Agriculture Reference
In-Depth Information
and clamped-down tight. Compression moulding is similar to making waffles. Heat
and pressure forces the material to flow and occupy all areas of the mould and, after
a pre-determined cooling cycle, the part is removed. Sometimes, excess material will
flow out through the vents and the part will have to be buffed to remove the flash.
To remove moisture from materials used in powder form, they are pre-heated using
infrared, induction or other heating methods, before introduction into the mould.
This will also help reduce the production cycle. To increase output, some systems
may use a screw extruder, which will produce preformed 'slugs' that can be loaded
directly into the mould cavity and also giving more control of waste material.
Common plastic materials used in compression moulding are: thermosetting bulk
moulding compounds, phenolics, urea-formaldehyde and melamine. This method
of processing is selected if large parts with thick walls are to be made. Some items
produced in this way include: melamine plates, cups, saucers, plug tops, and decorative
items. This is the third process where the use of PCRH resins in pellet form can be
used and will be discussed in detail later.
The processes shown below are also important for the conversion of resins to products.
They are highlighted for the benefit of the reader, but are not discussed because they
are not relevant to this topic:
•
Compounding
•
Laminating
•
Casting
•
Thermoforming
•
Expansion
•
Foaming
•
Coating
•
Blow moulding
Of the processes listed above, injection moulding forms ≈70% of processing activity.
However, extrusion will take precedent with the production of PCRH resins in pellet
form and the conversion of these pellets into end products, which will be presented in
detail. The use of composite resins in injection moulding and compression moulding
Search WWH ::
Custom Search