As the name suggests, it is tubing made from the class of chemicals known as polyurethanes. These were first made in 1937 by Otto Bayer and his co-workers. Polyurethanes belong to a class of polymers called reaction polymers; molecules containing two or more isocyanate groups per molecule (R-(N=C=O)n) react with polyol molecules containing, on average, two or more hydroxyl groups per molecule (R’-(OH)n) in the presence of a catalyst. The degree of cross-linking in the polymer determines how rigid or flexible the resulting material is; clearly, tubing requires a relatively high degree of flexibility.
They are also known as...
Polyurethane is often abbreviated to either PU or PUR
How does polyurethane tubing work?
The nature of the material makes it impervious to air under a stated pressure, so it is an ideal ‘conduit’ for compressed air in a system that requires flexibility for connection. The material also makes it well suited to providing a good seal in push-in and push-on type connectors.
How do I select polyurethane tubing?
There are a number of factors to consider:
- operating pressurethe required pressure of the pneumatic system must be considered. The maximum pressure for the tubing ranges from 9 bar to 12 bar, dependent on the outside diameter and tube thickness (see table at end of article and manufacturers datasheet for detailed advice)
- operating temperature - whilst polyurethane has good temperature stability, the operating temperature will impact the maximum advised working pressure. The maximum working temperature is rated at +600C and, at this temperature, a factor of 0.5 must be applied to calculate the maximum operating pressure. So, for example, whilst at -400C to +200C the maximum pressure for a 4mm outside diameter tube is rated at 10 bar, this must be reduced to 5 bar when working at 600C. Again, see the end of the article and consult the datasheet for more detail.
- system design - flow considerations in a system may require a minimum internal diameter to avoid restricting the flow; alternatively, a pre-existing design may call for a specific diameter tubing. It is always good practice to avoid undue kinks and bends in a system design; there is also a minimum bend radius allowed for the tube, dependent on diameter. For example, for a 6mm outside diameter tube, the minimum bend radius is 9mm (see table at end of article); it should be noted that this is significantly ‘tighter’ than for polyamide (PA) tubing. Finally, the run length of the tubing must be considered; standard lengths of 25m and 100m (for some diameters/colours) are sufficient for most applications.
- working environment - the nature of the environment must be considered. As stated above, temperature is a critical consideration and the combination of temperature and a hostile chemical environment could make polyurethane an unsuitable choice.
- application standards - there may be certain standards that must be met; for example, for food environments or use on commercial vehicles.
Types of polyurethane tubing?
There are a variety of types to suit the selection requirements above
- tube diameter - common selections from 3mm to 16mm outside diameter
- tube colour - a variety of colours – natural, red, green, yellow, blue, black, silver – to allow pneumatic circuits or spurs to be distinguished from each other where necessary.
Typical applications for polyurethane tubing?
As can be imagined, the excellent mechanical properties and flexibility of polyurethane tubing make it ideal for many industrial applications.
Do I need anything else for polyurethane tubing?
Fittings will be required in order for the connections to be completed within the system. Push-in or push-on fittings are ideal.
A tube cutter should be used to ensure a perpendicular, clean cut end of the tube; tube channel or clips allow the tube to be secured neatly in a pneumatic circuit.
