Guides are absolutely essential elements in the world of hydraulics and pneumatics. They are installed in the piston rods and pistons of hydraulic and pneumatic cylinders, in order to allow good guidance between the piston and the cylinder liner or between the piston rod and the cylinder head. The use of guides prevents damage caused by contact between metal surfaces.
Furthermore, the guides must allow smooth, straight movement with as little friction as possible in order to minimising energy losses as much as possible due to friction. For this reason, you need to choose the right material for your slides. In this article we want to make your decision a little easier.
Index
Materials for guides on hydraulic or pneumatic cylinders
The main materials for guides in hydraulic or pneumatic cylinders are:
- PTFE loaded with carbon.
- PTFE loaded with bronze.
- Resin with fabric.
- Thermoplastics, including polyamides and acetal resins.
The first thing to bear in mind when selecting the most appropriate material for the guide is that friction between moving parts of a mechanism is a two-way affair. That is to say, you must take into account between which materials the friction is going to occur: that of the guide itself and that of the contact surface in the cylinder, normally a metal.
We will choose the guide of PTFE + Carbon where contact is made with a non-ferrous metal (aluminium, copper, brass alloys, lead, nickel), or in contact with plastic materials, which is becoming more and more common in the world of pneumatics. The PTFE + Carbon guide material is particularly suitable for pneumatic applications or in poor lubrication conditions, as the air in the pneumatic system often contains moisture. In this case the contact between bronze, water and other metals can lead to corrosion.
On the other hand, the material for guides PTFE + Bronze is indicated when the contact surface is of ferrous metal (irons, cast irons and steels) and preferably with oils or lubricating fluids. This is often the case with hydraulic cylinders.
Another reason for using PTFE-based guideways is the high temperatures. However, you must take into account that, although its temperature limit is higher than other guide materials, its mechanical resistance decreases with temperature.
The guides produced in fabric reinforced resin, and also the thermoplastics are suitable for cylinders that work with high compressive loads on the guide itself. In these cases, these materials resist wear much better than PTFE guides.
Available sizes of guides in hydraulic or pneumatic cylinders
The bronze or graphite filled PTFE guides are usually supplied in the form of an open ring, i.e. with a cut-out for easy installation in the cylinder. These guides are preformed to better adapt to the required dimension.
There are also guide tapes or bands which are supplied in rolls of varying lengths, in sections and widths to cover any application. This allows the installer to cut the required length on each cylinder.
In the case of resin guides reinforced with fabric, are usually supplied either in the form of a shaped ring or in spiral form. The latter are available in both metric and inch dimensions.
In addition, in our production workshop, we can manufacture rings from guide in both filled PTFE and Thermoplastics, We are able to manufacture slides in rectangular sections or special shapes, such as T-sections, L-sections or special shapes to drawing. We are able to manufacture slides in a very short time up to 600 mm diameter, depending on the availability of raw material in our facilities.
Incorrect selection of guide material in hydraulic or pneumatic cylinders is one of the main causes of premature cylinder failure.
Do not hesitate to contact us at your needs.