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Extrusion Guidelines

Building a Profile

Wall Balance
Maintaining uniform wall thickness is essential to achieving a quality profile extrusion as material will fluctuate between thick and thin sections if walls are unbalanced. An unbalanced profile may require an extra cooling phase to prevent misshaping or bowing, which causes production to slow down, and costs to increase.
Balanced walls provide greater control of production costs through efficient production with better control of tolerances. You will also find that with balanced walls, you will have increased options in configuration and more material and surface finish alternatives.
Hollow Sections

The use of hollow sections is generally discouraged unless it aids in the achievement of wall balance.

The die for a hollow is more costly because of additional requirements to help maintain the shape as the part cools, such as air pressure, internal mandrels, and vacuum sizing. However, you will still save on total setup costs versus a die with unbalanced walls.

The following precautions may help minimize problems when a hollow is necessary:

  • Maintaining close tolerances is difficult on internal projections or legs inside a hollow, so try to avoid them when possible.
  • When an internal leg is necessary, ensure that it projects into the hollow no more than the thickness of the wall.
  • Another challenging design to avoid is a small hollow inside a larger one. Close tolerances are difficult to maintain, and it is costly to produce.
Sink Marks

Sink marks can be found opposite adjoining projections, caused by shrinkage of the material. To hide the marks, try raising or indenting the surface at the sink marks, or adding a surface design.

Corners and Radii

It is preferred that the inside radius, as well as outside corners, be a minimum of 1/64-inch. This will help reduce instances of breakage at a sharp corner, which is doubly important with rigid materials. There is less stress at the corners and less warpage when a larger corner is used.

Selecting Materials

Aluminum or Thermoplastic

Thermoplastic extrusions can be a better choice over aluminum for a variety of applications, as there are many benefits. For example, plastics can offer corrosion-resistance and out-perform aluminum with impact dents. The ability to perform secondary treatments in line can also make plastic a better choice, since aluminum may require adjustments after extrusion. The below chart highlights just some of the differences between these two materials.


 Energy Consumption

Less energy needed to produce and process extrusions in the 250° to 600° range

 More energy needed for mining and production as well as extruding at temperatures exceeding 1000°F


 Tensile yield to 10,200 psi for polysulfone, 9,600 psi for modified polyphenylene oxide

Tensile yield to 24,000 psi for 1000 series, to 36,000 psi for 3000 series, to 91,000 psi for 7000 series

 Impact Resistance

Excellent impact resistance in rigid plastics

Aluminum alloys offer minimal denting resistance


 Corrosion Resistance

Excellent, even without coatings

 Resists corrosion-weakening; however, surface treatment is required for appearance

Thermal Expansion Coefficient

Varies but higher for thermoplastics

Varies with alloy


Uniform throughout the part

 Must be painted or anodized; easily chipped and scratched

Multi-Function Extrusions

 Dual and tri-extrusions and other chemical/mechanical bonding of dissimilar materials is possible; saves cost of mechanical fastening

 Separately produced extrusions are later assembled with extrusions of other materials or with flexible sealing members, often plastic

Secondary Operations

 Productivity advantages with automated in-line fabrication to produce ready-to-install parts

Generally, requires heat treatment, straightening, and other post-extrusion operations in addition to fabrication processes

Co- and Tri- Extrusions

Carefully choosing two or three materials can result in an exceptional part for you. The below chart demonstrates the bonding characteristics of many plastics that we can use to make co- and tri-extrusions.

Shore Scale

The Shore scales are used to measure the hardness of plastic materials, with A scale plastics being flexible, C scales, semi-rigid, and D scales, rigid. There is some overlap in the Shore scales as exhibited in the below graphic.

Chemical Resistance

When a part will be exposed to chemicals, attention should be given to selecting the proper materials, as chemicals can affect the strength, flexibility, color, and surface of plastics. There are three types of interactions that can occur when plastics are exposed to chemicals: Stress cracking, softening or swelling from absorption of the chemicals, or changes in the physical properties of the plastics. Additionally, other factors can affect a material’s reaction to chemicals, such as temperature, pressure, grade of the materials, and length of exposure to the chemical. The below chart can assist with general guidelines only.


HPDE – High-density polyethylene
LDPE – Low-density polyethylene
NYL – Nylon (polyamide)
PA – Polyallomer
PC – Polycarbonate
PETG – Polyethylene terephthainte copolyester
PP – Polypropylene
PS – Polystyrene
PUR – Polyurethane
PVC – Polyvinyl chloride
TPE – Thermoplastic elastomer


E – Excellent, no effects on physical properties
G – Good, no dramatic effects
F – Fair, some effects
N – Not recommended

Calculating Thermal Expansion

The Shore scales are used to measure the hardness of plastic materials, with A scale plastics being flexible, C scales, semi-rigid, and D scales, rigid. There is some overlap in the Shore scales as exhibited in the below graphic.



(amount of movement per inch per 1°F)

Formula for Calculating Movement*
(COE x 10¯ x length in inches x temperature range)


Amount of Movement






.302 inches






.439 inches






.576 inches


Glass filled nylon




.166 inches






.425 inches






.439 inches


Rigid PVC




.245 inches






.086 inches


*Based on 6 feet (72 inches) of material exposed to a temperature range of 100°F.

Performance vs. Cost of Common Thermoplastic Materials
Fire Properties of PVC
Heat build-up is an important factor when determining the stability of a thermoplastic intended for outdoor use.
Black 288 74 41
Green 530 50 28
Blue 460 56 31
Gray 240 49 27
Ivory 035 45 25
White 138 45 25
White 145 45 25
Brown 382 52 29
Brown 372 50 28
Red 730 49 27
Tan 360 45 25
Gold 070 50 28
Olive 080 50 28
Yellow 650 36 20

For a vertical* wall, calculate heat build-up by adding the maximum temperature for the region to the above figures.

Example: If the air temperature can reach 105°, Black 288 can rise to 179°F.

*Heat build-up for an incline or horizontal position would be about 20% higher.