Processing of polymeric product (Runner (types (Improved, Balanced “H” ,…
Processing of polymeric product
Plastic Injection Molding
Probably the most common, most important, most economical process
To apply high pressure on the fused plastics, make them eject
and fill the mold cavity
To heat plastics and make them fuse
Types of Injection Molding Machines
(not suitable for
plastics with low
Rapid Prototyping (RP)
Manually & Automatically
Manually Trimmed Gates
Requires an operator to
separate parts from runners
during a secondary operation.
Some shear-sensitive materials
(e.g., PVC) should not be
exposed to the high shear rates.
Simultaneous flow distribution
across a wide front to achieve
specific orientation of fibers of
The gate is too bulky to be
sheared from the part as the tool
Automatically Trimmed Gates
Incorporate features in the
tool to break or shear the
gate as the molding tool is
opened to eject the part.
Maintain consistent cycle
times for all shots.
Minimize gate scars.
Avoid gate removal as a
Distribution system for the resin from the sprue to the cavities
Flow characteristics (viscosity), temperature and other factors
are important in determining the runner diameter and length.
Full Round channel give the best flow characteristics but
difficult to machine (Can also be Trapezoidal or Half Round).
If the diameter of the runner is too small or the length is too
long, the resin can freeze in the runner before the mold is
If the runner system is too large, excess material would be
ejected and too much regrind is created.
If the resins have a high viscosity, larger runners are needed
compared to low viscosity resin.
The gate shape can also affect the filling of the
cavity, dimension and properties of the parts
Single gate has always been selected as a priority
unless the distance of the mold flow is too big and
beyond the limits of the injection molding pressure
The end of runner and the entry path into the cavity
Multiple gates always cannot avoid the problem of
weld line where the flows meet from different gates.
This weld line are NOT allowed especially when the
injection molded parts have critical appearance or