From 3aba2282a4fa0f1277bfd5487c7ca282d2fed1b3 Mon Sep 17 00:00:00 2001 From: Bdale Garbee Date: Mon, 15 Nov 2021 10:06:49 -0700 Subject: [PATCH] document failed KNER batch --- rockets/research/2021.11.12.mdwn | 53 ++++++++++++++++++++++++++++++++ rockets/research/index.mdwn | 4 +++ 2 files changed, 57 insertions(+) create mode 100755 rockets/research/2021.11.12.mdwn diff --git a/rockets/research/2021.11.12.mdwn b/rockets/research/2021.11.12.mdwn new file mode 100755 index 0000000..0f436b1 --- /dev/null +++ b/rockets/research/2021.11.12.mdwn @@ -0,0 +1,53 @@ +# Batch 2021.11.12 # + +5 grains of 75mm KNER, intended to be a reload for a Loki 76/6000 case. +with Loki-style #36 short nozzle. Grains to be cast 5.25" long using Delrin +coring rods of 0.75" diameter. Liner calculates to be 28 inches long. Will +"glue" grains in liner using clear silicone and o-ring spacers. + +Nakka's SRM spreadsheet suggests this could be an 84% L968, with 3473g +of propellant, a 4.88 second burn time, and max pressure of 655psi. + +Will mix a 3500g batch, the formula for which is: + +* 65% KNO3, 2275g +* 35% Erythritol, 1225g + +I started by setting the multi-cooker to 300F indicated for this batch, but +had to turn that up to 350F to get the entire batch melted, or the heating +element would keep turning off. It still took a very long time to all melt. +Once it did, I dialed back to 300F indicated. It's true that the ambient +temperature was lower in the shop than on other days I've cast sugar. + +The 5.25" grains were poured to a 122mm fill line, and then an 0.75" Delrin +coring rod was twisted down into the goo puncturing foil over the coring rod +hole at the grain base. A casting cap was then placed over the top to hold +the coring rod centered and protect the grain during cooling. + +The first four grains poured easily. There was enough propellant sticking +high on the sides of the pot that I couldn't figure out how to break loose, +though, that I paused and added 3 old 38mm KNER grains to the pot and waited +for them to melt and get mixed in before casting the last grain. The last +grain was also problematic in that the casting cap didn't want to go down +over the casting tube, perhaps due to a bit of KNER splash already hardening +on the outside of the tube? + +I noted that there were lots of small bubbles visible on the surface +of the melt, all of which were popping easily at the time of the pour. I did +the usual thing of twisting the coring rod as it went in and saw bubbles +come to the grain surface, then tapped each grain on the table top after the +cap was on to hopefully further settle the propellant. It's hard to imagine +vacuuming KNER helping this, as the KN wants to settle to the bottom of the +pot, requiring re-stirring to homogonize the mixture before pouring... which +necessarily lets more air back in? + +## Results ## + +The grains came out very poorly, with lots of cracks and voids. My guess is +that since the shop was colder than normal, and I could see massive amounts +of propellant solidifying on the sides of the multi-cooker, that rapid and/or +differential cooling as the propellant was being poured into cold casting +tubes and cold Delrin coring rods were inserted was the root cause. + +The only credible choice is to set them aside to be re-melted in a future +batch. diff --git a/rockets/research/index.mdwn b/rockets/research/index.mdwn index 8d0ea4c..abf3c2d 100755 --- a/rockets/research/index.mdwn +++ b/rockets/research/index.mdwn @@ -10,6 +10,10 @@ ## Activity Log ## +### 2021 ### + +* [2021 batch 01](2021.11.12.html) - 12 November 2021 - 5 75mm KNER grains + ### 2020 ### * [2020 batch 01](2020.08.31.html) - 31 August 2020 - 8 75mm KNSB grains -- 2.30.2