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At least 19 recordsLinked to original sources
PubMed2004

Development of casting investment preventing blackening of noble metal alloys part 3. Effect of reducing agent addition on the strength and expansion of the investments.

Different reducing agents (B, Al, Si and Ti) were individually added to two gypsum-bonded investments to prepare investments preventing surface blackening of some noble cast alloys. The effect of different additive contents on green-body and burnout compressive strength, setting and thermal expansion of the investments were evaluated. The strength and expansion of the investments were changed by the additives. The compressive strength of Al-, Si- and Ti-added investments decreased with the increase of additive contents. The burnout strength of B-added investments significantly increased while green-body strength remained unchanged. The setting expansion of the B-added investments increased while those of the Al-, Si- and Ti-added investments decreased with the increase of additive contents. The thermal expansion of the Si- and Ti-added investments decreased, and that of the Al- and B-added investments remained unchanged. Further study is necessary to evaluate the effects of these additives on the accuracy of dental castings.

Aluminum↗
PubMed1995

The effect of potential investment expansion and hot strength on the fit of full-crown castings made with a gypsum-bonded investment.

OBJECTIVES: It has been claimed that the strength of the investment mold at the casting temperature affects the dimensional accuracy of castings (e.g., Markley, 1953; Earnshaw, 1957; Asgar, 1972), but the relationship has not been studied quantitatively. In this investigation, the effects of both mold expansion and hot strength on the relative inaccuracy of full-crown castings have been measured and analyzed. The likelihood that a strong investment could cause distortion of the casting by non-uniform restriction of casting shrinkage (Earnshaw, 1969b) was also considered. METHODS: Castings were made with a commercial gypsum-bonded inlay investment, used both as supplied and with modifications that increased its expansion and reduced its hot strength. In both series of tests, the investments were used over a wide range of liquid/powder (L/P) ratios in casting rings fitted with dry ceramic liners, and set under dry conditions. RESULTS: Casting inaccuracy showed a significant linear correlation with total expansion and a highly significant linear correlation with the combination of total expansion and hot strength. The modified investment, with its low hot strength, gave less distortion of casting shape than did the much stronger unmodified material. However, it was found that to ensure sound castings, the hot compressive strength should not be less than 1.8MPa. SIGNIFICANCE: This investigation showed that while investment expansion is the major variable affecting casting inaccuracy, hot strength is an important modifying factor which also has to be considered when predicting casting inaccuracy from measured properties of the investment.

Calcium Sulfate↗
PubMed1997

The effect of potential investment expansion and hot strength on the fit of full crown castings made with phosphate-bonded investment.

In an earlier investigation, it was shown that when full crowns are cast in gypsum-bonded investments, their relative inaccuracy is affected by both the investment's potential expansion and its hot strength. This study repeated the earlier one, but used a high-melting gold alloy and two phosphate-bonded investments. The investments were used under conditions which gave a range of potential expansions and hot strengths. Casting inaccuracies were determined both diametrally and axially. All castings showed distortion, which varied under the different conditions. All were oversized axially, by amounts varying from + 0.8% to +2.3%. Diametral inaccuracies ranged from -0.2% to +0.7%. Investment expansion had a strong effect on axial inaccuracy, but a negligible effect on diametral inaccuracy. Conversely, hot strength had a strong effect on diametral inaccuracy, but only a very weak effect on axial inaccuracy. With phosphate-bonded investments, both potential expansion and hot strength are important parameters of relative casting inaccuracy. In combination, these properties showed very strong correlations with both diametral and axial inaccuracies. The observed distortions were the result of anisotropic mould expansion and anisotropic alloy shrinkage. The best fit, and least distortion, occurred with an investment setting under dry conditions.

Analysis of Variance↗
PubMed2002

Study of resin-bonded calcia investment: part 2. Effect of titanium content on the dimensional change of the investment.

In the present study, titanium powder was chosen as an expanding agent of an experimentally prepared resin-bonded calcia investment. The effect of Ti content on the dimensional change was investigated. In addition, the effects of the heating rate and heating temperature on the dimensional change of the investment were investigated during setting and after heating. The expansion increased with Ti content and the highest expansion (1.57%+/-0.58) was obtained at 10 mass% Ti. The highest expansion was obtained at 900 degrees C for 30 min heating and was independent of the heating rate. These findings mean that the titanium powder in the calcia investment oxidized sufficiently at that heating condition. It was found that the developed resin-bonded calcia investment was able to compensate for casting shrinkage of pure titanium by adding some Ti powder to the investment.

Algorithms↗
PubMed2003

Development of casting investment preventing blackening of noble metal alloys part 1. Application of developed investment for Ag-Pd-Cu-Au alloy.

The objective of this study is to develop a casting investment that prevents the blackening of the cast surface of noble metal alloys. The experimental investments were prepared using a gypsum-bonded investment in which the metallic powders such as boron (B), silicon (Si), aluminum (Al) and titanium (Ti) were added as oxidizing agents. An Ag-Pd-Cu-Au alloy was cast into the mold made of the prepared investment. The effect of the addition of each metal powder was evaluated from the color difference between the as-cast surface and the polished surface of the cast specimen. The color of the as-cast surface approached that of the polished surface with increasing B and Al content. A lower mean value in the color difference was obtained at 0.25-1.00 mass% B content. B and Al are useful as an additive in a gypsum-bonded investment to prevent the blackening of an Ag-Pd-Cu-Au alloy. The effects of Si and Ti powder addition could not be found.

Aluminum↗
PubMed2003

Development of casting investment preventing blackening of noble metal alloys Part 2. Application of developed investment for type 4 gold alloy.

The objective of this study was to evaluate the efficacy of the developed investment for the prevention of blackening of a cast Type 4 gold and to analyze the oxides on its surface in relation to the blackening of the alloy. The experimental investments were prepared using a gypsum-bonded investment in which boron (B) or aluminum (Al) was added as a reducing agent. A Type 4 gold alloy was cast into the mold made of the prepared investment. The effect of the additives was evaluated from the color difference (deltaE*) between the as-cast surface and the polished surface of the cast specimen. B and Al were effective to prevent the blackening of a Type 4 gold alloy and the color of the as-cast surface approached that of the polished surface with increasing B and Al content. The prevention of the blackening of the gold alloy can be achieved by restraining the formation of CuO.

Aluminum↗
PubMed2004

Gypsum-bonded investment and dental precision casting (III) Composition of investment for the quick casting technique.

A simultaneous differential thermal analysis and thermogravimetry method previously established was used to estimate the composition of gypsum-bonded investment marketed for the quick casting technique. Three commercial investments of this type were heated to 700 degrees C at 10 degrees C/min and the hemihydrate content was estimated by the mass decrease reached at 300 degrees C after subtracting the mass decrease at 100 degrees C as moisture content. The hemihydrate contents were between 25% and 30%, which appears to be the range also chosen for the conventional gypsum-bonded investment of cristobalite type over 70 years by the industry. However, the new type of investment contained both cristobalite and quartz. The small sample size is a disadvantage of the present method but this can be overcome by more frequent use of the method by investigators.

Calcium Sulfate↗
PubMed2003

Gypsum-bonded investment and dental precision casting (II) investment for the quick casting technique.

Part I of this study presented a hypothesis that the thermal expansion of gypsum-bonded investment should become higher under heating conditions favorable for the formation of ahemihydrate. The present study aimed at proving this hypothesis by simulating the rapid heating condition employed in the quick casting technique. The expansion values obtained were 1.72-1.93% after 30 min in three investments, two rapid heating and one conventional types. Under a comparable measuring pressure a common laboratory measurement (5 degrees C/min) gave significantly lower expansions of 1.32-1.36% at 700 degrees C for the same investments (p<0.01). The shrinkage observed at 350-400 degrees C in this measurement was not observed in the rapid heating. Realistically large molds prepared from the conventional gypsum-bonded investment need to be investigated for their potentially high thermal expansion.

Calcium Sulfate↗
PubMed2003

Gypsum-bonded investment and dental precision casting (I) two investments.

The present study compared the TE of two gypsum-bonded dental casting investments, the oldest K and more recent G. They had almost identical composition, 70% refractory (cristobalite) and 30% binder, but had different recommended water/powder ratios, 0.40 (K) and 0.33 (G). The average TE was significantly less (1.19%) in K than in G (1.45%); the volume decrease accompanied by the phase change of gypsum was more pronounced in the less dense K. When the dehydration conditions around gypsum are similar to those prevailing in wet calcinations methods, an expansion is likely to occur in the mold due to the formation of dental stone by recrystallization. This additional expansion has not been detected in ordinary laboratory measurement but can effectively increase the actual TE of an investment. The present study has proved the formation of dental stone by rapid heating of an investment. Specific laboratory techniques may have been supplementing low TE by this mechanism.

Calcium Sulfate↗
PubMed1980

[The effect of vacuum vibration investing and vacuum mixing on the properties of "LAW-Modellguss investment" and the fit of cast structures from cobalt-chromium-molybdenum alloys. 1. Technologic-experimental tests].

Using materials-scientific test methods, the author studied the effect of vacuum mixing and vibration on the setting and the thermal expansion and contraction behaviour of the investment compound "LAW-Modellgusseinbettmasse" as well as on its hardness and structure after setting. The results obtained show that vacuum processing may considerably improve the properties which are of importance in model casting.

Chromium↗
PubMed1999

Self-resolution of alcohol problems as a process of investing and re-investing in self.

Resolution of alcohol problems without formal treatment or participation in support groups was studied using a grounded theory approach. Thirteen former problem drinkers and their close associates were interviewed, and verbatim transcripts were analyzed using grounded theory methods. The core of self-resolving alcohol problems involves investing and/or reinvesting in self to gain or regain the essence of who or what one wants to be. Self-resolvers tend to independently change for their own benefit rather than the benefit of others, and personal resources may promote or delay the process. The effort required to self-resolve drinking problems varies, and close associates tend to be minority investors in the process. Input from health-care providers regarding the health-related hazards of drinking are largely ignored because threats to who or what one wants to be are perceived as more significant. As such, clinical interventions should emphasize personally relevant threats to self versus focusing solely on the physical consequences of alcohol abuse.

Adaptation, Psychological↗
PubMed2004

Manifesto for sustainable investment: investing for a sustainable future.

Environmental, labor, and non-governmental organizations in Europe are waging a campaign for sustainable investment to hold members of the European Union to their pledges to work for sustainable development and sustainable societies. The comment explains how to achieve sustainability by taking action at many levels of society.

Journal Article↗