Why some pegboard does not fit properly in your gondola?
Pegboard, Slatwall, and Wood Based Products: Part II of II
Wood Panels & Humidity
In this [part of the] article, we hope to give Designers and other interested persons a basic understanding of how wood based panels behave with changes in the humidity of the environment surrounding them.
Most people recognize a “humid” day as one in mid-summer which is “hot and muggy”. Few people realize that a cold, crisp day in mid-winter with temperature below freezing is often as “humid” as the “muggy” day in summer. Wood based display panels react insignificantly to temperature changes so people are often puzzled why these panels will expand the same when exposed to a sweltering 100 deg. Fahrenheit or a frigid 0 deg. Fahrenheit temperature.
Wood Behavior
To demonstrate the behavior of wood based panels with change in relative humidity we exposed panels of wet process hardboard, dry process hardboard, and HDF to what we consider the most severe extremes that could be experienced in field exposure.
A detailed description of this trial is contained in an appendix to this article. Briefly, results were as follows:
- With exposure to high relative humidity panels that were manufactured under our normal climatic conditions and cut to 48” expanded approximately 5/32”.
- With complete drying out these same panels then shrank a bit over 3/16”.
- (We dried out the test panels by holding them in an oven for 15 minutes. A similar “drying out” would occur if a van-load of panels were left standing in hot summer sun for a few days where ambient air temperatures inside the trailer could easily reach 160 deg. F.)
- After drying out, the panels were returned to high relative humidity exposure. In two weeks the panels returned to nearly their original maximum width.
- When moved to an area of low relative humidity, the panels shrank up to 3/32”.
After reviewing the results of this trial a designer may ask, “Hey, do you mean I have to allow for expansion and contraction of a 48” wide panel of plus or minus 1/8 of an inch?” The answer we’d give is “No”. Conditions in this trial were extreme. Consider the billions of square feet of wood based paneling in attractive use throughout the world.
If expansion and contraction of 1/8” per 48” occurred commonly this product would be unfit for use.
Extreme Conditions
In our trial we purposefully exposed the specimens to extreme conditions in order to emphasize problems which can arise if precautions aren’t taken and reasonable tolerances aren’t allowed.
IN OUR EXPERIENCE, A DESIGNER WHO WILL ALLOW TOLERANCE FOR 0.13% EXPANSION OF A WOOD BASED PANEL (1/16” PER 48”) WILL DEVELOP A PRODUCT WHICH IS 99.5% TROUBLE FREE.
In actual practice we agree to supply panels cut to a tolerance of plus or minus 1/32” and don’t attempt to explain that in order to do this we must try to anticipate how much the panels will change in dimension between our time of cutting and eventual point of Wood Based Panels – How to deal with expansion characteristics use. We commonly set to trim to the lower limit of tolerance, knowing that in most areas we ship to, the panels will expand. For shipments into the southwestern U.S. we do, however, set to cut the exact dimension specified.
In summary, the designer must allow for movement between dissimilar materials such as metal, plastic, and wood based components when two or more of them are combined in an assembly. Wood based components will change dimension with changes in relative humidity whereas metal and plastic parts react to temperature changes. Under common conditions an allowance of 0.13% for expansion of the wood based retail shelving panels will avoid any trouble.
However, the designer and the consumer should be aware of extreme conditions which could occur. For example, if a product is stored in an unheated warehouse during cold weather or if it is allowed to stand for a few days in a van or enclosed trailer exposed to hot sunlight. In such cases, large and opposing movements by the dissimilar materials might totally destroy the assembly.
Midwest Retail Services hopes this two-part article has been informative, especially for our customers.
For more information, call 800-576-7577 or email us at info@mw-rs.com.
APPENDIX
The full article and appendix is available upon request.
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