The piston rod is too smooth, which also affects the sealing life of the hydraulic cylinder

The piston rod is too smooth, which also affects the sealing life of the hydraulic cylinder

       For hydraulic cylinders, high-precision parts, sometimes the cleanliness is not as bright as possible. Too smooth will shorten the life of the seal.

 

       We all know that hydraulic parts have high requirements for manufacturing accuracy. They are precision parts. As an executive part in a hydraulic system, hydraulic cylinders are naturally very demanding. High precision does not necessarily require good surface roughness. It’s the finish, it’s not that the smoother the better

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Why is the surface of the piston rod too rough?

 We all know that hydraulic cylinders perform reciprocating linear motion during work. Pistons often extend out of the hydraulic cylinder during work. In industrial applications, dust in the external environment is unavoidable. When dust and other debris adhere to the piston rod The dust-proof seal removes all of it when it is mounted. When the piston rod is retracted into the hydraulic cylinder again, the dust and other impurities attached to the piston rod will be mixed in the oil. Over time, the oil will have more and more impurities. At this time, the oil mixed with impurities is equivalent to the abrasive. The continuous grinding of the seals when the system is working will cause damage to the seals of other parts in the hydraulic system and the seals of the hydraulic cylinder itself. With the increase of grinding time, the wear of the seals becomes more and more serious, which gradually causes leakage.

02

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The piston rod is too light to shorten the life of the seal. Why?

If the piston rod is too smooth, or the surface roughness of the piston rod is too low, the hydraulic oil that passes through the sealed piston rod for lubrication will be scraped off, and there is no lubrication effect of the lubricating oil, between the piston rod and the sealing ring The coefficient of friction will increase, and friction will generate more heat and wear will increase, eventually leading to premature seal failure and leakage.

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So what kind of surface roughness is just right?

In general, we use Ra and R z to evaluate the surface roughness of parts, but when it comes to the surface roughness of the piston rod, it is necessary to introduce a surface roughness evaluation parameter Rmr.

The supporting length ratio Rmr(c) of the contour refers to the ratio of the length of the solid material Ml(c) of the contour at a given horizontal position c to the assessed length.

 Under different Rmr values, the surface microscopic profile is as shown in the figure below.

The higher the Rmr value, the flatter the micro-profile surface, that is, the fewer the spires, or the narrower the gap. This surface can store oil without adhering to large particles of dust and other impurities, and there are no sharp peaks that cause great damage to the seal. Wear and tear, such a surface is beneficial to extend the life of the seal.

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How can we get this kind of surface roughness that is beneficial to sealing?

After grinding, rolling, grinding can obtain the required Ra value, and the rolling process can obtain a satisfactory Rmr value, and rolling can also enhance the fatigue resistance of the surface of the part.