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COMPETITION
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CROSBY
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PROCESS IS IMPORTANT
The material used in a forged fitting, such as carbon or alloy steel, determines
the potential properties. The manufacturing processes determine what the properties
will actually be. The material must be special bar forging quality steel
and fine grained. The heating of steel to forging temperature must be properly
controlled to insure that the steel is not injured by overheating. Proper
forging equipment and techniques must be employed to assure proper material flow
in the dies and tooling. The heat treatment process must be well defined and
precisely controlled. |
Ask: What processes
do they consider important?
Ask: How do they select their material?
Ask: Is the steel fine grained?
Ask: Are standards established to insure sufficient cleanliness
of the steel? |
Crosbys attention to material
selection, forging techniques, machining, and heat treatment processes assures the
properties required will be attained, thus providing superior performance of the
product. Crosby has specific and demanding cleanliness requirements.
Crosby provides a video on metallurgy that highlights these facts. |
TENSILE STRENGTH AND DUCTILITY
The mechanical properties that are important when lifting a load under normal conditions
are tensile strength and ductility. The ability to carry a load increases
with the tensile (pulling) strength of the steel. The ability of steel to
deform in an overload condition is known as its ductility. Both of these factors
enter greatly into determining the working load limit of a forging. Ductility
is measured by standard engineering tests of elongation and reduction of area.
It is also measured by how much deformation the fitting incurs when overloaded.
The tensile strength determines the actual working load, while ductility allows
the product to deform significantly when overloaded, thus giving warning before
ultimate failure. |
Ask: Do they have
an active program to determine tensile and ductility properties?
Ask: Are testing audits performed continuously on all products?
Ask: Is the actual deformation of a fitting when overloaded a major
consideration for their shackles? |
Crosby has an active program to
determine tensile and ductility properties. Testing audits are continuously
performed on all products. Crosbys design philosophy considers the deformation
of a fitting when loading is a key requirement. |
FATIGUE PROPERTIES
The mechanical properties of steel when a load is repeatedly applied is known as
its fatigue strength. Fatigue testing determines the ability of a material
to withstand repeated applications of a load. The load by itself may be too
small to produce a failure. There are three factors involved when considering
fatigue strength. They are: the number of cycles at which a crack initiates,
the number of cycles at which the crack starts to grow, and the number of cycles
at which the fitting fails. One accepted method of fatigue rating fittings
is to test them to 1 times the working load limit for 20,000 cycles, without failure.
This standard test is accepted as indicating indefinite life when used within the
working load limit under normal circumstances. |
Ask: Does the
material selection process recognize fatigue properties?
Ask: Do they have an active program to design in and test fatigue
properties?
Ask: Is there
a program in place to fatigue rate all load bearing products that are used in critical
applications?
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Crosby has an active program to
determine fatigue properties. Included in this program is the use of finite
element design methods to predict possible weak areas, which in turn allows
us to design in superior fatigue properties. Crosby specifies material of
specific cleanliness and guaranteed hardenability which enhances fatigue.
Crosby designs and manufactures its products with fatigue in mind. Crosby
has a program in place that will result in all loadbearing products used in critical
applications being fatigue rated. |
IMPACT PROPERTIES
The mechanical properties of steel when a load is very rapidly applied is known
as its impact strength. Impact tests are made by applying a sudden load to
a test piece and measuring the energy absorbed when the specimen breaks. The
tougher the material the greater the energy required to break the piece. A
brittle piece can absorb virtually no energy upon breaking. The Charpy V Notched
Impact test is one common method of performing the testing and measurement. Fittings
must be able to have impact strengths that match the requirements of their application
at all temperatures, even low temperatures commonly found in winter conditions.
The difficulty of crack initiation and crack growth under impact is an important
consideration. |
Ask: Does the material
selection process recognize impact properties?
Ask: Do they have an active program to perform actual testing of
impact properties?
Ask: Do they recognize the need for good impact properties, i.e.,
the need for crack initiation and growth to be difficult throughout the normal operating
temperature 0 to 75 F (-20C to +25C) ? |
Crosby recognizes the importance
of impact properties and has an active program to determine impact properties at
various temperatures of each material used in the various heat treat conditions.
Crosby products are designed to be used in a wide range of temperatures. Crosby
specifies material of specific cleanliness and guaranteed hardenability which enhances
fatigue and impact properties.
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PERFORMANCE
Performance of a fitting requires a tensile strength that meets working load limits,
ductility that allows deformation when overloaded, fatigue properties that support
use time after time and impact properties that provide toughness. All of these
properties are essential if the product is to perform time after time in adverse
conditions. They are also important to assure that the inspection criteria
set forth by ANSI will effectively monitor the ability of the fitting to continue
in service. |
Ask: Does the
fitting have required tensile strength, ductility, fatigue and impact properties?
Ask: Are
all the material properties met?
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Crosby designs its fittings to
include required working load limits and design factors. Equally important
are the ductility, fatigue, and impact properties.
Crosby provides you with material
properties that minimize the risk of failure. No short cuts in processing
are made to save cost while sacrificing any of these performance elements.
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