Nowadays there are two commercial microinjection technologies:
­    Direct injection moulding by a plasticizer screw.
­    Injection by a direct piston.

Apart from these expanded technologies, there are some auxiliary devices permitting microinjection.


7.3.1 Direct injection with plasticizer screw

The direct injection with a plasticizer screw uses the same technology as conventional injection machines. Actually the plasticizers groups have just been scaled down. The screw used is usually 12, 14 or 18 mm.

This system has the advantage of simplifying the plasticizer system, since a small screw is used to plasticize, dosing, decompress and press the plastic into the mold (injection).


7.3.2 Injection by direct screw

In the injection by direct piston, the plasticizer unit is composed of a extrusion group independent of the injection unit, which consists of a screw that only plasticizes and dosages a quantity of plastic, which is transferred to the piston chamber to be pushed into the mold by the piston

To prevent the degradation of the material exist alternative plasticizer units, such as the injection molding machine designed by Battenfeld in which the plasticizer is composed of a extrusion group that plasticizes and doses the exact amount of material needed for injection.

With this system it is possible plasticize the exact amount of material that requires an injection with the screw extruder. The material is placed in the injection chamber and then a piston injects it into de mould: this permits that the material don’t degrade, because it is only plasticized the amount of needed material for an injection.

It can be seen below the difference between a conventional hydraulic injection unit and injection unit with extruder screw and plunger, in terms of injection speed:

7.3.3 Machinery and auxiliary devices for microinjection

Some manufacturers of processing machinery use assistance techniques to obtain micropieces with auxiliary devices. A clear example is the X-MELT used by Engel, which is applied regardless the used screw technology and for completely electric operated machines with a certain tonnage. This technology consists in a high pressure prechargeon plasticized material in the in injection chamber. One valve opens the mechanism at the time of injection and the material expands with high virulence into the mold.

Another auxiliary mechanism which helps microinjection was patented by the machines manufacturer Ettlingen. It was based in direct injection technology with a plasticizer screw, and is formed by a mouthpiece of prolonged machine that acts as a piston working on a hot camera system that flows into the mold, combining the screw and the piston.

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