Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Pilot end having means enhancing fastening or installation
Reexamination Certificate
2000-02-11
2001-06-26
Wilson, Neill (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Pilot end having means enhancing fastening or installation
C411S412000, C411S426000
Reexamination Certificate
active
06250866
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to attaching materials to concrete substrates. In particular the present invention relates to a self-drilling, self-tapping screw for light concrete blocks.
Concrete is a hard and friable substance difficult to penetrate and engage with a threaded fastener. The properties of concrete conventionally dictate that a clearance hole be provided before any fastener may be affixed to the concrete. Conventionally, when fastening an item to concrete block one typically first uses a carbide tipped drill to provide a clearance hole before a self-tapping fastener can be installed. After the hole is drilled with a drill bit in a hammer drill, a screw gun is used to install the screw. In some applications, a lead or plastic insert may be placed in the clearance hole before the screw is installed. While this process works well, it may be characterized by relatively high labor and material costs because the process involves several steps, multiple tools and frequently the handling and installation of multi-piece fasteners.
U.S. Pat. No. 4,034,641 to Williams et al discloses one type of self-drilling anchor to which the present invention generally relates. The self-drilling anchor has a driving head, a shank having a threaded portion and an unthreaded portion and a drill tip. A conventional drill tip at the end of the shank is defined by a taper and flutes. The unthreaded portion of the shank is forged in a configuration having major and minor diameters.
A drill tip capable of reliably penetrating concrete must be made of material having a hardness which typically renders the material too brittle to be used for the driving and holding functions required of the shank and head portions of the fastener. The unitary fastener composition of conventional related fasteners must compromise either the hardness constraints of the drill tip or the durability constraints of other parts of the fastener often leading to mechanical failure at either the head or shank or to an unnecessarily expensive fastener.
SUMMARY OF THE INVENTION
Briefly stated, the invention in a preferred form is a self-drilling, self-tapping screw for light concrete blocks or other such concrete substrates of limited thickness. The present invention is a one-piece drill/fastener combination constructed of a unitary piece of steel which mounts a carbide drill tip. The fastener is composed of a head and a specially configured shank extending from the underside of the head to the drill tip. The shank has a threaded portion adjacent the head and an unthreaded portion extending from the threaded portion to a distal slot for holding a carbide drill tip. The head is adapted for rotational engagement with a driving tool and includes a radially enlarged flange for bearing against the material to be fastened. The threaded portion of the shank includes dual diameter threads which are capable of forming and mating with grooves in the clearance hole. The distal end of the unthreaded portion of the shank provides a location for mounting the carbide drill tip in an axially spaced relationship to the threaded portion of the shank. The length of the unthreaded portion of the shank is preferably at least equal to the thickness of the concrete substrate.
More particularly, the length of the unthreaded portion of the shank is selected such that the drill tip can fully penetrate the concrete substrate prior to the threaded portion engaging the clearance hole. This relationship is significant because the axial progress of the self- drilling tip through the concrete will vary depending on the hardness of the material being drilled, the amount of pressure axially exerted on the drill tip and the rotational speed of the drill tip. In contrast, the axial progress of the threaded portion of the shank through the concrete substrate is determined by the slope of the threads and the rotational speed of the shank.
Simply put, if the hole is not completely drilled through the concrete substrate prior to threaded engagement with the clearance hole, the threads will attempt to force the drilling tip through the concrete substrate at an axial rate faster than the drill tip is capable of penetrating the concrete substrate. The axial and rotational forces presented by such a mismatch will lead to mechanical failure of the fastener or failure of threaded engagement with the concrete substrate (stripping of the threads).
This invention thus allows the boring of a clearance hole and installation of a concrete fastener in one step producing significant material and labor savings. The steps of drilling a clearance hole and installing a fastener are combined into one operation requiring one installation tool and one piece of hardware. The invention is specifically adapted for use with light concrete blocks, it is equally applicable to affixing materials to any type of masonry, stone or other such substance having a predetermined thickness.
An object of the present invention is to provide a new and improved fastener for concrete blocks which eliminates labor intensive steps and creates significant labor savings.
A further object of the present invention is to provide a new and improved fastener for concrete substrates which eliminates material and tool costs of installation.
A yet further object of the present invention is to provide a self-drilling, self-tapping screw for concrete substrates which permits the drilling of a clearance hole and installation of a fastener in the clearance hole in one step.
Other objects and advantages of the invention will become apparent from the drawings and the specification.
REFERENCES:
patent: 3207023 (1965-09-01), Knohl
patent: 4034641 (1977-07-01), Williams, Jr. et al.
patent: 4439077 (1984-03-01), Godsted
patent: 5061136 (1991-10-01), Dixon et al.
Alix Yale & Ristas, LLP
Olympic Manufacturing Group, Inc.
Wilson Neill
LandOfFree
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