RMH upgrades and repairs

There were several things that I wanted to test and upgrade with my 6" batch box that I built last winter that I worked on and completed last night.

1. To replace one of the 4 firebrick splits that was acting as my roof. Hard to say if it was from the heat or had a small crack in it already as some of these bricks were reused from my J tube I replaced it with.

2. To make the port opening to an official size according to Peters chart. For a 6" batch box, the height of the port is supposed to be 9 1/2" tall and earlier I decided to keep it simple without the need for cutting and made it an even 9" (which is the length of the brick anyways). To compensate, I made the port about a 1/4" wider.
Didn't take too long with the diamond blade anyways and now its taller and narrower.
I have no idea whether to expect any noticeable differences but it just made sense to me to keep the firebox dimensions as close to stock as Peter has spent a lot of time trying different shapes and designs to settle on these figures. My conscience is now clean....and perhaps the burn a little more too!

3. To make a 6 minute riser. This of course is based on the 5 minute riser design but goes all the way to the floor surrounding the port also.

Our forum leader Thomas has already posted his 6 minute riser construction details and just wanted to share some of my experiences also that may complement his build.

Photo 1 shows my homemade bricks made out of perlite, clay slip and some furnace cement. Other than some shifting at the joint between these bricks and back of the port and some minor surface pitting, they were in exceptionally good shape. I would still consider them to be a great alternative if you can't get your hands on superwool or just want to keep the build as inexpensive as possible. The pear shape of the opening was not intentional but rather happened by mistake. A superwool seal fixed that.

Photo 2 shows my experiment with cutting the pipe to accommodate the port opening. Since I used sheet metal and folded it into a circle 8" in diameter and secured with rivots, I thought at first I would cut tabs and fold them back to give the edges more rigidity to hold its shape better. I folded them inwards and outwards for comparisons but ended up just cutting them off because they didn't really help out much and decided they were not needed.

Photo 3 shows how the interface between the metal and the back sides of the port connect. They fit pretty snug with only a minor gap. I thought it would be a good idea to cut the opening in the metal a little larger to keep it away from the high heat and melting. Once the superwool is in place, it will act as the edge of the port help protect it. It still may corrode over time but time will tell.

Photo 4 shows the superwool creating a seal around the pipe.

Other tidbits:
- The width of my sheet metal and superwool was both 24" wide, so I just kept them uncut. I made a 5 minute riser to set on top of this base so total riser height is now 48" tall.
Peters chart calls for 43 3/16" but extra height can't hurt anyone and since I have a double barrel setup, plenty of top gap.

- I put a small wall of cob around the base of the riser to keep it from shifting at all and help keep the seal intact.

A thing of beauty Gerry!   Nice to make little upgrades as time and weather permits.
That Morgan Superwool is just a pleasure to work with!  And it really does the job!
Please update this if you notice an improvement in performance.

UPDATE:

A few days ago, I noticed that looking through the port revealed that the cf blanket of my new 6 minute riser had shifted somehow and leaving a gap between the back of the port and the blanket.
Not good......An emergency autopsy was required.
A fair amount of my dragon is easily taken apart so the decision was not a hard one to make.

Upon removing the lower portion of the heat riser that is coupled to the back of the port revealed that the metal skin had buckled from the heat and pushing the cf blanket away creating the gap.
A few pictures:





As you can see, the cf blanket is in really good condition (that's ash sticking to the inside of it), but not so much for the metal.

So after a few iterations, this is what I came up with: Create a small bridge formed out of firebrick splits, then cut the metal jacket back further along with the cf blanket port opening big enough to fit around this bridge.
The metal is now much further away from the intense heat rather than being in contact with the back of the port bricks.





The little bridge accomplishes a few things.

1) It provides a sharp right angled edge that Peter has commented on his site Working of the air streams as being beneficial for proper mixing of the gases.
Using the cf blanket alone as the port opening produces an edge that is anywhere from being sharp and actually rounds a bit as it shrinks and deforms a bit through heating and turbulence.
The port size is now fixed without the natural shifting and wearing the blanket was experiencing.

2) It provides a very tight seal for the cf blanket to mate with and no other sealing was required. Note: this was only because when I cut the blanket, I made it about 1/4" smaller on all sides so that it would have to be slightly stretched to get it to fit onto the bridge.

I've burned it about 4 times now and so far it appears very stable with no visible movements. Taking the barrel off during one of the burns, I peeked down the riser to take a look at the double rams horns.
They were much more defined, even on both sides and burning all the gases very well. With the previous configuration, the rams horns were less even and sometimes a bit of smoke would come out the riser as logs shifted.

So with the extra bridge added into the equation, I don't think it can be realistically called a 6 minute riser anymore. Cutting the firebrick with a wet saw maybe took another 10 minutes.... so perhaps now its a "16 minute riser"?

Matt Walker and Peter van den Berg over the years have often said that small changes can make a big difference in the core so its best not to modify it. This to me is a perfect example of that and experiencing it first hand is very helpful in understanding their logic and wisdom much better. Thanks guys!

Excellent observation and improvement  Gerry!
I like it... the 16 minute riser!
Now I'll have to inspect mine to see if the same issue is happening on it!
Thanks a lot Buddy! No rest for the wicked I guess!

I might suggest cutting out the sheetmetal far enough to do as you did, but wider, and wrapping the cf out around the edges of the sheetmetal to form the seal with the firebox. If it is done so that the riser cross section at port level leaves maybe an inch of the port bricks exposed to the riser interior, you would still have the sharp edges for good vortex formation. Cutting out the cf in a "Y" shape at the top, not removing any of it, and folding to sides and top, would make a superior seal and metal protection.

I also think bending the sheetmetal out at the sides (not in small tabs but as a single tab on each side) to double the thickness of the edge would stiffen it significantly.

Thank you for the suggestions Glenn.
The cf blanket is 1" thick and not sure if it would bend that much at that sharp enough of an angle....unless it was scored or something?

I've found that as cf blanket gets blasted with heat, it forms an egg shell semi-hard skin which when pressed with a finger, breaks and powders off. The rest becomes a little less flexible than when new but still bendable. This is actually a good thing as this way it somewhat stiffens up and doesn't rely so heavily on the metal skin to hold its shape. The metal is nice though as it helps protect the blanket from getting torn apart when cleaning with a vacuum. The sheet metal could even be replaced with hardware cloth I suppose if that's all you had.  

Going to let it stay this way for a week or more, then pop the top again to take a peek at how the metal and seals are holding up.

Yes, I wouldn't advise further altering what you have, that was a suggestion for new builds.