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 plant’s 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?