O&MM Fabricator - January/February 2018 - 35

G

alvanic corrosion cells? A cell has four components: an anode,
cathode, return path and electrolyte (see drawing). Bare steel
has three of the components: anodes, cathodes and return paths.
With just the three components, bare steel will not rust. Add dirty
or salty water on the steel, which becomes an electrolyte, and
a complete cell has been created. An extreme example of the
four components at work, is when you put a crescent wrench
across the two posts on a car battery. If you keep the wrench on
the posts, watch out, the dead-shorted battery might explode.
We paint steel to create barrier protection. The paint becomes
a barrier, keeping water from becoming an electrolyte on
the steel.
Hot Dip Galvanizing
Hot dip galvanizing under paint, when done correctly, produces rust protection that is far superior to simply adding extra
layers of paint. The lifespan of zinc is much longer than that of
paint. And, as long as the zinc is sealed off from the elements
with paint, its lifespan will not start to diminish.
When steel is submerged into molten zinc and painted, the
combination of the two sealers is called a Duplex System. Duplex,
because both the zinc and paint are complete systems within
themselves. They do not rely on each other, but work in harmony.
Preparing Galvanized Steel for Paint
To prepare a freshly galvanized surface for paint, most small
shops take the metal to a sandblaster for sweep blasting. Sweep
blasting removes oxides and gives the slick zinc a slight texture
(tooth) for paint adhesion.
For metal preparation information:
Google the "American Galvanizers Association". Once on
their website, follow these steps:
A. Opening page, upper right, Education & Resources
B. Once on the Education & Resources page, left side
Publications
C. Publications page, left column, scroll down to Painting over
HDG
D. Once on the Painting over HDG page, Preparing HDG Steel
for Paint (CD Version) download free. Download the page
E. Once on the free downloaded page, click on the blue type,
Preparing HDG Steel for Paint (CD version) (download)

Note: Zinc oxidizes fast, so the American Galvanizers
Association recommends the sweep blasting be done on the
same day the primer is applied.
Mohs Hardness Scale
There is a hardness scale that goes from one to 10. This
scale is called the Mohs Hardness Scale. On this scale, talc
has a rating of one and diamond has a rating of 10. When
sweep blasting, The American Galvanizers Association (AGA)
specifies sweeping with a blasting medium that has a Mohs
rating of 5 or less. The AGA states that this medium should
be blasted at a 30-60 degree angle with only 40 pounds of air
pressure. The concern, A) with a Mohs rating above 5, B) a
perpendicular approach; and C) high air pressure, the blasting
medium will remove the zinc from the steel.
The sandblasting shops in my area, and I suspect nationally,
blast with crushed coal slag. Previously, they used silica sand;
however, because of silicosis, silica sand has become outlawed
for blasting.
Silica sand has a Mohs hardness rating of 5-6, and the
Mohs hardness of coal slag is 7. The AGA specifies 5 or less.
What is typically used for sweep blasting is ground corn cobs
with a Mohs rating of 4.5 or walnut-pecan shells with a rating
of 3-3.5.
Corn cobs are a little cheaper and more aggressive than
walnut shells, but my supplier tells me that walnut shells are
heavier, easier to use and produce less waste.
Why are we addressing the above? Because, what you do, not
want to do, is have your blaster simply turn down the air pressure
and blast with coal slag. This does not work. What your blaster
needs to do, is have the supplier drop off the volume of ground
corn cobs or walnut-pecan shells needed for the job, turn down
the air pressure and change the angle of blasting.
Painting a Galvanized Surface
How do you know what kind of paint and primer to use?
There are many choices. Again, Google "American Galvanizers
Association". Once on their website, follow these steps:
A. Open page, upper right, Education & Resources
B. Once on the Education & Resources page, left side
Publications
C. Publications page, left column, scroll down to Painting over
HDG
D. On the painting over HDG page, center right Duplex Systems:
Painting over Hot Dip Galvanized Steel - download free.
Download the page.
E. On the free downloaded page, in blue type, open up the download. You will be asked for your email and postal address.
This is optional. The primers and paint in the PDF are found
on pages 9 and 10.
Note: When looking at page 9, the Epoxy-Polyamide is
"Cured". The curing time between paints varies considerably.
Sherwin Williams Tile Clad 2 High Solids requires 21 days to
cure. Sherwin Williams Macropoxy 646 requires 7 days to cure.
Diamond Vogel has an epoxy-polyamide that dries in a day, but
is not on the MnDot approved list. My applicator assured me
the Diamond Vogel paint would perform well on a large railing
January/February 2018 * O&MM Fabricator | 35



Table of Contents for the Digital Edition of O&MM Fabricator - January/February 2018

President’s Letter
Letter From the Executive Director
NOMMA Network
NOMMA Education Foundation
2018 Metalfab / Fencetech Attendee Brochure
Three Things You Need to Know* to Save Money and Time When Commissioning Custom Metal Castings
The Collective Mind Gate Series - Part Vi
Change Orders
Women in Industry
What Experience Modifiers Do, and What You Can Do About It
How to Handle Your Toughest Employee Problem
Supplier Members
New & Returning NOMMA Members & Iron Club Members
Gold Members
Take a Stroll Down Memory Lane - Nomma’s First Years
2018 Product Preview
Index of Advertisers
O&MM Fabricator - January/February 2018 - Intro
O&MM Fabricator - January/February 2018 - cover1
O&MM Fabricator - January/February 2018 - cover2
O&MM Fabricator - January/February 2018 - 3
O&MM Fabricator - January/February 2018 - 4
O&MM Fabricator - January/February 2018 - 5
O&MM Fabricator - January/February 2018 - 6
O&MM Fabricator - January/February 2018 - 7
O&MM Fabricator - January/February 2018 - 8
O&MM Fabricator - January/February 2018 - 9
O&MM Fabricator - January/February 2018 - 10
O&MM Fabricator - January/February 2018 - President’s Letter
O&MM Fabricator - January/February 2018 - 12
O&MM Fabricator - January/February 2018 - Letter From the Executive Director
O&MM Fabricator - January/February 2018 - 14
O&MM Fabricator - January/February 2018 - NOMMA Network
O&MM Fabricator - January/February 2018 - NOMMA Education Foundation
O&MM Fabricator - January/February 2018 - 17
O&MM Fabricator - January/February 2018 - 18
O&MM Fabricator - January/February 2018 - 2018 Metalfab / Fencetech Attendee Brochure
O&MM Fabricator - January/February 2018 - 20
O&MM Fabricator - January/February 2018 - 21
O&MM Fabricator - January/February 2018 - 22
O&MM Fabricator - January/February 2018 - 23
O&MM Fabricator - January/February 2018 - 24
O&MM Fabricator - January/February 2018 - 25
O&MM Fabricator - January/February 2018 - 26
O&MM Fabricator - January/February 2018 - 27
O&MM Fabricator - January/February 2018 - 28
O&MM Fabricator - January/February 2018 - 29
O&MM Fabricator - January/February 2018 - Three Things You Need to Know* to Save Money and Time When Commissioning Custom Metal Castings
O&MM Fabricator - January/February 2018 - 31
O&MM Fabricator - January/February 2018 - 32
O&MM Fabricator - January/February 2018 - 33
O&MM Fabricator - January/February 2018 - The Collective Mind Gate Series - Part Vi
O&MM Fabricator - January/February 2018 - 35
O&MM Fabricator - January/February 2018 - 36
O&MM Fabricator - January/February 2018 - 37
O&MM Fabricator - January/February 2018 - Change Orders
O&MM Fabricator - January/February 2018 - 39
O&MM Fabricator - January/February 2018 - 40
O&MM Fabricator - January/February 2018 - 41
O&MM Fabricator - January/February 2018 - 42
O&MM Fabricator - January/February 2018 - What Experience Modifiers Do, and What You Can Do About It
O&MM Fabricator - January/February 2018 - 44
O&MM Fabricator - January/February 2018 - 45
O&MM Fabricator - January/February 2018 - 46
O&MM Fabricator - January/February 2018 - How to Handle Your Toughest Employee Problem
O&MM Fabricator - January/February 2018 - 48
O&MM Fabricator - January/February 2018 - 49
O&MM Fabricator - January/February 2018 - 50
O&MM Fabricator - January/February 2018 - 51
O&MM Fabricator - January/February 2018 - 52
O&MM Fabricator - January/February 2018 - Supplier Members
O&MM Fabricator - January/February 2018 - 54
O&MM Fabricator - January/February 2018 - New & Returning NOMMA Members & Iron Club Members
O&MM Fabricator - January/February 2018 - 56
O&MM Fabricator - January/February 2018 - Gold Members
O&MM Fabricator - January/February 2018 - Take a Stroll Down Memory Lane - Nomma’s First Years
O&MM Fabricator - January/February 2018 - 59
O&MM Fabricator - January/February 2018 - 60
O&MM Fabricator - January/February 2018 - 2018 Product Preview
O&MM Fabricator - January/February 2018 - 62
O&MM Fabricator - January/February 2018 - 63
O&MM Fabricator - January/February 2018 - 64
O&MM Fabricator - January/February 2018 - Index of Advertisers
O&MM Fabricator - January/February 2018 - 66
O&MM Fabricator - January/February 2018 - cover3
O&MM Fabricator - January/February 2018 - cover4
O&MM Fabricator - January/February 2018 - outsert1
O&MM Fabricator - January/February 2018 - outsert2
O&MM Fabricator - January/February 2018 - outsert3
O&MM Fabricator - January/February 2018 - outsert4
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