comparing alternate foundry refractory coating measurement

$: Comparing Alternate Foundry Refractory Coating Measurement$
Comparing Alternate Foundry Refractory Coating Measurement Systems

M.K. Joyce, M. Rebros, S.N. Ramrattan Western Michigan University, Kalamazoo, Michigan

Copyright 2008 American Foundry Society ABSTRACT The Baumé test to control the dilution of refractory coatings adds variability to the % solids of the coating. Increasing the variability in the % solids translates to changes in the refractory dry deposit on the core’s surface and molds which ultimately results in an increased number of casting defects and changes to the dimensions of the casting. The foundry industry is in need of a set of tools to properly characterize refractory coatings. The paper industry has a set of standard test methods to characterize and measure properties of the coatings and use them as QC tools at the mill prior to application. This paper explored the use of alternative methodologies for characterizing the physical, flow, and leveling properties of refractory coatings. Several new testing techniques for the foundry industry has been identified through testing on a generic refractory coating that can be used on chemically bonded cores and molds.

BACKGROUND

Most foundries in the United States purchase their water based refractory coatings in a concentrated form, either as a paste or high viscosity slurry. This practice reduces the weight of water shipped and assists the suspension of the refractory coating during shipment. Receiving the refractory coating in a concentrated form necessitates the in-foundry dilution of the coating to application specifications and the most common test used to determine the end point during dilution is the Baumé test. For many years in the United States the domestic refractory coating manufacturers have recommended that foundries not use Baumé as a singular coating control test during the dilution of refractory coatings. The Baumé test is not commonly used by European foundries or by the American Lost Foam casting industry because it does not offer adequate control of coatings. The AFS 4-F Mold-Metal Interface Reactions Committee has given a panel presentation and has since published papers indicating that the use of the Baumé test to control the dilution of refractory coatings adds variability to the % solids of the coating1. The Baume’ test is appropriately used for low solids, Newtonian coatings, which are not thixotropic and do not lend themselves to sedimentation. The test also requires that the coating be homogenous, at the correct temperature and have no air bubbles1. Foundry coatings do not meet these criteria which leads to testing errors (AFS 409-87-TS)2. The underlying hypothesis of the coating manufacturer’s and the 4-F Committee’s position is that the inherent variability of the Baumé test increases the variability of the % solids of a coating during dilution. Increasing the variability in the % solids translates to changes in the refractory dry deposit on cores and molds which ultimately results in an increased number of casting defects and changes to the dimensions of the casting.

INTRODUCTION

The foundry industry is having higher demands placed on it to produce cleaner, thinner, and closer tolerance castings3. Regardless of the tolerances achieved in a sand core at room temperatures the distortion of the core upon exposure to molten metal and rapid heating may introduce additional variances to the finished casting. New resins and sand systems are being explored to meet these requirements; however, the foundry industry has pressed refractory coating manufacturers to produce coatings capable of enhancing the performance of chemically bonded sand systems. To date, refractory coating’s primary function has been to enhance casting surface finish and minimize metal penetration defects by reducing the capillary dimensions of the substrate and by changing the surface tension of the substrate surface4. In most domestic core applications the final dry coating deposit is typically limited to 0.004 to 0.010 inches (0.10 - 0.25 mm), compare this to iron lost foam coatings that range between 0.015-0.025 inches (0.38 - 0.64 mm) or higher. In Europe, dry coating deposits on sand disks have been observed that are much heavier, ranging from 0.010 to 0.015 inch (0.25 – 0.40 mm) and have demonstrated some anti-veining characteristics which implies that heavier coating deposits may reduce the thermo-mechanical stress development in resin bonded sand systems.

Paper 08-126(04).pdf, Page 1 of 19AFS Transactions 2008 © American Foundry Society, Schaumburg, IL USA

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Currently, the uniformity of refractory dip coated chemically bonded sand cores can range from 0.002 – 0.010 inch. The quality of refractory dip coating is an issue and alternative refractory coating techniques are needed in the foundry industry. For both paper and foundry coatings, coat weight and coating thickness above the porous substrate are dependent on coating solids for a given set of application and metering conditions. Like cores, paper is a porous substrate and the depth of coating penetration can drastically change the optical and functional properties. To avoid problems, the paper industry has adapted a strict set of standardized test to reduce variability and improve its processes. How can refractory coating uniformity be controlled? It is believed that the foundry could benefit from the use of the same standardized tests used by the paper industry or test with slight adaptations. However, an ability to non-destructively precisely measure the thickness of a paper and refractory coating is missing. The process control of refractory coating will enable precision sand casting technology to lend itself to closer tolerances in thin wall castings, weight reduction, and improved fuel economy. With alternative refractory coating techniques and by controlling certain material properties such as leveling index (thixotropy), surface tension, percent solids and water retention (drainage rate), a more uniform coating and improved refractory technologies can be developed. NEED AND PURPOSE The AFS Sand Division estimate approximately $60 million is spent on labor, energy, and scrap to control metal penetration defects in iron castings. This situation is most serious for short production runs where adequate quality control is critical for on-time delivery of quality components. The AFS 4-F Mold-Metal Interface Committee has begun a multi-phase refractory coating control project. Phase I and which involved the evaluation of conventional coating control tests to determine the degree and source of variation in water diluted refractory coatings has been completed. The purpose of this study was to determine what effect Baumé testing has on in-process control when foundries dilute refractory coatings to a specified Baumé. It was discovered that using Baumé as a process control test increases the variability of the “as used” % Solids relative to the “as made” % Solids (AFS 4-F Mold-Metal Interface Reactions Committee). These facts were further evidenced in casting trials completed at Metals Technology Incorporated, Three Rivers, MI. Baumé is an ineffective process control tool as a sole test to relate casting quality to refractory coating control. The foundry industry is in need of a set of tools to properly characterize refractory coatings. The paper industry has a set of standard test methods to characterize and measure the properties of coatings and these standard tests are used as QC tools at the mill prior to application. The focus of this study was to determine if any of these tests could be directly modified for use by the foundry industry. Current techniques employed by the foundry industry for measuring refractory coating thickness suffer poor reproducibility and are thus incapable of maintaining consistent casting quality. Internal surface defects are consistently attributed to large variations in coating thickness and limitations on coated core application methods. A coating control program is necessary to compete in the global market. The paper industry has a sophisticated set of standardized tests used as quality control tools at the mill to characterize and measure properties of many multi-purpose coatings. OBJECTIVES Explore the use of alternative methodologies for characterizing the physical, flow, and leveling properties of refractory coatings.

To identify control techniques for refractory coating on Phenolic Urethane Cold Box (PUCB) disc shaped core by evaluating potential tests (See Table 1) to determine how they relate to Baumé and % solids. APPROACH Table 1 shows the tests studied. Foundry refractory coating tests are listed vertically in the first column of the table and the wet paper coating tests are listed horizontally in the first row. Results from these tests were compared to the performance of Phenolic Urethane Cold Box (PUCB) disc shaped cores coated after thermal distortion and the change in mass of the coated discs at cast iron temperatures5.

One well characterized formulated coating was obtained from participating sponsors along with commercially treated robotic dip coated discs, which served as the control samples. Discs were then dip coated with the commercial coatings. The coat weights of the coatings were adjusted by altering the solids of the coatings. The coatings were then air dried and coat weights determined gravimetrically. To determine the uniformity of the coating layer, the thickness of the coating layer at several points on each sample were measured using a microtribometer.


464

Table 1: Summary of Paper and Foundry Coatings to be Measured

Surface Tension

fta3

2a

Solid

s A

naly

zerb

Her

cule

s R

heog

ram

Wat

er

Ret

entio

n

Lev

elin

g In

dex

Den

sity

c

Stat

.

Dyn

.

Dyn

amic

Str

ess

Rhe

omet

ry

Perm

eabi

lityd

IMS

Baume' X

Brookfield viscosityA

X X

Thixotropic indexB

X

Zahn viscosityC X X

% Solids X

DensityD X

PermeabilityE X

Surface tensionF

X X

Dry coating depositG

X

Refractory penetrationH

X

Matte Time X A fixed spindle, constant speed x 30 sec; B rotational viscometer; C or flow cup, sec; D wt / gal, gravimetric;

E Dietert core tester; F static, DuNouy; G gravimetric; H microscopic,a CCD camera; b microwave; c pyncometer; d Gurley tester; e GlossDrop Method

The static surface tensions of the coatings were measured for at least ten individual drops using a dynamic contact angle analyzer FTA200. Surface tension is defined as the amount of energy required to increase the surface area of a liquid by a unit amount. In general there are two measurable types of surface tension, static and dynamic. Static surface tension is for a surface that is in equilibrium (maximum of surface agents are on the surface). In the case of dynamic surface tension, the surface agents have limited time (interface age) to reach the surface and affect the surface properties. The static surface tension of each coating was calculated from the shape of its pendant drop formed by the coating when suspended from the end of a syringe (Figure 1, right). The dynamic surface tensions of the coatings were measured using a SensaDyne Tensiometer. In this method, the dynamic behavior of the system is obtained with air bubbles, created at the end of two orifices that pass air through the coating (Figure 1, left). The surface tension of the coatings is computed from the change in pressure conditions and the radius difference of orifices. Unlike static testing, this measurement method is immune to surface contaminants and surface foam. Since bubbles are generated continuously, this method is applicable to real time continuous on-line measurement and control.


465

r2 r1

p 2 p 1

Figure 1: Schematic image of SensaDyne capillary system (left) and example of shape of pendant drop for calculation of static surface tension (right)

The immobilization solids point, IMS, of a paper coating is defined as the % solids where the free drainage of water from the wet coating to the basepaper ceases. One technique for measuring this property is the drop in gloss method6. The test is performed by measuring the % solids of the coating when an exponential decrease in gloss is observed from a gloss meter placed over a wet film of the coating under slight vacuum. The set-up scheme of the immobilization testing apparatus is shown in Figure 2. The test apparatus consists of a fritted filter onto which a 5 micron polycarbonate Millipore filter is placed. A plastic template with a rectangular die cut in its center is placed on top of the filters. Coating is applied with a syringe to the die cut area of the plastic template and the excess coating metered off with a flexible blade. A gloss meter is then placed over the wet coating layer and vacuum applied. When a significant drop in gloss is observed, the vacuum is turned off and the solids of the coating measured using a microwave solids analyzer. In addition to IMS measurements, the drainage rates of the coatings were obtained by measuring the % solids of the coatings after applying vacuum for 15 seconds.

Figure 2: Scheme of equipment for Immobilization test

Die cut plastic lid


466

The rheological properties of each coating were measured using a TA instrument AR2000 controlled stress rheometer. Dynamic stress sweeps and steady flow step tests were performed using a couette geometry arrangement. All rheological measurements were performed at 25 °C. The rheology of each coating was also measured using a high shear Hercules according to TAPPI standard test method T-648. The principal of the Hercules Hi-Shear Viscometer is based on the Searle method of measurement where a cylinder (bob) suspended in a liquid sample starts from rest and begins spinning to a preset rotational speed (shear rate). The spinning effect of the bob is resisted (shear stress) by the liquid surrounding it (Figure 3). This viscous drag causes the adjoining cup to rotate against a known resistance thus producing a torque value. The viscosity of the liquid is calculated from the torque measurement at the maximum shear rate. In addition to reporting viscosity, a rheogram is generated whose shape can be used to predict the flow performance of a material under varying rates of shear. From the data collected a leveling index can be obtained. All tests were performed using an E bob and 20.4 sec ramp time.

Figure 3: Cup and bob

The water retention of each coating was measured using an AA-GWR water retention tester according to TAPPI standard procedure T-701. A constant pressure of 20 psi was maintained while taking readings for time intervals of 15 seconds, 30 seconds, 60 seconds and 120 seconds. Five measurements were conducted for each time interval for each coating.

The density of the each coating was measured using a 100 ml. pyncometer cup. The density cup was tared when empty and its weight measured after being filled completely with coating. The final weight dived by 100 gave the density in g/ml. Five measurements were performed on each coating. This average density determined for each coating from these measurements were the input values entered into the Static and Dynamic surface tension software.

All coatings were applied to Mylar film using a Bar film applicator (Figure 4). A bar applicator was used instead of wire-wound rods to eliminate wire markings.

The coating thickness was measured according to TAPPI standard T-551. Coat weight was measured gravimetrically. The surface topography of the coated film was then measured using Verity IA Print Target software using a specially modified scanner7. From these measurements, a Topography Number, which represents surface uniformity, was obtained.

The coatings were applied to the sand disc samples (sand cookies) sent to WMU using a Lynx 6 robotic arm. To determine the dry coat weight, the weight of the discs was weighed before and after dipping and drying. In order to grip the cookie, the “hand” of the robotic arm was replaced with cylindrical extension machined in our lab. This extension, along with the

Figure 4: Bar film applicator


467

application of a silicone gasket material to the edges of the specimen, prevented the bottom and edges of the cookie from being covered with coating while being dipped. Movement of robotic arm during the dipping process was controlled by using RIOS software, which enabled the same dip procedure to be replicated for each cookie.

The position of the robotic arm at the start and completion of the loading and unloading stages was the same. During the dipping stage, each cookie was immersed at a slight angle to prevent air bubble entrapment. The coatings were lightly stirred with a magnetic stirrer to prevent foaming and assure that the coating pigments remained in suspension. The final position of the dipping stage was horizontal. The total time that the cookie was in contact with the coating was 2 sec. The drainage stage of the dip process provided the time needed to remove any excessive coating from the surface of the cookie. To enable the already coated cookie surface to remain uniform, the extension was tilted (angle app. 45°) and a rotational movement applied. The coated cookie was removed during the unloading stage. During this stage, the arm position was maintained in the same position as used for the loading stage. The four stages of the dipping process are shown in Figure 5.

Robotic arm Lynx 6 Loading/Unloading stage

Dipping stage

Draining stage

Figure 5: Stages of robotic dipping program

The specimens were placed horizontally (refractory coated surface up) and air-dried for 24 hours at TAPPI standard conditions (T-402). Coated specimens were sectioned and coating thickness and penetration were measured using a CCD camera and software fta32.

The permeabilities of disc specimens were measured according to TAPPI standard test method T-460, using a Gurley porosimeter. The test was slightly modified to account for the leakage of air from the sides of the thicker cookies. To account for the air leakage from the sides, an O-ring was placed around the circumference of the specimen and the specimen then sandwiched between to two rubber gaskets to prevent damage of the coating layer by the clamps of the instrument.


468

Measurements were made on the coated and uncoated discs. Figure 6 shows a picture of the testing apparatus and gaskets used.

Figure 6: Figure Gurley tester with specimen sealed within gaskets

A statistical analysis was performed on all the data collected using Minitab to determine which coating test correlated best to the change in solids RESULTS AND DISCUSSION Measurements on the microtribometer failed to produce meaningful results due to the high noise contribution of the samples. The high noise in the measurements was attributed to the non-uniformity of the sample surfaces. It was determined that the particle size of the sand resulted in a course sand cookie surface which was too variable in roughness to reliably measure the thickness of the coatings by this means. Multiple tests were performed using tribometer tips of different geometries and dimensions. As nothing worked, this measurement procedure was abandoned. For most coatings, the plot of surface tension vs. bubble frequency exhibits a decreasing trend (dynamic zone) until the system reaches an equilibrium (static surface tension) where the surface tension no longer changes (static zone, Figure 7).

Figure 8 shows the change in surface tensions of the coatings with time. Since the difference between samples is only in the % solids present in the coating, the trend should show that with an increase in the percent solids, the value of the surface

Figure 7: Common characteristic plot of surface tension vs. bubble frequency (diffusion rate).


469

27

28

29

30

31

32

33

34

0 5 10 15 20 25 30

Time / sec

IFT

/ dyn

/cm

34% 36% 38% 40% 42%

tension should decrease, which it does. It can be also seen that the appropriate drop shape for the evaluation of the static surface tension is reached at approximately 2 sec. after the start of the measurement. Between 15 sec. and 20 sec. it was observed that a partial solidification of the coating occurred on the syringe needle. From the variation of surface tension values (results for 34.04% to 39.85%) it can be concluded that the addition of water into the coating solution did not significantly change the surface tension of the coating.

Figure 8: Change in static surface tensions of coatings with time. [Note: In the black and white print version of this paper please see the CD for the figure in color.]

The Figures 9 and 10 shows a 3D display of the dynamic surface tension results. Figure 9 represents a trend of surface tension change for diffusion rates ranging from 0.5 sec to 1.2 sec. The maximum surface tension and lowest diffusion rate was observed for the 42.05% solids coating. . If we assume (from the chart for static surface tension) that the static surface tension is reached after 5 sec., the 3D plot would look like it is displayed in Figure 10. Overall, for a low rate of diffusion, the highest surface tension was observed for the 42.05% solids coating but at the highest rate of diffusion, the 34.04% solids coating had the highest surface tension.


470

Figure 9: 3D plot of dynamic surface tension

Figure 10: 3D plot of dynamic and static surface tension The IMS point of all the coatings was found to be the same (75%) indicating that the particle size distribution of the coating did not significantly change with dilution. Instead, only the time to reach the IMS point changed due to differences in the amount of free water contained within each coating.

The results from the drainage test in Figure 11 represent how fast the structure of the coating consolidates. The trend is obvious. With an increasing percent in starting solids, the percent solids at the end of the test (15 sec) increases.

12

34

56

28303234363840424446485052545658

34

36

38

4042

Surfa

ce te

nsio

n / d

yn/c

m

% of

solid

Diffusion rate / sec

0.50.6

0.70.8

0.91.0

1.11.2

51

52

53

54

55

56

57

58

59

34

36

3840

42

Surfa

ce te

nsio

n / d

yn/c

m

% of solidDiffusion rate / sec


471

54

56

58

60

62

64

66

68

70

72

% o

f sol

ids 34%

36%38%40%42%

Figure 11: Change in coating solids with drainage time Figure 12 shows the results obtained from the viscosity measurements made with the dynamic stress rheometer. These results confirm the assumption that viscosity decreases with a decrease in coating solids. From the shear rate vs. shear stress curves shown in Figure 13 (logarithmic scale), the rate of particle sedimentation is obtained. In Figure 13, it can be seen that for all samples there is a point where there is a significant increase in shear rate. This indicates the presence of a yield stress, after which the coating flows. According to the value of the yield stress, the sample with the highest sedimentation rate can be determined. The higher the stress value before coating yields to flow, the faster is its sedimentation rate. This is because the viscosity of the fluid around each particle is low, which prevents the particles from moving under the stress of gravity.


472

0.1000 1.000 10.00 100.0shear stress (Pa)

1.000E-3

0.01000

0.1000

1.000

10.00

100.0

1000

10000

1.000E5

1.000E6vi

scos

ity (P

a.s)

AFS34AFS36AFS38AFS40AFS42

0.1000 1.000 10.00 100.0shear stress (Pa)

1.000E-7

1.000E-6

1.000E-5

1.000E-4

1.000E-3

0.01000

0.1000

1.000

10.00

100.0

1000

shea

r rat

e (1

/s)

AFS34_SSFlow-0002f, Steady state flow stepAFS36_SSFSWP-0001f, Steady state flow stepAFS38SSFlow-0001f, Steady state flow stepAFS40SflowSweep-0001f, Steady state flow stepAFS42DFlowSweep-0001f, Steady state flow step

Figure 12: Change in coating viscosity with shear stress. [Note: In the black and white print version of this paper please see the CD for the figure in color.]

Figure 13: Plot of relation shear rate vs. shear stress [Note: In the black and white print version of this paper please see the CD for the figure in color.]


473

The ability of a coating to level itself after application and metering can be predicted by calculating the leveling index. The leveling index is calculated by dividing the viscosity at peak shear rate by the viscosity at the lowest measurable rate of shear. The values used to calculate the leveling index are given in Table 2.

The leveling index measures the degree of departure of a coating from Newtonian behavior. The low shear viscosity controls the leveling properties of the coating while the high shear viscosity controls the transfer properties. From Figure 14, it is clear that the leveling index of the coatings increased slightly with coating solids.

Table 2: Leveling Index of Coatings

% Solids Viscosity (centipoises)

Leveling Index

High shear rate (50338 sec-1)

Low shear rate (4576 sec-1) L.I.

34% 9.0 7.3 1.23 36% 8.0 6.6 1.21 38% 9.1 6.0 1.52 40% 11.2 7.3 1.53 42% 15.3 8.7 1.76

Figure 14: Influence of coating solids on leveling index.

The Hercules rheograms for all the coatings (34%, 36%, 38%, 40%, 42% solids) are shown in Figure 15. All coatings exhibit a slight degree of thixotropy.


474

0100020003000400050006000

-500 0 500 1000

torque(kilodyne-cm)

RPM

34%36%38%40%42%

Figure 15: Hercules rhenogram [Note: In the black and white print version of this paper please see the CD for the figure in color.]

The change in apparent viscosity with shear is shown in Figure 16. All the coatings are shear thinning. The low and high shear viscosities increased with solids.

0

5

10

15

20

25

0 10000 20000 30000 40000 50000 60000

shear rate (1/sec)

appa

rent

vis

cosi

ty (c

p)

34%

36%

38%

40%

42%

Figure 16: The graph of apparent viscosity vs. shear rate

[Note: In the black and white print version of this paper please see the CD for the figure in color.]

The change in the WRV with time is shown in Figure 17. The average values are given in Table 3.

Table 3: Average Water Retention Values for All Trials Average 15 secs 30 secs 60 secs 120 secs

42% 1016.9 1469.9 2228.3 3188.4 40% 1074.5 1585.6 2336.2 3407.0 38% 1153.5 1803.5 2440.5 3593.5 36% 1133.3 1755.0 2540.0 3672.1 34% 1163.9 1765.9 2627.8 3848.5


475

0

1000

2000

3000

4000

5000

15 secs 30 secs 60 secs 120 secs

time(Sec)

wat

er r

eten

tion

valu

e (g

/m2)

34%36%38%40%42%

Figure 17: Change in water retention value with time.

[Note: In the black and white print version of this paper please see the CD for the figure in color.]

Figure 18 shows the average densities of each coating. These values were used in the calculations performed by the First Ten Angstroms and SensaDyne instruments to obtain static and dynamic surface tension values. Figure 18 shows an increase in density with coating solids.

Figure 18: Coating density values of one coating diluted to different solids.

Results for the thickness and coat weight measurements on Mylar are shown in the Figure 19 and Figure 20. From these figures, it can be seen that coating thickness and coat weight increased with solids.


476

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

wei

ght /

gra

ms/

100

cm2

34%36%38%40%42%

0.0015

0.0017

0.0019

0.0021

0.0023

0.0025

0.0027

0.0029

0.0031

0.0033

0.0035

thic

knes

s / i

nch

34%38%42%

Figure 19: Influence in coat solids on coat weight of coatings on Mylar film.

Figure 20: Influence of coating solids on thickness on Mylar film


477

0

10

20

30

40

50

60

70

Topo

grap

hy N

umbe

r

34%36%38%40%42%

The results from the topography scans on the coated Mylar films are presented in the Figure 21. There is a trend of the “topo-number” increasing with increasing percent of solids (34.04%, 36.05%, and 38.12%). After this increase, a sudden drop was observed. The decrease in Topo-number is believed to correspond to the coat weight in which complete surface coverage is obtained. For samples 39.85% and 42.05%, complete coverage is achieved.

Figure 21: Results from topography measurement There was significant variation in the porosity data. It is believed this may be due to gasket leaks that surrounded the specimen. Increasing the clamping pressure upon sample loading greatly reduced these variations. Unfortunately, the higher sample loading pressure resulted in damage to the surface of the specimen, preventing it from being used for thermal distortion testing. Further modification to this instrument may provide useful information for refractory coating control because it provides insight into the contribution of percent solids to coating thickness. Unfortunately, the permeability results could not be correlated to dry coat weight due to the interference of the silicone gasket material applied to the edges, preventing accurate coat weights measurements. Additional modifications to the robotic arm sample holding device are being made to prevent these problems in the future. It was observed that the smoothness of the coated samples improved with coated weight, but efforts to measure surface roughness with the microtribometer and other measuring devices failed to produce reproducible data, due to the high roughness of the samples. The permeability was found to vary with percent solids, coating pickup and depth of penetration (Figure 22).


478

Uncoated disc Disc coated at 34% sol. Disc coated at 38% sol. Disc coated at 42% sol.

Figure 22 : A. Surface coating at various percent solid levels. B. Coating thickness and penetration

Table 4 shows a summary of all the results and the results of the statistical analysis performed. The statistical analysis was performed using Minitab to determine the correlation between wet coating measurements and coating solids. A Pearson coefficient was calculated for each coating test. The Pearson coefficient is a statistic which estimates the correlation between two given random variables. The coefficient ranges from −1 to 1. A value of 1 shows that a linear equation describes the relationship perfectly and positively. A score of −1 shows that all data points lie on a single line but that Y increases as X decreases. A value of 0 shows that there is no linear relationship between the two variables. From the coefficient values in Table 5, it is clear that there is a strong correlation between all wet coating measurements and coating solids. Although the Baume results appear to correlate well to coating solids as did the paper coating tests, there was great difficulty in achieving consistent readings. A considerable amount of time was required to achieve a standardized method to obtain reproducible results. Such measures are not practiced in industry, hence the need for a more accurate and reliable test method.

B

A

34% 38% 42%


479

Table 4: Summary of Results

Factor #1

Resp. #1

Resp. #2

Resp. #3

Resp.#4

Resp.#5

Resp.#6

Resp. #7

Resp. #8

Resp. #9

Resp.#10

Solid

s (%

)

Surf

ace

Tens

ion

(dyn

es/c

m)

Bau

mé

(Hyd

rom

eter

29

-41)

Rhe

olog

y (L

I/η)

Imm

obili

zatio

n So

lids (

%)

Den

sity

(g/c

c)

Wat

er R

eten

tion

(gsm

@

15 se

c)

Coa

ting

Thic

knes

s (m

m)

(Dra

wdo

wn

on M

ylar

)

Coa

ting

Thic

knes

s (m

m)

(Dep

osit

on th

e sa

mpl

e)

Topo

grap

hy

**Pe

rmea

bilit

y (s

ec/3

00 c

c)

42 29.5 ± 0.6

35.9 ± 0.4 1.76/12.0 cp 69.0

± 0.9 1.313 ± 0.001 1016.9 0.0727

± 0.0051 0.08 ± 0.01

32.8 ± 4.4 30

40 30.7 ± 0.6

34.4 ± 0.2 1.53/11.5 cp 67.9

± 0.8 1.306 ± 0.000 1074.5 33.9

± 4.4

38 31.0 ± 0.3

33.4 ± 0.2 1.52/8.0 cp 65.8

± 0.6 1.299 ± 0.001 1153.5 0.0615

± 0.0071 0* 58.6 ± 7.5 20

36 31.3 ± 0.4

32.3 ± 0.2 1.21/5.0 cp 64.4

± 0.5 1.296 ± 0.000 1133.3 47.8

± 6.8

34 31.6 ± 0.4

30.6 ± 0.5 1.23/2.0 cp 59.9

± 0.5 1.291 ± 0.000 1163.9 0.0538

± 0.0056 0* 41.1 ± 2.9 3

* Penetration of the coating into the sample ** Additional tests are needed to statistically verify

Table 5: Statistical Analysis

Surf

ace

Tens

ion

(dyn

es/c

m)

Bau

mé

(Hyd

rom

eter

29

-41)

R

heol

ogy

(vis

cosi

ty)

Leve

ling

Inde

x

Imm

obili

zatio

n So

lids (

%)

Wat

er R

eten

tion

(gsm

@

15 se

c)

Coa

ting

Thic

knes

s (m

m)

(Dra

wdo

wn

on M

ylar

)

Coa

ting

Thic

knes

s (m

m)

(Dep

osit

on th

e sa

mpl

e)

Topo

grap

hy

(Dra

wdo

wn

on M

ylar

)

Perm

eabi

lity

(sec

/300

cc)

PC -0.936 0.996 0.982 0.945 0.964 -0.903 0.994 0.866 -0.451 0.989 P-value 0.019 0.000 0.003 0.015 0.008 0.036 0.068 0.333 0.446 0.095

PC - Pearson correlation coefficient Level of significance α = 0.05


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CONCLUSIONS AND RECOMMENDATIONS

Several standardized paper coating tests have shown applicability as new foundry coating control tests. These wet coating tests showed a strong correlation to changes in solids, as does the Baumé. However, previous work by the AFS 4F committee has shown the Baumé to be an ineffective process control tool as a sole test to relate casting quality to refractory coating quality control. The findings of this work indicate that some standardized paper coating tests should be considered for use by the foundry industry.

A proper non-destructive measure for refractory coating penetration and thickness does not currently exist in the foundry industry. This is a prerequisite to proper refractory coating control especially for elevated temperature tests. The percent solids in refractory coatings influences coating penetration and dry coating film thickness. A novel technique for measuring coating thickness has been introduced in this work, but it is a destructive test. Measurements using this method confirmed that the thickness of the dry coating film above the surface of the specimen increases with increasing coating solids. Further work is needed to identify, modify and optimize standard paper coating tests for application by the foundry industry as coating control tests. Coating application studies and casting trials will be pursued predicated and contingent upon the results and findings found in the next phase of work. ACKNOWLEDGMENTS This paper would not be possible without support and input from AFS 4F Committee especially the Research Steering Committee (Brian Guyer, Larry Stahl, and Joe Muniza). REFERENCES 1. AFS Molding Division Mold-Metal Interface Reactions Committee (4-F), “Baume’: Complete Coating Control?”, Metal

Casting, October 1, 2003, pp. 28-30. 2. Mold and Core Test Handbook, 3rd. Edition, AFS (2001). 3. Cuttino, J., Andrews, J., Piwonka, T., “Developments in Thin-Wall Iron Casting Technology,” AFS Transactions, 1999,

vol. 107, page 363. 4. Stefanescu, D., Giese, S., Piwonka, T., Lane, A., “Cast Iron Penetration in Sand Molds, part I: Physics of Penetration

Defects and Penetration Model”, AFS Transactions, 1996, vol. 104, page 1233. 5. Guyer, O.B., Emptage, R.C., Ramrattan, S.N., “The Effect of Refractory Coating Thermal Heat Transfer on Phenolic

Urethane Cold Box Core Distortion at Iron Temperature and Pressure,” AFS Transactions, Paper 05-192 (2005). 6. Herbet, J. Albert, Whalen-Shaw, J. Michael, Gautam, Navin, “A Simple Method for Measuring Immobilization Using

the Surface Gloss Technique”, 1990 TAPPI Coating Conference, pp. 431-441. 7. Rosenberger, Roy, Cruz, Mario, Joyce, Margaret, Fleming, Paul D., “Comparative Study Between a New Verity

Topography Measurement Device to Parker Print Surf and Emveco Instruments Evaluating Basecoated Board and Subsequent Air Knife and Blade Coating, and Calendering”, 2007 TAPPI Papermakers and PIMA International Leadership Conference.


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comparing alternate foundry refractory coating measurement

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