US3044720A

US3044720A - Impact crushing apparatus

Info

Publication number: US3044720A
Application number: US59631A
Authority: US
Inventors: Thomas E Bridgewater
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-09-30
Filing date: 1960-09-30
Publication date: 1962-07-17
Anticipated expiration: 1979-07-17

Description

July 17', 1962 T. E. BRIDGEWATER 3,044,720

IMPACT CRUSHING APPARATUS Filed Sept. 30, 1960 3 Sheets-Sheet 1 July 17, 19-62 T. E. BRIDGEWATER 3, 4

' IMPACT CRUSHING APPARATUS Filed Sept. 50, 1960 s Sheets-Sheet 2 INV EN TOR. 772227245 6.

Wafer July 17, 1962 T. E. BRIDGEWATER 3,044,720

IMPACT CRUSHING APPARATUS 3 Sheets-Sheet 3 Filed Sept. 50, 1960 INVENTOR.

United States Patent Ofiice 3,044,720 IMPACT CFUSHiNG APPARATUS Thomas E. Bridgewater, Elmhurst, Ill. Adams Engineering Co., 2151 E. 83rd St., Chicago 17 111.) Filed Sept. 30, 1960, Ser. No. 59,631 12 Claims. (Cl. 241-275) The present invention relates to a novel crushing apparatus and more particularly to a novel impact crushing apparatus. One of the major problems which is encountered by impact crushing apparatus of the type contemplated herein is the problem of abrasion or Wearing away of parts of the apparatus which come into contact with the material being treated or crushed. It is therefore an important object of the present invention to provide a novel impact crushing apparatus which is constructed so as to substantially reduce the rate of wear of various portions of the apparatus whereby maintenance costs and shutdown time can be reduced.

Another important object of the present invention is to providea novel impact crushing apparatus of the type in which material being processed is thrown outwardly at a high velocity from a central impeller and toward circumferentially arranged breaker plate meanspwhich apparatus is constructed so as to facilitate adjustment thereof for accommodating various different materials and for producing various different desired results.

Still another important object of the present invention is to provide a novel impact crushing apparatus of the above described type which is constructed so as to minimize any possibility of severe damage in the event of entry of oversized or foreign material into the apparatus. 7

Other objects and advantages of the present invention will become apparent from the following description and the accompanying drawings wherein:

FIG. 1 is a partial sectional view taken generally along line 11 in FIG. 2, and showing an apparatus incorporating features of the present invention;

FIG. 2 is a sectional view taken generally along line 22 in FIG. 1;

FIG. 3 is a plan View on a reduced scale of a portion of the apparatus which is partially broken away in order to show a feature of the present structure;

FIG. 4 is an enlarged partial sectional view taken generally along line 44 in FIG. 2;

FIG. 5 is a fragmentary perspective view showing a portion of an impeller constructed in accordance with features of the present invention;

FIG. 6 is an exploded perspective view of an impeller shoe constructed in accordance with thepresent invention;

. FIG. 7 is a sectional view taken generally along line 7-7 in FIG. 8; and b 7 FIG. 8 is a partial sectional view taken generally along line 8-8 in FIG. 7.

Referring now more specifically to the drawings wherein like parts are designated by the same numerals throughout the various figures, an impact crushing apparatus 10 incorporating features of the present invention is shown in FIGS. 1 and 21 The apparatus comprises a cylindrical housing 12 mounted on a suitable base or frame 14. A cover structure 16 extends across the upper end of thehousing and the lower end of the housing communicates with a discharge funnel '18.

An impeller structure 20 is mounted for rotation about a vertical axis located centrally within the cylindrical housing 12. The impeller structure includes an upstanding spindle or shaft 22 having a drive pulley 24 secured to its lower end. An electric motor 26 or other suitable prime mover is mounted outside of the housing 12 for Patented July 17, 1962 driving the pulley 24 through another pulley 28 secured to a lower end of the motor shaft and a drive belt 30 which encircles both pulleys.

In the embodiment shown, the impeller structure 20 includes a hub member 32 secured to the upper end of I the spindle or shaft 22. Anannular impeller disc 34 is connected to and carried by the upper end of the hub 32 and a similar disc or plate. member36 is also secured to the hub member at a position spaced vertically below the upper disc or plate member 34 as shown in FIG. 1. Each of the impeller discs carries a plurality of blade means 3-8 all of which are substantially identical. As shown in FIGS. 2 and 5-8. Each of the blade means 38 comprises a bracket member 40 welded or otherwise fixed to its associated impeller disc and an impeller shoe structure 42 which will be described in detail below.

Removable wear plates

43 and 45 are secured over the discs 34 and 36 for protecting the discs from the material to be processed. 'These wear plates are slotted at 47 for accommodating the blade means 38.

Material to be'processed or crushed is introduced into the apparatus through a central opening 44 in the cover structure 16. A distributor cone 46 is secured to the upper end of the impeller hub member 32 for receiving the material entering through the opening 44 and initially directing the material laterally outwardly to the blade means 38. The material is then rapidly accelerated and thrown radially outwardly by the blade means 38. Breaker plate structures 48 which will be described more in detail below, are arranged around the periphery of the disc 34, or in other words, the first stage of theimpeller 20, and the material thrown from the impeller is pro-' jected at a high velocity against the breaker structures so that the impact of the material against the breaker structures causes the desired crushing of the material.

A further crushing of the material is accomplished by utilizing the blade means on the second stage plate member 36 of the impeller for again accelerating and throwing the material radially outwardly and against another series of breaker plate structures 50 which are substantially identical to the structures 48 and are arranged around the periphery of the second stage of the impeller. Inorder to promote uniform treatment of all of the material, a funnel-shaped annular bafile 51 extends from beneath the lower edge of the annular series of breaker plate structures'48 to a position over the blade means at the second stage of the impeller so that substantially all of the material being processed will be directed to the second stage of the impeller. Suitable bracket arms 53 welded or otherwise secured to the conical bafile are provided for supporting the bafile;

While ideally all the material being processed is projected directly from the impeller blade means to the breaker plate structures and ultimately falls directly to the bottom of the housing, portions of the material are, in fact, impinged against parts and areas of the apparatus other than the breaker plate structures in a manner which causes undesirable wear. In accordance with an important feature of the present invention the apparatus is constructed in a novel and simple manner so as to minimize or eliminate such wear. Thus it is to be noted that the cylindrical housing 12 is formed so that its upper marginal portion extends well above the flipper end of the impeller 20so that the cover structure 16 is spaced well above the upper end of the impeller for reducing any possibility of impingement of the material being processed against the undersurl cover structure includes three sections 52, 54 and 5'6 so that the cover structure may be more easily handled and opened and closed without the necessity for providing heavy lifting equipment. The inner wear plate means also includes three

sections

58, 6t and 62 which correspond generally in size and shape to the

outer plates

52, 54 and 56. However the outer dimensions of the wear plates are less than the outer dimensions of the

plates

52, 54 and 56 so as to avoid interference with the upper margin of the housing. In addition, it is to be noted that the width of the intermediate wear plate 60 is less than the width of the intermediate outer plate 54 and the

wear plates

58 and 62 are disposed for substantially abutting the longitudinal edges of the intermediate wear plate 60. Thus, as shown best in FIG. 3, the cracks between the intermediate wear plate 60 and the opposite side wear plates are offset from the cracks between the intermediate outer cover plate 54 and the adjacent

outer cover plates

52 and 56 so as to prevent the escape of dust and the like from the interior of the housing through the cracks in the cover structure.

The cover structure is provided with an upstanding cylindrical member 66 secured on top of the cover panel 54 and surrounding the central aperture 44. As will be understood material to be crushed or processed may be poured into the upstanding cylindrical member 66 for passage through the opening 44. In order to insure that the material to be processed will be directed centrally on to the upper end of the impeller, an elongated tubular guide member 68 is provided. The guide member 68 depends from the cover structure into close proximity to the upper end of the impeller so that the material entering the housing cannot be blown away from the center of the impeller by the turbulent currents of air which are created by the rapidly rotating impeller. Preferably the guide tube 68 is disposed in a central aperture with a slip fit so that it may be readily removed and replaced when necessary, and annular flange means 69 is provided at the upper end of the guide tube for overlying a portion of the cover structure and thereby retaining the guide tube in position. The annular flange means 69 may, of course, be either continuous or interrupted.

In order to prevent wearing away of the inner surface of the cylindrical housing member 12 at locations which are not protected by the breaker plate structures 48, guard ring assemblies 70 and 71 are disposed below and above the breaker plate structures. The guard ring assembly '70 includes vertically spaced annular plate members or

rings

72, 74 and 76 which are adapted to he slipped within the housing or shell 12. The ring members are preferably welded or otherwise secured to spacing blocks 78 therebetween and the assembly 7!} is supported at the desired level within the housing on a plurality of lugs 80 spaced around the interior of and welded to the housing 12.

The ring members of the assembly 70 have an outer diameter similar to the interior diameter of the housing 12 and a radial cross-section of substantial extent although only a small portion of the radius of the ring members. With this arrangement deep

annular pockets

82 and 83 are provided between the ring members 72-74 and 74-76. Processed material leaving the second stage of the impeller will become packed into the relatively deep narrow

annular pockets

82 and 83 and such packed material serves to protect the housing member 12 continued direct impingement by and abrasion or Wear from the material being processed. In other words the processed material packed between the rings will absorb a major portion of the abrasion and wear and while the rings will eventually become worn they may be replaced easily and relatively inexpensively.

The portion of the cylindrical housing member 12 directly behind the breaker plate structures is also protected against abrasion and wear by means of a cylindrical liner 84 which is adapted to be slipped into the housing and to rest on the upper margin of the ring assembly 7 t The ring assembly 71 rests on the upper edge of the liner 84 for protecting the housing shell immediately above the breaker plate structures. The ring assembly 71 is shown as including a pair of annular plate members or rings 86 and 88 secured to and separated by blocks 90. These rings are identical to the ring members of the assembly 70. While the assembly 70 is shown as including three rings and the assembly 71 is shown as including only two rings, it is to be understood that these assemblies must include a minimum of two rings and may include any desired number of additional rings.

The spindle means of the present structure is also protected from injury by the processed material. This protection is provided by a conical shield 92. enclosing a lower portion of the spindle and supported on a tunnel structure 94 which in turn encloses the drive belt 30 and the pulley 24. A cylindrical shield 96 is welded or otherwise secured to an upper portion of the conical shield 92 at a location spaced downwardly from the upper margin of the conical shield. The cylindrical shield extends to a point immediately adjacent the impeller plate member or disc 36 so as to minimize any possibility of processed material entering between the disc 36 and the upper end of the cylindrical shield 96. However small amounts of dust and the like may enter the cylinder 96 and therefore openings 98 are provided around the lower end of the cylinder 96 to permit such dust and the like to escape.

As shown in FIGS. 1 and 2, each of the breaker plate structures 48 comprises an elongated arcuate bracket or back-up plate member 100. The bracket or back-up plate member 109 carries one or more arcuate shoes 102 formed from wear resisting material. In the embodiment shown these shoes are provided with foot portions 104 adapted to be applied over the upper margin of the plate member for detachably connecting the shoes to the plate memher.

It has been found that, in general, the most effective breaking or crushing action is obtained when the breaker plate structure 48 is formed and disposed so that the surface against which the material being processed impinges is substantially normal to the trajectory of the material leaving the impeller. Therefore the acruate plate members 100 and the breaker plates or shoes disposed thereon are arcuately formed so that the various portions of the exposed surface of the breaker plates will be disposed generally perpendicularly with respect to the trajectories of material particles travelling at certain velocities. However, it will be appreciated that the direction of the trajectories of the material particles may be changed by varying certain factors such, for example, as the speed at which the particles are thrown from the impeller. Therefore in accordance with a feature of the present invention it is to be noted that the breaker plate structures 48 are mounted so that they may be located in numerous different positions which will be determined in accordance with the direction of the trajectories of the material particles and the result desired.

Each breaker plate structure has its arcuate bracket or plate member 100 pivotally connected either to the liner 84 or directly to the housing wall 12. This is accomplished by means of a pivot pin 206 extending through aligned apertures in a pair of ears 108 and 110 welded to the liner member 84 and a lug 112 welded to the back of the plate member and extending between the ears 108 and 110.

End portions of the plate members 100 located oppositely from the pivotal connections with the liner member are adjustably secured by the means shown in FIGS. 1, 2 and 4. More specifically, pairs of ears 114116 and 118120 are welded to the back of each plate member 100, and eye-

bolts

122 and 124 are pivotally connected between the pairs of cars by suitable pin means 126 and 128. The eye-bolts extend generally radially outwardly through aligned apertures in the liner and housing members '84 and 12.

Outer end portions of the bolts are enclosed by tubular sleeves 130 and 132 which also extend through the aligned apertures in the housing and liner members and are provided with radial flanges 134 and 136 respectively at their inner ends, which flanges overlie the inner surface of the liner member for positively locating the sleeves with respect to the liner member. The flanges may be spot Welded or otherwise secured to the liner member so that the sleeves or cylinders 130 and 132 are fixed against axial displacement but at the same time may be relatively easily disconnected from the liner member in the event it is desired to remove and replace the liner member.

Other ends of the sleeves or cylinders 130 and 132 are respectively substantially closed by annular

inturned flanges

138 and 140 having central apertures through which threaded end portions of the bolts slidably extend. Annular flanges or abutments 142 and 144 are respectively fixed on or integrally formed with the shanks of the

bolts

122 and 124. These annular abutments provide pistons respectively slidable within the sleeves or cylinders 130 and 132, and heavy compression springs 146 and 148 are respectively located within the cylinders 130 and 132 for engaging the pistons and thereby urging the bolts and the breaker plarte structure connected thereto in adirection extending inwardly of the housing.

Nut members

150 and 152 are threaded onto the outer ends of the

bolts

122 and 124 respectively so that the position of the. bolts and thus the breaker plate structure supported thereby may be readily adjusted merely by tightening or loosening the nut members.

The compression springs 146 and 148 are sufficiently strong so as substantially rigidly to support or back up the breaker plate structures during a normal crushing operation. In [the event however that some relatively large article enters the apparatus and tends to become wedged between the impeller and an end portion of a breaker plate structure adjacent the impeller, the compression springs are adapted to yield sufficiently to permit the breaker plate structure to retract for enabling the article to pass without injury to the apparatus.

The breaker plate structures 54) at the second stage of the apparatus are essentially identical to the breaker plate structures 48. Furthermore, the breaker plate structures 55) are adjustably and yieldably supported in the same manner as the breaker plate structures 48. Therefore a detailed description of this duplicate structure need not be given.

The particular construction of the shoe 42 of each of the impeller blade means 38 which is constructed in accordance with a feature of the present invention is shown best in FIGS. -8. Each shoe 42 comprises a main body portion 154 having a bottom 156,

opposite side walls

158 and 160, and inner and

outer end walls

162 and 164 respectively. Preferably the outer end wall 164 is diagonally disposed in the manner shown. A lug 166 extends laterally from the rear of the body member 154 for entry into a dovetail slot 168 in an upstanding wall 170 of the impeller bracket 40. In this embodiment the lug only partially fills the dovetail slot and a key member 172 is adapted to fill the remainder of the slot for securely locking the lug within the slot. The key member is provided with a laterally extending upper end portion 174 beneath which a tool may be relatively easily'inserted for prying the key member upwardly for removal from the slot in order to permit the shoe to be disassembled from the bracket. Preferably the lug 166 will be assembled in or removed from the dovetail slot through the lateral opening of the slot since a screw 176 is provided for proiecting loosely into an oversize aperture 178 in the lug 166 for limiting axial movement of the lug within the slot.

In order to protect the body member 154 from abrasion during a crushing operation, sideliner members 189 and 182 are provided for covering the inner surfaces and forwardly facing edges of the

side walls

158 and 160 respectively and inner and outer

end liner members

184 and 186 are provided for covering the inner surfaces and forwardly facing edges of the inner and

outer walls

162 and 164 respectively. During a crushing operation the pocket formed by the side and end walls of the shoe and the liner members will become filled with the material being processed so that the bottom Wall 156 of the body member will be protected against undue abrasion. Referring particularly to FIG. 7 it is seen that inner marginal portions of the

inserts

180 and 182 which correspond substantially in length and height to the

side walls

158 and 160 are relatively thin sincethese portions of the insert will also receive substantial protection from material packed within the shoe pocket. Outer marginal portions of these inserts are substantially thickened and are formed for overlying the edges of the walls of the body member in the manner shown. Preferable the

inserts

180 and 182 are secured to the

sidewalls

158 and 160 by means of

screws

188 and 190.

As shown best in FIG, 8, the end inserts 184 and 186 are also formed with relatively thin inner marginal portions which'cover the end -

walls

160 and 164 and relatively thick outer marginal portions which overlie the edges of the endwalls of the body member. It is important to note that the width of the inner

marginal portions

192 and 194 of the end inserts 184 and 186 respectively is substantially equal to the corresponding width of the

end walls

162 and 164. The relatively thick outer marginal portion of the end insert 184 is provided with

opposite end extensions

196 and 198 and the relatively thickouter marginal portion of the end insert 186 is provided with similar

opposite end extensions

200 and 202. These end extensions project so that the relatively thick outer marginal portions of the end inserts. 184 and 186 overlie not only' the edges of the

end walls

162 and 164 bu-t also the edges of the ends of the

side walls

158 and 160.

The side inserts 180 and 182 are sufficiently shorter than the side walls of the body member 154 so that they fit between and substantially abut the end inserts 184 and 186. It is particularly important to note that with this arrangement the cracks indicated by

lines

204, 206, 208 and 210 in FIG. 5 between the abutting surfaces of the side inserts and the end inserts extend substantially perpendicularly to the direction of movement of the ma terial being processed across the shoe structure. In this connection it will be observed that upon rotation of the impeller in a counter-clockwise direction as viewed in FIG. 2, the material being processed will travel from the central distributing cone of the impeller over the inner end insert 184 of the shoe, across the face of the shoe which is covered by previously packed material and outwardly over the outer end insert 186. Thus there is little or no force tending to project the material flowing across the shoe into the cracks 284410 in a manner which will be injurious to the shoe structure.

In order to retain the end inserts 184 and 186, the side insert 188 is provided with

opposite end extensions

212 and 214 which are adapted to overlie the end extensions 196 and 290 of the end inserts 184 and 186 respectively. Again it will be noted that the cracks indicated by

lines

216 and 218 between the end extensions 196212 and 200-214 extend in a direction perpendicular to the movement of material being processed across the shoe.

While the preferred embodiment of the present invention has been shown and described herein, it is obvious structure disposed adjacent the periphery of said impeller means for receiving material thrown from said impeller means, and means for angularly adjusting and for yieldably supporting the breaker plate structure for presenting a surface thereof at a predetermined angle with respect to the direction of movement of material to be crushed thrown from the impeller and for minimizing any danger of injury to the apparatus in the event an article becomes wedged between the impeller means and the breaker plate structure.

2. An impact type crushing apparatus comprising rotatable impeller means for projecting material to be crushed laterally outwardly therefrom, a breaker plate structure disposed adjacent the periphery of and extending generally circumferentially of said impeller means for receiving material thrown from said impeller means, means pivotally supporting said breaker plate structure toward one end thereof, and adjustable spring means connected with said breaker plate structure toward an opposite end thereof for angularly adjusting and yieldably supporting said breaker plate structure.

3. An impact type crushing apparatus, as defined in claim 2, wherein said adjustable spring means comprises a fixed cylinder extending generally radially with respect to said impeller means, elongated bolt means connected with said breaker plate structure and'axially shiftably extending through said cylinder, nut means threaded onto said bolt means and engageable with said cylinder for limiting movement of the bolt means and therefor the breaker plate structure toward said impeller means, abutment means on said bolt means and axially spaced from said nut means, and a compression spring disposed Within said cylinder and engaging said abutment means for yieldably biasing the bolt means and the breaker plate structure toward the impeller means.

4. An impact type crushing apparatus comprising an upstanding rotatable impeller for projecting material to be crushed laterally outwardly therefrom, upstanding housing means encircling said impeller and having upper and lower end portions extending substantially above and below said impeller, a cover structure extending across the upper end of said housing means and substantially above an upper end of said impeller, guide means extending through said cover structure and into close proximity with the upper end of said impeller for directing material to be crushed to the upper end of the impeller, breaker plate means mounted around the interior of said housing means and adjacent the periphery of said impeller for receiving the material thrown from said impeller, means for angularly adjusting and yieldably supporting said breaker plate means for presenting surface means thereof at a predetermined angle with respect to the direction of movement of the material to be crushed thrown from the impeller and for minimizing any danger of injury to the apparatus in the event an article becomes wedged between the impeller and said surface means, and sets of a plurality of ring members respectively disposed around the interior of said housing means above and below said breaker plate means and providing annular pockets into which a portion of the material being crushed is adapted to pack for protecting the housing means from contact with subsequently processed material.

5. An impact type crushing apparatus, as defined in claim 4, wherein said impeller includes an upstanding spindle, a generally radially extending member connected with an upper end portion of the spindle and blade means mounted on said radially extending member, said apparatus including shield means around a lower portion of said spindle, said shield means comprising a lower imperforate frusto-conical section and an upper section extending from said frusto-conieal section into close proximity to an under side of said generally radially extending member, said upper section having opening means therein adjacent a lower margin thereof for permitting any dust or the like which may pass over an upper edge thereof to escape therefrom.

6. An impact type crushing apparatus, as defined in claim 5, wherein each of said impeller blade means con.- prises a removable shoe including a body member having a side Wall and an end wall projecting from a bottom surface for providing a pocket adapted to be substantially filled by a portion of material being processed, a removable insert disposed against and substantially covering said end wall, and a second removable insert disposed against and substantially covering a major portion of said side wall and having an end edge substantially abutting said first mentioned insert for providing a narrow crack between said edge and said first mentioned insert, said crack extending transversely with respect to a primary direction of movement of material being processed across said shoe for minimizing any tendency for particles of said material to be forced into the crack.

7. An impact type crushing apparatus comprising rotatable. impeller means for projecting material to be crushed laterally outwardly therefrom, annularly arranged breaker plate means disposed around the periphery of said impeller means for receiving material thrown from said impeller means, housing means enclosing said impeller means and surrounding said breaker plate means, and a plurality of sets of adjacently disposed spaced ring members mounted around the interior of said housing means and providing a plurality of annular pockets, one of said sets being disposed adjacent one axially facing margin of said breaker plate means and another of said sets being disposed adjacent an opposite axially facing margin of said breaker plate means for locating said pockets for receiving and retaining a portion of the material being processed for preventing engagement of subsequently processed material against areas of said housing means covered by said pockets.

8. An impact type crushing apparatus, as defined in claim 7, whterein said housing means comprises a removable cylindrical liner member disposed between said sets of ring members located adjacent opposite axially facing margins of said breaker plate means.

9. An impact type crushing apparatus comprising an upstanding rotatable impeller for projecting material to be crushed laterally outwardly therefrom, generally annularly arranged breaker plate means disposed around the periphery of said impeller for receiving material thrown from said impeller, upstanding cylindrical housing means surrounding said breaker plate means and including an upper end portion extending substantially above an upper end of said impeller, a cover structure extending across the upper end of said housing means at a location substantially above the upper end of said impeller, and a plurality of ring members extending around the interior of said upper housing means end portion and providing an annular pocket for receiving and retaining a portion of the material being processed for preventing subsequently processed material from engaging a portion of said housing means covered by said pocket.

10. In an impact type crushing apparatus of the type described, an impeller structure including blade'means for projecting material to be crushed laterally therefrom, said blade means including a shoe comprising a body member having forwardly projecting side and end walls at least partially defining a forwardly facing pocket adapted to be filled with material being processed, a first insert disposed against and substantially covering said end wall, and a second insert disposed against and substantially covering a major portion of said side wall, and having an edge substantially abutting said first insert, said edge and a substantially abutting surface of said first insert defining a crack therebetween which extends transversely with respect to a primary direction of movement of material being processed across said shoe for minimizing any tendency for a portion of said material to be forced into the crack. t

11. An impeller shoe for an impact type crushing apparatus of the type described comprising a body member having a first wall, side and end walls extending forwardly from said first wall with respect to the direction of movement of the shoe when the shoe is installed in an impeller rotatable about a predetermined axis, said walls at least partially defining a pocket adapted to be substantially filled with material being processed, a first insert disposed against and substantially covering said end wall, and a second insert disposed against and substantially covering said side wall and having an end edge substantially abutting a surface of said first insert, said end edge and said surface defining a crack therebetween extending generally parallel to said axis of rotation when the shoe is installed in the impeller and transversely with respect to a primary direction of movement of material across the shoe so as to minimize any tendency for a portion of the material to be forced into the crack.

12. An impeller shoe, as defined in claim 11, wherein said first insert is disposed along an inner surface of said end wall and includes a portion overlying a forwardly facing edge of said end wall and a projecting portion overlying an end of a forwardly facing edge of said side wall, and said second insert being disposed along an References Cited in the file of this patent UNITED STATES PATENTS 13,713 Anderson et a1. Oct. 30, 1855 493,531 Straker Mar. 14, 1893 1,499,455 Hadsel July 1, 1924 1,547,385 Hadsel July 28, 1925 2,012,694 Runyan Aug. 27, 1935 2,046,711 Van Law July 7, 1936 2,124,393 Benner et al. July 19, 1938 2,192,606 Symons Mar. 5, 1940 2,525,650 Clark et a1. Oct. 10, 1950 2,637,502 Bond May 5, 1953 2,752,098 Adams June 26, 1956 FOREIGN PATENTS 184,609 Great Britain Aug. 24, 1922 394,478 Great Britain June 29, 1933