Ferrules Detail

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Email: AV Young avytasmania@gmail.com



Ferrules are most commonly made using nickel silver which could be considered to be a type of bronze but is in reality more of a brass because of the high content of zinc and like all alloys consists of a mixture of basic metals.
Typically NS will be mostly copper with zinc, nickel which gives it strength as well as the silver colour perhaps a small amount of lead and tin depending upon the specific alloy. No silver though uness it's been plated.

NS is in rod form not considered to be a particularily strong material, however when the right alloy is drawn it can be moderately to very strong depending upon its alloy and degree to which is is drawn.

When I decided to return to ferrule making I had to decide on what to use as a material and which process to use.

NS is the obvious 1st thought because it's traditional, Duronze was the 2nd because most people have heard of it but in my current line of work I use aerospace materials and one type of bronze is a standout material as far as strength and durability is concerned and that is Nickel Aluminium Bronze alloy (AMS 4640) which you can google to see the specs for if you're interested.

Comparing AMS4640, Duronze (C64200) and NS you can see AMS4640 is the stronger of all the alloys listed in the following chart of nominal strengths:

Alloy............Tensile MPa......Yield MPa
AMS 4640.............760.............470
Duronze C64200 ....620.............310 AKA AMS 4631 THE Duronze
Duronze C95400 ....655.............310
NS Rod CA754........434.............220
NS CA752 18% FULL DRAWN Tensile MPa 655

NS CA752............ 0.316 lb/Cubic inch
AMS 4640.............0.274 lb/Cubic inch

Clealy AMS 4640 is the outstanding material and it has largely superseded Duronze in most of the aerospace applications it was used for in the past. AMS 4640 can also be blued just like NS using most of the same solutions.
As well as this AMS 4640 is 13% lighter than 18% NS while being around 15%-20% stronger so it came down to a very easy decision to use AMS 4640 because in my opinion it is the best material to make ferrules from.

At its most basic the Ultimate Tensile Strength (UTS) is the greatest resistance to a force applied to a material that it may withstand before it fails in tension while the Yield is the force required to cause the material to enter its plastic deformation stage on the way to its UTS just before it fails.
Once the forces have exceeded the UTS of the material it will continue to deform requiring less force to do so until it fails.

Special note must be made for Nickel Silver because of the way the ferrules are made.

1stly it's difficult to give accurate figures for NS as the term Nickel Silver covers a whole range of different alloys varying in the amounts of nickel which is where it derives it's strength from less than 12% to 18%. Aluminium bronzes derive their strength mainly from the aluminium content with the nickel adding further strength.

Also, the term drawn covers a lot as it could be 1/4, 1/2, 3/4 or fully drawn and each will have it's own yield point because each is at a different stage of reaching the UTS.
Because of this I have shown a NS of 18% nickel that is used as rod stock as well as fully drawn to allow a best case comparrison.

Drawn ferrules or ferrules made of drawn tube by definition place the ferrules inside of the plastic deformation curve Yield point but short of the UTS.

Fully drawn NS is very close to the Ultimate Tensile Strength of the material and while it has not yet reached the Ultimate Tensile Strength of the material it is close to it.

This is why well designed drawn ferrules of NS are stronger than machined NS ferrules, even if the alloys are identical which they normally aren't.

The machined NS ferrule hasn't yet reached its Yield stage when made, but having a relatively low yield point reaches it in use allowing the ferrule to become loose in time.
To alievate this problem machined NS ferrules may be made thicker walled than you would make them from tube making them heavier.
The drawn ferrule is already beyond the Yield point closer to the UTS so stronger.

However for a drawn NS ferule to be strong enough to work well it also has to be drawn to close to its UTS.

But AMS 4640 is the strongest material of all listed drawn or machined.
The nominal UTS of AMS 4640 is 20% higher than Duronze and fully drawn 18% NS.

The downside to using AMS 4640 is that it's un-suitable for cold forming or reliable soldering so it must be machined and maching it is realtively slow going.

The up side is that there are no solder joints at all and because its strength is superior to fully drawn 18% NS the ferrule is stronger even though it is machined.

Obviously, NS works, it always has but for all of these reason I believe that Nickel Aluminium Bronze makes the superior ferrule and the extra few dollars that it costs over NS due to the relative difficulties in machining it is not that much. Since the ferrules are machined I'd rather use AMS 4640 than Duronze.
Also I can be assured of always obtaining the correct alloy because it is an aerospace standard material and when I buy it I am provided with an annalysis report of each batch I buy. An example is below with Yield and UTS shown in ksi (1 ksi = 6.879MPa):

As you can see this particular batch shows a Yield of 661MPa and UTS of 868MPa.