Oven controllers and relays
- Thread starter MikeS
- Start date
scott.livesey
Dealer - Purveyor
what are you going to heat treat? High carbon steels such as 1095, O1, 80CrV2, 1084, and 52100 have straight forward heat treat where all you are asking of the furnace and controller is to maintain 1475F(or 800C or your favorite temperature) +/-15F. Blades of these steels usually go straight into a furnace pre-heated to your temperature. Stainless is a little more complicated but even then, the procedure seems to be blade into furnace at temperature #1, equalize, ramp to temperature #2 as fast as possible, soak then quench. the most basic controller should be able to do this. spend your savings on a second thermocouple and display so you can monitor your blades more closely.
EdCaffreyMS
"The Montana Bladesmith"
Unless I'm misunderstanding your intent, there's going to be a SSR already built into the oven, so you wouldn't need one of those. It should basically be "plug-n-play". I've seen the TAP controllers (at Blade this year), but not used them. The RampMaster is a very capable controller, but just not as "fancy" as the TAP.
As Scott mentioned, your going to see a variance from whatever set point you choose.... don't be too surprised at the "swing" the oven displays..... I've mentioned it before, but in general the cost difference in knifemaking type heat treat ovens is based on their +/- percentage value of the temp they hold from the set point. The more expensive ovens will generally have a 2-3% +/- temp variance, with less expensive brands/models correspondingly having higher variance/percentage values.
As Scott mentioned, your going to see a variance from whatever set point you choose.... don't be too surprised at the "swing" the oven displays..... I've mentioned it before, but in general the cost difference in knifemaking type heat treat ovens is based on their +/- percentage value of the temp they hold from the set point. The more expensive ovens will generally have a 2-3% +/- temp variance, with less expensive brands/models correspondingly having higher variance/percentage values.
The SSR or relay is triggered by the controller on a time-proportioning output cycle. If your oven needs 50% power to maintain a given temperature, the controller will power the elements for half the cycle time and leave them off for the other half.
This produces a saw-tooth effect on the temperature: long cycle time; big saw teeth. Short cycle time; little saw teeth. SSRs are able to operate reliably with shorter output cycle times than relays, so they have the potential to give tighter temperature control.
Most ceramics kilns seem to run a 30-second output cycle. I used 10 seconds for the relay output on my first homebuilt HT oven, seeing a measurable difference on temperature stability (using a datalogger) with reducing cycle time output. I now use 2 seconds on an SSR (we only have one "hot" wire on our 230V mains supply here in England, so only need one SSR)
In reality, there are many other factors that affect how tightly the temperature will be maintained and most of them have a bigger impact than the cycle time, but SSRs are the way to go if you have the choice and want tight control.
This produces a saw-tooth effect on the temperature: long cycle time; big saw teeth. Short cycle time; little saw teeth. SSRs are able to operate reliably with shorter output cycle times than relays, so they have the potential to give tighter temperature control.
Most ceramics kilns seem to run a 30-second output cycle. I used 10 seconds for the relay output on my first homebuilt HT oven, seeing a measurable difference on temperature stability (using a datalogger) with reducing cycle time output. I now use 2 seconds on an SSR (we only have one "hot" wire on our 230V mains supply here in England, so only need one SSR)
In reality, there are many other factors that affect how tightly the temperature will be maintained and most of them have a bigger impact than the cycle time, but SSRs are the way to go if you have the choice and want tight control.
Thanks guys,
I understand what you are saying about the cycling of the oven and the % of variance in the temp. As far as alloys. I am starting with simple alloys, lots of O-1 to start with. ( after chatting with Ed.) However, depending on time etc I would like to try other alloys and eventually forge some blades but thats a ways off.
Mike
I understand what you are saying about the cycling of the oven and the % of variance in the temp. As far as alloys. I am starting with simple alloys, lots of O-1 to start with. ( after chatting with Ed.) However, depending on time etc I would like to try other alloys and eventually forge some blades but thats a ways off.
Mike