Electric heating – Metal heating – By arc
Reexamination Certificate
2002-08-23
2004-05-25
Stoner, Kiley (Department: 1725)
Electric heating
Metal heating
By arc
C219S137420
Reexamination Certificate
active
06740848
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a welding torch for use in gas metal arc welding.
BACKGROUND OF THE INVENTION
Welding torches for use in gas metal arc welding are well known. The gas metal arc welding is often referred to as MIG (metal inert gas) welding. The known welding torches comprise a neck portion, a diffuser at a first end of the neck portion, a contact tip which extends from the diffuser, and connector means which is at a second end of the neck portion and which is for connecting the neck portion to a power cable assembly. The power cable assembly supplies electricity and gas to the welding torch. The gas is for protecting welds from atmospheric contamination as the welds are made using the welding torch. The welding torch is usually operated by a trigger switch in a handle part of the welding torch.
The neck portion of the welding torch is often referred to a swan neck or a goose neck. The neck portion is such that it comprises an electrical conductor for carrying electrical current to the welding arc that occurs during use of the welding torch. The neck portion also comprises a passageway for the gas. The neck portion operates in a very harsh environment. The neck portion has to protect a welding operator from possible dangers of electrocution. Therefore the strength and insulation integrity of the neck portion are of paramount importance. Insulation designs for the neck portion vary between torch manufacturers but the insulation designs normally fall into two categories. The first category is where the insulation material is rubber tubing or glass weave fabrics and where there is no hard surface protection of the insulation material. The second category is where the insulation material is rubber, fabrics, pressed fibre wrappings or polytetrafluoroethylene tubing, and where the insulation material is provided with hard surface protection in the form of a metal sleeve. The metal sleeve is often referred to as the body armour of the neck portion. With both of these known types of insulation, there is always a possibility that the insulation will slip along the electrical conductor part of the neck portion, usually a copper tube, thereby exposing an electrically live area to the welding operator. In addition, the insulation often utilises poorly fitting insulation joints which are prone to short circuiting due to moisture ingress. Generally, the more components used in the insulation design, then the more likely is the risk of insulation failure.
SUMMARY OF THE INVENTION
It is an aim of the present invention to obviate or reduce the above mentioned problems.
Accordingly, the present invention provides a welding torch for use in gas metal arc welding, which welding torch comprises a neck portion, a diffuser at a first end of the neck portion, a contact tip which extends from the diffuser, connector means which is at a second end of the neck portion and which is for connecting the neck portion to a power cable assembly, and a trigger switch: the power cable assembly being such that it supplies electricity and gas to the welding torch with the gas being for protecting welds from atmospheric contamination as the welds are made using the welding torch; the neck portion being such that it comprises an electrical conductor and a passageway for the gas; the neck portion being such that it comprises insulation in the form of an overmoulding of a plastics material, the overmoulding being such that it also provides rigidity and impact strength to the neck portion; the trigger switch being a snap fit in position in a socket in the neck portion; and the welding torch being one in which the trigger switch comprises a housing and a recess at opposite ends of the housing, and in which walls defining the socket have male profiles for being received in the recesses in order to enable the snap fit in position of the trigger switch in the socket.
The use of the overmoulding of the plastics material overcomes the above mentioned problems with the known insulation. Thus the use of the overmoulding of a plastics material provides the solution to a long established problem that has faced welding torch manufacturers. In addition, the overmoulding is able to provide rigidity and impact strength to the neck portion, thereby providing additional benefits over and above non-slip insulation.
Because of the construction of the neck portion with its electrical conductor, and because of the very harsh environment in which the neck portion operates, the use of the overmoulding of the plastics material is surprising. Initially, one would have thought that the overmoulding would not have been possible because of the environmental conditions to which the neck portion is subjected. However, modern engineering polymer plastics materials have outstanding mechanical, thermal, electrical, dimensional and processing properties and we have realised their potential for use in the construction of the neck portion of the welding torch.
The overmoulding is especially advantageous in that the overmoulding can be to an ergonomic shape. The use of the overmoulding provides the facility to provide the neck portion with a wide variety of outer profile shapes which may be aesthetically pleasing and/or comfortable to welding torch operators.
Any suitable and appropriate plastics materials may be employed. Presently preferred plastics materials are nylon and liquid crystal polymer resins.
The overmoulding may be conducted using known thermoplastic moulding techniques.
The trigger switch operates the stopping and starting of the welding process. The trigger switch is exposed to a lot of use in very arduous environmental conditions. The trigger switch is invariably operated with a heavy gloved hand, which accentuates rough usage of the trigger switch. Failures in the trigger switches thus frequently occur. In addition to the cost of replacing the trigger switches, there is the considerable cost and inconvenience of lost welding time.
Advantageously, the trigger switch is one which is easily replaced because it is a snap fit in position in the socket in the neck portion.
The use of the snap fit trigger switch enables the trigger switch easily to be replaced in the event of failure. The trigger switch is able to be formed as a stand alone module which snaps directly into position in the socket in the neck portion. The trigger switch is able to be manufactured so as to allow easy switch wire connections to be made. A handle cover grip for the neck portion is able to be easily placed in position around the trigger switch, with less chance of accidentally trapping wires than commonly occurs with known trigger switches. Known trigger switches are difficult to install. The known trigger switches are often held in place by two halves of a handle part, and the known trigger switches are prone to sticking because of interference conditions where the two halves of the handle part join.
Preferably, the upper part of the trigger switch carries at least one contact for mating with at least one contact located in the socket.
The overmoulding is advantageous in that the overmoulding can be so shaped as to form mounting and securing means for the trigger switch and the handle, without the need for additional parts.
REFERENCES:
patent: 4543461 (1985-09-01), Hill
patent: 4727238 (1988-02-01), Mann
patent: 4916270 (1990-04-01), West et al.
patent: 5260546 (1993-11-01), Ingwersen et al.
patent: 0 689 895 (1996-03-01), None
Iandiorio & Teska
Parweld Limited
Stoner Kiley
Tran Len
LandOfFree
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