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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

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2022

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Vol. 22, iss. 4

72--78

EN

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.

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Tynki renowacyjne

Siemiński W., Brachaczek W.

Materiały Budowlane

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2013

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nr 6

52--56

EN

The article concerns the subject of effectiveness of refinishing plaster. Complex damp-proofing in already existing buildings is one of the most difficult and expensive actions. Such works are connected with interference with the building substance, therefore they are accompanied by noise and dirt, which makes them bothersome, especially when they take place in inhabited buildings. There are situations, when complex damp-proofing is impossible due to technical or economical reasons. In such cases there is the need to partly renovate the building by using only refinishing plaster. The evaluation of effectiveness of efinishing plaster functioning in such situations is the subject of this paper. 7 buildings have been selected for analysis. 2 objects were fully renovated, 2 – partially, and in the case of the remaining ones only refinishing plaster was applied. The results showed that in the beginning the level of moisture content did not vary from the one set for the walls of buildings in which complex renovation took place. Functionality of refinishing plaster on the walls which were partially renovated will only be effective in the beginning. However, as soon as the pores of refinishing plaster are filled with crystallizing salts, the layer will lose its hydrophobic properties and it will no longer constitute an effective solution against aggressive action of salt.

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Migracja soli rozpuszczalnych w otynkowanych, murowanych ścianach obiektów poddanych długotrwałemu zawilgoceniu

Kamiński K.

Materiały Budowlane

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2011

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nr 3

33-34

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Modelowanie procesów przepływowych w przegrodach budowlanych przy zachodzącej kondensacji pary wodnej

Świrska J.

Zeszyty Naukowe. Budownictwo / Politechnika Opolska

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2002

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z. 46

227-239

PL

W pracy wyprowadzono, na podstawie równań bilansowych termodynamiki ośrodków wieloskładnikowych, równania opisujące przepływ ciepła i migrację wilgoci w przegrodach budowlanych przy uwzględnieniu zjawiska kondensacji pary wodnej.

EN

In the presented paper the equaiions describing of heat transfer and hurnidity migration in building envelopes with taking into account a phenomenon of water vapour condensation were derived. The starting point of above considerations is the set of balance equations of thermodynamics multicomponent media.