Thread: Through hardening small parts made from silver steel

You can see the shims in question to the left in this picture... they are 8mm on the big OD and 2.8mm on the small, 4mm long. Tiny!

Hi Andrew,
How thick are they? O-1 is oil quenching steel, but 60hrc is pretty high and they will be brittle at that. The point you are looking ot heat them to is called the Curie point Curie temperature - Wikipedia, the free encyclopedia the easiest way to find this is with a magnet. The steel will loose its magnetism at this point and then they should be quenched. The biggest problem will be scale/oxidization. You really need to make them over size and grind them to thickness or seal them in a stainless steel pouch/ use an anti scale compound. The last 2 options work best in an oven not with a torch.
For tempering your normal kitchen oven should get them hot enough.

There is some HT info here http://www.bucorp.com/files/aisi_o1.pdf. For something like valve shims (and i presume this is a hot motor) i would have thought you would really need consistency and this means an oven.

Ew

Edit, i see you put the dimensions up now...

Hi Andrew,

Being so small a part, you may be able to keep the heat up to them to achieve the desired temp with your torch. There are other members on this forum that have heat treatment furnaces and will be able to guide you further. There is a really interesting book in the worksop practise series on heat treating (can't remember number or author) which may be worth a purchase if you plan on doing more heat treatment later. I would suggest at the very least you get yourself a few refractory bricks so that you can make a small enclosure and keep the heat enclosed, to some extent. A couple of points from one novice to another, you need to know exactly what temp you need to reach AND have a way of measuring, you need to know long long have to keep the part at that temp (depends on the size of the part). My understanding is that quenching is also quite technical in terms of making sure the entire surface is quenched equally.

Also, how critical are these parts? If they fail due to poor heat treatment, will it destroy the rest of the engine? If them failing is of small consequence or more in inconvenience then just have a crack and experiment! If they are a critical point of the engine then perhaps someone on this forum can perform the task, it looks like they could be sent in the mail quite easily/cheaply?

I know it's of no help to you now, but that book is very interesting reading. I didn't realise how much science was involved in heat treating. Also there are a few videos on youtube on heat treatment.

Good luck!

Simon

Hi Andrew,

Do them one at a time, heat to non-magnetic after you've done the first few you'll get a feel for the colour and you can forget the magnet. Drop them in oil with a stirring action to try and get an even quench.

Temper as soon as possible after quenching, use the kitchen oven at 250C, that should give you around 60 rc ( you could do a meatloaf at the same time.. )

I think you could rattle through them pretty quick, small parts like that they will heat almost instantly. So scale might not be too much of a problem.. warping and distorting might be more of a problem. That depends on shape and how even the quenching is. Only one way to find out.

Ray

Hi
No need for a soak time on something so small I guess?

Maybe going a little over the top but how about setting up an electromagnet over the top of a tin of oil? You wouldnt want to be picking them up with a pair of pliers would you?

Stuart

Thanks for the replies guys.

Couple more questions-
How long do i hold them at the Curie point for?
How long do they stay in the quench oil for?
How long do i temper them in the oven* for?
How soon after hardening do i temper?


Due to the shape of the parts it isnt really an option to make them oversize first. The thickness of the large section sets the valve clearance, this could be machined after hardening, but the spigot which locates into the lifter.... well i cant really get to that again. I also need the spigot in particular to hold its dimensions fairly closely (+/- 0.01mm) so they are the correct fit into the lifter (cant have them falling out!)
Any suggestions for anti-scale agents? sounds like i will need to use something...


One at a time sounds ok to me. When heating them with the torch, do i just do this with the part sitting on a brick or tile? whats the best way to transfer them over to the quench? im happy to pull them out with pliers, is it ok to pick them up like this when they are cherry red though?


*There will be no meatloaf, the only setting on my oven is "Pie Time" which my friend kindly marked for me. Apart from heating up pies, which is only a new experience, i have NFI how to use the "magical heating box" in my kitchen. My cooking skills are next to nil...

Just twist a bit of wire around it to hold it in the flame. If you pick them up with cold pliers, you won't get the right quench.. Maybe you could make up a little wire basket. No soak time needed for that size part, just as soon as it gets to over the curie temperature you can drop them straight into the oil, and leave them there until they have cooled. I'd just keep heating and dropping until they were all done. The quicker you can get the part into the quench without cooling the better,

Temper for at least an hour, you can't over temper, but it might be a good idea to check the actual oven temperature, they aren't usually very accurate. The rule of thumb for the time is one hour per inch of material thickness. I'd still temper for an hour. and leave them in the oven till they are cool.

Temper as soon as you can after quenching.

I can't help with the scaling question, If you are quick i'd expect very little scaling. The scaling is caused by exposure of the red hot metal to the air. It's more of a problem when you have long soak times for larger parts. You will get blackening and burnt oil coating the parts. I'd be more concerned about warping and size changes than scaling.

I have some Rosemill PBC antiscalant, but I've never used it. I must try it one of these days.

Ray

PS.. Do it outside, just for when the oil catches fire..

WRT to the application and issues with the parts failing -of course it depends how they fail.

This particular batch are for my own engine, a test bed of sorts, im pretty used to breaking it now.... if you're going to push the limits, you are bound to find them from time to time! This particular engine does 8200rpm with stock crank, rods and pistons, all on straight LPG (at 12:1CR). It's good fun, not bad out of a big I6

If the shims are too soft, the valve stem will pound into them, resulting in excessive valve clearance. The engine gets rattly, you lose a fair bit of cam lift and duration, it will run rough and be down on power but no real damage done. Had this issue with the first set of shims which were titanium (a bit too soft)
If they became brittle and cracked/exploded it wouldnt be so great, there is a (slight) chance broken bits could interfere with the collets, resulting in dropping the valve into a piston. Id like to avoid this if possible! That said, the shims are in compression only and i think the likelyhood of this happening is fairly low (happy to be corrected here)

Here is a picture of where they sit in the engine... you can just see the shim hiding at the top of the valve stem. The camshaft operates on the top of the bucket/lifter so no direct contact with the shim.



In a factory engine the shim sits on top of the bucket, by going shim under bucket you can use more radical cam profiles and run much higher rpm as there is no risk of the cam lobe flicking the shim out of the bucket (been there, done that). Not to mention the SUB setup is about 30% lighter than stock.

Thanks ray, very helpful. Ill give it a crack once i have finished 'turning' them on the 'lathe'

This takes me back a bit. The original Jaguar twin cam 6 used shims under the cam followers to set valve clearance, a time consuming system to set up but once done it was done for a long time. Inlet .004" exhaust .006".

The Jaguar shims were flat discs maybe 1/2" diameter, they were located by a recess in the valve spring cap.

Originally Posted by RayG

Just twist a bit of wire around it to hold it in the flame. If you pick them up with cold pliers, you won't get the right quench.. Maybe you could make up a little wire basket. No soak time needed for that size part, just as soon as it gets to over the curie temperature you can drop them straight into the oil, and leave them there until they have cooled. I'd just keep heating and dropping until they were all done. The quicker you can get the part into the quench without cooling the better,

Yep - can be a real issue. Even dropping them thru air into the oil can be enough.

At work when we needed to treat small pieces we always did this with the pieces loosely fitted in or alongside another larger piece of steel.

What about using a piece of steel about 8 mm thick and 12-15 mm wide and drilling holes into the strap for a loose fit of the pieces just below the surface. It can even be long enough to be able to grab the other end with a leather glove

Preheat the area of the strap with the holes drilled in it to red heat and then drop the required pieces into the holes and continue to heat the pieces to the required temp. Then put the end of the bar into the oil. This will reduce the temp loss during transfer to the oil which can be a big problem.

Seeing as you only have a small torch you can probably only do ~4 at a time because your torch won't be able to heat a big volume of steel.

Originally Posted by bob ward

This takes me back a bit. The original Jaguar twin cam 6 used shims under the cam followers to set valve clearance, a time consuming system to set up but once done it was done for a long time. Inlet .004" exhaust .006".

The Jaguar shims were flat discs maybe 1/2" diameter, they were located by a recess in the valve spring cap.

Same deal with Alfas - except a smaller diameter shim - maybe 10mm tops to sit on a 9mm valve stem.

Originally Posted by andrew_mx83

WRT to the application and issues with the parts failing -of course it depends how they fail.

Assuming you are using top hats (lash caps) to reduce the reciprocating mass of the valve train to grab some rpm? I had top hats for one of my engines, and I decided against them. They can come out with valve float. Even though I have triple race springs, I did not trust them.

Why not purchase some lash caps/top hats? I know you mentioned the time issue with them being made, but you might be able to find some off the shelf? Alternatively you might be able to seat the valves deeper and not run shims as thick (if you have the option of going with traditional shims or find a smaller size)? Even more out there, longer valve stems?

Jegs have a few different lash cap sizes off the shelf (not sure if the size you need): Valve Lash Caps - Free Shipping on All Orders @ JEGS

I think mine came from Arrow Precision..

I found this discussion pretty interesting. Ross's posts on PM are always worth a read IMHO.


Help with material choice