F€M. 79 nosi# nv-mst

Reference N83

Publi - cations

AlllDt T 7 A A 3 7

CASTABILITY OF DENTAL CASTING GOLD ALLOY

A Procedure for evaluation of castability

developed under order number DSA-120-76-F-BG36

for the Defense Personnel Support Center.

George Dickson

Dental and Medical Materials Section

National Bureau of Standards

Washington, DC 20234

This document has been prepared for the use of the Defense

Personnel Support Center. Responsibility for its further use

rests with the Support Center. NBS requests that if release to

the public is contemplated, such action be taken only after

consultation with the Office of Public Affairs at the National

Bureau of Standards.

Q C —100

»U56

78-1451

Certain commercial materials and instruments are identified

in this report to adequately specify the experimental procedure.

In no instance does sucn identification imply recommendation

or endorsement by the National Bureau of Standards, nor does it

imply that the material or instrument identified is necessarily

the best available for this purpose.

^iiional Bureau of Sfandartfs APR 17 1979

Castability of Dental Casting Gold Alloy

INTRODUCTION

This report describes a procedure developed for measuring the castability

of dental casting gold alloys and presents a proposed castability requirement

and test method. The report is made up of three parts. Part I, which

consists of the preliminary report prepared in May 1977, describes the procedure for measuring castability and gives results obtained on four 'fepecif ication type" alloys, three of which were suggested by the Defense Personnel

Support Center, and on two alloys of lower noble metal content. Part II contains data on additional alloys including a fourth alloy suggested by the

Defense Personnel Support Center and several alloys for porcelain-fusedto-metal applications. Also included in Part II are data on the effects

that variations in procedures and casting conditions have on castability

and a discussion of the proposed castability requirement and test method.

Part III consists of the proposed castability requirement and test method

in specification form.

i
CASTABILITY OF DENTAL CASTING GOLD ALLOY

Part I

The development of a method for evaluating the castability of dental casting

gold alloys was undertaken to provide a test procedure which will distinguish

between alloys that have routinely produced satisfactory castings in military

dental facilities and alloys which have proven to be unsatisfactory in castability. Characteristics to be incorporated in the test procedure were:

1. The procedure should be primarily a measurement of the capability of

the alloy to fill the mold.

2. The test should use equipment and facilities generally available to

the dental gold industry.

3. The test procedure should simulate dental prosthetic laboratory

procedure.

4. The pattern and mold employed should be easily reproducible in

different laboratories.

5. The method for evaluating the finished casting should be objective and

-preferably uncomplicated.

Various procedures have been used for measuring the castability of alloys.

~ For example, Asgar (1) has described a method using a spiral shaped wax pattern.

Sorensen and Ingersoll (2) used a stainless steel mold in the shape of a six

spoked wheel with thin web sections between the spokes to measure fluidity of

casting gold alloys. A recent publication by Vincent, Stevens and Basford (3)

describes a method of measuring casting ability using a pattern with a range of

rod diameters.

I

9
Method and Materials

After experimenting with several different specimen designs, a pattern made

from polyester sieve cloth was selected for use in development of the castability test. Figure 1. This material has several advantages (1) the pattern

comprising a rectangular piece of the sieve cloth, a wax runner bar, and a

wax sprue can be prepared with little difficulty, (2) the sieve cloth can be

burned out with the usual procedure for wax patterns, (3) the sieve cloth is

manufactured to comply with opening dimension requirements of ASTM Ell-70 and is

therefore uniform in size, (4) since the sieve cloth is available in a range

of sizes, the test specimen can be easily varied to accomodate different types

of alloys if necessary, (5) the mesh pattern provides a simple objective method

for determining a castability value.

The procedure for assigning a numerical value for "castability" to the cast

specimen is very simple. The combination of pattern size and mesh size used,

Figure 1, provides a pattern with 100 open squares and 210 segments where a segment is defined as the part of a sieve filament perpendicular to and connecting

two adjacent parallel sieve filaments. Evaluation of the cast specimen can be

made by direct examination, but particularly where a large number of castings

are to be evaluated, it has been found more convenient to prepare a photomicrograph

of the specimen, make a xerox copy of the photomicrograph and make the evaluation

on the xerox copy. If necessary the photomicrograph or the specimen can be examined

to determine the completeness of any segment which cannot be seen clearly in the copy.

A sample evaluation is shown in Figure 2. The number of segments in the

casting is counted, divided by 210 and multiplied by 100 to obtain the percentage

of complete segments. This percentage is designated as the castability value.

As an alternative the number of complete squares could be counted to obtain

a castability number. In general the value obtained by counting squares is

slightly below the value based on segments. Although there is little choice
between the two procedures, the segment count was selected since it is more

sensitive to small differences than is the squares count. (Loss of one segment

always reduces the segment evaluation by approximately 0.5, but loss of one

segment may reduce the squares count by 0, 1 or 2 depending on location of the

segment.

)

Part I of

For the series of tests covered in/ this report six alloys including two with

low precious metal content were used. The alloys were cast by two techniques,

"hygroscopic expansion” and "thermal expansion”. The alloys, other materials,

and conditions employed are listed in Tables 1 and 2. The choice of casting conditions, which is somewhat arbitrary, was designed to determine the relative

castibility when all of the alloys are subjected to the same treatment. An

acceptable alternative would be to adjust the casting temperature to each alloy,

for example, to some set temperature interval above the liquidus or to the

temperature recommended by the manufacturer.

Results

Table 3 gives castability values for the six alloys cast by the two techniques.

The values, based on the percentage of complete segments, are averages of five

castings for each combination of alloy and technique. Figures 3a through 3f show

typical castings (that is, a casting with a castability value near the average)

for each of the alloys when made by the thermal expansion technique. Figures 4a

through 4e show a typical range of variations for five duplicate specimens; in

this example, for five specimens of alloy H made by the hygroscopic technique.

Discussion

The results indicate that there are differences in castability among the

six alloys tested and between the hygroscopic (H) and thermal expansion (B)

techniques. In the thermal expansion series, alloys A and C have average values

4
much larger than does alloy P, Table 3 and Figures 3a, b, f. In the hygroscopic

series, the differences between the average castability number for alloy A and

the averages for the other alloys are large. Table 3. The standard deviations of

some ’’duplicate" specimens (for example specimens B-B, M-B, P-B and C-H) indicate

that the differences between averages must be large to be significant. The

causes of these wide variations are not yet known. Although attempts were made

to control factors such as mold preparation, burnout temperature and time, casting

temperature and casting machine speed, it may be that more precise control or

the casting of a greater number of "duplicate" specimens will be required to reduce

the uncertainty of the results.

One of the problems with tests for castability including the method described

in this report is that small variations in the casting equipment or procedures

may cause significant variations in the results obtained. Because of this, the

test procedure may be more reliable as a comparative rather than an absolute or

independent measurement procedure. This would mean that evaluation of an

unknown alloy could best be accomplished by comparing results for the unknown with

results for a known satisfactory alloy cast at the same time under the same conditions rather than comparing the unknown to a specific castability number.

Additional studies of the effect of variables such as casting temperature and

further statistical evaluation of the significance of the variations in results

are needed. This work is in progress.

One of the major difficulties in evaluating the testing procedure has been

the unavailability of any samples of gold alloys which have been found to give unsatisfactory castability performance in use. Until data on such alloys are available there will be uncertainty as to the level at which limits for castability

should be set.

5
Summary

A method for objective evaluation of the castability of dental alloys has

been developed. The method employs easily reproducible specimen patterns and

uses procedures and equipment generally used in dental prosthetic laboratories

Results obtained so far indicate that it may be necessary to reduce the variability to make the proposed test suitable for specifications purposes. Another

problem is the impossibility of correlating the test procedure with practical

usage until samples of alloys which have been found unsatisfactory in use are

available.

6
References

1. Asgar, Kamal, Metal Castings in Dentistry, in Wachtel , L. W. , editor,

Symposium: Dental Biomaterials - Research Priorities, 1973. DHEW

Publication No. (NIH) 74-548, pp 27-44.

2. Sorensen, S. E. and Ingersoll C. E. A Method for Determining Fluidity

of Casting Gold Alloys, Abstract No. 191, I.ADR Program and Abstracts of

Papers, 44th General Meeting, March 1966.

3. Vincent, P. F. , Stevens, L. and Basford, K. E. A Comparison of the Casting

of Precious and Non-Precious Alloys for Porcelain Veneering. J. Pros. Dent.

37 (5) :527-36 , May 1977.

7
Table 1. Alloys (Part I)

Alloy Code Manufacturer

Ney-Oro B-2 B

Harmony Line, Hard H

"C" Bridge C

A6 A

Midas M

Paliney C-B P

J. M. Ney Company

Williams Gold Refining Company, Inc.

J. Aderer, Inc.

Howmedica, Inc.

-Jelenko, Penwalt Corp.

J. M. Ney Company

8
Table 2. Casting Materials, Equipment and Conditions

Pattern

Test Portion:

Runner bar:

Sprue

:

Mold

Investment

:

Ring:

Asbestos

:

1 mm opening (No. 18)* polyester sieve cloth, 10 x. 10 squares,

dipped in Kerr Debubblizer

6 gage 1/2 round, 2 pieces

6 gage round, 6mm length

Beauty Cast, Whip-Mix Corp., W/P ratio 15/50, vacuum

mix, 20 sec.

Whip-Mix, 32 x 48 mm

1 layer, wet

Setting and

Burnout Conditions: Hygroscopic expansion (Code H) 30 min in water bath,

burnout next day, 1 hr to 482°C (900°F), 1 hr at 482°C

Thermal expansion (Code B) bench-set, burnout next day,

1 hr to 649°C (1200°F), 1 hr at 649°C

Casting

- Weight of alloy:

Machine

:

Temperature

:

Speed:

9 g (6 d wt)

Howmedica Electromet, induction melting

1079°C (1975°F) read on graphite crucible

400 rpm

*The nominal wire diameter listed in ASTM Ell-70 for 1.00 sieve cloth is 0.580 mm. The measured diameter of the filaments in the sieve cloth used was 0.496 + 0.007 mm.

9
Table 3. Castability of Dental Alloys

Specimen

Code Alloy Technique

Castability

Average

' (%)

S.D

A-B Howmedica A-6 Thermal 100.0 0.0

C-B Aderer "C" Thermal 91.7 5.5

H-B Harmony, Hard Thermal 69.3 6.6

B-B Ney-Oro B-2 Thermal 67.1 21.2

M-B Midas Thermal 62.8 16.4

P-B Paliney C-B Thermal 29.2 17.8

A-H Howmedica A6 Hygroscopic 95.0 1.6

C-H Aderer MC" Hygroscopic 59.1 22.4

H-H Harmony, Hard Hygroscopic 48.9 9.7

P-H Paliney C-B Hygroscopic 43.1 13.3

M-H Midas Hygroscopic 42.9 9.1

B-H Ney-Oro B-2 -Hygroscopic 40.7 5.6

10 '
Figure 1. Pattern made of polyester sieve cloth. Magnification 5X.

11
u\ 4

C, 7 S JO it /D 7 7 V

Segments

:

Vertical 77

Horizontal 66

Total 143

Castability

:

143 x 100

210 68.1

Figure 2. Example of castability evaluation work sheet,

for photograph of casting.)

(See fig. 3c

12
Figure 3a. Typical specimen of Howmedica A6 thermal expansion series

Average castability 100.0; Spec. A1B 100.0

Figure 3b. Typical specimen of Aderer "C" thermal expansion series.

Average castability 91.7; Spec. C4B 91.4.

13
Figure 3c. Typical specimen of Harmony thermal expansion series. Average

castability 69.3; Spec. H1B 68.1.

Figure 3d. Typical specimen of Ney-ORA B-2 thermal expansion series. Average

castability 67.1; Spec. BIB 73.3.

14
Figure 3e. Typical specimen of Midas thermal expansion series. Average

castability 62.8; Spec. M3B 60.5.

Figure 3f. Typical specimen of Paliney C-B thermal expansion series.

Average castability 29.2; Spec. P4B 33.8.

15
Figure 4B. Specimen H2H, castability 37.1.

Figure 4a. Specimen of Harmony hygroscopic series H1H, castability 49.0.

16
Figure 4c. Specimen H3H , castability 62.4.

Figure ^d. Specimen H4H, castabilitv 42.9.

17
i

Figure 4e. Specimen H5H, castability 52.9.

18
Castability of Dental Casting Gold Alloy

Part II

This part of the report includes:

(1) data relating to effects on castability of variations in some

of the procedures and conditions used in the preparation and casting of test

specimens

,

(2) data on some alloys (Table 4) used for porcelain-fused-to-metal

(PFM) applications and on one Type III gold alloy (Table 4) not included in

Part I, and

(3) discussion of the proposed castability requirements and test

procedure.

During the time of development of the test for castability, research on

alloys for porcelain-fused-to-metal crown and bridge castings was also in

progress in the laboratory, and the castability test was used in this investigation. Some of the data on the PFM alloys are included to demonstrate the

applicability of the castability test to different types of alloys and to

point out some of the effects of casting conditions on castability.

Effedt of casting temperature

The effect of casting temperature over a range extending approximately

40°C (75°F) below and 70°C (125°F) above the proposed test temperature was

investigated for one gold alloy, Ney-Oro B-2 , using the thermal expansion

technique (Table 2) . Temperature of the alloy at the time of casting was

determined, as indicated in Part I, by the optical pyrometer system supplied

with the casting machine used (Table 2) . The data in Table 5 indicate that

over the range investigated the castability values for the gold alloy do not

show a large variation with casting temperature*.

*A11 of the castability values in Table 5 are higher than the value of^ 67.1

in Table 3 for the same alloy cast under similar conditions. Although --ie

reason for this difference is not known it was noted that the average oi

67.1 includes one particularly low value of o3.o

19
The effect of casting temperature was much more apparent in a series of

castings of four PFM alloys. For this series of castings the alloys were

"superheated" to casting temperatures ranging from 111°C (200°F) to 278°C

(500°F) above the liquidus temperature of the alloy as reported by the

manufacturers. Table 6 shows that for these PFM alloys, in almost every

instance castability values increased as casting temperature was increased.

Also for all of the alloys the highest castability values were obtained

when the alloy was cast at a temperature higher than that recommended by

the manufacturer.

Effect of mold temperature

The effect of mold temperature on the castability of PFM alloys is

shown in Table 7. Castabilities at mold or burnout temperatures of 816°C

(1500°F) and 927°C (1700°F) were compared. In every comparison the average

value is higher at the higher burnout temperature. This is consistent with

the results for gold alloys shown in Table 3 where five of the six alloys

have higher castability values for the thermal expansion techniques with a

burnout temperature of 649°C (1200°F) than for the hygroscopic technique

with a burnout temperature of 482°C (900°F)

Effect of melt soak time

The molten alloy was routinely held at casting temperature for 60 seconds

before casting. To determine whether the length of this holding period or

melt soak time had a significant effect on castability, a series of castings

was made with a 90 second melt soak time. Data for this series (made by the

hygroscopic technique) are given in Table 8. Values from Table 3 of castability for specimens made with a 60 second melt soak time are shown for

comparison. In five of the six alloys for which both 60 and 90 second melt

soak times were used, higher average castability values were obtained after

20
a 90 second melt soak time. The reason for the decrease in castability

of the Howmedica specimens at 90 seconds is not known. Testing of additional specimens would be required to determine whether or not this difference is actually dependent on melt soak time. The castability of one Type

III dental gold casting alloy, Firmilay, not included in Part I is shown

in Table 8.

Effect of sprue length

The effect of sprue length on castability values was investigated for

one alloy (Howmedica A6) . As shown in Table 9 when specimens of this alloy

made with sprue lengths of 12 mm were compared with specimens with 6 mm sprue

lengths, the differences were not significant. The average for the 12 mm

sprue length specimens were slightly higher than for the 6 mm specimens,

but the difference is not large relative to the standard deviations for

specimens of either 6 or 12 mm sprue length (Table 9)

.

Use of 24K gold castings for verification of test procedure

Because the castability value of an alloy depends upon testing conditions

as well as upon the properties of the alloy, some means of verifying that the

testing conditions are as specified is meeded. One method of evaluating the

entire combination of procedure, test equipment and casting conditions is

to make castings of a standard test material. Twenty-four karat gold was

selected as a readily available standard test material. Since the casting

characteristics of 24K gold differ somewhat from those of dental gold alloys,

it is necessary to use a higher casting temperature and a longer melt soak

time than for the alloys. With these modifications in procedure, castability values for the 24K gold are within the range of values obtained for

the dental gold alloys as shown in Table 10. It is believed that with the

required modifications, the procedure for making 24K gold castings remains

close enough to the proposed test procedure to provide a valid verification

of test conditions. 2
Discussion of proposed castability requirement and test method

It must be emphasized that the proposed castability requirement and

test methods are based only on alloys which are considered to cast satisfactorily. No samples of alloys which had been found, in service, to have

unsatisfactory castability characteristics were available. The proposed

limit for castability is therefore set at a level which will pass the

tested alloy but will reject alloys which are inferior to the tested alloys

in castability.

The proposed test method is based on the hypothesis that while it may

be possible to adjust temperatures and other conditions so that complete

castings can be made from any gold alloy that complies with the composition

and other requirements of present specifications, it is reasonable to require

that the alloys can be cast satisfactorily by a procedure that falls within

the range of normal dental laboratory practice. For this reason, for example,

the test method calls for specific burnout and casting temperatures to be

used for all alloys, thus tending to reject alloys which would require unusually high temperature for casting.

The proposed test method employs a hygroscopic rather than a thermal

expansion casting technique because data (Table 3) show that the hygroscopic

technique is generally a more severe test of castability than is the thermal

expansion technique with its higher burnout temperature.

The use of polyester sieve cloth* as a pattern material insures that

uniform patterns can be produced in different testing laboratories. The pattern

dimensions and sieve size (1 mm opening or No. 18) were chosen so that satisfactory gold alloys will produce a casting that is only partially complete

when the specified procedure is used. Thus the range of the proposed test

* Polyester sieve cloth obtained from Nalgene Labware Division/Nalge Co.,

P. 0. Box 365, Rochester, NY 14602

22
method is wide enough to evaluate gold alloys that are either significantly

inferior or significantly superior to those covered in this report.

Many details of the test method such as the sprue length, the ring

liner of one layer of asbestos, the orientation of the pattern during casting,

the melt soak time, the length of the casting machine arm, the speed of

rotation of the casting machine and the method of cleaning the casting are

specified primarily for uniformity of procedure rather than for merit of the

particular procedural detail. Data relating to some of these, sprue length

(Table 9) and melt soak time (Table 8) suggest that small deviations from the

specified procedures will not greatly affect the castability values, but

close adherence to the specified procedures is recommended.

In the proposed castability requirements and method, castability has

been specified and calculated not as a percentage but as a decimal fraction

to avoid suggesting that a satisfactory alloy should have a castability of

100%. As indicated above the specified test specimen and procedures were

intentionally selected so that castability values of less than 100% (or 1.00)

are obtained for alloys considered to be satisfactory in service.

23
Table 4

Additional Alloys (Part II)

Alloy Typ< Manufacturer

Firmilay Type III gold alloy J. F. Jelenko and Co.

Jelenko 0 High noble PFM J. F. Jelenko and Co.

Cameo Medium noble PFM J. F. Jelenko and Co.

Biobond Non precious PFM Dentsply International , Inc

NP-2 Non precious PFM Howmedica, Inc.

Ceramalloy Non precious PFM Ceramco, Inc.

Jelbon Non precious PFM J. F. Jelenko and Co.

24
Table 5

Effect of Casting Temperature on Castability of Gold Alloy

Ney B-2, 649°C (1200°F) burnout

Casting

°C

Temperature

°F

Castibility

%

s. : %

1038 1900 96 5

1093 2000 81 17

1149 2100 100 00

25
Table

6.

Effect

of

Casting

Temperature

on

Castability

of

Porcelain-Fused-to-Metal

Crown

and

Bridge

Alloys 1 1 1 4-» •H 1 1 1 i—f fa 1 1 1 fa o O CN 00 U0 o CO m co CM fa CO

cd co fa ON 1 rH1

un fa 1 CO fa 1 CM fa VO

Uw 1 1 1 cd cj 111 111 111 O o o 11 o o o 11 o o o 11 in

O

m

fa bn

O U0 o 1 o in o 1 o m o 1 CM uo

cd o CM CO

m CN COm CM com CM CO

0) 1 1 1 faU 1 1 1 aia 1 1 1 3

co f—1

-CT CO 1 rH <r CO 1 1—1

<r co 1 in mT

O il fa rH fa p- 1—1

CT* r-'- CM fa \D o rfa fa CN 11

i—l fa CM 11 I—1

rH CM 11 i—I

fa CN o o o 11 o o o 11 o o O 11 o UO O

>H a- fa UO o m 1 O in o 1 m o in 1 in I-". o

cd

b o ro in v£>

m fa COm r^ co n- 00 o

fa 3 CM CM CN 1 CN CM CM 1 CM CN CM 1 CM CM CO a h 3 1 1 I B co

fa

d 1 1 1 U fa

a) fa 1 1 1 fa Cd CO i—1

rH MT CO fa CN fa o fa cr*

X cd cj CO r~-

m 1 r^ fa co 1 fa CO fa 1 1—1

I-" fa a o CM co CO <r uo co in in uo i—1 i—!

rH 111rH <—i

fa 111 i—i

rH i—i 111 i—i i—irH

fa o 111 o 111 o 111 o 3 E fa o o m in - CD o co z 1 z z 1 I-'- z z 1 z z 3 H CM CN CM CM 3 1 1 1 fa 00d 1 1 1 U fa

4-1 fa o 1 I O 1 o S 111 U M3 rH i—1 i—i

cd o CM 1 CO 1 m 1 in

fa i—1 11

rH 1! i—i 11 i—i o 11 O 11 o 11 fa

fa u~l 1 o 1 in 1 CM

co cd o fa Z z co z z CO z z fa z z 3 4-1 CM 1 CN 1 CM 1 CM

T3 to •H fa 1 1 1 3

cr • 1 1 I •H d

fa fa P- 1 o 1 CO 1 in S fa v£> CO co O t—l 1 CN 1 CM 1 CO i—i 111

rH 111 i—1 111 i—i

So 111 111 111 o 1 1 1 rH

rH

O 1 1 1 <5 O 1 1 fa 1 z z d d 1 O 1 o 1 3 CD fa CM i—! 1 B z z 1 o z z 1 1 z z

<3 a3 fa Pd

fa 1 CJ 1 P3 1 2

26 '
Table

7.

Effect

of

Mold

Temperature

on

Castability

of

Porcelaln-Fused-to-Metal

Crown

and

Bridge

Alloys 1l iI 1I 11

AJ i 1 1 fa 1 fa

fa O' CM rm i '•T vO 1 O fa 1 O r>. JO CM vO 1 fa CM cO vO CM CO vO 3

AJ I 1 1 w 1 3

CJ 1 li 11 11 o o 11 O o l O O 1 o o 1 O

O

T3 fri o o O o o o o o O o

fa o m r^.

m r>. i m 1 m 1 m r*^ o o- fa fa 1 fa fa fa fa fa fa fa fa S S3 I 1 1 • H l DcX I 1 1 W i CJ vd r» vO O r- o M0 © fa CM fa CM I fa CM 1 fa CM 1 fa CM

00 o> 11

CO O' l00 o> 100 ON 1

00 ON

O 1 o lI o - 11 o 11 o o 1 o o in o • O- o CO CO m -a- O £ fa fa I fa 1 fa 1 fa 3 3 1 « H i 1 | o T3 1 l U fa

<fa o >3- l vO 1 00 1 o 2 2 u O 1 o fa CO v£> o 1

r^ l!

00 11 11

r"»

AJ fam 11 O 1 m 1 m 1 O

03 o r>. o 1 CM 1 1 O

<D fa 1 CM CM fa CM U 1 1 1 3 i o=3 f 1 1 c/3 1 a fa m CM fa o o> fa 1 CM 1 o> I fa 11

fa 1

fa 1 1

fa

m 1 o 1 o 1 m 1 O

ha fa CN o 1 m 1 CM 1 m

03

a o CO 1 in r*> CO

AJ 0) CM CM CM CM CM d H 1 1 1 3 1 £ 00

TJ 5 1 1 1 1 3 aj fa o CO

Cu 03 CJ 1 fa I 1 X 03 © CM 1 CO m CM co W CJ fa 1

fa 1 fa 1 fa 1 fa o 1 O 1 o 1 o 1 o

fa o o 1 m 1 o 1 m

Cu o CO 5 <r CO <r ° £ CM CM CM CM CM U 0) 1 1 1 0) H 1 H

00 1 1 1 .* C 1 fa *H fa AJ O vO 1 o 1 o 1 CO 2 to CJ vO 1 fa pH jo 3 0 CM CO m CM CO

CJ fa 1 »H 11fa 11

fa i1pH

O 11 o 1 m 1 o i o

fam o CM uOm o fa CO 1 m 1 fa 1 CM

to 3 CM 1 CM CM CM CM 3 AJ T3 CO 1 1 1 fa Q 1 3

cr . 1 1 1 fa fa 1 ^3 fa o in CM CM 2 CJ n*. \D 1 00 I 00 1 CO w o fa 1 CM co fa CM

fa !

fa 11fa 11fa 11fa 11 11 11 11 >N O 1 o O fa

pH

O 1 1 fa 1 d

r*H Jrf 1 3 o

<c 3 o a 03 3 3 1 CM 1 3 1 fa 1 £ 1 u fa 3 3 Cu 3 3

*o 1 CJ 1 z 1 CJ 1 •n

27
Table 8

Effect of "Melt Soak" Time on Castability

Alloy Soak Time

S Castability

%

S.D.

%

Howmedica A6 60 95 2

90 59 14

Aderer C 60 59 22

90 89 3

Harmony, Hard 60 49 10

90 67 9

Paliney C-B 60 43 13

90 50 12

Midas 60 43 9

90 60 25

Ney-Oro B2 60 41 6

90 63 16

Firmilay 60 — —

90 57 13

Burnout: 482°C (900°F)

Casting Temp: 1079°C (1975°F)

28
Table 9

Effect of Sprue Length on Castability

Howmedica A-6 : 482°C (900°F) burnout

1079°C (1975°F) casting temperature

Sprue Length Castability S.D

6 mm 59 14

12 mm 66 14

Table 10

Castability of 24K Gold

4 min. melt soak time

1107°C (2025°F) casting temperature

Relation of casting time

to on-off cycle of

Castability S.D.

induction melting % %

Random 45.9 15.6

Cast at initiation 62.8 11.4

of on period
Castability of Dental Gold Alloy

Part III

Castability Test

Requirement - The castability of the alloy shall not be less than 0.40 when

tested as described in the method below.

Method - The pattern used for the castability test shall be made from a

section of polyester sieve cloth complying with the dimensional requirements

of ASTM Ell-70 for 1.00 mm sieves with the exception that filament diameter shall

be 0.50 mm. The sieve cloth section (Fig. 5) shall consist of a square of 100

openings. A runner bar made of 6 gage (4.2 mm diameter) round wax shall be waxed

to one edge of the sieve cloth section. The runner bar shall enclose the

sieve filament (or "wire") on one edge of the sieve cloth section but shall not

extend into the openings of the sieve cloth. A 6 gage round sprue 6 mm in length

shall be attached to the center of the runner bar at a right angle to the bar

and in the plane of the sieve cloth section.

The pattern shall be positioned as shown in Fig. 5 in a 32 x 48 mm

ring lined with one layer of wet asbestos and shall be invested using a Type

II investment complying with ANSI/ADA Specification No. 2. The ring shall be

indexed to indicate the pattern orientation. The ring shall be allowed to

set for 30 min in a water bath at 37°C and shall then be removed from the bath

and allowed to set at room temperature and 100% humidity for 16 to 24 hours.

The pattern shall be burned out by heating the ring to 485°C over a period

of one hour and holding at 485°C for one hour.

The casting shall be made using 9.3 g (6 dwt) of alloy in an induction

type centrifugal casting machine at a speed of 400 rpm and with an arm

length of 200 mm from the center of rotation to the far end of the casting

30
ring. The alloy shall be heated to 1080°C, held at this temperature for 60

seconds, the ring transferred to the casting machine with the sieve cloth

mold cavity vertically disposed, and the casting made immediately.

The casting shall be devested using 50 ym alumina in an air abrasive

unit and examined to determine the number of complete segments where a segment

is defined as that part of a sieve filament connecting two adjacent intersection points. A segment shall be considered to be complete if the cross

section is full size over the full distance from intersection to intersection.

Fig. 6. Counting of complete segments shall be done either by examination

of the casting with low power magnification (5 to lOx) or by examination of

photographs or Xerox copies of photographs at this magnification, Fig. 7.

If photographs or copies are used, direct examinations of the casting shall

be made to determine completeness or incompleteness of any segments that cannot

be seen clearly in the photograph or copy.

The castability value is the number of complete segments in the casting

divided by the number of segments in the pattern:

Number of complete cast segments

= castability

210

The reported value shall be the average for a series of five castings.

Verification of Equipment and Procedures - Equipment and procedures to be used

for making castability specimens shall be verified by making castings of 24K

gold. Procedures used for making 24K castings shall be as described in the

method above with the following exceptions: (1) The 24K gold shall be heated

to 1107°C (2025°F) and held at this temperature for 240 seconds before casting.

31
(2) If the induction melting apparatus cycles on and off at the end of

this 240 second period, the casting machine shall be started at the initiation

of an "on" portion of the cycle.

If the average castability value for a series of 5 castings of 24K gold

is not less than 0.40 and not more than 0.90, the equipment and procedures

shall be considered to be satisfactory. If the average castability of the

24K gold specimens is not within this range, details of the equipment and

procedures shall be investigated, particularly burnout and casting temperatures,

and corrected as necessary so that castings within the range of 0.40 to 0.90

are produced.

32
3 2 ->i

Figure 5

.

Ring and invested pattern for castability test. Dimensions in millimeters.

33
Figure 6. Examples of complete (C) and incomplete (I) segments.

34
Segments

:

Vertical

Horizontal

Total

Castability

:

d.3

S S’

LLl

nj_

KJD (>

Figure 7. Example of castability evaluation.

35

NBS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

78-1451 (Defense)

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

Castability of Dental Casting Gold Alloy

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S) 8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No. DSA-120-76-F-BG36

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Defense Personnel Support Center

Philadelphia, PA 19102

13. Type of Report & Period

Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

This report describes a procedure developed for measuring the castability

of dental casting gold alloys and presents a proposed castability requirement

and test method. The report is made up of three parts. Part I, which consists

of the preliminary report prepared in May 1977, describes the procedure for

measuring castability and gives results obtained on four "specification" type

alloys, three of which were suggested by the Defense Personnel Support Center,

and on two alloys of lower noble metal content. Part II contains data on additional alloys including a fourth alloy suggested by the Defense Personnel

Support Center and several alloys for porcelain-fused-to-metal applications.

Also' included in Part II are data on the effects that variations in procedures

and casting conditions have on castability and a discussion of the proposed

castability requirement and test method. Part III consists of the proposed

castability requirement and test method in specification form.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Castability; dental casting alloys; dental materials; gold alloys; test

method for castability.

18. AVAILABILITY j

j Unlimited 19. SECURITY CLASS 21. NO. OF PAGES

(THIS REPORT)

1 1 For Official Distribution. Do Not Release to NTIS

UNCL ASSIFIED

! 1 Order From Sup. of Doc., U.S. Government Printing Office 20. SECURITY CLASS 22. Price

Washington, D.C. 20402. SD Cat. No. 03 (THIS PAGE)

! Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151 UNCLASSIFIED

USCOMM.DC 29042- P74
1

I

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