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Thread: Timing the PC Cure Temperature

  1. #1
    Boolit Master
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    Timing the PC Cure Temperature

    Over the years I have seen so many posts from those having problems with powder coating. Powder coating is a pretty simple process and getting a good coating involves just a few steps. Start out with a quality powder suitable for your application. Apply the powder to completely clean bullets. Apply an ample amount of powder coating your bullets with no bare spots. Then properly cure your bullets.

    It seems that the last step, curing, generates more questions and creates more problems. Actually the curing process is very straight forward from the manufacturer's of most of the powders powders and that is bring the substrate (the surface of whatever has been coated) up to 400F degrees and keep the temperature stable for a minimum of 10 minutes. Problem is even with an accurate thermometer placed behind the glass oven door where the temperature can be monitored, the thermometer is reading the air temperature not the substraight and typically they are not one and the same. So most just add more time using a guesstimate, I know that is what I used to do.

    Now I think I have a better way. I purchased an inexpensive Chinese made digital thermometer and several cheap thermocouples. Checking against my mercury serviceman's oven thermometer I found the digital thermometer, which only reads in centigrade, to be quite accurate.

    I drilled a hole in a 45 caliber bullet inserted the thermocouple into the bullet then sealed it in with lead solder. Now I just set my sensor bullet on the rack in my oven with the other bullets and use its reading to know when my bullets have actually reached 400F degrees. Doing several racks at a time I found variations between the racks so placing my sensor on a center rack seem to provide a good reading.
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  2. #2
    Boolit Buddy
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    Nice. Ty.

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  3. #3
    Good information

    Links to what you bought and prices would be nice.

    I believe that the first, most common cause of failure is these cheap countertop ovens temperature settings are WAYYYYY OFF (up to 75 )

    Test your oven with a couple thermometers and adjust your oven setting until you oven reaches 400 this wetting will change when the surrounding temperature changes due to the location and type of heat sensor they use.

    IF you're not sure of the boolit temp, bake them for 20 min in an oven at 400 and you should be safe (unless your oven is very slow to recover after the door has been opened or your baking a lot of boolits



  4. #4
    Boolit Master Petander's Avatar
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    Yes.

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    IR meters are handy,too.

  5. #5
    Boolit Master Traffer's Avatar
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    Now you have to start marketing the rig. Put me down for one if it is reasonably priced.
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  6. #6
    Boolit Master
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    Yes, the thermostats on most of the toaster ovens are off. I have a new Black & Decker quartz convection oven I picked up for $7 at the local Goodwill and patted myself on the back all the way home for finding such a deal. Then when I checked the oven out I found it wouldn't go over 380 degrees even though the thermostat was maxed out and read 450. I guess I could do a PID, but why? I do have two Hamilton Beach Ovens that come to temp and hold it rock solid and the thermostats are almost right on, but I still monitor the temp with glass thermometer I can read through the door.

    OK, here is the requested info on the cheap digital thermometer. I bought the "TM-902C Digital LCD K Type Thermometer Single Input+Thermocouple Probe BBC", you see in the photo back in 03/2014 and used the original long probe sensor that came with it to check the metal temp in my Pro Melt furnace.

    Well now it looks like I got robbed because I paid $8.99 delivered for the thermo back then. Doing a search I find the same thermometer on Evil Bay for $4 delivered from China with a single K-sensor. I would suggest purchasing more than one of the K sensors as they do go bad; my original sensor only lasted a few months, but I found cheap K- type sensors on Amazon for just a few bucks for a multi pack.
    For the bullet, I just used solder to set the end of the thermocouple into the HP bullet drilled out a little deeper. But first check and make sure the thermocouple is working properly. I would guess you could just as easily cast the sensor into a bullet cavity; two people would probable make the job a little easier.
    So far this gadget is working great, but realize it is cheap and the longevity may not be there.

  7. #7
    Boolit Master slide's Avatar
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    The credit for this idea belongs to Ausglock. He came up with the idea several years ago. I have been using this setup for about three years now. My multimeter came from wal-mart. The good thing about this setup is when the temp changes you know it. It tells you what the temp of the bullets are not the air.
    Boolits !!!!! Does that mean what I think it do? It do!

  8. #8
    Boolit Master
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    Quote Originally Posted by slide View Post
    The credit for this idea belongs to Ausglock. He came up with the idea several years ago. I have been using this setup for about three years now. My multimeter came from wal-mart. The good thing about this setup is when the temp changes you know it. It tells you what the temp of the bullets are not the air.
    Interesting, in my 6 years on this site I have never read such a post, but I certainly have not read everything that is posted, even in this single catagory. But you have hit on a problem on this site and that is a lot of worthwhile information once it leaves the first page is lost and gone forever. May I suggest that since you are aware of this post, find the post made by Ausglock, yourself or any other that instructs fellow caster on putting a thermocouple inside a bullet to monitor equal mass temperature. I know I would enjoy reading the post and I think others would also, as it should be made a "Sticky".
    Last edited by Dragonheart; 02-06-2019 at 08:11 PM.

  9. #9
    Boolit Master slide's Avatar
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    I am not going to go through Ausglock's posts to find that post. Not very computer savy. However. on 10-29-18 at 3:10 pm I posted in the thread,Most people are not baking their powdercoat pc long enough, describing the set-up. At 3:28 pm you posted saying you thought it was a good idea. I don't care who gets credit for it. I was only interested in trying to help some people who might be having temp trouble.If you want it, take it. I have always believed in the old saying give credit where it is due.
    Boolits !!!!! Does that mean what I think it do? It do!

  10. #10
    Boolit Master
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    Not trying to start a war, but the only value I see to this site is the sharing of information. My post was about doing just that, sharing information. No where in my post do I claim to have been the original inventor of anything. But I did share a step by step process with photos of how I made a custom thermocouple so others could duplicate something I found useful. I don't need credit for thought, processes, my posts or any information I have shared and freely given over the years with those that share my shooting interests.

  11. #11
    Boolit Master

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    I drilled a small hole thru the top of my oven. I use my Lyman lead thermometer by sticking the stem thru into the body of the oven. When it stabilizes at 400 I know the oven is hot enough to cure the powder. That's when I start my 10 minute time.

  12. #12
    Boolit Master Hick's Avatar
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    I use the same oven as Conditor22--preheated to 400 by the gauge then cook them for 15 minutes to be sure they get up to temperature. I haven't tried measuring bullet temperature but they always come out good, so I haven't worried about it. I've done smash tests and also resizing after PC and verified that the coating stays fine.
    Hick: Iron sights!

  13. #13
    Boolit Grand Master fredj338's Avatar
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    I don't have any issues with my PC curing & guestimating bake time. I put them in a preheated 400deg oven for 13-14m. I have never had coating not cure??
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  14. #14
    Boolit Buddy Sig556r's Avatar
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    IMHE, poly PC takes about 12-15mins while HF epoxy takes about 20mins, taken after boolits start to sheen, respectively.
    Immediately dumping in cold water not only helps in quenching but also easier to separate.

  15. #15
    Boolit Master
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    Quote Originally Posted by jimb16 View Post
    I drilled a small hole thru the top of my oven. I use my Lyman lead thermometer by sticking the stem thru into the body of the oven. When it stabilizes at 400 I know the oven is hot enough to cure the powder. That's when I start my 10 minute time.
    Sounds reasonable, but the problem is you are measuring the air temperature of the oven, which may be 400 degrees, but that doesn't mean the surface of all the bullets is 400 degrees. For example I have a PID installed in a 30" wall oven and this oven will easily accomodiate five 1/2 size baking sheet pans holding thousands of bullets. I can assure you that when the PID indicates it is at 400 degrees, all the pans and all the bullets are not at 400 degrees. The PID is reading the temperature of the convection circulated air. I can see the differences in the surfaces as the powder begins to flow.

  16. #16
    Boolit Master
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    The smash test is a great indicator for testing the elasticity of the polymer, but the polymer still may not have reached complete hardness. In addition to the smash test try the "Scrape Test" by scraping the polymer with a razor knife with the blade held at 90 degrees to the polymer surface. If layers of polymer easily scrape off then there is a problem.

  17. #17
    To check if PC is completely cured, put a little of the gun powder you use in small containers and cover a pc'd boolit with it. If there is no reaction over a couple weeks it's cured.

  18. #18
    Boolit Master
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    Another test the commercial guys use is putting some methyl ethyl ketone (MEK) on a white rag and seeing if the color wipes off.

  19. #19
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    I don't know how this got so overcomplicated. Directions for Eastwood PC from their website: "They are suitable for any metal surface and most cure at a temperature of 400 degrees F at 20 minutes after flow out." Says nothing about temperature inside the middle of whatever you are coating or air temperature or anything else. "Flow out" is not difficult to establish and you count to 20 from there.

  20. #20
    Boolit Master
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    Quote Originally Posted by scotner View Post
    I don't know how this got so overcomplicated. Directions for Eastwood PC from their website: "They are suitable for any metal surface and most cure at a temperature of 400 degrees F at 20 minutes after flow out." Says nothing about temperature inside the middle of whatever you are coating or air temperature or anything else. "Flow out" is not difficult to establish and you count to 20 from there.
    What can I say, this is just plain wrong! Eastwood doesn't make powder. I would suggest you follow the instructions of the powder manufactures instead, which for most powders is 10 minutes minimum once the substraight reaches 400 degrees.

    Most powder starts to flow just past 150 degrees. Oven seal, insulation, power and load determines the amount of time a substraight takes to reach 400 degrees, so 20 minutes is meanness. This is simple thermodynamics and cannot be accounted for by simply picking an arbitrary time. For example I have a toaster oven that won't get to 400 degrees regardless of how long it is on, but it will get hot enough for the powder to flow, so how can 20 minute timing from flow work on this oven? I recently did a post where I coated almost 3000, 9mm bullets in a single cook. So would it make sense that the cure time would be the same for 30 bullets on a single rack as opposed to 3K of bullets on 5 completely full racks? I can assure you after flow started these bullets were not even close to being properly cured in 20 minutes.

    PC is not a complicated process and being able to measure the bullets substraight as well as the air temperature for me makes the process less complicated to achieve a proper cure. But if you are happy with 20 minutes for everything by all means continue on.

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