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Articles
by Chris A. Paschke, CPF GCF CMG
"TTPM - Pressure"
March 1995
In review, time
and temperature are determined by individually selected adhesives, artwork or
materials to be mounted, individual substrate thickness and desired end
result. Though there are loose basic
standards for time and temperature, there will always be variables effecting
specific selection of these two elements.
Continuing with the TTPM elements, this month we're tackling
"pressure".
Pressure is the
exertion of force upon a surface by an object or fluid in contact with it. In framing, pressure is the force that
squeezes the air from between the substrate, adhesive and artwork being mounted
then holds it while the bond is created.
WET AND SPRAY
PRESSURE
Use of pressure
during the set-up process of wet or spray mounting encourages a good bond and
helps reflatten the moistened substrate as it dries. This pressure may be as simple as a piece of
1/4" plate glass or as complex as a cold vacuum frame, but is a somewhat
variable portion of successful hand mounting.
There is no
designated appropriate poundage established for wet glue pressure to be
effective, it remains moreover simply "good technique", a good idea
to maintain maximum contact while the glue dries.
PRESSURE SENSITIVE
Both pre-adhesived
pressure sensitive boards and two-sided adhesive sheets such as PMA also
require pressure to properly bond. The
major difference being these adhesives don't need to remain under pressure as
they dry. They actually require the
pressure of a squeegee, rubber brayer or roller machine to activate the
adhesive and create the initial bond.
Although a basic bond is established almost immediately, the most long
lasting one occurs after 24 hours.
DRY MOUNTING
PRESSURE VARIATIONS
Whether hot vacuum
or mechanical presses are used, dry mounting is by far the most predictable and
reliable form of mounting available...if the elements of time, temperature,
PRESSURE and moisture are properly controlled.
Both hot and cold
vacuum presses are self adjusting in relation to the substrate or mounting
board being used. The rubber diaphragm
or bladder which forms the bottom of the unit naturally conforms to the
thickness of each individual substrate during the draw of the vacuum, adjusting
for pressure automatically. Therefore,
it never needs to be manually adjusted.
On the other hand,
dry mounting pressure required in a mechanical press is very specific. Inadequate pressure might allow air bubbles
to remain within the center of a mounting, while too much pressure could create
unsightly indentations in a foam board substrate during a multiple bite
project. This then requires manual
control.
Average pressure
poundage in a vacuum press is somewhere between 11-15 pounds "per square
inch" (psi) while pressure in a properly adjusted standard mechanical (aka
softbed press) is 2-4 psi. Hardbed
presses, used most often outside the United States, have a much higher range of
psi pressure potential.
CHECKING
MECHANICAL PRESS PRESSURE
Unlike the
simplicity and user friendly concept of a vacuum press, a mechanical press must
be manually set to apply the appropriate pressure for the thickness of
substrate. Demonstrating on a Seal
210M-X, first check for proper pressure adjustments.
Cut a 20"
square piece of foam board, join the two opposite corners by scoring the board
corner to corner, but only penetrate half way through the thickness of the foam
(diagram 1). Fold the square in half and
you have a perfect 45 degree pattern (photo 1).
By using a large piece of foam for the pattern, it is easier to compare
the angle of the pattern to that of the press handle. Plus by folding the board in half rather than
cutting it into an angle, it remains self-supporting.
If the arm is
higher than the 45 degrees of the foam pattern the press will be too tight for
the thickness of substrate checked (photo 2).
If the arm is lower than the pattern, the press will be too loose for
adequate pressure to ensure proper mounting results (photo 3).
ARM ADJUSTMENTS
If you routinely
mount on 3/16" foam, it is most time effective to adjusted a mechanical
press to 3/16" as a standard thickness.
Place the board in the press with the handle at the closed, but not
locked, position. Check to see if the
press arm is at the proper 45 degree angle for this substrate thickness.
The "locking
nuts" are the doughnut shaped outer rings which loosen when turned
counter-clockwise. These nuts must be
loosened to adjust the taller, inner "pressure adjusting
screws". If the locking nut is too
tight to loosen, insert an additional board into the press and lock the arm
down to release excess pressure from the locking nuts. Unscrew them until they are out of the way or
off (photo 4).
If the additional
board was added to loosen the locking rings remember to remove it prior to
setting the 45 degrees. Pop the press
handle open and freely adjust the tall inner pressure screws to appropriately
adjust the arm. Twist both screws at the
same time in the same direction, the resistance should feel equal.
Twisting the
screws evenly to the right or in a clockwise position will drop the lever arm
down, lightening or decreasing the press pressure. Twisting the screws to the left or
counter-clockwise will raise the arm up and increase press pressure. Align the 45 degree foam pattern with the
lever arm for whatever substrate thickness is desired, lock the arm closed and
replace the locking nuts snugly, but only finger tight.
SHIMMING FOR
PRESSURE VARIATION
If mounting a
4-ply mount board prior to a 1/2" foam board and then 1/8" foam
board, no adjustments need to be made with a vacuum press. If variations in substrate thickness are
routinely required, constant readjusting of the pressure settings would be
required when using a mechanical press.
This can be a very time intensive and annoying preparation.
Readjustment of
the press is required each time the substrate changes or the pressure will also
change. Once the press is adjusted to
3/16" substrates, as an alternative to physically readjusting the locking
screws, shims may be cut to accommodate the variation in substrate thickness and
placed beneath the masonite board to make up the difference in thickness. The shims must always be used beneath the Masonite,
not within the platen/sponge pad mounting area.
Place a strapping
tape tongue on the front edge of the lower masonite pressure board for easy
accessibility (diagram 2). Cut three
4-ply equivalent scrap mat or mount boards about 1" smaller than the size
of the sponge pad or masonite. Then
simply slide a shim beneath the masonite whenever a thinner substrate is selected. For quick adjustments, 1 shim will be added
for 1/8" foam substrates and 2 shims will be added when 4-ply mat board
becomes a substrate (diagram 3).
When no solid
substrate is used, as in pre-mounting adhesives or canvas transferring, three
shims will equal the entire 3/16" inner press adjustment.
PREDICTABLE
RESULTS
The plates of any
mechanical press must always be clean and properly adjusted in order to achieve
repeatedly reliable, consistent, predictable results necessary for successful
mounting. If the pressure is too light
gaps or air pockets may result from the air not being squished from between
substrate and artwork. If the pressure
is too tight it can compress foam boards or create indentations when mounting
oversized projects. Follow the standard
guidelines of 45 degrees for appropriate pressure placement of the lever arm.
If problems do
occur, it is rarely equipment or materials causing the deficiency, check the
elements. Mounting should be routine and
predictable and the only pressures associated with it should be in never
forgetting the basic mounting principles of time, temperature, pressure...and next
month's TTPM: moisture.
There are many
types of pressure. The pressure of
paying bills, the pressure of deadlines, the pressure of dealing with
customers. If we can avoid creating high
blood pressure over worrying about the pressure required for successful
mountings, maybe life might be simpler.
END
For more articles
on design or mounting search your desired topic under Articles by Subject.
If you know your specific title check Articles by Title.
Additional
information on mounting basics is found in
The Mounting
and Laminating Handbook, Second Edition, 2002, and
The Mounting
And Laminating Handbook, Third Edition, 2008.
Creative
Mounting, Wrapping, And Laminating, 2000
will teach you
everything you need to know about getting the most from your dry mount
equipment
and materials as
an innovative frame designer. All books are available from Designs Ink
Publishing through this website.
Chris A Paschke,
CPF GCF
Designs Ink
Designs Ink
Publishing
785 Tucker Road,
Suite G-183
Tehachapi,
CA 93561
661.821.2188
info@designsinkart.com