Sheet Extrusion is a very popular
process in case of plastic materials. As the name suggests it is typically
used for procuring sheets from plastics. Sheets generally has thickness
which is more than 0.010 inches or 0.254 mm widths can be as big as 30 feet.
Sheet extrusion essentially means a process that converts plastic pellets or
powder into cut sheets. This sheet is then processed further into parts
through the process of thermoforming. Typical plastic materials used in the
sheet extrusion process includes polypropylene, polyethylene, polystyrene
ABS etc. Not all the materials are suitable for sheet extrusion.
Parameters in Sheet Extrusion
Some of the parameters which are used for sheet extrusion includes the
following:
- Strength and weight
- Ability for resistance to heat
- Stress cracking
- Clarity
- Resistance to solvent and chemicals
Sheet Extrusion Process
A typical sheet extrusion line looks like this:

Sheet
extrusion is typically a continuous process. In this process, melted polymer
is forced via a die for achieving the requisite width and thickness. It is
important that the extruded sheet should display a temperature profile that
is relatively uniform. A calender has a strong impact on sheet quality.
Uniformity of the Calender roll temperature has a considerable influence on
the quality of flat sheets and makes them warp free.
Some of the important factors that plays a crucial role in the success of
sheet extrusion process are the following:
- Temperature settings
Depending on the extrusion design this may vary. The melt rheology or
the melt flow of the polymer decides the selection of temperature
settings.
- Back Pressure
A recommended back pressure is crucial to ensure that the uniformity
problems associated with extrudate like surging, voids, and non melting
resins are better avoided.
- Screw Speed
As a thumb rule the extruder speed is set very high, this is in order
to increase the efficiency.
- Roll stacks
- Die design
- Dryers
If moisture content is not reduced it can have an impact on the
strength of the extruded sheets.
- Polish Rolls
Polish roll temperatures can considerably affect sheet clarity.
- Purging
The optimum purge technique mainly depends on an individual plants
capability to reuse the blended materials.
- Winding
Sheet material, should be wound ideally at a temperature that is lower
than its heat deflection temperature.
- Regrind
Advantages of Sheet Extrusion
- Economy as sheet extrusion is capable of manufacturing large thick
sheets, so the advantage lies in its ability to produce considerably
bigger parts on very economical basis. The parts produced through sheet
extrusion if produced through injection molding would cost a fortune.
- Another distinct advantage that the extruded sheets enjoy is that
the different polymers are co-extruded for producing a multi layer
structure. What it means for the fabricator is that he can easily put
together polymers for adding functionality or has an option to better
the final product's cost performance ratio.
Industrial Application of Sheet extrusion
There is a large number of important industries where the extruded sheets
find appreciation. Let's see some of the applications.
- Building and Construction Industries
In the ambit of building sector, sheet extrusion finds a variety of
applications. One of the primary uses of extruded sheet lies in its use
as a thermal insulation material. They are typically used in walls,
roofs, and even under floors.
- Automotive Industry
In the case of automotive industry, extruded sheet is used for
producing interior trim, panels, to dashboards.
- Other Applications
Other popular products where profiles made out of sheet extrusion finds
a place are the Boat hulls, shower units, camper tops, luggage, spas,
hot tubs, refrigerator liners and a host of other products.
Buyer's Guide to Sheet Extrusion
For gaining a complete control of the sheet extrusion process a careful
consideration about the following points might prove to be useful.
- How much polymer storage capacity can be made available?
- Is drying capability available? If yes what is their capacity?
- Is there capacity to crystallize pellets or regrind?
- Is there polymer blending capacity available?
- Is there a precise regrind sheet available?
- Is the extruder twin screw or single screw?
- What type of polymer filter is used?
- Is there a gear pump?If yes what is the capacity?
- What is the type of die used along with the capacity?
- What type of roll stack is used? Vertical/ inclined/horizontal? If
vertical, then whether it is upstack or downstack?
- What type of winder is used?
- What type of quality control test is performed?
- Is there a safety system in place?