TM 1-1500-204-23-6
(b) Use. Vulcanizing is used where the strongest possible adhesion is needed.
(c) Types. Two types of vulcanizing cements are air vulcanizing, which cures by exposure to normal room
temperature, and heat vulcanizing, which is used where a combination of heat and pressure are mechanically applied.
(d) Room temperature vulcanizing (RTV) silicone sealants. Many RTV silicone compounds give off acetic
acid during their cure cycle. Some corrosion problems can potentially occur when curing by products come in contact
with sensitive metals. This is of particular concern when RTV silicones are used in and around delicate electronic
components. Therefore, in applications near electronic equipment, RTV silicone compounds which conform to MIL-A-
46146 (Adhesive- Sealants, Silicone, RTV, Noncorrosive) should be used. Also, it would be preferable to use RTV
silicones per MIL-A-46146 for other aircraft applications whenever possible, provided that the properties of the cured
RTV silicone are adequate for the specific application. This cannot always be done as in applications which require very
high temperature and/or fuel/oil resistance. RTV silicones to be used in aircraft are determined by the location of the
application, the surrounding materials, and the final required properties. Substitution of specified materials must not be
made without approval from AVSCOM Engineering.
WARNING
Acrylic monomer and polymer base adhesive MIL-A-8576 contains a volatile liquid which
may prove toxic If vapor is inhaled over extended periods. Use only with adequate
ventilation. When accidentally spilled on hands or skin, remove immediately by
dissolving with ethyl alcohol, Federal Specifications O-E-760, followed by washing with
soap and water. Over-exposure symptoms are drowsiness, dizziness, and nausea.
Treat by wrapping patient in blankets, provide plenty of fresh air, and obtain medical
assistance.
b.
Acrylic Monomer Base Adhesive. MIL-A- 8576. Type I. Solvent Type. This cement is used in patching acrylic
plastics and in cementing acrylic plastics to other type plastics. It cures by evaporation of solvent, but a catalyst,
furnished as a separate ingredient, is required to be added to the packaged cement. This cement is nonflammable and
has a thick, syrup-like consistency. It is clear or amber in color and is resistant to oil and water. It is mildly toxic, but
used in such small quantities this is not too important. Do not attempt to thin with dichloromethane (methylene chloride)
when the material has become too thick while in storage, as the chemical composition may have changed.
(1) Shelf life. Before adding the catalyst, and provided the container is kept tightly closed, the cement has a
shelf life of at least 1 year. After the catalyst is added, and when the container is kept tightly closed, shelf lives at the
temperatures given in table 6-1 will apply.
Table 6-1. Shelf Life
Temperature
Shelf life
122°F (50°C)
20 hours
104°F (40C)
3-1/2 days
77°F (25°C)
45 days
41°F (5C)
5 months
(2) Thinning. In use, the solvent will evaporate, causing the cement to thicken. In this case, dichloromethane
(methylene chloride), MIL-D-6998, may be added to keep the proportion of monomer to solvent correct. The specific
gravity of the cement provides a quick method of checking the relative proportions of the two components. Table 6-2
gives the correct specific gravity ranges for given temperatures.
Table 6-2. Specific Gravity Ranges
Specific
Temperature
gravity range
68°F (20°C)
1.17- 1.21
77°F (25°C)
1.16- 1.20
86°F (30°C)
1.15- 1.19
95°F (35°C)
1.14- 1.18
104°F (40°C)
1.13 - 1.17
6-3
