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guest editorial
All
Screws Are Not Created Equal
Even
if they look the same-they probably aren't.
by Andrea Basalay
|
The
fundamental premise behind the U.S. Constitution does not hold true
for fasteners in the hurricane protection industry.
Whether you are manufacturing or installing windows, accordions, roll
shutters or panels, the fasteners used to join the metal together
or attach to the structure are essential and critical components to
the integrity of the protection. The two most important factors for
hurricane protection fasteners are their material composition and
coatings/platings.
FASTENER MATERIALS
Most of the fasteners in the hurricane protection industry may be
divided into two general categories: low carbon steel and stainless
steel. Many manufacturers make the same parts in both carbon and stainless
steel. The price of carbon steel fasteners generally runs three to
four times less than stainless steel.
Carbon steel provides a very strong, hard fastener with good drilling
and tapping properties. Carbon steel is ferrous (contains iron) and
magnetic. Generally the amount of carbon in the steel determines the
hardness of the material. While carbon steel fasteners are strong,
they are not rustproof. As hurricane protection products are exposed
to harsh conditions, stainless steel is the more widely specified
material on product approvals and engineering.
When most people consider stainless steel, they think of rustproof.
Virtually all stainless steel will develop rust (or stain) over time.
The choice becomes which type of stainless steel should be used in
different applications. In the hurricane protection industry there
are two types of stainless steel that are commonly used.
The first is 18-8 stainless (many times referred generically as 300
series, although there are many types of stainless within the 300
series). 18-8 stainless steel is nonmagnetic for all essential purposes.
It is recommended that the 18-8 stainless steel be passivated. The
passivation process cleans the impurities (dirt) from the metal. If
the impurities are not removed, the fastener may develop rust on the
impurities. This gives the appearance that the fastener is rusting.
While 18-8 stainless steel fasteners are very good for corrosion resistance,
the metal is softer than the second commonly used stainless, 410,
in the hurricane protection industry. Another reason why 18-8 stainless
is not as strong as 410 is that it cannot be heat treated or hardened.
We believe this is the reason why there is not an 18-8 name brand
Tapcon®—it is not hard enough to tap its own thread into
the concrete. While 18-8 stainless steel does hold up to corrosion
better than 410, it is not usually used in testing for shutter systems
where the strongest fastener is need for cycling or impact tests.
Many engineers specify 410HT stainless steel for the assembly and
installation of hurricane protection because it is hardened and heat
treated. Without getting into technical metallurgical discussions,
there are methods to increase the strength and hardness of stainless
steel. A common method for greatly increasing the strength of 410
stainless steel is the heat treat process.
Heat treating is the heating and cooling of solid material under controlled
conditions to produce desired properties that in the hurricane protection
industry means a stronger fastener. Because of the ability to harden
by heat treating, there are Tapcons, Teks® and self-drill screws
available in 410. 410HT is translated to 410 stainless steel heat
treated under the “Fastener Standards, 6th Edition,” as
specified by the Industrial Fasteners Institute (IFI).
The bottom line is a 410 and a 410HT fastener look the same, but are
not equal.
FASTENER COATINGS AND PLATINGS
While 410HT stainless steel is stronger than 18-8, it will develop
rust. A common method in retarding the rust is the use of platings
or coatings. Coatings and platings also help the problem of galvanic
reactions between dissimiliar metals such as aluminum and stainless
steel.
There are two main plating methods: mechanical and electro. Mechanical
plating is also called barrel plating. Barrel plating is essentially
dumping and tumbling the parts in a barrel and immersing the barrel
in a series of chemical process tanks. Electroplating uses interior
cathode electrical contacts to polarize the parts and metals are attracted
out of the plating baths and onto the fasteners.
Fasteners may be coated using a dip-spin, dip-drain spin or spray
coating process. Coatings are generally applied to the parts, with
excess coating removed, then the parts are baked at a specified temperature
to achieve proper curing of the coating. Most coating systems require
multiple layers of base coats to be applied, with the option of a
topcoat or sealer to help the coating adhere.
There are so many name-brand coatings and plating available to the
hurricane protection industry. Examples of these various coatings
are ITW Buildex’s Ultrashield™, Elco Textron’s Stalguard®,
Dacromet® and Xylan. These proprietary coatings have published
salt spray test results. If a fastener distributor substitutes named
coatings for generics without published testing data, the results
are suspect.
Once a fastener is coated or plated, it is very difficult to determine
the base metal. As with the determination of base metals, a generically
coated fasterner may look like a named brand, but not all coatings
are created equal.
As the hurricane protection industry grows, manufacturers, platers,
coaters and distributors are continuing to improve the corrosion protection
of the fasteners. As the coating and plating industry rapidly changes
to develop new and improved parts, your educated fastener supplier
is the best source to keep you informed on the product to suit your
needs.
Andrea Basalay, ITW Buildex, Itasca, IL; (800) 323-0720; fax: (630)
787-3211;
www.itw buildex.com. |
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