Pattern and corebox



What is the difference between pattern and corebox?


The term pattern generally refers to a form that serves as model or guide from
which to produce a mold used in casting an object or part.

In pump terminology a pattern is a form used to produce a mold from which to
cast a pump part – casing, cover, impeller, bearing housing, etc. Normally the
term pattern applies to the entire part - inside and out. Thus a pattern for bearing
housing will refer to the whole bearing housing – to both its external and internal
shape and dimensions.

In pump hydraulic terminology, pattern makers and foundry personnel make a
distinction between the outer portion of a part and its inner portion or
wetted
surface
– the surface that is in direct contact with the pumped liquid. The “pattern”
that defines the outer or external portion of a part is referred to as
pattern, and the
“pattern” that defines the inner portion or wetted surface is referred to as
corebox.

Single stage pump

For example, in single stage, end suction pump, the term case pattern refers to
the “pattern” that defines the outside of the casing, and the term
corebox  refers to
the “pattern” that defines the inside of the casing. The corebox that represents the
volute inside the casing is called
volute corebox.

Multistage pump

In multistage pump where the liquid passageway is more complex the entire
corebox is divided into sections called suction corebox, first stage volute corebox,
crossover corebox, series stage volute corebox, discharge corebox, etc.

Setting apart a pattern from a corebox is important because a design change can
be made either to the pattern, or to the corebox, depending on the specific reason
for the change. Changes for mechanical reasons (such as increasing the case
thickness to increase the casing pressure rating, or adding a boss for external
piping connection) are usually applied to the pattern, whereas changes for
hydraulic reasons (such as changing the pump specific speed, or suction specific
speed) are usually applied to the corebox.
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What are the advantages of wood pattern over fiberglass
pattern, and vice-versa?

A wood pattern is easier and cheaper to make. It can be made in segments and it
offers flexibility such as when setting up the patterns for horizontal multistage
pumps since the segments can be stacked together to the required number of
stages to avoid the need to make separate patterns for each of the different
stages. A wooden pattern made primarily to cast common materials, such as cast
iron or carbon steel, can also be shimmed to increase its length to compensate
for the increased shrinkage when the pattern is used to cast high shrinkage
metals such as stainless steel, or duplex stainless steel.

The main disadvantage of wood patterns is that they are easy to wear and tear. By
one estimate of a major foundry a wooden pattern can become dilapidated after
about two dozens of use, and may require replacement not long after that.

Fiberglass or synthetic material

On the other hand, fiberglass pattern, or that made of similar synthetic material, is
harder and more expensive to make. But it withstand better to wear and tear, and
can be used many times over than a comparable wooden pattern. Although it is
more expensive to make initially, it is cheaper in the long run because its initial
cost can be spread over many casting jobs, and its maintenance and repair costs
are cheaper.

The main disadvantage of a pattern made of fiberglass, or of other similar
synthetic material, is that it does not provide the same flexibility as the wood
pattern. In multistage pumps separate patterns are usually made for each of the
different stage configurations of the pumps.


R: PAAN-0511
C: design, manufacturing
F: patterns

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