A dual-extrusion is the combination of two different thermoplastic materials as a single profile. The materials used for dual-extrusion must have compatible physical and chemical properties in order to flow together and create homogeneous or mechanical bonds.
As the name implies, a tri-extrusion is a combination of three dissimilar materials that are bonded to form a single profile. Tri-extrusion is usually done with vinyl materials and reflects one of the following combinations:
- One rigid and two flexible components.
- One rigid component and a combination of semi-rigid and flexible materials.
- One rigid and two semi-rigid components.
- Flexible or semi-rigid PVC may be used as a protective capping layer. This layer prevents loss of color or glossiness during exposure to the sun and weather. The other two parts of this type of tri-extrusion perform the same functions as the materials in a dual-extrusion.
Materials expand and contract in length when exposed to changing temperatures. For some materials, the amount of movement can be substantial. That’s why it is essential to account for movement in the final part application, part fabrication and inspection.
The following chart shows how to apply the formula for calculating movement for thermoplastic materials and aluminum, which we included for comparision purposes. The formula incorporates the coefficient of linear expansion (COE), or the amount of movement per inch per 1° F.
Please note when referring to this chart that the COE values are averages of the different grades of materials within that group.
|Material||COE (amount of movement
per 1° F)
|Formula for Calculating Movement*
(COE x 10-5 x length in inches x temperature range)
|Amount of Movement|
|Rigid PVC||3.4||.000034 x 72 x 100||=||.245 inches|
|30% Glass Reinforced PVC||1.2||.000012 x 72 x 100||=||.086 inches|
|Acrylic||3.9||.000039 x 72 x 100||=||.281 inches|
|PPO (Noryl)||3.7||.000037 x 72 x 100||=||.266 inches|
|Polycarbonate||3.75||.0000375 x 72 x 100||=||.27 inches|
|30% Glass Reinforced Polycarbonate||1.4||.000014 x 72 x 100||=||.1 inches|
|Polypropylene(copolymer)||5.1||.000051 x 72 x 100||=||.367 inches|
|30% Glass Reinforced Polycarbonate||1.3||.000013 x 72 x 100||=||.094 inches|
|ABS||5.8||.000058 x 72 x 100||=||.418 inches|
|Aluminum||1.2||.000012 x 72 x 100||=||.086 inches|
*Based on 6 feet (72 inches) of material exposed to a temperature range of 100° F
Amorphous plastics are for structural applications only (not suitable for bearing and wear).
- Soften over a broad range of temperature
- Easy to thermoform
- Tend to be translucent or transparent
- Bond well using adhesives and solvents
- Prone to stress cracking
- Poor fatigue resistance
- Poor chemical resistance
Semi-Crystalline plastics are good for bearing & wear as well as structural applications.
- Sharp melting point
- Difficult to thermoform
- Tend to be opaque
- Good resistance to stress cracking
- Difficult to bond using adhesives and solvents
- Good fatigue resistance
- Good chemical resistance
- Low coefficient of friction