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Flexibility – finding the right polyurethane tubing part 3


Flexibility – one of the key characteristics of polyurethane tubing

Overview of the article series:

  1. Polyurethane resistance against environmental influences
  2. Working pressure and bursting pressure
  3. Flexibility – the minimum bending radius
  4. The Pricing of polyurethane tubing

The minimum bending radius as a measurement of flexibility

Certain metrics are familiar to everyone: The temperature gets measured in degrees Celsius. Pressure gets expressed in Bar. But what about a tubing’s flexibility? There is a metric for that as well to make polyurethane tubing comparable to each other:

The minimum bending radius.

Of course, this comparison to the well-known metrics is not really accurate. Nevertheless, the minimum bending radius enables reliable statements concerning the flexibility of tubing. Here, the measured parameter shows how tight a tube can get bent without kinking. For example, polyether-based polyurethane tubing with an outer diameter of 16mm, can be installed with a radius of at least 55mm without kinking. In the case of a polyester-based one, at least 65mm has to be ensured to not damage the tube. Thus, polyether-based tubing is the better alternative if an installation in tight spaces is the plan.

In general, flexibility is one of the strengths of polyurethane compared to other materials. For instance, the much stiffer material polyamide needs significantly more space during the installation. Read more about the comparison of polyamide vs. polyurethane.

What is relevant to the flexibility of polyurethane tubing? 

The material type got already mentioned as an influencer of tubing’s flexibility. Polyurethane is very flexible in general. But there are significant differences between the varieties. If polyurethane tubing has to get installed where space is scarce, a type as flexible as possible has to get found. However, other factors as the needed pressure durability or the resistance to environmental factors, should not be neglected. The most flexible tubing, therefore, is not always the best choice.

The hardness: Similar to working and bursting pressure, the degree of hardness plays a noticeable role in flexibility. To a certain extent, pressure resistance and flexibility are antagonists. The stiffer the material, the more pressure the tubing can endure. On the other hand, the minimum bending radius increases with the rising hardness levels of the material.

The wall-thickness: Wall thickness plays a role in the flexibility of polyurethane tubing as well. Unfortunately, the rule of thumb is the same as with the hardness: The thicker the wall, the higher the pressure resistance, but the lower the flexibility.

Special variants: If one bends a plastic tubing, it will eventually kink as soon as its minimum bending radius is undershot. Not even the highly flexible material polyurethane is an exception to that. However, there are some special variants that make even smaller bending radii possible, such as the anti-kink tubing KSS. This special product has an inner profile that enables flow regardless of how much the tubing is bent.

Conclusion on the flexibility of polyurethane tubing

The minimum bending radius is a metric that makes it possible to compare the flexibility of different tubes with each other. The smaller this radius is, the higher the flexibility. The type of polyurethane used has a significant impact on the tubing’s flexibility. In terms of hardness and wall thickness, flexibility can be seen as an antagonist to pressure resistance to a certain extent. If the material gets softer and the wall thinner, the flexibility increases. On the other hand, the pressure resistance decreases. In the end, every single application has its perfect tubing, and the challenge is to find it. The easiest way is to contact the manufacturer of your choice!

Several kink-proof pneumatic tubes wound into each other