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Humidity Migration in Surface Layers of Sand Moulds During Processes of Penetration and Drying of Protective Coatings

Jamrozowicz Łukasz, Zych Jerzy

Archives of Foundry Engineering

2022

Vol. 22, iss. 4

72--78

The results of investigations of humidity migration in near surface layers of sand mould during processes of penetration and drying of protective coatings are presented in the hereby paper. The process of the humidity exchanging between surroundings and moulding sands as porous materials, is widely described in the introduction. In addition, the humidity flow through porous materials, with dividing this process into stages in dependence of the humidity movement mechanism, is presented. Next the desorption process, it means the humidity removal from porous materials, was described. Elements of the drying process intensity as well as the water transport mechanisms at natural and artificial drying were explained. The innovative research stands for measuring resistance changes of porous media due to humidity migrations was applied in investigations. Aqueous zirconium coatings of two apparent viscosities 10s and 30s were used. Viscosity was determined by means of the Ford cup of a mesh clearance of 4mm. Coatings were deposited on cores made of the moulding sand containing sand matrix, of a mean grain size dL = 0.25 mm, and phenol-formaldehyde resin. Pairs of electrodes were placed in the core at depths: 2, 3, 4, 5, 8, 12 and 16 mm. Resistance measurements were performed in a continuous way. The course of the humidity migration process in the core surface layer after covering it by protective coating was determined during investigations. Investigations were performed in the room where the air temperature was: T = 22oC but the air humidity was not controlled, as well as in the climatic chamber where the air temperature was: T =35oC and humidity: H = 45%. During the research, it was shown that the process of penetration (sorption) of moisture into the moulding sand is a gradual process and that the moisture penetrates at least 16 mm into the sand. In the case of the drying (desorption) process, moisture from the near-surface layers of the moulding sand dries out much faster than moisture that has penetrated deeper into the sand.

Wysychanie powłok ochronnych nanoszonych na elementy form piaskowych o zróżnicowanym kształcie

Matonis Natalia, Jamrozowicz Łukasz, Zych Jerzy, Snopkiewicz Tomasz

Przegląd Odlewnictwa

2020

Vol. 70, nr 5-6

120--127

W artykule przedstawiono wyniki badań przebiegu procesu suszenia wybranych powłok ochronnych oraz jego kinetykę. Badaniom została poddana alkoholowa powłoka ochronna oraz wodna powłoka ochronna. Powłoki nakładano na powierzchnie „zewnętrzne” i „wewnętrzne” rdzeni przygotowanych z masy ze spoiwem furanowym na osnowie piasku kwarcowego o średniej wielkości ziarna . Na rdzenie nanoszono powłokę o lepkości kinematycznej: v=16 · 10-6 ; v=61 · 10-6 ; v=122 · 10-6 m2 /s; co odpowiada lepkości umownej wynoszącej 10, 20 i 30 sekund. Aby wyznaczyć kinetykę przebiegu procesu wysychania powłok ochronnych zastosowano technikę grawimetryczną. Pomiar szybkości odparowania rozcieńczalnika prowadzono w sposób ciągły i rejestrowano go na bieżąco w komputerze. Pomiary zostały przeprowadzone przy stałych warunkach temperatury (T=24°C) (wilgotności (42%) i ruchu powietrza. W toku prowadzonych badań został wyznaczony przebieg procesu wysychania wodnej i alkoholowej powłoki ochronnej nałożonej na powierzchnie „wewnętrzne” i „zewnętrzne” rdzenia. Ponadto rdzenie poddane badaniom posiadały różne wysokości (3/3 H, 2/3 H i 1/3 H) oraz kształt (kwadratowy, cylindryczny), by zbadać wpływ smukłości i kształtu rdzenia na przebieg i kinetykę procesu suszenia alkoholowego i wodnego pokrycia ochronnego. Co więcej określono czas „całkowitego” wysuszenia dla pierwszej i drugiej warstwy pokrycia i oceniono jakość wysuszonej warstwy powłoki.

Results of investigations of the courses and kinetics of drying processes of the selected protective coatings are presented in the hereby paper. The alcohol protective coating as well as the water protective coating was subjected to inve¬stigations. These coatings were deposited on 'external' and 'internal' surfaces of cores prepared of a moulding sand with a furan binder on the matrix of quartz sand of the average grain size L=0,28 mm. Coatings of a kinematic viscosities: v=16 · 10-6 ; v=61 · 10-6 ; v=122 · 10-6 m2 /s, which corresponds the conventional viscosities being 10,20 and 30 seconds, were deposited on the cores. In order to determine the kinetics of the drying process of protective coatings the gravimetric technique was applied. The evaporation rate of the diluent was continuously measured on -line by the computer. Measurements were performed at constant conditions of a temperature (T=24°C), humidity (42%) and air movement. During the performed tests the courses of drying processes of water and alcohol protective coatings deposited on 'internal'and 'external' surfaces of the core, were determined. In addition, the cores subjected to investigations had various heights (3/3 H, 2/3 H and 1/3 H) and shapes (square, cylindrical), to enable testing the influence of slenderness and shape of the core on the course and kinetics of the drying process of alcohol and water protective coatings. What's more, the time of 'complete' drying of the first and the second layer of the coating was determined and the quality of dried coating layers was assessed.