Electric heating – Metal heating – By arc
Reexamination Certificate
2001-10-26
2003-11-18
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
By arc
Reexamination Certificate
active
06649871
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to welding systems, and particularly to a welding system having a welding gun.
BACKGROUND OF THE INVENTION
Welding is a method of joining pieces of metal together into one solid piece. Welding guns are used in a number of different types of welding. For example, welding guns are typically used in arc welding. An arc welding system typically comprises an electric power supply coupled to a welding gun that houses an electrode. The electric power supply typically includes a conductive cable and a clamp for securing the conductive cable to the metal piece to be welded. The electrode in the welding handle, along with the metal piece and conductive cable, completes an electrical circuit with the power supply when the electrode is placed against the metal piece. The contact between the electrode and the metal piece produces an electric arc between the electrode and the metal piece. The heat of the electric arc is concentrated on the metal piece, or pieces, to be joined. The heat of the arc melts the metal piece, or pieces. A filler material is added to the molten metal. The molten mass then cools and solidifies into one piece, joining the metal pieces.
MIG (Metal Inert Gas) welding is one type of arc welding. MIG welding is also referred to as “wire-feed” or GMAW (Gas Metal Arc Welding). In MIG welding, a metal wire is used as the electrode to produce the arc. Electricity passing through the electrode wire melts the workpiece at the point of contact. Additionally, the electrode wire acts as the filler for the weld. The electrode wire is shielded at the point of contact by an inert gas. The inert gas shields the molten metal at the point of contact from outside contaminants and gases that may react with the molten material. Non-inert gases, such as CO
2
, also may be used in MIG welding systems.
The wire and gas are typically fed through a welding cable and a hand-held welding gun. The welding cable feeds the wire from a wire feeder and gas from a gas cylinder to the welding gun. The welding cable also has additional conductors to assist the wire in conducting power from the power source. The welding gun has a neck that is used to direct gas and wire toward a workpiece. The neck is connected to a connector in the welding gun. The neck has an inner portion through which the electrode wire passes and which is electrically coupled to the conductors in the welding cable when the neck is secured to the welding gun. The inner portion of the neck, in turn, is electrically coupled to the electrode wire via a conductive tip. The neck has an outer portion and insulating material disposed between the inner and outer portions so that the outer portion is electrically isolated from the inner portion.
The welding gun enables a user to control the welding process. The welding gun, typically, has a switch, or trigger, that is coupled to the wire feeder. When the trigger is operated, gas and wire are fed to the welding gun from the gas cylinder and wire feeder via the welding cable. Additionally, the power source applies electrical power to the electrode wire and to the conductors in the welding cable. A first portion of the current flows through the electrode wire in the welding cable. A second portion of the current flows through the conductors in the welding cable, to the inner portion of the neck, and then merges with the first portion of the current in the electrode wire at the tip.
Submerged Arc Welding is another type of wire fed arc welding. In submerged arc welding, a granular flux, rather than a gas, is used. Typically, the flux is fed from a reservoir to the welding gun through a power source coupled to a wire feeder. As in MIG welding, the electrode wire is fed from the wire feeder. The electrode wire completes the electrical circuit and creates an arc to melt the object metal. In submerged arc welding, the actual point of metal fusion and the arc are submerged within flux, not gas. Typically, the flux is a granular composition of chemical and metallic materials that is continuously deposited just ahead of the electrode. The electrical current melts the electrode to form the weld puddle. The portion of the flux that is adjacent to the electrode tip and the puddle will melt, forming a slag layer that refines the weld and excludes air.
As in MIG welding, the welding handle, typically, has a switch, or trigger, that is coupled to the power source/wire feeder. When the trigger is operated, the flux and wire are fed to the workpiece through the welding gun. The welding gun also has a neck that is used to direct wire and/or flux toward a workpiece. The neck electrically couples the conductors in the welding cable to the wire, typically, at a point on the wire near the end of the neck. When the welding gun trigger is operated, flux and wire are fed to the welding gun from the flux reservoir and wire feeder via the welding cable. Additionally, power is applied to the electrode wire and to the conductors in the welding cable.
In both of these systems, the neck is secured to the welding handle by a retaining nut. The retaining nut secures the neck to the welding gun so that electricity can flow from the welding cable to the inner portion of the neck. There are different types of retaining nuts used to secure welding gun necks to a welding handle. Some retaining nuts are made of a nylon piece with a threaded brass insert. The welding handle has a corresponding threaded portion adapted for threaded engagement with the brass insert. The nylon serves as an insulator to prevent electricity from flowing through the retaining nut. If the retaining nut loosens, the area of contact between the neck and the handle will decrease. This increases the electrical resistance between the neck and the welding cable. In some applications, such as with electrical currents above 400 amps, the increase in electrical resistance results in the production of a substantial amount of resistive heating. The heat from the resistive heating produced at the interface may heat up the handle to the point where it cannot be held.
Consequently, it may be desirable to wrench tighten the retaining nut to the welding handle so that neck does not come loose. A normal torque generated to hand-tighten a retaining nut is in the range of 5-6 foot-pounds (ft-lbs). However, the normal torque generated to wrench-tighten a retaining nut is in the range of 35-40 ft-lbs. The low tensile strength of the nylon prevents a retaining nut made of nylon with a brass insert from being tightened to this range of torque using a wrench. Therefore, in the applications where wrench-tightening is desired the retaining nuts are made of metal, such as copper. However, metal retaining nuts are electrically conductive. Consequently, an electrical insulator is typically placed between the electrode wire and the retaining nut to prevent electricity from flowing from the electrode wire through the neck to the retaining nut. Additionally, metals, such as copper, are more expensive than polymeric materials, such as nylon.
There exists a need for a retaining nut that be may formed of a polymeric material, but which has sufficient strength to enable a neck to be secured to a welding handle by wrench tightening the retaining nut.
SUMMARY OF THE INVENTION
The present technique provides a novel retaining nut designed to respond to such needs. According to one aspect of the present technique, the retaining nut consists essentially of a polymeric material. The polymeric material may be polyphenylene sulfide (PPS). In another aspect of the present technique, the retaining nut comprises polyetheretherketone (PEEK).
According to still another aspect of the present technique, a welding gun is featured. The welding gun has a handle and a neck. The handle is used to position the welding gun and the neck is used to direct electrode wire towards a workpiece. The neck is secured to the handle by a retaining nut. In this aspect of the present technique, the retaining nut consists essentially of a polymeric material, such as
Elve M. Alexandra
Fletcher Yoder
Illinois Tool Works Inc.
Kerns Kevin P.
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