case hardening mild steel

[TerrydParticipant @terryd72465]

Posted by kristian woolf on 07/12/2011 17:13:26:

……………….

 

Its for my A level project so we have pretty much unlimited time and our engineering workshop is pretty good for a schools. We have just had a new ALC block built with around £1 million worth of equipment.

I have managed to get hold of some large round 6 inches ish cast iron bar which i will use for the cyclinder now.

 

Hi Kristian,

 

Sounds very much like the environment I taught in for many years to A level and beyond. I saw very many student projects to successful fruition which I am sure yours will achieve. A good number of my ex students are now fully qualified and successful engineers who often thank me for my inspiration. I think that I enjoyed inspiring others as much as actually making things.

 

Cast iron is a very good choice of material. We were fortunate in that we could melt and cast our own in all materials up to cast iron. I wish you every success. Please post some pictures for us to enjoy.

 

Regards

 

Terry

[Sub MandrelParticipant @submandrel]

Good luck Kristian,

 

Your school clearly has much better facilities than mine did (thirty+ years ago).

 

Things may look gloomy now but in a few years this country will be crying out for new engineers.

 

Neil

[kristian woolfParticipant @kristianwoolf80751]

I will get some pictures up of the process as soon as possible.

[kristian woolfParticipant @kristianwoolf80751]

Iv posted a design of the engine on another topic page. http://www.model-engineer.co.uk/forums/postings.asp?th=61343

[SpringbokParticipant @springbok]

Hi Mick I now see where this thread is going could you please tell us what you are planning to build the scale, type and other details I am sure everyone will help

Regarding rust yes there has been a number of threads on this and everyone please do not bring up the hoary subject of WD40 again it has been done to death.

 

Dick is correct my personal faviorate is cast iron. The trick is to get the bore honed as smooth as you can like a mirror finish, not so hard as you think to do..

 

Good luck and keep us all posted

 

Bob

 

[Jeff DaymanParticipant @jeffdayman43397]

Hi Kristian,

 

I had a look at your youtube link, nice CAD work there. I noticed your design has two eccentrics and two valves, and the valves are direct coupled to the eccentrics. One question – what’s the second eccentric and valve for? A single cylinder steam engine can run with just one eccentric and valve, just in case you weren’t aware. Have a look at the Stuart Models engines online to see this. If you have something else in mind for the second valve I am interested to hear about it.

 

JD

[kristian woolfParticipant @kristianwoolf80751]

There is one for the inlet which is nearest to you when you see it on the video, then the other eccentric rod is for the exhaust so all the steam or air doesnt escape when it is under pressure, if that makes sense.

[Jeff DaymanParticipant @jeffdayman43397]

Hi Kristian,

 

Your valve system may work fine, I’m not saying it won’t. However there are simpler ways of valving your engine that I wanted to point out to you. (simple = less to go wrong)

 

One example of a very simple engine valve gear is at the link below. The bell crank is only needed if the valve passage is at 90 degrees to the cylinder, you can do a similar valve gear with the valve bore parallel to the cylinder as in your CAD design, just omit the bellcrank and plug the inlet port hole outboard of the valve bore after you drill the inlet hole. You could use a press fitted plug or a short screw to plug the hole. The designer of the shown engine implemented the valve bore at 90 degrees to the cylinder to allow boring the inlet hole in line with the cylinder and thus needing no plugged holes after drilling. 

 

 http://www.youtube.com/watch?v=rbXwH5IL49U

 

If you go to the website mentioned in the video, at the bottom of the page there is a link to a schematic diagram that shows exactly how this valve works.

 

Good luck. JD

Edited By Jeff Dayman on 11/12/2011 15:50:23

Edited By Jeff Dayman on 11/12/2011 15:50:47

Edited By Jeff Dayman on 11/12/2011 15:52:26

Edited By Jeff Dayman on 11/12/2011 16:01:49

[TerrydParticipant @terryd72465]

Hi Kristian,

 

Here is an animation
of how a steam engine slide valve works. This is for a double acting
valve. The exhaust ‘port’ is from the centre. The valve is usually a
square or rectangular block with the underside hollowed out, not a cup
shape as shown here The push rod is usually threaded so that the length can be adjusted to get the length adjusted for optimum performance.

 

Part
of the design task is to get the spacing of the inlet positions and the
size of the rebate (hollowed out section) just right. There are many
drawings of basic cylinders on the internet in various projects. The
design is pretty universal it is the detail that is different. A good example is in teh drawings for Dacre, a steam engine project Here. You can download the drawings from the LH sidebar. They are for a locomotive but the basic design or the cylinder and valve gear is the same for a stationary engine. A bonus is that a much smaller piece of brass is needed as well

 

Best regards

 

Terry

[michael howarth 1Participant @michaelhowarth1]

Terry……I couldn’t resist a look at the animation site and whilst there was also interested to see the oscillator animation which brought to mind a current problem that you or other forum members might be able to assist me with. I am building an LSBC design steam fire engine which has a steam powered double acting oscillator driving another D/A oscillator on a common crankshaft. The second oscillator is used as a water pump and pretty effective it is. The left hand ports pick up water (suction) which is pumped to the right hand ports to which the delivery hoses are attached. The problem is that the pump oscillator is lifting from the stand when pumping……I am guessing because of back pressure as it tries to deliver the pumped water through the RH ports. All ports, including cylinder are the same size at 3/32″. The spring on the pivot pin of the cylinder has been tightened up as far as possible without causing detriment to performance. Do you think that increasing the size of the delivery ports by about 50% in area ie up to 7/64″ would enable a greater volume to be passed and ease the “lifting” without affecting performance? Would countersinking those ports achieve a result ? I am wary of going too far and having to totally dismantle and rebuild the motor unit on what is now an almost complete model.

 

[Jeff DaymanParticipant @jeffdayman43397]

Terryd – Kristian’s CAD animation shows a single acting engine with piston type round valves uncovering drilled ports. These valves are simple to make with just a close fitting round bar in a reamed hole, very easy for the beginner to do.

 

Why complicate a first engine with a slide valve? Lots of time for that on later, more complex engines.

 

JD

[TerrydParticipant @terryd72465]

Hi Jeff,

 

Why have the complication of timing two valves, constructing two sheaves and valve rods, and trebling the amount of material used. How does that compare with the simplicity of a single valve chest and sheave (which can produce a more efficient double acting engine)? Where is the simplicity, good design, efficient use of materials and advantages in that? Perhaps if single acting is better he should design a simple oscillator and remove the need for valves completely! I would have thought that with 1 million pounds worth of facilities and two years of an A level course the student would be looking to producing a valid and efficient design. I certainly would have expected it of my students. It is not as if it is a first project in a damp garage with an old worn out set of files to work with.

 

I remember an article in a commemoration edition of ME where an unknown Indian child of 12 in, I think it was the ’30s produced a working model of a steam engine in a remote village with only simple hand tools and no prior knowledge of their construction.

 

Perhaps the need for simplification you are suggesting is why we have no real engineering industry any longer. I thought that the sort of course this A level student was following was supposed to close that gap. Perhaps not.

 

Regards

 

Terry

[kristian woolfParticipant @kristianwoolf80751]

Posted by Terryd on 11/12/2011 17:47:07:

Hi Kristian,

 

Here is an animation
of how a steam engine slide valve works. This is for a double acting
valve. The exhaust ‘port’ is from the centre. The valve is usually a
square or rectangular block with the underside hollowed out, not a cup
shape as shown here The push rod is usually threaded so that the length can be adjusted to get the length adjusted for optimum performance.

 

Part
of the design task is to get the spacing of the inlet positions and the
size of the rebate (hollowed out section) just right. There are many
drawings of basic cylinders on the internet in various projects. The
design is pretty universal it is the detail that is different. A good example is in teh drawings for Dacre, a steam engine project Here. You can download the drawings from the LH sidebar. They are for a locomotive but the basic design or the cylinder and valve gear is the same for a stationary engine. A bonus is that a much smaller piece of brass is needed as well

 

Best regards

 

Terry

Thanks Terry , I had seen a animation like this before but disgarded it because i thought it may get too complex but obviously not, I have 3 free lessons tomorrow so i will spend them trying to work out how I can make this happen. It could save me £40

[kristian woolfParticipant @kristianwoolf80751]

Iv worked out some drawings which work on CAD Ill get it all together tomorrow an put up again.

[kristian woolfParticipant @kristianwoolf80751]

Right new update blunted 2 cutters at school cutting down 5 mm of cast iron. Going to have to use brass or gun metal i think

[Jeff DaymanParticipant @jeffdayman43397]

Hi Kristian,

 

Sounds like you have found some iron with hard spots or chilled areas. These can be very hard to cut. Instead, see if you can get a small piece of ‘meehanite’ grade cast iron stick. It machines beautifully and I have never had a hard spot in a piece of that. You may be able to get a brand called ‘Durabar’ cast iron which is good.

 

You can certainly use brass or gunmetal as we have discussed, if you can find it and can afford it.

 

Good luck.

 

JD

[kristian woolfParticipant @kristianwoolf80751]

right Iv had a thought, I am going to use an aluminium cylinder with a gunmetal sleeve inside it, this way I don’t have to weight out on materials. I can get a piece of gun metal the size I want for about a tenner !!

[Ian S CParticipant @iansc]

Old bronze bearing bushes are good for cylinders, or if you must, use new ones, you wont need to finish the bore on the new one.

I had trouble with one bit of cast iron, I was a bit uncertain about it before I started machining it, it was a window weight, I dropped it and it broke in half. I started with a HSS tool, the end soon went on that, so I tryed a carbide tool, and that didn’t touch it either at first, I went a bit deeper, and got it to cut, it came out as hard as glass, and a surface finish like glass, its been laying in my junk heap for about 4 years now and its just as shiney now as when it came off the lathe. Tried another weight, it cut like butter! Ian S C

[TerrydParticipant @terryd72465]

Hi Kristian,

 

You can get a piece of excellent quality cast iron from here. You can use it to make a sleeve for your aluminium engine. Cast iron always has a hard ‘skin’ as it chills after casting. You need to get the initial cut underneath this skin which is quite thin, then the material machines beautifully. You shouldn’t get ‘hard spots’ in continually cast iron bar.

 

Industrially the skin is removed by other means such as grinding or acid etching. Companies often left castings outside to rust for several months or years. This had two purposes, it allowed stresses to relax as the castings aged otherwise they would distort after machining, and the rusting process removed much of the harder material in the ‘skin’

 

By the way, many builders actually use aluminium for cylinders on small engines, especially in the USA. I don’t know if you have seen this site, it has many designs, some of which use aluminium for the cylinders. Whatever you do remember to use dissimilar metals for moving parts which are in contact. E.g. aluminium pistons in cast iron, cast iron pistons in brass, brass in aluminium, etc. That way wear is minimized. In fact it is usually the harder metal which wears before the softer as hard particles become embedded in the softer material and leads to the inevitable wear. The designers job is to minimise this effect. A common example is hard steel shafts such as the crankshaft on a car engine which is frequently worn by the rubber oil seal. Abrasive particles, which get embedded in the rubber, slowly grinds away the surface of the metal. Engineering is full of surprises

 

Best regards and have a great Christmas,

 

Terry

Edited By Terryd on 16/12/2011 03:52:19

[Ian S CParticipant @iansc]

Hi Terry, sounds like a mate, and I did OK, went half each in a mater of 60 mm dia cast iron (in 100 mm lengths) for $NZ100. One bit is earmarked for a piston in an IC motor that I’v been building for a number of years. I was going to use aluminium (the piston is nearly finished), but I was worried about the aluminium scuffing. In that case the cylinder is steel, but a better choice friction wise might have been cast iron for the cylinder as well. Ian S C

[kristian woolfParticipant @kristianwoolf80751]

Hope everyone has had a good Christmas and new year. I have made the eccentric rod and nearly finished the cylinder block and sleeve, ect. but we are waiting to bore it out until we get an internal micrometer. And I am going to cast the flywheel out of aluminium and fill the outer rim with cast lead to bring up the kinetic energy whilst in motion without making the whole flywheel weigh to much. At the moment I am making the mould for it on the wood turning lathe and is coming along pretty well.

[Jeff DaymanParticipant @jeffdayman43397]

Hi Kristian,

 

Do you suppose steam engine builders of 120 years ago would wait for a fancy internal mike to bore a cylinder ? Doubtful they would wait, even more unlikely they would spend the money either, even if these fancy instruments were available then.

 

My point is, an internal mike is not necessary to build a steam engine. Nice to have, very handy for high precision jobs, but not necessary for model steam. Just bore the cylinder as carefully and accurately as you can on lathe or mill, then make the piston to fit it. Clean out the bore really well before trying to fit the piston (especially if bore is cast iron). When the piston JUST slides into the bore and will pass through it, you are done.

 

Many engines including my first one were made this way, and work fine. A good sliding fit is perfectly adequate, extreme precision is NOT required in steam engines.

 

If the piston is made with a single groove round it, say 2 x 2 mm, this can be packed with oiled graphited yarn, or PTFE string valve gland packing, from the plumbing shop. The yarn packing will seal even a really loose piston to bore fit, and enable the engine to run. Many a flubbed cylinder boring job was saved that way!

 

Good luck, have fun, JD

[kristian woolfParticipant @kristianwoolf80751]

Hi

I understand what your saying and I’m pretty sure they wouldn’t have waited. haha. the problem is my engineering teacher was a aeronautical engineer and if its not to pin point accuracy its not good enough, which i suppose is quite understandable from him.

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