Mar 2015 – Fundamentals of reliable dewaxing
The removal of wax from molds is an important stage in the investment casting process that reduce yield if not performed correctly.
There are basically two generic methods for dewaxing – use of air i.e. flash fire or steam i.e. autoclave. Due to the unique heat transfer properties of steam – just put your hand over a boiling kettle with steam at only 212 oF to appreciate it’s properties – the use of steam autoclaves is the more common technique used.
To ensure successful dewaxing, it is necessary to follow certain guidelines.
- Main objective to avoid shell cracking is to melt the wax at the wax/mold interface to allow the wax to be absorbed into the prime coat and create space for the remainder to expand. The critical time is from the mold being removed from the shell room to being at pressure in the autoclave.
- Keep this time to a minimum by having
- A simple effective loading system
- Fast reliable door operation with push button actuation to integrate with safety interlocks
- Short simple steam transfer from boiler section to autoclave section.
- Minimal restriction on steam entry and automatic air venting
- Aim for time from cycle start to achieving 90 psi to be under 3 seconds
- Control the rate of steam depressurisation
- Use steam from autoclave to ‘force’ wax to a large container through steam heated pipework
- Have clear push button operation and record basic system data through data collection or by network integration
The LBBC dewaxing Quicklock® Boilerclave® has been supplied to the industry for over 50 years and is used by most of the leading investment foundries in the world.