Racks and hooks for hanging workpieces in industrial coating systems

A rack for hanging workpieces in industrial coating systems having a horizontal bar or beam with an upper flange, a lower flange, and a web joining those flanges, wherein the upper flange has a hook receiving aperture, and the flow flange has a hook receiving slot. The aperture and the slot are aligned to receive a hook from which a workpiece may be hung. The hook is bent near its upper end to form a spring with a terminal leg and a depending leg. The end of the terminal leg extends into the aperture in the upper flange, and the depending leg extends through the slot in the lower flange, behind a detent. The force of the spring biases the depending leg against release from behind the detent.

FIELD OF THE INVENTION
 The present invention relates to racks for supporting workpieces in
 industrial coating operations and, more particularly, to such racks having
 removable hooks for hanging such workpieces. It finds particular
 application to industrial electrostatic coating systems.
 BACKGROUND OF THE INVENTION
 Industrial coating systems employ a conveyor from which workpieces are hung
 on support racks and are conveyed through several stations, usually
 including stations for performing the steps of cleaning, rinsing, drying,
 coating, and baking. In many industrial coating operations, the workpieces
 travel through an electrostatic coating booth wherein the electrically
 grounded workpieces are sprayed or coated with electrically charged
 coating particulates, either liquid or powder. After coating and baking,
 the coated workpieces are removed from the racks and the racks are reused
 for another coating cycle. Because of the recycling of the racks, they
 become coated and encrusted with multiple layers of the coating material.
 It is important in those instances where electrostatic coating is employed
 that the support rack be electrically conductive so that workpieces can be
 maintained in a grounded state. The workpieces are electrically connected
 to ground through a conductive support rack so that electrically charged
 particulates are attracted to the workpieces by the electrostatic field.
 Thus, it is desirable to provide a support rack wherein the electrical
 contact between individual hooks depending from the rack are maintained in
 low-resistance electrical contact with the rack so that the workpieces
 suspended from the hooks will be satisfactorily grounded.
 Each coating cycle applies a coating layer to the exposed,
 workpiece-engaging portion of the support hook, which covers the entire
 surface of the hook except for the small area of contact with the
 workpiece. Unless identical workpieces are coated in subsequent cycles, so
 that the workpiece is in electrical contact with the hook at an identical
 position, it becomes necessary to clean the support hook to assure the
 requisite electrical contact between the workpiece and the support hook.
 Accordingly, it is desirable that the support hooks be detachably engaged
 with the rack so that coated hooks can be periodically removed and
 replaced with new or cleaned hooks. Simple and rapid interchangeability of
 the support hooks is also desirable so that different sizes and shapes of
 support hooks can be interchanged as desired for the rack to be used for
 coating a wide variety of workpieces. It is desirable to provide this
 interchangeability while still maintaining good electrical contact between
 each support hook and its respective rack during coating operations.
 In this connection, it has been found desirable to form a support hook in
 the shape of a spring to bias a clean surface of the hook against a clean
 surface of its support rack. An early example of such a cooperative hook
 and rack construction may be found in U.S. Pat. No. 1,533,805, relating to
 a rack for electroplating workpieces. A more recent example of such a
 cooperative hook and rack construction may be found in U.S. Pat. No.
 5,531,334, for electrostatically coating workpieces.
 Such prior art hook and rack constructions have been found to have certain
 shortcomings in industrial coating operations, and it is the principal
 object of the present invention to provide a hook and rack construction
 having substantially improved performance.
 SUMMARY OF THE INVENTION
 In accordance with the present invention, there is provided an inexpensive
 support rack and cooperating hook for supporting workpieces during
 transport through the various stations of an industrial coating operation.
 The rack comprises a horizontal bar or beam having an upper flange, a
 lower flange, and a web joining the flanges. The upper flange has a
 hook-receiving aperture formed in it, and the lower flange has a
 hook-receiving slot formed in it extending inwardly from the edge of the
 flange toward the web and thence outwardly toward the edge to thereby
 provide a detent. The opening and the slot are aligned to receive a hook
 from which a workpiece may be hung. The hook is bent near its upper end to
 form a spring having a terminal leg and a depending body leg. The end of
 the terminal leg extends into the aperture in the upper flange, and the
 depending leg extends through the slot formed in the lower flange behind
 the detent. The spring formed from the hook biases the depending leg
 against release from behind the detent.
 The bar and hook in combination provide means by which the hook may quickly
 be installed in the bar, with spring bias enhancing the conductivity of
 the junction between the bar and the hook, and the hook is easily removed
 from the bar for substituting a different hook or installing the same hook
 after the hook has been cleaned. An important feature of the present
 invention is the provision of a horizontal bar or beam of increased
 stiffness, which resists bending along either the x-axis or y-axis of its
 cross-section. Prior art horizontal bars, such as those disclosed in the
 patents cited above, while providing acceptable stiffness along the
 y-axis, have provided inferior stiffness against bending along the x-axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Shown in FIG. 1 is a rack embodying various features of the present
 invention, referred to generally by the reference numeral 21. The rack 21
 is designed to be supported from a chain conveyor in the manner shown in
 my U.S. Pat. Nos. 5,147,050 and 5,524,774, the disclosures of which are
 hereby incorporated by reference. The rack includes a generally horizontal
 bar or beam 23 suitably attached to vertical members of the rack 25.
 Releasably secured to the bar 23 are a plurality of hooks 27 from which
 workpieces may be hung as the conveyor conducts the rack through various
 stations of a coating operation.
 As shown more particularly in FIG. 2, the bar 23 has three beam elements,
 an upper flange 29, and a lower flange 31 and a web 33 joining said
 flanges. The beam has a generally S- or Z-shaped cross section, with the
 upper flange 29 having an aperture 35 formed therein, and the lower flange
 31 having a slot 37 formed therein. The hook 27 is bent near its upper end
 to provide a terminal leg 39 and a depending leg 41.
 The slot 37 extends inwardly from the edge of the lower flange 31 toward
 the web 33, and thence outwardly toward the same edge to provide a detent
 43.
 The hook 27 is shown in FIG. 2 in its unrestrained position, before it is
 inserted into the hook receiving aperture 35 and the hook receiving slot
 37. To detachably secure the hook 27 in the bar 23, the terminal leg 39 of
 the hook is first inserted into the aperture 35, in the direction shown by
 the broad arrow in FIG. 2, and the depending leg 41 is then forced into
 the slot 37 until it clears the detent 43, and is retained behind the
 detent.
 It will be seen that the aperture 35 is diamond shaped with one vee of the
 diamond pointing toward the edge of the upper flange element 29. The
 aperture is preferably formed by punching through the steel flange with a
 diamond-shaped punch leaving relatively sharp edges around its periphery.
 These sharp edges enhance the conductivity of the junction between the
 terminal leg 39 of the hook and the edge of the aperture 35.
 Similarly, the terminus of the slot 43 is formed in a general diamond shape
 with one vee of the diamond pointing through the edge of the lower flange,
 so that the depending leg 41 of the hook is also in enhanced conductive
 relationship with the lower flange 31.
 It will be understood that when the depending leg of the hook 27 is urged
 into position behind the detent 43, there is a spring bias urging that leg
 against the vee of the slot 37, and also urging the terminal leg 39
 against the vee of the aperture 35. This bias may readily be overcome by
 manual pressure, releasing the depending leg 41 from behind the detent and
 allowing the hook to readily be removed.
 An advantage of the vee-shape of the bearing surfaces of the aperture 35
 and the slot 37 is that it permits the use of hooks made of various gauges
 of wire to be received securely therein. The tapering width of the vee
 accommodates hooks formed of wire of substantially smaller diameter than
 the breadth of the aperture 35 or the slot 37, while maintaining the
 desired enhanced conductive relationship between the hook and the bar.
 The bar or beam 23 advantageously is made from flat steel stock, which is
 punched to form the apertures 35 and slots 43 while the stock is in its
 flat state. The punched flat stock is then bent or folded to provide the
 upper and lower flanges 29 and 31, respectively.
 Illustrated in FIG. 3 is an alternative embodiment of the bar and hook of
 FIG. 1, in which the aperture 35 is bridged at the edge of the flange by a
 semi-cylindrical retainer 45. The hook is inserted into the aperture and
 under the retainer, which functions to restrain the terminal leg of the
 hook against movement. Although this construction may be advantageous in
 some situations, it is less preferred than the embodiment of the aperture
 shown in FIG. 2.
 FIG. 4 discloses means by which the bar or beam 23 may be attached to a
 vertical member 49 of a rack. A threaded rod 47 is welded or otherwise
 secured to the bar 23, and extends through an opening in the member 49.
 The rod 47 is secured by a nut 51.
 FIG. 5 shows another alternative means of attaching the bar 23 to a
 vertical member of the rack. The vertical member 53 is a tubular member of
 rectangular cross section and includes a plurality of openings 55. An arm
 57 is welded or otherwise secured to the end of the bar 23, with an
 upturned elbow 59, the diameter of which is sized to be received snugly
 with an opening 55. The bar 23 is secured by inserting the elbow 59 into
 an opening 55, and locking the elbow on the inside of the tubular member
 53, against its inside surface. A similar means of attachment is disclosed
 in my U.S. Pat. No. 5,524,774, cited above.
 FIG. 6 illustrates yet another means for suspending a plurality of bars 23,
 one above the other. An aperture 61 is provided near the end of the bar 23
 in the web 33 of the bar. Two C-hooks 63 are inserted through the aperture
 63, extending above and below the bar 23, for hanging a plurality of bars
 23.
 FIG. 7 discloses yet another means for attaching the bar or beam 23 to a
 vertical member 65 of a rack. A bracket 67 is secured to the member 65 by
 riveting, spot welding, or the like, bent so as to be parallel to the web
 33 of the bar 23. The bracket 67 may be spot welded to the web 33 to
 provide its support.
 Although the bar or beam 23 has been described as having an S- or Z-shaped
 cross section, it should be understood that the principles of the present
 invention may also be enjoyed with beams of various cross sections. For
 example, a beam having a channel cross section, with upper and lower
 flanges extending from the web in the same direction instead of in
 opposite directions, may also be employed, with apertures and slots formed
 in the upper and lower flanges, respectively. Other beam cross sections
 will be apparent to one skilled in the art in light of the foregoing
 description and drawing.
 Further in this connection, while the invention has been described with
 reference to a preferred embodiment and alternative embodiments, it will
 be understood to those skilled in the art, that various changes may be
 made and equivalents may be substituted for elements thereof without
 departing from the scope of the invention. In addition, many other
 modifications may be made to adapt a particular workpiece or material to
 the teachings of the invention without departing from the essential scope
 of the invention. It is therefore intended that the invention not be
 limited to the particular embodiments disclosed as the best mode in
 carrying out this invention, but that the invention be construed to
 include all embodiments falling within the scope of the following claims.