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Five Minute LOI Test

S. N. Ramrattan, P.G. IkonomovWestern Michigan University, Kalamazoo, Michigan

Copyright 2006 American Foundry Society

ABSTRACT

Loss-on-ignition (LOI) is an important thermo-chemical property test for many foundry materials. Applications include new

sands, green sand systems, chemically bonded cores and molds, sand additives, and reclaimed sands. LOI has been animportant quality control measure carried out off-line. The AFS-defined LOI test uses a muffle furnace that is time

consuming, often requiring three hours; a modified method, using a microwave furnace, provides results in about 20 minutes.

With faster testing and analyses LOI can serve as a process control tool.

Now a new, faster LOI method has been developed at Western Michigan University. It uses induction heating and a metallic

crucible. It can produce test results in less than five minutes without sacrifice of accuracy. In addition, the new technique

has a data acquisition system that allows real time analysis of sample mass change as a function of time and temperature that

can be graphically represented. The acquired data can be saved for further analysis, comparison, and record keeping. Test

procedures are explained and the equipment needed is shown in schematic drawings and photos.

INTRODUCTION

BACKGROUNDThe loss-on-ignition (LOI) is the difference in weight before and after ignition of the sand sample. LOI is performed at an

AFS-defined temperature or at metalcasting temperature, (e.g. cast iron requires a 2600 F (1427 C)). The main method for

determining LOI involves heating samples to a temperature at which organic materials volatilize and decompose. Theresulting loss in weight from the sample is the LOI measurement. LOI measurement indicates the amount of combustibles in

raw sand. For green molding sand, these combustibles consume water added to activate the clay. In chemically bonded sand,

they absorb binder and reduce its effectiveness. Thus, LOI measurements can provide essential information about the overall

quality of a foundry's sand system.

Foundries depend on a test of combustibles (LOI) to help manage their new sands, green sand systems, chemically bonded

cores and molds, sand additives, and reclaimed sands. Each application has an established control range. The testing

procedures defined by the AFS (Mold & Core Test Handbook) calls for use of either a muffle or microwave furnace.

Unfortunately those tests are considerably slow. The time lag between testing and results can allow certain sand relateddefects if high levels of organic materials are present in foundry sand systems. Currently, foundries cannot identify the

organic materials in real time. The presence of excessive organic materials in foundry sands is problematic, because some of

these materials can volatilize at temperatures much lower than that required for the casting process. The outcome is usuallygas porosity defects in the castings. This paper addresses those problems.

PURPOSEWhile LOI is a well-recognized test for evaluating foundry materials, it is time consuming, requiring up to three hours for theLOI test using a muffle furnace. A modified method, using a microwave furnace provides results in about twenty minutes

(Laitar et al., 1995 & 1996). Though the microwave furnace method has reduced testing time to about one-tenth the time

required for the muffle furnace method, twenty minutes can be considered a significant amount of high production molding

lines. Further, these LOI methods cannot be used as on-line process control tools because samples still need to be taken to a

sand testing laboratory.

With respect to quality control of green sand components a recommended test to be run on incoming sand is LOI. It shouldbe noted that the test procedure could be found in the AFS Mold & Core Test Handbook. Carbonaceous materials should be

checked for volatile combustible matter (VCM), fixed carbon, and ash (Schleg, 2003).

The basic tests commonly used as controls for green sand systems include sand temperature, moisture, compactability,density and sample weight, permeability, green strength, AFS/25 micron clay, AFS grain fineness, methylene blue clay, and

Paper 06-124(04).pdf, Page 1 of 6AFS Transactions 2006 American Foundry Society, Schaumburg, IL USA


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LOI. These tests relate to the control of the five basic variables in green sand: water, bonding agent, sand, sand additives,

and carbonaceous materials. In addition, LOI test are run on chemically bonded sands (Krysiak, 1990 & 1994).

There is not total agreement between green sand experts on how often to run the basic tests. These basic tests can be

broken down into two classifications: daily tests and weekly tests. The sand technician in the foundry may find it necessaryto run certain tests more or less frequently to produce quality sand systems. The carbonaceous material is an important

constituent of the sand, particularly in iron sands. Many foundries determine the carbonaceous material on a daily or weekly

basis using the combustibles test (Roshan, 1989). In many other foundries LOI is considered a weekly test only because it is

a time consuming procedure.

LOI testing can be an effective quality check of chemical binder additions to sand mixes and has often been discussed as a

control tool for the sand reclamation process. But unlike tests for compactibility or compressive strength, which take little

time and can be done on-line for immediate control, conventional LOI testing results are too slow to be used as an effectivetool in on-line process quality control. An LOI test that is both fast and accurate provides a much needed process control tool

for monitoring carbonaceous materials in the foundry.

PROBLEM TO BE INVESTIGATEDThis study examines a new and faster LOI test when compared to the more laborious and time-consuming LOI tests currently

available. This research project focused on quantifying LOI data from the new technique and comparing it to that obtainedfrom the AFS-defined LOI test. The equipment used for the new LOI test was a redesigned induction power supply. Graphs

showing change in mass as a function of time and temperature are provided for sand systems studied. Real-time plot of those

graphs are generated on a computer screen for monitoring of the test; in addition, the measured data is saved for furtheranalyses and comparison.

OBJECTIVESThree key issues required proving:

1. confirm that the new test is faster,2. determine the real time rate of mass change as a function of temperature, and3. confirm that the new system can accurately measure LOI.

METHODOLOGY

TESTING APPROACHIn the experiments the same lake sand system was use for all samples. Table 1 provides the raw lake sand properties. Sand

was coated with a chemically bonded shell resin at three different levels (1%, L1; 3%, L2; and

5%, L5) and used as samples for LOI testing. In addition, clay bonded (8% pre-mix) green sand used in a working foundrywas sampled and dried for LOI testing.

An induction power supply is redesigned for heating a metallic crucible within its coils in ambient conditions. Induction

heating provides rapid heating to the metallic crucible and its sand contents. Using a computer data acquisition system, anon-contact infrared pyrometer is used to constantly monitor and control the temperature of the crucible (Figure 1 and 2).

The induction field within the coil heats the crucible that transfers the heat onto the sand sample. The temperature is

achieved whereby organic materials in the sample decompose and certain components volatilize. The resulting loss in weightfrom the sample is the LOI measurement.

Table 1. Raw Sand Properties

Type Source AFS/gfn Shape ScreensRoundness/Sphericity

(Krumbein)pH

Aciddemand(pH-7)

459L(Lake)

MI62 Rounded

40.6/0.6 Neutral


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ont,sF

T

g

DAC

57.68g

1

2

3

4

5

6

7

1. Crucible within induction coil

2. Ceramic support

3. Linear bearing with frictionless

support system

4. Induction power supply

5. Analytical balance

6. Non-contact pyrometer

7. Computer data acquisition systemont,sF

T

g

DAC

57.68g

1

2

3

4

5

6

7

1. Crucible within induction coil

2. Ceramic support

3. Linear bearing with frictionless

support system

4. Induction power supply

5. Analytical balance

6. Non-contact pyrometer

7. Computer data acquisition system

Figure 1. Schematic of induction LOI testing system

Figure 2. Crucible within coils being heated (left) and non-contact pyrometer (right)

To operate the induction LOI tester (Figure 1), the electrical power was switched on, and the temperature control was set to

2,000 F (1093 C) and controlled by a data acquisition system. In addition, the computer and data acquisition system

provide monitoring and plotting graphs of temperature/time versus distortion in real time.

The crucible is positioned within the induction coils and simultaneously engages the data acquisition system thatautomatically logged and plotted the sample mass versus time/temperature curve.

The length of the test for these experiments is set for five minutes; however, this can be varied. The test can be automatically

stopped when the LOI curve starts to flat line. A predetermined test temperature can be set or some heat history chosen to

represent a molten metal solidification simulation can be programmed into the test.

Note that all samples were tested in laboratory conditions at Western Michigan University. Ambient conditions were

controlled: temperature at 75F 3F (24 1C) and relative humidity at 50 2%.

INDUCTION LOI TEST PROCEDUREIn performing the induction LOI test, the following procedure was followed:

1. Turn on the computer data acquisition and induction LOI tester.

2. Weigh 3.00 g sample (sand dried at 200F (93C)) into crucible using an analytical balance.

3. Place crucible with sample on ceramic support of the induction LOI tester.



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4. Position crucible with sample into the induction coil.

5. Test (heating up to 2,000 F (1093 C)) and data acquisition starts, logs data, and stops automatically after five

minutes or no further mass change.6. Remove sample and cool.7. Interpret the LOI curve for results.

RESULTS & DISCUSSION

The induction field within the coil is critical for maintaining uniform heating of the sample and for achieving the LOI test

temperatures. Insufficient induction power can result in a sample failing to achieve a stabilization of weight. Conversely, toomuch induction power can overshoot desired testing temperatures and, worst yet, sinter the sand and melt the metallic

crucible. Thus, the controls parameters of data acquisition system for the operation of the induction power system have to be

established prior to starting LOI testing.

Induction power provides rapid heating of a metallic crucible and its sand contents. Though the crucible design is not a focus

of this paper, it should be pointed out that proper coupling between the crucible and the induction field within the coil is

critical for maintaining uniform heating of the sample and for achieving the LOI test temperatures. Figure 3 shows pictures

of various crucible designs that were fabricated and tried. The design furthest left failed because of inappropriate materialselection, the two designs in the middle were not effective since the central core did not couple well with the induction field,

but the design on the right was capable of heating the sample sufficiently.

Figure 3. Various crucible designs

While there have been attempts to cut testing time for chemically bonded and green sand by using smaller samples andshorter furnace times, accuracy may be lost with a less than representative sample size and incomplete combustion. With thecombination of higher precision in analytic balance measurements and the ability to achieve the combustion temperature

rapidly with induction heating, those shortcomings are resolved. Further, the test is conducted in ambient conditions so

oxygen can get to the sample for rapid oxidation. This plays a role in cutting test time, compared to the relatively staticcombination conditions in closed chamber furnaces.

The fast organic removal rate allows quick and accurate LOI testing. The new induction LOI testing system provides

automatic temperature control with sufficient power to achieve and maintain steady state test temperatures. In addition

heating of the crucible provides adequate heat transfer to the sample. Apart from providing an ease of temperature controlduring testing the data acquisition system (Figure 4) allows real-time analysis of sample mass change as a function of time

and temperature that can be graphically represented; this provides some additional information when compared to just a

percent LOI obtained in conventional testing. Additionally, the computer data acquisition system can be programmed to

reproduce heat history profiles from previous simulation studies. This allows LOI to be used in shakeout analysis ofchemically bonded sands used to heat treat castings and cores used in semi permanent molds. Further, the acquired data can

be saved for further analysis, comparison, and record keeping. The foundry application of the new LOI test can providetechnicians with technology to get an early handle on quality problems that might just be creeping into the sand system.



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Figure 4. Data control and acquisition system

In lieu of a cost comparison among the muffle furnace technique, the microwave furnace technique, and the new inductiontechnique, the authors offer another consideration. Many foundries have chosen to replace the older technology of

carbon/sulfur determination with a spectrometer. The old equipment possesses an induction power supply that can be

modified to become an induction LOI tester. Within two weeks the system was designed, parts procured, the test system

installed, and tests performed. By making such a modification the induction LOI tester saves on energy costs and there are

no consumables required in testing.

These findings bear out a good correlation between the muffle furnace method and the new induction LOI testing (Table 2

and Figure 5). From an evaluation of the test machines performance and an analysis of LOI test data, a proof-of-principle isshown. The results from LOI testing show that the new method is faster and just as accurate as the conventional test. The

authors identified a process whereby the total combustibles can be separated from silica sand at a faster rate than the

conventional AFS LOI tests. The test is simple to run, and the required equipment is easily obtained.

Table 2. Properties of the Chemically Bonded Sand

ChemicallyBonded

Sand (Shell)

HotTensile (#)

ColdTensile (#)

Density(g/cm

3)

MuffleFurnaceLOI (%)

InductionLOI (%)

L1 110 135 1.74 1.3 1.5

L3 400 460 1.71 3.7 3.5

L5 570 645 1.55 6.1 6.5

Green Sand NA NA 1.50 3.5 3.2

LIMITATIONS

Only systems with silica sand have been studied. The work in this paper represents three chemically bonded lake sands(shell) and green sand as examples of an application for LOI tests. Specialty sand, alternative molding media, and reclaimed

sands were not considered in this study. There are numerous other materials from which additional data can be gathered to

learn more about the LOI properties.



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2.75

2.8

2.85

2.9

2.95

3

3.05

0 50 100 150 200 250 300 350

Weignht[g]

LS 1%

LS 3%

LS 5%

GS

0.00

1.67

3.33

5.00

6.67

LO

I[%]

Time [s], (Temp. [C])

(999)(78) (1015) (1019) (1006) (1064) (1046)

Figure 5. Sample mass versus time/temperature curve showing percent LOI

CONCLUSIONS

The new LOI tests were run and the following are key findings:

The induction LOI test provides a quick method for removing organic material and water of hydration in clay fromsilica sand. The induction LOI method provides testing results in less than five minutes.

The induction LOI technique has a data acquisition that allows real time analysis of sample mass change as afunction of time and temperature that is shown on a graph. The acquired data can be saved for further analysis or

record keeping. Further, this allows the LOI test to be an effective process control tool in the foundry industry.

Tests show that there is a strong correlation between the new induction LOI method and the AFS muffle furnaceLOI method when using silica sand.

RECOMMENDATION FOR FUTURE WORK

A complete gage R&R study involving correlation among the three LOI testing techniques needs to be carried out forvalidity. Also, the design of the crucible shape needs to be optimized to increase the surface area contact of the sample toachieve the best heat transfer.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the technical support of G. Hall, J. Fiala, A. Poot, and P. Thannhauser, all from Western

Michigan University.

REFERENCES

Krysiak. M.B., Reducing Casting Defects--A Basic Green Sand Control Program, Georg Fischer DISA Inc., Holly, MI

(Jan. 1994).

Krysiak, M.B., Pedicini, L.J., Sand Testing Design, 3 parts, Modern Casting, (Feb., Mar., Apr. 1990).Laitar, R. A., Cavanaugh, J E., Rapid Method For Loss-0n-Ignition Testing,AFS Transactions, vol 103 Paper 95-101 pp.

693-698, (1995).

Laitar, R. A., Cavanaugh, J E., Microwave Technology Brings LOI Testing Up To Speed, Modern Casting, V 86 N 2 P 40-

41, (Feb. 1996).Mold & Core Test Handbook, 3rd. Edition, AFS (2000)

Roshan, H. Md., Quality Control of Molding Materials,Foundry Engineering Handbook, Utility Publications Ltd, IndiaChapter 13, pp.110-144, (1989).

Schleg, F. P., Technology of Metalcasting, AFS, pp. 49-76, (2003)


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