ТОР 5 статей:
Answer the following questions.
1) What is the text D about?
2) What forms of facing do you know?
3) Where and when is the facing material applied?
4) Why is the facing material applied?
Read Text E. Translate it.
Molding materials may be classified into some groups: molding sand, bonding material, facing and some others.
Molding sands may be light, medium and heavy. Light sand is used for castings which may have very finely produced detail on their surfaces. The sand should be very fine to bring out this detail. It must be strong so that the mold could retain every detail as the metal flows in.
Medium sand is used for making machinery castings having from ½ to 2 in. sections. The molding sand for this type of castings is coarser than those molded in light sand. The bond mixed with medium sand must be sufficiently strong to retain the shape of the mold. The large proportion of clay necessary for a strong bond makes the sand less porous. For the better sand porosity the sand of larger grain size is to be used.
Heavy sand is used for very large iron and steel castings. This sand is high in silica, and its grain is coarse to withstand the heat of the molten metal and the better porosity.
light sand – тощая земля
medium sand – полужирная земля
heavy sand – жирная земля
to bring out – выполнять
to retain – сохранять
in. = inch – дюйм
section – сечение
grain – зерно, крупица
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