History of the Meehanite Process
Conceived in the USA by Meehan and Smalley in the early 1920's, Meehanite originated the very revolutionary concept that cast iron would be treated as a quality material manufactured to precise specifications. Previously grey cast iron with its coarse graphite structure and phosphide eutectic had been regarded as unreliable by designers. The change in outlook was brought about by the fact that the structure of iron, especially the graphite form, could be controlled - Meehanite Metallurgy.
This process became known as inoculation and produced not only high strength irons, but ones which were less sensitive to variations in casting thickness. The effect of inoculation is easily measured before pouring any castings. Wedge testing, for process control, was originally developed by Meehanite. The test indicates the tendency of the metal to chill and is directly related to ruling casting section. Meehanite foundries make particular use of the information gained from the wedge test with regard to the constitution of the metal before and after inoculation.
Process advanced through the development of a range of Meehanite metal types with analytical compositions which correlate to the castings being made. Control was extended to cover all foundry process parameters and developed as an inseparable extension to Meehanite metallurgy. The Meehanite Process employed in 1945 was the earliest form of foundry statistical process control. More stringent control was exercised through the implementation of standardized Meehanite gating and feeding practices. The Process incorporates a continuous system of inspection of all process parameters recording and recognizing deviations and acting upon such events in time resulting in a practical quality assurance system. In the interests of casting quality recommendations on the manufacturing equipment suited to the production of the foundry's casting range are made during the introduction of the Process.
A structured programme of audit (service) visits are applied to assess a foundry's quality level and reports detailing practical remedial actions are provided. A scrap control system is introduced and monitored during audit visits. Metallurgical principles developed in the production of Meehanite flake irons were extended enabling the manufacture of nodular irons even from the cupola. Many patented procedures were developed to overcome magnesium recovery and fade. Ultrasonic determination of nodular iron structures was pioneered as a control tool. Meehanite metallurgy was further expanded to create a family of irons to withstand heat, wear and corrosion service conditions
More recently the Process has advanced to cover the manufacture of high strength austenitic ductile irons - Meehanite ADI. Following a number of years development 1996 saw the introduction of the first Meehanite realtime Casting Solidification Simulation and mould filling software, providing:
- Mould filling sequences (single & multiple cavity)
- Casting solidification (time elapsed tomography)
- Defect risk analysis
- Nodularity evaluation
- Hardness profiles