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When a pattern is to be withdrawn from the mould, it is first shaken, by striking over it from side to side, so that its surface may be free of the adjoining sand wall of the mould. That causes the size of the mould cavity increases a little and a negative allowance is to be provided in the pattern to compensate the same, is known as:

When a pattern is to be withdrawn from the mould, it is first shaken, by striking over it from side to side, so that its surface may be free of the adjoining sand wall of the mould. That causes the size of the mould cavity increases a little and a negative allowance is to be provided in the pattern to compensate the same, is known as: Correct Answer Rapping allowance

Explanation:

Rapping Allowance: 

  • Before the withdrawal from the sand mold, the pattern is rapped all around the vertical faces to enlarge the mold cavity slightly, which facilitate its removal. Since it enlarges the final casting made, it is desirable that the original pattern dimension should be reduced to account for this increase. 
  • It is a negative allowance and is to be applied only to those dimensions that are parallel to the parting plane. The importance of this is high in large castings, for small castings, it can be ignored. 

Shrinkage or Contraction Allowance: 

  • All most cast metals shrink or contract volumetrically on cooling.
  • The metal shrinkage is of two types. In solidification of metal during casting, compensation for solid contraction is (shrinkage allowance) is provided by the oversize pattern. 

Draft or Taper Allowance: 

  • By draft is meant the taper provided by the pattern maker on all vertical surfaces of the pattern so that it can be removed from the sand without tearing away the sides of the sand mould and without excessive rapping by the moulder.

Machining or Finish Allowance: 

  • The finish and accuracy achieved in sand casting are generally poor and therefore when the casting is functionally required to be of good surface finish or dimensionally accurate, it is generally achieved by subsequent machining.
  • Machining or finish allowances are therefore added in the pattern dimension.

Related Questions

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The Alaskan pipeline ends
Read the passage carefully and choose the best answer to each question out of the four alternatives and click the button corresponding to it. The Alaska pipeline starts at the frozen edge of the Arctic Ocean. It stretches southward across the largest and northernmost state in the United States, ending at a remote ice-free seaport village nearly 800 miles from where it begins. It is massive in size and extremely complicated to operate. The steel pipe crosses windswept plains and endless miles of delicate tundra that tops the frozen ground. It weaves through crooked canyons, climbs sheer mountains, plunges over rocky crags, makes its way through thick forests, and passes over or under hundreds of rivers and streams. The pipe is 4 feet in diameter, and up to 2 million barrels (or 84 million gallons) of crude oil can be pumped through it daily. Resting on H-shaped steel racks called "bents", long sections of the pipeline follow a zigzag course high above the frozen earth. Other long sections drop out of sight beneath spongy or rocky ground and return to the surface later on. The pattern of the pipeline's up-and-down route is determined by the often harsh demands of the arctic and subarctic climate, the tortuous lay of the land, and the varied compositions of soil, rock, or permafrost (permanently frozen ground). A little more than half of the pipeline is elevated above the ground. The remainder is buried anywhere from 3 to 12 feet, depending largely upon the type of terrain and the properties of the soil. One of the largest in the world, the pipeline cost approximately $8 billion and is by far the biggest and most expensive construction project ever undertaken by private industry. In fact, no single business could raise that much money, so 8 major oil companies formed a consortium in order to share the costs. Each company controlled oil rights to particular shares of land in the oil fields and paid into the pipeline-construction fund according to the size of its holdings. Today, despite enormous problems of climate, supply shortage, equipment breakdowns, labour disagreements, treacherous terrain, a certain amount of mismanagement, and even theft, the Alaska pipeline has been completed and is operating.
What is the capacity of the Alaskan pipeline?
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How was the fund for pipeline - construction generated?
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