Gunmetal, etc.....

[ironhorseriley]

Hello everyone,

I am appreciating the expertise and advice from the well seasoned in this group and hope to not be reopening a subject that may have a thread I have missed.

Not being a machinist, I am trying to wrap my head around the uses of some materials, specifically, what is gunmetal? I have seen it mentioned in sevaral projects in other build groups as well. It is mentioned a lot in Jack's book on building the Sweet Pea also. It got me thinking about the axle boxes he specifies for the drive wheel axles and to make them out of gunmetal. The drawings and the book do not mention bushings for the axles to rub on and nothing in the prints either. I know the axle boxes will be rubbing and sliding against the horn blocks in the frame.

I am wondering about making aluminum axle boxes with bronze or brass bushings also, but overall I have noticed by and large aluminum is frowned upon for most uses in making a live steam locomotive model.

Can brass or bronze be substituted for gunmetal? I do need to get it right on the appropriate uses of the differant metals used in this hobby, such as brass and bronze.

Thanks again,

Jim

[SteveM]

In Joe Nelson's book there was a chart showing different metal to metal contacts and which were good bearing surfaces and which were not.

Aluminum pretty much sucked with everything, while cast iron was great and bronze was a close second, IIRC.

Aluminum tends to gall easily.

Gunmetal is red brass (a type of bronze):
https://en.wikipedia.org/wiki/Gunmetal

LBSC recommends it on may parts, particularly cylinders.

Steve

[FLtenwheeler]

You need to remember that "gunmetal" covers 7 or more metals. Some machine nice some are very hard. LG1 has a machining Index of 90, LG2 has a machining Index of 84, LG3 has a machining Index of 42, were G1 and G2 are even harder to machine with a machining Index of 30 (Compared to "free machining brass" of 100).

Here are the specs. This is from the Yahoo hobbicast group provided by Deon Styger

Abstract:
The term gunmetal applied today originates from the mid-19th century, when zinc was first added to binary bronze ordnance parts to improve their casting characteristics. British Admiralty gunmetal, with its nominal composition 88% copper, 10% tin, and, 2% zinc, was thus developed.
Although these alloys are now no longer used for ordnance parts the term "gunmetal" has remained; they are extensively used today in many different engineering fields.

I have found the relevant information about Gunmetal. According to BSS 1400 there are seven different grades with the following composition of Copper (Cu), Tin (Sn), Zinc (Zn) and Lead (Pb):


G1: Admiralty gunmetal, 88% Cu, 10% Sn, 2% Zn, 0% Pb (UNS C90500 Tin Bronze, G Bronze. Hardness, 75 Brinell )

G2: U.S. Ordnance alloy, 88% Cu, 8% Sn, 4% Zn, 0% Pb (UNS C90300 Tin Bronze, Modified G Bronze. Hardness, 70 Brinell)

G3: Nickel Gunmetal 85% Cu, 7% Sn, 2.5% Zn, 0% Pb, 5.5% Ni

(UNS C94700 Nickel tin bronze, or UNS C94800 Leaded nickel tin bronze)

LG1: 83% Cu, 3% Sn, 9% Zn, 5% Pb (UNS C84400 "close match" Leaded Semi-Red Brass. Hardness, 55 Brinell)

LG2: 85% Cu, 5% Sn, 5% Zn, 5% Pb (UNS C83600 Leaded Red Brass. Hardness, 60 Brinell )

LG3: 86% Cu, 7% Sn, 5% Zn, 2% Pb (UNS C92200 "close match" Leaded Tin Bronze, Navy M Bronze, Steam Bronze. Hardness, 65 Brinell )

LG4: 86% Cu, 7% Sn, 2% Zn, 3% Pb, 2% Ni (UNS C92410 Leaded Gunmetal)

SAE 660 Bearing Bronze: 83% Cu, 7% Sn, 3% Zn, 7% Pb. (UNS C93200) Hardness, 65 Brinell.

[ironhorseriley]

All that info is way too complicated for me to digest. I had hoped for some simpler basic rules to apply. I feel like I have been wearing my dunce cap!

[SteveM]

All that info is way too complicated for me to digest. I had hoped for some simpler basic rules to apply. I feel like I have been wearing my dunce cap!

Just think:

"It's kinda bronze"

Steve

[Chris Hollands]

Gunmetal from what I have seen over the years is a "very" English term for certain bronzes , outside England it the would be classed by the makeup of the bronze / applications .

[Builder01]

Gunmetal is bronze, simple as that. Of course there are many types of bronze, but, in general, it is made from copper and tin. Brass is made from copper and zinc. This is why, in general, brass is not recommended for boiler fittings, as the zinc may leach out of the copper. Many of the castings for the English locomotives are available in cast iron, or gunmetal (Bronze). Bronze, of course, will not rust.

In general, bronze is tougher than brass and makes for a much better bearing material than brass. The Sweet Pea has a very similar wheel/axle set up as my Simplex. My horn blocks (pedestals) are solid bronze (gunmetal) castings. The bearing blocks (journal blocks) are solid steel with oilite bushings. Bronze could very well be substituted for the bushings. My axles are ground drill rod. The ground finish makes for a nice bearing surface against the oilite. I don' recommend oilite in any of the coupling rods or connecting rods, use bearing bronze.

As for aluminum, I would avoid it altogether. It makes a fine material for test lengths for con rods and the like. But otherwise, you will not have much permanent use for it on a steam locomotive.

David

[LivingLegend]

Let's cut to the chase and make it simple....

If you are inquiring about bronze for use as a bearing material for axle bearings, main and side rod bearings, valve motion bushings, etc. First choice would be phosphor bronze. Second choice would be 932 (aka 660) bearing bronze. Aluminum bronze would also be a good bronze for bearings, but it's tough as hell to machine and abrasive on the cutting tools.

I would not consider the use of Oilite for driver bearings, especially if it's to be used on a heavy loco (include other loco axles for that matter), or main and side rod bearings or valve motion bearings. The pounding Oilite receives in those applications will lead to replacement in short order.

Other than using it for the main and side rods, also for valve motion work of a live steamer, aluminum is best left to the airplane builders. That said, many have used aluminum for those afore mentioned applications. 7075 would be my preferred alloy if they were to be made from aluminum.... Assuming I wanted to make them from aluminum at all. My choice would be steel.... Mild, free machining, or 303 stainless. Still, there is nothing wrong with using 7075, which is an aircraft grade alloy.

LL

EDITED.... 04/16/2016 @ 0055 Hours DST

[Glenn Brooks]

The other thing is, Bronze has become violently expensive. So much so, that a typical today build willhave sealed bearings everywhere possible and few if no bronze bearing surfaces, compared to what might have been designed and built even 20 years ago - unless money is no object. But It is still a magnificent material.

[Cary Stewart]

Charlie Docksteader used 7075 Aluminum for his rods with out bronze bushes. They lasted for 30,000 actual miles of use before having to be bushed. The trick is to do a first class job of machining to the correct limits and make sure that all journals are lubricated all the time when running. 7075 is almost like steel in its strength and other characteristics. However, it is not for everybody.
Cary

[LivingLegend]

As Cary Mentioned, Charlie used 7075 for his side and main rods. Charlie also used needle bearings instead of bronze bushings in the rods along with hardened crankpins on his El Gobernador. I left Los Angeles during the late 1980s and wasn't around when Charlie built is CP 4-8-0. But knowing Charlie, I would think he would have used the same practice with that engine.

LL

[Steve Goodbody]

Hello Jim,

I had the same problem many years ago when I first moved from the UK to the USA - trying to figure out the closest analog to gunmetal when specified for boiler fittings and bearings. Long story short, the answer is 932 Bronze (aka SAE 660). The chemical composition was the closest I could find, and in practical terms it machines, solders and behaves exactly as the gunmetal that I was used to.

Best regards
Steve