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Autoclave De-Waxing Recommendation We recommend the autoclave is able to pressurise to 6 Bar (165ºC/330ºF) in 3 seconds or less. The pressure will then continue to regenerate to the set pressure of approximately 9.5 bar (182ºC/360ºF). Note that the rate of pressure rising is significant for the temperature/energy it transfers to the wax, rather than the pressure itself. Whereas conversely during depressurisation, it is the pressure which is significant as a high rate of depressurisation will cause the condensed steam and pressure pockets in mould pores to expand rapidly and potentially crack the moulds if not allowed to be released in line with the pressure in the chamber. Current Boilerclaves®


pressurise to 6 bar in 2-3 seconds ensuring minimal shell cracking and giving the casting designer increased flexibility in geometry and shell systems. In order to ensure the Boilerclave®


Homogeneous crystalline substance Wax Resin


Figure 6: Comparing thermal expansion behaviour of wax and resin (5) typically


uses


as much of its steam on pressurisation for heating the shell/melting the wax, it is important to minimise heat loss and therefore keep the Quicklock®


closed between cycles. Prior to doing the first batch of


moulds for the day, it is important to make sure the Boilerclave®


to pressure and warmed through. It is a good idea to run a couple of dummy cycles before the first batch. The reliability of the door closing,


locking and then the unit pressurising is so important. It is during this time that the shells are exposed to heat and the wax starts to expand, therefore, the inner chamber must pressurise to 6 bar (170oC) as fast as possible and melt the interface layer to minimise the chance of cracking. Regular maintenance, seal inspection, door operation and most importantly safety systems checks should be part of an everyday routine. Thanks for reading. Keep updated


for more in Part 2. The article will focus more on practical consideration of de- waxing.


Figure 7: Comparison volumetric expansion of unfilled and filled waxes (Remet UK laboratory)


References 1. Adhesion Tension Force Between Mould


and Pattern Wax in


Investment Castings. Lee, Kevin, Blackburn, Stuart and Welch, Stewart T. 2015, Journal of Materials Processing Technology, p. 225.


2. Modelling of the De-waxing of Investment Cast Shells. Gebelin, Jean-Christophe, Jones, Samantha and Jolly, Mark. 2002.


3. Boilerclave Thermal Profiles and the ®


Effect of Moisture Upon Ceramic Shells During the Steam De-wax Process. Jones, S., et al. 2002, IRC in Materials Processing.


4. Thermal Expansion of Investment Casting Pattern Wax. Sunderland, B. and Richards, V. s.l. : Investment Casting Institute, 2001. 49th Annual technical meeting.


5. Investment Casting. Beeley, P and Smart, R. London: The Institute of Materials, 1995.98=8=78


November 2018 ❘ 29 is fully up door


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