test sheet mold, made by the cut-off bar method with a lower
plate thickness of about 20 mm (0.75 in.), is shown in Fig. 2.
8.2.2.2 The mold for 150 by 75 by 2-mm (6 by 3.0 by
0.08-in.) sheets shall have cavity sections similar in dimensions
to that shown in Fig. 3 or Fig. 4. The cavities of this mold shall
meet the requirements described in 8.2.2.1.
8.2.2.3 The molding surfaces shall be cleaned, highly polished,
and hard chromium-plated. Molds constructed of hardened
steel are preferred, but chrome-plated mild steel and
stainless steel are also acceptable. The cover of the mold shall
be a flat plate at least 10 mm (0.4 in.) in thickness and
preferably hinged to the cavity section to minimize scratching
of the mold surfaces. Instead of a separate mold and cover, the
cavities may be cut directly into the platen of the press. Unless
required, do not use a mold lubricant on the mold surfaces.
When a mold lubricant is required, use only a residual-type
lubricant, which does not affect the vulcanized sheet, and
remove the excess lubricant by vulcanizing and discarding at
least one set of sheets. A silicone-type lubricant or mild soap
solution has been found satisfactory.
8.3 Vulcanization Procedure:
8.3.1 Bring the mold to curing temperature within 60.5°C
(1°F) in the closed press, and hold at this temperature for at
least 20 min before the unvulcanized pieces are inserted. Verify
the temperature of the mold by means of a thermocouple or
other suitable temperature measuring device inserted in one of
the overflow grooves and in intimate contact with the mold.
8.3.2 Open the press, insert the unvulcanized pieces into the
mold, and close the press in the minimum time possible. When
the mold is removed from the press to insert the pieces, take
precautions to prevent excessive cooling of the mold by contact
with cool metal surfaces or by exposure to air drafts.