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The primary
features of a sizing cage are the size range, the
arm material, and the compatibility with internal bubble cooling
control sensors.
Secondary
features include the speed of diameter movement
(particularly important for auto
cage control applications), the height range of
the cage, and the ability to easily realign the cage after
installation.
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| Size,
Style, IBC |
Cage
Arm Material
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| Size
range: identifies
the size of the bubble diameter or layflat that can run with
the bubble touching the cage arms. Ranges can be specified with
a minimum and a maximum size, or with a maximum and a size ratio.
Many cages come with a 3:1 size ratio, but some are available
with a 4:1 size ratio. |
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Segmented
Rollers - Each
arm is made up of many insulating rollers. Common materials
are Teflon and PTFE. This style of roller arm is good for
low and high density polyethylene (LDPE and HDPE). These style
arms require periodic cleaning to ensure the rollers do not
drag on the film.
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| Cage
Style and Levels: Each
sizing cage uses either a
radial or iris style arrangement to move the cage
arms in and out. Levels refer to the number of cage arm levels
on the cage. Most IBC cages use between 6 and 8 levels. |
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Single
Rotating Cylinder Arms - A special covering provides
a soft, insulating contact with the film. No scratches, no
markings, no film thickness variation. The covers can be easily
cleaned or replaced. Tacky films, very soft and thin
materials benefit (LLDPE and Metallocenes).
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| IBC
Compatible: Most sizing
cages can be fitted with IBC sensors. The sizing cage must provide
a means to move the IBC
sensor with the sizing cage so the sensor always
points towards the vertical centerline of the bubble (+/- 6°)
for all bubble sizes. For IRIS style cages, the cage manufacturer
provides any special mounting arrangements for the sensor. |
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Low COF Arms
- This type of cage arm does not have a rotating surface.
Instead the entire surface of the arm is specially treated
to provide very low coefficient of friction (0.056) and are
very good for tacky films. Liquid cooling can also be incorporated
into the arm to remove heat. Very soft and thin materials
benefit (LLDPE and Metallocenes).
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| Diameter,
Height, and X-Y Axis Controls |
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Diameter
Control: All sizing cages
have diameter control. The issue is whether the control is manual
(via a turn-crank), or motorized. Further, some cages also can
provide variable speed for the motorized control. The variable
speed feature is useful when the IS-IBC1 is providing auto
cage control. Contact
us if you need help on deciding which level of control
to specify. |
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Height
Control: Most blown film
extrusion lines that run more than one size will require a height
control mechanism. Similar to the diameter control, the choices
are no control, manual control and motorized control. The motorized
control is recommended for almost every application. This control
allows the operator to set the cage properly above the frost
line which gives the bubble optimum stability. |
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X-Y
Axis Controls: The X-Y Axis Control feature allows
the cage to be moved in the X or Y axis after it is installed.
This allows for alignment changes which may be necessary if
the die is moved after cage installation. Some cage manufacturers
offer a motorized version as well. The manual version is generally
sufficient for most applications. |
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