Patent Publication Number: US-7712515-B2

Title: Municipal casting frame and method of manufacturing same

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to municipal castings and more particularly to municipal casting frames that support covers, and to method for manufacturing the same. 
   Municipal castings are a broad range of products used in conjunction with municipal and construction applications to enclose, trim and/or provide access to infrastructure, such as drainage and sewer infrastructure. Some of the most common municipal castings include manholes, covers and frames. 
   In many applications, municipal casting are used in connection with an access point to underlying infrastructure. For example, municipal casting may be used to provide a frame and cover over an access point to the infrastructure. Typically, the frame will be securely affixed to the infrastructure in an essentially permanent manner. The cover will be removably fitted to the frame to close the access opening. 
   If desired, a cover and frame may be configured to allow the cover to be bolted to the frame. This provides improved security and helps to avoid unauthorized and inadvertent removal of the cover from the frame. In conventional applications where a bolt-down cover is desired, a specially configured frame is installed. The frame is typically provided with lugs that are drilled and tapped to provide structure for threadedly receiving a bolt. The process of a preparing a frame for use in a bolt-down application adds additional cost. Accordingly, it is desirable to prepare a frame for bolts only when a bolt-down cover is expected. As a result, the majority of existing and new frame installations do not include a frame that is configured for a bolt-down cover. 
   It is not uncommon for a customer to request conversion of an installation from a standard cover to a bolt-down cover. If the installation includes a frame prepared for a bolt-down cover, the conversion process is simple and straightforward. However, if the installation does not include such a frame, it is necessary to either replace the frame or perform field modifications to the frame. Typical field modifications include drilling and tapping holes in the frame capable of receiving the cover bolts. In some applications, the frame may not be suitable for field modifications of this type. For example, the frame may not include a wide enough support flange to be drilled and tapped for this purpose. Further, with repeated use, threads can be damaged. If the threads become damaged, it may be necessary to replace the frame or to undergo even more extensive field modifications. 
   In an effort to facilitate the use of bolt-down covers, some existing frames include one or more nut shelves on the undersurface of the frame in alignment with the bolt holes. The nut shelves include a plurality of walls that define a nut compartment beneath each bolt hole. In use, a nut is slid sideways into the nut compartment. The nut shelf loosely holds the nut beneath the bolt hole and prevents it from rotating when a bolt is installed. Although an improvement in some respects, experience has revealed that it can be difficult to align the nut with the bolt hole and that the nut can move within the slot making it difficult to install the bolts. 
   SUMMARY OF THE INVENTION 
   The aforementioned problems are overcome by the present invention wherein a municipal casting frame is provided with cast nut retainers that allow the frame to be retrofitted with a bolt-down cover. The frame defines one or more bolt holes of sufficient dimension to allow free passage of the cover bolts. The undersurface of the frame defines a cast nut retainer adapted to securely receive a nut. 
   In one embodiment, the nut retainer includes a plurality of beads that are spaced a sufficient distance to permit a nut to be forced into the nut retainer, but close enough so that the nut with not fall from the nut retainer once on place. In this embodiment, the spacing between the beads is slightly smaller than the width of the nut. According the nut can be pushed past the beads up into the nut retainer if sufficient force is applied. In this embodiment, the nut retainer may include defined a nut-shaped void and may include a single bead an each wall of the void. In this embodiment, the nut may be somewhat loosely held in the nut retainer so that the nut is able to move to facilitate alignment with the cover bolt. 
   In one embodiment, the nut retainer is configured to frictionally receive the nut in a wedge-like manner. In this embodiment, the retainer corresponds in shape to the nut and includes angled walls that exceed the dimensions of the nut at the retainer opening but are smaller than the dimensions of the nut at the retainer base. Accordingly, when a nut in inserted into the cast nut retainer, it becomes wedged in place in the frame so that bolts can be installed from above the cover. 
   In one embodiment, the frame includes one or more lugs that define the cast bolt hole and the cast nut retainer. The lugs may be positioned wherever a bolt is desired. 
   The present invention also provides a method for manufacturing a frame with integral cast nut retainers. The method generally includes the steps of (a) providing a mold for casting a frame, (b) providing a core corresponding in shape to the bolt hole and the cast nut retainer, (c) positioning the core within the mold at the desired location, (d) casting the frame in the mold about the core, (e) removing the cast frame from the mold and (f) removing the core from the cast frame. In one embodiment of this process, the core is configured to define a cast nut retainer that corresponds in shape with the nut and includes angled walls that exceed the dimensions of the nut at the retainer opening but are smaller than the dimensions of the nut at the retainer base. In this embodiment, the process may also include the step of inserting a nut into the cast nut retainer until the nut is firmly wedged in place. 
   The present invention provides an inexpensive and practical frame that can be used with or without a bolt-down cover. The bolt holes and nut retainers are formed as an integral part of the casting process. Accordingly, the present invention does not require drilling, tapping or other operations following casting. As a result, a frame can incorporate the present invention without adding significant cost. This permits the frame to be used in all application whether or not a bolt-down cover is anticipated. The initial installation may include a bolt-down cover or the installation can be easily retrofitted to include a bolt-down cover. The frame is retrofitted simply by seating a nut into each cast nut retainers, placing a bolt-down cover over the frame and installing bolts through the cover and bolt holes into the nuts. Unlike drilled and tapped arrangements, damage to the threads of the nut can be remedied simply by replacing the nut. 
   These and other objects, advantages, and features of the invention will be readily understood and appreciated by reference to the detailed description of the current embodiment and the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a manhole frame and cover installation in accordance with an embodiment of the present invention. 
       FIG. 2  is an exploded perspective view of the installation. 
       FIG. 3  is a bottom perspective view of the frame. 
       FIG. 4  is a bottom plan view of the frame absent the nuts. 
       FIG. 5  is an enlarged partially sectional view of a portion of the installation. 
       FIG. 6  is an enlarged section view of a portion of the frame. 
       FIG. 7  is an enlarged section view of a portion of the frame showing the nut. 
       FIG. 8  is a perspective view of an alternative frame having four lugs. 
       FIG. 9  is an exploded perspective view of a portion of another alternative embodiment having a square nut. 
       FIG. 10  is a perspective view of a portion of the frame of another alternative embodiment. 
       FIG. 11  is a partially sectional view of a portion of the alternative embodiment of  FIG. 10 . 
       FIG. 12  is a sectional view of a portion of the frame of the alternative embodiment of  FIG. 10 . 
       FIG. 13  is a sectional view of a portion of the frame of the alternative embodiment of  FIG. 10  with a nut contained in the nut retainer. 
       FIG. 14  is a perspective view of a core used to form the nut retainer of  FIGS. 10-13 . 
       FIG. 15  is a front elevational view of the core. 
   

   DESCRIPTION OF THE CURRENT EMBODIMENT 
   A municipal casting frame and cover installation  120  in accordance with an embodiment of the present invention is shown in  FIG. 1 . As perhaps best shown in  FIG. 2 , the installation  120  generally includes a frame  10  and a bolt-down cover  100 . The frame  10  includes a plurality of cast nut retainers  12   a - b  that are configured to selectively hold nuts  110   a - b . The nut retainers  12   a - b  are integrally cast into the frame  10 . In use, nuts  110   a - b  can be fitted into the cast nut retainers  12   a - b  to receive cover bolts  112   a - b . The present invention is described in connection with an otherwise conventional manhole assembly  120  having a frame  10  and cover  100 . The present invention is, however, well suited for use in other types of municipal castings that include a cover. 
   The cover  100  is generally conventional and therefore will not be described in detail. Although the illustrated cover  100  is a bolt-down cover having bolt holes  130  configured to receive standard cover bolts  112   a - b , the frame  10  can be utilized to support a standard cover (i.e. a non-bolted cover). When the frame  10  is to be used with a standard cover, it is not necessary to install the nuts  110   a - b . In the illustrated embodiment, the nuts  110   a - b  are forcefully inserted into the nut retainers  12   a - b  until they are retained by interaction with nut retainers  12   a - b , and the cover  100  is placed on the frame  10 . The cover bolts  112   a - b  are fitted through bolt holes  130  in the cover  100  and are threadedly installed in the nuts  110   a - b . In this way, the bolts  112   a - b  secure the cover  100  on the frame  10 . 
   In the illustrated embodiment, the frame  10  is generally peripheral structure defining a central opening  70 . The frame  10  generally includes a flange  72  shaped to receive the cover  100  and a shoulder  74  shaped to rest on an underlying structural component. Although the frame  10  and cover  100  of this embodiment are generally square, the present invention can be easily incorporated into installations of other shapes, such as circular or rectangular installations. The frame  10  includes a plurality of lugs  14   a - b , each defining a bolt hole  16   a - b  and a coaxial cast nut retainer  12   a - b . The lugs  14   a - b  provide an enlarged region in the frame  10  having sufficient structural integrity to receive the bolts  112   a - b . The size, shape, and configurations of the lugs  14   a - b  may vary from application to applications. The lugs  14   a - b  may be eliminated when the frame  10  is otherwise capable of defining the cast nut retainer and  12   a - b  and of bearing the forces associated with bolting down the cover  100 . The cast nut retainers  12   a - b  are essentially identical to one another. Accordingly, only a single cast nut retainer  12   a  will be described in detail. Referring now to  FIGS. 5 and 6 , the cast nut retainer  12   a  is defined in lug  14   a . In the illustrated embodiment, the nut retainer  12   a  is intended to receive a hexagon nut. As a result, the nut retainer  12   a  is a generally hexagon-shaped void  54  having a base  20  and a mouth  56 . More specifically, as shown in  FIG. 4 , the illustrated nut retainer  12   a  includes six walls  52  arranged in a hexagon configuration. The nut retainer  12   a  need not fully correspond is shape with the nut  110   a  as long as it is capable of firmly seating and preventing rotation of the nut  110   a . In the illustrated embodiment, the nut retainer  12   a  is configured to frictionally receive the nut  110   a . In this embodiment, the walls  52  defining the nut retainer  12   a  are angled to provide a wedging interaction with the nut  110   a . More specifically, the walls  52  are configured such that the nut retainer  12   a  is a larger than the dimensions of the nut  110   a  at its mouth  56 , which permits the nut  110   a  to be inserted freely into the mouth  56  of the nut retainer  12   a . However, the walls  52  are angled a sufficient amount so that the nut retainer  12   a  is smaller than the dimensions of the nut  110   a  at its base  20 . As a result, continued insertion of the nut  110   a  into the nut retainer  110  beyond the mouth  56  causes the nut  110   a  to ultimately become wedged into the place within the nut retainer  12   a . In the illustrated embodiment, the walls  52  are angled from mouth  56  to base  20 . It is not strictly necessary for the angled walls  52  to be angled along there entire length or width. If desired, only a portion (or portions) of the angled walls  52  may be angled to provide the desired wedging interaction. Although all of the walls  52  are angled in the illustrated embodiment, the number of angled walls may vary from application to application. For example, in some applications only a single angled wall (or angled wall portion) may be necessary (not shown). As another alternative, the angled wall(s) of the nut retainer may be replaced by a nut with one or more angled walls (or angled wall portions)(not shown). 
   Referring now to  FIGS. 4-6 , the bolt hole  16   a  is coaxial with the nut retainer  12   a . Accordingly, a bolt  112   a  extending through the bolt hole  16   a  with be aligned with the approximate center of the nut  110   a  (See  FIG. 7 ). In the illustrated embodiment, the bolt hole  16   a  is generally circular having a diameter substantially greater then that of the bolt  112   a . This permits the bolt  112   a  to pass freely through the hole  16  to engage the nut  110   a . The bolt hole  16   a  need not, however, be circular and may have alternative shapes as desired. For example, the bolt hole  16   a  may be sufficiently larger than the diameter of the bolt  112   a  so that the bolt  112   a  can be moved as necessary to align with the nut  110   a.    
   The frame  10  may be manufactured using conventional casting techniques and apparatus modified to provide for the nut retainers  12   a - b  of the present invention. For example, the frame  10  may be formed from iron using conventional casting techniques using a core configured to define the nut retainers  12   a - b . The method includes the steps of (a) providing a pattern (not shown) corresponding in shape to the frame  10 , (b) using the pattern to define a mold cavity (not shown) in the shape of the frame  10 , which in this example includes lug portions (not shown) to define lugs  14   a - b , (c) providing one or more cores (not shown) corresponding in shape to the bolt hole  16   a - b  and the cast nut retainer  12   a - b , (d) positioning the cores within the mold cavity at the desired location, which in this embodiment are within the lug portions, (e) introducing molten material (e.g. iron) into the mold cavity, the molten material filling the mold cavity and at least partially surrounding the cores, (f) curing the molten material to form the cast frame, (g) removing the cast frame from the mold cavity, (h) removing the cores from the cast frame  10  to leave the bolt holes  16   a - b  and cast nut retainers  12   a - b . In one embodiment, each core (not shown) includes a nut retainer portion to define the cast nut retainer  12   a - b  and a bolt hole portion to define the bolt hole  16   a - b . The nut retainer portion and holt hole portion may be in coaxial alignment. In this embodiment, the nut retainer portion generally corresponds in shape with the nut  110   a  and includes at least one angled wall that exceeds the dimensions of the nut at one end but is smaller than the dimensions of the nut at the other end. Accordingly, the nut retainer portion defines a cast nut retainer  12   a - b  in the frame  10  that is capable of frictionally receiving the nut  110   a . In this embodiment, the process of using the frame  10  may include the step of inserting a nut  110   a  into the cast nut retainer  12   a - b  until the nut  110   a  is firmly wedged in place. The nut  110   a  can be removed from the cast nut retainer  12   a - b  when desired, for example, if the threads become damaged. 
   In the illustrated embodiment, the frame  10  and cover  100  include two bolts  112   a - b  that are intended primary for security (e.g. to deter unauthorized removal of the cover  100 ). The number of bolts may, however, vary from application to application as desired. For example, the installation may include three or four bolts, which will typically be spaced evenly around the frame and cover. The present invention may be incorporated into watertight applications. In watertight applications (not shown), a gasket may be fitted between the frame and cover and a rubber washer may be fitted over each bolt. Installation of this type are likely to include three, four or more bolts. For example,  FIG. 8  shows an alternative frame  200  that is intended to receive up to four bolts (not shown). As shown, frame  200  includes four lugs  204   a - b . Each of these lugs  204   a - b  defines a bolt hole  206  and a nut retainer (not visible), which may essentially identical to the bolt holes  14   a - b  and nut retainers  12   a - b  described above or those described below. 
   The present invention is described above in connection with a hexagon shaped nut  110   a . The present invention may alternatively be confirmed for use with nuts having other shapes. For example,  FIG. 9  shows a portion of an alternative embodiment  300  having a lug  302  with a nut retainer  304  shaped to receive a square nut  306 . As in the above illustrated embodiment, nut retainer  304  includes at least one angled wall  308  that permits the nut  306  to be wedged into place with in the nut retainer  304 . 
   Another alternative embodiment of the invention is shown in  FIGS. 10-13 . In this embodiment, the wedge-type nut retainer is replaced by a snap-type nut retainer. Except as otherwise described, the frame  410  and cover  500  of  FIGS. 10-13  are essentially identical to frame  10  and cover  100 .  FIG. 10  shows a bottom perspective of a portion of the frame  410  including a single lug  414  and associated nut retainer  412 . The frame  410  may include essentially any desired number of lugs  414  and nut retainers  412  spaced as desired about the frame  410 . As shown, the nut retainer  412  includes six walls  460  arranged in a hexagon shape to receive a hexagon nut  510 . The number and configuration of walls may vary from application to application. The nut retainer  412  also includes a plurality of beads  450   a - f  positioned around the nut retainer  412  near the mouth  462 . In this embodiment, the beads  450   a - f  are generally semispherical, but the shape of the beads may vary from application to application. Although the nut retainer  412  is shown with a bead  450   a - f  on each wall  460 , the number of beads may vary from application to application. For example, in some applications only a pair of beads positioned on opposing walls may be used. Further, the beads may be replaced by other types of protrusions capable of receiving a nut in a snap-like manner. To provide an installed nut  510  with some movement, the walls  460  of the void  454  may be confirmed to be slightly larger than the nut  510  in one or more directions. This difference in size will allow a limited amount of movement of the nut  510  within the nut retainer  412  to facilitate alignment of the nut  510  with the cover bolt  512 . As perhaps best shown in  FIGS. 11 and 13 , the beads  450   a - f  of the illustrated alternative embodiment are positioned to hold the nut  510  in relatively close contact with the base  464  of the nut retainer  412 . If desired, the beads  450   a - f  may be spaced farther away from the base  464  to provide the nut  510  with movement in the vertical direction. For example, the beads  450   a - f  may be lowered one millimeter to reduce the likelihood of problems associated with imperfections in the base  464  and/or to give the nut  510  a limited ability to cant within the nut retainer  412  to facilitate alignment with the cover bolt  512 . In this embodiment, the mouth  462  is defined by a plurality of angles walls  463 . The angled walls  463  facilitate insertion of the nut  510  into the nut retainer  412  by guiding the nut  510  into the center or the nut retainer  412 . In the illustrated embodiment, the walls  463  of the mouth  462  are angled at approximately 45 degrees with respect to the axis of the nut retainer  412 , but the angle of the walls may vary from application to application as desired. 
   This alternative frame  410  may be manufactured using the methods described above in connection with frame  10  using cores (See  FIGS. 14 and 15 ) configured to define the beads  450   a - f  or other desired protrusions. A single core  600  is shown in  FIGS. 14 and 15 . Separate cores  600  may be inserted into the mold cavity (not shown) at each of the locations where a nut retainer  412  is desired. The core  600  generally includes an upper segment  620 , a lower segment  622  and a central segment  602 . The upper segment  620  and lower segment  622  assist in securing the core  600  in place within the mold cavity (not shown). The central segment  602  defines the nut retainer  412  and is accordingly formed in the reverse of desired shape of the nut retainer  412 . The central segment  602  generally includes a head portion  604  that defines the main void of the nut retainer  412  and a shoulder portion  608  that defines the mouth of the nut retainer  412 . The head portion  604  and shoulder portion  608  that defines of this embodiment are hexagon shaped to correspond with hexagon nut  510 . A plurality of indentations  606  are defined in the head portion  604 . The indentations  606  define the beads  450   a - f  and, as show, are positioned adjacent to the shoulder portion  608  in this embodiment. The shoulder portion  608  includes angled surfaces  610  that, as noted above, create an angled entry (or mouth  462 ) that, in turn, facilitates insertion of the nut  510  into the nut retainer  412 . The core  600  is removed from the cast frame  410  after casting in a conventional manner. 
   The above description is that of the current embodiment of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be considered as limiting the element to the singular.