Multiple Pouring Research Articles

X-ray computed tomography reveals special casting techniques used with unusual bronze objects unearthed from the Sanxingdui site

Scholars in a wide range of disciplines are interested in the casting techniques used to create the extraordinary bronze objects unearthed from the two pits of the Sanxingdui site. Although researchers have carried out a number of studies on this topic, many technical details remain unclear. This paper offers the first examination of bronze objects from the Sanxingdui site using industrial computed tomography (CT) and provides direct evidence for interpretation of the complicated casting process involved. We show that multiple pouring and various joining techniques were widely used during the casting of bronze objects from the Sanxingdui pits. The precast parts were mechanically connected with one another by the later pouring, which was the crucial technique for the casting of complicated objects. Representative features include the cast-on cramp device of the sun-shaped objects and the tenon connection with dowel found inside many branches of the bronze trees. This paper also describes evidence of core rods made of different materials, which is the earliest example of this technique in ancient China.

Reliability of Multiple Pour between Two Classes of Polyvinyl Siloxane Impression Materials

Objective: To evaluate the accuracy and dimensional stability of casts made from regular set alginate alternative (AA) and monophase additional silicone (MAS) impression materials following multiple pours. Materials and Methods: A hard typodont master cast with index holes was used. A total of 20 impressions were made using a modified perforated metal tray with 10 impressions of each material. Each impression was poured four times with type IV die stone with a total of 80 stone casts (40 for each material). The horizontal anterior–posterior (HAP), horizontal cross-arch (HCA), and vertical distances were measured in the recovered stone casts using a stereomicroscope with an accuracy of 0.001 mm. The obtained data were statistically analyzed using two-way analysis of variance and Tukey's HSD post hoc test (P < 0.05). Results: The dimensions on the typodont master cast and stone casts were significantly different (P < 0.001), except for the first pour from MAS (P > 0.05). There was a statistically significant difference in the dimensions of the stone casts made from the AA and MAS impression materials among the four pour groups (P < 0.001), with exception of MAS-based casts between first pour and second pour groups at HAP and HCA dimensions. Pairwise comparisons showed statistically significant difference between the two impression materials at all measurement locations, with only one exception of HAP measurements for second-poured casts. Conclusion: A clinically acceptable casts can be made by pouring AA and MAS impressions twice. In addition, the third and fourth pours were accurate in the AA group when compared to MAS group. Clinical Significance: According the knowledge of the authors, this study is the first to evaluate the predictability of re-pouring alginate alternative impression material and compare to a standard polyvinyl siloxane impression material such as monophase. Therefore, the statement of clinical significance in the abstract will help the dentists to realize the potential uses for alginate alternative impression material and recommendations of this study.

Reliability of Repour of Varying Thickness Alginate Impression Following Extended Storage Time Intervals

Background: Obtaining multiple casts from an impression is desirable for the completion of numerous procedures for a patient. Recent literature on newly introduced extended-pour alginates reveals promising results for delayed pouring. However, literature on multiple pouring of impressions and the effects of impression thickness and storage time is not available. Subjects and Methods: Conventional and extended-pour alginates of various thicknesses (2, 4, and 6 mm) were evaluated for linear dimensional changes in both the intra-abutment and inter-abutment distances. Casts were poured twice with the time difference between the pours being 45 min; the storage time, however, was varied (15 min, 1 h, and 1, 3, and 7 days). The intra-abutment and inter-abutment measurements were compared with those of the standard metal die. Results: Compared with that of the metal die, the casts poured with 6 mm thickness of the impression material showed better accuracy between the first and the second pours and also revealed smaller statistical differences. Further, Cavex performed better than Major and GC brands. Conclusions: The dimensional stability of different alginate materials vary with thickness, storage time, and multiple pouring in both conventional and extended-pour alginates. Shorter storage time and greater thickness of the impression material are preferred when the same impression has to be poured twice. Clinical Significance: Alginate impressions can be poured twice, if made in adequate thickness and stored for short storage time, to generate additional set of accurate casts that aid in documentation, diagnostic and treatment procedures.

Effect of multiple pouring on the accuracy of casts made using 3D-printed custom trays with different spacer thicknesses: A research study.

Background. This study aimed to evaluate the effect of different pouring times and spacer thicknesses on the three-dimensional accuracy of casts made of 3D-printed custom trays. Methods. A partial edentulous maxillary model was scanned for fabricating custom acrylic trays. Twenty custom trays were created using a CAD/CAM system and divided into two groups in terms of their spacer thicknesses (2 mm and 4 mm). All the trays were designed with 2-mm thickness, multiple retentive holes measuring 2 mm in diameter, and three interior seating stops (two on the edentulous ridge and one on the incisal edge of the central incisors). Impressions were made using monophasic polyvinyl siloxane and poured in two different times (one hour and 24 hours after removal) with type IV dental stone. All the casts were scanned to measure three distances (inter-buccal cusps, inter-palatal cusps, and inter-fossa distances) between the two first premolars. The data were analyzed with two-way ANOVA and Bonferroni test at a significance level of 0.05. Results. There was no significant difference between the 3D accuracy of casts made using two different spacer thicknesses poured at 1-hour and 24-hour intervals. However, there was a difference between casts made after 1 hour and 24 hours when using custom trays with 2 mm of spacer thickness in terms of inter-buccal distance. Conclusion. There was no significant difference between the accuracy of casts made using custom trays with either 2 or 4 mm of spacer thickness, which were poured 1 hour or 24 hours after tray removal.

A Numerical Study of the Effect of Multiple Pouring on Macrosegregation in a 438-Ton Steel Ingot

In present paper, a ladle–tundish–mold CFD model and a macrosegregation model were utilized to investigate the effects of the multiple pouring (MP) process on the macrosegregation in a 438-ton steel ingot. Firstly, the model was partially proved as compared to the measured carbon distributions along the transverse sections in the riser of ingot. Then, the comparison between the single pouring (SP) and MP process has been carried out to study their influences on the macrosegregation in ingot. Besides, the predicted macrosegregation results in MP process which introduced the improved riser fixed with an insulating sleeve were compared with that in traditional MP process. The traditional MP process leads to certain favorable initial carbon distribution in the mold, which has some favorable influence on suppressing the positive segregation in ingot. The holding time of the low carbon in the riser is the main factor to suppress the positive segregation in ingot. Improved insulating sleeve can prolong the holding time of the low carbon in the riser and release the positive segregation in the riser of ingot. Improvement of the insulating effect of the riser is an efficient method to control macrosegregation in large steel ingot.

Numerical study of macrosegregation in a large steel ingot with multiple pouring process

Multiple pouring (MP) process with a higher concentration in the beginning and a lower concentration at the last is generally utilized to reduce macrosegregation in the large steel ingot production. However, it is insufficient to demonstrate the practical efficiency of MP process from the point view of theory. In this paper, the whole filling and solidification processes were investigated to analyzethe formation of macrosegregation in a large steel ingot. Firstly, a filling transportation model considering the entire MP process was presented. The carbon concentration variation through the outlet of the tundishat different times was predicted and provided as the boundary conditions for the moldfilling and the solidification processes simulation. Secondly, the macrosegregation model was integrated into the filling transportation model to investigate the influence of the MP on the macrosegregation in the ingot through the comparison of the MP and the single pouring process (SP). Finally, the top section of a 438-t steel ingot was cut off and the carbon concentration was measured to validate the numerical results. The results indicated that the MP process has a certain favorableeffect on reducing the positive segregation in the top region of the ingot.

Modeling of Species Transport and Macrosegregation in Heavy Steel Ingots

In the current study, two significant phenomena involved in heavy steel ingot casting, i.e., species transport and macrosegregation, were numerically simulated. First, a ladle–tundish–mold species transport model describing the entire multiple pouring process of heavy steel ingots was proposed. Carbon distribution and variation in both the tundish and the mold of a 292-ton steel ingot were predicted. Results indicate high carbon concentration in the bottom of the mold while low concentration carbon at the top of mold after the pouring process. Such concentration distribution helps in reducing both negative segregation in the bottom of the solidified ingot and positive segregation at the top. Second, a two-phase multiscale macrosegregation model was used to simulate the solidification process of industrial steel ingots. This model takes into account heat transfer, fluid flow, solute transport, and equiaxed grain motion on a system scale, as well as grain nucleation and growth on a microscopic scale. The model was first used to analyze a three-dimensional industry-scale steel ingot as a benchmark. Then, it was applied to study macrosegregation formation in a 53-ton steel ingot. Macrosegregation predicted by the numerical model was presented and compared with experimental measurements. Typical macrosegregation patterns in heavy steel ingots are found to be well reproduced with the two-phase model.

Dimensional Accuracy of Stone Casts Obtained with Multiple Pours into the Same Mold

Aim. The aim of the present study was to compare the dimensional accuracy of stone casts obtained with vinyl polysiloxane molds through the double-impression technique with three pours into the same mold. Methods. A stainless steel master model was constructed simulating a three-unit fixed prosthesis. Twelve impressions were taken of this master model with addition silicone, using the double-impression technique. Three pours of type IV gypsum were then made into each mold, thus producing 36 casts. The pours were made 1 hour, 6 hours and 24 hours after the impression procedure. Next, intra- and interabutment measurements were made in a coordinate measuring machine. Results. Comparative analysis of the dimensional accuracy of stone casts resulting from multiple pours was not statistically significant in pours first and second (P > 0.05). These values, however, were statistically significant at third pour in the height in abutment 1 and upper distance interabutment. Conclusion. The wait time (1 hour, and 6 hours) observed before pouring the stone into the same molds did not cause significant dimensional accuracy of the casts.

Elastomeric Impression Materials: A Comparison of Accuracy of Multiple Pours

The aim of the present study is to compare the various elastomeric impression materials in terms of accuracy and dimensional stability, with respect to obtaining multiple casts from a single elastomeric impression at various times of pours. Three master dies were prepared for the impression making, two of these were made of brass containing a central hole with undercuts. The third die simulated a conventionally prepared typodont maxillary central incisor. Three elastomeric impression materials were chosen for the study. Each impression was poured at various time periods. Casts thus obtained were evaluated under a traveling microscope to evaluate various dimensional changes. Addition silicones provided dies which were shorter in height and bigger in diameter. Polyethers provided dies which were shorter in both height and diameter. Condensation silicones showed insignificant changes from the master die at the immediate pour but deteriorated rapidly after that in subsequent pours. None of the impression material showed a consistent behavior up to the fourth pour. They occasionally showed deviation from the pattern, but all these values were statistically insignificant. Polyethers showed lesser ability than both the addition silicones as well as the condensation silicones to recover from induced deformation. Addition silicones as well as the condensation silicones have better ability to recover from induced deformation when compared to polyether.

Shear Stiffness and Strength of Horizontal Construction Joints

This paper presents test results of unreinforced concrete construction joints subjected to in-plane shear forces. The main aim of the study was to determine whether concrete foundations cast in multiple pours with horizontal construction joints could offer the same initial (uncracked) stiffness of those cast monolithically. The experimental program included 36 push-off shear units as well as 6 slab specimens. The study included several methods to bond fresh to hardened concrete and considered both technical and practical aspects related to the preparation, casting, and curing procedures of the joints. Based on test results, it is concluded that members with a properly prepared and moist-cured joint offer the same initial stiffness as that of a member cast monolithically. Recommendations concerning the preparation, curing, and casting procedures to achieve a proper performance of the joint are provided.

Dimensional Accuracy of Dental Casts: Influence of Tray Material Selection and Multiple Pours at Varying Elapsed Times after Impression Making

Dimensional Accuracy of Dental Casts: Influence of Tray Material Selection and Multiple Pours at Varying Elapsed Times after Impression Making