DIY Powdercoat Oven - Val6 Diesel heater?

[martyy]

No sir. Didnt even know there was such a thing.. I just used regular copper conductor thermostat wire that would be used in a home. I have ordered a longer k-type thermocouple which has both longer probe and length of wire. That way, I wont have to splice. Figured it was cheaper to do this than get just the splice wire and connectors. I appreciate your help.

[34by151]

The wire itself is the sensor which is why you cant extend with copper
Shielded Leads (stainless cover) can be up to 900m long
Thermocouples (depending on type) are accurate to 2degC

A thermocouple with a longer cable is often the best answer
One with a longer probe is good too as it moves the measurement away from the wall and into the airflow (100-200mm probe)

[martyy]

The wire itself is the sensor which is why you cant extend with copper

Ha! Did not know that. No wonder I struggled to fray the shielding and splice into the wire. Just assumed it was my poor eye sight. New sensor wont be here till mid-late next week. I guess this project is on hold for a bit longer.

[34by151]

The probe is made from two dissimilar metals (each wire) and the wires are joined together at the sensing end
The type of probe J,K ect tells you the wire types and ranges

[martyy]

New sensor showed up but only little time to test. Preliminary results are looking better.
400F on PID took 21:02 minutes. Unfortunately, i forgot to place the oven thermometers in during the test.
More testing to come.

[34by151]

Making progress well done

You can also run a calibration test of the probe (ice water or boiling water) but its rare for it to be out by more than 3 degC

[martyy]

New sensor is much quicker to update and defiantly more accurate. Not so sure about this REX C100 PID though. Anyway, ran a few more tests and decided to try and coat a few small items to see how it goes. Unfortunately, got about 360F degrees and tripped the overheat sensor on the burner and that put a halt on things for the day. Let them cool and finished them in the small oven. Found a good deal on a new Carlin EZ Gas burner that had not been used, but it may have been a scam as the guy has not responded in days. Probably going to grab a new one from PCom supply as he has the best price and is willing to support them. Gonna have to rework the burner hole a bit. Dont really want to cover the hole and cut a new one lower as I am going to have to build a burner box anyway. I can likely just use a deflector to push the heat where needed.

[34by151]

Tripping the burner means you need to increase the vent size. As far as the burner is concerned the oven is blocking the airflow. You will still need to deal with the vent even if you replace the burner. If you do get a new burner check the specs as I read it the max on that burner is about 40kw, which is about the same as the Val6 @32kw. My burner is 240kw which give a really fast response time the old 50kw burner it replace was quite slow which is just a function of the heat input. The bigger you go the less fuel you use and the better the coating will be (faster and quality)

[martyy]

Tripping the burner means you need to increase the vent size. As far as the burner is concerned the oven is blocking the airflow. You will still need to deal with the vent even if you replace the burner. If you do get a new burner check the specs as I read it the max on that burner is about 40kw, which is about the same as the Val6 @32kw. My burner is 240kw which give a really fast response time the old 50kw burner it replace was quite slow which is just a function of the heat input. The bigger you go the less fuel you use and the better the coating will be (faster and quality)

The Val6 MPX is 60,000 BTU/h and EZGas Pro is 50,000-275,000 BTU/h, so it should be enough. Not the best at conversions. I read some decide to bypass the snap discs sensors for overheating, but not willing to risk this heater. I agree though, will need to tune the venting.

[34by151]

50,000 btu = 14.65kw
275,000 = 80.59kw

I guess that why they quote btu (bigger number)
Im guessing you will have it cranked all the way up (80kw)

I also see there is a "1 band" and "2 band" versions not sure what that is haven't seen a carin burner
The 1 band is limited to 175,000 btu (51Kw)
So make sure its a "2 band"

14KW to 80kw is a decent upgrade
You can get 50kw from a turbo turbo heater cheaply, get a standard start one and add an autostart

I started with 50Kw (170,607 btu/h) and upgraded to the Riello which has 240kw (818,914 btu/h) max

In rough terms 30min to get parts up to temp (20 for oven) using 50kw
under 5 min with the 240 to get parts to temp and around 3 for the oven
I generally add 5mins to the powder time to get parts to temp.
so 12min cooking for powder, add 5 mins to get parts to temp, timer set to 17 from a cold start

[martyy]

Built out the burn box (circular) to accept the new burner (Mr. Heater propane 175k BTU due to cost). Would have loved to go Carlin but the funds are needed elsewhere. Gonna run off a 100lb tank until I can run the permanent line. Now, just waiting on the new Auber PID which will handle controlling the load directly to the heater. The REX C100 would not handle without another relay, but I really did not like that PID. The Auber also has wifi so I can set the parameters from my phone as well as alerts. Should be able to do some further testing on Friday, but from the brief test run I did, things are looking very promising.

[34by151]

Let us know how it goes

[martyy]

Did some temp wiring with switches and REX PID just to get some testing done. With the Mr. Heater at low 125k the oven comes to temp (400F) at just over 7 minutes. On high, 175k the oven comes to temp (400F) just under 4 minutes. Before I install the deflector/baffle i was seeing 30-40 degree temp differences from top to bottom. With baffles it is around 10-20 degrees difference. Wondering if I will need to install a circulation fan, especially for when the temp is reached and the burner shuts down as the oven seems to hold fairly well depending on vent adjustment. Happy with the progress and glad the wife has not locked me in the oven due to the amount of time spent on this...

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Above- Inside the burn tube I have a sleeve that slides over the end of the burner. Hoping this will be a sacrificial shroud that will reduce the heat on the outside of the burn box. Might end up wrapping the tube in rock wool.

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Above- temp wiring for old PID. switch to power pid, switch to power heater. New PID will handle load directly.

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Above- added sleeve to create a burn box. originally sleeve was intended for the Val6 but figured I'd keep the same diameter and just extend it. Ultimately this should work for a Carlin burner too. When that day arrives.

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Above- Diffuser/Deflector added to help keep temps stable high/low areas. It helped quite a bit.

[sonbakler]

Just checking this topic out now and am pretty impressed with your oven! Very ingenious design, pretty awesome and to get to temp in 7 minutes is amazing. Have you baked any parts in it yet?

[34by151]

I'd be running the heater flat out as 4 min is a good time to get the oven to temp
You next need to check the delay in getting parts to temp
Put in a typical load, no need to coat them yet
Use your non contact thermometer to check the part are up to temp

BTW you wont get an accurate measurement through the glass window
You either have to open the door or have an access port
The access port is ideal now but not needed once you get to know your oven

You wont need a fan as the turbo heater is doing that.
Some of the difference may be errors in the mechanical thermometers, try swapping them around and see if you get the same results.

Did you try the deflectors pointing up?
I have mine pointing up to give the airflow the longest path from the heater to the vent, down would harve the path to the vent
Either way because it will mix more when you have parts in the oven

The wool insulation cant do any harm, not a bad idea if you have some left over.

You can get into making it perfect but it sounds like your ready to try it out.

[martyy]

Just checking this topic out now and am pretty impressed with your oven! Very ingenious design, pretty awesome and to get to temp in 7 minutes is amazing. Have you baked any parts in it yet?

Appreciate the kinds words, however most of what I have done is just mimicking what I have seen on other builds. Was hopeful the Val6 was up to the task, but the oven was just too big for it to get to temp fast enough. The short answer is yes, I actually baked 2 small items in it yesterday. Black Rock texture from Prismatic, and it turn out excellent. Received the new PID today, but have not had time to hook it up. Will do so tomorrow.

[martyy]

I'd be running the heater flat out as 4 min is a good time to get the oven to temp
You next need to check the delay in getting parts to temp
Put in a typical load, no need to coat them yet
Use your non contact thermometer to check the part are up to temp

BTW you wont get an accurate measurement through the glass window
You either have to open the door or have an access port
The access port is ideal now but not needed once you get to know your oven

You wont need a fan as the turbo heater is doing that.
Some of the difference may be errors in the mechanical thermometers, try swapping them around and see if you get the same results.

Did you try the deflectors pointing up?
I have mine pointing up to give the airflow the longest path from the heater to the vent, down would harve the path to the vent
Either way because it will mix more when you have parts in the oven

The wool insulation cant do any harm, not a bad idea if you have some left over.

You can get into making it perfect but it sounds like your ready to try it out.

New PID will be installed tomorrow and I think I will do as you suggest with the burner set at 175k. Then I will run the auto tune program on the PID. I have already baked a couple items but I didnt document the time from oven temp to part temp for 14ga as it was.

I have not tried the deflectors up although you may not be able to tell but the bottom deflector is straight out while those above it are down. I am sure I will have lots of experimenting in front of me. The hard part is waiting for it to cool down before I go back in there. Always looking over my should to ensure nobody locks me in!

Have a few more things to cut but I should have a small batch of things to baked tomorrow afternoon.

Appreciate all your help!

[34by151]

Glad to help

I haven't seen ad PID that the autotune gets even clone to what I'd call "tuned". In fact it makes it harder to tune

To tune a PID use the following steps:

1. Set all gains to zero. (P, I and D to zero)
2. Increase "P" until you get a good overshoot
3. Increase "D" until you reduce the overshoot
4. Repeat steps 2 and 3 until increasing the D gain does not stop the oscillations.
5. Increase "I" gain until it brings you to the setpoint with the minimal oscillations

If you allow for some oscillation in step 5 you get to stabilise on the setpoint quicker
If you set it for minimal oscillations it will approach the setpoint slower but not overshoot at any point
The quickest way to get to and hold on the setpoint will be with "I" close to or set to 0

I have my oven set at a compromise allowing for a 5degC overshoot on the first oscillation

I use a pid for the heater on my gun bluing pot. I have this set the other way. Lots of "I" so I never go over the temp but get there slower
I use this for blackening excavator pins.

I have a pid controlling a heat exchanger between my compressor and storage tank. This one has "I" somewhere in the middle as it not measuring the temp but the temp delta

Getting back to your oven its not a bad thing to oscillate above temp then settle down to the set temp.
The oscillations above set point just get your parts to temp quicker as they get a heat boost
Remember its not the oven temp we care about its the part temp, so getting that to temp (but not over) is the goal.
As the temp of the parts will lag behind the temp of the oven the oscillations are your friend