Which Valve Is Best for Your Plastic Injection Molding Project

Which Valve Is Best for Your Plastic Injection Molding Project?

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A plastic injection screw valve is a crucial component in the plastic injection molding process. It is the part of the injection molding machine responsible for controlling the flow of molten plastic into the mold. The screw valve operates by rotating and moving axially within a heated barrel, melting plastic pellets and pushing the molten material forward. As the screw rotates, it creates pressure that forces the molten plastic through a nozzle and into the mold cavity. The precise control of the screw valve ensures consistent flow, pressure, and temperature, which are essential for producing high-quality plastic parts with accurate dimensions and minimal defects.

Several types of valves can be used, and the main types include (but are not limited to):

  • MDP Valve: The MDP valve is the most advanced injection molding valve on the market. It takes the place of all of the valves we will discuss below. An MDP valve consists of a retainer body, free flow check ring, rear seat, and a carbide pin. This valve offers the highest flow level and least restriction through the check ring vs. any other. The carbide pin is inserted into the retainer body up against the front of the check ring, allowing for an extremely long life for the valve. This high-flow design allows for any type of resin to be used; glass-filled, thick, or thin resins do not affect performance or reduce the valve’s life. Unlike other designs, it is also excellent for precision short-stroke shots, for there is virtually zero pressure drop. Allowing the check ring to move back and seal the second the screw injects forward, eliminating or minimizing the need for decompression in your process. 
  • Ball Check Valve: This valve uses a ball mechanism to achieve a one-way flow while preventing backflow during the screw’s recovery phase. When the screw rotates, the ball moves to allow the plastic to flow, and when the screw injects forward, the ball seals the flow. It provides good sealing but may be more prone to wear and leakage.
  • Check Ring Valve: Also known as a check valve or non-return valve, it is the most commonly used type of valve in injection molding. The check ring valve ensures the plastic flows in only one direction, preventing backflow and maintaining consistent pressure. It consists of a ring that moves forward to allow the flow of plastic during charging and moves back to seal off the flow during the screw’s injection forward phase. It is simple and reliable.
  • Free-Flow Valve: This type of check ring valve allows for a continuous flow of molten plastic without any significant restriction. Unlike other valves that may have mechanisms to control or restrict the flow to prevent backflow or to seal tightly during certain phases of the injection process, a free-flow valve focuses on maximizing the flow rate of the material. This can be beneficial in specific applications where high-speed injection is required, or the material needs to fill the mold cavity quickly and uniformly. It is also a good choice for glass-filled resins.
  • Locking Valve: Also known as a lock ring valve, this check ring type valve is designed to lock or seal tightly when the screw is in the forward (injection) position, preventing any backflow of material. This mechanism ensures that the molten plastic is consistently pushed forward into the mold cavity without any leakage or loss of pressure. These valves are particularly useful in applications utilizing thin viscosity resins requiring high precision and consistency, producing complex or high-tolerance plastic parts. A locking check ring is not recommended for glass-filled resins; the glass fiber will get on top of the check ring, acting like a hone and wearing your barrel out prematurely. 
  • Poppet Valve: This valve operates using a poppet mechanism, which consists of a movable poppet that opens and closes to regulate the flow of plastic through the injection screw. When the screw retracts and charges, the poppet is pushed backward, opening and allowing molten plastic to flow into the mold cavity. Conversely, when the screw moves forward for injection, the poppet seals tightly to prevent backflow. Poppet valves are known for their precision and reliability, providing excellent sealing performance and ensuring consistent injection pressure. They are particularly beneficial in applications utilizing thin viscosity resins requiring high accuracy and quality in molded parts. It is a modern-day ball check valve with a higher level of precision.

Choosing the correct type of valve for your project depends on the specific requirements of the injection molding process, including the type of material used, the desired precision and consistency, and the production speed. When in doubt, contact a valve professional such as Santa Fe Machine. They can give you better insights into how your machinery is running, put together a comprehensive package to enhance optimal efficiency and match the best valve design to your screw and project specifications.

How can we help you?

The doors have been open at Santa Fe Machine Works, Inc. since 1923, and for the past 45 years, we have been dedicated solely to manufacturing and supplying new & rebuilt injection & extrusion screws, barrels, end caps, tie bars, & valves to the plastics industry. We also offer custom-tailored screw, barrel, and valve combinations, allowing our customer’s production goals to be met in the best, fastest, and most cost-effective ways possible. Our employees have over 200 years of combined experience in the plastics industry and are eager to support your specific extrusion or injection needs. Have a question, need assistance, or looking for a quote? Contact us today!