Installation Guide

22
Polymerizable Cements
Polymerizable cements are those in which a catalyst is added
to an already thick monomer/polymer syrup to promote rapid
hardening. Cements PS-30 and Weld-On 40 or 42 are polymerizable
cements of this type. They are suitable for cementing all types of
Plexiglas
®
acrylic sheet. At room temperature, the cements harden
(polymerize) in the container in about 45 minutes after mixing the
components. They will harden more rapidly at higher temperatures.
The cement joints are usually strong enough for handling one to
two hours after assembly depending upon part configuration. The
joints may be machined four hours after assembly, but it is bette r
to wait 24 hours.
PS-30 and Weld-On 40 or 42 joints retain excellent appearance
and color stability after outdoor exposure. These cements
produce clear, transparent joints and should be used when the
clarity and appearance of the joints are important.
PS-30 and Weld-On 40 or 42 should be used at temperatures
no lower than 65°F. If cementing is done in a room cooler
than 65°F, it will require a longer time to harden and the joint
strength will be reduced. The cement should be prepared with
the correct proportions of components (preferably fresh) as
given in the supplier’s instructions and thoroughly mixed,
making sure neither the mixing container nor mixing paddle
adds color or affects the hardening of the cement. Clean
glass or polyethylene mixing containers are preferred. Table 4,
page 23, summarizes these procedures.
PS-30 may be thinned by adding up to 25 percent MMA inhibited
monomer to Component A to minimize bubbles when laminating.
Up to twice the normally recommended amount of Component
B may be used to increase the polymerizing rates.
Adding about 10 percent (by weight) Plexiglas
®
VS-100 acrylic
molding resin will reduce shrinkage of the cement during poly-
merization, but also decreases joint strength slightly. The pellets
must be thoroughly dissolved before mixing the components.
Because of their short pot life (approximately 45 minutes),
Cement PS-30 and Weld-On 40 or 42 must be used quickly
once the components are mixed. Time consumed in preparation
shortens the effective working time, making it necessary to have
everything ready to be cemented before the cements are mixed.
For better handling, pour cement within 20 minutes of mixing.
For maximum joint strength, the final cement joint should be
free of bubbles. It will usually be sufficient to allow the mixed
cement to stand for 10 minutes before cementing to allow
bubbles to rise to the surface.
To remove the bubbles quickly, spin the cement with an electric
drill. This is done by drilling a hole in the center of a metal jar cap
and placing a bolt through it, then placing a nut on the outside. This
bolt is gripped by the chuck of an electric drill. Screw jar into cap
and spin cement for one minute. This is for up to 6-ounce jars only.
For large sizes, a centrifuge that contains the jar should be used.