Materials.

[Wagger]

For those of you who cannot sleep. This may be a cure.

Many moons ago on 'Day Release' one of my five a week lectures was named 'Materials and their properties'.

It was a very tedious topic causing most of us to yawn and some to succumbe altogether. (Sent outside too).

However, I was 'Taught' the Electrical and Mechanical fundamentals of most metals and alloys.

Here is what I remember, in completely random order. There will be errors, some of you will notice. Just want to pass on these memories in some form somewhere.

 

Silver is the best conductor of electricity and Copper is second. Gold is not so good, but is used on connectors, usually over copper or silver plating. Why?

Because silver tarnishes, copper develops verdigrie and gold stays clean. Tarnished silver does not conduct easily. Copper and copper oxide sandwiched together form a Copper Oxide rectifier. Used on 1950's motorcycles that were built with alternators. Gold just prevents the oxidation. A thin layer over silver or copper guarantees reliable connections.

Aluminium conducts well but cannot be joined without corrosive fluxes. BT tried it out and many of us still suffer the noisy lines as a result. They try to deny it, but the engineers sent out admit it. If you trap a copper wire between two layers of aluminium, it will corrode away in no time due mainly to electrolytic action. Aluminium in a copper idc connector is a disaster.

Iron and steel are not wonderful conductors and do not disperse heat as well as copper and aluminium. However, their magnetic properties are  used widely in transformers .

 

Now for the mechanical properties. (Are you asleep yet)

Iron is refined to produce steel in various grades. Pure iron is the softest form and is used in transformers because it does not retain magnetisation as permanently as other types. Alternating current requires alternating magnetism.

Low carbon steel (2% carbon) is called 'Mild steel' and is used widely (or was) for car bodies, cabinets some tools, nuts and bolts.

Medium carbon steels exist (3 to 4% carbon) but I do not remember what they are used for. Maybe light duty springs.

High carbon steels (5% carbon) are used for tools, springs, High tensile bolts and some magnets.

These have very special qualities.

If made red hot and cooled very quickly (cooling in water or oil) they are as hard as glass and will shatter or snap under sudden load or shock.

If made red hot and buried in hot ash and allowed to cool, they will be soft and workable. Many of you 'Oldies' may have made tools of this before hardening and tempering them. The process is, harden as above, then polish them up to a mirror finish, heat one end gently and watch the colours flow. Light straw for hard, blue for softer. This works well for screw drivers and punches but using a controlled furnace is more accurate and used for spanners and springs where the whole part needs to be consistent (High tensile screws too).

When cutting threads, beating or drilling this metal, care must be taken not to heat it or it will harden due to sudden cooling.

Reading what has been written on hand thread cutting all that I can add is that I was taught half a turn forward, quarter turn back. Impatience gets the better of me, so I just add oil and plough on. All machines used for this just do it in one using lubricating coolant, so, why bother? Just keep the temperature down.

All steels can be 'Case hardened'by heating to red and dipping in carbon. This just hardens the outside surface, It can make it impossible to cut a thread on or drill through.

Wrought iron was very complex. Probably no longer made. It was 2% carbon but rolled hot, folded over and rolled again. It was folded and rolled many times producing a laminated grain structure making is very strong and ductile. It was used for crane hooks and chains because it would show grain stresses long before it broke. It also resisted sea water as well as cast iron. Used in the build of victorian piers. The Menai bridge was constructed using this. Fire destroyed it and is was no longer made in the sizes required for rebuilding as designed.

Still awake?

Copper is used for wires and pipes. Cold drawn copper is quite hard and does not bend easily. Soft copper 'Work hardens' so that if bent or beaten, it will take more force to straighten it. It can be softened easily by heating to red and allowing it to cool. Cutting threads on it is tricky. Dies will wander.

Brass is roughly 60% Copper/40% Zinc. It can be worked like copper and polishes nicely. Both take chrome plating well. However, it is 'Hot Short'. If you make it red hot and drop it onto a hard surface, it will shatter into hundreds of fragments.

Bronze is roughly 60% copper/40% tin. It is used to make bearings and springs. Phosphor Bronze is the best for this. About 2% Phosphorous if my memory is working properly.

Berylium Copper (don't know the ratios) Hardens with age over two days. It can be softened with heat, formed in shape, then relied upon to work as a strong spring. Don't file it as the particles are carcinogenic.

Aluminium is widely used nowadays in sheet form. Again there are many alloys. Duralumin is another that hardens with age over two days. It can be softenened and formed, then becomes as strong as the same gauge of spring steel at a third of the weight over a few days. Widely used in aircraft.

Magnesium alloys are even lighter and just as strong. However, they deteriorate in sunlight and burn very easily.

I have left out many, Cadmium, lead and others, but feel free to look them up.

Stainless steels are another 'Chapter'. I would have to look them up.

Hope some of that was useful.

 

 

[Unkel Kunkel]

Three books( I doubt they  appear on any dreary school curriculum)  helped me understand so many fundamental aspects of science in general  and materials.

They helped me understand things that, for what ever reason , I didn’t readily grasp at school.

Later, they helped me  with what I heard at university - not only to make it more understandable- but a lot more interesting.  

They helped me , as back- to- basics revision / information,  throughout my working years and still provide reading material to dip into, teetering near the top of what my nearest and dearest calls my “book tower” on my bedside table:

1.“ New Guide to Science” - Isaac Assimov.

2.”Metals in the Service of Man” -Alexander and Street.

3.”Structures - Why Things Don’t Fall Down “-  J.E.Gordon

OK .. If you want to go for a fourth: 

4.”The New Science  of Strong Materials - or Why You Don’t  Fall Through the Floor  “ - again , by J.E Gordon.

You may  all have them,

if not,  a treat awaits.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Ian Smith]

I suggest that extra information can be gained by having a look at the 'Workshop practice series' by Nexus or Special Interest books. There's about 40-odd books in there. I keep about 12 of these which are relevant to what I need. They are normally available on 'Bay, and only cost a couple of quid:  Cheaper still on second hand.  The list is extensive.

If you ever find copies of Newnes Complete Engineer, then possibly add them to your collection. The practices are 70-odd years old, but the cars were designed & built in that same era.  I was taught " The best joint, is no joint". which for me means that things like car wiring is from start to finish. Anyone remember Minis, with all of the bullet connectors on the front subframe?  Yeah, right.....

[Colin Lindsay]

2 minutes ago, Ian Smith said:

I was taught " The best joint, is no joint"

Isn't that an anti-drugs slogan?  Sorry... but re the posts above, some of the best books on cars were written in the 1950s and 1960s when the enthusiast motorist was hands-on, mechanicals were simpler, and things were much less complicated. The emphasis is on maintenance rather than upgrade, which is where many of the modern 'guides' fall down. I like that ethos, making sure than what you have works to its' best efficiency, rather than putting it down as old-fashioned and replacing it with modern stuff.

 

[Ian Smith]

Yes indeed. The 'best joint' adage was-is to make the joint as thin as possible, with regard to what is required. Old hacksaw  machine blades were always re-used as fine scrapers or chisels. Larger plant gasket joints were made  with a sheet of the required standard, and tapped out with a small ball pein hammer. Either that, or a set of hollow punches. Gaskets are of little use when the surface is like corrugated iron, unless it's a special requirement, so cleanliness is a must.

A little- known fact is that aluminium expands slightly as it cools from its molten state. With certain alloys, we'd let the fresh castings 'weather' for a month or so in the open air. This promoted a surface skin on the casting, and ensured an airtight seal.  If your alloy wheel has a slow let down, then porosity in the casting might be at fault. I've cured that by putting a full layer of Shultz on the inside of the wheel. The rationale being that the air pressure forces the sealant into the interstices (look it up ) and plugs the hole.

[RogerH]

1 hour ago, Ian Smith said:

 

.  If your alloy wheel has a slow let down, then porosity in the casting might be at fault. 

At British Airways I was asked to investigate an aircraft nose wheel as it kept letting the air out.

I took an X-ray and was surprised to see what looked like a giant 'Aero' bar.  Never seen that before

 

Roge

[Wagger]

Glad to get you all going. It took a while.

On alloy wheels, I have had porous ones, but the worst was a cracked wheel that let differing amounts of air out depending upon position when parking up. I noted where the valve was each time. Found it, eventually.

Following this and sudden deflation on a four lane section of the M6, I fitted those 'Tyrepal' sensors that screw on instead of the valve cap. They saved me four times in ten years when I had cars without warning systems, cracked wheels, split valve, and a nail.

I'll put them on the Vitesse now.

I made a support for the valve, however, because they do force it to flex. Best to fit the heavy duty valves where possible.

[PeteH]

11 hours ago, Wagger said:

'Tyrepal' sensors

I can vouch for those too. I`ve had them fitted to my R-V`s for some years now. (High pressure Metal valves) They saved the front N-S wheel once when the temperature sensor went off. and I discovered a dragging front caliper. Cured it before it did permanent damage. I removed a set from a car I sold recently. Maybe put those on the 13/60?.

Many alloys go pourous its not that uncommon. Coating the inside does help. GOOD alloy refurbishers tend to do it automatically.

Pete.

[Ian Smith]

12 hours ago, RogerH said:

At British Airways I was asked to investigate an aircraft nose wheel as it kept letting the air out.

I took an X-ray and was surprised to see what looked like a giant 'Aero' bar.  Never seen that before

 

Roge

A double whammy with the air pressure on aircraft tyres, I'd guess. Assuming the wheel is fully pumped up, lets say, a nominal 10 bar (other pressures are available) then every 1 metre in height gain, should reduce the pressure by 0.1 bar. So, let's assume, therefore, that a height of 100 metres will reduce the nominal pressure to zero.* The tyre  'should' expand, as the air within is acting on the rarefied upper atmosphere. Although I've never worked on aircraft (apart from Airfix kits), the physics remains the same. The air (or gas) will try to escape to atmosphere.  I should imagine an aircraft taking off, fully A1, and landing with an under-inflated tyre. It's gotta go somewhere!

 

Aluminium can be a tricky alloy at times. It starts to go liquid at, or about, 600 degrees C and upwards. When it approaches 800 C or above, the molecules expand to such a rate, that it allows Hydrogen molecules into the molten state. When the metal cools down, it traps  the Hydrogen within, which as we all know, is porosity. To counter this, Nitrogen is introduced to purge the metal, with added chemicals to encourage any inclusions in the metal to rise out, and removed.

Barometric pressure can play havoc with molten metal, with things like Strontium & Magnesium disappearing off the scale.  Compensation of molten elements is indeed a 'black art' where nearly  all of the human senses come into play. 

* Please feel free to check my maths; it's been a long time....

Ian. 

[NonMember]

6 minutes ago, Ian Smith said:

Please feel free to check my maths; it's been a long time....

Clearly, since common sense would tell you that reducing pressure to zero at only 100m can't possibly be right. If it were, you'd have a serious problem going to the top floor of a tower block.

The reduction is not a straight line - more like the atmospheric pressure halves every few kilometres - but at sea level the rate is approximately 1.2kPa per 100m, which is only 0.12mBar per metre (millibar!) so you're about a factor of 800 out.

If the tyres are at, say 4 bar gauge (so 5 bar absolute) then taking them up to aircraft cruising altitude of 10km, where atmospheric pressure is 0.3bar, is only a 15% change in the delta pressure across the potential porosity.

[Ian Smith]

16 minutes ago, NonMember said:

Clearly, since common sense would tell you that reducing pressure to zero at only 100m can't possibly be right. If it were, you'd have a serious problem going to the top floor of a tower block.

The reduction is not a straight line - more like the atmospheric pressure halves every few kilometres - but at sea level the rate is approximately 1.2kPa per 100m, which is only 0.12mBar per metre (millibar!) so you're about a factor of 800 out.

If the tyres are at, say 4 bar gauge (so 5 bar absolute) then taking them up to aircraft cruising altitude of 10km, where atmospheric pressure is 0.3bar, is only a 15% change in the delta pressure across the potential porosity.

Like I said, check my maths.... It's been a long time, and I've been to bed since then...

[PeteH]

18 minutes ago, Ian Smith said:

Like I said, check my maths.... It's been a long time, and I've been to bed since then...

Yes, At School (50`s), we where told to take the Aneroid barometer up 2 flights of stairs. And Note the difference in Pressure. (imperial of course, back then).

Pete

[RogerH]

1 hour ago, Ian Smith said:

A double whammy with the air pressure on aircraft tyres, I'd guess. Assuming the wheel is fully pumped up, lets say, a nominal 10 bar (other pressures are available) then every 1 metre in height gain, should reduce the pressure by 0.1 bar. So, let's assume, therefore, that a height of 100 metres will reduce the nominal pressure to zero.* The tyre  'should' expand, as the air within is acting on the rarefied upper atmosphere. Although I've never worked on aircraft (apart from Airfix kits), the physics remains the same. The air (or gas) will try to escape to atmosphere.  I should imagine an aircraft taking off, fully A1, and landing with an under-inflated tyre. It's gotta go somewhere!

 

 

Ian. 

Hi Ian, 

you have left some noughts off.

At 100Mtr the airpressure is 990mB - a reduction of 0.01mB/100Mtr.

It is still a lot when you consider aircraft fy at 10Km   

Have seen an aircraft tyre and Wheel close. These are not delicate things.

 

oger

[PeteH]

4 minutes ago, RogerH said:

Have seen an aircraft tyre and Wheel close. These are not delicate things.

Yup!. The one`s on the last of the big US bombers where huge. I Suppose in reality the pressure difference on take off, and on landing, will only differ by the difference in the height of the Airfield above sea level?.

[PeteH]

5 minutes ago, Mathew said:

We were asked to go to metalwork for a long weight. 

No Bucket of steam or 1/2" holes?

Pete

[Ian Smith]

One gent on another forum spoke about sending his Mother to one of the  major tool stores in Cardiff. She was asked to purchase some 'brass magnets'.....

 

On steam locomotives, it's  red oil for the tail lamps, and orange steam to help build up the fire.

[Wagger]

I love going to Coventry. Good Transport Museum.

Has anyone mentioned the 'Luminous Sundial' or the 'Solar powered torch'. (No battery allowed).

[Colin Lindsay]

23 minutes ago, Wagger said:

I love going to Coventry. Good Transport Museum.

Has anyone mentioned the 'Luminous Sundial' or the 'Solar powered torch'. (No battery allowed).

Last time I was in Coventry was for the Stoneleigh Show...

The solar-powered torch is now a reality, but it does have batteries... and uses solar power to charge the batteries during daylight so that it can be used at night.... so not so much of a catch as it used to be.

It reminds me of the old adage: which is more useful, sunlight or moonlight? Moonlight of course, as it lights the darkness - you don't need the sunlight so much as it's daylight anyway...