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HOW TO PROCESS COMPOSITE FIBERS AND PRE-FABS

Perpedes acrylic composite materials made from glass and carbon fibers are developed and manufactured in Germany and are ideally suited for producing hand-made, bespoke foot orthoses. All Perpedes pre-fab orthotic blanks have an incorporated glass or carbon fiber shell.

A suitable composite fiber material for most applications and for every desired characteristic regarding deformability behavior, rigidity, material thickness and weight can be found in the Perpedes assortment.



APPLICATION

Basic material to manufacture supportive elements of various orthopedic appliances, e.g. foot orthotic shells or reinforcing elements of AFOs/DAFOs.


COMPOSITION

Perpedes composite fiber materials are made from acrylic resin (PMMA - polymethyl methacrylate) with embedded carbon or glass fiber woven or knitted fabric, often in combination with polyamide. Such composites ensure high loading capacity with low material thickness – a valuable advantage in foot orthotics. However, note that composite fiber materials are tougher at shaping than other “plastic” shell materials known in the industry.


MATERIAL PROPERTIES

Woven and knitted glass/carbon textile have different properties that affect the thermalmoldability and rigidity of a shell

  • Composites with knitted glass or carbon are recommended for 3D-moldings, e.g. higher cupped foot orthotic shells (G431, G422, C602), although we advise to combine less rigid materials to stabilize the hindfoot area to avoid irritations with the heel’s soft tissue
  • Composites with woven glass or carbon fabric are suitable for moderate arch supports in foot orthotic shells with flat or only slightly cupped heel portions, as well as for shoe reinforcements (C801, BF7003)


Note that a rigid shell should not be in direct contact with a soft foam, as every hard material will eventually damage a cushion – especially at the front end of the shell. Consequently, in Perpedes’ pre-fab blanks the fiber shells are covered with a tough textile to prevent damages of cushions and top layers as well as to provide the best possible transitions without irritations for sensitive foot areas.


PREPARATIONS

The positive (plaster cast, insole last) should have an even forefoot area to avoid wrinkles in the foot orthoses. 

We strongly recommended to prepare the composite fiber shell in the exact size, as such materials do not shrink. Too much material can easily cause wrinkles in the heel area when shaping under vacuum. However, little wrinkles are easy to smooth manually with help of a heat gun after the vacuum process.


HEATING

Heating is suggested either in a convection oven or between warming plates. Thermal alterations on orthotic shells or blanks with already glued top covers should be done only partially from the bottom side with an heat gun.

Recommended heating temperature is at about 140° C (284° F). Note that thermal molding at too low temperatures leads to damage of the material, while too high temperatures (> 160° C / 320° F) may cause damages to the surface and the composite material becomes brittle.

Heating instructions for "orthotic shells"

Self-supporting glass or carbon fiber composite shells without base covers

  

  • Heat up in a convection oven or - less recommendable - with a heat gun from the top (surface heating, approx. 20 cm distance).
  • Temperature: approx. 140°C (284° F)
  • Heating time: approx. 4 min (depending on heating device, material, thickness, heat source), material must be thoroughly warmed and flexible prior to vacuum shaping.
  • Direct contact between the shell and the oven‘s grate should be avoided (Teflon film recommended).
  • Watch the processing video for orthotic shells here

 

Heating instructions for "foot orthotic blanks"

Self-supporting glass or carbon fiber composite shells incl. base covers and optional cushion pads (= pre-fab blanks)

 

  • Heat up in a convection oven or with a heat gun, preferable on the bottom side if cushions are on the blank (surface heating, approx. 20 cm distance)
  • Temperature: approx. 140°C (284° F)
  • Heating time: approx. 4 - 8 min (depending on blank materials, thickness, heat source), the incorporated orthotic shell must be thoroughly warmed and flexible prior to vacuum shaping.
  • Direct contact between the orthotic‘s base layer and the oven‘s grate should be avoided (Teflon film recommended).
  • When heating base cover and padding materials there is a possibility of delamination
  • Watch the processing video for foot orthotic blanks here

 

THERMAL MOLDING AND FURTHER PROCESSING

A heated composite fiber is best molded under vacuum onto a positive. Further processing is recommend only after complete cooling under vacuum. To shorten processing time, a cold wet towel proves useful onto the vacuumed shell or orthotic blank.


When warming up, the adhesive in pre-fab blanks is being activated, so the layers of the various components might slightly delaminate. This effect is reversible when the foot orthotics have cooled down while being pressed together.

Composite fiber materials made of carbon and glass fiber can easily be cut and ground with tools, available in orthopedic labs (jig-saw, band-saw, sander).

Perpedes’ blanks are also suitable to be used for direct molding, e.g. between the foot and a vacuum pillow. To avoid skin damages the foot needs to be protected by cotton socks and the blank’s hot surface with an approx. 2-3mm layer of (disposable) EVA.


CAUTION!

 

  • Do not heat material above 140° C (284° F)!
  • Do not work with open fire. Flammable!
  • Do only use grinders/sanders with exhaustion!

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