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Magnetically coupled cylinders are air cylinders that have been designed to fill a specific need! For some reason, the application will not allow a normally-connected air cylinder with rod.
Unlike other types of rodless air cylinders, like band cylinders or cable cylinders which have the cylinder carriage mechanically attached to the piston, there is no mechanical connection between the external carriage and the piston inside the cylinder in a magnetically coupled air cylinder.
Instead, the magnetically coupled rodless air cylinder has a strong rare-earth magnet as a component of the cylinder piston. Another similar high-strength magnet will be part of the cylinder carriage.
The attraction between these two magnets is what allows the carriage to be propelled along outside the cylinder barrel without any mechanical connection between the two.
In the drawing above I focus on the piston inside the cylinder barrel, conceptualizing the magnet built in as part of the piston assembly.
Each manufacturer of magnetically coupled air cylinders will have their own design, of course. This drawing is to show concept, not engineering details.
The sketch below shows the carriage on the cylinder to the left, and then an end view of the carriage, with the magnet as part of the carriage itself.
Coupling Force in a Magnetically Coupled Cylinder
Depending on the manufacturer, there may be a single magnet design, with one magnet only as part of the the piston and in the carriage, or a different brand may have multiple magnets in each of the piston and carriage. Each design is unique to that manufacturer and to the designed in coupling force.
A smaller magnetically coupled cylinder will have less coupling force due to only having room for smaller magnets. The design may try to overcome this by having more than one magnet in the piston and the carriage.
Magnetically Coupled Cylinder Mounting Styles
Mounting styles of the magnetically coupled cylinders vary too. The simplest is the cylinder with a threaded tang on each end. These tangs fit through a hole in another piece of equipment, and then a jam nut is threaded onto the tang which clamps the cylinder in place.
Different styles from different manufacturers offer variations on plumbing compressed air to the magnetically coupled cylinder, some having air ports in the end, others on the sides of the end caps.
How you need to install the magnetically coupled cylinder in your application might determine which manufacturer you acquire the cylinder from, as not all have the cylinder mounting style that may be needed.
Benefits of the Magnetically Coupled Cylinder
Benefits of the magnetically coupled cylinder design include…
- leak proof, making them ideal to use in areas where compressed are leaks would be a problem
- many can be used for low pressure hydraulic service
- re-coupling of carriage to piston simply requires moving the carriage to where the piston is located inside the barrel
Negatives to the Magnetically Coupled Cylinder
Negatives of the magnetically coupled design include…
- high speed carriage movement combined with rapid or hard deceleration can uncouple the carriage from the piston
- the carriage has no mechanical connection to the cylinder itself, therefore, an external load and carriage guidance system is almost always required
- tend to be higher cost solutions over other rodless cylinders
Selecting a Magnetically Coupled Cylinder
What are some of the things you need to know to select the appropriate magnetically coupled air cylinder?
- the weight and size of the load you wish to move
- how will the carriage be supported
- distance the load will be moved
- the speed required in distance per second
- load deceleration and stopping
- is position sensing required
- how will the cylinder be mounted
There is no question that, in load-moving applications, the only solution is the magnetically coupled cylinder. Knowing this style of air cylinders are available may help make the machine design a little less complex.