Sprue pickers are industrial robots that are designed to remove sprue from molded parts.  The term “sprue” refers to the passage through which liquid or molten material is introduced, and to the excess material that forms. During plastic molding operations, the material in the sprue solidifies and must be removed from the finished part.  

How Sprue Pickers Work

Sprue pickers are pick-and-place machines that feature vertical motion and a horizontal swing arm. Most are pneumatically-driven, with an air cylinder that operates at about 60 to 80 psi.  First, a vertical main-stroke follows the centerline and grips the sprue. After the pneumatic cylinder returns to the vertical up position, the horizontal arm extends and releases the sprue. Typically, this excess material is dropped into a tote, or released into a granulator for regrinding.  An unloader then returns the regrind to the hopper, where the sprue is mixed with virgin material and reintroduced into production.

Types of Sprue Pickers

The GlobalSpec SpecSearch database contains information about both manual and automated sprue pickers.

  • Manual sprue pickers are suitable for applications where operating time is not critical, and the number of mold changes is limited. Some suppliers refer to these machines as simple or mechanical sprue pickers.
  • Automated sprue pickers are recommended for applications where rapid operating times are important, and there are a large number of mold changes.  These machines are controlled by microprocessors, and operators can program complex sequences of mold changes into memory. 

Semi-automatic sprue pickers may also be available.

Product Specifications

Buyers of swing-type industrial robots need to specify both the swing angle and swing direction. Typically, the swing angle ranges from 50 to 90 degrees.  The swing direction can be to the operator side or to the rear side. Mold clamping force, which is typically measured in tons, is also important to specify.

Additional parameters for sprue pickers include power voltage, control method, working pressure, and maximum allowable pressure. There are three components to the adjustable stroke: descent, kick, and swing. Buyers of sprue pickers should also consider air consumption per cycle, maximum weight capacity, and the weight of the robot.

References

Yushin America – Swing Arm Sprue Pickers

Tool and Manufacturing Engineers Handbook, Chapter 17 – Plastic Manufacturing