Металл и литье Украины (Jan 2020)
Some features of drying casting forms and cores in the field of standing waves of microwave radiation
Abstract
The article discusses some of the features of drying sand-liquid glass foundry molds and cores in the region of standing waves of microwave radiation of low power (700–1200 W) with a frequency of 2450 MHz and a wavelength of 122.5 mm. It has been established that convective-thermal drying at 90–100 °C of a sand-liquid glass mixture provides casting molds/ cores with high strength and gas permeability, low crumbling. At the same time, drying by microwave radiation of low power of the same mixture dramatically reduces the strength and gas permeability and increases its crumbling. Drying by microwave radiation of the mixture in the foundry tool does not completely remove moisture from it. Moreover, the nature of the distribution of residual moisture along the mold/core does not depend on the duration of its treatment with microwave radiation in the foundry tool, the power of the magnetron and the frequency of rotation of the table of the microwave oven. According to the results of irrelevant heating and evaporation of water in the working space of the microwave oven, it was found that in the group of simultaneously heated water samples of different weights, but of the same geometric dimensions and equally spaced from the axis of rotation of the microwave oven table, the duration of water evaporation will be almost the same. For similar water samples of the same mass, under the same conditions, the duration of water evaporation will differ by ± (4–16) %, which is explained by the difference in the initial position of the samples in relation to the distribution of standing waves in the working space of the microwave oven. That is, the initial position of the hanging on the table in the region of the standing waves of the microwave oven is one of the main factors that determines the duration of heating and evaporation of water from them. An increase in the power of the magnetron of the microwave oven from 700 to 1200 W increases the uniformity of the duration of the evaporation of water from the samples, reducing this time difference from 16 % at a power of a magnetron of 700 W to 3.6 % at a power of a magnetron of 1200 W.
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