Accuracy Of Castings Research Articles

Dimensional accuracy of small gold alloy castings. Part 2. Gold alloy shrinkage

The extensive literature about the casting shrinkage of gold alloys is reviewed.

Dimensional accuracy of small gold alloy castings. Part 1. A brief history and the behaviour of inlay waxes

Part 1 reviews published studies which relate to materials and techniques contributing to the dimensional accuracy of small dental castings. A brief history of the cire perdue or lost-wax method of casting alloys and the development of modern dental casting materials and techniques are presented. Data on the behaviour of inlay wax, in particular its contraction and distortion, are reviewed as is the extensive literature about the casting shrinkage of gold alloys (Part 2) and the setting and thermal expansion of investments under both laboratory and practical conditions (Part 3). Part 4 discusses the role of the casting ring and its asbestos liner. Asbestos as a liner has now largely been replaced by two alternative materials, one based on cellulose and the other on ceramic fibres. The limited literature on the effect of these newer materials on casting accuracy is also reviewed, as their introduction may require significant changes in the traditional technology of dental casting.

Casting accuracy and shrinkage of titanium castings made with zirconia investments

To obtain inlay, crown and bridge types of titanium castings with sufficient size accuracy, zirconia investments with 10 mol % calcia were studied for their setting expansion, thermal expansion, total expansion, casting shrinkage compensation deficiency on fabrication method, particle size of zirconia, calcia and mixing liquid. Addition of calcia caused the change from contraction to expansion in setting and the additional thermal expansion at 900-1,200 degrees C. The choice of calcia and mixing liquid makes great influence on setting expansion, which is grouped into saturation type and delayed expansion type. By the use of the saturation type, total expansion could be controlled in the range of -2-(+)3%. Titanium castings of inlay, crown, bridge types with the values -2-(+)2% of casting shrinkage compensation deficiency could be successfully obtained. The casting shrinkage of titanium was estimated as 1.8-2%. The castings have the surface with a metallic brilliance as cast.

The Influence of Processing Variables on the Dimensional Integrity of Spheroidal-graphite Iron Castings

This investigation was carried out to identify the major factors and their degree of influence on the dimensional accuracy of spheroidal-graphite iron castings produced in chemically- bonded sand m...

Setting expansion of investment and accuracy of castings

Setting expansion of 4 phosphate-bonded investments was measured under 3 different conditions: a hygroscopic condition, a condition using a ring lined with a wet liner and a condition using a ring lined with a dry liner. Accuracy of castings of a Ni−Cr alloy made in each of the 4 investments in rings lined with a wet liner was measured. One investment exhibited negative potential for hygroscopic expansion. Expansion of all investments in wet-lined rings was not significantly different from their expansion under the hygroscopic condition. There was no significant difference in setting expansion between the investments when a wet liner was used. Significant differences in accuracy existed between castings produced in the different investments using a wet liner. The correlation between the setting expansion of the investments using a wet liner and the accuracy of castings produced using a wet liner was not high and was not significant. Comparison between investments with regard to their ability to produce accurate castings in terms of mould expansion by measurement of setting expansion is of no value.

Accuracy of one-piece castings, preceramic and postceramic soldering

An investigation was conducted to evaluate the relative accuracy of one-piece castings of FPDs of three, four, and five units with those assembled by preceramic soldering and postceramic soldering. The preceramic soldered FPDs were subjected to six simulated porcelain firing cycles to assure a homogeneous sample. A total of 15 FPDs, five of each length, were evaluated for each test condition. A three-piece aluminum mold with stainless steel dies, which allowed for varying the length of the prosthesis, was used to fabricate the FPDs in 52% gold-palladium alloy. Marginal discrepancies of the castings on the dies were compared for the three test techniques. The mesiodistal length of the FPDs that were pre- and postsoldered were also measured at the occlusal and at the gingival margins and compared with the restorations before soldering.

Comparison of accuracy of multiunit one-piece castings

An investigation was conducted to evaluate the accuracy of one-piece castings of FPDs consisting of three, four, and five units with a ceramometal alloy cast in a large circular ring. A three-piece aluminum mold with stainless steel dies simulating the various lengths of the FPDs was used. A total of 18 castings, six castings for each FPD, were fabricated. Marginal discrepancies of the castings on the dies and the length of the castings were compared before and after sectioning the castings at the connectors. The following conclusions were drawn from the study. Seating of the castings improved approximately 50% after sectioning, which indicates that the castings were distorted. The distortion was a three-dimensional phenomenon, with the greatest discrepancy on the mesiogingival surface of the anterior retainer and on the distolingual surface of the posterior retainer. The distortion was least for the three-unit FPDs and greatest for the five-unit FPDs. The lingual-facial diameter of the castings at the gingival axial line angle was significantly larger than the dies in most cases. The mesiodistal diameter of the castings at the gingival axial line angle was smaller than that of the dies but was only significant with the three-unit FPDs. Although the castings were slightly oversized or undersized, the primary reason the castings did not seat was warpage.

Expansion of the Phosphate-bonded Investment and Preciseness of the Casting : Part 2 Effects on Dimensional Accuracy and Fit of Ni-Cr Alloy Castings

Expansion of the Phosphate-bonded Investment and Preciseness of the Casting : Part 2 Effects on Dimensional Accuracy and Fit of Ni-Cr Alloy Castings

Effect of casting methods on accuracy of peridental restorations

The present study has shown that the accuracy of peridental gold alloy castings depends 1) on the type of casting machine used, 2) on the diameter of the casting sprue, and 3) on the strength properties of the investment material. The dependence between the accuracy and the three factors mentioned is based on erosion of the investment mold by the inflow of the liquid casting alloy. The vacuum casting technique proved to be a more gentle casting method than centrifugal and vacuum/pressure techniques.

Accuracy of Small Base Metal Dental Castings

Abstract : The obvious and important advantage of low cost offered by the test base metal alloys is countered by their inadequate casting accuracy. Until this problem can be overcome, the acceptance of such alloys for routine use in military dental practice is not warranted. (Author)

The accuracy of castings produced by various investments

A total of 232 castings were made, and each investment material was used eight times for the three different types of restorations. The manufacturers' directions I Average measurements of the different groups of castings MOD Class I Full crown Product Mean (mm.) S.D. (mm.) Mean (mm.) S.D. (mm.) Mean (mm.) S.D. (mm.) Shiny Brite Cristobalite 0.07 ±0.004 0.14 ±0.014 0.10 ±0.05 Beauty Cast 900 °F. 0.06 ±0.011 0.13 ±0.043 0.00 ±0.00 R & R No. 1 0.08 ±0.017 0.15 ±0.017 0.05 ±0.03 Cristobalite and Control Powder 0.09 +0.011 0.14 +0.017 0.05 +0.07 Whip Mix Cristobalite 0.07 ±0.007 −0.13 ±0.017 0.05 ±0.08 Hygrotrol 0.04 ±0.014 −0.10 ±0.038 0.25 ±0.05 R & R Gray Investment 0.05 ±0.010 1.01 ±0.110 0.20 ±0.05 Beauty Cast 0.06 ±0.015 ∗ ∗ 0.25 ±0.05 Baker's Scientific Investment 0.06 ±0.007 0.06 ±0.026 1.60 ±0.40 Healey's Perfected Investment 0.04 +0.010 0.07 ±0.048 † † ∗ No measurements because all castings were finned. † No specific directions for full crowns. were followed. Although only nine investments were used, ten different casting techniques were followed, because both hygroscopic and high heat techniques were used with the Beauty Cast investment. In Class I inlays (Table I), Whip Mix Cristobalite and Hygrotrol produced only slightly undersized castings (−0.1 mm.). The remaining castings were only slightly oversized except those made with Gray Investment, which were oversized by an average of 1.0 mm. To check the results of Beauty Cast 1,200 °F. investment, an additional four castings were made, and they too were finned, as were the initial eight castings. The MOD castings were all found to be slightly undersized by a few hundredths of a millimeter. Whether or not they would be clinical failures cannot be stated. Beauty Cast 900 °F. investment provided sufficient expansion to produce full crown castings which seated completely in all eight samples. However, the crowns from Beauty Cast 1,200 °F. investment did not seat by an average of 0.2 mm. Shiny Brite Cristobalite, R & R No. 1, Cristobalite and Control Powder, and Whip Mix Cristobalite produced castings which seated completely in six out of eight samples. Although excellent results were obtained with Baker's Scientific Investment for inlays, the same was not so for full crowns, which did not seat by an average of 1.6 mm. Thermocouples placed in the investment molds compared to a thermocouple in the furnace demonstrated that mold temperatures and furnace temperatures may differ as much as 250 °F. Burnout time for a 1,200 °F. investment mold may be over an hour and fifteen minutes to insure proper mold temperature for adequate expansion.

Influence of investments and duplicating procedures on the accuracy of partial denture castings

The total compensating expansion of several partial denture casting investments was determined by a new method that allowed the casting of a partial denture framework on the specimen being evaluated. The accuracy of the resulting casting was then compared to the total compensating expansion of the investment used to make the casting. The effects of changing duplicating materials, soaking refractory casts in water, applying the paint-on layer and outer layer of investment on casting accuracy were determined. Also, the compressive strength at the casting temperature of several investments was determined in an effort to correlate the strength of investments with the accuracy of casting.

精密鋳造品の寸法精度について(最新の鋳造技術)

精密鋳造品の寸法精度について(最新の鋳造技術)

The Accuracy of Large Castings

The Accuracy of Large Castings

Medium batch die casting

This paper deals with die casting from the design and production viewpoints. The general sequence of operations is described. Shrinkage allowance, venting, elimination of porosity, and the use of inserts are among the factors considered. The discussion includes references to the maximum casting weight and number of shots per hour, the materials used for die cores and castings, the effect of shrinkage stresses between casting and die, the dimensional accuracy of castings, ejection of castings from the die, and the problem of small quantity die casting.

Medium batch die casting

This paper deals with die casting from the design and production viewpoints. The general sequence of operations is described. Shrinkage allowance, venting, elimination of porosity, and the use of inserts are among the factors considered. The discussion includes references to the maximum casting weight and number of shots per hour, the materials used for die cores and castings, the effect of shrinkage stresses between casting and die, the dimensional accuracy of castings, ejection of castings from the die, and the problem of small quantity die casting.