Evaluating sand, coatings, thin wall casting. (Molding Methods & Materials).

This year's Molding Methods & Materials Div. provided the AFS Casting Congress audience with 20 presentations to choose from, including a joint session with the Cast Iron Div. focused on thin wall iron casting.

In one joint-session presentation, J.F. Cuttino, E.O. Morse and S.R. Patterson, Univ. of North Carolina at Charlotte, A. Kachru, Cummins, Inc., and T.S. Piwonka, Univ. of Alabama, discussed a parametric study to determine the effects of casting parameters on the dimensional variation of thin wall iron castings (02-102). The study was designed to determine the impact that changes in clay content, pouring temperature, sand compactability in the mold, and shakeout time have on the dimensional quality of a six-on molded, star casting.

In terms of dimensional variation, clay content had the highest effect in the cope of the mold, while pouring temperature had the highest effect across the parting line and in the drag. An increase in clay content always increased dimensional variation, but the effect of the pouring temperature depended on the elevation of the feature in the casting.

As the pouring temperature was increased, the standard deviation in the cope decreased while that in the drag increased and that across the parting line fell in-between the two extremes. This effect, however, is less pronounced in the cope than in the drag and may be due to the dynamics of fluid motion during fill.

An opposite trend was seen for shakeout in which an increase in shakeout time increased the dimensional variation in the cope, decreased variation slightly across the parting line and decreased it more in the drag. An increase in sand compactability resulted in a slight increase in the dimensional variation for most cases.

In terms of gross dimensions, clay content had the highest effect in the cope and drag, while pouring temperature was dominant across the horizontal parting line. Increases in clay led to corresponding increases in the dimensions, but increases in pouring temperature decreased the dimension.

Shakeout time had a negligible effect in the cope but had a relatively high effect across the parting line and in the drag. An increase in shakeout time increased the nominal dimension across the parting line and in the drag.

Sand compactability had a very small and varying effect in the drag and across the parting line, but it had a stronger effect in the cope where higher sand compactability decreased the nominal dimension.

In an operator's session delivered by the division, two presentations from Indianapolis Casting Corp. examined practical approaches to evaluating refractory coatings and core sand.

In a discussion led by S.G. Baker (02-026), coating evaluation tests for phenolic urethane coldbox coremaking binders were examined as ways to determine which coating is best for a specific foundry operation. The tests discussed in the presentation were core degradation, Baume, weight per gallon, viscosity, solids content, coating deposit, penetration and permeability, Pyrometric Cone Equivalent, biological growth and pH.

In terms of viscosity, there are several test methods for coatings including flow cup, run and drip, and the electric spindle viscometer. The electric spindle method is the most accurate, but it is a laboratory test not suitable for the foundry floor. Both the flow cup and run and drip can be performed in the foundry, but operator consistency is critical to ensure proper results.

For coating control, the weight per gallon test is used to complement the Baume test. This measurement requires the coating material to be poured into a volumetric vessel. This vessel is then weighed to determine the weight per known volume for comparison to other coatings (although a direct comparison of weight per gallon isn't possible).

In the operator's session discussion led by J. Werling, various tests used to evaluate coremaking sand were outlined (02-030). The tests discussed were sieve analysis, sand pH/ADV, dry sand density, turbidity, tensile evaluation, dip redry tensile strength, core density, cure speed, bench life, hot strength, permeability, delayed tensile strength, humidity chamber and test casting.

Referred to as a phase one test, turbidity assists in identifying the levels of fines in a sand and attains the correct resin level to achieve proper immediate tensile strength. In this test, deionized water is mixed with sand and the cloudiness of the water is measured.

Other presentations from the Molding Methods & Materials Div. discussed various topics including thermal distortion, sand density gradients, investment shells and wax patterns, mold release agents, advanced oxidation and fly ash additives.