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Publication numberUS3592100 A
Publication typeGrant
Publication dateJul 13, 1971
Filing dateMay 9, 1968
Priority dateMay 9, 1968
Publication numberUS 3592100 A, US 3592100A, US-A-3592100, US3592100 A, US3592100A
InventorsCzeslaw Mackiewicz, James E Meehan
Original AssigneeHubbell Inc Harvey
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Binding screw having electrically insulated head
US 3592100 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United States Patent [72] Inventors Cuslaw Mncl lewlcz Trumbull; James E. Meehan. Bridgeport, both 01, Conn. 211 App]. No 121.939 [221 Filed May 9, 1968 [45] Patented July [3, 1971 [73] Auignee Ihrvey l-lubbell, Incorporated lrldgepurt, Conn.


(52] U.S.CI. 85/1, lO/IO. l0/27, 85/9, 1I7/2l, 117/113, lI7/l28.4, 174/54. 200/ I 53 [51] Int. Cl ..F16b 23/00, Fl 6b 35/00 [50) run-rm 85/1C,

NH. 1 JP, 9, 1,54, 37,45; l5l/38,7; 10/10, 27 P, 27.5.3; 117/21, 3, 116?, 128.4, I27, 132C, 23033,4; l74/l66, I93, 54, 58

[S6] Relerenees Clted UNITED STATES PATENTS 268,697 12/1882 Lewis .1 85/54 UX 1,717,388 6/1929 KeeIerW 10/10 2,145,744 1/1939 Whitneyum 4 85/9 UX 2,191,171 2/1940 Leeetal 174/166 2,326,455 8/1943 Gray .4 85/37 2,724,303 11/1955 l-lolcomb.... 85/10 2.844.489 7/1958 Gemmer 117/21 X 2,981,651 4/1961 Arnold 117/21 X OTHER REFERENCES MATERIALS IN DESIGN ENGINEERING, February, 1960, pp. 91- 95,copy available in I I7 21.

Primary Examiner- Ramon S. Britts Anorney- Wooster, Davis & Cifelli ABSTRACT: A binding acrew having a threaded shank and an enlarged head coated with a plastic insulating material. The head includes a usual slot which is cut through the insulating material exposing the base metal.

BINDING SCREW HAVING ELECTRICALLY INSULATED HEAD BACKGROUND OF THE INVENTION This invention relates to a binding screw and a method of making the same and, more particularly, to such a screw having a layer of plastic insulation material deposited upon its head. This invention further relates to the use of insulated head binding screws with grouped switches to prevent arcing between adjacent screwheads.

It is common to group switches in an outlet box for conveniently providing a group of AC switches at a single location. However, when high-voltage circuits, for example, 20 a. 277/480 v. AC, are controlled by the switches a potentially hazardous condition exists in the outlet box. The usu =.l laterally outwardly extending binding screws of each of the closely mounted switches present exposed live metal parts across which arcing may occur when a 700 volt potential exists between adjacent binding screws. To prevent this condition, the National Electrical Code provides in part that: "Snap switches shall not be grouped or ganged in outlet boxes unle s they can be so arranged that the voltage between exposed live metal parts of adjacent switches does not exceed 300 volts.

One solution to the problem of grouping AC switches in high voltage circuits has been to eliminate the binding screws altogether and to back wire current-carrying leads to the switch bodies. The leads may be captured by suitable internal spring clips in a known manner. However, these clips often lose their resilience and become unreliable. Therefore, it would be desirable to retain the positive mechanical securing action of a binding screw of either a back-wired switch or a binding-head type while ensuring that no arcing will occur between adjacent switches when closely mounted in an outlet box.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of this invention to provide a binding screw with an electrically insulated head and a method ol'forming the same.

Another object of this invention is to provide a binding screw having a layer of plastic insulating material deposited upon its head and having the base metal material exposed in the slot.

A further object is to provide a plurality of grouped switches with the binding head screw described in the above paragraphs.

To accomplish the primary object, in one form, there is provided a binding screw having a threaded shank with an enlarged electrically insulated slotted head at one end. The head includes a layer of plastic insulation material surrounding the metal head of the screw and the slot extends through the layer of plastic insulation material and into the metal head to expose the base metal of the head.

BRIEF DESCRIPTION OF THE DRAWING Other objects and further details of that which is believed to be novel and the present invention will be clear from the following description and claims taken with the accompanying drawing wherein:

FIG. 1 is a front elevational view of an outlet box with the cover removed housing a series of grouped AC switches having binding head screws constructed in accordance with this invention;

FIG. 2 is a perspective view of a screw blank with a coated head;

FIG. 3 is a perspective view of the screw blank of FIG. 2 in which a shank has been threaded;

FIG. 4 is a perspective view similar to that of FIGS. 2 and 3 in which the head has been slotted;

FIG. 5 is a side elevational view partly in section showing a binding head screw constructed in accordance with the invention;and

FIG. 6 is a schematic side elevational view of a holding rack of screw blanks positioned above a trough of coating material DESCRIPTION OF THE PREFERRED EMBODIMENT With particular reference to the drawing there is illustrated in FIG. I a plurality of AC switches 10 mounted in an outlet box 12 upon mounting lugs 14. Each switch includes a cover 16 made of a plastic insulating material, a toggle l8, and a plurality of laterally outwardly extending binding screws 20. A mounting strap 22 carrying securing screws 24 retains each switch in position in the outlet box upon the mounting lugs. The lateral position of each binding screw 20 is determined by the size lead captured thereby when the lead is secured by the head. Therefore, it should be noted that the heads of the bind ing screws of adjacent switches may be extremely close together and in fact may be in direct contact. In order to satisfy the above-quoted requirement of the National Electrical Code the binding screws 20 have been formed to eliminate the conventional exposed live metal parts of these screws.

The novel binding screw 20 of this invention is clearly illustrated in FIGS. 4 and 5. This screw includes a metallic threaded shank 26 having an enlarged metallic head 28 at one end. A layer of synthetic plastic insulating material 30, such as nylon, is bonded to the top and sides of head 28 and a slot 32 is formed through the plastic layer 30 into the head 28 (see FIG. 5). The dielectric coating material has been selected to be hard enough to allow it to be machined in the slotting operation without hurting while also being resilient enough to prevent chipping and cracking. The design of this novel binding screw 20 relies on a dielectric coating thickness of at least 0.010 inch to provide adequate insulation. It has been determined that when binding screws constructed in accordance with this invention are positioned with their heads touching one another (i.e. having a total insulation thickness of 0.02 inch) they are able to withstand approximately 3,000 volts therebetween without breakdown of the dielectric. Therefore, it should be apparent that their use in 277/480 v. AC circuits is well within acceptable limits. It should also be pointed out that although these binding screws 20 have been developed to solve a particular problem-viz grouped AC switchesthey will find usage in a great number of applications where exposed live binding screws are present.

Although the screwheads 28 may be coated after slotting, this has been found to be disadvantageous for several reasons. First, the screwdriver will often cut through the insulation in the slot and tear out sections of insulation in the slot and on the top surface of the head. Second, the coated slot generally does not have flat walls to transmit applied torque from a screwdriver which has a tendency to slip out of the slot. Third, the resilient insulating material in the slot presents a plastic cushion between the screw and the screwdriver which results in an uncertain feeling when tightening the screw. Fourth, the slot does not coat uniformly giving a poor appearance to the finished article. Finally, there is no visual means of inspecting for adequate coat thickness. The novel binding screws 20 illustrated in FIGS. 4 and 5 overcome the above disadvantages with the base metal material exposed in the slot thus eliminating the false sense of security which might be associated with a totally coated head.

The binding screws 20 of this invention are formed by heading a usual screw blank 34, loading a plurality of blanks 34 in a holding rack 36 (note FIG. 6), heating the screw blanks and immersing the heads of the blanks into a trough 28 of suitable insulating material 40 which may be in the form of an airagitated fluidized bed of nylon powder or a liquefied plastic. Holding rack 36 is moved downwardly to allow only the head of the blank to be immersed in the insulating material. The immersed heated screwheads melt the nylon particles or react with the liquefied plastic so that a layer of plastic insulation is firmly adhered to and is built up upon the screw blanks. The thickness of the layer is controlled by the temperature of the blanks as well as the length of immersion time. The coated screw blank 42 (note FIG. 2) is removed from the holding rack 36 and may be transferred to a threading apparatus where a thread 26 is rolled upon its shank in a known manner. it then may be slotted as at 22 to form the finished article (note H68. 4 and 5).

It is believed that the many advantages of this invention will now be apparent to those skilled in the art. As set forth in the objects above there is provided an inexpensive binding screw which may be used in high-voltage circuit AC switches, particularly those grouped in a common outlet box to prevent arcing between binding head screws of adjacent switches. Of course, the binding screw will find numerous applications in other environments.

It should be understood that the present disclosure has been made only by way of example and that numerous changes in details of construction and the combination and arrangement of parts may be resorted to without departing from the true spirit and scope of the invention as hereinafter claimed.

What we claim is:

l. A binding screw comprising: a threaded metallic shank; an enlarged metallic head integrally formed with said shank at one end thereof, said head having a top and sides; a relatively thin layer of plastic electrical insulation material secured to and surrounding the top and sides of said head; and a transverse slot extending through said layer of plastic insulation material into said head, thereby exposing the base metal of said metallic head throughout the sidewalls of said slot.

2. The binding screw defined in claim I wherein said layer of plastic insulation material is bonded to said head.

3. A method of forming a binding screw comprising the steps of: forming a head screw blank; heating the blank; immersing the heated head in a mass of plastic insulation material for a predetermined time thereby bonding the insulation material to the head and building up an insulation layer of desired thickness; removing the coated blank from the mass of insulation material; threading the shank of the screw blank; and slotting the head of the screw blank through the insulation layer and into the metal head.

4. The method of forming a binding screw as defined in claim 3 wherein said mass of plastic insulation is a fluidized bed of nylon particles formed by continuously agitating the nylon particles with an airblast passing therethrough.

5. The method of forming a binding screw as defined in claim 3 wherein said mass of plastic insulation is a bath of liquid plastic material.

Patent Citations
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US268697 *Sep 7, 1863Dec 5, 1882 Furniture-pad
US1717388 *Jul 16, 1928Jun 18, 1929Keeler Brass CoMethod of making screws
US2145744 *Dec 13, 1935Jan 31, 1939Gen Motors CorpTerminal
US2191171 *Aug 28, 1937Feb 20, 1940Line Material CoInsulator
US2326455 *Mar 13, 1942Aug 10, 1943Glenn L Martin CoFastening means
US2724303 *Mar 29, 1950Nov 22, 1955Robert L HolcombDriver fastener having coating of elastic insulating material
US2844489 *Dec 20, 1957Jul 22, 1958Knapsack AgFluidized bed coating process
US2981651 *Aug 2, 1956Apr 25, 1961American Marietta CoSealing members and methods
Non-Patent Citations
1 *MATERIALS IN DESIGN ENGINEERING, February, 1960, pp. 91 95, copy available in 117 21.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4041834 *Aug 24, 1976Aug 16, 1977Illinois Tool Works Inc.Plastic headed fastener assembly
US4507035 *Nov 18, 1983Mar 26, 1985Roller Corporation Of AmericaImpact resistant assembly
US4630168 *Dec 16, 1985Dec 16, 1986The Boeing CompanyIn an aircraft
US4631640 *Aug 19, 1985Dec 23, 1986Nippon Electric Co. Ltd.Portable radio device for protecting a radio circuit from static electricity
US4760493 *Sep 30, 1985Jul 26, 1988The Boeing CompanyLightning protection system for composite material aircraft structures
US4813833 *Sep 6, 1983Mar 21, 1989Brock Manufacturing, Inc.Threaded fastener having jacketed head
US5122021 *Mar 22, 1991Jun 16, 1992The Fastron CorporationEncapsulated fastener and washer
US5360639 *Aug 17, 1993Nov 1, 1994Kenji KawabataThree dimensional screws, covering heads with patterns and grinding a film off of projections to form decoration
US5590495 *Jul 6, 1995Jan 7, 1997Bressler Group Inc.Solar roofing system
US5830779 *Jan 6, 1997Nov 3, 1998Bressler Group Inc.Method of making photovoltaic module
US6315485Aug 13, 1999Nov 13, 2001Northrop Grumman CorporationLow observable aircraft fastener treatment
US6475094Mar 27, 2000Nov 5, 2002Mark W. BrunsMethod for making product and product having ultra high molecular weight plastic parts
US6676351Nov 4, 2002Jan 13, 2004Pride Solutions, LlcProduct having ultra high molecular weight plastic parts
US7744321 *Feb 13, 2007Jun 29, 2010Arris Group, Inc.Insulated fastener
US8032221Mar 24, 2009Oct 4, 2011Medtronic, Inc.Sealing setscrew
US8190260Mar 24, 2009May 29, 2012Medtronic, Inc.Lead retention and sealing device
EP0391023A1 *Jan 17, 1990Oct 10, 1990Textron Inc.Improvements in non-corrosive headed composite fasteners and a method of producing the same
WO2006033946A2 *Sep 13, 2005Mar 30, 2006Jeffrey L StrunkSelf-filling fastener and method of making
U.S. Classification411/403, 425/270, 427/185, 411/908, 470/9, 174/159, 174/54, 470/11, 411/903, 411/914
International ClassificationH01R4/70, H01R4/30, F16B33/00
Cooperative ClassificationH01R4/70, Y10S411/908, Y10S411/903, H01R4/30, Y10S411/914, F16B33/004
European ClassificationH01R4/70, F16B33/00B
Legal Events
Aug 31, 1987ASAssignment
Effective date: 19870401