is less commonly stocked than sheet or rod because the range of OD/ID combinations is large and demand per specific size is low. Tube can be machined from rod (for thin-wall, short-length applications) or ordered as near-net-shape molded tube.

Typical parameters:

• OD range: 1/2″ through 6″ in custom combinations
• Wall thickness: minimum 10% of OD recommended; thinner walls are possible with consultation
• Standard lengths: 6″ – 24″ depending on OD
• Lead time: 8–16 weeks for non-standard combinations

For applications that require precise ID bore tolerances, it is generally more economical to bore rod stock to ID specifications on the machine tool than to rely on as-molded tube tolerances.

Post-Cure Requirements

Why Post-Cure Is Necessary

Torlon's polyamide-imide chemistry involves imide ring closure reactions that continue at elevated temperature after initial molding. As-molded stock contains incomplete ring closure, manifesting as:

• Tensile strength 20–30% below rated values
• Compressive strength similarly reduced
• Higher susceptibility to creep under load
• Greater sensitivity to thermal cycling

Post-Cure Schedule

A full post-cure cycle follows a staged temperature ramp. The specific schedule varies by shape size and grade, but a representative protocol is:

Total elapsed time: approximately 2–4 weeks when counting queue, ramp, hold, and cool-down phases at a certified converter facility. Thick sections require longer hold times at each stage.

Machining Around Post-Cure

Parts machined from as-molded (green) stock to final dimensions before post-cure will shrink during cure. Typical shrinkage is 0.3–0.5% of linear dimension, but it varies by section geometry. Two approaches:

1. Rough-machine before cure, finish-machine after: Leave 0.020–0.030″ of material on all critical surfaces, complete post-cure, then finish to final dimensions. This is the most reliable method.
2. Machine fully cured stock: Obtain post-cured stock from supplier and machine directly to final dimensions. This requires confirming cure certification from the supplier and is simpler for small-quantity projects.

For more detail on machining sequences, see the Torlon machining guide.

Applicable Standards and Testing

Material certifications (tensile, hardness, lot traceability) are available on request for aerospace and semiconductor procurement. Confirm certification requirements at time of order.

Color, Surface Finish, and Identification

All standard Torlon stock shapes are natural color: dark amber to brown. The amber tone deepens with thickness. There are no standard pigmented grades; custom colors require resin-level compounding and are not practical for small quantities.

As-molded surfaces have a dull skin with slight porosity at the surface layer. For bearing bore and contact surfaces, machine away a minimum of 0.005–0.010″ to reach homogeneous material below the skin. This applies to both rod OD and sheet surfaces.

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