The present invention relates to perforated food casings and more
particularly to a food casing having die cut perforations and to a method of forming
BACKGROUND OF THE INVENTION
Use of casings in the food processing industry is well known. One
segment of this industry uses casings in the production of food products involving
whole muscles or large chunks of meat. An example would be smoked ham wherein the
whole ham is stuffed into a casing for the smoking operation. Another example is
a so called chunk-and-formed product where large meat chunks are combined for stuffing
into a casing. For these types of food products, it is desirable that the casing
have a plurality of vent openings in order to enhance or facilitate the expulsion
of air from the casing as the large meat mass is stuffed into the casing, and to
enhance or facilitate the draining of liquids such as water, meat juices and the
like formed during or after processing.
A common stuffing method for producing these types of food products
involves the use of flattened casing on reels and the stuffing apparatus as described,
for example, U.S. Patent No. 4,696,079. In this apparatus, a measured length of
casing is pulled from the reel. The end of the casing is opened and a meat mass
is rammed into the open casing. The open end is gathered and clipped to close it.
Then the casing on the opposite side of the meat mass is gathered and the casing
is pulled back from the clip closure so the casing wall is drawn up tightly around
the meat mass thereby expelling entrapped air from between the casing and the meat
mass. A second clip is applied to close a second end of the casing and then the
casing is cut to separate the encased food product from the reel.
The speed and force of drawing the casing tight about the meat mass
necessitates a perforated casing to facilitate the venting of air and excess liquids
which may be squeezed from the meat mass as the casing tightens around it. Thereafter,
during processing such as by cooking or smoking, additional gases and juices are
released which are vented and drained from the casing through the perforations.
The most common method of providing the casing with vent holes is
to flatten the casing and then prick through both plies of the flattened casing
with sharp, pointed needles. If the casing is pricked from above, the perforations
created will have inwardly disposed flaps in the upper ply of casing and outwardly
disposed flaps in the bottom ply of the casing. The use of pointed needles also
makes the vent flaps in the upper ply slightly larger than those in the bottom
ply and all perforations may have somewhat jagged edges.
Due to the non-uniform configuration and size of the vent openings
in the upper and lower plies, the venting of air, water and meat juices is not
uniform about the circumference of the casing. The non-uniform venting also is
the result of the closing of the inwardly disposed flaps during stuffing. This
is because the pressure and meat mass tend to force these flaps outward so as to
close off the vent openings. On the other side of the casing, the internal casing
pressure forces the outwardly disposed flaps to remain open.
A further drawback of this casing is that the flaps produced by needle
piercing are somewhat jagged and these jagged edges provide points of stress concentration
where tearing can initiate when the casing is drawn tight about the meat mass.
It also is possible for moving elements of the stuffing apparatus to snag on these
flaps and initiate a tear or other casing failure.
Various efforts have been made to improve perforated casing. For
example, U.S. Patent No. 3,779,284 discloses use of a flat faced punch to make
the vent opening. The punch is on a roller which interfaces with a backup roll
having a resilient surface. As the punch presses the casing into the resilient
surface, it tears a slug of casing from the upper and lower plies of casing and
deposits them in the resilient surface of the backup roll. Since the backup surface
is resilient, the lower ply still exhibited an outwardly flared edge caused by
the passage of the punch. These flared edges still provide snag points and areas
of stress concentration where tears can initiate. Moreover, venting still is not
uniform around the casing perimeter and the backup roll has a relatively short
life due to the constant contact with the punches.
Other attempts have been made to provide an improved perforated casing
by using knife points. However, slits produced with knife points are not entirely
One drawback with prior art methods using pin or knife points to
form the vents, or using punches against a resilient backup roll to knock slugs
from the casing is that care had to be taken to avoid damaging the folded edge
of the laid flat casing. This is because a sharp pin, knife point or punch which
nicked the casing edge tended to produce a more ragged perforation in this area
so the casing was more susceptible to tearing when drawn up tight against the meat
mass. For this reason, care was taken to insure that the perforating apparatus
did not operate out to or beyond the folded edge of the laid flat casing. This
required a change in the set up of the apparatus for each different flat width
Accordingly, there is a need for perforated casing having improved
venting properties and for methods and apparatus for making such a casing.
OBJECTS OF THE INVENTION
One object of the present invention is to provide a tubular food
casing having vent openings substantially free of inwardly and outwardly disposed
Another object of the present invention is to provide a food casing
having a vent rate of air and liquids which is uniform around the casing perimeter.
A further object of the present invention is to provide a vented
food casing wherein the vent openings are formed by die cutting such that the edges
defining the openings are substantially clean cut and are flush with the casing
Yet another object is to provide a method for obtaining a perforated
casing having vent openings which are uniform and clean cut and which have no inwardly
or outwardly disposed flaps or lips or the like.
SUMMARY OF THE INVENTION
In accordance with the present invention, a casing article is provided
for use in stuffing whole muscle meat and chunk-and-formed meat products having
enhanced venting of air and liquids such as water, meat juices and the like. The
enhanced venting results from die cut vent openings wherein the die cutting physically
removes casing material to provide a substantially clean cut edge which is flush
with the wall of the casing. Moreover, the vent openings are die cut with the casing
in a laid-flat condition so openings on both sides of the casing are in registration,
are of equal area and have edges which align. All of these features contribute
to provide a vent rate through diametrically opposite areas of the casing which
is substantially constant.
The die cut method according to the present invention utilizes both
male and female die cutting members so the openings have a relatively smooth clean
edge free of stress concentration points. Consequently, there is no danger of weakening
the casing by providing vent openings even at the casing edge. This simplifies
production in that no special adjustment need be made when perforating casings
of different flat widths. The die cutting members are in the form of rollers with
punches on a first roller and die openings on a second roller. Except for the meshing
of the punches and die openings, the rollers are not geared together or motor driven.
Instead, the drawing of the casing between the rollers and against the punches
drives the first roller and the meshing of the punches with the die openings drives
the second roller.
It is important for the rotation of the two rollers to be synchronized
so that each punch mates with only one given die opening. To accomplish this,
the punches and the associated die openings are staggered about the roller peripheries
so that at a given increment of rotation there is at least one punch fully inserted
in its counterpart die opening and several more punches which are at different
stages of insertion and retreat. In this fashion, the second roller is continuously
driven in synchronism with the first roller by the progressive insertion of punches
into their counterpart die openings and subsequent retreat of the punches from
the die openings.
The die cutting operation removes a slug of casing to form a clean-cut
opening having a smooth edge which is generally flush with the casing wall. That
is, there are little or no portions of the casing such as a lip, flap or shred
about the openings which extend outward or inward with respect to the plane of
the casing wall.
The slugs of casing or "chad" are forced progressively down the die
opening and into the interior of the second roller which is hollow The chad is
then removed from the hollow interior by any suitable means such as by a vacuum
line communicating with the hollow interior.
DESCRIPTION OF THE DRAWINGS
An embodiment of the invention will now be described by way of example
with reference to the drawings, in which:
DETAILED DESCRIPTION OF THE INVENTION
- Figure 1 is perspective view showing a casing embodying the present invention
- Figure 2 is an enlarged view of a portion of the Figure 1 casing partly broken
away and in sections;
- Figure 3 is a schematic view illustrating apparatus and a method for making
a casing embodying the present invention;
- Figure 4 is a schematic view on an enlarged scale showing a portion of the
apparatus of Figure 3 for die cutting the casing and practising the method of the
present invention; and
- Figure 5 is a schematic view illustrating the progression of die openings along
the surface of the die cutting apparatus of Figure 3.
Referring to the drawings, Figure 1 shows a casing embodying the
present invention generally indicated at 10. The casing is tubular but is shown
flattened in Figure 1 so that two plies 12 and 14 of the casing are laid flat one
against the other. The plies each represent one-half of the casing perimeter so
the flat width of the casing is one-half its circumference. The casing preferably
is of regenerated cellulose but it could be of any other well known food casing
material such as a plastic casing, for example, nylon or a multilayer film. Most
preferably, the casing is a fibrous casing which is a regenerated cellulose casing
having a reinforcing web of a nonwoven paper. Fibrous casings are will known in
The casing is perforated by a plurality of die-cut vent openings 16.
These openings preferably are circular or oval so there are no stress concentration
points as would be produced by sharp corners of square or rectangular openings.
Die cut openings are produced by removing plugs or slugs of the casing material
to provide openings 16. These openings 16 may vary in size from 0.015 to 0.040
inches (0.38 to 1.02 mm) in diameter and extend over the surface of the laid flat
casing in a predetermined defined pattern. As shown in Figure 1, it is possible
for the die cut operation, as described further hereinbelow, to cut openings 16
out to and including the edges 18, 22 of the laid flat casing.
The die cut openings 16 have relatively clean edges in that they
are free of flaps, flanges or the like which extend inward or outward from the
casing surfaces. This is best seen in Figure 2.
As shown in Figure 2, the laid flat plies of casing 12, 14 of Figure
1 are shown separated for purposes of illustration. The die cut vent openings
16a in upper ply 12 and the openings 16b in lower ply 14 each have relatively clean
cut edges 24. Further, the edges of the openings are substantially flush with the
plane of the casing and there is no portion of the casing wall about the openings
which extends outward from the outer surface 26 of the casing wall or inward from
the inner surface 28 of the casing wall.
Moreover, since both the openings 16a, 16b are formed by a single
combination of male and female die cut members, as set out hereinbelow, there is
a registration of the openings including an alignment of the edges 24 and they
have substantially the same open area. It should be appreciated that given the
small size of the die cut openings 16 and the nature of the cellulosic material
of the casing, some fraying of the edges can occur depending upon various manufacturing
parameters and as the punches and dies wear through use.
The apparatus for die cutting the vent openings is shown in Figure
3. The apparatus includes a roller 30 which is mounted for rotation about an axis
32. Roller 30 has a plurality of punches 34 extending from its surface. The roller
and punches comprise the male member of a die cutting set. The second member of
the set also is a roller 36, mounted for rotation about an axis 38 which is parallel
to axis 32. The roller 36 is provided with a plurality of die cut openings (not
shown) arranged for receiving the punches 34. Roller 36 and its die openings comprise
the female member of the die set. As further set out hereinbelow, the arrangement
of the punch and die openings is such that each punch 34 mates with only one given
die cut opening.
The surface 40 of roller 36 is rigid and the two rollers are spaced
apart so the space between them is greater than the thickness of the flattened
The flattened casing which passes between the two rollers 30, 36
is die cut by the operation of punches 34 on roller 30 mating with the die openings
on roller 36. In this respect, an unpunctured laid flat casing 41 is drawn from
a supply reel 42 and between the two rollers 30, 36. The casing is perforated as
it passes between the rollers and the casing, now perforated, is taken up by a
rewind reel 44. Idler rolls 46 are optionally disposed to press and partly wrap
the casing around female roller 36. With this arrangement, the female roller 36
is driven by the casing as the casing is pulled through the space between the rollers.
Preferably, the rewind reel 44 is driven for pulling the casing from
the supply, or unwind, reel 42 and drawing the casing between the set of die cut
rollers 30, 36. The two rollers 30, 36 are not themselves driven by an independent
drive. Also, gears for interconnecting the two rollers 30, 36 and driving them
in synchronism are optional. The driving of both the die cut rollers preferably
is accomplished simply by advancing the casing between the rollers.
For example, if the casing is drawn straight through the gap between
the rollers, the casing first engages punches 34 and this causes the rotation of
the first male roller 30 about its axis 32. As the roller 30 turns, the punches
34 first press plies of casing against the rigid surface of the female roller 36
and then drive through the casing and into its mating die opening 48 as shown in
Figure 4. The mating or meshing of the punches 34 and die openings 48 serve as
the drive for rotating the female roller 36.
In a preferred embodiment, as shown in Figure 3, where the casing
is partly wrapped around the second roller 36, advancing the casing will drive
the second roller. This in turn causes the rotation of the first roller.
In any event, as each punch mates with its associated die cut opening
48 in roller 36, a slug or plug 50 is die cut from both plies of casing. The female
roller 36 has a hollow interior. Accordingly, as shown in Figure 4, the plugs 50
of casing, otherwise known as "chad", work down the die opening 48 and into the
hollow interior 52 of the female die member. From here the chad is removed by any
suitable means, such as a vacuum line (not shown) connected to the hollow interior
of roller 36.
The punches 34 and die openings 48 are arranged so there is a progressive
engagement of punches into their associated die openings and this keeps the rollers
moving in synchronism. This is illustrated in Figure 5.
Figure 5 shows a portion of the surface of the second roller 36 with
the direction of rotation indicated by arrow 56.
As seen in Figure 5, the die openings 48 (and therefore the associated
punches on roller 30) are arranged in columns which are equally spaced across the
width of the second roller. Each column (numbers 1-21) contains the same number
of die openings equally spaced about the periphery of the second roller. Further,
the die openings 48b (and their associated punches) in the second column (2) are
offset from the die opening 48a in the first column. The offset can be either leading
or trailing in the direction of rotation as indicated by arrow 56. If the offset
leads in the direction of rotation, the amount of the offset is slightly more than
one-half the arc length between the equally spaced die openings. If the offset
trails or lags in the direction of rotation the amount of offset is slightly less
than the arc length between the equally spaced die openings. The openings 48c (and
their associated punches) in the third column (3) are offset a like amount from
the die openings 48b in the second column. The offset of the die opening in one
column from those in an adjacent column continues across the roller for each successive
column of die openings. With this arrangement, the offset from one column to the
next is n/2 plus or minus a small increment of arc (say 1 °) where "n" is the number
of degrees between the die openings in a column.
Offsetting one column of die openings from another slightly more
or less than one-half the arc length between die openings, is important to the
synchrononous driving of the rollers. For example, if the offset was simply 1 °
of arc, then the progression of punches into full engagement with their respective
die openings would progress straight across the width of the rollers from column
1 to column 21. However, with the offset being n/2 + 1° or n/2 - 1° the progressive
engagement of punches into the die openings across the width of the rollers is
scattered between the columns and this results in a smoother meshing and synchronous
driving of the rollers. For example, given a distribution of die openings as shown
in Figure 5, an offset of n/2 + 1° and a spacing between die openings of 20°, then
the line 54 represents an instant in the rotation of the rollers where only the
punches corresponding to the openings 48 in columns 1 and 21 would be centered
and fully engaged with these die openings. However, scattered along line 54 are
punches in various stages of advancement into the die openings and others in various
stages of retreat from the die openings relative to the time at line 54. In particular,
and as shown in Figure 5, punches associated with die openings in columns 12, 3,
14, 5, 16, 7, 18, 9, 20, and 11 would be respectively 1°, 2°, 3°, 4°, 5°, 6°, 7°,
8°, 9° and 10° of arc past full engagement and in retreat from the die openings.
On the other hand, punches associated with die openings in columns 10, 19, 8,
17, 6, 15, 4, 13 and 2 would be respectively 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8° and
9° of arc away from full engagement with their associated die openings.
Thus, not all the punches across the roller are fully engaged with
a corresponding die opening at any given instant of rotation. The arrangement
as shown, provides a continuous progression around the rollers so that each degree
of rotation brings at least one punch into full engagement with its associated
die opening and there is a continuous driving of the second roller 36 by the first
roller 30. However, the action of punches entering and leaving their mating die
openings is not in a progression from column to column straight across the width
of the rollers. Instead the progression of punches which are fully inserted into
a die opening alternates back and forth from one column to another across the width
of the roller. For example, in the Figure 5 embodiment, the progression of punches
from time line 54 which are fully inserted into a die opening would be in the following
column order: 10, 19, 8, 17, 6, 15, 4, 13, 2, 11, 20, 9, 18, 7, 16, 5, 14, 3, 12
and then 1 and 21 simultaneously. Accordingly, the location of a punch which is
fully inserted into a die opening moves back and forth between columns which are
not adjacent so the progression is not linear across the rollers. It is this arrangement
which maintains a synchronous rotation of the two rollers 30 and 36. While no gears
are needed for this synchronous rotation, it is important that the rollers be
secured in a suitable frame (not shown) which maintains the axis of rotation of
each member parallel and at a fixed distance apart. Means for such securing are
well within the skill of the art.
To demonstrate the present invention, rollers 30 and 36 were made.
The female roller 36 had a diameter of about 3.25 inches (8.25 cm) and was 12.5
inches (31.75 cm) long. The roller was hollow and its surface 40 was a hardened
steel. The roller was provided with 378 of the die cutting openings 48 arranged
in 21 columns with 18 openings in each column. The columns were about one-half
inch (12.7 mm) apart and the die openings in each column were spaced about 20°
apart. As noted above, the openings in one column were offset about 11° (or n/2
+ 1°) from the openings in an adjacent column. The die openings were each about
0.028 (0.71 mm) inch in diameter and each opening communicated with the hollow
interior of the roller.
Male roller 30 was provided with 378 punches similarly arranged.
The punches projected about 0.120 inches (3.05 mm) from the surface of the roller
and the effective diameter of the roller, including punch length, was about equal
to the diameter of the female roller 36.
The punches were of a softer steel than the surface of roller 36
and had a hardness of about 25-30 Rc. The punches were formed with a diameter slightly
larger than the diameter of the die openings. During the maiden engagement, the
punches were sheared upon entering the die openings and in this way each punch
was sized to fit closely into its associated die opening.
For operation, the rollers were set about 0.115 inches (2.92 mm)
apart so that the depth of punch penetration into the die openings was about 0.005
inches (0.13 mm). It should be appreciated that the number of punches and penetration
depth as noted above, clearly can vary depending upon the selected diameter of
the roller and the desired number and length of the punches.
The frame holding the rollers must be sufficient to maintain an alignment
of the two rollers to insure a proper mating of each pin and its associated die
opening. As noted above, it is this alignment together with the progressive entry
and removal of punches into the die openings which drives the female roller 36
and keeps the two rollers rotating in synchronism.
A Viskase Corporation size 11 fibrous casing (8.25 inches or 20.95
cm flatwidth) was run through the die punch apparatus at a speed of about 200 feet/min
(60.96 m/min). No special care was taken to position the flat stock to insure that
the casing edges were outside of the die cut area. Accordingly, the perforated
casing did exhibit die cut openings at intervals along the casing edge.
The die cut casing contained die cut vent openings arranged in a
hexagonal pattern which mirrored the array shown in Figure 5, the openings in the
machine direction (columns) being about 0.56 inch (14.22 mm) apart and in the transverse
direction (rows) being about one-half inch (12.2 mm) apart. This produced about
3.5 openings per square inch and on inspection it was determined that over 95%
of the die cut openings were free of casing material.
A test was devised to determine the vent rate of the casing. In this
respect one end of the casing is gathered and closed. The casing is oriented vertically
with its closed end down and open end up. Water is poured into the casing. The
rate of the inflow is controlled to just keep the casing filled while avoiding
an overflow from the open top. In this fashion, the rate of inflow balances and
is equal to the vent rate through the casing wall. With the casing formed as noted
above, it was determined that the vent rate of a casing section about 12 inches
(30.48 cm) long was 10.8 gals (40.8 liters) per minute. In contrast, a similar
size fibrous casing made in the conventional manner using 0.060 in. (1.52 mm) diameter
presticking pins arranged in essentially the same pattern had a vent rate of only
6.4 gal/min (24.21 liters). Thus, the inventive casing, with die cut openings of
only 0.028 inches (0.71 mm) in diameter had a greater vent rate than the same size
casing prestuck with needles of more than twice the diameter.
The draining of the water from about the casing parameter was observed.
It was evident that for the inventive casing, the flow rate appeared uniform from
around the casing. However, for the prestuck casing formed using presticking pins,
it was evident that there was a greater flow from one side of the casing than from
the other . Thus, the vent rate of the casing of the present invention was both
greater than that of the casing stuck with a larger diameter pin and more uniform
around the casing. These features are highly desirable.
The higher vent rate allows the rapid venting of air during stuffing.
This permits a faster operation and decreases the likelihood of bursting the casing
as it is drawn up tight about the food product. The smaller openings and uniformity
of venting contributes to the appearance of the food product as further noted below.
The casings were stuffed and processed to produce a chunk-and-form
ham product. The stuffed samples were visually inspected after processing. Product
formed in the casing of the present invention had a uniform distribution of "nubs"
on the product surface. These nubs are formed by meat juices which exude through
the vent openings and coagulate under processing conditions. In contrast, the conventionally
prestuck casing was less uniform in appearance because the nubs at one side of
the stuffed casing were more prominent than those at the opposite side of the casing.
Thus, it should be appreciated that the present invention provides
a perforated casing having improved venting properties. The improved venting,
as provided by the die cut openings, increases the rate of venting over larger
vent openings made by needle presticking and provides for a more uniform venting
about the casing periphery for enhancement of product appearance.