163
6
5 Compatibility of Mould Design with a Matrix—Mould design
dictates the path to be travelled by a polymer melt, the
volume it needs to fill, what is the filling time, etc. A suitable
polymeric matrix needs to be selected to fill the mould
cavity optimally in an injection moulding process and to
ensure percolation of the resin in a compression moulding
process.
5 Production Rate—Production rates have always been one
of the guiding rules for choosing a processing method. In
thermoplastic composites, very high production rates are
achieved for short fibre-reinforced thermoplastic composites using an injection moulding process. The rate of
production may be up to 20 products per minute,
depending upon the volume of the product, capacity of
the injection moulding machine, mould design, material
used, processing parameters, etc. In compression moulding processes, very high production rates are not achievable. However, with multi-daylight compression
moulding machines, high production rates are feasible,
enhancing the production rate. The major difference
between the production rate of an injection moulding
process and a compression moulding process is the
process cycle time. The process cycle time is 30–60 seconds on an average in an injection moulding process,
whereas in a compression moulding process, this time
may range from 2 to 6 hours.
5 Cost of Production—The cost of production is usually low in
thermoplastic composites due to high production rates.
Also, the processes used in thermoplastic composites are
more automated; therefore, chances of rejection of the
products moulded are very less. The rejects do have scrap
value, and this will offset the production cost.
5 Product Size and Shape—Product size and shape has a
bearing in the selection of the matrix because it has to travel
a path to fill the mould cavity in an injection moulding
process and the thermoplastic resin needs to percolate into
the entire mould in a compression moulding process. For
large products, crystalline or semi-crystalline polymeric
matrices (such as nylons, polypropylene, and polyethylene)
are preferred. Amorphous polymeric matrices (such as PC
and PMMA) are also used for small- to medium-sized
composite products in an injection moulding process.
High-temperature semi-crystalline matrices (such as PEEK
and PEK) need thermal management in order to control the
heat losses; therefore, they are not preferred for large
composite products using an injection moulding process.
Similarly, high-temperature amorphous matrices are also
used for small composite products due to thermal management considerations and low flowability. Compression
moulding processes may be used for all sizes of products
having any kind of matrix.
6.5 · Selection Criteria for Thermoplastic Matrices
6
5 Compatibility of Mould Design with a Matrix—Mould design
dictates the path to be travelled by a polymer melt, the
volume it needs to fill, what is the filling time, etc. A suitable
polymeric matrix needs to be selected to fill the mould
cavity optimally in an injection moulding process and to
ensure percolation of the resin in a compression moulding
process.
5 Production Rate—Production rates have always been one
of the guiding rules for choosing a processing method. In
thermoplastic composites, very high production rates are
achieved for short fibre-reinforced thermoplastic composites using an injection moulding process. The rate of
production may be up to 20 products per minute,
depending upon the volume of the product, capacity of
the injection moulding machine, mould design, material
used, processing parameters, etc. In compression moulding processes, very high production rates are not achievable. However, with multi-daylight compression
moulding machines, high production rates are feasible,
enhancing the production rate. The major difference
between the production rate of an injection moulding
process and a compression moulding process is the
process cycle time. The process cycle time is 30–60 seconds on an average in an injection moulding process,
whereas in a compression moulding process, this time
may range from 2 to 6 hours.
5 Cost of Production—The cost of production is usually low in
thermoplastic composites due to high production rates.
Also, the processes used in thermoplastic composites are
more automated; therefore, chances of rejection of the
products moulded are very less. The rejects do have scrap
value, and this will offset the production cost.
5 Product Size and Shape—Product size and shape has a
bearing in the selection of the matrix because it has to travel
a path to fill the mould cavity in an injection moulding
process and the thermoplastic resin needs to percolate into
the entire mould in a compression moulding process. For
large products, crystalline or semi-crystalline polymeric
matrices (such as nylons, polypropylene, and polyethylene)
are preferred. Amorphous polymeric matrices (such as PC
and PMMA) are also used for small- to medium-sized
composite products in an injection moulding process.
High-temperature semi-crystalline matrices (such as PEEK
and PEK) need thermal management in order to control the
heat losses; therefore, they are not preferred for large
composite products using an injection moulding process.
Similarly, high-temperature amorphous matrices are also
used for small composite products due to thermal management considerations and low flowability. Compression
moulding processes may be used for all sizes of products
having any kind of matrix.
6.5 · Selection Criteria for Thermoplastic Matrices