A 50% to 66% overlap spiral overwrap with Saint-Gobain CHR TH is applied to unrestrained wire harness bundles in unpressurised fuselage zones using 12 mm to 25 mm wide tape. Silicone pressure-sensitive adhesive permits repositioning during manual layup, but final anchorage to polyimide and crosslinked ETFE jackets requires 24 h dwell at 20°C to 25°C. The skived PTFE film exhibits a limiting oxygen index above 95% when tested per ASTM D2863, which supports low-flammability surface characteristics where FAR 25.853(a) is invoked; completed harness assemblies still require burn test qualification according to the certification plan. Application on unetched fluoropolymer-insulated wire is known to reduce peel adhesion, therefore a 70:30 isopropanol-to-deionised water wipe is specified before wrapping. Peel adhesion after dwell is measured at 180° angle per ASTM D3330/D3330M-18 Method A; reported values on lightly abraded polyimide jackets fall between 1.5 N/cm and 4.0 N/cm, while published data for unetched PTFE jackets remains limited. Wrapping tension is held at 2 N to 5 N to avoid necking the skived film and to prevent adhesive transfer at overlap edges.

Chafe protection between harness bundles and metallic structure is evaluated under SAE AS50881C guidance; the tape does not replace sleeving in high-abrasion zones, but acts as a sacrificial low-friction separator. Overlap geometry is set at a 50% minimum to ensure no exposed insulation. Motorised spiral wrapping heads maintain a lay angle of 20° to 30° from perpendicular; angles outside this range create wrinkles and reduce coverage continuity. Silicone adhesive shear resistance at 85°C continuous remains adequate on horizontal harness runs, but vertical runs in engine nacelle zones require additional mechanical tie-down where ambient temperature exceeds 120°C. Terminal products include commercial aircraft harness assemblies, regional transport aircraft avionics looms, and high-temperature industrial cable harnesses.

What limits dwell time on impulse sealing jaws at 165°C to 205°C?

Impulse sealing lines operating at jaw surface temperatures of 165°C to 205°C are fitted with the tape on L-bar sealers and hot-jaw packaging machines, with the skived PTFE film facing outward and the silicone adhesive in contact with the metal platen. The tape functions as a release boundary for molten polyethylene and polyethylene terephthalate films at seal initiation temperatures; it is not a heat-seal coating and does not eliminate jaw temperature compensation. Because skived PTFE has a thermal conductivity in the order of 0.25 W/m·K, measured per ASTM C518, a surface setpoint increase of 10°C to 15°C is commonly required to achieve the same seal interface temperature relative to an uncovered jaw. Dwell time is limited by edge curl and silicone adhesive hardening, not by PTFE melting; at continuous jaw surface temperatures above 260°C, the skived film begins to discolour and the silicone adhesive can embrittle within 500 to 1,000 cycles.

Installation parameters specify butt joints or a maximum 3 mm overlap at jaw ends; an overlap across the nichrome impulse wire creates a double thickness that retards heat transfer and produces inconsistent seal strength. Adhesive transfer at exposed edges is controlled by pressing the tape with a 0.5 bar to 1.0 bar roller after application. Seal integrity is verified per ASTM F88/F88M-21; because seal initiation temperatures differ among LDPE, LLDPE, and PP, a full jaw-length temperature mapping using thermocouple arrays is required before production release. Replacement intervals in continuous food packaging lines are typically recorded between 8,000 and 20,000 cycles, but no universal figure is published for all line configurations; the limiting variable is adhesive edge lift at jaw ends.

For food-contact packaging, the skived PTFE film is generally covered by 21 CFR 177.1550 and the pressure-sensitive adhesive is evaluated under 21 CFR 175.125 where indirect or incidental contact may occur. Direct contact of the silicone adhesive with the package is not intended; the PTFE film is the relevant compliance boundary. End products include heat-sealed pouches for frozen foods and industrial shrink films.

During autoclave cure of epoxy-prepreg carbon fibre laminates at 177°C and 0.62 MPa (90 psi), resin flash at caul plate edges and mould flanges bonds tenaciously to aluminium and steel tooling. Strips of Saint-Gobain CHR TH are placed with the silicone adhesive against the tool and the skived PTFE film exposed to the resin face; the backing provides a release surface with a surface energy below 20 mN/m, verified by contact angle measurement or wetting tension per ASTM D2578. The silicone adhesive maintains anchorage during the thermal cycle if the steel or aluminium surface is degreased with methyl ethyl ketone or isopropanol and dried before application. Tape application is limited to 5 mm to 10 mm wide strips around flash zones; full-area tool face coverage is avoided because the tape creates a thickness step of 0.09 mm to 0.13 mm at the laminate edge and may mark the part.

The main process conflict in this application is silicone outgassing. Silicone pressure-sensitive adhesives can liberate low-molecular-weight siloxanes at elevated temperatures, and if the tape is placed inside the vacuum bag or adjacent to surfaces destined for secondary adhesive bonding, residual contamination can reduce lap shear strength. Surfaces intended for structural bonding should be tested after cure using water break or dyne pen methods per ASTM D2578; values below 44 mN/m on epoxy surfaces may indicate contamination requiring solvent cleaning or plasma treatment. Published data for siloxane migration from this specific tape configuration is limited, so process qualification is required for each autoclave load. For tool flange protection outside the vacuum bag, the tape can be used through repeated cycles up to 260°C without adhesive transfer, but edge creep under pressure may occur if the tape is clamped beyond 0.7 MPa.

The terminal product includes carbon fibre structural panels, string-stiffened skins, and cured prepreg components for motorsport and aerospace applications. Release performance in service is assessed by removal without residue; if silicone adhesive splits during removal, the cause is usually inadequate tool surface preparation or exposure above 260°C for extended periods. Post-cure residue inspection is performed at 10× magnification followed by water break testing.

Surface energy and coefficient of friction on idler roll circumference

Water-based ink and varnish deposits on low-tension idler rollers in flexographic and converting lines are controlled by applying the tape circumferentially. The skived PTFE surface lowers dynamic coefficient of friction to approximately 0.05 to 0.10 against polypropylene film, measured per ASTM D1894, and reduces the frequency of web tracking defects caused by deposit formation. Rollers are prepared by solvent degreasing with isopropanol followed by a dry wipe; surface roughness of Ra 1.6 µm to Ra 3.2 µm, measured per ISO 4287:1997, is sufficient for mechanical anchorage of the silicone adhesive. Butt joints with a gap of 1 mm to 2 mm are preferred over overlap joints because an overlap creates a single revolution bump that imprints into tension-sensitive films at speeds above 150 m/min.

Adhesive failure at roller edges is the primary failure mode. The silicone adhesive swells in contact with toluene, methyl ethyl ketone, and selected acetate solvents; compatibility is evaluated by immersion testing per ASTM D543-21 before deployment. On rollers operating above 150°C, the silicone adhesive can lose shear strength; edge clamping or a mechanical lapping ring is required if wrap shear exceeds the adhesive’s shear adhesion failure temperature. Terminal products include pressure-sensitive label stock, flexible packaging laminates, and coated paper webs, where roller cleanup intervals are extended by the tape surface.

When dry-type transformer coil leads require Class 180 layer insulation

Dry-type distribution transformers and air-cooled reactors use CHR TH as a supplemental non-hygroscopic dielectric barrier on copper coil leads and interlayer bus connections. The skived PTFE film provides dielectric strength generally measured between 40 kV/mm and 60 kV/mm for 0.09 mm films per ASTM D149-20, with the exact value dependent on void content and electrode geometry. Silicone adhesive is not relied upon for through-thickness electrical insulation; the tape is applied in a half-lapped configuration over a primary layer of Nomex or polyimide, with the silicone adhesive providing placement and tack. Environmental thermal class is evaluated under IEC 60085:2007; silicone pressure-sensitive adhesive systems in this category are generally considered Class 180 in dry air, while the PTFE backing can withstand higher continuous temperatures.

Wrap tension must be maintained at 1.5 N to 3.0 N; higher tension causes necking of skived PTFE and introduces residual strain that can open gaps at the butt edge. The tape is not a substitute for impregnated glass or mica insulation in Class H transformer systems; it is used as a supplemental protective barrier on lead transitions and tap-changer connections. Dielectric withstand testing on completed coils is performed according to IEEE C57.12.91-2020 or IEC 60076-11:2018, depending on the regional grid standard.

If the tape is used on a vertical bus bar at continuous temperatures above 120°C, the silicone adhesive may creep under the weight of the tape overlap; mechanical retention by cable ties or glass tape is required. Edge-sealing with a silicone varnish is recommended where partial discharge resistance is specified, because air voids at overlap edges can act as partial discharge initiation sites.

Tunnel oven discharge chutes and guide rails are prepared with longitudinal panels of CHR TH, with the silicone adhesive against stainless steel or anodised aluminium. The PTFE surface reduces adhesion of sugar-based, fat-based, and dough residues on inclined transfer surfaces; residue removal is governed by the non-porous film, but high-pressure steam washing above 80 bar can lift exposed adhesive edges and is not recommended. For food contact surfaces, the skived PTFE film falls under 21 CFR 177.1550, and the silicone adhesive is evaluated as an incidental-contact pressure-sensitive adhesive under 21 CFR 175.125; direct food contact with the exposed adhesive boundary is excluded by design.

Because tunnel oven air temperatures can exceed 240°C in radiant sections, the tape is specified only on surfaces where contact temperature does not exceed 205°C continuous. Above this threshold, skived PTFE begins to show thermal ageing at edges, and silicone adhesive crosslinking may progress to embrittlement, evidenced by edge lift and residue on removal. Adhesive anchorage on horizontal surfaces is generally stable, but vertical chutes above 120°C require mechanical fastening at the upper edge. Panels are butt-jointed with 1 mm to 2 mm gaps to allow stainless steel expansion; gaps larger than 3 mm permit residue accumulation at the seam. End products include baked goods, chocolate-coated confectionery, and ready-meal packaging transfer lines.

In hydrochloric acid vapour zones, flange face masking during shutdown

During shutdown of hydrochloric acid storage and dosing lines, flange sealing faces are masked with CHR TH to prevent solid contamination and accidental mechanical damage from tooling. The skived PTFE backing resists aqueous hydrochloric acid vapour at ambient temperature, but the silicone adhesive is not rated for continuous immersion in 37% HCl. Application is therefore limited to temporary masking with a maximum exposure of 72 h at 20°C to 25°C. Removal must be followed by solvent cleaning to eliminate any silicone residue before gasket installation.

Chemical compatibility is assessed by weight and tensile change after immersion per ASTM D543-21; the silicone adhesive layer is the limiting component, not the PTFE film. The tape is not a substitute for flange gaskets or sealant compounds, and it must not be used under flange torque because skived PTFE can cold-flow and lose thickness. After removal, solvent cleaning with isopropanol and a lint-free wipe is specified to remove silicone residue; surface contamination is verified by water break testing per ASTM F22. Terminal products include lined chemical storage systems, dosing skids, and hydrochloric acid transfer pipework.