Customizing your Airpot Series: Connecting a Rod to Airpot or Airpel Piston
One issue that comes up when customizing your Airpot or Airpel pneumatic cylinders is how to connect a rod to the piston.
The simplest way to connect the piston to the rod in pneumatic cylinders is usually the worst, but is sometimes actually appropriate, so let’s discuss it. The type of connection is a rigid connection between the rod and the piston. Usually the best way that this is done is by epoxy bonding the two parts together while holding the rod in a simple alignment fixture to keep it coaxial with the piston. The big disadvantage of this type of connection is that unavoidable side loads applied to the rod can lead to large moments applied to the piston, which leads to high reaction loads to the cylinder, which leads to high friction of the piston. To minimize the friction, short rods and very carefully applied axial loads are needed.
For Airpot’s standard designs of pneumatic cylinders, the most common way we connect the piston to the rod is with a ball-and-socket joint. We have some standard ball and socket joints that are just great because they use a Teflon alloy liner in the socket, so there’s no need for oil or grease which gives a clean and low friction ball and socket joint.
However, a very low-friction ball joint must have some clearance between the ball and socket which is not good for some applications. Also, high cycling, especially with alternating push and pull forces on the rods can cause wear and increase play (shuck) in the joint over many cycles which for some applications is very undesirable. In those cases we have another scheme, which is to use what’s called a wire flexure connection.
A wire flexure is just simply a thin piece of very strong stainless steel spring wire connecting a rigid rod to the piston and so the very slight bending of that wire gives us a motion that’s very similar to a ball-and-socket joint for “small motions”. The wire flexure joint although it has a bit of spring to it, is truly frictionless and has exactly zero play and it has zero wear, so it has many advantages over a traditional ball and socket joint. Below, we have some pictures of both the cutaways of the standard ball and socket joint, and a wire flexure joint. The wire is usually brazed to another stainless steel part that bolts to the piston.
Sometimes a pin joint is best, especially if it’s important that the rod must pivot relative to the piston in one plane. Care must be taken to consider what happens if there is a small pivoting of the rod out of the normal rotation plane.
For more information on Airpot’s pneumatic cylinders, visit our website at https://www.airpot.com/, or call 203.846.2021 and ask to speak to one of our engineers about your specific project and how we can help your business work more efficiently.