KILO 6G – Flight 2

KILO 6G – Flight 1

20-09-2013 – Static test of the new KILO 4 grain KNSB motor did not went without hick ups. Due to a driver conflict after a service pack update we were unable to record any data from the test bench. After some tinker time we decided to test the motor anyway and record the voltage output by filming the Fluke multimeter display with a Gopro. This actually worked better than anticipated. The smoke plume was reflected in the display which helped us to determine the time of ignition of the motor. Refresh rate was about 4Hz all put into an excel file and a nice thrust curve was derived from that 20130920 – Thrust curve 90 mm motor . More details on the KILO 4 grain KNSB motor can be found here.

Various:

3″ phenolic coupler tube – length 916mm. Mass 258gr. ID 73,17mm. OD 75,60mm

3″ phenolic body tube – length 916mm. Mass 320gr. ID 76,57mm. OD 79,27mm.

 References spring loaded compression mould:

54mm DECA series by Vertical Limts

Alcomex spring  – type: DR3580.

• Fn = force under full tension = 710N.
• Surface area of 54mm sping loaded mold (ø44mm ID inhibiter) = 1520mm² = > 0,47N/mm² = 47N/cm² = 4,7kg/cm² (shows excellent compression results >99% – 400gr KNDX batch)
• Surface area of 100mm spring loaded mold Thrust (ø76mm ID mold) = 4536mm² = > 0,157N/mm² = 15,7N/cm² = 1,57kg/cm² (shows poor compression results +/- 88% but large 2,0kg KNDX batch)

Sugar shot to space MSS & DSS motor

Century spring – type: 11789

• Fn = force under full tension = 452N.
• Surface area of  6″ U-line card board mailing tube (ø152mm ID ) = 18145mm² = > 0,025N/mm² = 2,5N/cm² = 0,25kg/cm²

Proposed spring for 90mm motor

Alcomex spring  – type: DR3830.

• Fn = force under full tension = 1020N.

New spring loaded mold.

• ID=73mm = 4185mm².
  • When 0,15N/mm² => F= 628N
  • When 0,24N/mm² => F=1020N
  • When 0,30N/mm² => F=1255N
  • When 0,45N/mm² => F=1883N

Casting

Grain I – 19.08.2013

The mould was prepared: base, piston and core were given a light coat of WD 40. Core and base secured with big washer and nut. The rough edges of the casting tube (3″ phenolic coupler tube) were lightly sanded away with P240 sand paper. Casting tube was weighed. L= 135,7mm, mass is 40,0gr. On the top end of the casting tube PVC electrical tape was applied. This tape is sort of flexible and stretches a bit. Reason was to protect the casting tube edge from molten KNSB slurry and to aid cleaning up afterwards. 50% of the tape width was placed on the outside and de rest was folded inwards. When applying the tape try not to stretch the tape since the stretch is needed when folding inwards. If the tape is too much stretched it will not stick to the inside of the casting tube. For extra (maybe false) sense of security the base was taped to the casting tube with painters tape.

The goal was to cast a single Bates grain of 784gr with length of 120mm, a core of 25mm and a density ratio of 0,96. The casting tube setup allowes for a spare 10mm at the top to cope with the reduced initial density which later gets compressed by the spring. A batch of 850gr – 65/35 KNSB was molten in the electrical pan. Melting was quick and easy and KNSB showed some reduced viscosity over KNDX. The casting tube set up was placed on a digital 0-5000gr scale with 1gr accuracy and pressed on TARE. I tried to pour in the 784gr but soon found out that that was never going to happen as the casting tube was already completely filled prior to reaching the 784gr. The piston (this time at room temperature) was quickly placed on top and put under slight tension by the spring. Some KNSB oozed out between core and piston. Tension was released to a minimum, no play on the parts: piston, spring, distance piece, washer and nut. After an hour outside at 18º C (it really helps placing the set up outside to have it cool down quicker) the casting set up was hand warm – approximately 20º C. When kept inside a full 1,5 hours could be required to have it cooled down to 20º C. 30º is still too warm (KNS SB oozes out when compressed). Full tension was put on the piston by tightening the spring but was soon physically stopped by the core due to the lack of initial filling of KNSB. This was set aside since not much could be done about it. After awhile though an extra identical spring was placed and tightened in such a way that each spring was compressed to 31mm (29mm max compression) of its original 51mm length. Grain was allowed to cure for 22 hours while the piston sunk deeper and deeper in the casting tube.

De-moulding was easy. First the tension was removed after which the lower nut and washer at the base was removed. Subsequently the base was put in a vise and wiggled loose. With the base removed the tension was put on again to its original setting (length spring 31mm) and a light tap of the hammer at the lower end of the core against the M12 thread was enough to launch the core out of the grain. The slightly tapered core (23,7-25,5mm over a length of 170mm) was captured in a carton box to prevent any damaged to the core as this reaction was anticipated.
Finally the piston was put in a vise and again wiggled loose. With more than 20mm in the casting tube and less than 10mm still outside this required a bit more persuasion than the base but still come out easily. All what was left to do was to remove the electrical tape and the finished grain was soon assessed and weighted.

Results:

• Segment length: 109,5mm
• Core: 25mm
• Mass:  713gr
• Density ration: 0,958
• Spring compression 51 – 31 = 20mm => 20 x 46 = 920N => 0,22N/mm2

Final thoughts:

• This casting set up works and produces flight worthy grains
• Base can have the same OD as casting tube. Casting tube does not bulge under the compression
• If the initial filling can be increased a 784gr grain might be possible.

Grain II – 20.08.2012

A similar approach was done for grain II however:

• The KNSB mix was set aside to settle for 15min at 130 C to compact and air to escape (did not help) but viscosity was a bit higher.
• Casting tube was over filled to 732gr  which resulted in oozing when the piston was placed
• No tension was placed for the first hour but the parts (2 springs, washer & nut)  were mounted without play
• 2 springs were used for compression without the distance piece and tightened until physical stop of the core.

Results:

• Segment length: 110,5mm
• Core: 25mm
• Mass:  710gr
• Density ration: 0,948
• Compression 51 – 35.6 = 15,4mm => 15,4  x 46 = 708N => 0,17N/mm2

Final thoughts:

• Settling the KNSB for 15min does not improve density by letting air to escape. Melting under vacuum might solve this.
• Better not to over fill the casting tube as it does not result in a heavier grain
• More compression is better for the density. Try to use 2 springs and distance piece for full (compressed spring l=29mm) compression.

Grain III – 21.08.2012

A similar approach to grain I was done for grain I however:

• KNSB was heated to 160gr C thermostat setting on the electrical pan and directly poured into the casting tube.
• The casting tube was filled with 724gr KNSB with little to no oozing after piston installation.
• No tension was placed for the first hour but the parts (2 springs, washer & nut)  were mounted without play
• Casting set up was kept in side and after 1 hour did not cool down enough to apply compression.
• After 1,5hours full compression was applied with 2 springs, distance piece, washer and nut. Some minor oozing was noticed between the core and piston.

Results:

• Segment length: 109,3mm
• Core: 25mm
• Mass: 714gr
• Density ratio: 0,960
• Compression: 51-29 = 22. 22 x 46 = 1010N 0,24N/mm2

Final thoughts:

• This is as good as it gets for atmospheric melting.
• It did require some effort to place the 2 springs, distance piece, washer and nut with this limited length of thread. A longer thread and one long spring is advised if the casting mould is re-designed.
• No need for distance piece when longer spring is used. Measuring the compressed spring is an accurate way of determining the compression on the KNSB.

Grain IV – 22.08.2012

Grain IV was cast exactly the same as grain III.

Loaded casting set up was tapped on a work bench a couple of time prior to piston installation.

Results:

• Segment length: 109,8mm
• Core: 25mm
• Mass: 710
• Density ratio: 0,951
• Compression: 51-29 = 22 => 22 x 46 = 1010N => 0,24N/mm2

Grain I-IV were put in a desiccator for 7 10 days (grain IV – I) days after being vacuum packed and sealed by a foodsaver.

POM @ Locloods.nl:

Mechanische waarden van POM zijn:SG is 1,41 G/cm3–Trekstrekte is 70 N/mm2–Rek bij breuk is 40 %–Kogelhardheid is 160 N/mm2–Max.temp.kortstondig is 140 C– Max.temp.langdurig is -40 t/m +100 C–Uitzetting per 10 C/mtr is 1mm.

Below motor beautiful machined bij LD.