Heat treat rings

[MachineTom]

While everyone has Opinions on what to do for HT of cast iron, this is not the best place for Facts. Having done a fair amount of home HT work, I go the the makers of the material for Facts. In this case these guys ( https://www.dura-bar.com/resources/upload/Dura-Bar-Heat-Treating-Guide.pdf)

Until any kind of iron can be Hardened it needs to hit a Curie point, evidenced by losing it ability to be attracted to a magnet. A temp of less than 1700F+ is needed to get there. Heating to 1000-1200 will anneal so materials, which is opposite what you want. With most after Curie point it needs to be quenched, meaning rapidly cooled. With thin sections like the piston ring, they have little cross section so they can often be air quenched, then tempered, by heating to temps from 400 to 1000F then allowed to cool.

While you can get by with just a propane torch. You chould get an infared Temp gun, which the cheap ones go to 1000F great for tempering, and temp crayons for 1600-1800. There is somewhere on the web a great color chart for temperatures, Bright cherry red 1750, will almost always work, for hardening, but following the makers with some tools is the way to go.

 

[stuartblack]

Theres ones like this because its electric the temperature can be easily controlled

 

[WOB]

While everyone has Opinions on what to do for HT of cast iron, this is not the best place for Facts. Having done a fair amount of home HT work, I go the the makers of the material for Facts. In this case these guys ( https://www.dura-bar.com/resources/upload/Dura-Bar-Heat-Treating-Guide.pdf)

All true, but we aren't trying to harden the piston rings. We want them to take a permanent set in the expanded condition. Annealing them on the fixture with a controlled gap leaves them soft enough to resist breakage on installation but still springy enough to put the desired uniform circumferential pressure on the cylinder bore wall to make a good seal. They aren't very hard, but wear against the typical soft steel cylinder is negligible for our purposes. Even though they are soft, occasionally one will break when expanded enough to go over the piston OD. So it's always a good idea to make several spares when building an engine.

WOB

 

[WOB]

My furnace is a early version of the Neycraft JFF-2000. I bought it many years ago for about $600 new IIRC. The control was one of those electric stove element analog types that takes a lot of time and guesswork to get the desired temp and the temp stability was not too good. I finally got fed up with it and converted it to a digital PID controller using the existing thermocouple and adding a solid state relay. The controller is an early version of the current Fuji PXR3. It fit perfectly in place of the original temp. meter and the existing thermocouple leads were right there to connect to the controller. I added a couple of pilot lights ( main power and heater power) , a main power switch, plus a bit of wiring and it was done. Temp range is room temp to 2000 degF. It works perfectly and is a pleasure to use.

WOB

 

[MachineTom]

The idea is to get the rings "Springy". If you just heat to 1000F you have maybe annealed them, which is the opposite of "springy", annealed is meant to bend a shape and stay that way, not the desired effect. If you harden then Temper them that is how you make them "Springy".
Have you ever watched Forged In Fire, some guys overheat the metal before quench, the blades crack during the quench, or break when tested. Another guy using the same material, can flex the blade a huge amount without breaking, its all in the temps of quenching and tempering.

I recently purchased an Induction Heater, I made a 1" dia profile cutter out of M2 material, it is generally used to make end mills. I used my temp color chart, by eye, but too hot and cracked when quenched, right through 1" material. Now I have an infared temp gun that goes to 2200f. second one came out fine.
The induction heater is like a microwave oven, for metal, takes steel to 2000F in seconds.

 

[Gordon]

Just picked up a kiln on Craigslist. $105 6x6x6 @2000* max. That should solve the problem.

 

[tornitore45]

WOB Wrote:
I finally got fed up with it and converted it to a digital PID controller using the existing thermocouple and adding a solid state relay.

How a SS relay can fulfill the requirements of a PID control, escapes me.

 

[doc1955]

I think there is confusion here. When you so called heat treat rings you are not going for a hardness increase. What you are going for is a normalizing and an increase in tinsel strength making them a little more springy. That is why when you heat them you set the gap wider and the basically normalize them. When I say heat them to a cherry red it would be more of a real dull red you want a temp of 800 to 1200 degrees f. Anyway the backing plate and torch for just a few works fine for me and has not failed me yet. But you do have to be careful and put flame as close to center as you can.

 

[WOB]

WOB Wrote:
I finally got fed up with it and converted it to a digital PID controller using the existing thermocouple and adding a solid state relay.

How a SS relay can fulfill the requirements of a PID control, escapes me.

Calling it PID is not really accurate (my mistake) since it actually uses "fuzzy logic" according to Fuji. The system response is similar to traditional PID control, but the controller is simpler and cheaper. For the readers whom are control engineers ( I'm not) the difference is described here: https://www.controleng.com/single-article/temperature-control-pid-vs-fuzzy-logic. Suffice to say the controllers are cheap, physically small, readily available to hobbyists and work perfectly well.

The controller output is a variable width/freq. pulse train that turns the SSR on and off. The initial "on" time can be several minutes on start-up of a cold furnace and will gradually reduce to about 1 sec. on and maybe 15 sec. off once up to set-point temp, depending on the thermal characteristics of the furnace. Plotted over time, the temp. is a smooth curve with minimal overshoot on start-up. It will settle out to set-point and hold it to plus or minus about 1 deg. indefinitely.


WOB

 

[dkwflight]

Click spring does some interesting heat treatment. The big feature is protecting the items from air during the heat,
He uses clay sometimes and an eye wash chemical other times. I can't recall what the chemical is at the moment.
making files.
It will be worth your time to watch his vids.
Dennis

 

[petertha]

Not sure if this was the same 'table top' mini HT oven I saw referenced on another forum. Thought it was a bit cheaper. But something similar might be an option for small temperature controlled & heat treating applications. Makes me wonder why they are less than the more common brands though.
https://www.amazon.com/dp/B00CUKD1UY/?tag=skimlinks_replacement-20

I found a local knife blade making supplier that hardened my cam plates quite reasonably & has all the proper equipment. I know we are not talking hardening specifically, but just mentioning another possible resource that might be in your area in that particular hobby facet. Personally I'll probably keep going that route unless I have sufficient projects to warrant an oven.

 

[tornitore45]

The idea is to get the rings "Springy".

Not really. Any annealed steel is still springy within its elasticity limits. The idea is to set the ring in a NOT ROUND shape with an open gap. The annealed rings will return to the same open gap after compression due to the intrinsic elasticity. It will be ~round when compressed radially uniformly. This is what we are after. It just happen that even annealed cast iron has very little plasticity (the opposite of "springiness"). Cast Iron goes very quickly from flexing to broken without taking much deformation in between.

Lots of good info here

http://adriansmodelaeroengines.com/catalog/main.php?cat_id=10

 

[Gordon]

Well I got the kiln and now I have to do a bunch more learning. I put some rings in and it took about 35/40 minutes to get to 1100° where it stayed for about 30 minutes. Then it shot up to 1500°. I set the analog electric stove type control back down but it still continued to cycle on and off. Finally just shut it off. Now about an hour later it is still at 1100°. Plan is to just let it cool down naturally and take them out when they get down to 500°. It looks like I should have some type of temp control that is more responsive than what I have. I look at eBay and there are PID temp controls selling for anywhere from $25 to $800. I assume that there is already a thermocouple on the existing control which could be connected to a new control so even the $25 unit should be an improvement. +/- 10° is not necessary. I would think that +/- 100° would be OK.

The kiln came with a couple of stainless steel mesh pads to set the material on. Kiln shelf material is available in paper as well as ceramic grid. I am not sure if that is necessary or if it would be OK to just set the material on the floor of the kiln.

Any input?

Gordon