Instruction manual

OPERATING_MANUAL_MC20V.DOC 18.03.11 KS Seite 30
flask size
investment powder
in grams
water in ml
mixing time in
min:sec
Ø 30mm x 55 mm
60
21
3:00
Ø 50mm x 55 mm
150
52
3:00
Ø 65mm x 55 mm
270
95
3:00
Ø 80mm x 55 mm
390
136
3:00
Ø 50mm x 80 mm
220
77
3:00
Ø 65mm x 80 mm
370
130
3:00
Ø 80mm x 80 mm
560
196
3:00
3.19. Burnout cycles of flasks
After investment process the flasks have to undergo a firing process. For this
purpose the flasks have to be placed in the furnace with the button (opening) down to
ensure a complete flow-out of wax.
The firing cycle of gypsum bonded flasks has normally 3 phases:
Phase 1. Melting out of wax and steaming out remaining moisture of flasks
very slowly. This steaming out process should be done very gently to prevent
gypsum against cracks. In case of the flasks for MC20V (comparatively small)
we recommend to reach a temperature of 300°C (= ramp of 2,5°C/min) in 120
minutes. On bigger flasks we recommend to go to 150°C - 180°C in 120
minutes.
Investment powder is a good insulator, that’s why the heat takes time to reach
the core of the flask. To ensure that the flasks heat up homogeneous, let the
flasks have a rest at the hold temperature of 30 minutes on small flasks and
up for 60 minutes on bigger flasks.
Phase 2 burning process of flasks. This process is similar to a sintering
process: single particles bake together (bonding) and the investment material
becomes much stronger. Gypsum bonded investment materials need 730°C
for this bonding process. To reach this temperature starting at 300°C, ramp
should be 4°C/min = process takes around 2 hours. On bigger flasks (starting
at 150°C, we recommend to select ramp 5°C/min. Duration in the furnace: for
small flasks like MC20V around 1 hour, on bigger flasks up to 5 hours.
Phase 3 Bringing flasks to casting temperature. After reaching the casting
temperature in the furnace, please give flask a rest of 30 – 60 minutes
(depending on size) to ensure that set the temperature is also inside flask.
For phosphate bonded investment material you can go, after phase nos. 2,
directly to the final casting temperature for example 900°C. Give flask a rest at
this temperature of 30-60 minutes at least, depending on the size of the flask.