Bolt heater assembly unit having junction housing configuration

A bolt heater including a junction housing, a handle attached and secured to a wall of the housing solely from an exterior of the housing, such as by a threaded connection, a power cable including a fitting attached directly to the wall of the housing, and an electrical resistance heater rod attached to the wall of the housing. The wall may have a boss with a recess therein for receiving a portion of the handle. The housing may be a hollow cylinder with a circular top wall, a circular bottom wall, and a cylindrical side wall. The heater rod may be attached to the housing via a threaded connection and the housing may have a non-circular portion near the threaded connection point, the non-circular portion being engageable by a tool to assist in the threading attachment of the heater rod to the housing.

BACKGROUND OF THE INVENTION

The present invention relates to bolt heaters.

The present invention has a particular application to bolt heaters used in the heating of studs or bolts, such as the bolts of a steam turbine casing. Although the invention is not limited to such an application, the invention will be described in such an environment and use.

It is desirable to heat the bolts used in a steam turbine casing during the fastening and unfastening thereof in that the bolt will elongate due to expansion during heating, allowing the nut to be threaded onto the bolt to a greater degree during the fastening process. When the bolt cools and shrinks, the nut is pulled tighter against the surrounding surface, thus assuring a secure fasting of the nut on the bolt and a clamping of the parts held together by the nut and bolt. In order to ease the removal of the nut from the bolt, such as during the servicing of the turbine, it is helpful to again heat the bolt to elongate it, in order to move the nut away from the surrounding surface, or at least to lessen the force holding the nut against that surface.

It has long been known to heat bolts, for example see U.S. Pat. No. 2,176,601, and to use induction heating to heat such bolts, for example, see U.S. Pat. Nos. 3,771,209 and 5,397,876.

Commonly available resistance type bolt heaters have a junction box, typically a standard hardware type box, to which is attached a handle, a power cable, and a resistance heating element. The resistance type bolt heater presently sold by Power House Tools, Inc., an assignee of the present invention, includes these components, in which the handle has a threaded stud projecting from one end, which is inserted through a non-threaded opening in a removable cover of the junction box, and is held in place on the cover by means of a nut which is secured to the stud from an inside side of the cover. The power cable is attached to an insert which is threaded to the side wall of the junction box, and the resistance heating element is threadingly attached to a bottom of the junction box. Individual wires from the power cable are connected to conductors on the resistance heating element inside the junction box. A power indicator lamp is supplied on the cover to indicate when the resistance heater is being supplied with power.

A standard junction box has several shortcomings which detract from its usefulness as part of a resistance type bolt heater. For example, by requiring the handle to be secured from the inside of the cover adds time required for assembly. The covers have a relatively thin wall thickness which detracts from the stability of the handle/junction box connection, and is insufficiently thick to support a threaded connection of the handle to the cover. The use of a separate insert component for attaching the power cable to the side wall of the junction box adds to assembly time, and becomes a potential point of weakness in the connection of the power cable to the junction box. The attachment of the resistance heater rod to the junction box can be made directly only when a three quarter inch resistance rod is used. When larger resistance rods are used, an adapter piece must be attached to the junction box, and then the rod attached to the adaptor piece, also becoming a potential point of weakness in the connection of the resistance rod to the junction box.

It would be an advance in the art if there were provided an easy to assemble bolt heater which would overcome one or more of the problems and limitations discussed above.

SUMMARY OF THE INVENTION

The present invention provides a bolt heater comprising a junction housing, a handle, a power cable, and an electrical resistance heater rod.

In an embodiment, the handle may have an externally threaded portion for connecting to an internally threaded opening in a wall of the junction housing.

In an embodiment, the junction housing may have a wall thickness sufficient to support a threaded connection of the handle to the junction housing.

In an embodiment, the handle may have a projecting threaded stud for threadingly connecting to the top wall of the junction housing.

In an embodiment, the handle may be attached and secured to a wall of the junction housing solely from an exterior of the junction housing.

In an embodiment, the power cable may include a fitting having external threads for connecting to an internally threaded opening in a wall of the junction housing.

In an embodiment, the power cable and fitting may be attached and secured to a wall of the junction housing solely from an exterior of the junction housing.

In an embodiment, the power cable and fitting may attach directly to the wall of the junction housing.

In an embodiment, the heater rod may have an end portion with external threads for connecting to an internally threaded opening in a wall of the junction housing.

In an embodiment, the heater rod may have a non-circular portion near the threaded end for engagement by a tool to assist in the threading attachment of the heater rod to the junction housing.

In an embodiment, the heater rod may be attached and secured to a wall of the junction housing solely from an exterior of the junction housing.

In an embodiment, the junction housing may comprise a body and a top wall, with the top wall removably connected to the body.

In an embodiment, the top wall may have a boss with a central recess therein for receiving a portion of the handle.

In an embodiment, the junction housing may comprise a hollow cylinder with a circular top wall, a circular bottom wall, and a cylindrical side wall.

In an embodiment, the junction housing may have a non-circular portion near the internally threaded opening for receiving the heater rod, the non-circular portion being engageable by a tool to assist in the threading attachment of the heater rod to the junction housing.

In an embodiment, the junction housing non-circular portion may comprise a projection formed on the bottom wall of the junction housing surrounding the threaded opening.

In an embodiment, the junction housing non-circular portion may comprise a recess formed in the bottom wall of the junction housing.

In an embodiment, the bolt heater may include an indicator lamp visible on the wall where the handle is attached.

In an embodiment, the indicator lamp may be an LED.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As illustrated in the Figures, the present invention provides a bolt heater20comprising a junction housing22, a handle24, a power cable26, and an electrical resistance heater rod28.

The handle24may have an externally threaded portion30for connecting to an internally threaded opening32in a wall33of the junction housing22. For example, the externally threaded portion30may comprise a projecting threaded stud, as illustrated, or may comprise a threaded ring formed on an end34of the handle24. In either arrangement, the wall33of the junction housing22would have a wall thickness sufficient to support the threaded connection of the handle24to the junction housing.

The handle24may be attached and secured to the wall33of the junction housing22solely from an exterior of the junction housing, without requiring any other attachments or connections from an interior of the junction housing, such as a separate nut positioned on the interior of the junction housing. The handle24may be attached by manually gripping the handle and rotating it relative to the wall33of the junction housing22, or a tool receiving area35(FIG. 1), such as a slot for a screw driver, may be provided on the handle to assist in the secure attachment of the handle to the wall of the junction housing. The handle24could also be attached solely from the exterior of the junction housing22by other than a threaded connection, such as by a bayonet connection, or other secure and simple connection means.

The power cable26may include a fitting36having external threads38(FIG. 3) for connecting to an internally threaded opening40in the wall33of the junction housing22. In such an arrangement, the wall33of the junction housing22would have a wall thickness sufficient to support the threaded connection of the power cable26and fitting36to the junction housing. For example, the wall33may be stepped as at41to assure that the thickness in the area of the opening40is sufficient to support the threaded connection.

The power cable26and fitting36may be attached and secured to the wall33of the junction housing22solely from an exterior of the junction housing. The power cable26and fitting36may attach directly to the wall33of the junction housing22without any intervening adaptors or inserts. The power cable26and fitting36could also be attached solely from the exterior of the junction housing22by other than a threaded connection, such as by a bayonet connection, or other secure and simple connection means.

The heater rod28may have an end portion42with external threads44for connecting to an internally threaded opening46in the wall33of the junction housing22. In such an arrangement, the wall33of the junction housing22would have a wall thickness sufficient to support the threaded connection of the heater rod28to the junction housing. The heater rod28may have a non-circular portion48near the threaded end42for engagement by a tool to assist in the threading attachment of the heater rod to the junction housing22. The heater rod28may come in different diameters, depending upon the wattage and power of the heater, and the voltage supplied to the heater rod. For example, the rod may have a diameter of three quarters of an inch, one inch or one and a half inches. The internally threaded opening46should be sized to receive the particular size heater rod28that is being assembled to the junction housing22so that no separate adapters or connectors are required to assembly the heater rod to the junction housing. This would require different junction housings22for different heater rod sizes.

The heater rod28may be attached and secured to the wall33of the junction housing22solely from an exterior of the junction housing. The heater rod28could also be attached solely from the exterior of the junction housing22by other than a threaded connection, such as by a bayonet connection, or other secure and simple connection means.

The heater rod28includes a plurality of electrical conductors50which are connected to resistive heating elements in the heater rod. The power cable26also includes a plurality of electrical conductors52for supplying electric power to the heater rod28. Depending on the voltage and number of phases of current being supplied and used by the heater rod28, there may be 2 or 3 electrical conductors50at the heater rod, and 3 or 4 conductors52at the power cable26. The electrical conductors52of the power cable26may be provided with terminals54which may be secured to the electrical conductors50of the heater rod28in a known manner. The power cable electrical conductors52also include a ground conductor which may be attached to a ground connection56at the wall33of the junction housing22, to assure that the junction housing will be grounded.

The junction housing22may comprise a body60, a top wall62and a bottom wall63, with the top wall and the bottom wall removably connected to the body. This will allow access to the interior of the junction housing22to permit connection of the power cable conductors52to the heater rod conductors50. The top wall62may have a boss64with a central recess66therein for receiving a portion68of the handle24. A snug fit between the handle24and the recess66will provide a more secure and stable connection between the handle and the junction housing22. The top wall62may be secured to the body60in various ways, such as via the use of a plurality of threaded fasteners70extending through openings72in the top wall and into holes74in an end wall75of the body. Alternatively, a threaded connection may be provided between the top wall62and the body60, particularly where the top wall is circular and the body comprises a hollow cylinder, such as shown in the Figures. There could be provided a flange on the top wall62with an internal thread to mate with an external thread on the body60, or an external thread on the top wall to mate with an internal thread on the body. The top wall62could also be secured to the body60with interlocking detents or other known connection arrangements.

In an embodiment, the bottom wall63may have a non-circular portion76(FIGS. 2 and 3) near the internally threaded opening46for receiving the heater rod28, the non-circular portion being engageable by a tool to assist in the threading attachment of the heater rod to the junction housing. For example, the non-circular portion76may comprise a projection78, such as a square or hex shaped projection, formed on the bottom wall63of the junction housing22surrounding the threaded opening46. Alternatively, the non-circular portion76may comprise a recess or a series of recesses formed in the bottom wall63of the junction housing22to be engaged by a tool to prevent rotation of the junction housing22while the heater rod28is being threaded into the junction housing. The bottom wall63may have a circular perimeter80threaded to threadingly engage with an opening82at a bottom end of the body60. The bottom wall63could also be secured to the body60with interlocking detents or other known connection arrangements.

The bolt heater20may include an indicator lamp90visible on the wall33where the handle24is attached. The indicator lamp90may have a conductor92directly or inductively connected to one of the power conductors52to provide a visual indication that power is being supplied to the heater rod28. The indicator lamp90may be an LED, an incandescent bulb, or other type of visual indicator energized by power being supplied to the heater rod28.