Stelmi Italia S.p.A.

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La Calidad de una superficie cromada

The quality of a chromium plated surface is essential for the gaskets life, the seal and the coupling accuracy; the corrosion resistance and the quality of lubrication depend on this factor as well.
The values Ra Rt (or Rmax), Rz and the bearing ratio Tpstrong> are commonly in use to define its technical characteristics.


It is given by the arithmetical average, extended to the measuring length lm, of the absolute values of the distances of the roughness profile R from the centre line. A good chromium plated surface must have Ra values below 0.2 µm; the best average values is around 0.1 µm.

La Rugosità della Superficie Ra


In this case the attention is focused on the isolated marks on the surface. Rt gives the value of the maximum peak to valley height found on the measuring length lm. Rmax gives the same value but choosing the largest among 5, referred to a unitary length = 1/5 lm. It is always Rt µ Rmax.

La Rugosità Superficiale Rt o Rmax

A good chromium plated surface has Rt values always < 3µm on isolated points; the average among various readings is undoubtedly < 2 µm.Values around 1 µm are excellent. The correspondence between metric (micrometer, µm) and imperial (microinch, RMS) units in use for roughness is the following.


La Portanza della Superficie Tp

It corresponds to the ratio, in percentage, between the bearing length and the measuring length lm, in correspondence to a defined reference level c. This quantity indicates how much of the surface under examination would be incontact with an ideal coupling surface. A well coupling surface has a high bearing ratio, in any case over 50%. This value increases reducing the heights of the peaks on the surface.

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Since 2001 Stelmi is world leader in corrosion resistence of its chrome bars and tubes.

The HIPERCHROMIUM technology has established new standards in the fluidpower industry:

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200, 500 and 1000 hours of corrosion resistance in Neutral Salt Spray test ( in compliance with ISO 9227 standard) with a minimum rating ) ( according to ISO 10289 standard). A technological milestone than many companes still try to reach.
Thousands tests in our quality laboratory confirmed by indipendent laboratories and by the most prestigious Customers around the world proved the reliability of this technology.

The HIPERCHROMIUM TECHNOLOGY is fully developed in our R&R Department: more than 35 years of technological know-how, proudly MADE IN ITALY.

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