back down the capillary. It requires a
standard volume of 7.464 cubic millimeters, to minimize evaporation and
to remain tight against the high pump
pressure. For this seal, as well as three
others in the Respimat, Boehringer
Ingelheim microParts turned to a part
of Trelleborg ( www.trelleborg.com)
that specializes in liquid silicone seals
for the life sciences industry.
“We’re used to defining dimensions
by size,” says general manager of the
Trelleborg silicone manufacturing
facility in Stein am Rhein in Switzerland,
Matthias Jakob. “We had to develop a
new volume-measuring method for this
product.” Surfaces have to be perfect
without any trimming, and the burr
where the two halves of the mold join
has to be under 0.05 millimeters. “That
has placed high demands on our tooling
and process performance,” says Jakob.
In fact, there are limits to perfection.
Liquid silicone is a difficult material,
and Boehringer Ingelheim microParts
has to allow a tolerance in the o-ring
of ±1.0 cubic millimeter. This has to
be compensated for by variations in
the volume of the plastic central tube.
Böhmer explains, “We have three
different versions of the central tube so
that we can match it with the o-ring
and reach the correct total volume.”
Trelleborg and Boehringer Ingel-
heim microParts are now working
on improving the tolerance in the
manufacture of the o-ring to just
±0.3 cubic millimeter, which will make
this matching process unnecessary.
The Respimat is an innovative
tool for the treatment of asthma and
COPD, and its development has
pushed manufacturing technology
a little further, all so patients just
have to “take a deep breath” and the
medication is delivered where it needs
to be. MDT
Silicone o-rings are used in the design
to give the tightest tolerances.
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