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Senin, 04 Oktober 2010

Air, have your hydraulic cylinder rods turned black?

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Hello again Air,

In your last hydraulic maintenance email,
I explained the benefits of installing
a bellows or shroud on a hydraulic cylinder.

Today I want to talk about alternative rod-surface
treatments - to conventional electro-plated hard chrome
and the life extension benefits they can offer.

The first of these is High Velocity Oxygen Fuel (HVOF)
which is essentially a metal spraying process. When applied
correctly this surface treatment has superior hardness and
impact, corrosion and wear resistance to hard chrome. This
means HVOF cylinder rods typically last longer in abrasive or
corrosive environments than their hard chrome counterparts.

Black nitride is another alternative. It's an atmospheric
furnace treatment developed and patented in the early 1980's.
It combines the high surface hardness and corrosion resistance
of nitriding with additional corrosion resistance
gained by oxidation.

When it comes to its performance, I've heard mixed reports.
One client reports three times the service life in
corrosive environments when compared with conventional
hard chrome.

While another client trialled black nitride on salt trucks
and found the rods started flaking after one year's service.

I've also heard one report of long, small diameter black nitride
rods snapping under load.

A third alternative is nickel under chrome. In the USA,
Prince Hydraulics markets this rod treatment as Royal Plate.
And this nickel/chrome coating is also offered by Socatri of France.

Although I've had no direct experience with nickel/chrome plating,
according to reports from a reliable source, its corrosion resistance
is superior to conventional hard chrome and black nitride - but
not as good as hard chrome plated stainless steel.

Yours for better hydraulics knowledge,

Brendan Casey
Author of 'Insider Secrets to Hydraulics'; and
'Preventing Hydraulic Failures'.

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