Warped grates on coverted Leader 42" X 9' arch

[Three Maples]

I converted a 42in X 12 Ft drop flue to a 42in X 9 Ft raised flue. Boils about 90 gal/hr. Fired with softwood slabs and some round hardwood. Worked great untill i got to the end of the woodshed and got into some 2 year old hardwood slabs. While the fire did not seem hotter all of the grates warped some to the point of being junk. I had cleaned out the ashes before i fired and the grates are about 3/4 in apart. There was a hot bed of coals under the grates from about 5 hours of burn. The draft door full open for the entire time. Any thoughts? I hate to replace them and have it happen again. Gary

[maple flats]

Did you have the grates in with the open V facing up? That allows ash to fill the V and then protects the grate from the intense heat enough to retard warping. If you had the open V down, that was the issue. I also think forced draft under the fire helps protect the grate. I draw my air from outside and blow it in under the grates. I burn some very hot wood at times and do not have a warping problem, unless they started out flat. I bought my arch which had been used 1 year and they had a uniform sag. They still have the same sag after 8 or 9 seasons. Never clean the ash from in the V during the season. Then start your fire slow enough next season to fill the V's again before you push it hard. I take ashes from my home woodstove to fill the V's.

[Three Maples]

My grates do not have the v style they are flat on top with a tapered from the center to each end rib. I have wondered it blowing air under the grates would help. I am concerned about the doors as they are cherry red now with natural draft. Any thoughts?

[maple flats]

Mine do not glow after adding air under fire (AUF) and air over fire (AOF). They did before. I never run one without the other and I never move the valves that control the distribution of air, 1 AUF 1 AOF so I don't know if they would with just 1. My AUF is run in thru the back, lays on the floor and is just a 4" stove pipe, that ends about 6" from the front and is plugged. Then 3 rows of 1/4" holes are drilled about every 4" to let the air (high pressure) in. The design of the AOF has 1/4" nozzles every 6" all around the fire box and placed 6" below the pan and aimed down about 10 degrees. There is even 1 each side of the door facing towards the back wall. While the door gets real hot and the fire is extremely intense the doors no longer glow. This being said, I don't think a slight glow hurts the cast, but it is heat that can't help the boil.