Costs of running a heat treat furnace??

[Gert Odendaal]

Good day members, I believe all is well and good on your side? I am contemplating purchasing a heat treat furnace in the near future...I am residing in South Africa and our electricity per unit is extremely expensive ..so we all are paying a lot of money every month for electricity...when using such an oven to heat treat mostly high carbon chrome/stainless steel blades , will this get to be a expensive procedures in regards to electricity consumption every month??

 

[KenH]

Well, if you have a 3,000 watt oven, each hour you run it will use slightly over 3KW of power. With my Evenheat 18" it will typically run close to 3 hours from time of start until finished with HT'ing SS. That's 9kw, and since we only pay around 12 cents/kw that's 36 cents to run oven. If heating high carbon knock an hour off that time. My oven takes around an hour to settle down at 1500°F, and around 2 hours to settle at 1950°F. Then another hour for soaking, removing blades, piddling around, etc.

How much per KW do ya'll pay in South Africa? OR, if not figured on KW, how is it figured?

 

[MarcWeitz]

Ken, is that oven a 120 volt or 240 volt? My understanding there is little difference in cost between the two for the same size oven, but a 240 volt oven ramps up to target heat faster, not necessarily cheaper in electric costs, just quicker..

 

[KenH]

Doesn't really matter if it's 120 or 240 since it's the watts that count. The 120 vac will most likely be lower wattage, so has to run longer to reach temp (for same size oven). The 240 vac "might" be just a "tad" less expensive to run, but I wouldn't think there would be major differences.

Marc, I don't remember where you are (Your profile isn't filled out), do you happen to know about what ya'll pay per KW for electric?

 

[MarcWeitz]

Sorry - updated account...I live in Metairie (New Orleans) LA. I had to call Entergy (elec. co.) because I frankly didn't understand the bill. They said my base charge per kW is 2 cents a kW. Last month, for March, kW used cost $186....plus storm restoration charges $10.22, fuel adjustment charges $61.10, and a Federal mandated EDC (no idea what that is) $00.20 that add to it. Last month's bill was $257.52.

 

[John Wilson]

Hi Marc,

Ken’s info is spot on. To simplify your bill, electricity is either charged by Kilowatt-hours or total kw. It is a computation of power used x hours.

simple example: If your oven draws 3kw and runs for 3 hours, that is 3 kilowatt-hours or 9kw total. so take what a kilowatt-hour costs you and multiply that by your oven’s usage and you jave the cost to run the oven for a cycle.

In easy terms, it costs about the same as doing a load of laundry in your dryer.

 

[Drew Riley]

I would think that once the oven reaches temp, the wattage used (per hour) is going to reduce at least a little bit. I would also think that for basic carbon steels, having your own oven is still going to be cheaper than sending it out to somebody else, especially if they pay the same rate per kwh.

 

[Gert Odendaal]

Members, thank you kindly for your input, it is much appreciated..
Question, if you have a choice to build your own heat treat oven ( how practical is such a build that needs to be really functional) or buy one( I looked at prices...it is an extremely costly item for a knife maker in South Africa due to our weak Rand currency ..will you rather build your own heat treat oven??

 

[bladegrinder]

I can't answer the question of buying or building but I'll add to the cost to operate equation.
I bought an evenheat oven about 25 years or so ago, back when I did sub work for Florida Power, the electric company here back then.
I had a friend that worked in the meter shop, he gave me a meter that was rigged on a small platform with a 220 plug in cord and a 220 receptacle,.

I took it home and heat treated a couple 440-C knives,
ramp up, heat treat, let oven cool, then two two hour tempers.
I then brought it back to him and couldn't believe what he told me, I forget the exact amount but it was under $2.00.
that oven has been really good over the years. I replaced one of the two elements about 8-10 years ago.

 

[Drew Riley]

Members, thank you kindly for your input, it is much appreciated..
Question, if you have a choice to build your own heat treat oven ( how practical is such a build that needs to be really functional) or buy one( I looked at prices...it is an extremely costly item for a knife maker in South Africa due to our weak Rand currency ..will you rather build your own heat treat oven??

I built my own before I had made my first knife, and the cost was probably around 1/4 of what the available ovens at that time would have cost me for a similar size and wattage. That said, I did cheap out in a few regards, and there weren't nearly as many options available then as there is today (though I'm not sure how that pertains to your location).
I do plan on building a replacement for my oven, hopefully this year or early next, but I have some specific requirements in mind and already have some experience in building one. Would I recommend someone else do the same? Not necessarily. If you've got the money and the means, just buy one and get cooking. That said, if you do some more research and think you could build one for cheaper than you can buy a pre-fabbed unit, and you like building tools, and have the time, knowledge and other resources to do so, then go for it.

 

[Bill Hubbell]

OK, Drew. Now you did it... I can't justify the purchase price of an oven, but would sure like to have one. I can probably handle the task. Built my gas forge, 2x72 grinder, and am in the process of a power hammer (but on the other hand, I ain't getting any younger!).
So, could you expound a little on your 'specific requirements' mentioned for your next build, now that you've been through it before? I don't expect detailed instructions, but just a few pointers for someone contemplating building one. My main reason for doing so would be cost, but don't want to cheap-out on important features. TIA!
Bill

 

[Gert Odendaal]

Drew/Riley would it be possible to make this a "group build" more in the line of the better quality components since technology really changed the past five years??? I really would appreciate it if you see your way open to conduct a tutorial of your build Sir???

 

[Drew Riley]

OK, Drew. Now you did it... I can't justify the purchase price of an oven, but would sure like to have one. I can probably handle the task. Built my gas forge, 2x72 grinder, and am in the process of a power hammer (but on the other hand, I ain't getting any younger!).
So, could you expound a little on your 'specific requirements' mentioned for your next build, now that you've been through it before? I don't expect detailed instructions, but just a few pointers for someone contemplating building one. My main reason for doing so would be cost, but don't want to cheap-out on important features. TIA!
Bill

Haha. Never too many projects right?
Basically I want to improve what I skimped on with my first build. The main "shortcoming" was not building a shell, so that will be priority #1. It'll likely be somewhere around 14 gauge mild steel. I'm not sure if I'll do a swinging door, or one that flips down with a counterweight, but that's a minor detail. I also want it to be relatively well insulated, so it will likely add a layer of fiberboard or kaowool between the bricks and the shell.
As for the heating elements, I recently saw a maker use a top mounted "rod hanging" system that I like, so I'll probably do something similar.
As for controls, I basically aready have what I need, so I'll just use my existing control from my current oven. Eventually I'll probably upgrade to a TAP controller or something with a little more capability, but that should get me going in the mean time.

 

[Bill Hubbell]

Thx, Drew
Ok, I officially started a Building an Oven Notes/Tips document to gather info like this for my build.
And, yeah, a tutorial would be great when you start building! - but if you're anything like me, I always come up short when it comes to doing informational videos. etc. And, I feel like kind of a creep cuz I have learned so much from those makers who take the time to provide videos and instruction that way. I get wrapped up in a build and lose track of what I should be videoing or documenting. -and I kind of stink at videos, etc.

But, I appreciate your input here. Can you explain a little about the 'top-mounted rod hanging' system you saw, so I can research that? Do the knives hang from it?

 

[KenH]

As for the heating elements, I recently saw a maker use a top mounted "rod hanging" system that I like

I think Drew is talking about a way to hang the heating elements - please do tell more about that method.

 

[Drew Riley]

Here's a link to the maker who built his oven with top mounted elements:

Heat Treat Oven - WIP

The time has finally come for me to build a heat treat oven. I have been getting by with my pid controlled forge for many moons and it has served me well but it's time for an upgrade. I have pulled design elaments from lots of deffrent sources and combined them into one super Franken-oven. The...

www.bladeforums.com

Basically, instead of carving into the sides of your bricks, you thread the element onto ceramic rods and hang the rods in the top of the oven.

 

[KenH]

Drew that is a very good link for building an oven. I have an 18 inch evenheat but it takes almost 2 hrs to stabilize at 1975F. I would like to build a small oven that would handle 2 blades but heat up faster.

Here is another detailed link.

DIY Heat Treat Oven Build

I was asked to put something together on my heat treat oven so I'l try to provide some of the details and issues I ran into. This will be long so I'll try to break it up into sections. This project isn’t nearly as complicated as you might think and you can build an oven for 1/3 the price of...

www.bladeforums.com

 

[soundmind]

I just bought a bunch of firebricks. Looking at them all piled up I have to say I've thought about building one. I'll check out these links.

I didn't think it was so inexpensive to run one.

 

[timgunn]

2 hours to stabilize at 1975 degF seems like a long time.

The last couple of HT ovens I built were 230V, 3000 Watt (the UK uses 13A-fused domestic plugs and 230V nominal mains Voltage, so the elements were sized for around 12.5A on 240V: 3 kW. The rationale being that there is some tolerance on mains Voltage and popping a fuse in the middle of a HT session would be worse than a slightly slower ramp-up to temperature). The chambers were 28" long, 7" wide and 6" tall.

From my initial testing notes: "800 degC was reached in 22 ½ minutes, 1100 degC took 54 ½ minutes, the temperature at an hour was 1125 degC and 1177 degC (2150 degF) took 71 minutes."

Assuming the oven runs at full power throughout is the "safe" thing to do when working out the power cost.

If you preheat the oven, it will draw full power during the heat-up process. Then it will cycle the elements on and off to maintain temperature.

The controller I was using could display the percentage output cycle. From memory, for those ovens, it was between about 15% (at 800 degC, 1472 degF) and about 40% (at 1177 degC, 2150 degF) of "on" time during the output cycle to maintain the setpoint with the oven closed: between 450W and 1200W during the hold period.

Batch-treating 5 or 6 stainless blades would probably use less than 5 kWhr all-told, even pulling them out one-at-a-time for plate-quenching and letting the oven temperature re-stabilize each time. I find it pretty difficult to envisage a scenario in which the cost of the power to run the HT oven approaches the cost of the HT foil used.

 

[soundmind]

we pay $0.87/kw out here. There's a residential break that makes it about $0.60, but rumor is that were going to lose that soon.
With no TV or video games I think we'll still land like the average customer if I ran an oven even at our high rate. And it sounds like its still worth it.