Conventional screw-tips consist of a tip, a locking ring, and a thrust ring. During plasticizing, the mass flow pushes the locking ring forward against the vanes of the rotating tip. This contact causes wear on both components. To prevent wear, the contact surfaces are often hard-faced or carbide-tipped.
The patent-pending inmex non-return valve takes a different approach. It uses a two-part locking ring, with both ring halves internally guided by a fit with the extended vanes of the tip. The front ring segment engages with claws between the vanes of the tip, allowing the ring to rotate during plasticizing. The outer diameter of the front segment is smaller than the screw diameter, preventing the barrel from being worn by the rotating ring. The second ring segment, positioned toward the screw, corresponds to the nominal diameter of the screw, ensuring that it seals with the thrust ring during injection as usual. During metering, the first ring half is actively rotated, but the second ring half is not. As a result, the wear surface is no longer located between the vanes and the locking ring, but between the two ring segments, and is now three to four times larger than the standard size. This significantly extends the service life of the locking rings in the event of abrasive wear.
In addition, the locking rings are pre-centered by the internal guide and close reliably for longer during injection, even with progressive wear. Another advantage concerns the screw, which is supported at its tip by the internally guided locking ring. This prevents the screw’s vanes from being pressed against the barrel, which also has a positive effect on the screw’s service life.
