Mainspring steels

[Kuyajonathan]

Not in same vane but connected, does tempering make any difference when manufacturing air gun springs?
If so can they be revived by re tempering ?
Seems BSA Mod / LJ springs seem to survive usage after 100 yrs, or were they just exceptionally well made at the time compare to later springs ?

[FPoole]

I think it is down to the heat treatment and how close the temps were kept to optimum. There is an optimum temp for hardening and an optimum temp for the tempering back to spring hardness. This is assuming a quality steel was used. The tempering process can be anything from brittle and stiff to near mush and I've had springs that were soft and went flat as well as springs that broke in a few 1,000 shots. I've also had springs that stay at the intended performance level for 10,000 shots, but that's about the limit. I always wanted a spring made from Vasco-wear valve spring wire. I've heard of knives made from it that were almost un-sharpenable, but they held their like nothing else. In the end I just buy a few springs at a time and they are almost always just fine.

[Black Beard]

It is the hardening process that extends the yield point up so that when the spring is compressed the material doesn't yield. If it is too hard the yield point will be very high but the spring will be brittle. If it is too low the spring will yield and not spring back properly. The alloying elements let you push the yield point up further while avoiding brittleness. You need to get the heat treatment right though.

[trajectory]

Just had a look at this thread & some of the points raised. Yes there ar lots of formulations for steel carrying in both elemental composition & elemental ratios all of which will interact together with the manufacturing process & post manufacturing handling ( of the steel). Ie drawing, tempering etc

Springs can be made out of all sorts of stuff, the trick is choosing the right stuff for the right job
Years ago there were SAE specifications for things. Just as an example ard drawn wired could be to SAE 1350 or 1360.1360 hada little mor e carbon in it, similar manganese content,silicon & sulphur levels were similar. The elastic limits as a percentage of tensile strength both in tension & torsion had the same limits as each other. Modulus of elasticity were the same spec as we're the allowable compression spring working stress. Both could be used as inexpensive springs with low stress, least expansive applications, bed springs, general upholstery etc toys etc where stresses were low, SAE1350 was used for springs under 100 ins. whereas 1360 was usedd for springs over 100 ins.
Then there's Music wire SAE1085 or 1890, Swedish steel music wire , annealed HC, Oil tempered,Cv steel, CV valve wire, silicon Manganese, Si Cr, clock spring (more than one type) various stainless steels just to give an idea of the variations.
It's a big subject...

[Phil Russell]

This information is fascinating, thank you all. I had long suspected that springs were not all equal even if their dimensions were. I have also often thought that Titan springs were of a different composition to other brands. I asked the question above as to what composition was best for mainsprings but if composition information is not available for any mainsprings offered to the general public then it becomes somewhat academic and people can only choose based on experience. Maybe it really is a case of 'buy what you know from a reputable source'. It would be interesting to know, just for information, where the major airgun manufacturers source their springs from, or if not a single source, the spring spec. But I guess this information is not available; not that it is a secret (or is it?) but just that it is hidden in the files of the department responsible for ordering the springs or the wire to make them from.
Interesting that 'trajectory' mentioned Swedish music wire as I had not found any reference to this in the specifications list I looked at. So I assume it is a specific type and not marketing hype. Did ABBA use this wire on their instruments?
Cheers, Phil

[trajectory]

Think Swedish music wire pre dates Abba...

Springs are a complicated business, well they are to me. The metallurgy involved is complex as the interaction of elements present effects other properties which in turn can effect the performance of the final product. If you look at an element, say phosphorus for example it's addition can cause a loss of ductility & an increase in embrittlement. It can also influence the integration of other elements such as carbon if surface treating it. Then there is also a possibility that it can effect spring performance if the rate of energy release is not constant. ie rapid unloading compared to slower rate unloading. Maybe not necessarily an issue with an air rifle/ pistol spring as you'd hope it would release at a constant rate but could be an issue in some applications. It's percentage inclusion may well also influence the austenitc content too.
Heat treatment will also influence the final product as well. So a batch of steel, assuming it to be consistent from initial to final run out might conceivably give rise to an end product with different properties if the heat treatment is inconsistent. There are a great deal of variables that can interact. I guess the best option is to go for the make of spring that has a good reputation. Their degree of control of the variables coupled consistency & good quality control is what might set them asside from the others.

[TonyL]

Some excellent posts on a most fascinating subject. As you say Phil, for the time being the safest approach might well be to buy known product from reputable sources. There will be ways and means of ascertaining composition but, as said above, that would have to be allied to the manufacturing process.

With so many variables, you can understand why the Theoben team were tempted to look at the gas strut. And it might well have some advantages in certain areas, the main disadvantage being the lack of adjustability / tuneability for length and pressure in most cases.

[Black Beard]

The important thing is that physically identical springs will give identical performance as long as they don't yield, no matter which type of steel they are made from. The one made from the best spring steel won't break at the same stress as the rubbish steel. Better steels are just giving you better reliability. This is important as a bad spring is like having a bad engine in your car.

If the springs were made different to give their best performance then the one from the better steel could be made with less coils, tighter coils and thicker wire- all of which will make a stronger spring.

[trajectory]

Forgot to mention Krupps spring steel... Had a good reputation, not sure exactly what it was composed of but I think it was a generic name for a range of products for varying purposes.

As to calculating any theoretical values for springs........yikes, modulus, stress, strain, % elongation etc etc there are books with pages of calculations & the mathematical derivations of the formulas. Some of its quite interesting but it's heavy going.


Was once told a helical springs were not what I thought they were. I thought they had a constant coil diameter. Apparently, so I was told, a helical spring has a coil diameter that reduces in one direction over its length. Apparently somewhat like the thread on an old fashioned wood screw, anyone else heard of that?

[Phil Russell]

Was once told a helical springs were not what I thought they were. I thought they had a constant coil diameter. Apparently, so I was told, a helical spring has a coil diameter that reduces in one direction over its length. Apparently somewhat like the thread on an old fashioned wood screw, anyone else heard of that?

Ah, now you're talking. The good old Bugelspanner in .25 ... two volute (not helical as I called them) springs if I remember correctly. Not a powerhouse but fascinating. I think they were sold as parlour guns i.e. for use indoors at ranges of up to maybe 5 yards or so, or maybe even as fairground guns? But they may have been deemed rather expensive for use in fairgrounds.
EDIT: Senior moment: Not helical springs: I was thinking of volute springs made from sheet steel rather than round or square section wire as in helical springs.
Cheers, Phil

[trajectory]

Just had a look at some composition figures.
Swedish music wire % C 0.85-.95 (0.55-0.7) ;Mn 0.25-0.4 (0.6-0.9); P 0.025 max (0.04 max); Si 0.15-0.3 (0.25-0.3); S 0.025 max (0.055 max)
Figures in brackets are for Music wire to SAE 1085 & 1090.

Might not help much but it shows the small percentage variations in composition between specs.

Goodness knows how they guarantee the even distribution of constituent elements throughout the batch to maintain properties/performance... more wizardry or another possibility to variations when you are using a 100g (?)or so of wire out of X hundreds, probably a couple of thousand or more kilos from a crucible batch?

[BTDT]

Was once told a helical springs were not what I thought they were. I thought they had a constant coil diameter. Apparently, so I was told, a helical spring has a coil diameter that reduces in one direction over its length. Apparently somewhat like the thread on an old fashioned wood screw, anyone else heard of that?

It has long been recognised by anyone making their own spring guides that one end of a spring is usually a slightly tighter fit than the other.

[Thegreg]

As to calculating any theoretical values for springs........yikes, modulus, stress, strain, % elongation etc etc there are books with pages of calculations & the mathematical derivations of the formulas. Some of its quite interesting but it's heavy going.

To add another dynamic to calculating spring suitability is the resistance (by friction, damping, environmental etc.) of the components you're trying to actuate with said spring. I know we're talking about air gun mainsprings here which is a relatively straight forward compression spring. Things get more complicated in the world of torsion springs and designing those for a specialist purpose is something of a black art.

To add an interesting note to spring materials..I've worked in aerospace & defence most of my life (and designed quite a few springs in that time!) and a spring material that is predominantly used is Elgiloy (there are different grades). I did a brief stint working in R&D for a Oil & Gas company and was tasked with redesigning a compression spring used in a valve chest (very similar to a valve arrangement in a car engine) which suffered from high cycle fatigue and was a common failure. Well, Elgiloy stepped in and saved the day! I'm still in contact with a few of the designers at that company and over 5 years later they've still not had a valve spring failure to report.

It's probably overkill getting an Elgiloy spring made to fit an airgun (and no doubt eye-wateringly expensive!) but I'm confident it'd produce very consistent results and last a lifetime.

Cheers
Greg

[TonyL]

This thread is getting more and more fascinating. Elgiloy; will look that up.

[trajectory]

Tere are a stack of things to consider when specifying a spring or indeed designing one from scratch for a specific application. Material is obviously one choice, the type of spring may dictate the material profile but in a simple(ish) coil spring the profile is commonly circular although BSA owners will recognise square or perhaps rectangular sectioned springs. The latter more commonly in pairs to counteract 'Unbalanced forces' that can & do arise effecting both expansion & sompression characteristics.
The ends of the spring are design choices under the control of the designer, they may be open, closed, squared un-ground or ground. The external dimensions are also under the designers control. Pitch, external diameter at rest, number of active coils, total number of coils & length at rest diameter of material used or x sectional area of non circular material. Grinding is not always required as in some cases whera a small wire diameter is used or the ratio of wire diameter to outside diameter permits. But for air rifles the dimensions are such that grinding & polishing the ends has merit. Plain ended springs can bind in compression & so ground or polished ends are often preferable in many other applications too.
Expansion on compression needs to be allowed for.
A spring should ideally be capable of being compressed to its solid height & the desired load at the correct compressed length. The spec may be expressed asa percentage. Sometimes load at other lengths my also be specified too.

Generally air rifles use one spring, that's complex enough but two springs have been used & ideally they should in theory be wound in opposite directions. Not sure if Relum ones are or not but in theory it should be a benefit.

I mentioned expansion....this is something which I suppose could be regarded as 'instabillity' too. If a spring is long relative to its diameter then it will probably buckle as its compressed. In fact it's not really a probability. It will buckle. That's why guide rods/ tubes are used but the spring will in all likelihood push against the surfaces of these to some degree or another. Technically buckling happens when the springs deflection expressed as a percentage of its free length equals or exceeds a factor that was called 'the slenderness ratio'. Which was the free length divided by mean diameter.


Ok...

That's probably enough typing from me. Goodness knows how many spelling mistakes there are or what auto correct thought was a good idea but I fancy some lunch.