Material selection

Is there a handbook or website which states which material is best for what. I appreciate that there are perhaps thousands of materials available today, but for the model Engineer, there is probably a much shorter list.

Eg:-

Steels, Stainless steels, Cast Iron,

Brasses, Bronzes, sintered bronze etc

Copper

Aluminium

Plastics

Wood

And I suppose after such a list is how to identify each.

Bob Humphrey

Hi Bob,

Here is a link to a desciption of various metals. Have you checked the book "Workshop Materials" by Alex Weiss (Workshop Practice Series #30)?

Thor

Edited By Thor on 11/11/2014 18:28:12

Thanks for that Thor, but I think ME's would need much more. Like what is Silver Steel and why use this for certain parts, what is EN1B, EN8 etc One could look up a particular specification on the internet, but it is difficult to choose a suitable spec for a particular application. Having once said that, how could we identify what material is in our come in handy boxes. Should we colour code our purchases, or even use number and letter stamps to mark our material when we have bought something special. At least Stubbs Silver Steel is usually marked on one end.

Keep the ideas coming

Bob H

Hi Bob,

Material selection is an interesting subject and in all honesty I approach this choice from a number of perspectives.

But I am going to add my input in relation to unfired pressure containment:

For pressure containment an engineer would need to review the full material specification and the recommendation from BSI is that the title should state 'for pressure containment' and the procurement specification should describe the end use where the level of material inspection is agreed between the supplier and end user.

This last bit is difficult because the hobbyist engineer cannot control the inspection done before he/she receives the stock, all I do is select a trusted supplier.

As an example a pressure vessel may be made of '304L' and in this example the engineer should use the SAE specification that specifically states 'for pressurised equipment'. But I prefer using BSI standards and under the EN system of numbering the material will not be called 304L it will have a number specific to the BSI and EN standards.

I have found that some pressure vessels can be sized and proof tested to a level where the need for fracture analysis or safe life analysis can be avoided (for unfired vessels). I cannot remember the size limits and proof factors, but is best to look these up as the requirements and standards can and do change.

Generally away from pressure vessels, material selection is less stressful.

Kind regards,

Graeme

As Graeme has indicated, in the field of ME the only areas where correct metal is important is in matters of safety, boilers or pressure vessels being the commonest.. For many of us above that it's a case of what we have or can afford, or what is available in small quantities. IF only a static model then that it looks right is important, only if a working model does it's strength, or wearing properties Etc matter. As Howard nearly always points out to newcomers, here is a VERY good reason to join a local ME club or society. This information is available in countless volumes BUT it would take longer to research the materials Etc than to build the model. Noel.

Tubal Cain's ME's Handbook is helpful on this.

+1 on both Tubal Cain's ME Handbook and the Workshop Practice series. Always a good starting point.

Re identifying material in your scrap box, you can't really. There are so many different types of steels and brasses and bronzes and aluminium these days, that you are best off to buy in what you need and if there are leftovers, mark clearly with a paint pen or letter stamps etc. I keep my silver steel in a special separate container clearly labelled so it does not get mixed up with the bright mild steel rod etc.

There are old books with descriptions of identifying some steels etc from the coloured sparks produced when held against the bench grinder which might distinguish between a carbon steel and mild steel but not that easy to do.

Edited By Hopper on 04/02/2023 11:34:46

I have been a professional mechanical engineer all my working life and a model engineer for longer. I haven't stopped learning more about material selection in all that time, so l would say a single book could not do it justice.

I dont think the repeated revision of steel grade codes in recent years has done anyone any favours (possibly excepting the EU beauraucrat mountain).

So for a beginner best advice is follow the drawing or ask club members.

If you actually know what a bar is definitely stamp it on the end, he said as a council of perfection he seldom achieves.

Martin

Occasional spark testers might find it helpful to have known samples to hand by the bench grinder for comparison.

What do you mean by 'in recent years' Martin?

The EN system was forced by government on the British trade in 1940 because what they offered was a shambles. EN had to be revised in 1955 to cover gaps, and the flaws were such that it was replaced by BS970 in 1972.

This all happened half a century ago, a year before the UK joined the EEC. That steel codes are in a mess has nothing to do with EU bureaucracy! Whoever told you the EU was to blame was a naughty fibber...

Dave

Commercial steel stockists generally mark one end of each stock steel bar with coloured paint according to a code likely to be its own.

We tend to buy lengths cut by "our" retailers from what they buy from the trade stockists (some of whom do not sell to private buyers, by the way), so unless they also colour-code their goods and tell you the code, your only way to be sure is to match carefully the goods to your order and label your own stock in your own way.'

In our favour though, by making life simpler, is that the hobby suppliers keep a relatively small range of steel grades, those being the ones suitable for the majority of the components we make....so the "best sellers"!

...

I was no fan of the EU either but I think the "EU" grades were compiled from the range of different national standards, and to suit industrial customers who do need to know exactly what they are buying, often for very critical reasons. Intrinsically there is no practical difference between BS-this and DIN-that for a given flavour of steel - just a single new "name".

...

Graeme -

The requirements you cite for pressure-vessels for model-engineering are not quite as onerous as you imply. For our purposes they apply primarily to boilers made from steel and copper, and if you build your own boiler from stock copper sheet and tube you don't need trade-standard metal certificates.

If you design it as well you will need satisfy the club boiler-inspector it will be of suitable strength, perhaps by direct comparison with a similar, known example; but you won't be expected to show all sorts of bumph for the copper.

Steel boilers need "certified" plate and proper-quality welding whoever makes them; but otherwise it is the commercial boiler-makers who need jump through all the regulatory hoops.

We've not yet progressed to accepting boilers can be made from an appropriate stainless-steel, though that's so specialised it would almost certainly be a trade-only prospect.

It's all laid down in the MELG Handbook on miniature boiler construction and testing - and though a proper boiler-tester can decline to test a boiler on ground of limits of personal experience, he or she will not gold-plate the rules and procedurea. Nor refuse a test on spurious grounds such as plates being thicker than the published design, or feed-clacks having been moved to their prototypical positions. (Yes, these are real examples!).

Gas tanks on small-scale steam models come under the MELG test system.

For other non-fired pressure-vessels such as air-compressor receivers, we have no specific rules within the hobby but if you are making one for your own use you would certainly be wise to be really sure of your design and workmanship; and of course have the vessel tested hydraulically as with a boiler. (I'd think the same test regime would be appropriate.)