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Design and Processing Information
Extrusion post-forming is the process of continuously forming
a hot, flat, extruded sheet into a shape. This process is usually
done at the extrusion process, and is normally done with rigid
PVC. Typical products formed by this process are vinyl siding
and accessories, vinyl skirting and accessories, rain gutter,
some fence products, and some decking products. Some of the advantages
of the post-forming process include:
- Processing speeds are much greater with the post-forming
process. Typical line speeds for post-formed vinyl siding range
from 90 to 150 feet per minute, with extrusion rates running
as high as 3500 pounds per hour.
- Because a standard sheet die is used as the extrusion head,
very little die tuning is required for new products. Formulations
and colors changes can be made often with little or no effect
on the extruded sheet. The simple adjustment of the lip bolts
can even out the thickness of the sheet if changes are required.
- With the advent of co-extrusion and tri-extrusion dies, capping
materials can be run at a minimum thickness, creating a more
cost-efficient product. Also, different materials can be used
as the capping material versus the substrate material. The cost
of the extruded material can be greatly lowered if only the
cap contains the weatherable materials. Most sheet dies do not
have to be re-cut to run the different materials.
- Each sheet die can be used to run different products that
are similar in undeveloped lengths (undeveloped length is the
cross-sectional width of a post-formed product before the product
is formed to shape). The hot, extruded sheet can be stretched
some at the die by the embosser (nip device) and/or by the haul-off
(puller) to adjust the sheet width before the post-forming process.
- The extruded sheet can be embossed with many different patterns
after the sheet's exit from the die. Laminate materials also
can be applied at this time. Neither of these processes greatly
affect the ability to form the sheet to the desired shape.
- The calibration (sizing) tooling is simple to set-up and
run. The amount of calibration tooling required to do the forming
greatly depends on the accuracy required for the finished product.
- The down-stream equipment required to run a post-formed extruded
product is similar to the equipment required to run profile
extrusions. Cutting, punching, and notching equipment can also
be used in-line with the post-formed parts.
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ADDITIONAL DESIGN INFORMATION
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