To show our TP 125 torpedo nozzle in action during the next K fair in Düsseldorf we will exhibit a 100 tonne BM Biraghi machine on our stand to demonstrate the molding of acrylic lenses for light-emitting diodes (LEDs). The lenses, 1 cm thick and 2.5 cm in diameter, will be molded in an eight-cavity hot-runner mould with an injection orifice of just one millimeter.

LEDs are now widely used in all areas of illumination, from traffic lights to automobile front and rear lights, from giant displays to electronic devices, and many more. In most cases, the LEDs are fitted with synthetic lenses that enable the light beam to be adapted to all sorts of illumination requirements. Obviously the two essential characteristics demanded of all these lenses are transparency and absolute perfection.
The molding of thick parts is a practice used not only when the thickness is required to provide a particular functionality in the part, but especially when ‘playing’ with the thickness can be used to enhance the perceived value of a part. But molding thick parts requires the use of very high holding pressures, which in turn demands the use of adequately sized hot runners and injection points that prevent significant pressure drops between the injection unit and the mould cavity.

Put another way, to get a similar result requires very high flow rates and extremely low (if not zero) leakage, in order to guarantee an effective compaction of the plastic, sufficient to eliminate any possible shrinkage that would negatively affect part characteristics, as well as the esthetics, form and dimensions of the part.
These production demands can be met with the type of torpedo nozzle developed by us, which fulfills all necessary requirements despite having an injection orifice of just one millimeter. This demonstrates that even with its very small dimensions, the nozzle can still be used for molding technical parts at the highest level.

In conventional torpedo nozzles, the shut-off pin is normally positioned along the melt flow axis, up to the injection point, where the melt passes into the mould cavity through two or three very small orifices.

In our torpedo nozzle, however, the pin is set at an angle to the flow channel, allowing the melt to flow more freely all the way to the injection point. This solution has a particular advantage, for example, for injection molding materials containing masterbatches or reinforcements (especially long fibers), as it minimizes the tendency of the additives and reinforcements to separate from the polymer, yielding improvements in the finished product both in terms of properties and esthetics.

Normally, in fact, the torpedo has the effect of ‘directing’ the material, which ends up taking, in a manner of speaking, preferential paths into the mould, at the cost of a homogeneous fill. The particular construction of our nozzle with its angled needle, moreover, makes it possible both to reduce the pressure loss – since there is more space in the unrestricted flow channel – and also to reduce the time taken to make color and material changes, without having to take the mould out of the machine.