welcome I'm very pleased to introduce
mr. rich Barrett and the fastener design
course rich as you may well know it's a
NASA engineer he has been an engineer
for 40 years
and up with the Lewis Research Center
for 34 of those 40 years he's advised in
the materials and the materials of
fasteners and materials is well sought
by industry and by other government
agencies besides NASA he's faster design
Manuel has received widespread acclaim
and distribution and it led to his
earning of the federal laboratory
consortium award for technology transfer
all the awards that mr. Barrett has
received our de NASA exceptional service
medal and the Eldar statement of a VA
ssin award with not much more to say
here is mr. rich Barrett thank you very
much thank you Mario for the nice
introduction we will be presenting in
this course one of the it will be the
most extensive coverage is fastener
design that I have done to date because
it will be a about 385 pages of
presentation so we will move into it and
unless they say in the candy commercial
you're not going anywhere for a while so
relax and we'll cover everything we can
on fasteners thank you
so to start out with I'd like to give
you some acknowledgments year of the
people that had a hand in this will
Harkins and Mario Castro Mario is my
boss here at NASA Lewis will Harkins
from NASA headquarters sponsored this
course funded quite a bit of it
so this will
used by all of the different NASA
centers Harold Casper from Analects
corporation he wrote some of the
sections and found some information for
the others as well as editing the entire
course John Bickford who is the leading
author actually in the fastener field
he is the editor-in-chief of a book
which I was contributing author horribly
published the end of the year I used a
lot of John's stuff from his book on
fastener design in this course being
blend off from Clemson University and
he's actually chairman of the bolting
technology Council which is a council
dedicated to furthering the knowledge on
fastener design has contributed some and
Betsy dela Cruz who did all of the
typing retyping running someone to get
this thing together and we just about
ran out of time but that's why we did
not give it before and I say it's
approximately a two-day course then
rehoming from atf corporation edited the
entire course and had some very helpful
comments so with that in mind we'll
proceed with the little introductory
material now there's a statement
everybody knows about bolts and nuts but
do they really know about bolts and nuts
sometimes we oversimplify things because
we think because it's something that a
kid took off the wagon that it's simple
for everybody
the Joseph Dudley who is a
vice-president of automotive marketing
for nighlok passenger corporation gave
these two quotes 75% of the assembly
labor cost of an automobile is spent on
fasteners and 80 to 85 percent of all
automobile recalls or fastener related
now that gives you an idea about the
importance of fasteners and putting
things together and of course some of
you remember on the shuttle recently
when they had to cancel a spacewalk
because a couple screws came loose and
fell out in the gears they couldn't get
the door open
so things do go wrong like that here is
a summary of the causes for joint
failures and NASA's Skylab program some
of you say Ron Roman Chuck would
remember that he was here that that poem
back when that happened and the thing
that surprised me in this is the poor
design improper assembly here
24% poor design 28% for improper
assembly and yet only 10% for bad parts
and the 24% for parts damaged in
handling and the wrong preload 14% now
we have been hearing in the news for the
past several years about the counterfeit
fasteners and all of that and so it's
gotten quite a bit of publicity and it
should but it still boils down to the
fact that the designer has more to do
with it
then the manufacture of the fasteners
now here is a something from John
Bickford book on a bolted joint just a
spring concept because actually you
don't think of it this way but a the
joint material itself is a big heavy
spring and you're compressing it with
small Springs which are fasteners and we
even get into joint stiffness and
stiffness ratios and so on now here is a
summary of the different types of heads
on fasteners just to
for your reference and these this is use
some in the aerospace field although
it's not that common but of course the
flat the socket head over here and the
hex all of these are very common the
carriage bolt of course that one is I
guess dates back to the building wagons
when you drilled a hole and you pounded
that one in and the square part under
the head there locked it in place where
you put the nut on so Betsy that's how
you build wagons in case you ever go
into it
here's one on the internal drive systems
and you can't read it too well on on
this one but over on the view graphs I
think you can read them and a lot of
these are common only to the aerospace
world like for instance something like
this or something like the Tri wing type
here these are used only by certain
manufacturers the torques down here is
very common in the automotive field that
one I thought that I'm always looking at
conspiracy theories of designers and I
thought the torques was developed by the
automotive people just to make things
more difficult on working on your car
but I found out that the reason they use
it was that it centers better than the
Philips which various types of Philips
there and will not came out as much so
therefore it will work better in
automated assembly now getting into the
agenda for this program see we have a
lot of stuff and each one of these is a
section number in your handout so we
have a lot of stuff here to cover I
won't go over all of these but I'll
point out that at the end we have a do
and don'ts and frequently asked
questions sections that that will answer
some of the various questions that I
have been asked from time to time by
people so we'll move on into materials
and this this I feel is a very important
section because you need to choose the
right material to begin with or you're
dead in the water on a design now
fasteners can be made for many materials
but most of them that we're familiar
with are made out of steel the the
hardware store tape that are made out of
what's called low carbon steel then the
alloy steel for the greatest fives and
eights that we use around here in a
socket head cap screw titanium and
aluminum bolts have limited usage in the
aerospace industry but on the other hand
aluminum and titanium are used a lot on
the aircraft design particularly since
you have aluminum skins on most
airplanes and you want the rivets to be
of the same material because of the
differential temperature giving you
problems on expansion and contraction so
now the alloy steel fasteners you can
get them up to 300 ksi ksi being a
thousand psi so it's three hundred
thousand psi strength levels but I'll
try to point out to you here that in
most cases you really don't want to do
that okay now carbon Steel's
are not corrosion resistant so they
usually have to have some kind of a
coating to protect them from rusting and
the stainless steels you can get in all
all varieties of both heat treatable and
non heat treatable alloys with the
tensile strengths of 70 ksi to 260 the
seventy being the ordinary 300 series
stainless that we use here all the time
and the 260 or
talking work-hardened inconel 718 or
eight to eighty six and note that the
400 series materials contain only 12%
chromium which will allow them to rust
so if you're building something that you
want it to look pretty the 400 series
stainless would not be advisable and on
some of these subsequent tables we will
show various materials but just go on to
the in order here on the selection and
materials you should use common fastener
materials strength levels and coatings
if you can there's no sense in over
killing on any design because it can
just cost you money and time usually
weight savings versus cost must also be
evaluated for flight articles and there
you do spend a lot of money to save a
little bit of weight galvanic and stress
corrosion tolerance levels have to be
established and checked out and of
course the operating temperatures has to
have to be determined before the
material is chosen both the high and the
low to make sure that the materials are
compatible in the entire range and then
the type of loading static or fatigue
loading is also a factor in the material
selection now as far as availability and
materials the carbon steel fastener
materials of course everybody's familiar
with the 10 10 10 20 that we use around
here and that is just a iron with carbon
in it a few impurities and it's up to
0.28 carbon now that's I'll explain this
further in another chart but the carbon
content is usually called out in points
and it's actually hundreds of a percent
so so this is 0.28 here it's hundreds of
the percent of carbon and you need for
heat treating unless you add
something like boron to the material you
need about 25 points of carbon really to
get it the heat treat properly if you're
going to heat treat a fastener now the
the great files and great eights are in
the 28 to 55 point
carbon range so that their heat
treatable and the the eights of course
have other alloying elements in them in
order that you can bring them up to the
strengths that you want and 4037 is one
of the common materials for grade 8 now
here's something I just wanted to point
out to you that the Charlie Wilson from
the industrial fasteners Institute's
been trying to get this change for years
but it's still in there in jave SAE J
429 spec which is for grade 8 fasteners
there's a footnote there that allows the
manufacturer to furnish these and 1045
plain carbon steel
if the buyer agrees to it well the only
thing is if the buyer doesn't know he's
agreeing to it he can get one that will
not have very good impact resistance and
we had a problem that we were in on one
time with the Army on some Abrams tanks
that when they fired the cannon on him
it broke the bolts on the turret because
it remained out 1045 steel okay moving
on not the ASTM fasteners are used
primarily in the construction industry
so since a lot of you are not familiar
with them and I'm not that familiar with
them either I put in some equivalency
here like the a 307 is a great one in
the sae that we're familiar with and 449
354 and now they the a 193 they're the
the B five six seven sixteen and also
the b 8 stainless steel those are used a
lot for the pipe flanges that we design
around here so so a lot of you are
probably familiar with
them the 320 is an alloy steel for low
temperatures and 325 is a sort of
equivalent to agreed agreed eight in
strength and then the 490 is the highest
strength of the construction type
fasteners now
stainless steel which is a crest you'll
see that designation for it corrosion
resisting steel stainless steel is the
same generic terminology and the super
alloy materials now the 300 series that
we're familiar with around here you get
it up to about 80 ksi because it's not a
heat treatable material so the only way
that you can get the strength opponent
is by work hardening it and informing it
that's about the strength that they get
starting with annealed material eight to
eighty six we use all the time in the
aerospace world up to 160 ksi it is a
very common aerospace material and you
can you can get it in metric by special
order in a 286 the 400 series is
available in limited strengths up to 125
ksi and it's also available in metric
which I will show you further on now the
super alloy is here these are the ones
that you guys come around looking for
when you want something for a
particularly stringent environmental set
of conditions like high temperature
corrosion and so on these are all
stainless --is here in well titanium of
course is very corrosion resistant also
the MP 35 n an MP 159 are made by SPS
they have the patent on the material and
they are super corrosion resistant and
high-strength up to about 220 ksi
inconel at 750 s used for high
temperature and the Haines alloys and
then the 80 to 86 above 160 ksi strength
is a
because in order to get it above about
180 ksi you have to work harden it in
addition to heat treating it now here's
a here's a table of fastener materials I
won't go through each one of these but
one of the things I just wanted to point
out to you and you'll have to go to this
one over here on it is how to figure out
what the designation is now the the aisi
and SAE usually the the numbers are the
same for the steel and in this case here
we have the two as the class of
materials over from over here which is a
nickel steel in this case the three is
the approximate percentage of the main
alloying element which in this case is
is nickel and then the 17 is the carbon
content so this is a low carbon alloy
steel
2317 that has no special significance
other than the fact that it's used to
just illustrate the system now for the
nickel chromium steels and molybdenum
steels and so on here are the ones that
are used mostly for fasteners in alloy
steels the 4000 series you have 40 37 41
40 43 40 that type of thing that is that
are used for the fastener steels
now on chemical compositions I guess I
better stay with this one over here for
that also here you see here the the
ordinary hardware store of varieties and
you notice that all of these other
elements are not listed one of the
things you can run into if you if you're
having a real problem sometimes you can
get some of these steels that have
things in them that you don't want the
guy was pointing this out to me from
Lincoln Electric that in welding they're
running into that because a lot of Steel
is made out of scrap so the scrap has
most anything yet so they're getting a
lot of impurities that they don't want
in it and then then you get down here
the standard alloy is the stainless
steels one of the ones that I wanted to
call to your attention on that is the in
the 300 series stainless steel down here
one of the ones that they left out here
was the the L designations the
low-carbon because a lot of the times
you want to minimize the amount of
carbon in it so you use a 304 L or 316 L
or something like that and they did not
put that one in that table so you might
want to just flag it alright moving on
now to operating temperatures here I
have grouped this in categories and so
the minus 65 and below that's your
cryogenic temperatures now of course
those of you who have been around long
enough remember the Atlas and centaur
and curse their liquid hydrogen fueled
so the temperatures are running on that
type of a vehicle or anywhere from about
300 - 300 to minus 423 so you cannot use
carbon steels at those temperatures
because they will crack like glass even
some of the stainless steels will go
below about
- 150 aluminum is good down to those
temperatures then you go to the - 65 -
450 which is a ordinary range for most
engineering designs carbon steels are
okay and stainless steels are okay but
then you get into the business of
needing corrosion protection for the
carbon steel with the various types of
plating like the Sanker cadmium or
phosphate or black oxide or whatever and
those will be covered of course later on
in the platings encoding section now for
the 450 and above
believe it or not you can use unplayed
carbon steel up to about 700 degrees
because the only thing you're looking at
there is how much does the allowable
drop on it for the temperature so if you
go in one of the books like mill
handbook five you can find the
temperature curves for carbon steels and
you find it use it but to see the reason
I'm saying unplayed 'add is that an
awful lot of the platings for Steel's
burn up before you get to that
temperature so these are some some of
the ones that don't hurt you at least
now and I'm just giving these because of
their temperature range rather than the
fact that you'd normally would not
silver to plate a carbon steel but you
do silver plate stainless steel but
silver nickel chromium plating and
chromium plating is used on some
high-strength fasteners for aircraft
landing gear that type of thing the
black oxide coating that you're all
familiar with from your hardware store
bolts looks good and all that but it
burns off then you have diffused nickel
cadmium which is a special one that will
be covered later and then of course you
use the stain
steals and superalloys without anything
now we although we have a corrosion
section I elected to put the oh sorry
about that
here's here's the table of summary of
fastener materials and you can't read
this one so I'll go over to this one one
of the things that I wanted to point out
to you here is that if you look at the
useful design temperature on these you
find that a 286 is one of the best - for
23 to 1,200 but if you get down through
all of these and you find that this
Hanes 230 at the bottom is the only one
that will carry you up to 1,800 degrees
now the significance of this is that
we've gone through on the NASA program
the national air space plane and
developing all of these super duper
materials to build airplanes out of but
we never did anything on developing
fasteners to put them together because
the regular metal fasteners there's what
they the only thing they have to put
them together okay moving along now into
the galvanic corrosion and stress
corrosion area galvanic corrosion is
something that we're all familiar with
although we may not use that title for
it if you get a scratch on the chromium
plating on your car it will rust faster
that it would if it didn't have any
plating on it because you have a very
small anode in a large cathode being the
rest of the surface so the anode is
deposited on the cathode which means
that it rusts away so rusting is a
galvanic corrosion and later on we have
a table on the galvanic series that will
give you
the location in the table of these and
the farther apart they are in the table
the bigger galvanic corrosion cell you
developed between the two of them and of
course cadmium and zinc are adjacent to
the aluminum in that table which makes
them compatible as coatings for steel
fasteners used in aluminum then and to
further protect mating surfaces from
galvanic corrosion you particularly
where you're putting in rivets and you
drill you pilot drill one piece and and
then drill it through you have raw raw
surfaces that are not plated with
anything so you either use a zinc
chromate paste or there's a mill 8802
sealer that will deter galvanic
corrosion now here is the table or the
galvanic series and this is something
you can find I think marks handbook and
various places have it and one of the
things that I wanted to point out in
this is that if you look at cadmium over
here see it is right in the aluminum's
also zinc is there so if you use a
cadmium plated fastener and aluminum you
will get less galvanic corrosion than
you would say if you used a one of these
down here like a brass or or copper
inconel or something something like that
now notice that there are two different
designations for the stainless steel
that have active and passive normally
stainless steels are passivated which
they're treated with an acid dip to
remove the any kind of scale they had on
them from processing
and to form a protective oxide on the
surface the passivation of Steel
corresponds to anodizing of aluminum so
that's why that they have it shown
differently here passive and active
because the the passive is much less
corrosion a much more corrosion
resistant okay now going to stress
corrosion that is something that we're
all familiar with in a sense but there's
not much available in textbooks on it
because it the the study of it is a
fairly recent thing now stress corrosion
of course occurs when our sensitive
material is loaded in tension in a
corrosive environment now that sounds
pretty easy and what happens the surface
develops pits or cracks from exposure
and this of course gives you stress
risers which will cause the component to
fail at as little as twenty percent of
us calculated load capacity now the
thing about it one of the reasons why I
don't propose using the super high
strength alloy steel fasteners if you
can avoid it is the higher the strength
the more sensitive it is to stress
corrosion so so you try to steer clear
of using super high strength fasteners
in alloy steel for that reason the
stainless steels most of them are not
stress corrosion susceptible other than
the precipitation hardening 17:4 and
17-7 so you ought to look at that before
you select the fasteners that you're
going to use here's another one that you
can run into although it's it's not a
that common as decarburization when you
heat treat a carbon steel you can
actually precipitate carbon out on the
surface and i would compare this to like
charred whew
or something like that you know charred
wood is how it's very soft on the
surface because that this is essentially
what you're getting you're getting a
heavy carbon coat in the outer surface
and of course it's not as strong as the
parent material and on machine parts
they sometimes just machine that off and
and go ahead and and they can use the
part but of course on a fastener you
can't do that so you have to be careful
about decarburization and once again
it's on the strength above 180 ksi now
tempered brittleness is another thing
you can run into on the high strength
fasteners after you have clenched them
then you need to go back and tempura
much means holding a mat at a fairly low
temperature to get the strength that you
need but that also causes the material
to be brittle so carbon steel fasteners
above 190 ksi are a real risk as far as
having brittle failure now you can use
some of the the super alloys and
strengths higher than that but not the
ordinary carbon steel now going to
carbide precipitation this is something
that gets people in trouble a lot where
they don't want a stainless steel to
rest and believe it or not this is
fairly recent least recent for me maybe
for you guys it's ancient but we ran
into this on the Atlas and centaur
programs in which we had joints rusting
down at the Cape with this thing sitting
on the pad and this is stainless steel
it's not supposed to rest but what they
had on that some of these sections were
put together by fusion welding and of
course the only way that you can prevent
it from resting on the 300 these were
301 is to solution treat it after
welding which means you take it up to
about 1800 degrees or something like
that and get the chromium back in
solution
what happens the carbon will combine
with the chromium the form chromium
carbide in the well join and of course
that pulls the chromium out so if you
had your regular 301 is an 18 8 18
chromium 8 nickel so you pull the
chromium out if it falls below about 12
percent the steel rest so this is why
that normally if you're going to have
welded joints you try to use a 300
series with the L designation which is
low carbon and even use a low carbon
well dried or better yet and this is
what we did it mark mariette on the
titan you use 321 stainless because it
has titanium in it the titan or are you
use 347 which has columbium and the
titanium and columbium will combine with
the carbon before the chromium will so
that will leave the chromium in solution
so that you still have the corrosion
resistance so keep that in mind when
selecting fasteners for anything above
about 800 degrees in the stainless steel
to use 321 or 347 now in material
strengths after the temperature and
corrosion requirements have been
determined then you've got a look at the
material strength and once again keep in
mind it's the higher the strength of the
material the more stringent to
manufacturing and quality requirements
become because it's more sensitive to
imperfections if weight is not critical
it's better to use a lot of fasteners of
lower strengths than to use a few high
strength fasteners you use those old
grade eights
if you can use them and you don't have
to worry about weight
now here's metric fasteners and that is
one of the least understood I think
between most design engineers and and
I'll have to admit it's confusing to me
although my my buddy Ben Glenn Dolf who
came from Sweden says that metric is
way of the world he thinks it's great
but I still have trouble with it so go
through some of the peculiarities of
metric fasteners on the property classes
is the way that they specify the
strength and which is a tensile element
in a then yield as a percent of the
ultimate in mega Pascal's and somewhere
here at mega Pascal is one hundred and
forty five point oh four or psi for any
of those you need to convert now the
material is not specified in the
call-out so you have to specify the
material yourself or otherwise you don't
know what you're getting so if you have
like a property class six point eight
it's a carbon steel of some kind with an
ultimate strength of six hundred mega
Pascal's and a yield of eight tenths
times that because that's where the
point eight comes from now for for some
stainless steels they don't use those
rules and so I have a table further down
the line here that shows the peculiar
type stainless steels the way they're
called out the metric system now here's
something I had a little trouble with
getting people to understand around here
because when we had a government decree
to go to the metric fasteners for the CM
one project or for all new projects the
metric aerospace fasteners are not
available in the European market they
use American inch bound fasteners on
their airplanes and I toured the Huck's
rivet plant and to sign a couple years
ago and the chief engineer told me at
the time that it that the a300 people
were their biggest customer at that time
on fasteners because there aren't any
aerospace fasteners available in the
European market so you can get them in
this country on special order and due to
the fact that the property class is
not enough to define the fasteners the
Naas committee and our agency fastener
committee came up with doing it this way
you put out these AIA it's actually na s
specifications that are for metric
fasteners only and this is a very
similar to the m/s or na s sheets that
you see all the time for the inch stuff
but you actually cover everything on
there the heat treat the material
everything and all the dimensions
coatings and so on so that you're
completely covered and you can also
order a metric fasteners from ansi
specifications now here's here's that
kind of a weird duck type table here for
the stainless steel metric fasteners and
these different classes here the a1 a2
a4 and so on and then the 50 70 80 45 60
50 70 80 and so on for some reason or
other you need to add a zero to those in
order to get the actual strength of the
material they made them a class like
that with a that so in other words the
50 here is a 500 mega Pascal ultimate
strength and so so the only way to
identify them is to put them in a table
like that where you can refer back to
them now the next table covers the
different classes and the type of alloys
that are normally used for them the se
here is an S & S II as S is for sulfur
that's an S es for selenium that's
normally added to the 300 series to make
it more machinable so presumably on this
one if you wanted to make your own and
you wanted to cut them out of stainless
steel
then you
use those materials here you have the
304 L and the 321 and 347 which are the
titanium columbium stabilized and then
here the 400 series which are only 25 12
percent chromium and there's another
table further over here that will show
some of that now going to the figure 2 I
will not go through all of this stuff
but this is from the metals handbook it
just gives you a good overall view of
the 300 series and the things that you
do to it to tailor it to your your needs
in fact you probably can't read that
even here at all so it is in your
handout so you can go through it and you
can refer back to it at least when
you're picking a material the figure 3
shows the tailoring of the martensitic
400 series and for those of you who
always wonder what you should what your
Scout knife is made out of it's 440 C
which is down there in the corner
someplace and that's the one that has
the highest except in the upper right
hand corner there has the highest carbon
and a lot of chromium so that it will
give you a high strength you can go up
to about a Rockwell 55 with it C 55 but
it will Nick a lot more readily it's not
as ductile s carbon steel figure-four is
once again this is the standard ferritic
stainless steels of the 430 series and
the different ways of tailoring them so
I won't go through that then we go into
a glossary of terms for materials and
once again there's there's more here
than then I will cover in this
presentation but some of the things I
wanted to call to your attention here
about the the
steals that normally we use the 4000
series then on aluminum's which a cover
here if you want more information on
those you can go to the aluminum
handbook which is put out by the
aluminum association and will give you
more information there the if you look
in the under aluminum alloy is the 2024
2000 series is heat treatable the 3000
series isn't the 5000 series is not heat
treatable but some of them are crows
corrosion stress corrosion sensitive and
the curse the six and seven thousand are
we use all the time they are heat
treatable the down there the leaded
Steel's there are you sometimes I guess
for making one-of-a-kind types crews
they'll add once again is added to steel
to make it easier to machine okay going
over to the next one there
the stainless steels once again there's
there's also a 200 series stainless
steel is very similar than 300 and the
other thing we had a problem down at the
cake one time that they couldn't
determine whether they had used 300 or
400 series fasteners so the way you
check is with a magnet 400 series is
magnetic 300 series is not okay moving
on to the mechanical definitions part
you get into cold working plain carbon
Steel's with cold work can you read that
one over there or not the the plain
carbon Steel's
you can you can cold work them during
deformation in fact one of the reasons
that they start out with the so cold
wire if you will know where somehow
three-quarter inch wire doesn't strike
me as being wire because with the collet
in the
faster plants they run it through and
they but before they run it through they
run it through an annealing furnace to
get it to soft as possible before they
start
and so the fasteners are actually formed
out of this annealed wire and they are
cold worked during the farming in fact
we had I was involved in a quick case on
a product liability thing that the the
nut was actually harder than the bolt in
this case because the nut had been cold
worked more than the boat and it
stripped the threads off the Pope had
caused a chair to fail and a guy got
hurt so just wanted to point those out
to you now going on over to this next
glossary of terms on the process
definitions on one of the things I
wanted to point out there killed steel
is something that is defined here which
normally you don't don't find and that
is important because it it makes the
steel chemically stable so that you
won't get into troubles on it and I
always point out defects that have
happened along the line and one of the
things you remember the cars I believe
it was the Fords and Lincoln's that had
the bumper beam that disintegrated on
them that was because the steel was not
killed killed properly as I understand
it and so you can get disastrous effects
from it the pickling is also the removal
of oxide scale by dipping a steel in a
bath and these are important to have to
prevent corrosion on the material during
the manufacturing process whether it be
fasteners or or general Hardware now the
carburizing
covered so will will not go night
trading and and case hardening actually
in cases like that it's where
you have a material that you want it to
remain ductile because it's some sort of
an impact type thing and so you
case-hardened the surface of it by put
it putting enough carbon on it that you
can harden the surface just to get it
slightly hard okay now moving to
platings and coatings nearly all
commercial fasteners are made of sensors
made of plain carbon or alloy carbon
steel you need some sort of a protection
on them to keep them from rusting so you
can go from puting good old 10w30 oil on
them down all the way to gold plating
now gold plating is not used on
fasteners usually but other than pins on
tubes or something like that in the
electrical field electrical contacts and
so on but if something is small enough
gold plating does not become that
expensive to coat it but usually we go
with something that is less expensive so
but what you're looking for is a coating
that will give you the protection at the
lowest cost so the other thing is with
fasteners you got to have a thin coating
because the fastener threads have to be
within tolerance after the coating which
is important now I know that if you get
nails or something like that
Ron Roman Chuck drives nails all the
time they've been galvanized and that's
a dipping process but it's not used on
normally on threaded fasteners now on on
temperature limitations the coating is
more likely to set the temperature limit
in the fastener material itself and some
coatings can be a disaster when they
decompose like cadmium you get hydrogen
embrittlement from a decomposition of
cadmium and others like the good old
familiar black oxide baked off without
doing any harm
now cadmium plating is although people
say that it is going away because of
environmental problems that's really not
true in fact when I talk to a guy at
Boeing about their development of
replacements for cadmium he said as far
as we're concerned there isn't a
replacement for cadmium we're going to
go ahead using it so it's just the idea
that you have to control the process in
order to keep a PA off your back but it
can used for electro depositing alloy
steel up to 190 ksi if you get above 190
ksi then you can't prevent hydrogen
embrittlement and you have to go to a
vacuum deposit which runs the cost way
up now here's something that is
overlooked a lot and causes lots of
problems when parts are cadmium plated
they have to be baked within two hours
after plating and this the reason I said
eight to twenty three hours it depends
on who's baking them or if any baking is
done because some I have heard of cases
in which no baking had always done to
bake the hydrogen out whenever you do a
electroplating process it's done in a
some sort of an aqueous environment so
as you know from charging your battery
you get free hydrogen whenever you put
electrodes in water so you have free
hydrogen ions and of course hydrogen can
go where anything else can't go so you
get hydrogen given off during the
process so unless you bake the material
right after it you're in trouble now
cadmium melts at 610 degrees so it's
service temperature is limited to 450
now the advantages of cadmium it's good
salt spray resistance so it's very good
and marine environment for airplanes
where they're exposed to salt all the
time in the wintertime it's consistent
on the torque friction properties it has
a good Taliban ik corrosion location and
it doesn't decrease the base material
fatigue strength but the disadvantage is
it generates cyanide during the plating
process which is nasty stuff that the
EPA watches very closely and of course I
mentioned the plating and baking has to
be closely controlled and void hydrogen
embrittlement and it causes
embrittlement of titanium it's very
expensive and it has to be vacuum
deposited on high-strength parts to
avoid hydrogen embrittlement so but one
of the other advantages of it that I
didn't list there it does not support
fungus growth whereas a lot of platings
will since cadmium is kind of a toxic
type thing your moles and stuff like
that in a marine environment can't grill
on it now zinc plating zinc is very
common
most of the fasteners that you buy that
are plated or probably zinc plated and
of course hot dip zinc plating is called
galvanizing you get roofing nails that
type of thing our galvanized the roof
that corrugated roof and so on is
galvanized now the zinc plating doesn't
generate the toxic byproducts the
cadmium generates there's a lot cheaper
than cadmium but it will heal itself
over by migrating over scratch there is
if you scratch an area in fact down at
the keep they did a study on how far a
zinc would migrate and it would go over
a scratch about an eighth of inch wide
and go back and and heal it will kind of
heal itself desert extent and it has a
good galvanic location
but it's not as good as cadmium for
corrosion resistance and the Turk
tension friction characteristics in
other words when you're talking up a
fastener you can get such a variation in
the coefficient of friction that you can
get in real trouble on knowing what load
you're putting on it and but it can
adhere here's one of the other bad
things about it it has a useful
temperature limit of only about 250
degrees so you can't use it at all or
your have elevated temperatures and it
can cause hydrogen embrittlement
although it's not a serious a problem as
it is with the cadmium now the phosphate
coatings this is used a lot in the
automotive business because it's cheap
you throw a a cup of phosphate in a
barrel and put a bunch of fasteners in
and shake them a few times and you have
phosphate coated passengers more or less
and so the mildly protective layer of
phosphate is formed on the surface and
there's three different ones or zinc
iron and manganese and the ones usually
used for fasteners is the zinc or
manganese
now the advantages of phosphate coatings
they're cheap you can coat them with oil
or wax to increase the corrosion
resistance and the phosphate is a good
primer for painting so if you're going
to paint something after you've possibly
coated it that's great and you don't get
hydrogen embrittlement from it but
disadvantage it's not very good in
corrosion you get in consistent tension
friction properties which means if you
are supposed to torque ahead bolt to
exactly 2,000 pounds tensile load you
don't know what torque it will take to
do it if you have different fasteners
that were in a different location in the
barrel and they have a limited
temperature of 225 to 400 degrees now
nickel plating nickel with or without a
copper strike is one of the oldest
methods of preventing corrosion and
improving the appearance of steel and
brass it it'll tarnish unless it's
chromium plated but it has a fairly high
allowable temperature and good corrosion
resistance the disadvantage it's more
expensive than cadmium or zinc that
requires baking after plating to prevent
hydrogen embrittlement and it doesn't
look too good when it starts tarnishing
now moving on to chromium plating
chromium plating of course I thought you
all know is used for automotive and
appliance decoration and very thin coats
but it can be used for fasteners as I
mentioned earlier it's used for coating
fasteners for landing gear this type of
thing where you require the super
high-strength fasteners or components
and so you can't use something else that
would be like in a stainless steel so
you go to the the very high strength
carbon steel alloy steel and then you
chrome plate it but you've got to put to
get a good chrome plate you got to put a
copper strike on first and then a nickel
over that and then the chromium goes
over the two of them otherwise the
chromium is porous to a certain extent
so if you have unless you have something
under it to help it it doesn't work out
too well or you have to go with a fairly
thick coat so and it can be used up to
about 1,200 degrees and of course it
looks good
but your the thing you run into it's
just expensive a stainless steel so you
only use it for the special cases and it
requires very stringent quality control
because you know what a disaster it
would be if you get a hole through it
and the salt gets in it then you have
something rusting very fast and of
course you have to do the baking to
prevent hydrogen embrittlement with that
same as you do with the cadmium plating
now here's the ion vapor deposited
aluminum plating this is a special one
that was developed I believe yeah by
McDonnell Douglas for coating of
aircraft parts and it was going to be
used as an alternate to cadmium plating
well it doesn't give you hydrogen
embrittlement and it insulates to deter
the galvanic corrosion and can be used
up to nine hundred and twenty-five
degrees and is and doesn't give off any
toxic byproducts but it's expensive and
has to be done in a vacuum so you can
send it out to Joe Dokes plating outfit
to get it done and it's not as good as
cadmium in a salt spray test so it has
not had that wide usage that I know of
diffused nickel cadmium is another one
that was the
by the aerospace industry as a
high-temperature cadmium plating and you
put a nickel coating on first and then
put capping on over it and bake it for
one hour at 645 degrees now the
advantage you get up to about a thousand
degrees exposure temperature which is
good versus 450 for plane cadmium
plating but once again it's expensive
you you have to have extremely close
process controls and the nickel plate
has to cover the fastener at all times
to avoid cadmium damage to the fastener
material so and it's not recommended for
parts above 200 KS is strength okay
silver plating silver plating is used to
prevent corrosion and as a solid
lubricant for fasteners for instance
it's customary to silver plate a
stainless steel nut for a stainless
steel bolt in order to prevent galling
and serve as a lubricant now silver
plating can be used up to about 1600
degrees and its disadvantages though
it's expensive it tarnishes and it
shouldn't be used in direct contact with
titanium so its primary use in their
aerospace field is just to coat
stainless steel parts on stainless steel
to prevent the thing from galling
okay we will take a break now and resume
with passivation and oxidation on from
the next session