Would your additives pass an emissions test?

Inside This Story:

* Sand additives are necessary in some castings to reduce veining but can emit gases that affect tensile strength and casting quality.

* This in-depth study puts four anti-veining additives--red iron oxide, black iron oxide, aluminum silicate and a blended material--to the test to determine their effects on the total process emissions.

* Results from this study serve as a helpful tool to metalcasters when selecting additives.

Metalcasters continually strive to meet the increasingly stringent air quality requirements of the U.S. Environmental Protection Agency (EPA) while producing good quality castings with strong tensile strengths. In trying to meet these standards, metalcasters are faced with the challenge of measuring the emissions associated with the core and moldmaking processes.

For years, metalcasters have used additives to improve surface finish, reduce veining and control certain defects, but there are unanswered questions regarding the emissions from these additives. For this reason, metalcasters, with the help of the Casting Emissions Reduction Program (CERP), formulated a study that focused on the three most commonly used core additives--red iron oxide, black iron oxide and aluminum silicate--and blended materials and analyzed their effects on emissions, core tensile strength and casting quality.

Visual Inspection and Strength Testing

In order to determine the effect of emissions from the three different additives, the test was set up in two-parts. The first part consisted of green sand molds containing cores with various anti-veining compounds that were cast with molten iron at 2,630F (1,445C). The surfaces of these castings were visually inspected to assess surface finish and appearance. At the same time, core tensile specimens (dogbones) were produced from the core sand mixture to evaluate the impact of the additive packages on the resultant core strengths.

Emissions Testing

The emissions testing composed of evaluating four anti-veining additives: red iron oxide at 1%, black iron oxide at 2%, aluminum silicate at 5% and a blended material at 1.5%. The investigators performed all tests with a phenolic urethane coldbox (PUCB) core binder at 1.4% based on sand weight (BOS). They documented the emission results in both pounds of analyte per pound of binder and pounds of analyte per ton of metal poured.

The total air sampling time performed in the study was 75 min. This continuous collection of air samples was based on 45-min. mold pouring and cooling, 15-min. mold shakeout and 15-min. post shakeout periods.

Mold, Core and Metal Preparation

The production team prepared molds (using a jolt/squeeze molding unit) and cores according to a standard composition. A green sand mixture void of any carbon additives was produced for the test molds, and the Class 30 gray iron was melted in a 1,000-lb. (454 kg) induction furnace.

The sampling process consisted of replicate test runs on 35 molds after conditioning in five groups of four molds each. An individual green sand mold containing four step cores was placed into an enclosed test hood heated to 85F (29.5C). Iron then was poured into the mold through an opening in the top of the emission test enclosure, which was closed after pouring. (Fig. 4).

[FIGURE 4 OMITTED]

To measure the undifferentiated hydrocarbon emissions, the investigators employed two methods: TGOC as propane and HC as hexane. TGOC is weighted to the detection of more volatile hydrocarbon species. HC is weighted to the detection of relatively less volatile compounds.

The results revealed the sand additive with the most significant effect on emissions was aluminum silicate, which showed an emissions decrease of 25%. However, the blended material showed only a 1% decrease in emissions.

Tensile Testing

Tensile testing was performed to find out how much additional coldbox binder would be required to compensate for tensile strength loss due to the addition of the anti-veining compounds. For this test, batches were produced using a PUCB binder at 1.1%, 1.4% and 1.75% addition levels (BOS). Out of all the compounds, black iron oxide was the least affected with a loss of tensile strength at 14%. This was followed by red iron oxide (22%), aluminum silicate (25%) and the blended material (53%).

Best in Show

The study group compared the quality of each of the castings produced with the additives by placing them in a rank order sequence from the best to worst based on visual assessment. As shown in Figs. 1-3, the group noticed a wide range of variations in regard to the surface conditions of the five groups of castings. The best casting in both veining and surface finish was cast using the blended material. The castings with red oxide as the additive came in second in overall quality, with a significant reduction in veining but a rougher surface finish. The casting using aluminum silicate ranked third in overall surface condition with both the severity of the veining and surface finish showing better than the control, although the appearance was mid-range. Black iron oxide molds produced castings with less veining than the control but exhibited poor surface finish (Table 1).

Selecting Your Additives

The emission testing performed in this study demonstrated that the additives selected can affect the total emissions of a given system. The results of the study also showed that some of the additives can reduce air emissions in lb./lb, of binder by as much as 25% from the baseline values, while other additives can increase emissions (Table 2). When selecting an additive package metalcasters should note the interactions between additives and binder systems in use and understand that a binder increase may be required to maintain the needed mechanical properties.

About the Authors

George Crandell is the vice president of operations, Cliff Glowacki is vice president of measurement technologies, and Steve Knight is process engineering manager all for Technikon LLC., Sacramento, Calif. Vic LaFay is the vice president of research and technology development for The Hill and Griffith Co., Cincinnati. Larry Stahl is a development engineer for General Motors Corp., Saginaw, Mich.

For More Information

"Understanding Properties of Carbonaceous Additives and Their Potential to Emit Benzene," T.C. Dempsey, V.S. LaFay, S.L. Neltner, D.N. Taulbee, AFS Transactions (97-107).

Table 1. A Comparison of Step Core Castings and Anti-Veining
Additives Used Urethane Cores at 1.4% Resin with Anti-Veining
Additives Used

Qualitative    Reference      Red      Black
Appearance     No             Iron     Iron
Scale (1-10)   additives      Oxide    Oxide

10                  -          Best
9                   -                   Best
8                   -         Median     -
7                  Best         -        -
6                   -         Worst      -
5                 Median        -        -
4                   -           -      Median
3                   -           -      Worst
2                 Worst         -        -
1

Qualitative
Appearance     Aluminum       Blended
Scale (1-10)   Silicate       Material

10                 Best
9                   -          Best
8                   -           -
7                  Best         -
6                Med-Best       -
5                   -           -
4                 Worst         -
3                   -           -
2                   -         Worst
1                   -           -

Table 2. A Guideline Summary of Emission, Strength and
Casting Quality Attributes for Additive Selection

                         Measured
                         Emission              Calculated
                         TGOC                  Binder
                         Change     Strength   Level to
                         from       Change     Maintain
                         Lb/Lb.     from       Equivalent
Material                 Baseline   Baseline   Strength

Baseline                  -         -          1.4%
  1% Red Iron Oxide       -8%       -22%       1.63%
  2% Black Iron Oxide      2%       -14%       1.50%
  5% Aluminum Silicate   -25%       -25%       1.72%
  1.5% Blended Material   -1%       -52%       2.30%

                         Calculated
                         Emission
                         TGOC Change
                         From Lb./Lb.
                         Baseline with
                         Additional
                         Binder to
                         Have
                         Strength        Median
                         Equal to        Casting
Material                 Baseline        Quality

Baseline                   -              5
  1% Red Iron Oxide        7%             8
  2% Black Iron Oxide      9%             4
  5% Aluminum Silicate    -7%             6
  1.5% Blended Material   63%             9