Caliper finish

[rcombs]

AHM,

Good idea, i'll split the calipier and see if there is any finish left. Should have thought of that.

There is a lot of plating info here. Thanks for the input. I have gotten the impression from platers that Cad is difficult and expensive to get now because of the enviromental concerns.

Thanks,
Rick

[JohnDanbyRacing]

Rick,

Make sure you can get the centre seal for the caliper before you split them as they can be difficult to get hold of! CAD plating is almost impossible to get nowadays, as stated earlier zinc with a gold passivate is the closest option but maybe a darker grey powdercoated finish would be more subtle..

Ross

[Chancer]

Rick,

CAD plating is almost impossible to get nowadays, Ross

That may explain why so many rubber to metal bonded components like drive shaft donuts, engine and gearbox mountings, suspension bushes etc seem to be of such poor quality these days and often come apart at the bond line.

Both may parents worked in the 70's and 80's for the major UK supplier of these components, my father running the factory, one of the many essential parts of the process was cadmium plating of the components before the moulding, if it wasnt done properly the component would fail, they sure as hell would have used another plating processs were they able to.

Also the tricloroethylene vapour bath degreasing is another H&S and environmental problem these days.

New old stock is the way forward even if the stuff is d?cades old.

[JohnDanbyRacing]

Yes I agree parts like that do certainly not have a long life anymore. H&S taking over everywhere! I am sure both your parents survived cadmium just fine..
CAD is still used alot in the aerospace industry especially on fasteners (K-nuts and NAS bolts) with contact of aluminium. Also used by us a lot on race cars!!

[Plus 2]

Steve,

Zinc is silver grey in appearance. Electroplated zinc appears silver with a clear passivate. With yellow chromate (Cr6- Not very nice) and yellow passivate (Cr3 - nicer) it appears gold.

Hydrogen de-embrittlement is only necessary on high tensile fastners (10.9 /12.9) and there is no way to test if the de-embrittlement process has been successful. That is why the socket cap screws holding the reconditioned calipers together are a black phosphate finish - In critical applications we used to have socket cap screws mechanically plated.

Galvanising is the application of a protective layer of zinc. Hot-dip, electroplating, even paint! Like you, when someone says galvanised I assume hot-dipped!

Hi AHM,

Yes I know zinc (Zn) in appearance as a solid is silver however as a powder Zn(s) it is white and items can be plated using the powder process. Indeed as a schoolboy I remember we took old pennies (these were copper in the UK). Can't remember the whole experiment but it was some liquid boiled and the zinc powder in the base. We dropped the coins in and as you say they came out silver then place in front of the bunsen burner and heated they turned to what looked like pure gold.

Even tool steel used like on a screwdriver changes its surface colour when heated and a fundemental key to know when to dip/quench I recall to harden as it turned a tawny brown before purple or black.

I am no plating expert but IIRC the introduction of copper with the zinc can create the gold finish without a passivation process. Clear, black or yellow passivation I recall we used to specify on our fasteners after zinc plating.

Like you I am fully aware of the process on hydrogen ''de-embrittlement'' that is required on HT graded items. Hydrogen enbrittlement also often referred to as Hydrogen Assisted Cracking HAASC, affects many everyday items that many people are unaware of, even simple items like self tapping screws that have been plated MUST go through the process of being baked to ensure they do not just easily break or crack when in use.

Hydrogen Embrittlement

Cheap fasteners that have not been done properly perhaps making out intended for furniture or simple DIY jobs just shear off at the head with very minimal effort. So if this has happened to anyone don't blame yourself for too many Weetabix. We once had to stop the production line and clear every self tapping screw from the factory and stores due to breaking the heads off and it was caused due to a breakdown in the suppliers process that had not passed through the correct baking processes. Not everyone however may be familiar with the codes you quote as many fasteners are not marked.......... like 8.8, 10.8, markings once seen often on bolts have got less indication marked today.

So I quote a manufacturer, the latter sentence supporting exactly as you say plated items may not be suitable in certain applications but also why I made a simple comment originally ensuring at least buying fasteners from a reputable source.

HYDROGEN EMBRITTLEMENT
1) Description.
Hydrogen embrittlement is a physical process in which a metallic structure absorbs hydrogen
atoms. Hydrogen is small enough to penetrate the metallic web with negative consequences for
the mechanical properties of the material.
Hydrogen is mainly absorbed during the heat treatment, cleaning, pickling and electrolytic coating
processes.
The harder the metal the easier for the hydrogen is to occupy the structure of the material.
Increasing hardness, carbon content or cold heading grade, also increases the solubility of
hydrogen in the part. In general, parts with hardness greater than 320 HV have a high risk of
hydrogen embrittlement.
2) Hydrogen embrittlement.
In screws the main processes responsible for the hydrogen embrittlement are the electrolytic
coatings. During these coating treatments water is decomposed in its basic molecules, and vast
amounts of oxygen and hydrogen are released. This hydrogen could be absorbed by the screws
with high hardness.
Occluded hydrogen weakens the mechanical properties of the screw, decreasing its effective
resistance under tensile stress in a process called ?Hydrogen embrittlement?. This weakening of
the material is not detected by any standard mechanical test (tensile or shearing tests) because
the results show a typical performance for the parts.
A hydrogen embrittled screw installed at high assembly torque and under high tensile stress could
break after some service time. This break often occurs 24 to 48 hours after the assembly, making
difficult to detect the problem in line and increasing the risk for the end user to receive the
damaged parts.
3) Baking process.
Even though manufacturing processes are optimized in order to minimize the risk of hydrogen
embrittlement, there is no production method which guarantees its complete elimination. ''unquote''

Its amazing what can come out of a thread from a simple question and/or throw away statement. At least it keeps the grey/gray cells functioning.

Regards

Steve

[AHM]

Steve,

If the head shears off a screw when tightening it is due to too much Weetabix and not Hydrogen embrittlement; a characteristic of which I believe is failure some time after it has been done-up.

Most fasteners are not de-embrittled as there is simply no point.