Also, salt carryover from certain recycling operations and "bath" carryover from low-grade primary ingot can represent an exogenous inclusion type that is imported into the system.
Exogenous inclusions are imported to the molten metal stream from external sources, such as occluded particles on and within primary and secondary ingot, major alloying elements and master alloys, as well as containment refractories.
(KMF) described his foundry's work with filters to reduce scrap caused by exogenous inclusion
Answers to these questions can often distinguish between gas, exogenous inclusion and shrinkage defects, though they are not normally helpful in pinpointing microstructural problems.
The greater the amount of these elements in the alloy, or the greater the alloy addition level, the greater the chance of having exogenous inclusion problems.
Erosion of furnace and ladle linings, as well as of mold and/or core coatings, contribute to exogenous inclusion defects as does chipping of filters and failure to remove slag coagulants.
Sources for exogenous inclusions
include refractory particles, usually from degradation of furnace walls, transfer ladles, launders, riser tubes, filling funnels, and in some instances from pieces of the sand mold.
These inclusions interact with other endogenous or exogenous inclusions
resulting in inclusion agglomerates or even the formation of clusters, which can finally be the origin of casting problems or surface defects on the final product [1-3].
Factors that can influence tool life and machinability include metallurgical conditions, such as graphite size and distribution, composition, ferrite/ pearlite ratio, cooling rate from the eutectic through the eutectoid temperatures, and the presence of either endogenous or exogenous inclusions
These filters eliminate exogenous inclusions
by trapping slag and dross.