Cotton Phenolic Tube

Cotton phenolic tube is a compression-molded or wound thermoset sleeve form that bridges the gap between solid rod and flat sheet — providing the hoop strength and bore geometry of a ready-to-finish sleeve bearing, coil form, or insulating sleeve without requiring deep boring from solid rod stock.

TL;DR — Cotton Phenolic Tube Quick Facts

Standard Sizes — Cotton Phenolic Tube

Cotton phenolic tube is less rigidly standardized than sheet or rod. NEMA LI 1 provides property requirements; dimensional configurations are typically made-to-order around the buyer's ID and OD requirements.

Minimum order quantities apply for non-standard ID/OD combinations. Standard near-stock tubes (1", 2", 3", 4" OD with nominal wall thicknesses) are often available from distribution stock; confirm availability at time of quote.

Ovality on tube is held to ≤1% of OD for tubes under 6" OD.

Properties Relevant to Tube Form

The tube form is manufactured by wrapping resin-impregnated cotton fabric plies around a mandrel and curing under pressure, or by compression molding a tubular preform. This produces a hoop-optimized laminate — the cotton fabric planes run circumferentially, maximizing hoop (burst) and compressive strength in the wall.

Grade C tube maximizes mechanical performance for bearing and structural sleeve applications. Grade CE adds electrical isolation capability; choose CE when the tube must also block current flow (transformer coil forms, motor slot insulation, insulating bushings in live-metal assemblies).

For complete mechanical, electrical, and thermal properties, see the Cotton Phenolic properties page.

Typical Applications — Tube Form

The tube form uniquely enables applications that require both a precise bore and an outer structural surface — configurations that would require extensive boring from rod stock if tube were not available:

Sleeve bearings and journal bushings — The most common use. Cotton phenolic tube with the bore finished by honing or boring to shaft-clearance fits. Dry or oil-impregnated running suits agricultural machinery, water-treatment equipment, and marine shaft bearings where re-lubrication is impractical.

Coil forms and bobbin sleeves — Grade CE tube as the winding form for transformer coils, electromagnet bobbins, and motor field coils. The phenolic tube provides mechanical rigidity to support the wire winding, thermal resistance to handle coil self-heating, and electrical isolation between the winding and the core.

Insulating sleeves and stand-off tubes — Sections of tube cut to length as bus bar spacers, cable standoffs, and terminal isolation sleeves in switchgear and motor control center assemblies.

Hydraulic cylinder rod guides — Tube sections retained in cylinder end caps to guide the piston rod and resist side load — providing a non-metallic alternative to bronze guide rings on lower-pressure cylinders.

Chemical process pump sleeves — Cotton phenolic tube in Grade C for centrifugal pump wear rings and shaft sleeves in dilute acid and caustic services (check specific chemical compatibility for the process fluid).

Load-bearing structural tubes — Compression-loaded struts, insulating spacers in high-voltage transmission hardware, and structural spacers in outdoor electrical equipment.

Machining Notes — Tube

Tube stock arrives with an oversize OD and near-to-size ID; both surfaces typically require finish machining.

OD turning: Follow the same carbide tooling and speeds used for rod: 400–600 SFM, 0.003–0.006 IPR feed. Support the tube with a mandrel or steady rest for diameters above 3" to prevent chatter from thin-wall deflection.

Bore finishing (ID): Single-point boring or honing to final ID. Allow 0.001"–0.002" spring-back after boring — take a finish pass, withdraw, measure, and adjust before accepting the bore dimension. Honing with 180–320 grit stones produces a surface finish suitable for sleeve bearing applications (Ra 16–32 μin).

Parting/cutoff: Carbide parting blade, moderate feed. Support the tube close to the parting blade to prevent cracking. A steady rest or collet support prevents the tube from flexing and binding the parting blade.

End face squareness: Cotton phenolic tube can have slight warp on the end face from the molding cycle. Face both ends to a clean, square surface before bore finishing or length-to-length fitting.

Slotting and keyways: Machine keyways in tube OD using a carbide slot mill; back the tube wall with a mandrel to prevent collapse under milling forces.

Dust and vapor control: Same requirements as rod and sheet — localized exhaust ventilation, P100 respirator for operators, no open flame near phenolic dust accumulation.

See the Cotton Phenolic Machining Guide for detailed parameters.

Standards and Compliance

Tube configurations are frequently custom-made; request a Certificate of Conformance citing the NEMA LI 1 grade at order entry. For MIL-spec applications, the full MIL-I-24768 documentation set (C of C, lot test report, traceability to raw materials) must be requested before production release.

More related guides

Applications

• Bushings & Bearings — Material Selector
• Electrical Insulation — Phenolic & Laminate Options

Industries

• General Industrial Plastics
• Energy & Renewables

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Other cotton phenolic forms

• Cotton Phenolic Rod
• Cotton Phenolic Sheet