Malish Plastics: What to consider before designing a tube or profile extrusion

Design Considerations and Guidelines
As is the case with all manufacturing processes and disciplines, there are basic guidelines to be considered when designing a tube or a profile extrusion. Generally, more time spent on these questions at the outset of a project will result in significantly reduced problems later. The extrusion process, while a completely modern and viable one, has limitations that should be addressed at the beginning of any project. Any professional extruder should prompt questions in the following areas:

• Material Selection –
The most important issue from the standpoint of almost all other considerations. Cost, performance, wear/durability, environmental stability, mating part compatibility, and tolerancing all rely heavily on initial material selection. The experts at Malish can assist you in various material options.

• Environment –
Will the material be used in an exterior application or subjected to U.V. rays, ozone, heat, cold, or direct sunlight? Will the material come in contact with any caustic solvents, acids or petrochemicals? Will it be submersed?

• Color –
A major cost factor on smaller volumes if a custom match is required. Our wide array of stock color options can reduce costs when an approximate match is adequate. We also can custom match to your target if needed or add special items such as U.V. inhibitor, anti fungal, or phosphorescent additives.

• Wear/Durability –
Will the application be static or dynamic? Subjected to impact, compression, stress or strain?

• Mating Parts –
Does the part mate with another? If so, is a “functional fit” the ultimate goal? Are colors to match?

• Balanced Wall & Profile Symmetry –
Wherever possible, balanced, consistent wall thickness should be maintained to allow for even cooling. Large variation will result in excessive bow and twist and, ultimately, slow the process and increase your cost. Heavy sections can often be “cored out” to maintain balance as well as save material.

• Tolerances –
Working tolerance expectations should be established prior to starting on any project. Critical dimensions must be identified and agreed upon. Standard machining tolerances will not be applicable in most extrusion applications. Select the dimensions needing the highest degree of control to be toleranced. Any extruder will have a difficult time maintaining “across the board” tolerances. In most instances, the degree of tolerance is contingent on the relative size of the controlled dimension. A +/-.005” tolerance may work on a .250” dimension but not on a 4.00” dimension. Material also will determine the scope of tolerances applicable.

• Practicality –
Many times, the ultimate goal can be accomplished using a stock tube, rod, or other shape from a local plastic distributor, rather than a custom extrusion. If applicable to your situation, we do not hesitate to recommend and assist to that end.

• Packaging Options –
Is it more cost effective to run and ship in bulk sizes to be cut to finished length by the customer or cut to length at the extrusion line and packaged accordingly? Do parts require special individual packaging? Is special packaging required to prevent scuffs or scratches? Are reels or coils a better option?

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