For the first 50-60 years of the industry, chutes were manufactured of #16 gauge B&S Aluminum. This material was less expensive, corrosion-resistant, and easier to work with than steel and provided 15-20 years of durability before requiring to replacement.

In the mid 60’s US chute manufacturers shifted to the use of #16 gauge Galvanized steel sheet for several reasons. Primarily aluminum sheet pricing was on the rise, exceeding that of galvanized, and aluminum chutes installed more than 20 years prior had reached “end of life”, causing building owners to seek longer life products.

Around the mid-’70s to 80s, the health hazards associated with welding galvanized sheet had become known, and OSHA required the installation and use of expensive breathing and exhaust apparatuses for employee health. In response, the chute industry, like automotive, rail, and most other manufacturing, changed materials to use “Aluminized” steel. Steel sheet coated with aluminum and silicon. While this addressed the employment health issues related to the welding galvanized sheet, the aluminum plating is softer, reducing durability, and would not hold paint for primer or sound dampening coatings required in chutes. This period was the golden age of chute specifications being written, placing “Aluminized Steel” into every architect’s spec’s and they’ve not been updated to current industry standards. This was also and the beginnings of the NFPA #82 standards development.

In more recent history, last 10-20 years, the industry moved from the ever-increasing costs and challenges of production with “Aluminized”, which is manufactured primarily for high heat applications like furnaces, exhaust systems, etc., to a new product designed for durability and quality finishes in the automotive, rail, and most manufacturing industries of this type, commonly known as “Galvanneal”, “Satin Coat”, “Paint Lock” and Jet-Kate” for its durability and ability to bond well with coatings.

Material Definitions

Aluminized Steel:

Aluminized steel is steel that has been hot-dip coated on both sides with aluminum–silicon alloy. This process assures a tight metallurgical bond between the steel sheet and its aluminum coating, producing a material with a unique combination of properties possessed neither by steel nor by aluminum alone. Aluminized steel shows a better behavior against corrosion w and keeps the properties of the base material steel for temperature lower than 800 °C (1,470 °F). For example, it is commonly used for heat exchangers in residential furnaces, commercial rooftop HVAC units, automotive mufflers, ovens, kitchen ranges, water heaters, fireplaces, barbecue burners, and baking pans. This steel is very useful for heating things up because it transfers heat faster than most other steels.

Galvanized Steel:

Hot-dip galvanization is a form of galvanization. It is the process of coating iron, steel, or aluminum with a layer of zinc by immersing the metal in a bath of molten zinc at a temperature of around 840 °P (449 °C). When exposed to the atmosphere, the pure zinc (Zn) reacts with oxygen (O2) to form zinc oxide (ZnO), which further reacts with carbon dioxide (CO2) to form zinc carbonate (ZnCO3), a usually dull grey, fairly strong material that stops further corrosion in many circumstances, protecting the steel below from the elements. Galvanized steel is widely used in applications where corrosion resistance is needed without the cost of stainless steel and can be identified by the crystallization patterning on the surface (often called a “spangle”).

Galvanized steel can be welded; however, one must exercise caution around the resulting toxic zinc fumes. Galvanized steel is suitable for high-temperature applications of up to 392 °F (200 °C). The use of galvanized steel at temperatures above this will result in the peeling of the zinc at the intermetallic layer. Electrogalvanized sheet steel is often used in automotive manufacturing to enhance the corrosion performance of exterior body panels; this is, however, a completely different process that tends to achieve lower coating thicknesses of zinc.

Like all other corrosion protection systems, galvanizing protects steel by acting as a barrier between the steel and the atmosphere. However zinc is a more electronegative metal in comparison to steel, this is a unique characteristic for galvanizing which means that when a galvanized coating is damaged and steel is exposed to the atmosphere, zinc can continue to protect steel through galvanic corrosion (often within an annulus of 5 mm above which electron transfer rate decreases).

Galvanneal:

Galvannealed or Galvanneal is the result of the combined process of galvanizing and annealing to produce specialized sheets of steel. The galvanization is made through the hot-dipping (Hot-dip galvanizing) process and immediate in-line annealing and gives a very fine greyish matte finish. Galvanneal does not flake off the galvanized coating when formed, stamped, and bent as Galvanized does. The very fine matte finish acts as a primer, allowing the paint to adhere easily, and is very rust proof; only white to dark grey marks appear if it comes in contact with water. Galvanneal sheets offer good paintability, weldability, corrosion resistance, and formability. It is extensively used in the automotive, signage, electric equipment, and other industries requiring a metal with good paintability and long reliable service life. This steel process is produced by many steel mills and it is commonly referred by its trade name of Jet -Kote.

Notes:

Please keep in mind that Aluminum is softer than Zinc and chute products are about material handling and impact, not air. The “Galvannealed” steel product combines the corrosion resistance of Galvanized and annealed it with the steel sheet to provide superior wear and corrosion resistance with improved workability without the manufacturing health risks. Further, because it is a zinc coating it is galvanized, which has had the second process of annealing performed to better bond and mix it with the steel. As such, in my opinion, it meets the NFPA #82 criteria of being “Galvanized”. As a member of the NFPA #82 Technical Committee, I am submitting this revision and expect it to be listed in the next version.

Respectfully submitted,

James R Buchanan Jr., CEO

Western Chutes, Compactors & Recycling Systems.