To cope with the extended exposure to hot gases due to the moonburner grain configuration I decided to apply additional phenolic protection on the inside of the liner. Rather than adding a full length casting tube I decided to cut the casting tube in two pieces and applied an additional layer of phenolic near the core of the moonburner and no extra liner protection on the opposite site.
- The liner (3″ PML phenolic airframe tube) and casting tube (3″ PML phenolic coupler tube) were sanded from the inside with a honing device and 60grit sand paper taped to the stones. This worked surprisingly well.
- The casting tube was indexed into 6 and marked on the outside for alignment.
- The casting tube was cut to 897mm length so it is recessed in the liner approx. 9mm at both side corresponding with the nozzle and forward closure step(s).
- This tube was then longitudinally cut in 2 pieces with table saw. A 240° and 120° piece or a 2/3 and 1/3 strips.
- Both pieces were coated with a layer of HTPB on the outside. A 60gr batch of HTPB proved to be sufficient.
- First the coated 240° piece was inserted into the liner at an angle (to prevent the HTPB to be scraped of) and secondly the 120° piece was inserted.
- The casting base was wrapped in food wrap and inserted into the liner to make sure the casting tube inserts were recessed at the correct distance.
- Finally a 70mm OD aluminium rod was inserted to apply the necessary pressure and left to cure for 24 hours. Due to the casting base in place and a large overhang of the bar the pressure was not optimal at the casting base end. Next time make sure there is even pressure (no casting base in place, use a distance piece to position the inserts and keep the aluminium rod centered).