Surface World May 2020 Surface World May 2020 | Page 40

Low Cost Critical Cleaning
Solvent
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MASKING - TAPES, CAPS & PLUGS
Vents for masking
Trapped air under masks can
ruin your surface finishing.
Vents can be incorporated
into masks to release any
trapped air and maintain
consistent surface finishing.
Releasing trapped air from under masks can
be difficult. Masking needs to be tight and
form a seal, which by definition means
nothing should get passed the mask. The
problem is that as parts go through the
heating and cooling cycle of a surface
finishing process, any air that is trapped
behind the mask can expand and contract. In
some circumstances that expanding and
contacting air can cause a mask to move or
in extreme circumstances, blow off
completely.
There are options, though, and adding vents
to moulded masks is one of them. Vents can
come in a number of styles. There are vents
that are simply holes in the masking to
release the air; masks that channel air to a
particular area of the seal; as well as vents
that open and close to release air and reseal
the mask during the surface finishing process.
The most basic type of vent is a hole in the
mask. Holes can be punched into masking
caps or plugs in order to release pressure,
but they will not work in a liquid application.
A number of standard masking caps are
available that have a raised pip that can be
pulled off. When that pip is pulled off it
exposes a small hole in the cap which allows
the cap to vent.
Duckbill vents are vents which can open and
close during the process. These duckbill
shaped vents have a slit in them that opens
when the pressure behind them builds up.
Once the pressure equalizes, the vent closes
to ensure the mask remains operational. A
duckbill vent can be incorporated as a
permanent feature of a mask or it can be a
removable piece that can be changed over
time. Duckbill vents are ideal for liquid
applications
Another option for liquid applications is
dome vents. Dome vents are similar to
duckbill vents in that they can open and
close during the process. A dome vent is a
plug style vent that passes through a hole in
the mask and seals the hole. Channels in the
dome vent direct the air through the plug up
towards the dome of the plug. The dome of
the plug is flexible, so as pressure builds up
under the dome, it can lift to release the
pressure and then snap back down once
pressure equalizes.
These vents can all be manufactured in a
range of rubber materials to suit your surface
finishing process.
If you need more information on using vents
in masking, a good masking supplier such as
Caplugs or any of their distribution partners
can provide help.
John D. Gill
John D. Gill is an Engineer with
experience in masking and product
protection throughout the UK,
Europe and USA. He can be reached
at www.johndgill.com and via Twitter
@masking101
This large plug has a blue dome vent
in it to release pressure during the
surface finishing process.
Duckbill vents open and close based
on the pressure behind the Duckbill.
38 MAY 2020
twitter: @surfaceworldmag