Both types of wire, oil tempered springs and galvanized hard drawn springs, are made from the same basic raw material: a high-carbon steel rod which is “drawn” down to a specific wire diameter. The simple explanation of the drawing process is that the wire is “stretched” to a specific wire diameter by running the rod through a series of progressively smaller dies, coated with a lubricant until the required diameter is achieved.
Galvanizing is the process of applying/ bonding a zinc coating to the surface of the wire. In the case of galvanized wire for garage door springs, the galvanizing process is done prior to drawing. You may have heard the term “drawn after galvanizing” or DAG. This is the process currently used to manufacture galvanized spring wire for garage doors.
Oil tempering is an additional step in the process after the wire is drawn in which oil is used to heat-treat the wire to give it certain properties. The wire is heated to a very high temperature—in excess of 1500 degrees Fahrenheit—then cooled rapidly or quenched using oil, and then reheated again to a very high temperature. This process is intended for wire used in springs “that are subjected to static loads or relatively infrequent stress applications,” according to ASTM. This is meant to distinguish garage door spring applications with relatively low cycles from valve spring wire for automotive applications, which are very high stress, high-cycle springs for example.
Historically, the garage door industry used torsion springs made of oil tempered wire that conformed to ASTM 229 standards which detail, among other things, tensile strength ranges by wire size. This wire falls into two categories: Class I and Class II. The difference is that Class II has higher tensile ranges than Class I in the same wire size.
At one time, the garage door industry had a unique classification called Overhead Door Quality. It was a hybrid between Class I and Class II. Although some wire mills still supply Overhead Door Quality oil tempered wire, today the vast majority of the industry sees Class II.
Oil tempered springs has excellent performance properties for garage door torsion springs. A significant negative aspect of oil tempering material is the oil residue from the oil tempering process. This residue stays with the wire even after the spring has been coiled and heat-treated. This requires the installer to be very careful not to leave handprints on the garage door and walls after installation or else face an unhappy homeowner. This oil residue has no rust-inhibitive benefits, therefore oil tempering springs, as any unprotected steel product, will rust rather quickly, presenting yet another challenge to the hard-working door installer carrying springs in his service truck.
Some door manufacturers began to require the application of a painted finish to their residential torsion springs, thereby providing a clean spring surface as well as some degree of rust protection. As the average residential torsion spring weighs about 10 pounds, this process was, at that time, very labor intensive. The timing was perfect to present a product that provided the benefits of a clean, rust-inhibitive coating without the additional labor. Galvanized springs appeared to be the perfect solution.
This wire was a lead-patented hard drawn wire, galvanized to solve the residue and appearance issues. As an added benefit, according to press releases from that time, it also provided superior cycle life in comparison to springs made from oil tempering springs.
Galvanized hard drawn springs look great and usually are nice and shiny when installed. Springs manufactured from oil tempering wire and coated after coiling look great as well, thanks to the development of rust inhibitor coatings that offer a clean, non oily surface and a brilliant shiny, black finish. It’s important to mention that galvanized hard drawn wire has a limited shelf life. Over time, the finish on the galvanized hard drawn wire will begin to dull, and a white, powder-like substance will appear on the surface. This is known as white rust and is oxidation of the zinc coating. Springs made from galvanized hard drawn wire will exhibit this characteristic over time and will not maintain their shiny appearance indefinitely. Springs manufactured from oil tempering wire, even with the newest coatings available to the market, will also oxidize over time, although the appearance of the oxidation does not seem to be as apparent as that of the galvanized hard drawn.
ADM Garage Doors, Inc.
138 McFarland Drive
Folsom, CA 95630
CA Lic# 904244
Cell Number/Text (916) 595-5355
Folsom (916) 985-0151
Roseville (916) 451-5248
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Folsom (916) 985-0151
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