Consider using 1 of these 3 types of Rodless Air Cylinders for your next machine design
Most design engineers will specify air cylinders when simple point to point linear motion is required.
A standard piston rod type typically would be selected, but if space is restricted to fit a standard air cylinder or when a long stroke is required, then a rodless air cylinder should be considered.
Not only is the rodless air cylinder great for space savings, it has many other advantages;
- Self-Guiding: Self-supporting characteristics of the rodless air cylinder of the piston throughout the stroke of the stroke – an external guide mechanism is not required like a convention air cylinder.
- Long strokes: Some manufactures of rod cylinders can manufacture strokes over 20 feet.
- Equal Force: The piston area on each side is equal which makes it easier to stop the cylinder in mid-stroke.
- Inherent Rigidity: Integral strength and rigidity of the complete cylinder assembly will accommodate the heaviest of loads enabling the cylinder to form part of the structure or framework.
- External guides: In some applications when a cantilever load exceeds the cylinder rating, the manufacture will offer different types of external guild systems that will be attached to the total length of the rodless cylinder body.
- Joint clamp: Two cylinders mounted in a tandem configuration for increased load and force requirements. This design enhances lateral support and bending moment capabilities.
Types of Rodless Air Cylinders
Slot Type Rodless Air Cylinders, involve a barrel extruded aluminum with a slot running the entire length to form the main cylinder body. For added rigidity, the slot is eccentric to the outside of the diameter of the barrel. The method used to seal the slot differs among manufacturers. Some use a simple metal-to-metal stainless steel sealing band; others include composite plastic-and-rubber systems which interlock with the slot or an outer band of similar construction. The outer band sealing band acts as a dust cover to prevent migration of foreign particles.
Magnetically Coupled Rodless Air Cylinders, contain a piston carrying a series of permanent magnets and stroking within a cylindrical stainless steel tube. A second set of magnets mounted in the drive carriage provides a magnetic coupling between piston and carriage. This simple design requires no external seals . Its limitations includes a tendency for the piston and carriage to separate under high inertial loads, thus restricting high speed operation. Additional guidance may be necessary for any high direct or cantilevered loads. It is possible to use a magnetic piston rodless cylinder with low pressure hydraulic fluid with the correct piston seals.
A band type rodless cylinder cannot be used because it would leak. Using the cylinder with hydraulic fluid and two air/oil tanks would allow the rodless cylinder to move at a very slow and steady rate. Trying to move the same cylinder slowly and steadily with compressed air would cause the cylinder to move erractically.
Cable type Rodless Air Cylinders, this type cylinder contains a piston that has a cable attached to both sides of the piston. The cable on both ends goes through the end caps around a pulley to a mounting bracket. Cable Cylinders are designed for externally guided loads. They also can be configured with extra cable length for the purpose of mounting the main body away from work area. Just like a magnetic rodless air cylinder, they can be used with low pressure hydraulic fluid with the correct piston seals
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Written by Ralph Quarto
Senior Pneumatic Technical Support Engineer
Certified Pneumatic Specialist – CFPPS (818) 768-1200