Size & Shape

Size and shape of the fabrication is an important consideration to make, during the design process for parts to be galvanized.  Because hot-dip galvanizing is a total immersion process, the design must take into consideration the capacity of the galvanizing kettle; therefore, it is wise to verify kettle constraints with your galvanizer early in the design process.  Almost any component can be galvanized by designing and fabricating in pieces suitable for available galvanizing facilities.  Parts can also be progressively dipped by the galvanizer, to accomodate larger sizes and abnormal shapes.  For reference, the average kettle length in North America is 40 feet (13m), and there are many kettles between 50-60 feet (15.24 m - 18.28 m).

If you have any design questions relating to galvanizing, please give us a call: Hubbell Galvanizing 1-800-244-4258 (315) 736-8311 info@whyrust.com http://www.whyrust.com

Can Castings be Galvanized?

High-quality castings and forged parts are commonly and successfully galvanized. The quality of the galvanizing is strongly influenced by the quality of the casting.  As with all steel to be galvanized, cleanliness is very important to achieve completely galvanized cast iron or steel parts.  However, conventional cleaning processes employed by galvanizers do not always adequately clean castings.  This is because sand and other surface inclusions are not removed by chemical cleaning.  Thorough abrasive cleaning is the most effective method for removing foundry sand and impurities.  In fact, the preferred way to clean the casting is by abrasive blasting (either grit-blasting or a combination of grit and shot). Cleaning is traditionally performed at the foundry before shipment to the galvanizer.  However, some galvanizers are able to perform abrasive blasting at their facilities - check with your galvanizer before sending your parts.  

Sound, stress-free castings with good surface finishes will produce high-quality galvanized coatings. The following design and preparation rules should be applied for castings to be galvanized:

· Avoid sharp corners and deep recesses

·  Use large pattern numerals and generous radii to facilitate abrasive cleaning

· Specify uniform wall sections. Non-uniform wall thickness in certain casting designs may lead to distortion and/or cracking. Cracking results from stress developed as the temperature of the casting is increased during galvanizing. Uniform wall sections and a balanced design lowers stress.

As always, if you have any questions regarding this or any other galvanizing topic, please don't hesitate to contact us:

Hubbell Galvanizing

1-800-244-4258

(315) 736-8311

info@whyrust.com

Minimizing Distortion

Why do some fabricated assemblies distort during galvanizing?  

Stresses induced during steel production and in subsequent fabricating operations, are sometimes relieved when exposed to the high temperature of the molten zinc in the galvanizing kettle (generally around 840 deg. F).  Also, parts of dissimilar thicknesses that are welded together can expand and contract at differing rates, based upon their thickness.  When one of these materials tries to expand or contract and the other material is stationary, distortion can occur.  Galvanizing these types of materials separately can be of great benefit to the manufacturer, from a distortion control standpoint.  For example, with a channel frame and thin plate assembly, the frame and plate should be galvanized separately and bolted or welded together later, rather than welded together before galvanizing.

Guidelines for minimizing distortion and warpage are provided in ASTM A384,Safeguarding Against Warpage and Distortion During Hot-Dip Galvanizing of Steel Assemblies, and CSA Specification G 164, Hot Dip Galvanizing of Irregularly Shaped Articles.

Tips for Minimizing Distortion

To minimize changes to shape and/or alignment, design engineers should observe the following recommendations:

-Where possible, use symmetrically rolled sections in preference to angle or channel frames.

 I-beams are preferred to angles or channels.

-Use parts in assemblies that are of equal or near equal thickness, especially at joints (Figure 5).

-Use temporary bracing or reinforcing on thin-walled and asymmetrical designs (Figure 6).

-Bend members to the largest acceptable radii to minimize local stress concentration.

-Accurately preform members of an assembly so it is not necessary to force, spring, or bend them into position during joining.

-Continuously weld joints using balanced welding techniques to reduce uneven thermal stresses. Pinholes from welding are very dangerous in items to be galvanized and must be avoided. Staggered welding techniques to produce a structural weld are acceptable. For staggered welding of 1/8-inch(4 mm) or lighter material, weld centers should be closer than 4 inches (10 cm).

-Avoid designs that require progressive-dip galvanizing. It is preferable to build assemblies and sub-assemblies in suitable modules, so they can be immersed quickly and galvanized in a single dip. In this way, the entire fabrication can expand and contract uniformly.  Where progressive-dip galvanizing is required, consult your galvanizer.  

The last tip brings about a great point - if you have any questions regarding proper fabrication techniques to facilitate galvanizing, ALWAYS contact your galvanizer!  At Hubbell Galvanizing, we are happy to assist you with any questions you may have.  Feel free to contact us at the following:

(800) 244-4258 - Toll-free

(315) 736-8311 - Office

(315) 736-0381 - Fax

info@whyrust.com

http://www.whyrust.com

Galvanizing Appearance

A large portion of the questions we receive at Hubbell are regarding the appearance of the galvanized product.  One of the most frequent questions in the "appearance genre" is regarding a non-uniform (dull gray and shiny silver) finish.  While the contrast may look surprising and lead you to think there might be an issue with the product, we can assure you that this is a completely normal occurrence.  Most often, the non-uniform appearance results from the chemical make-up of the steel itself.  It is important to note that as the galvanized product weathers over time, the initial appearance differences you see will fade away, and the product will be a uniform matte grey.  Below is an excellent article from the American Galvanizers Association regarding this very topic:

 If you have any further questions about this, or any other topic, please let us know!  You can contact us at the following:
(315) 736-8311
(800) 244-4258
info@whyrust.com

Tubular Fabrications & Hollow Structurals Cleaning

Tubular Fabrications & Hollow Structurals Cleaning

Tubular assemblies (handrails, pipe columns, pipe girders, street light poles, transmission poles, pipe trusses, sign bridges) are commonly galvanized because corrosion protection is afforded to the interior and exterior of the product. To provide an optimal galvanized coating, hollow products require proper cleaning, venting, and draining.

Cleaning

As with all steel, pipe and other hollow materials must be thoroughly cleaned before the molten zinc will metallurgically bond with the steel. Pipe can present two special cleaning challenges. First, the mill coating (varnish, lacquer, and similar materials) applied by pipe manufacturers requires extra time and effort to remove at the galvanizing plant. Some galvanizers do not have the capability to remove this coating. Some organic mill coating formulations, both foreign and domestic, are

extremely difficult to remove with common cleaning solutions, so blasting may be required. Ordering uncoated pipe avoids costly attempts to remove these mill coatings. In some cases, it may be more cost effective to substitute tube for pipe.

Second, welding around mill coatings burns and carbonizes the varnish in the surrounding areas and cannot be removed

by the normal cleaning process at a galvanizer. This soot must be removed by blasting or other mechanical cleaning methods prior to delivering steel to the galvanizing facility. 

Allowing for Proper Drainage

For effective galvanizing, cleaning solutions and molten zinc must flow without undue resistance into, over, through, and out of the fabricated article. Failure to provide for this free, unimpeded flow can result in complications for the galvanizer and the customer. Improper drainage design results in poor appearance, bare spots, and excessive build-up of zinc. All of these are unnecessary and costly, and another example of why communication throughout the project is key.
A few common fabrications where drainage is important are gusset plates, stiffeners, end-plates, and bracing. Following these best design practices will help ensure the highest quality coatings:
• Where gusset plates are used, generously cropped corners provide for free drainage. When cropping gusset plates is not possible, holes at least 112-inch (13 mm) in diameter must be placed in the plates as close to the corners as possible (Figure 1).

Figure 7: Cropped bracing

• To ensure unimpeded flow of solutions, all stiffeners, gussets, and bracing should be cropped a minimum of 3/4-inch (19 mm) (Figure 8). Provide holes at least 112-inch (13 mm) in diameter in end-plates on rolled steel shapes to allow molten zinc access during immersion in the galvanizing bath and drainage during withdrawal.
corners as possible (Figure 1).

Cropped Corners (preferred) ​​Holes close to corners (alternatively)

Figure 8: Cropped gusset plate corners

Alternatively, holes at least 112-inch (13 mm) in diameter can be placed in the web within 1I4-inch (6 mm) of the
end-plate. To facilitate drainage, end-plates should have holes placed as close to interior corners as
possible (Figure 9).

Reactive Steels

Atypical coatings produced from reactive steels exhibit different coating characteristics than a typical galvanized coating such as:

Appearance: The atypical galvanized coating may have a matte gray appearance and/or rougher surface due to the absence of the free zinc layer. The free zinc layer present on typical coatings imparts a shinier finish to a galvanized coating.

Adherence: The zinc-iron alloy coating tends to be thicker than a typical galvanized coating. In the rare situation where the coating is excessively thick, there is the possibility of diminished adhesion under external stress (thermal gradients, sharp impact).

Reactive steels are still galvanized on a regular basis, and it is important to note differences in appearance have no effect on the corrosion protection afforded by the galvanized coating. The performance of the coating is based on the thickness of the zinc; therefore, often the duller (and thicker) coatings produced by reactive steels last longer. Furthermore, all galvanized coatings as they weather over time will develop a uniform matte gray appearance.

It is difficult to provide precise guidance in the area of steel selection without qualifying all steel grades commercially available. However these guidelines discussed will assist you in selecting steels that provide good galvanized coatings.

• Levels of carbon less than 0.25%, phosphorus less than 0.04%, or manganese less than 1.35% are beneficial

• Silicon levels less than 0.04% or between 0.15% - 0.22% are desirable

Silicon may be present in many steels commonly galvanized even though it is not a part of the steel's controlled composition, because silicon is used in the steel deoxidation process and is found in continuously cast steel. Both silicon and phosphorous act as catalysts during the galvanizing process, resulting in rapid growth of zinc-iron alloy layers.And even when both elements are individually held to desirable limits, the combined effect between them can still produce an atypical coating of all or mostly zinc-iron alloy layers. When possible, your galvanizer should be advised of the grade of steel selected in order to determine whether specialized galvanizing techniques are suggested.