|
| |
TM 9-254
9-7.
Decementing (Separating) Optical Components - Continued
(2)
Place the lens or lenses to be decemented on the hot plate for 1 to 5 minutes. A slight cracking noise
may be heard when the thermal expansion of the lens breaks the cement bond, also the cement will
become visible between the lens elements.
(3)
With a pair of lens tongs, carefully remove the lens from the hot plate and place it on a piece of
cardboard padded with cheesecloth.
(4)
To separate the lens elements position the lens on its edge. With a sharp knife apply pressure between
the two lens elements.
(5)
If the lens does not separate, place it back on the hot plate for an additional 1 to 3 minutes, and repeat
steps (3) and (4) above.
c.
Vacuum Oven Method. This method of decementing lenses is more involved than the hot plate method of
decementing and is used primarily to separate large lenses that would fracture when placed on a hot plate. This method
allows the lenses to be heated and cooled slowly in an air free atmosphere thus reducing the possibility of fracturing. The
procedure for decementing with this method is as follows:
(1)
Place the lenses in vacuum oven on shelves that are lined with fiberglass cloth.
(2)
Set the oven to a temperature of 350 to 450 degrees Fahrenheit and pump the air out of the oven. Heat
the lenses at this temperature for 24 to 36 hours.
NOTE
If oven is not equipped with a thermostat graduated in degrees Fahrenheit, place a thermometer
inside the oven so it can be viewed through the front window and adjust the temperature
accordingly.
(3)
Turn off the oven and let the lenses cool to room temperature before releasing the vacuum in the oven
and removing the lenses.
(4)
Place the lenses on a piece of cardboard padded with cheesecloth.
(5)
To separate the lens elements, position them on edge and use a sharp knife to apply pressure between
the two elements.
(6)
If lenses do not separate, repeat steps (1) through (5) above.
d.
Removing Cement from Lens Elements. After separating the lens elements, perform the following
procedures to remove the cement.
NOTE
This procedure only applies to lenses that do not require recoating.
(1)
Soak the lens elements in a bath of acetone for approximately 15 minutes.
(2)
Remove the cement from the lens elements with a piece of cotton. If all the cement cannot be removed
repeat step (1) above.
Change 2 9-24
|
