CA1247820A - Shirring wheel for use in a shirring apparatus for producing a tubular casing - Google Patents
Shirring wheel for use in a shirring apparatus for producing a tubular casingInfo
- Publication number
- CA1247820A CA1247820A CA000564956A CA564956A CA1247820A CA 1247820 A CA1247820 A CA 1247820A CA 000564956 A CA000564956 A CA 000564956A CA 564956 A CA564956 A CA 564956A CA 1247820 A CA1247820 A CA 1247820A
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- Prior art keywords
- shirring
- wheel
- casing
- tooth
- teeth
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Abstract
SHIRRING WHEEL FOR USE IN A SHIRRING APPARATUS
FOR PRODUCING A TUBULAR CASING
ABSTRACT
A shirring wheel for use in an apparatus for shirring a tubular casing, and wherein the wheel has teeth with each tooth having a face surface in which a curvature of the face surface of each tooth is derived from the diameter of the wheel and the diameter of a desired shirred casing or slug. The crest surface is part of a groove of substantially semi-circular cross-section in a radial plane and is uniform at all points around the shirring wheel, and the radius of the radial cross-section of the groove is that of the desired finished shirred casing or slug outside diameter less a factor which takes into account the flexing of the teeth during shirring.
FOR PRODUCING A TUBULAR CASING
ABSTRACT
A shirring wheel for use in an apparatus for shirring a tubular casing, and wherein the wheel has teeth with each tooth having a face surface in which a curvature of the face surface of each tooth is derived from the diameter of the wheel and the diameter of a desired shirred casing or slug. The crest surface is part of a groove of substantially semi-circular cross-section in a radial plane and is uniform at all points around the shirring wheel, and the radius of the radial cross-section of the groove is that of the desired finished shirred casing or slug outside diameter less a factor which takes into account the flexing of the teeth during shirring.
Description
This invention relates to a shirring wheel for use in a shirring apparatus for shirring a tubular casing, such as a collagen or regenera-ted cellulosic casing of the kind employed in the manufacture of sausages.
It is known to pass a casing, inflated by air pressure, over a mandrel and between shirring belts or toothed wheels (also known as paddles) having teeth designed to produce a particular fold formation during shirring.
It has been proposed in the past that the tee-th should be so designed as to produce a helical primary fold in the casing. It might be assumed -that to do this the teeth of a pair of rolls or of three rolls used in conjunc-tion should be so aligned as to form a helix when the teeth contacting the casing are diametrically opposite each other and adjacent to each, called for convenience the "bottom dead center position". We have found that this assumption is incorrect.
An object of the invention is to provide a confi-guration of shirring wheels which will enable a shirred stick to be produced substantially without discontinuities in the primary fold which occur in use of prior art machines.
In accordance with a broad aspect of the present invention there is provided a shirring wheel for use in an apparatus for shirring a tubular casing, and wherein the wheel has teeth with each tooth having a face surface in which a curvature of the face surface of each tooth is derived from the diameter of the wheel and -the diameter of a desired shirred casing or slug. The crest surface is part of a groove of substantially semi-circular cross-section in a radial plane and is uniform at all points around the shirring wheel, and the radius of the radial cross-section of the groove is that of the desired finished shirred casing or slug outside diameter less a factor which takes into account the flexing of the teeth during shirring.
~Z91~7~32(~
- la -In accordance with the present invention the teeth on at leas-t a pair of shirring wheels are so desiyned that at the point of contact of the leading edge of a tooth of a shirring wheel with the maximum diameter of the casing, i.e., at the point where the casing has already been pushed into a fold and the fold is about to be ironed, the leading edges of teeth on adjacent wheels are in substantially helical alignment. The heli.cal alignment should be precise, but if three wheels are used, it may be sufficient that the tooth form is a straight line.
t2~ 32
It is known to pass a casing, inflated by air pressure, over a mandrel and between shirring belts or toothed wheels (also known as paddles) having teeth designed to produce a particular fold formation during shirring.
It has been proposed in the past that the tee-th should be so designed as to produce a helical primary fold in the casing. It might be assumed -that to do this the teeth of a pair of rolls or of three rolls used in conjunc-tion should be so aligned as to form a helix when the teeth contacting the casing are diametrically opposite each other and adjacent to each, called for convenience the "bottom dead center position". We have found that this assumption is incorrect.
An object of the invention is to provide a confi-guration of shirring wheels which will enable a shirred stick to be produced substantially without discontinuities in the primary fold which occur in use of prior art machines.
In accordance with a broad aspect of the present invention there is provided a shirring wheel for use in an apparatus for shirring a tubular casing, and wherein the wheel has teeth with each tooth having a face surface in which a curvature of the face surface of each tooth is derived from the diameter of the wheel and -the diameter of a desired shirred casing or slug. The crest surface is part of a groove of substantially semi-circular cross-section in a radial plane and is uniform at all points around the shirring wheel, and the radius of the radial cross-section of the groove is that of the desired finished shirred casing or slug outside diameter less a factor which takes into account the flexing of the teeth during shirring.
~Z91~7~32(~
- la -In accordance with the present invention the teeth on at leas-t a pair of shirring wheels are so desiyned that at the point of contact of the leading edge of a tooth of a shirring wheel with the maximum diameter of the casing, i.e., at the point where the casing has already been pushed into a fold and the fold is about to be ironed, the leading edges of teeth on adjacent wheels are in substantially helical alignment. The heli.cal alignment should be precise, but if three wheels are used, it may be sufficient that the tooth form is a straight line.
t2~ 32
2 --This point will occur when the leading edges of the adjacent teeth of the paddles or wheels are at an angle of a few degrees past the bottom dead centre position. The precise angle "A" depends upon the requi.red radius of the external surfaee of the shirred slug and on the minimum radius of the shirrlng wheel teeth and is determined by the formula:
A = Cos~1 R - r ;
where A ls the angle in degrees of the leading edges of the adjacent teeth past the bottom dead centre position;
R is the minimum radius of the tooth from th~
shirring wheel axis; and r is the expected or predetermined slug radius.
Each tooth is preferably formed with a groove of substantially semi-circular section, in a radial plane, in its outer face and "R" is then the radius through the shirring wheel axis of the base of the groove in the tooth.
The form of the teeth is a very important aspect of the present invention, the teeth are spaced round the wheel at a clrcumferential distance apart so that the mark/space ratio lies in the range 3:4 to 4:3. The preferred mark/space ratio is 1:1.
The mark/space ratio is defined a~ the nominal ratio between the tooth thickness and the gap between teeth measured in the same direction, i.e. a mar~/space ratio of 1:1 means that half the c~rcumference of the paddle roll is tooth and half the gap between the teeth. The features which dictate the`selection of the mark/space ratio are that a bubble must be allowed to form in the space1 which leads to shirr formation~ ~nd so there must be sufficient space between the leading edge of one tooth and the trailing edge of the next one to allow a buckle or bubble to form. On the other hand if a very thin tooth is adopted it becomes more ~2~7~2(~
di~ficult to prevent the casing from rs-in~lating.
The active par-t of the too-th, that is the surface of the tooth which comes into contact with the casing or shirred material, is enclosed by concavo-convex surfaces,called ~or convenience the face of the tOothr and the flanks of the tooth. ~he intersections of the face, or crest, of the tooth and the flanks are termed, for convenience the edges. For a given direction of rotation one edge will lead the other and for conv~nience they are differentiated as the leading and trailing edges.
In accordance with the inventlon the curvatures of the crest or face surface are derived from the dia~eter of the paddle and the desired slug diameter as ~ollows:
The crest surface is part of a groove of substantially semi-circular cross section in a radial plane and is uniform at all points around the shirring wheel. The radius of the radical cross section o~ t~le groove is that of the desired finished slug outside diameter less a factor which takes account o~ the fle~ing of the tee~h during shirring.
This factor will depend upon the stiffness of the paddle material and the thickness o~ the tooth forms employed but will result in a radius notica~ly smaller than the casin~ The amount by which the radius of the cross section o~ the tooth is reduced may be be~ween 15 and 30% and in a typical case would be between 20 and 30%.
The leading edge of each tooth is defined by a series of points on the groove which cross the outside diameter o~ the slug coincidentally with the desired fold line on the casing, normally a helical fold.
The trailing edge of each tooth is defined by a series of points approximately parallel to the leading ~L247~21t) edge such that on any circular section perpendicular to the axls the ratio of the circumferential length between successive points where the leading and trailing edges cut that section and the circumferential length S between either point and the next such point is constant.
Each flank surface of each tooth is formed so that it meets the crest or ~ace of the tooth at a nominally constant angle, called for convenience the rake angle.
Thus a flank surface at a nominally constant angle is present~d to the casing at all points around its peripheryO
The shirring wheels or paddles perform three different functions. Firstly they move the casing along towards the shirring area and this is known as driving the casing. Secon~y they displace the casing to initiate a fold in ~e casing whlch is known as layering. Thirdly they press down the inltially formed fold into its final shape forming the sharply defined crease or fold line w~ich ls known as the primary fold. This process is known as ironing.
Driving the casing is difficult particularly when only two wheels or paddles are used. In order to improve the drive it is preferable, in accordance with the invention, to introduce a controlled degree of flexibility in the wheels or paddles in the cylindrical direction of the paddle wheel whilst retaining the torsional stiffness of the wheel.
Thus, in accordance with ano-ther aspect of the invention the wheels or paddles are provided with flexible teeth~ Preferably this flexibility is brought about by means of a series of selected cut-outs in the outer walls of the wheel and by selection of a suitable rubber or rubber like material for the wheel. The cut-outs in the wheel are designed to produce uniform . ... .
1~78~C~
flexlbility throughout the circumference o~ the wheel.
The flexibility is preferably related to the flexibility of the material of the casing so as to produce sufficient interference between the wheel and the casing to drive a casinB~
Having achieved the necessary drive we found that the interference between the wheel and casing is far too great during the formation of each primary shirr fold. By mi~king the wheel flex~ble we overcome this problem in that sufficient interference is pro~ided ~or drive without an excess of interference during the formation of the primary ~olds.
Although the cleirance between ~heels particularly with two wheels in accordance with the preferred embodiment of this invention, is preferably nominal, i.e.
the wheels are almost touching, it is also possible and a feature of this invention that the ~heel might be locked in phase by inter-engaging teeth on the two wheels.
In prior art constructions the teeth are in the form discrete teeth attached to th~ whee~r f~rmed o~
the wheel without connecting circum~erential walls.
To control the strength and flexibility of the wheel we have found it desirable to join the helical teeth by circumfe~ential walls so that in effect the teeth are cut out from a solid wall. Formation of these walls also helps to control tlle flexibility.
When a casing is shirred the resultant compact shirred casing, known as a stick, may contain a considerable length e.8. ~4;m~*Pé~ of casing in a relativelyishort length of "stick", e.g~ 23 cms~ The,ratio ~L~4~8~
between the original length o~ the casing and the length of the shirred stick is defined as the compression ratio, the length of the shirred stick being measured between the peaks on the ~irst and last of the primary ~olds.
A more accurate way of indicating the amount of casing which is included in a given shirred stick, taking account of the thickness of the ~aterial of which the casing is made, is to define in terms of "packing efficiency". The packing efficiency is the ratio of the volume of a casing when laid flat ~be~ore shirring~ divided by the ef~ective volume of the annular SlUg or stick, expressed as a percentage. It is calculated by the following formula:
Length of unshirred casing x 2 x wall thickness x wldth of laid flat casin~ x lO0 Stick or slug length x PI x (outside diameter of stick2 - - bore of stick2) ~Width o~ laid flat casing is known as '!lay-~lat").
The thickness of the ma~erial is preferably measured by use of an Elcometer thickness monitor~
By use of the present invention it i~ possible to produce sticks having increased compression ratios .
compared with those produced by other machines. In accordance with the present invention a shirred stick has a compression ratio in the range 95 to 140. This is achieved without reduction of the bore or detriment to the run~out properties of the shirred stick. Run-out is the de-shirring of the stick during filling in a sausage making process.
Also in accordance with the invention it is possible to produce a shirred stick having an increased packing efficiency, the packing efficiency being in the range 45 to 90%.
`` ~2~78;~
The advantage of the increase in compression ratio and packing efficiency is tha-t more rigid shirred sticks, despite increased internal bore diameters, can be produced.
In the accompanying drawings:-Figure l is a side elevation showing portions of a shirring machine embodying the present invention;
Figure 2 is a plan of ths central part only of the machine illustrated in Figure l;
Figure~3 is an enlarged diagrammatic plan of a po~rtion of the machine illustrating the tapered mandrel used in the present invention;
Figure 4 is an enlarged portion of the tapere~
mandrel shown in Figure 3;
Figure 5 is a circumferential development of a portion of one of the shirring wheels shown in Figures l to 3;
Figure 6 is a side elsvation of a portion of one of the shirring wheels;
Figure 7 is a part sectional plan on the line 7--7 shown in Figure 6;
Figure 8 is a section on the line 8--8 shown in Figure 5;
Figure 9 is an enlarged diagrammatic illustration of the central portion of Figure 3 showing the tapered mandrel and its relationship to the teeth o~ the s~rring wheels;
Figure lO shows diagrammatically the ~ormation of a primary fold; and Figure ll is a further stage in the formation of the fold shown in Figure lO.
The shirring machine shown in Fig~res 1 and 2 is diagrammatically represented and inc1udes only those parts of -the machine which are essential to an under ... ... . _ _ . .", . . _ ,.. _ .. _,, ., . . _ __.. _. _ _.~ .. ~ _ _ .~.. __ ____ . , , . . _ . . . .. .. , . _ 1~7~
standing of the invention.
As seen in Figure 1, on the left of the machine is a drier 10 from which prepared collagen or cellulose casing is led through guide rollers 14, which grip the casing fairly tightly so -that air which is put in the casing from the far end will no-t pass beyond rollers 14.
The inflated casing is shown at 15 and is seen to pass through pairs of rolls 16 and 17 and through a guidance block 18 to a pair of drive rolls 19,~0. The casing then enters the nip between the pair of shirring wheels 21~22. The casing as lt passes through the drive rolls 19,20 and shirring wheels 21,22 passes over a mandrel . 23. The mandrel has an inkernal passage 24 throu~ which air is supplied under pressure Yrom a source not shown via a pipe 25 and mandrel end fitting 26. The air ~lowing through pipe 25 and bore 24 enters the casing and keeps it expanded as shown in Figure 1. The shirring wheels 21 and 22 shirr the casing and the shirring takes place along a tapered portion 27 of the ~andrel 23~ whieh will be described in more detail later.
The shirred casing is compressed because the casing passes through compression rolls 28,2g which are rotated at about 100th of the speed of the drive rolls 19,20, and in the same direction of rotation as the drive rolls 19 and 20. The shirring rolls rotate in the same direction as the drive rolls but at about twice the .
speed of the drive rolls. The range of speeds within which they ma~ rotate according to the physical characteristics of the casing is from about 1.5 to 2.5 times the speed of the drive rolls. It will be seen that the outside edges of the wheels are almost touching, the spacing between them being o~ the order of 1 to 2 mm.
The compression o~ the casing takes place entirely during the formation of the shirr and as the shirred 3S stick or slug compresses between the shirring ~heels 32~
_ g and the compression rolls.
The shirred stick emerges from the compression rolls and when a suitable length has been formed can be cut off, slid along the mandrel 23 and off the end of the mandrel after removal of the end fitting 26, the air being cut-off temporarily while this occurs.
The shirring wheels 21,22 ars driven by a shirring wheel motor;29A which, through a gear-box 30 drives shirring wheel 21. Shirring wheel 22 is driven at the same speed by means of a belt drive 31 and pulleys 32,33. The drive rolls 19 and 20 are also driven through a system of p~lley wheels and belts 34,35. The com-pression rolls 28,29 are driven by a separate electric motor 36 via belts 37 and 37A.
The shirring wheels 21 and 22, which form an important aspect of this invention, are molded or otherwise formed from elastomer such as synthetic rubber or natural rubber, or polyurethane. The two wheels are identical and have at their outer periphery teeth 38 (see Figures 5 to 8) separated by spaces 39, the ratio of the tooth thickness (B in Figure 5) to the space or gap between the teeth measured in the same direction (shown as A) is the mark/space ratio which as shown is about 1:1. Each tooth 38 has a face or crest surface 40~ As seen in Figures S and 8 the face or crest of the tooth 39 has a semi-circular cross section in a radial plane and is uniform at all points around the shirring wheel. This point is seen clearly in Figure 6 wherein the two outer teeth have the semi-circular cross section referred to above, and it is also seen in Figure 8. Each tooth has two flank surfaces 41 and 42. Where the flank 42 ~oins the face or crest 40 is the leading edge 43 of the tooth 40, assuming rotation to be in the direction shown by the arrows in Figures 5, 6 and 7 of the drawings.
~78~) Similarly where the flank 41 meets the crest 40 is the trailing edge 44.
The flank 41 meets the crest 40 at a nomin~lly constant angle and similarly the ~lank 42 meets the crest 40 at a nominally constant angle. The edges 43 and 44 are of substantially helical formation as can be seen in Figures 5 and 6 the teeth 39 lare ~oined by walls 45 portions of which are cut away at 46 to improve flexibilityO
An impo~tant aspect of this invention is that the compression of the shirred stick takes place between the shirring wheels 21,22 and the compression rolls 28, 29, the compression, and the folding of the shirred stick, being controlled by the taper 27 on khe mandrel 23 (see particularly Figures 3 and 4). The mandrel is tapered so that there is a lmm change in dlameter for every 5mm length of the mandrel. This tapered mandrel is described and illustrated in more detail in our copending pa-tent application No. (Case hj.
The formation of a helical primary fold in the casing, which is part of the shirring process, is illustrated in Figures 10 and 11. The initial fold form is shown at 47 and this fold will be ironed or compressed into a helical primary fold by a subsequent tooth of the wheel. The leading edge of the tooth shown at 43 will create this ironing contact as shown in Figure 11. We have found that it is most important that when thls first ironing contact between the teeth of the wheels and the partially formed fold occurs the leading edges of the tooth should form a tr.ue helix and the leading edges of adjacent teeth should be aligned. This is illustrated in Figure 9 where the leading edge 43 of a tooth of one of the shirring wheels 22 is aligned (shown as joined by a nominal straight line 48) with the leading edge 42 7l~Z~
on the ad~acent tooth on the other shirring wheel 21.
It will be seen that this occurs not when the teeth are in the bottom dead centre position but at a point some degrees after the bottom dead cent:re, the line 49 indicating the bottom dead centre position. The amount by which the teeth have passed the bottom dead centre position is determined as previously described by the formula given.
Figure 9 also illustrates the position of the tapsr 27 of the mandrel and it is seen that the taper 27 commences just before the bottom dead centre position at 50. A fairly typical case is when the point of alignment is 8 to 10 past bottom dead centre.
The improved shirred stick which results from use of the improved apparatus and method described above is characterised by a minimum of random folds and i.ncreased packing efficiency compared with prior art shirred sticks.
-An advantage of the tapered mandrel used in con~unction with the shirring wheels of this invention is that slippage of the primary folds wm ch en~bles high packing efficiency to be achieved can be closely controlled and the axial symmetr~ arou~d the - circumference of the stick or slug is maintained and this results in straight slugs. The tapered mandrel also enables minor changes in the material thickness etc. to be catered ~or without altering the machine.
A = Cos~1 R - r ;
where A ls the angle in degrees of the leading edges of the adjacent teeth past the bottom dead centre position;
R is the minimum radius of the tooth from th~
shirring wheel axis; and r is the expected or predetermined slug radius.
Each tooth is preferably formed with a groove of substantially semi-circular section, in a radial plane, in its outer face and "R" is then the radius through the shirring wheel axis of the base of the groove in the tooth.
The form of the teeth is a very important aspect of the present invention, the teeth are spaced round the wheel at a clrcumferential distance apart so that the mark/space ratio lies in the range 3:4 to 4:3. The preferred mark/space ratio is 1:1.
The mark/space ratio is defined a~ the nominal ratio between the tooth thickness and the gap between teeth measured in the same direction, i.e. a mar~/space ratio of 1:1 means that half the c~rcumference of the paddle roll is tooth and half the gap between the teeth. The features which dictate the`selection of the mark/space ratio are that a bubble must be allowed to form in the space1 which leads to shirr formation~ ~nd so there must be sufficient space between the leading edge of one tooth and the trailing edge of the next one to allow a buckle or bubble to form. On the other hand if a very thin tooth is adopted it becomes more ~2~7~2(~
di~ficult to prevent the casing from rs-in~lating.
The active par-t of the too-th, that is the surface of the tooth which comes into contact with the casing or shirred material, is enclosed by concavo-convex surfaces,called ~or convenience the face of the tOothr and the flanks of the tooth. ~he intersections of the face, or crest, of the tooth and the flanks are termed, for convenience the edges. For a given direction of rotation one edge will lead the other and for conv~nience they are differentiated as the leading and trailing edges.
In accordance with the inventlon the curvatures of the crest or face surface are derived from the dia~eter of the paddle and the desired slug diameter as ~ollows:
The crest surface is part of a groove of substantially semi-circular cross section in a radial plane and is uniform at all points around the shirring wheel. The radius of the radical cross section o~ t~le groove is that of the desired finished slug outside diameter less a factor which takes account o~ the fle~ing of the tee~h during shirring.
This factor will depend upon the stiffness of the paddle material and the thickness o~ the tooth forms employed but will result in a radius notica~ly smaller than the casin~ The amount by which the radius of the cross section o~ the tooth is reduced may be be~ween 15 and 30% and in a typical case would be between 20 and 30%.
The leading edge of each tooth is defined by a series of points on the groove which cross the outside diameter o~ the slug coincidentally with the desired fold line on the casing, normally a helical fold.
The trailing edge of each tooth is defined by a series of points approximately parallel to the leading ~L247~21t) edge such that on any circular section perpendicular to the axls the ratio of the circumferential length between successive points where the leading and trailing edges cut that section and the circumferential length S between either point and the next such point is constant.
Each flank surface of each tooth is formed so that it meets the crest or ~ace of the tooth at a nominally constant angle, called for convenience the rake angle.
Thus a flank surface at a nominally constant angle is present~d to the casing at all points around its peripheryO
The shirring wheels or paddles perform three different functions. Firstly they move the casing along towards the shirring area and this is known as driving the casing. Secon~y they displace the casing to initiate a fold in ~e casing whlch is known as layering. Thirdly they press down the inltially formed fold into its final shape forming the sharply defined crease or fold line w~ich ls known as the primary fold. This process is known as ironing.
Driving the casing is difficult particularly when only two wheels or paddles are used. In order to improve the drive it is preferable, in accordance with the invention, to introduce a controlled degree of flexibility in the wheels or paddles in the cylindrical direction of the paddle wheel whilst retaining the torsional stiffness of the wheel.
Thus, in accordance with ano-ther aspect of the invention the wheels or paddles are provided with flexible teeth~ Preferably this flexibility is brought about by means of a series of selected cut-outs in the outer walls of the wheel and by selection of a suitable rubber or rubber like material for the wheel. The cut-outs in the wheel are designed to produce uniform . ... .
1~78~C~
flexlbility throughout the circumference o~ the wheel.
The flexibility is preferably related to the flexibility of the material of the casing so as to produce sufficient interference between the wheel and the casing to drive a casinB~
Having achieved the necessary drive we found that the interference between the wheel and casing is far too great during the formation of each primary shirr fold. By mi~king the wheel flex~ble we overcome this problem in that sufficient interference is pro~ided ~or drive without an excess of interference during the formation of the primary ~olds.
Although the cleirance between ~heels particularly with two wheels in accordance with the preferred embodiment of this invention, is preferably nominal, i.e.
the wheels are almost touching, it is also possible and a feature of this invention that the ~heel might be locked in phase by inter-engaging teeth on the two wheels.
In prior art constructions the teeth are in the form discrete teeth attached to th~ whee~r f~rmed o~
the wheel without connecting circum~erential walls.
To control the strength and flexibility of the wheel we have found it desirable to join the helical teeth by circumfe~ential walls so that in effect the teeth are cut out from a solid wall. Formation of these walls also helps to control tlle flexibility.
When a casing is shirred the resultant compact shirred casing, known as a stick, may contain a considerable length e.8. ~4;m~*Pé~ of casing in a relativelyishort length of "stick", e.g~ 23 cms~ The,ratio ~L~4~8~
between the original length o~ the casing and the length of the shirred stick is defined as the compression ratio, the length of the shirred stick being measured between the peaks on the ~irst and last of the primary ~olds.
A more accurate way of indicating the amount of casing which is included in a given shirred stick, taking account of the thickness of the ~aterial of which the casing is made, is to define in terms of "packing efficiency". The packing efficiency is the ratio of the volume of a casing when laid flat ~be~ore shirring~ divided by the ef~ective volume of the annular SlUg or stick, expressed as a percentage. It is calculated by the following formula:
Length of unshirred casing x 2 x wall thickness x wldth of laid flat casin~ x lO0 Stick or slug length x PI x (outside diameter of stick2 - - bore of stick2) ~Width o~ laid flat casing is known as '!lay-~lat").
The thickness of the ma~erial is preferably measured by use of an Elcometer thickness monitor~
By use of the present invention it i~ possible to produce sticks having increased compression ratios .
compared with those produced by other machines. In accordance with the present invention a shirred stick has a compression ratio in the range 95 to 140. This is achieved without reduction of the bore or detriment to the run~out properties of the shirred stick. Run-out is the de-shirring of the stick during filling in a sausage making process.
Also in accordance with the invention it is possible to produce a shirred stick having an increased packing efficiency, the packing efficiency being in the range 45 to 90%.
`` ~2~78;~
The advantage of the increase in compression ratio and packing efficiency is tha-t more rigid shirred sticks, despite increased internal bore diameters, can be produced.
In the accompanying drawings:-Figure l is a side elevation showing portions of a shirring machine embodying the present invention;
Figure 2 is a plan of ths central part only of the machine illustrated in Figure l;
Figure~3 is an enlarged diagrammatic plan of a po~rtion of the machine illustrating the tapered mandrel used in the present invention;
Figure 4 is an enlarged portion of the tapere~
mandrel shown in Figure 3;
Figure 5 is a circumferential development of a portion of one of the shirring wheels shown in Figures l to 3;
Figure 6 is a side elsvation of a portion of one of the shirring wheels;
Figure 7 is a part sectional plan on the line 7--7 shown in Figure 6;
Figure 8 is a section on the line 8--8 shown in Figure 5;
Figure 9 is an enlarged diagrammatic illustration of the central portion of Figure 3 showing the tapered mandrel and its relationship to the teeth o~ the s~rring wheels;
Figure lO shows diagrammatically the ~ormation of a primary fold; and Figure ll is a further stage in the formation of the fold shown in Figure lO.
The shirring machine shown in Fig~res 1 and 2 is diagrammatically represented and inc1udes only those parts of -the machine which are essential to an under ... ... . _ _ . .", . . _ ,.. _ .. _,, ., . . _ __.. _. _ _.~ .. ~ _ _ .~.. __ ____ . , , . . _ . . . .. .. , . _ 1~7~
standing of the invention.
As seen in Figure 1, on the left of the machine is a drier 10 from which prepared collagen or cellulose casing is led through guide rollers 14, which grip the casing fairly tightly so -that air which is put in the casing from the far end will no-t pass beyond rollers 14.
The inflated casing is shown at 15 and is seen to pass through pairs of rolls 16 and 17 and through a guidance block 18 to a pair of drive rolls 19,~0. The casing then enters the nip between the pair of shirring wheels 21~22. The casing as lt passes through the drive rolls 19,20 and shirring wheels 21,22 passes over a mandrel . 23. The mandrel has an inkernal passage 24 throu~ which air is supplied under pressure Yrom a source not shown via a pipe 25 and mandrel end fitting 26. The air ~lowing through pipe 25 and bore 24 enters the casing and keeps it expanded as shown in Figure 1. The shirring wheels 21 and 22 shirr the casing and the shirring takes place along a tapered portion 27 of the ~andrel 23~ whieh will be described in more detail later.
The shirred casing is compressed because the casing passes through compression rolls 28,2g which are rotated at about 100th of the speed of the drive rolls 19,20, and in the same direction of rotation as the drive rolls 19 and 20. The shirring rolls rotate in the same direction as the drive rolls but at about twice the .
speed of the drive rolls. The range of speeds within which they ma~ rotate according to the physical characteristics of the casing is from about 1.5 to 2.5 times the speed of the drive rolls. It will be seen that the outside edges of the wheels are almost touching, the spacing between them being o~ the order of 1 to 2 mm.
The compression o~ the casing takes place entirely during the formation of the shirr and as the shirred 3S stick or slug compresses between the shirring ~heels 32~
_ g and the compression rolls.
The shirred stick emerges from the compression rolls and when a suitable length has been formed can be cut off, slid along the mandrel 23 and off the end of the mandrel after removal of the end fitting 26, the air being cut-off temporarily while this occurs.
The shirring wheels 21,22 ars driven by a shirring wheel motor;29A which, through a gear-box 30 drives shirring wheel 21. Shirring wheel 22 is driven at the same speed by means of a belt drive 31 and pulleys 32,33. The drive rolls 19 and 20 are also driven through a system of p~lley wheels and belts 34,35. The com-pression rolls 28,29 are driven by a separate electric motor 36 via belts 37 and 37A.
The shirring wheels 21 and 22, which form an important aspect of this invention, are molded or otherwise formed from elastomer such as synthetic rubber or natural rubber, or polyurethane. The two wheels are identical and have at their outer periphery teeth 38 (see Figures 5 to 8) separated by spaces 39, the ratio of the tooth thickness (B in Figure 5) to the space or gap between the teeth measured in the same direction (shown as A) is the mark/space ratio which as shown is about 1:1. Each tooth 38 has a face or crest surface 40~ As seen in Figures S and 8 the face or crest of the tooth 39 has a semi-circular cross section in a radial plane and is uniform at all points around the shirring wheel. This point is seen clearly in Figure 6 wherein the two outer teeth have the semi-circular cross section referred to above, and it is also seen in Figure 8. Each tooth has two flank surfaces 41 and 42. Where the flank 42 ~oins the face or crest 40 is the leading edge 43 of the tooth 40, assuming rotation to be in the direction shown by the arrows in Figures 5, 6 and 7 of the drawings.
~78~) Similarly where the flank 41 meets the crest 40 is the trailing edge 44.
The flank 41 meets the crest 40 at a nomin~lly constant angle and similarly the ~lank 42 meets the crest 40 at a nominally constant angle. The edges 43 and 44 are of substantially helical formation as can be seen in Figures 5 and 6 the teeth 39 lare ~oined by walls 45 portions of which are cut away at 46 to improve flexibilityO
An impo~tant aspect of this invention is that the compression of the shirred stick takes place between the shirring wheels 21,22 and the compression rolls 28, 29, the compression, and the folding of the shirred stick, being controlled by the taper 27 on khe mandrel 23 (see particularly Figures 3 and 4). The mandrel is tapered so that there is a lmm change in dlameter for every 5mm length of the mandrel. This tapered mandrel is described and illustrated in more detail in our copending pa-tent application No. (Case hj.
The formation of a helical primary fold in the casing, which is part of the shirring process, is illustrated in Figures 10 and 11. The initial fold form is shown at 47 and this fold will be ironed or compressed into a helical primary fold by a subsequent tooth of the wheel. The leading edge of the tooth shown at 43 will create this ironing contact as shown in Figure 11. We have found that it is most important that when thls first ironing contact between the teeth of the wheels and the partially formed fold occurs the leading edges of the tooth should form a tr.ue helix and the leading edges of adjacent teeth should be aligned. This is illustrated in Figure 9 where the leading edge 43 of a tooth of one of the shirring wheels 22 is aligned (shown as joined by a nominal straight line 48) with the leading edge 42 7l~Z~
on the ad~acent tooth on the other shirring wheel 21.
It will be seen that this occurs not when the teeth are in the bottom dead centre position but at a point some degrees after the bottom dead cent:re, the line 49 indicating the bottom dead centre position. The amount by which the teeth have passed the bottom dead centre position is determined as previously described by the formula given.
Figure 9 also illustrates the position of the tapsr 27 of the mandrel and it is seen that the taper 27 commences just before the bottom dead centre position at 50. A fairly typical case is when the point of alignment is 8 to 10 past bottom dead centre.
The improved shirred stick which results from use of the improved apparatus and method described above is characterised by a minimum of random folds and i.ncreased packing efficiency compared with prior art shirred sticks.
-An advantage of the tapered mandrel used in con~unction with the shirring wheels of this invention is that slippage of the primary folds wm ch en~bles high packing efficiency to be achieved can be closely controlled and the axial symmetr~ arou~d the - circumference of the stick or slug is maintained and this results in straight slugs. The tapered mandrel also enables minor changes in the material thickness etc. to be catered ~or without altering the machine.
Claims (12)
1. A shirring wheel which has teeth, each tooth having a face surface, in which the curvature of the face surface of each tooth is derived from the diameter of the wheel and the diameter of a desired shirred casing or slug as follows:
(a) the crest surface is part of a groove of substantially semi-circular cross-section in a radial plane and is uniform at all points around the shirring wheel; and (b) the radius of the radial cross-section of the groove is that of the desired finished shirred casing or slug outside diameter less a factor which takes into account the flexing of the teeth during shirring.
(a) the crest surface is part of a groove of substantially semi-circular cross-section in a radial plane and is uniform at all points around the shirring wheel; and (b) the radius of the radial cross-section of the groove is that of the desired finished shirred casing or slug outside diameter less a factor which takes into account the flexing of the teeth during shirring.
2. A shirring wheel according to claim 1 in which said factor takes into account the stiffness of the paddle material and the thickness of the tooth forms employed and is such as to result in a radius noticeably smaller than the casing.
3. A shirring wheel according to claim 1 and in which the amount by which the radius of the cross-section of the tooth is reduced is between 15 and 30%.
4. A shirring wheel according to claim 3 and in which the radius is reduced by between 20 and 30%.
5. A shirring wheel according to claim 1 in which the leading edge of each tooth is defined by a series of points on a line which crosses the outside diameter of the slug coincidentally with a desired helical fold line on the casing.
6. A shirring wheel according to claim 5 and in which the trailing edge of each tooth is defined by a series of points approximately parallel to the leading edge such that on any circular section perpendicular to the axis the ratio of the circumferential length between successive points where the leading and trailing edges cut that section and the circumferential length between either point and the next such point is constant.
7. A shirring wheel according to claim 1 in which each flank surface of each tooth is formed so that it meets the crest or face of the tooth at a nominally constant angle known as the rake angle.
8. A shirring wheel according to claim 1 in which the teeth are flexible teeth.
9. A shirring wheel having outer walls according to claim 8 in which the flexibility is brought about by means of a series of selected cut-outs in the outer walls of the wheel and by selection of a suitable rubber or rubber-like material for the wheel.
10. A shirring wheel or paddle according to claim 9 and in which the cut-outs in the wheel are designed to produce uniform flexibility throughout the circumference of the wheel.
11. A shirring wheel or paddle according to claim 6, 7 or 8 in which said flexibility is related to the flexibility of the material of the casing so as to produce sufficient interference between the wheel and the casing to drive a casing.
12. A shirring wheel or paddle according to claim 6, 7 or 8 in which, to control the strength and flexibility of the wheel, the teeth are helical and are joined by circum-ferential walls so that in effect the teeth are cut out from a solid wall.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000564956A CA1247820A (en) | 1984-03-30 | 1988-04-22 | Shirring wheel for use in a shirring apparatus for producing a tubular casing |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8408330 | 1984-03-30 | ||
| GB848408330A GB8408330D0 (en) | 1984-03-30 | 1984-03-30 | Shirring tubular casing |
| CA000477856A CA1246824A (en) | 1984-03-30 | 1985-03-28 | Apparatus for shirring a tubular casing |
| CA000564956A CA1247820A (en) | 1984-03-30 | 1988-04-22 | Shirring wheel for use in a shirring apparatus for producing a tubular casing |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000477856A Division CA1246824A (en) | 1984-03-30 | 1985-03-28 | Apparatus for shirring a tubular casing |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1247820A true CA1247820A (en) | 1989-01-03 |
Family
ID=25670627
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000564956A Expired CA1247820A (en) | 1984-03-30 | 1988-04-22 | Shirring wheel for use in a shirring apparatus for producing a tubular casing |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1247820A (en) |
-
1988
- 1988-04-22 CA CA000564956A patent/CA1247820A/en not_active Expired
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| Date | Code | Title | Description |
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| MKEX | Expiry |