Injection molding machines - The hot way to get something
into shape
When we talk about injection molding machines, we are in
the field of plastics processing. The process is relatively old and the first
machine was invented at the end of the 19th century. Molded parts in a wide
variety of forms can be created from granules or powder and by adding alloys
(glass fibers, oils, carbon) and colouring pigments.
Depending on the structure and the associated
specifications for heating, supply and degassing of the injection molding
machine, different types of plastics can be processed. These include
thermoplastic, thermosetting and elastomeric materials.
What defines a plastic injection molding machine:
structure and function
Reduced to a minimum, an injection molding machine
consists of only two parts, the extruder and the clamping unit.
The granulate or powder is fed to the extruder via a
funnel by means of a dosing unit. Colorants and the alloying elements have
typically been premixed in a mixer prior to being fed into the funnel. Inside
the extruder, the granulate is heated by heating elements and put under
pressure by the ever decreasing pitch of the rotating extruder screw. The
granulate is plasticized by the heating. The extruder must be controlled in
such a way that the plasticized mass at the exit (screw tip), at the transition
to the injection mold, has the correct consistency. A shut-off valve is mounted
at the screw tip. This valve ensures that the material cannot flow back in the
direction of the feed funnel of the extruder during the injection process. This
is necessary because when the material is injected into the mold, the screw is
axially displaced without rotation and thus functions like a piston. In order
to have enough material available for the injection process, the rotating screw
moves back before the injection process and thus creates the necessary space
for the material. The screw stroke is regulated and determines the injection
process depending on the amount of material under holding pressure.
The clamping unit of an injection molding machine is
usually made of a panel construction. The plate, which is located on the
extruder, carries one tool half and has a hole in the center at the exit of the
extruder. The material enters the injection mold through this hole (nozzle).
This plate is firmly screwed to the extruder.
A second plate is designed to be movable and takes the
second half of the injection mold. The injection mold can be closed or opened
by the hydraulic or mechanical movement of the second plate. The injection
process takes place in the closed state. The locking of the mold must withstand
the injection pressure. When the clamping unit is open, the manufactured part
is ejected.
The drive for moving the clamping unit is located at the
front behind the movable plate. This can be done hydraulically using cylinders
or mechanically, e.g. using toggle levers.
Another movement required is ejecting the molded part
from the mold. This takes place after cooling or after crosslinking (depending
on the type of plastic). Pins enter the mold for ejection and eject the finished
part.
Clamping units are normally arranged horizontally.
However, with certain shapes of the components it may also be necessary to
arrange the clamping unit of the injection molding machine vertically. This
depends on the influence of gravity on the flow behavior of the material.
What can tramao offer you in terms of injection molding
machines?
Injection molding machines are available in a wide
variety of variants. The variance consists among other things in the size and
stroke of the extruder and the associated amount of material that can be
brought into the mold in one cycle. Furthermore, the pressure in the extruder
and in the clamping unit determine the possibilities of the injection molding
process and the workpiece contours.
That is why you will find injection molding machines from
various manufacturers on tramao, including Battenfeld, Arburg, Krauss Maffei,
Boy, Engel, Demag or Zhafir.