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Containment
Ring Problem
Inventive Problem Solving Case Study
NOTE: Click
here for a detailed case study of
this problem using the Innovation WorkBench (IWB) software.
STEP
1. DOCUMENT THE PROBLEM SITUATION
The containment ring is part
of a fan used in an aircraft air conditioning system. This ring is
designed to hold fragments of the fan in case the fan should burst. The
ring must be strong and, as a result, is thick and heavy.
The problem is to reduce the weight of the containment ring. However,
reducing the ring's weight reduces its strength to an unacceptable degree.
The high rotational speed of the fan
creates centrifugal forces that can cause the fan to break. Should this
occur, the fan fragments (some of which may be relatively large) are
propelled away at high speed. These fragments can destroy surrounding
equipment and injure anyone nearby.
Primary Useful Function: The Primary
Useful Function of the containment ring is to prevent the fragments
produced by an impeller burst from flying away.
| Drawback:
A thin containment ring is light, but cannot stop the flying
fragments. A thick containment ring prevents fragments of the fan
from flying away, but is also heavy. |
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STEP 2. FORMULATE
THE PROBLEM
The Problem Formulator model describing the
containment ring problem is shown below. Note that this problem contains
two contradictions, making it difficult to solve:
- The high rotational speed of the fan
provides air movement, but also causes the centrifugal forces that
pull apart the impeller.
- The thickness of the ring provides the
ring’s strength, but also results in the ring being heavy.
The Problem Formulator™
automatically creates Directions for Innovation from the model,
among which are included the following:
- Find a way to eliminate, reduce or
prevent the (Ring is very heavy), under the condition of the (Ring is
very thick).
- Find an alternative way to obtain the
(Ring is very thick), that provides or enhances the (Ring is very
strong), and does not cause the (Ring is very heavy).
- Find an alternative way to obtain the
(Ring is very strong), that provides or enhances the (Ring holds
fragments), and does not require the (Ring is very thick).
- Find a way to eliminate, reduce or
prevent the (Impeller bursts), under the condition of the (Centrifugal
forces pull impeller parts) and (Material not strong enough).
- Find an alternative way to obtain the
(Fan moves air), that provides or enhances the (Air conditioning
inside aircraft), and does not require the (Fan rotates quickly).
The above Directions are divided into three
categories, as shown below.
Category 1 – Directions important
for solving the problem. These Directions are directly related to
resolving the main problem: reducing the weight of the containment ring:
- Find a way to eliminate, reduce or
prevent the (Ring is very heavy), under the condition of the (Ring is
very thick).
- Find an alternative way to obtain the
(Ring is very thick), that provides or enhances the (Ring is very
strong), and does not cause the (Ring is very heavy).
- Find an alternative way to obtain the
(Ring is very strong), that provides or enhances the (Ring holds
fragments), and does not require the (Ring is very thick).
Category 2 – Directions important
for improving the system. This Direction is not directly related
to reducing the weight of the containment ring. However, it would result
in improving the system to the extent that the containment ring becomes
unnecessary—and a containment ring that is not present weighs nothing.
Thus, improving the system can indirectly resolve the problem.
- Find a way to eliminate, reduce or
prevent the (Impeller bursts), under the condition of the (Centrifugal
forces pull impeller parts) and (Material not strong enough).
Category 3 – Directions too
general to be considered. This Direction pertains to completely
substituting the entire system (i.e., the rotating fan) with a system
based on some other principle of operation. Such a Direction is not of
interest to a company that produces fans, and thus it is considered
"out of scope" in terms of solving the problem of reducing the
weight of the containment ring.
- Find an alternative way to obtain the
(Fan moves air), that provides or enhances the (Air conditioning
inside aircraft), and does not require the (Fan rotates quickly).
The following Direction is considered:
- Find a way to eliminate, reduce or
prevent the (Ring is very heavy), under the condition of the (Ring is
very thick).
The "map" below illustrates the
procedure for selecting the Operators by which the above
Direction can be carried out. Options available at each step are arranged
in columns. The selection made is shown in blue. Each selection leads to
the column to the immediate right. The right-most column contains the
Operators – the two selected Operators are described in detail following
the map.
Operator: "Abandon
Symmetry"
Recommendation: If an object is
symmetrical, consider reducing its weight by abandoning the symmetry.
Consider, for example, excluding a part of the object that does not bear
the main load.
Illustration: Designing
asymmetrical mounts
| For
aesthetic reasons, motor and generator mounts are often designed
with symmetrical shapes. But because the machines rotate, the load
on the mounts is actually asymmetrical.
To reduce the weight and conserve
material, mounts for non-reversible units should be designed to
support only the loads they must actually bear.
|
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Ideas Generated:
- Vary the thickness of the ring, reducing
the thickness where permissible.
Operator:
"Strengthen Individual Parts"
Recommendation: Consider
strengthening those parts that bear the main load, and also reducing the
weight of the parts that do not bear the main load.
Illustration: Pump housing made
of standard pipe
The housing of a high pressure pump, made
from a steel casting, was complicated in shape. Since cavities and uneven
surfaces were frequently found in the casting (necessitating repairs made
by welding), a very thick, heavy casting was used.
The defects were eliminated, and the weight
reduced by nearly half, when the housing was fabricated by welding several
pieces together. High-strength rolled pipe was used for the section that
was required to withstand the greatest pressure.
Ideas Generated:
- Make a multi-layer ring
- Add "ribs" to a thin ring
STEP 4. DEVELOP
CONCEPTS
From the above ideas, the following
concepts are developed:
| Concept
#1: Make the ring thin, but composed of several circular ribs.
These ribs can significantly increase the strength of the ring with
a less significant increase in mass. |
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| Concept #2: Make a
multi-layer ring as described by the following:
Internal layer made of a
thin steel ring
Intermediate layer to absorb
the energy of the fragments, made of:
- radial brush
- balls
- honeycomb
External layer to hold the
fragments, made of:
- steel pipe
- coil
- textile or wire needles
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Concept #1 requires the following
for implementation:
- calculations of strength and weight
- redesign of one part (the ring itself)
- additional manufacturing operations
(making the ribs)
All resources for producing such a ring
exist.
Concept #2 requires the following
for implementation:
- research to determine what type of
intermediate layer is best
- calculations of strength and mass
- redesign of the containment ring as an
assembly unit
- changes in the materials used
- changes in the manufacturing process
- testing of the new design
As it happens, all materials suggested for
this design are already used in the manufacturing processes of producing
the aircraft; thus, all the required resources exist.
A comparison of these two concepts shows
that:
- Concept # 1 is easier to implement
quickly; however, it achieves a limited reduction in mass.
- Concept # 2 promises a more significant
reduction in mass, but requires more time for implementation.
The implementations of Concepts # 1 and # 2
can be planned in the following manner:
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Concept # 1
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Concept # 2
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| calculate
strength and mass of thin ring with ribs |
|
test strength
of several types of intermediate layers |
| create design
of ring with optimal strength and mass |
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calculate
several variants of intermediate layers |
| produce rings
with new design for testing |
|
create
designs of ring with different intermediate layers |
| test rings
with ribs |
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produce rings
with different intermediate layers |
| correct
design according to results of test |
|
test rings
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| correct
manufacturing process for producing rings with new design |
|
correct
design according to results of test |
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start producing rings
with ribs
|
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correct
design according to requirements of mass production |
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|
create
manufacturing process for mass production of multi-layer containment
ring |
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produce rings
for testing |
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test rings |
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|
correct
design according to results of tests |
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correct
manufacturing process |
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start
producing multi-layer rings |
Problem which can appear during the
implementation of Concept #1:
Additional manufacturing operations (for
example, machining ribs from thick pipe or stamping and welding ribs onto
thin pipe) increases labor and cost.
This is a typical secondary problem;
Operators from the group "Reducing cost" can help to solve this
problem.
(END OF CASE STUDY)
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