ТОР 5 статей:
Using information given in Text B andswer the following questions.
1) What materials are used for producing dry-sand molds?
2) How are usually dried dry-sand molds?
3) What is the temperature of ovens for drying these molds?
4) What flasks do dry-sand molds require?
5) In what cases are dry-sand molds recommended?
12. What terms are defined below?
a) to remove all moisture from the mold;
b) the property of sand to pass through gases and steam;
c) to put two halves of the mold together in finishing operation;
d) the sand with large amount of water.
Compare green-sand and dry-sand models using the following questions and the information given in Texts A and B.
1) What molds (green-sand or dry-sand molds) are stronger?
2) What molds have harder surface?
3) What molds may produce smoother surface of the casting? Why?
4) Which molds are softer?
5) Which molds require higher permeability?
6) What molds are more expensive?
Read Text C and name how many molds and what types of molds are given in the text.
Skin dried molds can be constructed economically by one of two methods. By the first method, silica sand is mixed with a dry-sand bond. The mixture is packed around the pattern to a depth of about ½ or 1 inch. Them the mold surface is dried by heat. When this part of the mold is dried, the remaining portion of the mold is completed with green sand.
By the second method the entire mold is constructed of green sand. Certain binders are added to this sand, and a stronger, harder surface is produced. The mold is then dried by air, oven or gas torch.
Air-dried molds remain open to the air for a certain period of time before closing. Some moisture escapes from the mold surfaces, making the mold harder. Large molds, such as pit molds, become air-dried while they are being made. Additional drying by heating may be done to remove any remaining moisture, and they would then become dry-sand molds.
depth – глубина
to remain – оставаться
to complete – завершать, заканчивать
certain – определенный
to add – добавлять, дополнять
additional – добавочный, дополнительный
while – в то время как
pit – яма.
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