I Took the Plunge - New Oven

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rdj357
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Re: I Took the Plunge - New Oven

Post by rdj357 »

I use this.

https://carlincombustion.com/gas-oil-bu ... as-burner/

This entire discussion hinges around the fact that the thermal mass of the parts you need to powder coat are the highest load when taking time into consideration. That’s the most important thing and the side of the equation that is necessary for a good powder coat. There are powder coat lines that use radiant heat only and area on a constant conveyor. It’s all about getting the part to temp and holding it there for the specified cure time. I just have to KISS in my shop.
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Re: I Took the Plunge - New Oven

Post by 34by151 »

If you put a burner in the oven you are introducing a direct flame
A torpedo heater is an indirect flame

With a burner in the oven you need to get more air in as your turning the air into exhaust
IE more oxygen
It quickly will develop black soot from the burner due to incomplete combustion.

The reason you can use a small heater in your house to heat a room is simple
It does not take a big heater to lift the temp of a room a few degrees
Even so its takes a while

See how long it would take not to raise the temp 10degC but 180

Think of it another way
How long does it take your wall oven to get to 200c vs how many watts in the element
Now scale that up to your oven
Do an experiment on your wall oven
Time how long it takes to get to 200c
Log the time every 10degc
You will find each 10deg takes linger and longer
See the difference it has repeating the test with the the fan off

Plug your numbers into that calculator I posted its will give your best result
340f to 400f @ 12kw will take about 4mins
Again that's assuming your only heating the air not your parts
It will take longer the more volume your parts have and also the thickness of the parts

The 340f to 400f is critical, this is the time you want to minimise as 340 is where your powder begins to flow
Its flowing on a part that not up to cure temp
You really want to minimise this time if you want a quality coating

Assuming you preheat the over to 400f
Open the door and load your parts
A fair guess id you loose 20deg
So your looking at 10-15mins to bring the parts up to 400f and begin timing your cure

Re over temp this should occur as the PID is taking care of this
Once tuned in you wont get an over temp
On my oven I get 1deg over on the initial heat then its locked on the set temp of 204c
That requires tuning the PID parameters
From memory the initial setting produced a 15geg over and 5 deg under
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Re: I Took the Plunge - New Oven

Post by adbuch »

rdj357 wrote: Sun May 15, 2022 3:40 pm Sorry to have been so silent - I often utilize the KISS method on my projects - Keep It Simple Stupid. There is a lot of talk of over-engineering and that’s cool if it’s your thing! I considered a divider for my larger oven but just don’t think it’s worth my time or effort when I consider the operating cost.

My background is 30 years in the HVAC/R trade. It would take a tremendous amount of typing to arrive at the numbers I use but I’ll try to touch on the concepts. Essentially it is a combination of loads in BTU and then confining it to a time. I realize that I’m not being entirely accurate especially if you preheat the oven and take away some of that initial load before loading parts. Calculated at 4’x4’x75” lined with 14 gauge metal sheet and insulated to R-19 (.0526 U) with rock wool. 50F ambient and 50F entering part temp. 400 degree cure temp. Curing the equivalent of a full 4x8 sheet of 12 gauge parts.

First you have to add up all the ambient loads to get your box loss.
* Air in the oven (pretty negligible but I’ll put it for fun) 100 cu.ft.=8.07lb of air x .24 BTU/lb (specific heat of air)=1.9368 BTU x 350F increase = 678 BTU
* Interior skin - 132 sq ft of 14 gauge = 420.7lb of steel x .120 BTU/lb = 50 BTU x 350F increase = 17,500 BTU
Total static load: 18,178 BTU and if we want to preheat in 15 minutes then times 4 so 36,356 BTU/h

Add up dynamic loads:
* Heat loss through all oven walls (simplified to not take into account the varying delta T as oven warms on startup) .05626(U) x 132sq.ft x 350F (delta T) = 2599 BTU/h
* Air changes due to ventilation - assume 1 complete air change per hour so 678 BTU/h
* Calculate parts to cure load - 504# steel x .120 BTU/lb= 60.5 BTU x 350F increase = 21,175 BTU If we want to have part at temp in 30 minutes then we need to multiply that x 2 to get BTU/h so that is 42,350 BTU/h
Total dynamic loads: 45,627 BTU/h (walls and air changes plus parts to temp in 30 minutes)

Total oven load: 81,983 BTU/h

Convert that to watts for electric heat (divide by 3413 BTU/kWh) so 24 kWh is the requirement for ~30 minutes to part cure temp.

As you can see, the walls, ceiling, and floor and air changes are a pretty small part of the load (biggest part is heating up the internal skin) so I don’t worry about walling anything off on my ovens. Hope this helps - the rule of thumb you can find online recommends 150 watts per cubic foot and I find that to be very low and insufficient for my needs. My large oven is 500 BTUh/cu.ft. And small oven is 1,450 BTUh/cu.ft.
Thanks for that very useful information Robert! It makes perfect sense to me, and I have copied this to put in my Powder Coat Oven file to refer to when I actually start my build.
David
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Re: I Took the Plunge - New Oven

Post by 34by151 »

rdj357 wrote: Sun May 15, 2022 6:53 pm I use this.

https://carlincombustion.com/gas-oil-bu ... as-burner/

This entire discussion hinges around the fact that the thermal mass of the parts you need to powder coat are the highest load when taking time into consideration. That’s the most important thing and the side of the equation that is necessary for a good powder coat. There are powder coat lines that use radiant heat only and area on a constant conveyor. It’s all about getting the part to temp and holding it there for the specified cure time. I just have to KISS in my shop.
Well said
Here is the one have
https://www.accutherm.com.au/product/Ri ... urner/403/

This is the gas version i have the Diesel on
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Re: I Took the Plunge - New Oven

Post by Joe Jones »

Okay. Thank you both for your input.

However ... With all of those fancy numbers and calculations, how do you respond to the EASTWOOD 240VAC 4x4x6 powder coat oven?

http://www.eastwood.com/eastwood-hotcoa ... -oven.html

According to everything you are posting here, the oven they make is woefully inadequate for powder coating. Theirs is 39 Amps. Mine is 50 Amps. Theirs is 8,500 watts. Mine is 12,000 watts. Theirs has three elements. Mine has four elements.

Do you think the EASTWOOD oven is not able to live up to their claims? They sure seem to sell a lot of them.

I am not being "snarky" here. I am just looking at the EASTWOOD offering, and the oven that I am building which is (apparently) MORE powerful.

Joe
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Re: I Took the Plunge - New Oven

Post by Joe Jones »

34by151 wrote: Sun May 15, 2022 7:11 pm If you put a burner in the oven you are introducing a direct flame
A torpedo heater is an indirect flame

With a burner in the oven you need to get more air in as your turning the air into exhaust
IE more oxygen
It quickly will develop black soot from the burner due to incomplete combustion.
you are right! I guess I would build a heat exchanger, not unlike the old air cooled VW exhaust heaters. I could build a steel pipe suspended over a propane burner, and use a fan to blow the heated air into the oven from an external vantage point.
The reason you can use a small heater in your house to heat a room is simple
It does not take a big heater to lift the temp of a room a few degrees
Even so its takes a while

See how long it would take not to raise the temp 10degC but 180
I understand your point, and I agree. A Volkswagen van is much faster from 0 to 20 MPH than it is from 70 to 75 MPH.
Plug your numbers into that calculator I posted its will give your best result
340f to 400f @ 12kw will take about 4mins
Again that's assuming your only heating the air not your parts
It will take longer the more volume your parts have and also the thickness of the parts

The 340f to 400f is critical, this is the time you want to minimise as 340 is where your powder begins to flow
Its flowing on a part that not up to cure temp
You really want to minimise this time if you want a quality coating
Duly noted.

Tell me this ... What if the parts are heated FIRST, and then brought out of the oven to be powder coated, and then rolled back into to the oven? Can I spray powder onto HOT parts, or do they have to be at room temperature in order for the process to be successful? I know the parts would lose SOME heat, but they would not return to room temperature that quickly.

Too crazy? :lol: :roll:

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Re: I Took the Plunge - New Oven

Post by 34by151 »

Yes you can preheat parts but you dont want them at a point that the powder would flow.
in reality your just making it harder on yourself.

Re a heat exchanger
It think you will find its easier and cheaper to get a torpedo heater in the 40kw+ range or a Burner as we have suggested.
My oven is around the size of yours and my burner is 120Kw
I started with 4 x 2.5kw elements, went to a 40kw torpedo and then the 120Kw burner

I cant comment on the eastwood oven as we dont have eastwood here in OZ.
But from my understanding and I might be way off base there stuff is just low quality imported from china
From the specs I would not much performance from it

Would it get to temp, yes probally
Would it get give you issues, probally

Just my thoughts
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Re: I Took the Plunge - New Oven

Post by 34by151 »

Joe I looked up that eastwood oven and ran the numbers

8500W
48x48x72inch = 96cubic foot

I used an air density of 1.168 G/l
Internal air mass 3175.1g
Initial Temp 68F
Final Temp 400F
Coefficient 26.01 Wattsec/g°C

That gives you 29Min 52Sec

So I very much doubt the claims

Another point
They state 8500W and 35,000BTU's

8500W = 28,985 BTU/H
35,000 BTU/H = 10,257W

So again numbers dont add up

Given they cant state the heat source consistently Id not rely on the time claims
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Re: I Took the Plunge - New Oven

Post by adbuch »

34by151 wrote: Mon May 16, 2022 4:30 am Joe I looked up that eastwood oven and ran the numbers

8500W
48x48x72inch = 96cubic foot

I used an air density of 1.168 G/l
Internal air mass 3175.1g
Initial Temp 68F
Final Temp 400F
Coefficient 26.01 Wattsec/g°C

That gives you 29Min 52Sec

So I very much doubt the claims

Another point
They state 8500W and 35,000BTU's

8500W = 28,985 BTU/H
35,000 BTU/H = 10,257W

So again numbers dont add up

Given they cant state the heat source consistently Id not rely on the time claims
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Plus I think you can build the equivalent oven for much less money. I seem to remember the Eastwood oven priced at over $4k plus shipping.
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Re: I Took the Plunge - New Oven

Post by rdj357 »

Don’t powder coat hot parts. Ever. You’re trying to solve problems that do not exist and the result will be creating problems that didn’t exist. Ask any reputable powder coater and you’ll find that amateurs and those that don’t know how to do multiple coats are the ones shooting hot parts.

I use a direct flame in my ovens and it works fine. Technically, a torpedo heater is still a direct flame but it is housed in a tube outside the actual oven. It is still directly venting into the oven requiring air entering from outside the oven for combustion and being vented. As long as the flame has the correct balance of oxygen introduced, it will not produce soot or smoke. For the flame to be considered indirect there would have to be an actual heat exchanger in which the flame burns in a sealed, separate compartment. That would introduce an entirely new set of engineering to provide heat transfer with circulation airflow requirements - not worth the trouble.

You’re on the right path - just focus on getting the thing built and if you put in 24k of elements you can always work out a control system that can run them all simultaneously should you find that you’re not patient enough for the 12k to get it done.
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Re: I Took the Plunge - New Oven

Post by Joe Jones »

34by151 wrote: Mon May 16, 2022 2:41 am I cant comment on the eastwood oven as we dont have eastwood here in OZ.
But from my understanding and I might be way off base there stuff is just low quality imported from china
From the specs I would not [expect] much performance from it

Would it get to temp, yes probally
Would it get give you issues, probally

Just my thoughts
Their website boldly states MADE IN AMERICA. Granted, PlasmaCam makes the same claim, and I honestly believe their tables DO come from China.

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Re: I Took the Plunge - New Oven

Post by Joe Jones »

rdj357 wrote: Mon May 16, 2022 9:24 am Don’t powder coat hot parts. Ever. You’re trying to solve problems that do not exist and the result will be creating problems that didn’t exist. Ask any reputable powder coater and you’ll find that amateurs and those that don’t know how to do multiple coats are the ones shooting hot parts.

I use a direct flame in my ovens and it works fine. Technically, a torpedo heater is still a direct flame but it is housed in a tube outside the actual oven. It is still directly venting into the oven requiring air entering from outside the oven for combustion and being vented. As long as the flame has the correct balance of oxygen introduced, it will not produce soot or smoke. For the flame to be considered indirect there would have to be an actual heat exchanger in which the flame burns in a sealed, separate compartment. That would introduce an entirely new set of engineering to provide heat transfer with circulation airflow requirements - not worth the trouble.

You’re on the right path - just focus on getting the thing built and if you put in 24k of elements you can always work out a control system that can run them all simultaneously should you find that you’re not patient enough for the 12k to get it done.
Thank you Robert. you bring up a good point ...

Is this discussion about my oven failing miserably to produce powder coated parts successfully, or are we REALLY talking about SPEED? I am not a production shop, so if it takes 45 minutes to powder coat some metal do-dads in my oven, I will not lose sleep over it. I just don't want to spend a lot of money to pacify what may ultimately be little more than chest pounding. :roll:

34by151 seems to state that essentially ... my oven will not work AT ALL. He believes the oven will not achieve or maintain sufficient heat, in a time span that is short enough to be taken seriously.

I do not understand all of the math and formulas you have so thoughtfully presented, however I DO understand that when you cook a turkey, you are not cooking the STUFFING just because the oven is at temperature. The MEAT (in this case, the metal) must ALSO be at temperature for the cooking process to be successful.

I am having a hard time believing that the EASTWOOD ovens do not do the job, or that they perform poorly. I know a man in Kansas who has one, and he loves it! He demonstrated the process to me while I was there. He does a quick pre-heat to cook off any humidity that may be on the metal. Then he pulls the warm metal out and shoots the powder. Then it goes back into his EASTWOOD oven and about 22 minutes later, a beautiful and LARGE piece of metal art emerges.

I understand that "numbers don't lie" but I am having a hard time believing that a small, heavily insulated booth 4x4x6-ish cannot get Hellish HOT in a matter of several minutes, with four 240VAC oven burners inside, and two circulation fans stirring the air.

I am back to square one. Build the thing, and try it! I believe (perhaps foolishly) that it will perform MUCH BETTER than the dire predictions you and 34by151 have shared here.

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Re: I Took the Plunge - New Oven

Post by Joe Jones »

My mistake. My Kansas friend has a Kool Kote oven. :Sad

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Re: I Took the Plunge - New Oven

Post by 34by151 »

Joe, we are just trying to give you the benefit of our knowledge.
Take it or leave it.
It's not like we both have not been where you are at some point.

Im not telling you it won't work. As long as you can get to 400c you the powder will flow.
How well it sticks and the surface quality is is the issue.

Lets see your numbers after running 12kw
Maybe you can defy the physics
I wish you the best of luck and god on ya for having a go
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Re: I Took the Plunge - New Oven

Post by Joe Jones »

34by151 wrote: Mon May 16, 2022 6:49 pm Joe, we are just trying to give you the benefit of our knowledge.
Take it or leave it.
It's not like we both have not been where you are at some point.

Im not telling you it won't work. As long as you can get to 400c you the powder will flow.
How well it sticks and the surface quality is is the issue.

Lets see your numbers after running 12kw
Maybe you can defy the physics
I wish you the best of luck and god on ya for having a go
Oh, I understand that, and I am glad that you take the time to share your knowledge. I get lost in the math, but I guess I will just have to skin my own knee anyway. :HaHa

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Re: I Took the Plunge - New Oven

Post by Joe Jones »

The storm didn't do as much damage as it appeared at first. I was able to put the basic frame pieces back together. I added two cross braces to resist the "wiggle" of the loose frame, and added 100 pounds of concrete blocks to the base to help hold it in place until it is completed. I am back on track now!

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Re: I Took the Plunge - New Oven

Post by SegoMan DeSigns »

8-) Just another challenge thrown your way and you overcame it.
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Re: I Took the Plunge - New Oven

Post by Joe Jones »

SegoMan DeSigns wrote: Thu Jul 07, 2022 9:59 pm 8-) Just another challenge thrown your way and you overcame it.
The thin steel studs bent easily, but then they also bent BACK easily :HaHa

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Re: I Took the Plunge - New Oven

Post by adbuch »

Joe Jones wrote: Thu Jul 07, 2022 9:55 pm The storm didn't do as much damage as it appeared at first. I was able to put the basic frame pieces back together. I added two cross braces to resist the "wiggle" of the loose frame, and added 100 pounds of concrete blocks to the base to help hold it in place until it is completed. I am back on track now!

Joe

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Re: I Took the Plunge - New Oven

Post by Joe Jones »

If scientists could successfully slow down the rotation of the Earth, we would have more daylight to get things done, and more time to SLEEP between days!

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Re: I Took the Plunge - New Oven

Post by Joe Jones »

Another storm, and this time it was ANGRY.

This is the result.

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Re: I Took the Plunge - New Oven

Post by plasmanewbie »

Sorry to hear that Joe. What a bummer.
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Re: I Took the Plunge - New Oven

Post by Joe Jones »

I will rebuild it. I will make it bigger than it was. Stronger than it was. Faster than it was ... (Cue The Six Million Dollar Man theme Song...) :lol:

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