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Self-Indicating Clamp Bolt

IP.com Disclosure Number: IPCOM000101274D
Original Publication Date: 1990-Jul-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 116K

Publishing Venue

IBM

Related People

Woodworth, GK: AUTHOR

Abstract

The pressure clamping mechanisms for high power "hockey puck" components require precision forces to insure adequate cooling without destruction of the internal die assembly. Classical pressure clamps are functional but otherwise bulky and cumbersome for multiple device applications. Vibration can induce excessive stress to the support structure due to the mass of the massive clamp beam and bolt assembly.

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Self-Indicating Clamp Bolt

       The pressure clamping mechanisms for high power "hockey
puck" components require precision forces to insure adequate cooling
without destruction of the internal die assembly. Classical pressure
clamps are functional but otherwise bulky and cumbersome for multiple
device applications.  Vibration can induce excessive stress to the
support structure due to the mass of the massive clamp beam and bolt
assembly.

      Clamping electrically "hot" heat sinks to allow for optimum
cooling is limited due to the span capabilities of the beam design.
High profile heat sink designs are beyond the ability of the bolts to
clamp around and this adds stress thermally.  By blocking some of the
cooling airflow, this design increases the difficulties in packaging
high power devices.

      Another difficulty presented by simple clamping devices is that
there is no simple way to gauge the compressive force at installation
or during a preventative maintenance period.  Checking this
compression must be done by special calipers or by adding a
force-indicating beam pointer, as shown in the figure.  All component
manufacturers and heat sink vendors strongly recommend that torque
measurements are not sufficient and can lead to greatly varying
forces on the device.  Bolt torque can be as much as 90% friction in
the threads and 10% due to loading forces.  A change of loading from
9% to 11% provides a 20% shift in clamping, but would be seen as only
a few percent difference in torque at the bolt.

      The weight, size, and cost drawbacks make indicating clamping
force for components difficult.  The included clamping device
provides a calibrated and self-indicating bolt to allow design
freedom.  This will insure proper adjustment of critical pressures in
a non-factory environment.

      This bolt is composed of a piston that is compressed against a
stack of spring elements to provide the compression force required.
The figure shows the external threads by which the bolt is screwed
into a support member. As the bolt is screwed into the attaching
plate, the piston is pushed into contact with the clamping surface.

      Because this design is in the form of a bolt, the clamping
force can be applied to an assembly without regard to the overall
height.  Heat sinks can be of any design based on the cooling
requirements alone and are not constrained by the current clamp
designs.  The freedom to develop a custom design is another benefit
of this approach.

      Increasing force causes the piston to compress the springs
causing their height to diminish.  As the spring element is reduced
in hei...