Electric heating – Metal heating – Nonatmospheric environment at hot spot
Reexamination Certificate
2001-07-24
2003-08-26
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
Nonatmospheric environment at hot spot
C219S137900
Reexamination Certificate
active
06610957
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention relates to savingS of 50% or more of shielding gas primarily in the MIG welding process while improving weld start quality.
2. Description of Prior Art
Gas metal arc welding (GMAW) is commonly referred to as metal inert gas welding (MIG). The term MIG welding is used for the purposes of this invention. In the MIG welding process molten metal is produced by an electric arc. This molten metal is derived from the materials to be welded and a filler wire. The filler wire is fed into the arc zone by a feeding mechanism. The molten weld metal is protected from the surrounding air by a shielding gas. A suitable power source is connected between the workpiece to be welded and to the filler wire passing though a welding torch. Welding power, welding filler wire and shielding gas are usually transported through the torch. The welding torch is usually attached to a flexible cable assembly and is manipulated by the welding operator.
The shielding gas employed to protect the molten metal formed by the electric arc can be a number of gases such as argon, carbon dioxide, and helium Mixtures of these and small amounts of other gases are employed to provide the desired welding performance. This shielding gas is often supplied in high-pressure cylinders, one associated with each weld station. Fabricating shops with a large number of MIG welders may have the shielding gas distributed to each welding machine through a delivery pipeline from a centrally located gas source. A pressure-controlling regulator is employed to reduce the shielding gas pressure contained in the high-pressure cylinder or in the delivery pipeline to a lower pressure level. When an inert type gas or gas mixture is used it is common for this pressure to be reduced to a preset level or 25 psig (pounds per square inch above atmospheric pressure), 30 psig, or in some common regulators designed for shielding gas delivery service, 50 psig. The exact fixed output pressure level of the regulator is dependent on the manufacturer and model. For installations using carbon dioxide as a shielding gas supplied in cylinders, it is common to employ a regulator with 80 psig fixed output. This higher outlet pressure reduces the possible formation of ice crystals in the regulator/flow control system as the carbon dioxide gas pressure is reduced. A variable flow control valve or suitable flow control device is incorporated immediately after the regulator or is built into the regulator mechanism. This flow control device allows regulation of the shielding gas flow to the appropriate rate needed for welding. The flow control device may incorporate a flow measurement gauge.
It is also common for a flexible hose to be used to deliver the shielding gas from the cylinder or gas pipeline regulator and flow control device to the welding machine or wire-feeding device. It is most common for this hose to be ¼ inch in internal diameter. In some instances the hose may be {fraction (3/16)} inches in inside diameter. Some low current output welding machines, primarily designed for home use application, employ short lengths, usually less than 3 feet, of smaller diameter hose, small in internal and external diameter. To turn the flow of shielding gas on and off in commercial MIG welding systems, it is common to employ an electrically operated gas solenoid in the wire feeder or welding machine. A flexible hose connects the shielding gas supply to the solenoid at the welding machine. This hose is typically about 6 to 20 feet or longer in length to fit the needs of the welding installation. When welding is started, usually by means of an electrical switch on the welding torch, the gas solenoid is opened allowing shielding gas to flow through the welding torch to the weld zone. The electrical switch may simultaneously engage the wire feed mechanism and power source.
In most systems the flow of shielding gas is controlled by a flow control valve or other suitable flow control device at the regulator. The flow control device is adjusted to achieve the desired shielding gas flow. It is common for this flow to be set from 20 cubic feet per hour (CFH) to 40 CFH. Gas flows much in excess of this level can cause turbulence in the shielding gas stream as it exits the welding torch. This turbulence allows the surrounding air to be aspirated into the gas-shielding stream, degrading weld performance. In many systems, the pressure at the electrically operated gas solenoid needed to provide the proper flow of shielding gas is less than 5 to 10 psig. Therefore while welding is being performed, the pressure in the shielding gas delivery hose can be less than 5 to 10 psig.
While welding, the electric solenoid valve is open, and the gas pressure in the gas delivery hose is only that needed to establish the desired flow. The flow control device at the regulator is set for the desired shielding gas flow rate and indirectly establishes this pressure. This flow control device may incorporate a flow-measuring gauge to allow proper adjustment of shielding gas flow. Portable flow control gauges are also available. To use a portable gauge, it is put over the end of the torch, the wire feed mechanism is temporarily disengaged and the welding machine is activated with the torch held upward, away from the workpiece. The portable gauge is then used to set the proper shielding gas flow by adjusting the flow control device near the regulator. When the proper shielding gas flow is set and welding commences the pressure in the gas delivery hose near the solenoid is typically less than 5 to 10 psig depending on the torch type, length, and plumbing restrictions. When welding is stopped the solenoid closes and flow of shielding gas from the solenoid to the torch stops. However the gas flow continues to fill the gas delivery hose until the gas pressure in the hose reaches the pressure set by the regulator. The pressure in the gas delivery hose than rises from what was needed to establish the proper flow level to the outlet pressure of the regulator, typically 25 psig, 30 psig, 50 psig, or 80 psig as mentioned above. The excess pressure stores shielding gas in the gas delivery hose connecting the regulator/flow control device to the welding machine or wire feeder until the solenoid is opened again at the start of the next weld. Once the weld is restarted, this excess shielding gas is expelled very rapidly, usually within less than about ½ to 3 seconds. These shielding gas flow rates can momentarily reach in excess of 100 CFF, much higher than needed and also higher than desirable for good weld quality. Weld start quality can be impaired because of excess shielding gas flow creating air aspiration into the shielding gas stream. The wasted shielding gas, although small for each occurrence, can be very significant over time. Depending on the number of starts and stops versus the overall welding time, the wasted shielding gas can exceed 50% of the total gas usage. An article in the June 2000 Fabricator Magazine (referenced) sites the fact that most shops can reduce shielding gas consumption 50 to 80%. A significant waste is described as attributable to the excess storge of shielding gas in a commonly employed ¼ inch inside diameter shielding gas delivery hose.
There have been devices sold which provide solutions to this problem:
(a) One device designed to reduce shielding gas loss is described in U.S. Pat. No. 4,341,237. This device is of complex construction involving several mechanical elements to store and control this excess shielding gas. When properly functioning, this device does accomplish the objective of reducing shielding gas waste. However, it has a number of interconnected parts and must be inspected periodically to assure gas does not leak from the numerous internal connections creating gas waste.
(b) Another method occasionally used to reduce gas surge upon the initiation of the welding arc is to incorporate a flow control orifice at the solenoid end of the shielding gas delivery hose. This device is sometimes sold with t
Elve M. Alexandra
Kerns Kevin P.
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