They are also known as…
They can also be called rodless actuators and the term 'rodless slide' is sometimes used.
How does a rodless cylinder work?
A piston moves within a cylinder bore, driven by compressed air, very much like a conventional profile or tie-rod cylinder; the difference is that motion is transmitted to outside through the body length, rather than by a piston rod through an end cap.
A 'strut' connects the piston to a table which runs on guides along the length of the cylinder. Air pressure is maintained by a sealing strip which 'breaks' around the strut, as the table moves, then re-seals. Clearly, the sealing strip also maintains sealing around the strut to reduce leakage to an acceptable level. The IMI Norgren Lintra seal gives extremely low static leakage values when in use.
How do I select a rodless cylinder?
Firstly, does the application lend itself to the use of a rodless solution; for example, if turning moments, or torque, risk buckling of the piston rod of a 'conventional' cylinder, more likely over long traverse distances, then rodless cylinders are ideal.
You will need to consider the load (Kg) to be moved, the distance and the speed. The load can be equated to force by multiplying by the gravitational acceleration; the force tables can then be used to determine which type of rodless cylinder is best suited and the required bore calculated.
Don't forget, as outlined in an earlier article, we always recommend a safety factor in force calculations so that cylinders aren't working at their limit. As rodless cylinders will be operating 'dynamically' (i.e. they are almost always bearing a load), this factor will be 50%.
Any moment of inertia must be considered; put simply, this is a twisting action on the guide table and can be calculated in vertical, horizontal and transverse directions. The ability to withstand moments increases from internal guide, through external guide to precision roller bearing. For speeds up to 2m/s a calculation program, Lintra Pneucalc, can be requested.
The distance over which the load travels will determine the stroke length required.
Types of Rodless Cylinder
Our Lintra range of double acting cylinders is amongst the widest and most comprehensive offer of rodless actuators available.
The range covers light to heavy duty applications. For 63mm bore versions, the internal guide can bear a vertical force of 2,000N, the external guide version a vertical force of 3,200N and the precision roller guide version 6,400N. It should be noted that these values apply for maximum speeds of 0.2m/s and with constant movement over the whole stroke length.
The Litntra range also features integrated guides, which are housed in the main extrusion. There is also a user-friendly sealing strip that significantly reduces the risk of injury due to sharp edges.
Typical applications of a rodless cylinder
Rodless cylinders are ideal for applications where buckling of conventional cylinders may be a problem; this is particularly the case where long stroke lengths are required.
Strokes of up to 8.5m are available for 16mm to 40mm bores; 8m for 50mm and 63mm bores and 5.5m for 80mm bore.
Further, they can operate at much higher speeds than conventional cylinders. So, objects can be transported over large distances in an acceptable time.
Do I need anything else to make a rodless cylinder work?
Rodless cylinders need to be connected into the system, so fittings and tubing are essential. As a component, the correct filtration and pressure regulation will be important. Although not essential, slots in the extrusion allow use of the IMI Norgren M/50 series switches and grooves accept industry-standard aluminium machine building systems.