Casting Questions and Answers – Function of pattern

1. Which of the following is not a part of the pattern at most times?

  1. Mould cavity
  2. Cope
  3. Molten metal
  4. Core

Answer.3. Molten metal

Explanation

Casting is one of the important manufacturing processes in which the starting material is heated sufficiently to transform it into a liquid state. Such molten metal is poured into the mold cavity and allowed to solidify. The object after solidification is taken out from the mold. To manufacture a wide variety of products of desired shape and size. The department of the workshop where castings are produced is known as a foundry. The requirements of producing a casting are:

(1) Preparation of a pattern (replica of the desired casting).

(2) Preparation of mold or cavity with the help of pattern.

(3) Melting the metal.

(4) Pouring the molten metal into the mold.

(5) Allowing the molten metal to solidify.

(6) Breaking the mold to retrieve the casting then its cleaning and inspection etc.

The quality of casting and the final product will be affected to a great extent by the planning of the pattern maker. The important considerations of a pattern maker to properly plan the pattern for the desired results are:

(i) Appearance and surface finish of the casting to be produced;

(ii) Number of castings to be produced;

(iii) Metal to be cast;

(iv) Method of withdrawal of pattern;

(v) Size and shape of the casting to be produced.

Note:- Metal used in casting is a concern till its melted and molted metals fill the cavity. This does not affect the final product physically, once the metal has solidified. Hence molten metal is not a part of the pattern at most times.

 

2. The function of a gated pattern is ______

  1. To produce small castings in mass production
  2. To create castings of a very heavy mass
  3. To create castings containing complex design
  4. To create symmetrical castings

Answer.1. To produce small castings in mass production

Explanation:-

Gated pattern:- To produce a good casting, it is necessary to ensure that molten metal flows into every part of the mold. Provision of the easy passage of the flowing metal into the mold is called gating which cannot be made by hand operations for high volume production because of the time involved. In a gated pattern, a group of patterns is attached with gates and runners to facilitate the easy flow of molten metal. Times spend for cutting the gates and runners are eliminated by this arrangement. Gated patterns are used for the production of small castings on a mass scale.

 

3. From the following two statements select the correct statement

Statement 1:- Gate pattern consists of metal to form the runner

Statement 2:- Metal eliminate wrapping tendency in gate pattern

  1. Statement 1 is true but statement 2 is false
  2. Statement 2 is true but statement 1 is false
  3. Both statements are false
  4. Both statements are true

Answer.4. Both statements are true

Explanation

The gated pattern is used for the mass production of small castings. When a number of small patterns are placed in a single mold, then each pattern may be provided with a gate. It consists of pieces of wood or metal fixed to the patterns to form the runner and rising channels in the mold. In this way, a full supply of the molten metal flows into every part of the mold. The gated pattern eliminates the hand-cutting of gates and thus makes the molding easy. Such patterns are made of metal to give strength and to eliminate any warping tendency.

 

4.  The type of pattern selected  for a particular casting depends upon

  1. Shape and size of casting
  2. Number of casting required
  3. Method of modulation
  4. All of the above

Answer.4. All of the above

Explanation:-

The type of pattern selected for a particular casting will depend upon several conditions viz.:

(i) The shape and size of the casting.

(ii) Number of castings required.

(iii) Method of molding employed.

(iv) Anticipated ease or difficulty of the molding operation.

If the pattern is required for producing only a few castings, it should be constructed in the cheapest possible way. Similarly, when the casting is of simple and regular shape the corresponding pattern may also be identical and in single-piece. If the casting, on the other hand, is of intricate nature involving changes in section, the pattern may be made in the number of pieces involving the use of additional loose pieces, if necessary.

 

5. If the casting surface doesn’t require the finishing operation then it is indicated by the

  1. Black Color
  2. White Color
  3. Grey Color
  4. Any of the above

Answer.1. Black Color

Explanation:-

The surfaces of the casting that do not require any finishing operation. That is, the surfaces which are to be left as the cast are indicated by the black color on the pattern.

 

6. Which color in the pattern indicated when the surface is required to be machined

  1. Black
  2. Red
  3. Green
  4. White

Answer.2. Red

The pattern surface is painted with red color on all the surfaces which require to be machined.

 

7. From the following two statements select the correct statement

Statement 1:- There is no universally accepted color code for patterns

Statement 2:- Loose core prints are indicated by yellow color

  1. Both statements -1 and statement – 2 are true and statement – 2 is the correct explanation of statement – 1
  2. Both statements -1 and statement – 2 are true but a statement – 2 is not the correct explanation of statement – 1
  3. Statement -1 is true and statement – 2 is false
  4. Statement -1 is false and statement – 2 is true

Answer.2. Both statements -1 and statement – 2 are true but a statement – 2 is not the correct explanation of statement – 1

Explanation:-

Though there is no universally accepted color code for patterns, some pattern makers employ the following color code on patterns:

(i) Clear i.e. without any color on the pattern. The parting surfaces of a split pattern are left uncoated.

(ii) Black:- The surfaces of the casting that do not require any finishing operation. That is, the surfaces which are to be left as the cast are indicated by the black color on the pattern.

(iii) Red:- The pattern surface is painted with red color on all the surfaces which require to be machined.

(iv) Yellow:- Core prints and seats for loose core prints are indicated by the yellow color on the pattern.

(v) Red Strips on Yellow Background:- Red strips on a yellow background on the pattern surface indicate seat for loose pieces.

 

8. Which of the following is the function of the pattern?

  1. Pattern makes a mold cavity
  2. Pattern contains core print
  3. Pattern help in positioning the core
  4. All of the above

Answer.4. All of the above

Explanation:-

A pattern serves the following functions.

(i) A properly manufactured pattern having a good surface finish reduces casting defects.

(ii) Properly constructed patterns reduce the overall cost of casting.

(iii) A pattern makes a mold cavity to be used as a casting.

(iv) Risers, runners, and gates may form a part of the pattern.

(v) A pattern may contain core prints for placing the cores in the proper position.

(vi) A pattern helps in establishing a parting line between the cope and drug part of the mold.

(vii) A pattern helps in positioning the core at its proper position.

 

9. Holes, cavities, projection on external surface is achieved under

  1. Pattern Making
  2. Machining
  3. Casting
  4. Shrinkage

Answer.3. Casting

Explanation:-

Casting is sometimes required to be made hollow internally or having few holes, cavities, projections, undercuts, or pockets on its external surface. This is achieved by using cores during casting or by subsequent machining of the casting. Usually, the large hollows in the castings are achieved by cores. Contours of the core are exactly similar to the cavities, pockets, or holes it is supposed to create in the casting.

The use of cores thus helps in eliminating much of machining (drilling, boring) to make a hole or cavity in the castings. Cores also give strength to the mold. Cores are made from special core sands.

(a) The casting (to be made) is a pipe with the flange on either end.

(b) With two additional end-projections, called core prints, which during molding help in making ‘impressions’ or cavities in the sand to support the core in the mold (with its extended length at its either end).

 

10. What is a function of a riser in sand casting?

  1. Provide good mobility to the molten metal
  2. Prevent cavities due to shrinkage
  3. To develop holes or hollow cavities in the casting
  4. To provide differential cooling rates in specific areas of the casting

Answer.2. Prevent cavities due to shrinkage

Explanation:-

A riser, also known as a feeder, is a reservoir built into a metal casting mold to prevent cavities due to shrinkage. Most metals are less dense as a liquid than as a solid so castings shrink upon cooling, which can leave a void at the last point to solidify.

The principal reason for using a riser is to furnish molten metal to compensate for the solidification of the casting during the transformation from a liquid state to a solid state. In addition, a riser eliminates the hydraulic- ram effect (similar to the water ”pound” when a valve is closed suddenly) when the mold is full, helps to flow off cold metal, and vents the mold.

At the time the mold is completely filled with molten metal, there may be a sudden and large increase in pressure in the mold because of the motion of the flowing metal. This added pressure may be enough to cause a runout or may cause a deformed casting.

A riser permits the molten metal to flow into the mold cavity evenly instead of coming to a sudden stop. Therefore, the riser reduces the pressure (hydraulic-ram effect) which may cause a deformed casting.

When casting is poured, the permeability of the sand may not be capable of permitting air and other mold gases to escape fast enough. A riser open to the atmosphere provides an easy escape from the produced gases.

In addition, an open riser permits the Molder to see how rapidly the mold is being filled and provides a means of regulating the flow of molten metal.

During the casting process, the riser is a reservoir of molten metal attached to the casting from which the casting draws reserve metal during solidification to compensate for the internal shrinkage and contraction. If reservoirs of reserve molten metal are not available, voids or shrink cavities will develop within the casting. The use of risers to feed the casting during solidification is designed to prevent this type of shrinkage from developing.

 

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