US2973735A - Apparatus for producing reclosure container covers - Google Patents

Description

V. T. GRQVER March 7, 1961 APPARATUS FOR PRODUCING RECLOSURE CONTAINER COVERS 4 Sheets-Sheet 1 Filed Dec. 16, 1957 INVENTOR.

VICTOR T. GROVER ATTORNEYS March 7, 1961 v. T. GROVER APPARATUS FOR PRODUCING RECLOSURE CONTAINER COVERS Filed Dec. 16, 1957 4 Sheets-Sheet 2 INVENTOR.

VICTOR T. GROVER N QE ATTORNEYS V. T. GROVER March 7, 1961 APPARATUS FOR PRODUCING RECLOSURE CONTAINER COVERS Filed Dec. 16, 1957 4 Sheets-Sheet 3 FIG.3

INVENTOR. 'v I CTOR T. GROVER ATTORNEYS V. T. GROVER March 7, 1961 APPARATUS FOR PRODUCING RECLOSURE CONTAINER COVERS '4 Sheets-Sheet 4 Filed Dec. 16, 1957 INVENTOR.

VICTOR T. GROVER APPARATUS FORIPRODUCING RECLOSURE CONTAINER COVERS Filed 155.. 16, 1951s. No. 703,201 s Claims. c 113-48) The present invention relates to apparatus forproducing sheet metal reclosure covers and the like for' containers and has particular reference to. devices for forming locking projections on the covers to provide for securing them to the containers when used as reclosure covers.

An object of the instant invention is to provide an apparatus for producing locking projections in reclosure container covers wherein full backing-up of the cover material is had during the projection forming operation so as to produce sharp clear cut projections of-predetermined dimensions. A I I Another object is to provide such an apparatus which is sturdy in construction and which readily releases the cover after formation of the locking projections so that the formed cover may be easily removed from the app rat s.

Numerous other .objects and advantages of the invention will be apparent as it: is better understood from the following description, which, taken in connection with the accompanying drawings, discloses a preferred embodiment thereof. 1 I

Referring to the drawings:

Figure 1 is a top plan view of an apparatus embodying the instant invention,

shown in section;

Fig. 2 is a sectional view takensubstantially along the broken line 2-2 in Fig. 1, with parts broken away;

Fig. 3 is a sectionalview taken substantially along the line 3-3 in Fig. 1, the view including, a wiring diiwith parts broken away and parts agram of electric devices used in the apparatus; V

Fig. 4 is a fragmentary elevational view of certain details as viewed from the left in Fig. 2; V

"Fig. 5 is" an enlarged perspective view of an; inverted reclosure cover having locking projections produced inthe apparatus of the instant invention; 1

Figs. 6 and 7 are enlarged sectional views showing a fragmentary portion of the'apparatus illustrated in Fig. 2 with the parts in Fig. 6 shown in.their,norrnal positions Fig. 7 shown in projection forming and, with the parts in positions; and

Figs. 8 and 9 are fragmentary sectional views taken substantially along the lines 8-8, 99 in Figs. 6 and 7 respectively.

As a preferred and exemplary embodiment of their;- stant invention the drawings disclose an apparatus for producing locking projections A (Fig. 5) on sheet metal reclosure container covers or end members B to provide for the securing of the cover in place on a container, preferably after the container is initially opened and the cover is used as a reclosure. commonly used on coffee cans where a tearing strip is used toopen thecan and an interior collar having a smooth curled top edge is provided as 'a seat for the reclosure cover. Another example is cans used for baby food and other products whereinthe can is provided with bayonet joints or interrupted screw threads for holding the cover in place The locking projections A may be of any desired shape, such as the lugs shown in the/draw- The reclosure cover. B shown in inverted position in Fig. 5 of the drawings is an exemplary typeof sheet metal cover and briefly comprises an annular short side wall Cwhich at its. lower edge D surrounds a preferably flat countersunk panel or bottom wall E. At its upper edge the side wall C merges into an outwardly projecting substantially horizontal annular fiat shoulder F. The outer edge of the shoulder F merges into a short upright side wall G which at its upper edge merges into an outwardly extending flange H which is utilized to permanently secure the cover B to a container by an interfolding 'of the flange with a similar flange part on the container when it is desired to produce the well known double seam commonly used for this purpose. The flange H terminates in an edge curl J commonly provided to facilitate interfolding of the flanges. This curl J preferably is produced simultaneously with the formation of the lugs A the lugs A being formed preferably in the lower edge D of the lower side wall C at spaced intervals around the cover as shown in Fig. 5.

- The apparatus of the instant invention preferably inclu-des a conventional punch and die mechanism commonly used in punch presses of the character disclosed in United States Patent 2,136,933 issued November 15,

a plurality of angularly disposed lugging pins M (Figs.

6,7 and 9) which are carried in one of the die elements in such a manner as to slide radially outwardly when a downward pressure is exerted on the die element.

.The upper ends of the lugging pins M are formed with shaped lugging noses N to engage the cover side wall C, adjacent its inverted lower edge D, and thus force a portion of the wall C radially outwardly to produce the lugs A. An important feature of the invention is means to engage and back up theouterface of the cover side wall C during this lug forming operation so as to produce a sharp clear-cut lug. This backing-up is effected by wall support'protuberances 0 (Figs. 7 and 9) formed in one of the punch elements and movable into backing-up position 'by the punch when it moves down against the cover. Another important feature of the invention is to remove these backing-up protuberances 0 from under the locking'lugs A formed in the cover B, so that the punch Such reclosure covers are elements may be separated from the die elements to remove the. cover. This removal of the backing-up protuberances O is effected by shifting them laterally out of register with the lugging pin noses N and thus freeing the punch so it can be raised.

Referring to the drawings in more detail, the lower die elements comprise a plurality of concentric rings 21, 22, 23, 24 (Fig. 2) housed in a bolster plate or die block 25 which is secured to a bed plate 26 of a conventional punch press of the character above mentioned.

The outer die ring 21 is stationary and is seated in a recess 28 formed in the die block 25, the ring being secured in place by screws 29 asshown in Fig. 2. The inner upper edge of the outer ring 21 is provided with an annular channel 31 (see also Fig. 7) setting off a hot-icurl J.

:zontal shoulder 32 to accommodatethe flange H of the The draw ring 22 is yieldably disposed within the outer die ring 21 and is of a width slightly less than the width of the cover flange H so as to fully support the major portion of the flange H and to permit the outer edge of the flange to extend beyond the ring in unsupported fashion to engage the outer ring shoulder 32 as will be hereinafter explained. The top faceof the draw ring 22 normally is flush with the top of the outer ring 21 as shown in Fig. 2 for its initial cover supporting function. The draw ring 22 normally is held in this up position by a plurality of vertical rods 34 which slidably extend through the die block 25, the bed plate 26, a wear plate 35 and engage against a yieldable, spring backed pressure plate 36 commonly used in punch presses to exert a yieldable pressure against die elements.

The lugging or carrier ring 23 is slidably disposed within the draw ring 22 and normally rests on an annular flange 38 (Figs. 2 and 7) on the lower end of the drawring 23. This lugging ring 23 is yieldably' supported on a plurality of vertical rods 41 which slidably extend through the die block 25, the bed plate 26, a wear plate 42 and engage against a yieldable, spring backed pressure plate 43 similar to the pressure plate 36. The upper face of the lugging ring 23 is contoured to engage and partially support the panel or bottom wall E of the inverted cover B. This contoured face includes an annular notch 45 (see Fig. 6) in the upper outer edge of the lugging ring. This notch sets off a vertical support wall 46 for lateral supporting engagement against the inner face of the cover side wall C, and further sets off a horizontal shoulder 47 for vertically supporting the shoulder wall F of the cover B when the latter is in the die mechanism as will be hereinafter explained. This contoured upper face of the lugging ring 23 normally is disposed below the top face of the draw ring 22 as best shown in Fig. 2.

The lugging ring 23 is held within the die mechanism while allowing a predetermined axial movement therein,

by the retainer ring 24 which is a stationary element and which overhangs and provides a vertical stop for a hori- 'zontal flange 48 on the bottom of the lugging ring 23 .to limit the upward travel of the ring 23. Vertical movement of the flange 48 under the retainer ring 24 is provided for by a spacing boss 49 formed on the. bottom of the retainer ring and secured by bolts 50 to the bolster plate 25. i

The lugging ring 23 carries the lugging pins M hereinbefore referred to. There are a plurality of these pins M located at spaced intervals around the circumference of the ring and disposed radially at an angle to the axis of the ring. These pins M preferably are cylindrical in shape and are slidably disposed in inclined bores 52 which extend from the upper outer edge of the lugging ring vertical support wall 46, downwardly and inwardly as shown in Figs. 6 and 7, to and through the ring flange 48 so as to intersect the lower outer corner of the retainer ring 24 which serves as a stop for the flange 48.

The lug forming noses N on the upper ends of the pins 'M are normally disposed within the bores 52, in a retracted position, as shown in Fig. 6 for the reception of a cover B on the die elements. The lower ends of the pins M are formed with flat tongues 54 (Figs. 6, 7 and 8) which project into radial slots 55 in the top of the bolster plate 25 to hold the pins against rotation in their bores 52. Intermediate their ends, the pins M are formed with right angle notches 56 for the reception of the lower ;7 and continue the downward pressure to force the lugging ring down against the resistance of its spring backed pressure plate 43 (Fig. 2), said pressure being exerted through vertical rods 41 beneath the lugging ring 23. This downward movement of the lugging ring causes the lugging pins M, by reason of their angular position and their inability to move vertically, to shift laterally and radially outwardly to cause their noses N to engage and press outwardly the portion of the cover side wall C adjacent the inverted bottom edge D to form the lugs or projections A.

The punch elements of the die mechanism which cooperate with the die elements just described, comprise a plurality of concentric rings 61, 62, 63, 64 (Figs. 2

and 7) housed in a vertically movable punch plate 65 guided by a pair of pilot pins 66 having their lower ends secured in the bolster plate 25 of the die mechanism. The punch plate 65 is provided with the usual actuating stem 67 which is secured to and reciprocated by the crank of the press in the usual manner.

The outermost ring 61 in the punch is a curling ring which is fixed to the punch plate 65 in depending relation thereto and is vertically aligned with the yieldable draw ring 22 of the lower die elements or instrumentalities. This curling ring 61 is slightly narrower than the width of the draw ring 22, by an amount substantially equal to twice the thickness of the material of the cover flange H to facilitate forming of the flange curl J as best shown in Fig. 7.

The ring 62 constitutes a yieldable support or backingup ring and is slidably disposed within the fixed curling ring 61 as shown in Figs. 2 and 7. The lower end of the support ring 62 normally is disposed slightly above the lower end of the curling ring 61 as shown in Figs. 2 and 7. The backing-up or support elements or protuberances O hereinbefore mentioned are carried on the inner face fixed curling ring 61.

. a relatively thick flange 71 which is located for vertical travel in a deep recess 72 in the punch plate 65. The

flange 71 overhangs and seats against the top of the Compression springs 73 interposed between the punch plate 65 and the flange 71 normally retain the flange in this seated relation to the curling ring 61. Q

The ring 63 is a knockout ring and is disposed within the support ring 62 with its lower flat face substantially fflush with the shoulder 69 on the support ring. The upper elements at the conclusion of a lugging operation. .coiled spring 76 in the actuating stem 67 yieldingly re- ;end of the knockout ring 63 seats against stop bosses 74 in the recess 72 in the punch plate 65. The knockout ring 63 is mounted on a vertical rod 75 which extends up through the punch plate actuatingstem 67 for engagement by a conventional press element in the usual manner to knockout the cover B as it rises with the punch A tains the knockout ring 63 in engagement with its stop bosses 74.

The ring 64 is a stripper pad which is disposed within lthe knockout ring 63 and is fixed to the punch plate 65 through the medium of upright bosses 78 which extend up through openings in the top of the knockout ring 63 and are secured on the punch plate 65 by bolts 79. The lower face of this stripper pad 64 preferably extends slightly below the knockout ring 63 as shown in Fig. 2, to strip the cover from the knockout ring if necessary.

When a cover B is in place in the die mechanism for 7 a lugging operation the'flange H of the cover, in the inverted position shown in Fig. 5, rests on top of the rll e draw ring 22st;v that. when the punchelements move down toward the die elements the fixed curling ring-61 engages and clamps thecover curl H between the curling ring'61 and the draw ring22. With continued downward movement of the-punch elements, the curling ring 61"presses the cover B and the draw ring 22 downwardly. This movement of the punch elements carries the support ring-62 down into position over the cover bottom wall E audits side wall C as shown in Fig. 7 and carries the v knockout ring 63 down onto the cover bottom wall E thus clamping this wall against thelugging ring "23.

. Thereafter, the punch-elements, the clamped coverB, the

Duringfthis latterJrnovement, the outer edge of the cover flange His wipedpast the shoulder wall' 32 of the stationarygouter ring 21 to form thecurl J on the cover and simultaneously thelugging pinsM are bodily shifted radially outwardly as explained above to produce the lugs or projections A in the lower edge D of the cover.

Since the lower edge of the support ring 62 seats against the shoulder F of the cover when the support ring is in cover clamping position, the protuberances O on the support ring are disposed immediately adjacent the coverside' wall C in engagement or substantially in engagement therewith and thus set off a definite space of predetermined dimensions between the protuberances O and the support ring shoulder 69. It is into this space that the noses N on the lugging pins M reform the adjacent'portibn of the cover sidewall C, to produce the lugs A, the side wall being backed up laterally and verticall? by the support ring 62 and its protuberances O'and its shoulder 69 to insure the formation of lugs A' of clear-cutisharp contours.

After the lug forming operation, the punch elements 61-64 are moved up through a return stroke. At the beginningof this up-stroke, the draw ring 22 and the lugging ring 23 move up with the punch elements by reason of the spring pressure on and beneath these rings.

This initial up-movernent of the lugging ring 23. serves to bodily shift the lugging pins M laterally and radially inwardly to remove their noses N from the newly formed cover lugs A. "This releases the pins and lugging. ring so that the cover and .the punch elements can continue their up-stroke' movement, but it leaves the lugs-A locked above thesupport ring protuberances O to prevent'release ofthe cover.

The release or the cover B is elfected by a partial rotation of the support ring 62so as to shift the backing-up protuberances'Q "laterally, out of radial alignment with the-luggin'g-pins Maud to thereby remove such obstruction frombeneath the cover-lugs A. For this purpose, the support ring62 is provided with anoutwardly projecting radial arm 8l (Figs. 1, 2 and 3") whichlextends thro'ugh'an opening 82 in the side. of the punch plate 65,

for: oscillation through a horizontal radial angle .Y .(Fig l) sufii'ci'ent to shift the protuberances Ov out of radial alignment with the lugging pins M.

At its outer end, the support ring oscillating arm :81

carries 'a ball roller 83 which operatesin a straight verticar groove- 84 in the inner end of an oscil-latable hor-izontal lever 85 permit vertical movement of the roller 83 in itsgroove while the punch elements are moving vertically; The lever- 85 intermediate its ends is mounted on a pivot pin 86 secured in a bracket 87 attached to the bed plate 26. The outer end of the lever 85 is bifurcated and partially surrounds a ball roller 88 carried onone leg of a bell crank 89 mounted. on a pivot pin 91 securedin .the bracket 87. The other leg of the bell crank,89 is attached by way of a connecting rod 92 to the crank shaft of the press which lowers and raises the j punch. elements.

proper time and in the proper direction, to rotatably oscillate the lever 85. and thus shift the support ring'os cillating arm 81 and the support ring 62 connected thereto, through the radial angle Y (Fig. l) to shift the backing-up protuberances 0 out of vertical alignment with the lugging pins M and locking projections Am the container cover. While the support ring 62 is inthis shifted position and is moving up-with the other punch elements, the knock-out ring 63, through its actuatingrod 75 is pushed down against the cover B to push orknock it out of the support ring 62 and thereby "release the cover B from the punch elements for further operations if necessary. When the punch elements are moved downwardly to perform a lugging operation, the press crank shaft first rocks the bell crank 89 in the opposite direction to rotatively shift the sup port ring 62 in the reverse direction through radial angle Y to return the backing-up protuberances O thereon into axial alignment withthe lugging pins M. A pair of yieldable fingers 93 (Fig. 2) is provided on thebolster plate 25, over the die elements to locate a cover B in position over the die elements for the lugging operation and to prevent the return of the cover to the die elements after a lugging operation.

Briefiy summarized the initial upward movement of punch members 6ll64 after each cover lugging operation (Fig. 7) is accompanied by spring pressed upward movement of lugging ring 23 of the die assembly, which serves to axially withdraw the lugging pins M from the formed cover lugs A (Figs. 7 and 6). This occurs prior torengagement of lugging ring flange 48 beneath the stationary retainer ring 24 (Fig. 6) to terminate further upward movement of the lugging ring 23. Thereafter the cover B moves upwardly with said punch members with its flange H clamped against rotary movement between curling ring 61 and spring pressed draw ring 22 prior to engagement of draw ring flange 38 with and beneath the now stationary lugging ring 23 (Figs.

:7 and 2) to terminate further upward movement of the draw ring by spring pressed vertical rods 34 (Fig. 2). At this time support ring 62 is slightly rotated as described to free the backing-up protuberances 0 from beneath the cover lugs A. No damage to the cover lugs occurs during theslight rotation of support ring 62 relative to the clamped cover B since backing-up protuberances O are offset vertically from the formed cover lugs A and are thus free to move laterally from beneath the latter, as will be clear from Figs. 7 and 9. The lugged cover is now in readiness for ejection from the punch assembly by the knock-out ringedas hereinabove described.

' Provision is made for stopping the press when two covers B are inadvertently positioned on the die ele- 'end of the arm 94 extends beneath the support ring oscillating arm 81 and carries a roller 95 (see Fig. 2) which engages against the arm 81. A spring backed plunger97 in the punch plate 65 retains the roller 96 in this engagement with the arm 81. j

The opposite end of the detector arm 94 carries an adjustable screw 98 adjusted to just clear the actuating element of a normally closed electric switch 99, when the punch elements are at their lowest level during their down or lugging operation stroke. The switch 99 is part of an electric circuit which includes the press actuating motor 101, a source of electric current such as a generator 102, a normally open press starting switch 103, and 'a normally open relay 104 controlled by a solenoid 105.

When. starting the press, the starting switch 103 is momentarily closed and this energizes the solenoid 105 and thus closes the switch 104, thereby setting up through the normally closed detector switch 99 a circuit which connects the motor 101 with the generator 102 and simultaneously establishes a holding circuit through the solenoid 105 and by-passing the starting switch 103 to keep the motor 101 in operation as long as the covers B are fed to the die elements one at a time.

When two covers B are positioned on the'die elements, the punch elements descending upon the two covers B, causes the support ring 62 of the punch elements to yield upwardly against its springs 73 (see Fig. 2) and this causes the detector arm 94 to rock in a counterclockwise direction as viewed in Fig. 3. Hence before the punch elements complete their down stroke, the screw 98 on the shifted detector arm 94 engages and opens the detector switch 99 and thisbreaks the circuits to the motor 101 and causes the press to stop. This breaking of the circuits deenergizes the solenoid 105 and thus prevents reenergization of the motor 101 until the die elements are cleared of the double covers B and the press restarted through operation of the starting switch 103.

It is thought that the invention and many of itsattendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the parts without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.

Ielaim:

1. Apparatus for forming a locking projection on a side wall of a container cover, comprising relatively vertically movable axially aligned punch and die members for receiving and supporting a container cover therebetween, a projection forming element carried by one of said members and locked thereon against vertical movement, said element having means mounting the same for movement radially outwardly on and relative to said one member by vertical movement of said one member imparted thereto by the other member for forming a locking projection in said cover side wall, and

an axially rotatable cylindrical support element carried by the other member and movable vertically therewith into operative radial alignment with said projection forming element on said one member to back up said cover side wall during the formation of said projection thereon, said support element being fixed against radial movement, and means for axially rotating said support element into and out of cover side wall projection backing-up position.

2. Apparatus of claim 1 wherein one of said members includes an axially movable ring and said projection forming element comprises a pin slidably mounted in said ring at an angle to the ring axis, said pin having a notch therein engaged by a relatively fixed member concentric with said ring to lock said pin against vertical movement during the projection forming operation and permitting radial outward and inward sliding movement of said pin relative to said ring during and following said operation.

3. .The apparatus of claim 1 having means for rotating said support element out of radial alignment with said projection forming element to free said cover for removal from between said punch and die members.

4. An apparatus of the character definedin claim 3 wherein said support element comprises a support ring, and said rotating means comprise devices for axially rotating said ring through a predetermined radial angle.

5. An apparatus of the character defined in claim 4 wherein said rotating means includes an arm extending laterally from said ring and means connected with said arm for swinging it through a predetermined radial angle.

6. An apparatus of the character defined in claim 4 wherein said support ring is yieldably mounted for movement in a vertical axial direction, and means responsive to the axial movement of said ring to stop the operation ofsaid apparatus when said support ring encounters a plurality of covers disposed between said punch and die members.

7. Apparatus for forming a'locking projection on a side wall of a container cover, comprising relatively vertically movable axially aligned punch and die assemblies for receiving and supporting a container cover therebetween, a projection forming element carried by a member of said die assembly and locked against vertical movement by another member of said die assembly, said projection forming element having means mounting the same for axial sliding movement on and radially outwardly of said first mentioned die member and relative to said die assembly by downward vertical movement of said first die member imparted by said punch assembly for forming a locking projection in said cover side wall, means on said die assembly for locking said projection forming element against vertical movement during said radial sliding movement thereof, and a support ring carried by said punch assembly and movable therewith and relative thereto into radial alignment with said projection forming element on said die member to back up said cover side wall during the formation of said projection thereon.

8. The apparatus of claim 7 having 'means for axially rotating said support ring relative to said punch assembly out of radial alignment with said projection forming element to free said cover for removal from between said punch and die assemblies.

9. An apparatus for forming a locking projection in the side wall of a reclosure container cover and for simultaneously curling a flange on the cover, comprising a pair of axially aligned relatively vertically movable punch and die members for receiving and supporting an interposed cover therebetween, a projection forming element carried by one of said members and locked thereon against vertical movement, said element having means mounting the same for axial sliding movement radially outwardly on and relative to said one member by vertical movement of said one member imparted thereto by the other of said members for forming a locking projection in said cover side wall, a support element .carried by said other member and movable vertically thereby into operating position adjacent said cover side wall to back up said wall during the formation of said projection thereon, means for axially rotating said support element into and out of cover projection backing up position, and a vertically movable curling member carried by said other member for engaging and wiping the peripheral edge of said cover flange against a shoulder on said one member to produce a peripheral curl on the .outer edge of said cover flange.

10. The apparatus of claim 9 wherein said shoulder is fixed on said die member and said curling member comprises a depending curling ring carried by and movable vertically with said punch member and cooperating with said shoulder to form said cover curl coincidently with formation of said locking projection on the cover fside wall.

11. An apparatus for forming peripherally spaced locking projections on a side wall of a reclosure con- 'tainer cover, comprising relatively vertically movable axially aligned punch and die members for receiving and supporting therebetween an interposed container cover, a plurality of radially movable projection forming elements carried by said die member and locked thereon against vertical movement, said elements having means mounting the same for movement radially outwardly on and relative to said die member by vertical movement of said die member imparted thereto by said punch mem- .ber to form said locking projections in said cover side a wall, a cylindrical support element carried by said punch -member and movable vertically into radial alignment with said projection forming elements, means for vertically moving saidsupport element into operative posi- 9 tion surrounding said cover side wall to back up the wall during the formation of said projections thereon, and means for axially rotating said support element out of radial alignment with said projection forming elements to free said cover for removal from between said punch and die members.

12. An apparatus of the character defined in claim 11 having a plurality of said projection forming elements disposed in circumferentially spaced relation and a corresponding plurality of circumferentially spaced backing up support elements respectively cooperating therewith and. disposed on the inner peripheral surface of said cylindrical support element to form a plurality of said locking projections around the periphery of said cover side wall in a single operation.

13. Apparatus for producing locking projections in a side wall of a reclosure container cover, comprising a pair of axially aligned relatively vertically movable punch and die assemblies for receiving and supporting an interposed cover, a plurality of locking projection forming pins mounted for lateral sliding movement in a plurality of inclined bores in a member of said die assembly, said pins being responsive to vertical movement of another die assembly member to slide bodily and radially outwardly in said bores to form integral locking projections on said cover side wall, fixed means in said die member assembly for locking said projection forming elements against vertical movement relative to said die assembly, a cylindrical support element on said punch assembly and vertically movable thereby into operative position radially outwardly of said cover side wall, and a plurality of circumferentially spaced protuberances of predetermined contour on the inner wall of said cylindrical support element for backing up said projection forming elements and said cover side wall to impart a definite clear-cut configuration to said projections during the formation thereof.

References Cited in the file of this patent UNITED STATES PATENTS Almgren et a1. Jan. 27, 1953

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