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Non Return Valves: Screw Tips

Considerations in selecting the correct screw tip (Valve)

While the least expensive of all the processing components, the check valve may be the most critical to good processing. Therefore, it is very important to use excellent quality non-return valves. The old adage is usually true here: you get what you pay for.

Nozzle Valve Screw Tip Manufacturing and RemanufacturingObjective

  • Optimized flow off the end of the screw
  • Eliminate degradation of resin
  • Eliminate inconsistent shot (scrap)
  • Minimize Barrel wear
  • Maximize Tip component life

Key Elements in achieving the objectives

  • Optimized design (geometry)
  • Knowledge of resin processed and parameters
  • Correct matching of component alloys
  • Precision tolerance machining
  • Defined heat treatment procedure

Tip design groups

  • 3 piece free flow
  • 3 piece castellated (locking)
  • 4 piece
  • Ball check

There are many different screw tip designs available today, each with different features, benefits and limits. Choosing the best valve design will depend on the type of resins and fillers being processed. Optimized screw design and machine set-up are key factors in maximizing tip function.

There are many choices of steel alloys to select from depending on the process demands, Concor commonly uses: D2, CPM -9V, CPM-M4 and 20CV

What is most critical in valve performance is the precision of the machining of the contact surfaces and how “true” critical dimensions are aligned. This insures proper material flow and excellent shot repeatability.

Three Piece Free Flow Design

This design type has deep smooth flute areas on the tip allowing a “free flow” of material off the screw. Concor’s Veloci-T™ free flow design has improved shut-off over other free flow valves. Most of Concor's customers prefer the Veloci-T™ free flow 3 piece. Many are in stock.

Features & Benefits

  • Less restrictive than 4 piece or ball check designs - reduced wear and material degradation
  • Ideal for shear sensitive materials such as PC, ABS, PVC, because the ring floats "free"
  • The ring does not rotate with the screw, extending barrel life
  • Design allows for processing a variety of materials – provides flexibility for custom molding
  • Design eliminates dead spots minimizing material degradation
  • Ring is designed as sacrificial wear component –simple and cost effective

View our Veloci-T Flyer

Veloci-T™ tips provide large front face ring target area and specially engineered rear seat to assure positive shut off of low viscosity (i.e. Nylon) and high filled resins – minimize scrap.

Veloci-T™ tips are made of CPM M4 HIPPED tool steel providing high resistance to heat, impact & rotational wear of contact surfaces - extended wear life / reduced cost.

Locking (Castellated)

The tip and ring have interlocking cutouts that look similar to a castle turret; hence the name. The ring is always interlocked with the tip and rotates with the screw. It is commonly found on many OEM machines produced in Asia.

Advantages:

  • Good shut off.
  • Contact wear between ring and seat is reduced.

4 Piece Design

This design features the front seat as a separate replaceable wear part. The check ring contacts the “front seat” rather than against the tip itself. It is available with wear parts out of carbide or ceramic.

Advantages:

  • Provides good shut off
  • Front Seat can be replaced separately

Ball Check Valves

This design makes use of an internal ball to provide shut off. Designs can be front discharge or side discharge.

Advantages:

  • Accurate and consistent shut off.
  • Good for PP, PE, PS, nylons. Often used with larger presses (over 1000 T)