Harman PC45 auger tube erosion - cause and fix

[jp99]

So after reading about others having the auger tube erosion in the discontinued Harman PC45 stove, and then discovering it in mine, I decided to investigate this. I'm fairly certain I've found the cause and am testing a solution with good results so far.

This will be a long post to document this, so here is a summary:

• The erosion is caused by pellet/corn fuel trapped between the auger and the tube, dragging under high pressure and eroding the steel
• The fuel trapping occurs because of a lip of carbon buildup at the end of the auger tube
• The carbon buildup is caused by the small gap between the burn pot and the auger end plate, allowing a small amount of air entry and incomplete combustion at the joint, creating the carbon.
• One simple solution is wrap a small amount of aluminum foil around the burn pot end to seal the gap

Here is the long explanation and my test results:

If you look at the PC45 burn pot area in cross section, this is a simplified view:



The erosion occurs at a point inside the auger tube but in an area where the auger blade has a large gap to the tube surface:


In my stove, this eroded area was a clean steel surface showing wear marks with the same direction as auger rotation. It wore through to the air box below, and I sealed it with JB Weld from the underside.

So this wasn't a burning condition but a wearing away. The question is, how can this happen? Letting the stove burn for a while results in some important carbon deposits occurring at the end of the auger tube:



If these deposits are tall enough (say 1/8") then the fuel cannot easily slide out of the tube and into the burn pot. In fact, the fuel next to the auger tube is essentially trapped there as the auger turns, and if tall enough will be compressed by the auger blade (fuel seen as green circles here). I believe this causes the erosion.



To test this idea, I ran my stove this season for shorter periods of time and shutdown often to scrape the carbon buildup away. In doing this, I found no evidence of wear marks in the previously worn area, indicating no rubbing and erosion happened.

So if this carbon is the cause of the erosion, where is it coming from? If you check the burn pot assembly you'll find some needed looseness in the assembly so the pot fits in place. However, this also results in a small gap between the burn bot and end of the auger tube, which can allow a small amount of air to enter:



Since incomplete combustion results in carbon buildup, it's reasonable to think this air entry is creating the carbon in this area. To test this idea, I decided to close this small gap with some aluminum foil. I used the heavy duty thickness of foil, and used about a 3/8" wide strip to fold over the area where the burn pot is next to the auger end plate:



The burn pot fit is tighter and I had to use a small hammer to lightly tap the pot into position.

I ran a test of this for 12 hours on a constant burn (Stove Temp mode, my normal method in my house) and then shutdown the stove. After cool down, I checked and there was essentially no carbon buildup where I'd seen it before at the end of the auger tube. Additionally, I noticed the fire area is moved forward some - perhaps 1/2". I'm now in my second test burn with the foil and am noticing the same burn pattern shift.

Time will tell if this is the actual sequence of events, but the tests and observations I've made seem logical and early results look promising. If you have a PC45 and are concerned about erosion (or already have it) you may find this information helpful - and it certainly is a cheap fix!

 

[KNelson]

So after reading about others having the auger tube erosion in the discontinued Harman PC45 stove, and then discovering it in mine, I decided to investigate this. I'm fairly certain I've found the cause and am testing a solution with good results so far.

This will be a long post to document this, so here is a summary:

• The erosion is caused by pellet/corn fuel trapped between the auger and the tube, dragging under high pressure and eroding the steel
• The fuel trapping occurs because of a lip of carbon buildup at the end of the auger tube
• The carbon buildup is caused by the small gap between the burn pot and the auger end plate, allowing a small amount of air entry and incomplete combustion at the joint, creating the carbon.
• One simple solution is wrap a small amount of aluminum foil around the burn pot end to seal the gap

Here is the long explanation and my test results:

If you look at the PC45 burn pot area in cross section, this is a simplified view:

View attachment 237553

The erosion occurs at a point inside the auger tube but in an area where the auger blade has a large gap to the tube surface:

View attachment 237554
In my stove, this eroded area was a clean steel surface showing wear marks with the same direction as auger rotation. It wore through to the air box below, and I sealed it with JB Weld from the underside.

So this wasn't a burning condition but a wearing away. The question is, how can this happen? Letting the stove burn for a while results in some important carbon deposits occurring at the end of the auger tube:

View attachment 237552

If these deposits are tall enough (say 1/8") then the fuel cannot easily slide out of the tube and into the burn pot. In fact, the fuel next to the auger tube is essentially trapped there as the auger turns, and if tall enough will be compressed by the auger blade (fuel seen as green circles here). I believe this causes the erosion.

View attachment 237556

To test this idea, I ran my stove this season for shorter periods of time and shutdown often to scrape the carbon buildup away. In doing this, I found no evidence of wear marks in the previously worn area, indicating no rubbing and erosion happened.

So if this carbon is the cause of the erosion, where is it coming from? If you check the burn pot assembly you'll find some needed looseness in the assembly so the pot fits in place. However, this also results in a small gap between the burn bot and end of the auger tube, which can allow a small amount of air to enter:

View attachment 237551

Since incomplete combustion results in carbon buildup, it's reasonable to think this air entry is creating the carbon in this area. To test this idea, I decided to close this small gap with some aluminum foil. I used the heavy duty thickness of foil, and used about a 3/8" wide strip to fold over the area where the burn pot is next to the auger end plate:

View attachment 237555

The burn pot fit is tighter and I had to use a small hammer to lightly tap the pot into position.

I ran a test of this for 12 hours on a constant burn (Stove Temp mode, my normal method in my house) and then shutdown the stove. After cool down, I checked and there was essentially no carbon buildup where I'd seen it before at the end of the auger tube. Additionally, I noticed the fire area is moved forward some - perhaps 1/2". I'm now in my second test burn with the foil and am noticing the same burn pattern shift.

Time will tell if this is the actual sequence of events, but the tests and observations I've made seem logical and early results look promising. If you have a PC45 and are concerned about erosion (or already have it) you may find this information helpful - and it certainly is a cheap fix!

I know you posted this two years ago, but I just stumbled across this. It's an annual chore that I bust out a mig welder and build up the auger tube erosion, shape/contour with a die grinder and a carbide burr. All in the living room of course cause I'm not dragging this thing into the shop every year!

Did this work well for you long term? If so, how often are you replacing the foil? I put in a new auger hoping it would push the burn zone into the pot, but it's already starting to flake off the steel from being burnt. I had tried adding an extension to the old auger but it didn't last/burnt away within a season.

 

[jzm2cc]

I've welded up my tube also. I think the main contributor to auger and tube erosion is the lack of pellets around the exit to provide a thermal barrier. The other Harmans have an inclined firepot so pellets are always between the auger and fire. On the PC-45 the fire is right at the end of the auger eroding it constantly. Temped to just bolt up the P61 fire pot, and change to less expensive finned igniter as I don't burn corn anyways.

 

[jp99]

I know you posted this two years ago, but I just stumbled across this. It's an annual chore that I bust out a mig welder and build up the auger tube erosion, shape/contour with a die grinder and a carbide burr. All in the living room of course cause I'm not dragging this thing into the shop every year!

Did this work well for you long term? If so, how often are you replacing the foil? I put in a new auger hoping it would push the burn zone into the pot, but it's already starting to flake off the steel from being burnt. I had tried adding an extension to the old auger but it didn't last/burnt away within a season.

My apologies - I've been off this forum for a long time and did not watch this thread.

So - has it worked in the long term? Yes. My first JB weld fix wasn't quite robust enough, so I attached some sheet metal screws as anchors and the second JB weld fix is holding up fine. As for the aluminum foil, if I burn hard I replace it once a week. Low level burning that lets my natural gas furnace also kick on to heat, maybe every 3-4 weeks.

Even if you weld the auger tube opening, you still have the small gap that lets air in and seems to bring combustion and carbon buildup in the tube/burn pot joint. If you are good at welding/grinding, you probably can fix that on the burn pot. For me the aluminum foil is the only choice.

 

[jp99]

I've welded up my tube also. I think the main contributor to auger and tube erosion is the lack of pellets around the exit to provide a thermal barrier. The other Harmans have an inclined firepot so pellets are always between the auger and fire. On the PC-45 the fire is right at the end of the auger eroding it constantly. Temped to just bolt up the P61 fire pot, and change to less expensive finned igniter as I don't burn corn anyways.

I doubt that is the cause. The erosion leaves a clean steel surface behind. That doesn't indicate erosion from burning, but from heavy pressure wearing away metal.