simple Hi-Tek coating

[HI-TEK]

[QUOTE=flybyjohn;4903241][QUOTE=HI-TEK;4902953]

Ok, after 1st coat was dried, it went into a preheated, well insulated, modified convection oven set with PID at 393 deg F. The oven fell to 345 deg F in the first 30 seconds The oven then raised to 402 deg F air temperature measured 1/2" below the bullet tray at the 3 minute mark from placing them into the oven. The oven air temperature slowly dropped from this point to where it hit about 395 deg F by the 10 minute mark. I had the timer set for 12 minutes but after 10 minutes, the bullets were starting to turn gold to brown. So I pulled them out of the oven at the 10 minute mark.

Just a couple of things that may make things better.
Set your PID to 360F.
The coated cast must get to 356F and stay there for another 2 minutes.
Setting your PID to 360F will allow things to get to correct cure conditions, and this should not over bake coatings to make them golden tan at the 10 minute mark..
You really need to monitor the coated cast temperature and not oven temperatures.
An Infra Red thermometer sold on Ebay is ideal, as you can open oven door, aim at coated cast, and instantly will tell you load temperatures.
You can then work out how long a certain load will take to get to correct cure temperatures, (356F), and remain correct colour and cure adequately.
Please advise afterwards

[Ausglock]

I run separate coating trays to baking trays.
The coating trays get scraped with a razor blade scraper between every 3rd coating cycle to remove buildup.
Baking trays never need cleaning.
I use perforated stainless steel plate for trays.

In the picture, you can see the 4 top trays are clean and dark. they are baking trays.
the ones below are coating trays, thay are lighter and you can see green coating
on the mesh.

[flybyjohn]

I do have an inferred thermometer but I get pretty different temperatures on items of different color and texture that I didn’t think that it would be accurate enough for the bullet bake. For instance I have a galvanized pipe and a black steel pipe running the same air from my batch rocket stove and they show up to a 40 degree difference from each other. The shinny things always read cooler even though that pipe is closer to the fire. With bullets of different color will the thermometer read the same. I’ll have to try it out.

[flybyjohn]

for some reason I thought the temp had to get to 200 deg c that’s why I had the oven set to 393 deg f. But since it only has to get to 180 deg c then I will try the lower temp and see how things work out. Thank you for your suggestions guys.

[Tazza]

I have bought and sold many a bobcat over the years, only ever messed with real bobcat branded ones, i never sold a machine that was bodged, i always told the buyer that if you have issues to let me know and i'll help out, i never said i'd do it for free, but i' help. Had a guy i sold one to in kilkoy, i went out and sorted it or him at no cost, was an excuse for a day out, and he and his wife were were very firendly, caught up a few times over the years.

[Gremlin460]

Always wanted a Bobcat with a 4 in 1.

Thats what I got, the huge BHB 4tonner with a 4in1.

[Ausglock]

Thats what I got, the huge BHB 4tonner with a 4in1.

BHB???
Our yard crane is a Chaimberlian tractor with a BHB Crane conversion done in WA back in the 70's. Called a Mobilift crane 3 to 6 ton.

[Mozz]

The small convection benchtop oven can be improved.
1. Tear it down
2. Seal all the gaps of the oven compartment with silicone sealant.
3. Remove the convection fan and put more pitch on the fan blades. this improves air flow.
4. Place a clay paver block on the bottom of the oven.
5. Insulate the exterior of the oven compartment with rockwool or similar.
6. install PID control (you already have this).
Don't use the timer on the oven. get a digi timer (or stopwatch) from ebay etc.
I built one with a flasher/buzzer that alerts me when time is up. it is really annoying if you don't press the reset button...lol

Edit:
These small oven can have issues with wire connectors burning off where one heat element links to the next. this will cause heating failure.
When the oven is heating up, I visually check that all top and bottom elements are glowing red before baking anything. I have had to replace connectors a few times over the years.

Just getting back into this casting/coating game,
I am assuming that the fan 'moves' the hot air around and ideally not introduce new (cooler) air.?

Mozz

[Ausglock]

That is correct.

However, when I open the oven to rotate the tray of bullets 90degrees and re-insert it, there is cooler air entering.
But the radiant heat in the oven makes temp recovery a short time thing.

[Tazza]

That is correct.

However, when I open the oven to rotate the tray of bullets 90degrees and re-insert it, there is cooler air entering.
But the radiant heat in the oven makes temp recovery a short time thing.

I'm wondering if i could wire a switch up to the door like a fridge has for the light to come on. So the fan goes off to help not blow hot air out, i'm sure it won't make much difference, but just another thing to play with.

[HI-TEK]

I'm wondering if i could wire a switch up to the door like a fridge has for the light to come on. So the fan goes off to help not blow hot air out, i'm sure it won't make much difference, but just another thing to play with.

Tazza, you can add a micro switch to the door that is directly wired to turn fan on and off. Selection of switch and wiring, it is important to make sure that heat does not affect them. Get a sparky to do electrical work.

[flybyjohn]

My fan is on a switch separate the elements so I just turn off the fan switch before I open the door. I have done it both ways and loose much less heat with fan off before opening the door.

[Ausglock]

My converted wall oven had the switch as standard equipment.

[sierra1911]

I'm still using the liquid Hi-Tek and had been frustrated in using a plastic baby medicine syringe to measure the coating. I talked with a friend who has a chemical analysis lab and he suggested using a glass pipette with a safety bulb instead of the syringe. High quality pipettes and safety bulbs are separate items - the safety bulb has a hard cone shaped end which is pressed against the end of the pipette to suck the liquid into the pipette. The safety bulb is then removed and a finger is placed over the end to release the liquid in a controlled manner using the graduations on the pipette. The small opening in the bottom of the pipette makes a controlled release possible.

I found lower quality pipettes on Amazon which came with bulbs without the hard plastic cones - the bulb stretches over the end of the pipette, creating a long eyedropper with measurement markings. The 10 ml size works perfectly for dispensing Hi-Tek onto my 8 lb. batches of boolits. Unlike the baby medicine syringes, the markings on the pipette do not wash off with acetone. A set of four pipettes with bulbs, 2 glass stirring rods, and a pipette cleaning brush was $12. Be sure to get 'drop' or 'release' pipettes as they're calibrated to include the tapered tip so that releasing all the liquid in the pipette releases the amount indicated on the scale (other pipettes are only accurate for measuring between to marked graduations on the scale).

I also acquired a couple 100 ml graduated cylinders from Amazon to measure the coating, catalyst, and acetone components when mixing the coating. The pair was $12 from Amazon.

Lastly, the lab friend recommended Nalgene brand HDPE (high density polyethylene) bottles for storing the Hi-Tek and for storing the acetone used to rinse the pipette. He shared that the Nalgene lids seal better than other brands he's used and will prevent evaporation of the acetone. The bottles are available from Amazon in sizes ranging from a couple of ounces to a quart. Search for 'Nalgene round bottle'. They're available in both a narrow and wide mouth version.

He recommended 2 rinse bottles, but I didn't see a need for a second rinse as the little bit of Hi-Tek left in the pipette after a single rinse doesn't adversely affect anything. When mixing a new batch of H-Tek, I use the acetone from the rinse bottle as it also doesn't affect the new batch and gives me the opportunity to start with clean acetone in the rinse bottle.

[Ausglock]

They must be cheapass syringes.
The one we use are 10ml with external markings.
Only time we throw them away is when the acetone has started to bulge the black rubber plunger.
That is after about a solid month of coating. and they don't get rinsed. just left in the tray till next coating session.
And the graduation lines don't rub off...

[Tazza]

I was thinking of a switch on the panel to turn it on and off, knowing my luck i'd forget to turn the rotten thing back on

I may need to look for a switch that can handle some heat, even if mounted externally out of the way it will get warm, good job for when i get around to hooking it up to a PID. A fan uses stuff all power, so it won't take much of a switch to be able to handle the current, heat may be an issue though.

I too use throw away syringes, i use them till the black rubber bit puffs up too much to allow me to suck up coating. When i'm done, i suck up acetone, jiggle it and squirt it out. Pull the plunger and wipe of with a rag and let it dry for next time. Lasts me quite a while like that. They are cheap as chips, so when they die, i have no issue reaching for a new one, i have a box of 100 of them, they will out last me.

[Ausglock]

Taz.
You can mount the switch external. use a lever limit switch.
About 1" square with a lever that has a roller on the end.
Let it ride against the edge of the door at the bottom. easy.

[sierra1911]

They must be cheapass syringes.
The one we use are 10ml with external markings.
Only time we throw them away is when the acetone has started to bulge the black rubber plunger.
That is after about a solid month of coating. and they don't get rinsed. just left in the tray till next coating session.
And the graduation lines don't rub off...

They were cheap syringes - free from a local pharmacy. If not rinsed at least every other tray, they would stick in the tube and sometimes even pull the rubber end off the plunger. Cheap glass pipettes require only one hand and are long enough to reach into can of catalyst.

I don't cast that much but did smelt and cast 175 lbs of range scrap into 5,000 45's the last couple weeks and will start on 38's tomorrow - target ammo was getting low.

[Tazza]

Taz.
You can mount the switch external. use a lever limit switch.
About 1" square with a lever that has a roller on the end.
Let it ride against the edge of the door at the bottom. easy.

I like this idea, i think i'll give it a go when time allows, at the bottom is a good idea, out of the way and easier access to the wiring, nothing hanging outside to give you a little tickle if you brush up against it.

I do have a butt load of micro switches from old micro wave ovens, i collect all sorts of "crap", i can hook up the the NO contacts so a tab on the door closes the switch when the door is closed, when it opens, it lets go of the switch, opening the circuit.

[Ausglock]

Sounds like a solid idea..