This is especially true when hard water, hot return sand, high sodium bentonite or short mulling times are involved.
This is because calcium bentonite develops strength faster than sodium, allowing for shorter total mulling times to reach compactibility targets.
Continuous mullers use "retention time" instead of "true mulling time" when discussing how long the premix and water are being mixed.
Material percentages in green sand (methylene blue clay, moisture, grain size distribution, volatiles and combustibles) are all independent of mulling. Each foundry establishes target levels based on the molding equipment in their plant.
New rebond clays are more difficult to mull than the clays already in the return sand that have had the benefit of cumulative mulling
. This excessive influx of new material and the respective absence of cumulative mulling
are one cause of brittle sand.
These include the bentonite type and level, the temperature of the sand, the mulling
equipment, the molding setup, the conveyor and transport system, the shakeout, the reclamation, the volume and efficiency of the storage facility and the cleaning room practice.
can be defined as achieving the maximum amount of work on the sand during the time it stays in the machine.
Since the sand's moisture requirement will be higher, it may be more difficult to obtain desired compactibility in minimum mulling
Low green strength indicates low clay content and/or poor mulling
After thorough mulling
, sand was placed in covered pails numbered one through 10.
The most important observation was the negative interaction that was observed at low compactibilities at short mulling
is the application of work forces to cause kneading, smearing, compression and shear.