Herrmidifier Load Calculator User Manual
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L o a d C a l c u l a t i o n G u i d e
L o a d C a l c u l a t i o n G u i d e
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w w w. h e r r m i d i f i e r- h v a c . c o m
WHY DOES WOOD CRACK OR WARP?
As wood loses moisture it shrinks. However, the tangential
shrinkage is much greater than the radial shrinkage. This
causes dimensional changes and instability in the wood and
the wood pulls apart, along the grain causing cracks. If the
wood is strong enough not to crack it will warp as the un-
even shrinkage occurs. This is why it is important to condi-
tion wood to the proper Regain for best workability and then
stabilize it at the corresponding EMC by maintaining proper
humidity control.
WHAT IS THE BEST R.H. FOR WOOD?
The Regain should be between 5%-9% depending on the
species of wood and its use. This regain corresponds to the
EMC with 35%--45% R.H. air at 75°F. If you are able to
maintain the proper EMC Regain in the wood by maintain-
ing the proper R.H. in the air surrounding it, rejects will be
sharply reduced, production efficiency increased and profits
increased!
WHAT ABOUT GLUING AND FINISHING?
When dry thirsty air pulls moisture from it, the wood also be-
comes thirsty, so that when a varnish or other coating is ap-
plied the dry wood will act like a sponge and quickly absorb
the liquid. This leads to a dull finish or excessive use of coat-
ing to produce a bright finish. Glue will not cure properly or
quickly if the air and wood that it is in contact with are too dry.
WHAT R.H. DO I NEED FOR GLUING AND FINISHING?
Generally, 40%-50% R.H. is recommended for gluing and a
minimum of 60% R.H. recommended for finishing areas. You
must remember that if wood has not been conditioned previ-
ously and enters the humidified gluing and finishing areas
dry and thirsty, it will still produce the problems experienced
before. It is important to maintain the stability of your wood,
from start to finish, by proper humidity control. The econom-
ic gains from proper humidity control, can often pay for the
equipment in less than one year.
Paper Products And Humidification
The common problems experienced in every paper industry,
whether it involves manufacture of cardboard boxes, sheet
paper, etc. are: curling of stock, cracking on folds of paper
or boxes, failure to feed properly into machines and glue
that won’t hold. Generally these problems are experienced
in the winter heating season when the R.H. indoors is low.
Once again, the cause of these problems is moisture loss
from materials. Paper and paper products are made up of
fibrils. When these fibrils lose moisture they shrink and be-
come brittle.
Woodworking And Humidification
In the woodworking industry controlled humidification can of-
ten mean the difference between a profitable operation and
bankruptcy. A company, manufacturing wood products, that
must reject one (1) out of ten units due to cracking, warp-
ing, splitting or checking suffers losses due to wasted raw
materials, wasted labor and wasted energy in the production
of nonsaleable items. These losses can be profound- par-
ticularly the energy loss, as this goes all the way back to the
cutting of the tree and transporting of the lumber. If the dam-
aged unit can be reworked there is still the added cost of do-
ing so. These losses and added costs must be added to the
costs of producing the other nine out of ten saleable units. It
is not hard to see why controlled humidification can result in
substantial savings for the woodworking industry.
HOW IS WOOD AFFECTED BY HUMIDITY?
Wood is a hygroscopic material, able to take on or give up
moisture to the surrounding air. As wood takes on moisture
it swells. As it gives up moisture it shrinks. It does so in re-
sponse to the changing atmospheric conditions of tempera-
ture and humidity, humidity having the greater effect. The
amount of moisture in the wood, expressed as a percentage
of its dry weight, is referred to as its REGAIN. This Regain
varies with temperature, relative humidity and type of mate-
rial. When the Regain of a piece of wood reaches a balance,
where it is no longer taking on or giving up moisture, it is said
to have reached its EQUILIBRIUM MOISTURE CONTENT
(EMC) for that particular temperature and R.H. At this state
the wood is stable and will not change dimensionally. The
EMC changes with temperature and R.H. For example, a
piece of wood with an EMC regain of 9.3% at 75F 50% R.H.
will have an EMC regain of only 4.4% at 75°F 20% R.H. (See
Table 1-C.)