|
About Extruded Plastics Extruded plastic is plastic that has gone through
an extrusion process. In this continuous process, thermoplastic
resins or plastic polymers are melted, heated and pumped. Molten
plastic material is pulled through a calibration system, which includes
a die. The die shapes the plastic into the desired shape, or profile.
Single- or twin-screw extruders use one or more internal screws
in a barrel to melt, mix and push the melted plastic material through
the die. This process shears material between the root of the screw
and the wall of the barrel that surrounds it, creating frictional
energy that heats and melts the substance as it moves down the barrel.
The barrel is also heated electrically to provide the necessary
heat to melt the plastic material. High intensity mixers are another
type of extruder.
In sheet extrusion, plastic powder or pellets are cut into sheets
or rolls. The sheets are then thermoformed, a process in which they
are re-softened in ovens and then brought into contact with a mold
surface by either air pressure or vacuum. The mold determines the
inside or outside shape of the part, as it comes into contact with
only one side of the softened plastic. The sheet extrusion process
can form extremely large sheets, up to and exceeding 2” thick
and as wide as 30 ft, which allows the production of very large
parts on an economical basis. Two or more extruders can be used
to co-extrude sheet products to produce multi-layer structures with
distinct layers of polymers. This process adds functionality or
improves the cost performance ratio of the end product.
Another type of plastic extrusion is extrusion blow molding. Extrusion
blow molding is used to produce plastic bottles such as milk jugs
and shampoo and bleach bottles. This process utilizes a die similar
to that used for making plastic pipes. Plastic pellets are fed into
a blow molder, which is the hopper of the machine. A screw, located
inside a heated barrel, pushes forward the softened plastic, which
is then forced through a circular die, forming a plastic tube called
a parison. Inside a hollow mold, the parison is clamped and inflated
from within by pressurized air. The plastic bottle is then ejected
and sent on to trimming, printing and filling stations.
There are many different types of plastics that can be extruded,
and each has its own advantages. High impact styrene (HIS) has a
uniform mate finish after extrusion, is a cost effective material,
can be easily colored and has good impact resistance. HIS is suitable
for indoor applications and may have a UV inhibitor added. Rigid
vinyl (R/PVC) is moderately priced, tough and versatile, provides
good clarity and is available in clear to opaque colors with a moderately
lustrous finish. R/PVC is used for outdoor and indoor applications.
Butyrate (CAB) provides very good quality of clarity, has good flexural
strength and a high gloss finish and is typically used for its clear
form. ABS is tougher, shinier and higher priced than HIS, though
worth the cost, if its properties are necessary. Polyethylene (PE)
is an economically priced flexible material that can be coiled or
spooled in its extruded form and can be cut in the field. When more
rigidity is required for PE, high density formulations are available.
Other materials include flexible vinyl (F/PVC), acrylic (also called
Plexiglass), SAN, polypropylene (PP) and K-Resin.
Featured
Articles
http://www.machinedesign.com/ASP/strArticleID/55642/strSite/MDSite/viewSelectedArticle.asp
http://www.plasticsresource.com/s_plasticsresource/sec.asp?TRACKID=&SID=4&VID=46&CID=126&DID=228
Types
- is material that is a combination
of one or more polymers combined in the extrusion process.
- are strips of plastic that are shaped for
a specific purpose and cut to length.
- is produced in a continuous process resulting
in a stable net structure in which the hole size is held constant,
unlike a woven or knitted product. Extruded plastic netting is
typically utilized in vertical applications such as walls for pens,
separation
in water, filtration, predator control or barriers.
- are shapes that are formed through the
extrusion process.
- are plastic powder or pellets that have been
formed into sheet products with a range of thickness from less
than 0.010 in. (film) up to and exceeding 2.0 inches, with widths
as great
as 30 ft. This sheet can be further processed into parts via
thermoforming.
- is any tube product that has been made through the
extrusion process out of thermoplastic or other rigid, semi-rigid
or flexible materials.
- are extruded products that are made of polyvinyl
chloride (PVC), including pipes, siding and floor coverings
|
