Composite Utility Poles

 

Industry

Infrastructure

Application

Company makes epoxy/glass utility poles through a filament winding process.

Problem

Company was not using a film to overwrap the large diameter composite pole sections prior to oven cure cycle. The resulting surface finish was rough, filled with air voids, and inconsistent from part to part. A smooth surface finish is desirable both for aesthetic reasons and to decrease the build-up of dirt and debris over time on part surface. 

Dunstone Solution

Dunstone Hi-Shrink Tape 210S (.002” thick, 10% shrink)

Implementation

Use of 2” wide Hi-Shrink 210S tape allows the customer achieve a good surface finish without having to sand or gel coat the outer surface of the poles.  The 210S tape is spiral wound on the part prior to the oven cure. The part is not rotated during the cure cycle, so the Hi-Shrink Tape helps prevent resin pooling on the bottom of the part. 

Case Study – Aerospace Composite Fuselage Stringe

Industry

Aerospace Composites

Application

Release coating of silicone bladders with heat shrink tubing, replacing hand wrapping process

Problem

Often times, composite fuselage skins for aerospace structures use composite stringers to stiffen the composite skin.  Many times these composite skins are co-cured at the same time as the composite stringers. Composite stringers with trapezoidal or omega shaped cross section, typically 20’-40’ in length, require an inflatable silicone bladder on the inner mold line to provide internal compaction during cure.  It is necessary to cover the bladders with a release film prior to application of carbon fiber pre-preg, the release film allowing for removal of the tool after the autoclave cure cycle. The silicone bladders were wrapped by hand with release film, and taped into place using Teflon tape. This can be a costly and time consuming process required for each fuselage section, and it often resulted in difficulty removing the hand wrapped release film after part cure due to the adhesive tape becoming stuck on the ID of the cured stringer. Material that remains on the inside of the cured part has to be completely removed before the part can be cleared for subsequent processing. Re-work and labor to remove the trapped film is costly and needs to be eliminated.

Dunstone Solution

Dunstone Hi-Shrink FEP Tubing

Implementation

Dunstone Hi-Shrink FEP Tubing used in the bladder preparation process allows the customer to prepare more parts in less time in order to incorporate them into the larger fuselage section prior to autoclave cycle. Our FEP tubing shrinks quickly, and without wrinkles, requiring less heat to fully shrink when compared to other heat shrink release film tubes.   Dunstone Hi-Shrink FEP Tubing has uniform thickness which give it uniform shrink percentage throughout. 

 

 

 

Sacrifice Film on High Voltage Coils

 

Industry

High Voltage Motors and Generators

Application

Large OEM in the power generation industry looks to cost reduce their current release film.

Problem

Current film is expensive to use as a sacrifice layer and provides very little compaction when heated during the press cycle. Low compression force can lead to poor insulation consolidation and improper shaping of the corner radii on the HV coils. 

Dunstone Solution

Dunstone F-Series Hi-Shrink Tape with PVF Release

Implementation

The OEM was able to use Dunstone’s F-Series Tape 210F as the first layer of release film instead of the film currently used. Hi-Shrink Tape 210F is a polyester based shrink film, with 10% shrink, which has a fused coating of Tedlar® on one side for release. The product provides the high temperature release characteristics of Tedlar®, combined with the high shrink force of polyester film at an overall lower cost. 

Other applications for Dunstone tapes on high voltage coils

  • Heat shrinkable release film on resin rich insulation for DC Field Poles
  • Heat shrinkable release film on pre-consolidated coils

 

Aircraft ECS Ductwork

 

Industry

Aerospace Composites

Application

Compress & de-bulk lightweight ducts used to transport air in commercial aircraft environmental control systems.

Problem

Composite ducts layed up on plaster mandrels require external compression during cure process to eliminate voids in duct walls. Manufacturers' current process specified the use of a cellophane film, wrapped under high tension, to achieve sufficient compaction. After part cure at a temperature of 120°C, the cellophane stuck to the phenolic/glass prepreg, making removal of the film difficult and adding time to part processing. In addition to the difficulty in removal, the cellophane is a non-shrinking film, which tended to wrinkle the outer layer of prepreg on the part.

Dunstone Solution

Release Coated Hi-Shrink Tape 220

Implementaion

Replacing the cellophane with Dunstone 220R allowed the operators to continue wrapping the film in the same manner, with lower tension during tape wrapping.

The shrink characteristics of the 220R enabled the tape to shrink and apply its max shrink force at the same time the resin viscosity is dropping, enabling the tape to minimize resin voids between the plys and reduce prepreg wrinkling.

 

Aerospace Thermal Insulation Covers

 

Industry

Aerospace Composites

Application

Company makes epoxy/glass and phenolic/glass thermal insulation covers which are used as heat shields over the metallic ducting systems they produce.

Problem

Company was using cellophane film and PVA film to overwrap their parts and provide compression during the cure cycle. Production required two separate wrapping operations to cover each part, one with cellophane, and one for PVA. Cellophane used as release liner underneath the PVA layer was sticking to epoxy/glass prepregs after cure. Customer was soaking each part in water for 24 hours to soften up cellophane layer and subsequent production step was required to scrape the remaining cellophane from the part.

Dunstone Solution

Hi-Shrink Tape 210R (.002" thick, 10% shrink, release coated polyester shrink tape)

Implementation

The customer was able to reduce the wrapping step down to one operation, as they were able to achieve sufficient part compaction using only one layer of our film vs two layers (cellophane & PVA) previously. Because the PTFE release coated tape removes cleanly from the part post-cure, the Dunstone Hi-Shrink Tape allowed the customer to completely eliminate the 24 hour long H20 soak for all parts, which increased throughput in that work cell. The bottom line savings realized by the customer amounted to $150,000/year.