Lamination

Lamination is a process of creating a bond between two or more layers of material.  The materials do not need to be of the same type. In prosthetics and orthotics, we create low-pressure laminates by impregnating plastic resin into base materials (cloth) and allow to harden under pressure.

The resulting composite material is composed of two or more mechanically separable materials with unique properties:

1. Typical fiber materials used in P&O include carbon, Kevlar, dyneema
2. Typical resins used in P&O include epoxy and acrylic.

The factors that affect the specific strength properties of a fiber reinforced composite:

• Fiber type, e.g., carbon is stiffer than fiberglass
• Density
• Fiber orientation
• Volume fraction
• Fiber length

Fibers

The fiber ‘layup’ provides reinforcement and mechanical strength. Place the strongest fibers at areas that require the highest amount of strength. The figure (Strength of Fibers) shows the ultimate tensile strength of composites using three resins with eight fibers.

Avoid placing fibers in areas where you will be trimming or grinding. Please observe safety precautions as many of these materials are hazardous to the respiratory system (use respirator when grinding) and are irritants to touch.

• When cutting the cloth, cut it under the hood.
• Vacuum up the carbon materials so that others do not stumble upon the particles.

The layup refers to the number and type of fiber as well as the placement of the various materials.  The layup varies according to the needs of the patient with regard to the patient’s weight and activity level.

This article has some examples of various layups.  It also explains a little about how the weight of carbon braid and the angle of weave influence the layup.

Resin

Resins hold the base materials in the correct alignment, but are not a significant source of strength.  They provide rigidity and dimensional stability.

Table 1 describes some of the basic qualities of some common resins used in prosthetics and orthotics.  There are various types of resins – rigid, flexible, and elastomeric.

References