If, as the saying goes, "Misery loves company," then you will appreciate the
following. Whilst perusing the December 2017 issue of NASA's Motion Design
supplement to their Tech
Briefs publication, I ran across the image to the right in an article titled,
"Trends in Hydraulic Filtration" (areas of interest are quite
diverse here at RF Cafe). After reading the caption stating that the holes
were "fire holes," the first thing that came to mind was ESD damage. Sure enough,
upon going back and reading more of the story (provided by
Argo-Hytos), I found the following:
"In the past, conventional hydraulic oils often contained zinc dithiophosphate
(ZDDP) protecting them from wear and corrosion and acting as an antioxidant. Since
this component has now been classified as harmful, users have turned to zinc-free
oils. The reduction in the amount of organometallic additives such as ZDDP lowers
the conductivity of oil. Therefore, the elimination of this additive, e.g. in environment-friendly
oil, reduces the conductivity and increases the risk of electrostatic charging.
If a non- or low-conductive hydraulic oil flows through a system, an
electrostatic charge can be generated at the interfaces
between oil and non-conductive surfaces such as filter fleece and hoses. This charge
is generated by the rapid separation of two non-conductive
surfaces. Filter elements have a large non-conductive surface, and charge
build-up increases with increasing flow velocity of the oil. As soon as the charge
quantity is large enough, discharges occur in the form
Conventional filter material could be locally destroyed by discharge flashes
and associated high temperatures. This results in holes through which dirt particles
can pass unfiltered. This leads to increased wear of hydraulic components and later
to malfunctions and to the failure of the machine. However, the high temperatures
of the discharge flashes also contribute to an accelerated oil aging, thus to a
deterioration of oil properties and to the shortening of the oil life. Oil aging-related
byproducts additionally reduce the service life of the filter elements. Also adjacent
electronic components can be damaged due to electrical discharges. To avoid such
problems, the charges must be balanced.
For this purpose, a special filter element design was developed, which ensures
charge balancing and prevents destructive discharge flashes. Glass fibers in a filter
element are themselves not conductive, but, as already mentioned, the inner supporting
meshes and the outer protective mesh are made of metal."
The semiconductor industry has gone through a long, tedious, and very expensive
process of learning about and protecting against the damage caused when electrostatic
charges drain through gate regions or, in extreme cases, across insulator boundaries.
It is safe to say that the issue has been pretty much resolved through a combination
of semiconductor device construction with on-chip protection, packing changes, and
establishing proper handling procedures in the factory. The main risk these days
is an ESD event occurring at the point of use of the end product in which the IC
Who knew that a field as unassociated with semiconductor electronics as hydraulic
filters is would be experiencing the same ESD challenges? As with electronics, the
problem only really began to manifest itself once the scale of critical features
began shrinking in size. For ICs it was gate thickness; for hydraulics it was filter
You, too, can receive a free copy of
NASA Tech Briefs in the mail if you qualify
(which typically means you have a pulse).
BTW, for those of you not around in the 1970s, the "not just for semiconductors
anymore" line was borrowed from the Florida orange juice industry's "It isn't just
for breakfast anymore" commercials.
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
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