Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2000-05-15
2001-08-14
Yee, Deborah (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C148S642000, C148S644000
Reexamination Certificate
active
06273974
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to nails and similar elongated fasteners having portions selectively hardened to create desired properties and behavior, and a method of making the selectively hardened nails.
BACKGROUND OF THE INVENTION
Various techniques are known for treating the surfaces of nails and similar elongated fasteners. U.S. Pat. Nos. 5,655,969 and 5,564,876, both issued to Lat, disclose nails manufactured from carbon steel wire pre-coated with a protective metallic layer having corrosion resistant properties. The nails also have a protective corrosion-resistant cap. U.S. Pat. No. 5,178,903, issued to Lat et al., discloses coating a nail with zinc, followed by a polyurethane resin.
U.S. Pat. No. 4,486,248, issued to Ackert et al., discloses wear-resistant railroad rails produced by controlled forced cooling from above the austenite transition temperature, to yield a fine perlite metallurgical structure in the head portions of the rails.
One type of nail used in the construction industry is a positive placement nail. Positive placement nails are typically driven with a high powered driving tool to hold a 12-gauge or other steel plate to wood. The nails are driven through holes present in the steel plate, and into the wood. This construction method is used for building foundations, floor joists, and roofing. Some positive placement nails are hardened in a batch process to improve their strength. This process, which involves heat treating and hardening the entire length of the nail, is expensive and time consuming, and difficult to control.
The holes in the steel plate may only be slightly larger than the shank diameter of the nail, and are smaller than the head diameter of the nail. When the nails miss the holes and hit the steel plate at high speed, they become bent or distorted at the contact end and ricochet. Nails which ricochet create obvious hazards for the tool operator and others in the area.
Pallet nails used in the crating and construction industries hold pallets together. Pallet nails are generally long and thin so as not to split the hardwood boards of the pallet. A pallet nail with a larger shank diameter has a greater tendency to split the pallet boards during driving than a nail with a smaller shank diameter. If a pallet nail is too thin, it bends easily, especially at the junction between the top pallet board and the skid, which is typically about 0.5 inch below the nail head. This bending often occurs during severe service of a pallet, when the fork lift bumps into the side of the pallet creating stress between a pallet board and skid. It has been difficult to develop a pallet nail which minimizes board splitting and resists bending.
SUMMARY OF THE INVENTION
The present invention provides nails which are hardened only at selected locations for the purpose of improving performance in their specialized use. In one embodiment, only the pointed end and lower shank portion of the nail is made harder than the upper portion of the shank. In another embodiment, a central region of an elongated nail shank is made harder than portions of the shank above and below the region. Other embodiments are also contemplated.
The selective hardening is accomplished by heating a portion of the nail to a temperature higher than about 1400° F., and then quenching (i.e. rapidly cooling) it. The selective heating causes that portion of the nail to transform from a ferritic pearlitic structure to an austenitic structure. The quenching transforms the austenitic structure to a martensitic structure, which is harder and less ductile than the untreated structure. The untreated portion of the nail has a ferritic pearlitic structure, which is softer and more ductile. The treated portion of the nail is more resistant to bending.
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Marketing brochure of Elco Industries, Inc., entitled “DRIL-FLEX, A New Concept In Structural Fastening”, dated Feb. 1989.
Godsted Kent B.
Lat Geronimo E.
Spoto Louis M.
Illinois Tool Works Inc.
Pauley Peterson Kinne & Fejer
Yee Deborah
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