Does anyone know where to get isolation washers. Specifically the cone
shaped plastic pieces that fit under the head of a flat or oval head
screw to galvanicly isolate the screw from the item being attached
(such as an aluminum stanchion).

-Ryan

McMaster-Carr



RyanN wrote:

Does anyone know where to get isolation washers. Specifically the cone
shaped plastic pieces that fit under the head of a flat or oval head
screw to galvanicly isolate the screw from the item being attached
(such as an aluminum stanchion).

-Ryan

RyanN wrote:
Does anyone know where to get isolation washers. Specifically the cone
shaped plastic pieces that fit under the head of a flat or oval head
screw to galvanicly isolate the screw from the item being attached
(such as an aluminum stanchion).

-Ryan


Insulation and isolation are terms loosely used interchangably, but
in our context, isolation usually refers to low voltage DC current,
while insulation implies higher voltages and current carrying, or
not, structural parts. Insulation qualifies as excellant isolation,
except where RF signals may requires specific geometric spacings
and materials with known electrostatic hysteresis and capacitive
qualities are required to maintain impedance values in tuned radio
circuits.

Electronic suppliers sell transistor installation kits consisting of
tubes, flat and cupped washers used to insulate fasteners from
transistors and transistors from mounting heat sink surfaces. They
come in small to industrial strength sizes, suitable for anchoring
heat sinks, whatever.

Cabinet makers use show or dimple washers that will accept
countersunk screw heads, but being plastic, in structural
applications, they may be better faced with stainless dress washers,
so long as the sizes work together. You may cast your own from epoxy
and you could inglude glass or other fibers as reinforcement.

These could be used in combination for structural antenna mountings,
etc. Some roll their own from pipe clamps, hockey pucks, plexiglass
sheet, etc.

May we enquire as to what you may be isolating, and to what end? Do
you require high voltage low frequency AC or RF isolation, lightning
protection, or low voltage DC protection? These features can become
difficult to co-ordinate in some schemes.

Aluminium parts are sometimes protected from stainless fasteners
with lanolin oil, or some other concoctions such as locktite (TM)
used to prevent corrosion mediated by galvanic action. These are
useful for low voltage applications only, such as encountered in the
war against galvanism.

Concrete boats need only cast sockets with drains into the gunnels
or bulwarks to accept iron pipe for insulated stanctions.

I wonder if anyone ever tried to cast sockets into a fiberglass
boat? I suspect freezing standing water would be a serious problem.

Conductive parts mounted on insulating fiberglass structure are
isolated and insulated without further attention, but fasteners of
different materials may encourage galvanic corrosion if constantly
submerged.

Terry K

On Fri, 10 Dec 2004 07:17:10 -0800, RyanN wrote:

Does anyone know where to get isolation washers. Specifically the cone
shaped plastic pieces that fit under the head of a flat or oval head
screw to galvanicly isolate the screw from the item being attached
(such as an aluminum stanchion).

-Ryan

I used silicon sealant when I screwed mast steps into my aluminum mast
with stainless steel machine screws. Two years later the threads were
still clean, and the screws came out without too much drama.

I probably wouldn't use this on stanchion hardware, though. Maybe some
other sealant or adhesive would work well. 5200? It is also a reasonably
good insulator when cured.

Finally, if the aluminum is is black anodized, you may not need any real
isolation. The anodization is a pretty good insulator, although it is very
thin.

--Mac

There are several applications I'm looking at, but all involve
galvanically isolatinng the head of the fastener from the item being
fastened.
Two examples that come to mind are attaching aluminum hatches and
stanchions to the deck. In this application, only the head of the
fastener comes into contact with the aluminum, but there is enough
force that a viscous isolator, such as silicone or tef-gel, probably
won't work in the long term.
As for sizes, my current applications involve #14 oval head screws or
1/4" machine screws.
As for McMaster-Carr, I had spent a good amount of time looking on
their site before posting. Many types of washers, but I can't identify
the ones I'm looking for. There are cup washers for pan heads, and
finish washers for using oval heads on a flat surface, but nothing like
the washers I'm looking for.

Have you looked at some of the very dense, fiber-reinforced rubber faucet
washers in the plumbing section of a large hardware store?

Your post says that only the head of the fastener contacts the aluminum. How
do you prevent the neck or shaft of the screw from making contact as the
object shifts slightly when the boat "works"?

"RyanN" wrote in message
oups.com...
There are several applications I'm looking at, but all involve
galvanically isolatinng the head of the fastener from the item being
fastened.
Two examples that come to mind are attaching aluminum hatches and
stanchions to the deck. In this application, only the head of the
fastener comes into contact with the aluminum, but there is enough
force that a viscous isolator, such as silicone or tef-gel, probably
won't work in the long term.
As for sizes, my current applications involve #14 oval head screws or
1/4" machine screws.
As for McMaster-Carr, I had spent a good amount of time looking on
their site before posting. Many types of washers, but I can't identify
the ones I'm looking for. There are cup washers for pan heads, and
finish washers for using oval heads on a flat surface, but nothing like
the washers I'm looking for.

On Mon, 13 Dec 2004 06:16:20 -0800, RyanN wrote:

There are several applications I'm looking at, but all involve
galvanically isolatinng the head of the fastener from the item being
fastened.
Two examples that come to mind are attaching aluminum hatches and
stanchions to the deck. In this application, only the head of the
fastener comes into contact with the aluminum, but there is enough
force that a viscous isolator, such as silicone or tef-gel, probably
won't work in the long term.

I'm talking about adhesive sealants such as west marine silicone sealant,
or something more serious like 5200.

As for sizes, my current applications involve #14 oval head screws or
1/4" machine screws.
As for McMaster-Carr, I had spent a good amount of time looking on
their site before posting. Many types of washers, but I can't identify
the ones I'm looking for. There are cup washers for pan heads, and
finish washers for using oval heads on a flat surface, but nothing like
the washers I'm looking for.

Well, I've used screws to attach hatches, and had no problems with
corrosion. The point is that you have so much bedding compound in the hole
with the screw, that during installation the compound oozes out of the
hole and covers the everything, and the aluminum and stainless
are effectively isolated by the bedding compound. Since the screws on
hatches are normally on the dry side of the hatch, this is more than
enough protection, IMO.

Sometimes standing water covers stanchion bases, so extra caution is
order with them. If I had my preference, I would make sure the
stanchion bases were fully anodized. Then I would trust the annodization
along with the bedding compound to protect the aluminum. Second choice
would be powder-coated aluminum, I guess. Last choice would be aluminum
primed with a corrosion inhibiting primer and painted with a decent marine
paint.

But the bottom line is that all of the aluminum needs to be coated, and
the bedding compound will probably isolate the screw from the aluminum
well enough.

Just my $0.02.

--Mac