Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
2000-11-28
2002-08-20
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S098000
Reexamination Certificate
active
06437279
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the use of stud guns for welding a stud into a metal surface. More particularly the present invention relates to a method and apparatus for assisting the operator in leveling a stud gun particularly when installing a stud in an overhead workpiece. This invention further relates to a method and apparatus for permitting the operator to safely weld large diameter studs into an overhead workpiece without fear of molten substances produced during the welding falling by gravity onto and harming the operator.
BACKGROUND OF THE INVENTION
Arc stud welding is a process well known in the art and generally includes the two steps of developing the heat necessary for welding with an arc between the stud and the workpiece and then bringing the stud and the workpiece into intimate contact when the proper temperature is reached.
To achieve the welding of a stud, the apparatus necessarily includes a stud gun, a timing device for controlling the arc, a stud, a ferrule and a source of dc welding current. The stud is positioned into the chuck of the conventional stud gun, the ferrule is positioned around the end of the stud for engagement with the surface of the workpiece. When the trigger of the stud gun is depressed, an automatic welding cycle begins.
The body of the stud gun includes a solenoid coil that is energized to create an arc that raises the stud off the workpiece. This arc between the end of the stud and the workpiece melts both the stud and the workpiece at that precise location. The arc exists for a preset time period and when that time period passes the welding current is shut down and the spring of the stud gun plunges the stud into the molten pool between the stud and the workpiece to complete the weld. The gun is then removed from the stud.
The time for the stud welding process to be completed after initial contact between the stud and the workpiece ranges from a fraction of a second for smaller diameter studs and up to a second or more for larger studs of at least 19 mm in diameter. The diameter of the stud, however, can and usually does range for steel studs from about 3 to 32 mm, about an inch and a quarter. For these larger diameter studs, of course, the time required for the maintenance of the arc increases in accordance with the size of the stud.
Most arc stud welding processes require a ferrule that is placed around the stud at the weld end and is held in position by a ferrule holder then in turn is held by a conventional footplate. The ferrule is important in the welding operation because it concentrates the heat of the arc in the weld area while restricting the flow of air into the weld area to control oxidation of the molten metal produced and also attempts to confine the molten metal to the weld area.
The ferrule is composed of a ceramic material and is cylindrical in shape, flat across the bottom and serrated with a saw-tooth design at the working end for contact with the surface of the workpiece. The serrated end vents the gases that are expelled from the weld area. But particularly, for large diameter studs where it is necessary to have a longer timed arc producing a greater volume of molten metal, not only the gases escape through the saw-tooth end of the ferrule but also globs of molten metal are shot out with the gases.
Even though the ferrule is designed to keep most of the molten metal within the weld area, any molten metal that escapes with the high velocity gases creates a serious danger for the holder of the gun. Of course, the holder of the gun would not be in a dangerous position if the workpiece is below the level of the stud gun.
Many studs, however, are designed to be welded into an overhead workpiece and it is in that position where the molten metal escapes through the serrated ferrule and falls by gravity that the holder of the stud gun is in danger of being injured or at least his clothing set afire.
Accordingly, the safety of the holder of the stud gun is of paramount importance but is not the only problem facing the holder of the stud gun attempting to install a stud in an overhead workpiece. Particularly for the larger studs up through 32 mm, for instance, a larger, heavy duty gun is required to be supported by the operator. For shooting a large diameter stud in an overhead workpiece, it is particularly difficult to align the ferrule and stud perpendicularly to the workpiece. When the operator of the heavy duty stud gun does not place the centerline of the stud and therefore of the ferrule both orthogonally to the workpiece, not only would more molten metal fall onto the operator but the stud would not be positioned perpendicularly as it should be.
The closest prior art known to Applicant is Shoup, U.S. Pat. No. 4,531,042. Unfortunately for the operator, neither of the problems described above is solved by the method and apparatus disclosed in the Shoup patent.
After perusing the Shoup patent, it is clear that the disclosure relates to the installation of large diameter studs using a typical stud gun that includes a surrounding mechanism referred to as an arc blow coil. While it is disclosed that the coil assembly is used to support and align the stud gun when held against the workpiece, it is stated clearly that the apparatus and method is not for the installation of a stud in an overhead because of the added weight of the patented apparatus that is provided for the express purpose of not requiring as much downward pressure by the operator upon a workpiece that is below rather than above the stud gun. The fact that this patented apparatus and method is used only for a lower work surface, it is not possible for an operator to experience the gravity fall of molten metal substances from an overhead workpiece. Any radially outwardly extended surface from the notches or vents disclosed in Shoup that are located radially around the lower end of the ferrule would not and could not prevent flash or molten metal substances from coming down on the operator should the heavy stud gun be used contrary to the specific instructions in the patent and raised upwardly to weld a stud in an overhead workpiece.
Accordingly, it is the object and purpose of the present invention to solve the foregoing problems experienced in the prior art and particularly to present an apparatus and method for the welding of a stud, particularly a larger diameter stud, in an overhead workpiece without the danger of molten metal substances falling by gravity onto the operator and at the same time allowing the operator to easily align the heavy stud gun orthogonally to the overhead workpiece.
SUMMARY OF THE INVENTION
Apparatus for safely welding a stud into an overhead workpiece that includes a ferrule having an interrupted perimeter surrounding the stud for contact with the overhead workpiece and a support assembly for connection to a stud gun including a shield surrounding the support assembly and having a continuous perimeter defining a free space by being spaced from the stud and wherein the free space is in communication with the interrupted perimeter of the ferrule. The free space has a width and depth sufficient to receive and contain all molten substances produced during the welding. A fire resistant material is positioned within the free space to hold all these molten substances to thereby safely protect the operator of the stud gun from the gravity induced falling molten substances.
The method for safely welding a stud into an overhead workpiece with a stud gun that includes providing a ferrule with an interrupted ferrule perimeter, positioning the stud within the ferrule and surrounding the stud and ferrule with a shield having a shield perimeter. The shield perimeter forms a free space between the ferrule perimeter and the shield perimeter in which the free space is defined by a width dimension measured transverse to the axis of the stud of at least one half of the diameter of the stud and a depth dimension measured below the shield perimeter of between one quarter and five times the diameter of the stud.
REFERENCE
Burchett Johnnie N.
Sawyer David R.
Williams, III John B.
Dunn Tom
Hunton & Williams
Newport News Shipbuilding and Dry Dock Company
Pittman Zidia
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