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Heat Treatment Process for Stabilizing Die Cast Magnesium DASD Actuator Combs

IP.com Disclosure Number: IPCOM000102195D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 4 page(s) / 163K

Publishing Venue

IBM

Related People

Goeke, DC: AUTHOR [+4]

Abstract

An effective heat treatment process has been developed to create thermally stable die cast magnesium actuator combs for direct-access storage devices (DASD). This heat treatment process is defined as follows: 1. After casting, the die cast parts are to be heat treated at 260 degrees Celsius (500 degrees Fahrenheit) for two hours. The ramping temperature should not be more than 55 degrees Celsius (100 degrees Fahrenheit) per hour. 2. After machining, the final parts are to be heat treated at 218 degrees Celsius (425 degrees Fahrenheit) maximum for 5 hours minimum. The ramping temperature should not be more than 55 degrees Celsius (100 degrees Fahrenheit) per hour.

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Heat Treatment Process for Stabilizing Die Cast Magnesium DASD Actuator Combs

       An effective heat treatment process has been developed to
create thermally stable die cast magnesium actuator combs for
direct-access storage devices (DASD).  This heat treatment process is
defined as follows:
      1.   After casting, the die cast parts are to be heat treated
at 260 degrees Celsius (500 degrees Fahrenheit) for two hours.  The
ramping temperature should not be more than 55 degrees Celsius (100
degrees Fahrenheit) per hour.
      2.   After machining, the final parts are to be heat treated at
218 degrees Celsius (425 degrees Fahrenheit) maximum for 5 hours
minimum.  The ramping temperature should not be more than 55 degrees
Celsius (100 degrees Fahrenheit) per hour.

      The proper stress relief time/temperature can be identified by
holographic interferometry.

      The holographic interferograms shown in Fig. 1a were obtained
by first heating the actuator comb to around 45 degrees Celsius, and
then taking a hologram when the actuator comb had been air cooled to
equilibrium, say, T1 degrees Celsius.  As the temperature of the comb
assembly dropped, interference fringes between the actuator comb and
the hologram gradually appeared.  A TV camera linked to a VCR and a
screen printer were used to record the interferograms.  When the
interferograms were printed, the actuator comb temperature, say, T2
degrees Celsius, was recorded.  The temperature difference represents
the difference between T2 degrees Celsius and T1 degrees Celsius
mentioned above.  The optical setup of the holographic interferometry
was aligned such that each fringe represents 316.4 nm (half
wavelength of the He-Ne laser used) out-of-plane deformation.  For a
rotary actuator each interference fringe obtained under this type of
optical setup will then represent a 316.4 nm thermal track
misregistration between any two arms.  Therefore, a thermally
well-behaved actuator comb should possess interference fringes that
are parallel along the horizontal direction, i.e., normal to the arm
direction.

      The heat treatment process originally used was to heat treat
the die cast parts at 260 degrees Celsius (500 degrees Fahrenheit)
for one hour after rough machining to relieve the casting and
machining stress.  The holographic interferograms shown in Fig. 1a
indicate that a magnesium comb having gone through this process can
exert dimensional instability since the two interferograms are of the
same comb taken at different time periods.  In other words, two
distinctive thermal deformation patterns can be obtained from the
same comb, with a minimum of 5 minutes between the two interferograms
taken:  the first hologram  was taken to the difference in
temperature equal to 4.4 degrees Celsius, and the second hologram was
taken to the difference in temperature equal to 6.0 degrees Celsius;
both were reheated to 45 degrees Celsius then air cooled...