Segmental Pattern In Casting: Diagrams, Definition, Application, Advantages & Disadvantages

Segmental Pattern In Casting

Segmental Pattern Sand Casting

A sweep pattern is used to produce circular axisymmetrical castings such as kettles and decorative bells which have height and thickness. But when there is a need for producing casting with lesser thickness such as rings and rims segmental pattern is used in the sand casting process.

I have discussed the segmental pattern in the casting below with diagrams, applications, advantages and disadvantages.

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What is the segmental pattern in casting and what it is used for?

A segmental pattern can be defined as a pattern used to make circular or round castings such as gear blanks, rims, rings and wheels with a segment of wood or metal instead of using a solid pattern in the casting process.

The segmental pattern consists of a spindle that stands in the mould and supports the rotation of the segmental pattern with the help of a pivot or stake as shown in diagram (a) below.

(a) Segmental Pattern In Casting

This pattern has a design where the axis of the spindle is the centre of the circular casting. This pattern is rotated in the mould in segments to make the mould cavity shown below in diagram (b).

(b) Segmental Pattern Mould Cavity

Molten metal is poured into the mould cavity to make sand casting such as rims shown below in diagram (c).

(c) Segmental Pattern Casting

The steps required to make a mould cavity for sand casting using a segmental pattern are as follows:

• Step 1 - The spindle is fixed at the bottom of the drag in the centre of the flask.
  
• Step 2 - Sand is poured until a level where a pattern cavity is to be made.
• Step 3 - The wooden pattern is attached to the spindle.
• Step 4 - Sand is rammed as the pattern is rotated and the mould cavity is formed in segments. This step is repeated until the formation of a complete impression/cavity in the sand.
  
• Step 5 - The pattern is taken out once the circular mould cavity is formed in sand.
• Step 6 - Molten metal is then poured into the mould cavity.
• Step 7 - Molten metal is allowed to solidify and final casting is taken out of the sand mould. 

What material is used to make a segmental pattern in casting?

Wood is preferred for making patterns but metal and plastic are also used depending on application and volume of production in a foundry.

What is the difference between a segmental pattern and a sweep pattern?

The main difference between a segmental pattern and a sweep pattern is that in the segmental pattern mould cavity is made in segments, but if we use a sweep pattern mould cavity is made in one single sweep.

Using a sweep pattern complete 360° rotation of the pattern is done at one time in one sweep while in the segmental pattern, the cavity is produced incrementally which is a time-consuming process to create an impression in the sand mould.

Both segmental and sweep pattern are used to cast circular components in the sand-casting process in the foundry.

Segmental Pattern Advantages

The merits of using a segmental pattern in the casting process are as follows:

• Pattern material is not wasted as only a pattern segment is used in the process.
• Pattern-making is simple but mould-making is complicated.
• Best for simple design circular shape casting having a common axis.
• Cost-effective method for generating circular casting using a non-solid pattern.
• This pattern does not use full pattern-saving pattern material.
• Very large-size thin casting can be produced as compared to sweep patterns.
• Casting products such as pulleys produced by this pattern cannot be produced by any other pattern.
• This pattern produces more accurate casting than the sweep pattern.
• The pattern is more lightweight than other types of patterns used for producing large casting.
• Handling and assembly of pattern is easy and more convenient than other patterns such as gated pattern, match plate pattern and cope & drag pattern.
• Delicate casting can be produced using this pattern it is difficult to produce by sweep pattern.

Segmental Pattern Disadvantage

The demerits of using the segmental pattern in the casting process are as follows:

• Non-circular round casting cannot be produced.
• Not suitable for complex products having a higher thickness.
• Making cavities in the mould is time-consuming as sand needs to be rammed in segments as the pattern moves forward.
• Dimensional stability is to be taken care of as the mould is not made in one sweep but in segments.
• Hollow casting cannot be produced using this pattern.
• There is a limitation on the thickness of the casting produced by this pattern.
• Operator skills and experience count in producing defect-free casting as the operator needs to pour sand and rotate the pattern.
• Need machining allowance on the pattern because the process is to remove any difference in dimension caused by rotating the spindle and ramming the sand.
• Wearing this pattern is more than a sweep pattern.
• The operator needs to use physical strength to rotate the pattern if sand is rammed hard it becomes difficult to pivot the pattern.

 Segmental Pattern Application

Segmental patterns are used for producing circular casting and examples of them are as follows:

• Rims.
• External tooth gears.
• Rings.
• Wheels.
• Pulleys.
• Motor body.
• Gear blanks.
• Circular and round casting products.

Segmental Pattern In Casting MCQ (Multiple Choice Question & Answer) / Quizz

1) Which of the following pattern are used for producing castings such as rim and rings?

a) Follow board pattern.
b) Segmental pattern.
c) Sweep pattern.
d) Loose piece pattern.

Answer - b) Segmental pattern in the manufacturing process produces casting with lesser thickness as compared to sweep pattern in the casting process.

 

2) While using a segmental pattern sand is poured in increments moving the pattern in segments. Is this statement about patterns true or false?

a) True
b) False

Answer - a) True, this pattern is called segmental because the pattern in circulated and rotated about a common pivot point as sand is poured incrementally as we rotate the pattern ahead.

 

3) Segmental pattern is another form of which pattern?

a) Split pattern.
b) Lagged up pattern.
c) Sweep pattern.
d) Boxed-up pattern.

Answer - c) Segmental pattern is another form of sweep pattern in casting.

 

4) Where is the pattern fixed and rotated while using this pattern?

a) Upper moulding box.
b) Lower moulding box.
c) Middle box.
d) None of the above locations.

Answer - b) This pattern is supported by mounting it to the base means a lower moulding box is used in the casting process.

 

5) Both segmental and sweep pattern has the same design but what is the major difference while producing casting? 

a) Mould impressions are produced by an operator who rotates the pattern.
b) These pattern requires a highly trained and skilled operator.
c) In a sweep pattern, the pattern is swept in one go to produce casting and here mould is produced incrementally and the pattern is rotated accordingly.
d) All of the above statements.

Answer - c) Options (a) and (b) are common for both patterns while option (c) is the major difference between both patterns as mould making process is different for both patterns.

Segmental Pattern In Casting Conclusion

The segmental pattern is one of the patterns among 17 types of pattern in casting.

(d) Segmental Pattern

A segmental pattern in sand casting as shown above in diagram (d) is used to produce circular and round structures using a segment of the pattern instead of an entire solid pattern.

This casting remains in the cope section of the mould only when split mould boxes are used. At times only one mould box is used such as drag when making casting using this pattern.

Both segmental and sweep patterns have the same mechanism for producing impressions in the mould with differences in the mould-making process. In this process, sand is poured in segments as we rotate the pattern around the pivot having a supporting base.

This pattern is also called part pattern as the cavity is made in parts for producing round casting with low thickness but casting larger in size.