GB2175620A - Production of absorbent bodies - Google Patents

Abstract

The invention relates to a method and an apparatus for forming absorbent bodies, in which fibre material, suspended in an air stream, is introduced into the interior of a rotatable drum (2) and bodies (22-24) are formed in forming apertures (34) located in the cylindrical casing wall (33) of the drum and are transferred to an air-pervious web (20) which abuts the drum casing and partially embraces the same. The invention is characterized in that the drum includes two end-walls which adjoin the drum casing and of which at least one (45) is stationary and is provided with fibre-suspension supply conduit (48) directed towards the drum interior. The fibre suspension is directed towards a restricted area (D) on the inner surface of the drum casing. Arranged beneath this restricted area and beneath the web (20) is a vacuum box (53) effective to draw fibres to the forming aperture or apertures (34) located within the restricted area (D) at that moment in time. <IMAGE>

Description

SPECIFICATION A method of producing absorbent bodies and forming apparatus for carrying out the method The invention relates to a method for producing absorbent bodies intended, for example, for underwear protectors, sanitary towels, diapers and like articles which comprise an absorbent body enclosed in a non-woven and/or plastic foil casing.

Background prior art Profiled absorbent bodies made of fluff and substantially of rectangular shape or of hour-glass shape or some like shape are known to the art.

Such absorbent bodies are produced with the aid of apparatus which mill out or otherwise shape profiles from a web or string of fluff material while the web is transported along a path which lies in contact, for example, with a rotating drum having provided around the casing thereof a plurality of forming apertures which correspond to the profile desired and to which the fluff material is passed.

Examples of forming apparatus or machines of this general kind are found described in US Patent Specifications Nos. 3,518,726; 3,599,293; 3,717,905; 3,973,291 and 4,016,628.

Technical problem All of the known forming methods and apparatus have the drawbacks of low production rates and uneven fibre distribution, and all result in absorbent bodies of varying weight. In addition hereto, one serious disadvantage encountered with known apparatus of the kind provided with rotating knives or shears for severing an elongated absorbent body is that the shears for severing an elongated absorbent body is that the shears are unable to function at high speeds with the degree of precision required, due to the fan action generated as the drum rotates, this fan action causing the upper fibre layer to be blown away. Forming drums of the kind in which the fluff material is blown centrally thereinto parallel with the axis of rotation of the drum result in an uneven and uncontrollable distribution of the fibres in the forming space, due to the turbulent state of the fibres.Drums of the kind in which fibres are blown into the drum under overpressure also result in particularly uneven fibre distribution and also in a large amount of waste, since the fibres are pressed into and stored in mutually different spaces in the drum.

Solution These and other problems are solved fully by means of the invention, which, as beforementioned, relates to a novel method and to novel apparatus for carrying out the method. The method according to the invention for producing absorbent bodies of fibre matsrial, in which method the fibre material, suspended in a stream of air, is introduced into the interior of a rotatable forming drum and the absorbent bodies are formed in forming apertures located on the drum casing and then transferred to an air-pervious web which is driven synchronously with the drum and which lies against and partially embraces the wall of the drum casing, is mainly characterized in that the stream of suspension is guided by guide means towards a restricted area located on the inner surface of the drum casing and lying within that part of the drum casing embraced by said path; and in that an under-pressure is maintained, at least within said area, between the side of the web remote from the drum casing and the interior of the forming drum.

The novel apparatus for carrying out the method of producing absorbent bodies of fibre material, in which the fibre material, suspended in a stream of air, is introduced into the interior of a rotatable forming drum and absorbent bodies are formed in forming apertures located on the drum casing and transferred to an air-pervious web which is driven synchronously with the drum and which lies against the drum and partially embraces the same, is characterized in that the drum includes two endwalls which adjoin the drum casing and of which at least one end-wall is stationary and is provided with fibre-suspension supply means directed towards the interior of the drum, and guide means effective to direct the stream of fibre suspension so that it impinges on a restricted area of the inner surface of the drum casing located within that part of the drum casing partially embraced by the web; and in that arranged beneath at least said restricted area and beneath the air-pervious web is a vacuum box which is effective to draw fibres into that forming aperture or those forming apertures located within the restricted area at that moment in time.

In accordance with a preferred embodiment of the invention, those forming apertures which are not covered by the air-pervious web are open to atmosphere so as to generate an airstream towards the aforesaid restricted area, this airstream at least substantially surrounding the stream of suspension and partly preventing uncontrolled departure of fibres from the stream of suspension and partly, through the ejector effect thus provided, sustaining or increasing the speed at which the fibres move towards the restricted area on the inner surface of the drum casing.

Advantages The method and apparatus according to the invention afford full control of the stream of fibre suspension, which means that the absorbent bodies produced will all contain the same amount of fibre, in spite of a substantially higher production rate. The volumetric weight, or bulk density, of the absorbent bodies can also be adjusted as desired, with a constant amount of fibre in the stream of suspension, by adjusting the rotational speed of the forming drum and the underpressure prevailing in the vacuum box.

Brief description of the drawing Figure 1 is a side view of a forming apparatus according to the invention, with one end-wall removed; Figure 2 is an enlarged view of the drum casing; Figure 3 is a sectional view taken on the line Ill- Ill in Figure 1; Figure 4 illustrates examples of different absorbent bodies; . and Figure 5 is a detailed view of the combined drive belt and the carrier for the air-pervious path.

As illustrated in Figure 1, a forming drum 2, shown in more detail in Figure 3, is journalled on a frame 1. The forming drum 2 is carried on a shaft 4, which is journalled in two bearings, of which one bearing 5 is shown. The two bearings are mounted on respective bearing brackets or blocks, of which the bearing bracket 6 is illustrated in Figure 1. The bearing brackets are, in turn, welded to the frame 1, or attached thereto in some other suitable manner. The frame 1 has mounted thereon two further bearing brackets or blocks, of which the bearing bracket 7 is shown, and which rotatably carry the ends of a driven roll 9, said roller being driven by a toothed belt 10 from a motor 11.

A guide roller 12 is journalled for rotation on two bearing brackets or blocks mounted on the frame, of which the bearing bracket 13 is shown, and a guide roller 14 is journalled for rotation on further bearing brackets or blocks, of which the bearing bracket 15 is shown in Figure 1. These two guide rollers 12 and 14 are arranged closely adjacent the forming drum 2, and the axes of rotation of the guide rollers lie above the lowest point of the drum. Three further guide rollers 16, 17 and 18 are mounted on respective bearing brackets or blocks attached to the frame 1. All of the aforesaid guide rollers 12,14,16,17,18, and the drive roller 9 have mutually parallel axes of rotation and an axial length which corresponds substantially to the axial length of the forming drum 2.

An endless forming belt 19 extends around the aforesaid guide rollers and the drive roller 9, and passes beneath the forming drum 2. The forming belt 19, of which one exemplifying embodiment is illustrated in Figure 19, shall be substantially nonstretchable, at least in its longitudinal direction, in order to maintain full positional synchronization between the forming drum 2 and the forming belt.

A web 20 of air-pervious material, preferably nonwoven material, is drawn from a reel 21, which is supported by the frame and extends over the forming belt and takes-up the absorbent bodies produced, for example the illustrated bodies 22,23 and 24. A plan view of various absorbent bodies a, b and c, is shown in Figure 4.

An exemplifying embodiment of the forming belt 19 is illustrated in Figure 5, and comprises a gridmat incorporating transversal rods, for example the rods 25,26 and 27, whose end parts carry loose sleeves, for example the sleeve 28, and the ends of which are connected to links, for example the links 29 and 30. Stop plates 63 or the like are arranged adjacent the inner ends of the sleeves 28. In the illustrated embodiment, stirrup-like elements 31 or the like are provided to form a grid-mat. For the purpose of defining the outer contour 32 of the absorbent body, the body a in Figure 4, to be formed, the grid-mat is suitably sealed around the outer contour 32, for example with a silicone rubber, a silicone plastic or some other suitable flexible material capable of penetrating down into the apertures thus formed.Although such masking-off of the grid-mat has been found advantageous, it is not absolutely necessary.

As best seen from Figure 3, the forming drum 2 comprises a circular-cylindrical casing 33. Located in the wall of the casing 33 is a plurality of through-passing apertures 34 having a shape corresponding to the desired outer contours of the absorbent body, for example the contour of the body a illustrated in Figure 4. These apertures 34 suitably have outwardly converging side surfaces 35 (Figure 3), so that the formed body readily leaves the drum, as described hereinafter. Joined to the end edges of the cylindrical casing 33 are two sprocket rings 36 and 37 respectively, which are intended to engage the respective chains 38 and 39 formed by the rods 25,26,27 and the links 29,30 on respective sides of the actual grid-mat.Although not shown, preferably at least the drive roller 9 is provided with corresponding sprocket rings, so as to ensure that the grid-mat and the air-pervious web 20 placed thereon are driven positively, this air-pervious web forming part of the finished product in the direction of the arrow A (Figure 1). Naturally, the web 20 lies within the coqfines of the two chains 38 and 29 and shall solely cover, and project slightly outwardly of the apertures or openings in the grid-mat. When the motor 11 drives the gridmat, via its chains 38,39, the chains in engagement with the sprocket rings 36 and 37 will drive the forming drum 2.The openings in the grid-mat, for example the opening 40 (Figure 5) have the same mutual spacing as the apertures 34 in the cylinder 33, and the arrangement is such that the drum apertures 34 on the lower part of the drum, which is embraced, for example, through an angle of 180O by the grid-mat, always coincide with the openings 40 of the grid-mat, when the grid-mat is maskedoff.

The cylindrical casing 33 of the forming drum 2 is firmly joined to an impervious end-wall 41, the centre of which is connected to a hub 42, which in turn is non-rotatably mounted on the shaft 4. The free end 43 of the shaft 4, i.e. the end remote from the hub 42, is journalled for free rotation in a hub 44 on an end-wall 45, which is fixedly carried by the frame 1 with the aid of means not shown. The circular periphery 46 of the end-wall 45 will thus be in sliding contact with the inner cylindrical surface 47 of the casing 33, when the cylindrical casing 33 and the end-wall 41 rotate around the shaft 4 in the direction of arrow B (Figure 1). In order to provide adequate scaling, a scal, for example a felt scal (not shown) can be arranged, for example, around the periphery 46 of said end wall. The endwall 45 is provided with a supply pipe 48 for the air-fibre suspension. The mouth or exit orifice 49 of the supply pipe 48 is directed towards a deflecting plate or guide plate 50, which preferably has the form of a chute and is arranged to deflect or guide the inblown fibre suspension past the throughpassing shaft 4 in the direction of the broken-line arrow C (Figure 1) towards a well-defined fluff take-up part in which the grid-mat 19 and the web 20 are brought together with the peripheral surface of the cylindrical casing 33. The deflecting plate 50 is pivotally mounted on a hinge 51 for movement towards and away from the exit orifice 49, said plate being operated with the aid of a curved guide arm 52, the outer end of which can be reached externally of the end-wall 45.Subsequent to moving the guide arm 52 to its correct setting, the arm is iocked by means of locking means (not shown) and the contained and well-defined fibre-suspension jet reaches the aforesaid area and is in no way disturbed by other elements or components located in the space formed by the end-walls 41 and 45 and the cylindrical casing 33.

Arranged in the vicinity of the lower half of the drum 2 are three separate and regulateable vacuum chambers 53,54 and 55, which are connected to suction sources (not shown) via respective suction lines 56,57 and 28. Journalled on the bearing bracket or block 59 (Figure 3) attached to the endwall 45 in the interior of the drum is a wiper or doctor roller 60 which is provided on its periphery with a brush 61 or like element adapted to wipe-off or to smooth-out the fibre bodies formed.The roller 60, which is driven by its own motor (not shown) and which naturally lies outside the area in which the fibre suspension impinges on the inner surface of the cylinder 33, is liable, in certain instances, to throw-up fibres, and in order to prevent the fibres from being thrown into the area 62, from which the fibres would be returned and placed as a mat on the web 20, there is provided a guard plate 63 which extends in the axial direction of the drum 2 and which screens the area 62 from the remaining part of the drum interior. The outer surface of the cylinder 33 may be lined or coated with a layer of rubber or the like (not shown) which abuts the web 20.

The described apparatus functions in the following manner. When the motor 11 is started-up, and the chains 37 and 38 subsequently drive the gridmat 19 and the air-pervious web 20 placed thereon, while at the same time a partial vacuum is generated in the vacuum boxes 53,54 and 55, the suction parts of which are formed so that air can substantially only be drawn through the grid-mat and the web, the stream of fibre suspension is supplied through the pipe 48 and flows towards the deflecting plate 50, which in turn directs the fibre-suspension stream towards the area referenced D in Figure 1.Since the apertures or openings 34 located above the shaft 4 are not closed by means of a screen or the like, air is drawn in through said openings in directions which will initially disturb the fibre suspension, although there is soon reached a state in which all apertures in the lower part of the cylinder 33 are filled with fibres. When an empty aperture 34 reaches the web 20, during rotation of the drum 2 in the direction of the arrow B, the suction air passes substantially to the empty aperture 34 and forms an airstream screen around the fibre-suspension floor, since remaining apertures 34 located further forward as seen in the direction of rotation B are filled and offer a substantially higher resistance to flow than the empty opening.Thus, from a practical aspect the fibre-suspension stream is enclosed between at least two air-stream curtains adjoining the two end-walls, and as a result of the presence of these two air-curtains there is created an ejector effect which accelerates the speed at which the fibres move, or in all events prevents the fibres in the suspension stream from slowing down. In practice, the aforesaid two air-curtains are combined to form a single, tubular air flow, which surrounds the stream of suspension, therewith eliminating practically completely all risk of fibres flying around in an uncontrolled manner and causing uneven fibre deposition in the forming aperture in a manner to impair the quality of the absorbent body.Since the air drawn by suction into the interior of the drum forms a curtain directed towards the fibre-receiving aperture 34, or possibly the fibre-receiving apertures 34, and exhibits the aforesaid ejector effect, i.e. entrains the fibres in the fibre-suspension stream, the underpressure prevailing in the vacuum chambers, and then in particular in the vacuum chamber 53, which directly influences the filling area, is of the greatest significance, and hence the underpressure, as previously indicated, should be adjustable, in order to obtain the best possible effect and the best possible product. Examples of suitable underpressures, or partial vacuums, in a given arrangement are set forth hereinafter.When a forming aperture 34', Figure 1, enters the contact area D, i.e. the area impinged upon by the stream of suspension, the aperture is rapidly filled with fibres, the quantity of fibre supplied depending upon the density of the suspension, the rotational speed of the drum, and the partial vacuum prevailing in the vacuum chamber 53. The fibre portion in the forming aperture is very exact and consequently the products produced will only deviate negligibly one from the other with respect to the amount of fibres contained by respective products, that is to say if any deviation occurs at all.The fibre portion in the filled forming aperture 34 then passes over the vacuum chambers 54 and 55, where the fibre portion is compacted on the air-pervious web 20, which together with the finished fibre portions or fibre bodies is transported to a final processing plant, in which a foil, for example a plastics foil or an air-and-liquid permeable foil is placed on and around each fibre portion. The finished fibre bodies are then separated and optionally embossed.

The aforementioned compacting of the fibre body enables the thickness and density of the finished body to be determined by adjusting the partial vacuum in respective vacuum chambers 54 and 55.

In the following there is given an example of the dimensions of a machine or apparatus constructed in accordance with the invention and tested in practice.

Diameter of cylinder 33 - 950 mm Wall thickness of the cylinder = 10 mm Rotational speed of cylinder 33 = 57r/min Number of forming apertures (same mutual spacing): 20 This machine gave a production rate of up to 1100 fibre bodies min. with sustained product quality. In this machine, the vacuum chambers 53,54 and 55 worked at a partial vacuum of 900, 1200 and 1500 mm vp respectively. Tests have shown that the partial vacuums with the aforegiven machine dimensions should lie at 900-1300, 1200-1600 and 1500-2000 mm vp respectively.

The described apparatus can be modified in various ways, without departing from the concept of the invention and without needing to impair the quality of the finished product. For example, it is possible to replace the grid-mat together with the adjoining chains with a perforated stainless-steel bolt having sprocket holes provided along the parallel side edges thereof, and neither is it necessary for the profile 32 of the absorbent body to be punched-out in the belt, although the underpressure in at least the first vacuum chamber 53 should be increased in view of the fact that a perforated steel belt offers a greater resistance to throughflow than a grid-mat belt according to Figure 5. As beforementioned, it is also possible to use a belt which is devoid of masked-off openings.Although it has been found most advantageous to use a plurality of vacuum chambers in order to achieve well-regulated compaction of the fibre bodies, it is fully possible to use only one single vacuum chamber, which preferably extends along the whole of the contact area between the air-pervious web 20 and the lower part of the cylinder 33, although the vacuum chamber may also be arranged solely beneath the part D, in which case there is no successive compaction of the absorbent body. The illustrated construction of the forming drum 2, incorporating a stationary supporting end-wall 41 joined to the cylinder 33, constitutes a simple and inexpensive solution, although it is also possible to firmly connect the two end-walls 41 and 45 to the frame 1 and allow solely the cylinder 33 to rotate on the circular peripheries of the end-walls.

Neither is it necessary to provide the guide plate 50 for guiding the stream of fibre suspension exiting from the exit orifice 49, described in conjunction with the described preferred embodiment of the invention, since the pipe 48 can be extended into the interior of the drum 2 and the mouth 49 or exit orifice of the pipe directed towards the intended area D, as indicated in chain lines in Figure 3. This construction, however, would require an increase in drum volume in order to avoid disturbances in the suspension stream. It will be noted that the two end-walls 41 and 45 of the Figure 1 embodiment are dished, solely to afford the maximum air volume. A requisite inner volume can also be obtained, however, with the use of planar endwalls by increasing the drum radius without increasing the active width of the cylinder.

Claims (8)

1. A method of producing absorbent bodies from fibre material, in which the fibre material, suspended in an air stream, is introduced into the interior of a rotatable forming drum and absorbent bodies are formed in forming apertures located in the cylindrical wall of the drum casing and are transferred, with the aid of guide means, to an airpervious web which is driven synchronously with the forming drum and which abuts the drum casing and partially embraces the same, and in which a pressure difference is maintained between the side of the web remote from the forming drum and the interior of said drum, characterized in that the stream of suspension is directed, with the aid of guide means towards a restricted area on the inner surface of the drum casing, said area lying within that part of the drum casing embraced by said web; and in that air is drawn by suction through said web from the interior of the forming drum, at least within the aforesaid restricted area; and in that air is drawn by suction through the forming apertures located externally of the area of the drum casing embraced by said web, in order to generate an air curtain which completely surrounds the stream of suspension, or which at least substantially surrounds said stream.

2. A forming apparatus for carrying out the method according to Claim 1 in the production of absorbent bodies from fibre material, in which method the fibre material, suspended in an air stream, is introduced into the interior of a rotatable forming drum (2) and absorbent bodies are formed in forming apertures (34) located in the cylindrical wall (33) of the forming drum and are transferred to an air-pervious web (20) which is driven synchronously with the drum and which abuts the cylindrical drum casing and partially embraces the same, characterized in that the drum (2) includes two end-walls (41,45) which adjoin the drum casing (33) and of which at least one is stationary and provided with a fibre-suspension suypply line (48) directed towards the drum interior, and guide means (49; 50) for directing the stream of fibre suspension so that said stream impinges upon a restricted area (D) on the inner surface of the drum casing (3) within that part of the drum casing (33) partially embraced by the web (20); and in that arranged at least beneath said restricted area (D) and beneath the air-pervious web (20) is a vacuum box (53) effective to draw air through the forming apertures located outside the area of the casing wall of the drum embraced by said web, and to draw the fibres by suction into the formed aperture or apertures (34) located within said restricted are (D) at that moment in time.

3. A forming apparatus according to Claim 2, characterized in that the forming apertures (34) located externally of the part of the drum casing (33) partially embraced by the web (20) are open freely to atmosphere.

4. A forming apparatus according to Claim 2 or 3, characterized in that the vacuum box (53,54,55) extends beneath the whole of the part of the drum casing (33) embraced by the web (20).

5. A forming apparatus according to Claim 4, characterized in that the vacuum box is divided into a plurality of separate vacuum boxes (53,54,55), adapted to generate successively an increasing partial vacuum in the direction of rotation of the drum (2).

6. A forming apparatus according to any of Claims 2-5, characterized in that the guide means for guiding the stream of fibre suspension is formed by the exit orifice (49) of the supply line (48) discharging in the interior of the drum (2).

7. A forming apparatus according to any of Claims 2-5, characterized in that the exit orifice (49) of the supply line (48) is directed towards deflect ing means (50) arranged to deflect the stream of fibre suspension towards said restricted area (D) on the inner surface of the drum casing (33).

8. A forming apparatus according to Claim 7, characterized in that the deflecting means com prises a chute-like, adjustable guide plate (50).