PSI - Issue 71

Sameer S. Gajmal et al. / Procedia Structural Integrity 71 (2025) 430–437

436

Table 7 – Average Solid Shrinkage of Conventional Cast Specimens

Shrinkage along Diameter

Conventional Cast Specimen

Dia. as per drawing (mm)

Dia. of cast specimen (mm)

Position

% Shrinkage

Top

17.00

16.36

3.76

Middle

16.75

16.08

4.00

Bottom

16.50

15.90

3.64

Overall Average % Shrinkage along diameter

3.80%

Table 8 – Summary of the Solid Shrinkage Measurements Specimens

Remark

Avg. % shrinkage along dia.

Microwave Cast Specimens Conventional cast Specimens

2.86 % 3.80 %

Solid shrinkage is 32.88 % more in conventional castings

4.2 Porosity Fraction Analysis The casting defect, porosity was examined using an X-Ray Microscopy and the results are summarized in Table 9. The cast porosity was evaluated using ASTM B276 standard. The porosity fraction was found to be 0.43 % in microwave cast specimen. It was observed that the porosity is less than those of conventional castings. Preheating of the graphite mould is responsible for the decrease in porosity. At normal temperature, graphite is a good microwave absorber. Here, the process of irradiation causes microwave absorption, which causes the temperature to rise quickly. Also, low porosity is due to slow solidification rate because of low temperature gradient between the molten metal and mould wall. As a result, the cast's gas porosity and shrinkage porosity decrease as gases escape and molten metal fills the pores under the pressure of incoming molten metal. In Four-Dimensional X-ray microscope, the density of specimen is not measured directly. The density is measured by comparing the X-ray absorption pattern of the specimen with the X-ray absorption pattern of known (standard) material. Specimen with high density will absorb more X-rays and accordingly the densities of microwave and conventional cast specimens are measured using Four Dimensional X-ray microscope and mentioned in Table 9. Table9- Result of XRM XRM Result Microwave Conventional Remarks Minimum density 34534 2079 Density of microwave specimens is more Maximum density 60906 33636 Mean density 38442.8 31518.2 Porosity fraction 0.552286 % 0.984184 % Porosity is 78% less in microwave casting samples

Microwave casting samples shows 78% reduced porosity as compared to conventional Casting Specimens. [ 0.9841844-0.552286 0.552286 ] x 100=78 %

5. Conclusion Pin castings of tin-based Babbitt alloy were developed using a microwave furnace operating at a frequency of 2.45 GHz. The charge was melted using graphite mould and a microwave hybrid heating process. The process of pouring and solidification took place inside the microwave environment. In comparison to conventional specimens, the