Definitions: 1. to draw or be drawn by or as if by suction. 2 a pipe or tube through which something is drawn or sucked. 3 to take hold of and attempt to bring toward or after oneself or itself. 4. Pin or pins used to extract solidified plastic material from a runner path or void.

In the design of tooling sometimes we need to place the runner and or gate onto what can be called the wrong side of the tool and or because of design into the moveable plate. Examples of these types of arrangements can be found in 3-plate molds, stripper plate molds, and tunnel / submarine type gate arrangements. We than need to pull out or suck out the runner and or gate via the use of a puller pin or sucker pin (to be referred to as pin).

Now in a stripper plate mold we would place all runners into the A plate (cavity) of the tool and than pull the runner and possibly the gate out onto the B plate (stripper plate) via a pin arrangement. In my experience, more so years ago but even now I find that the placement of the pin is 80% in the runner path. Thus we have now just created a shear point in said runner path, along with a pressure drop. This could be a help creating shear, but in most cases it is a problem, a pressure drop and or impedance to flow.

A few things happen when we do this;

1-     The path must be opened up to accommodate the flow of material. This is seen as the bulge in the path

2-     The pin is now heating up as material rushes by, increasing cycle time.

3-     Due to the bulge and excess material now used to accommodate flow we are increasing both cycle time and material usage for the production of the part.

4-     The pin is incorrectly placed into the tool, creating a sticking issue via flash in the long term.

Now all these above mentioned issues are true for three plate molds too plus the pin directly over the drop. With a three plate the pin must be cut to provide enough force to pull and break the gate on the drop. In searches done it was found that only materials that are at or below a shore durometer of 35D need have the pin directly over the gate drop.

Designs of pins and how they are placed in the tool do vary. One design method has been to place directly into the flow path. This should be avoided as the issue above states the case for change. Another is to place the pin below the flow path and than create a column or dome on top of the runner that now encases the pin. This now allows an unimpeded flow path and if we are using a stripper sleeve around our pins works very well. If we are using a stripper plate arrangement than we have an issue as this bump, dome or column is now in the stripper plate and we are hoping that gravity does it's thing and allows our runner to fall even though we are cut into the stripper plate.

The other design is to place our puller tangent / besides the runner path. What this does is to pace it outside the flow path, cuts it into the same cavity plate as the runner and allows the stripper plate or X plate to work as it is designed to. There is no hold up points to stop the runner from falling. Flow can now be optimize within the flow path to a minimum size and still pull the runner out. The pin does not heat up as material is not rushing by. The wall thickness around the pin can be optimized to maintain a good cycle time.

From a tooling point anytime we have a pin / hole arrangement with movement we have wear. In all pin arrangement we should have clearance and or movement of pins that indicate they can adjust a bit when running. If our clearance is too much or we end up having too much wear flash can become an issue. This issue results in a hang-up area when trying to eject the runner. Being that we have flashed down the pin.

To eliminate wear issues, our pins should be created with a taper and upon clamp over of the tool seal to the matching taper in a hardened insert or the plate itself. This than creates a sealing point and becomes self aliening, with a loose arrangement thus eliminates wear. It is also going to cost more up front. If we were to just bush the pin at the seal point we can eliminate some wear but not all and it still will cost more to insert a bushing with a straight hole arrangement.