The invention is directed to an apparatus according to the preamble of claim 1 for the production of nonwovens using at least one carding machine designed for high production speeds of the fiber webs, from which a nonwoven is mechanically transferred to a conveyor belt, and a method for the production of nonwovens according to the preamble of claim 10.
High speed cards of the above type are known from DE-A 43 44 226.
By means of carding machines, high production rates can be obtained. Particularly with light-weight nonwovens, however, production speeds above 150 to 200 m/min. entail the problem that, during transport, the structure of the sensitive unbonded nonwoven is affected, resulting in an irregular nonwoven or even destruction of the non-woven.
FR-A-2545507 and DE-A-3832858 relate to an apparatus for the production of nonwovens comprising a plurality of carding rollers from which the fibers are thrown into an air stream The dispersed fibers are carried by the air stream onto a condensing means which is built by an air-permeable belt which is subjected to suction from below. This apparatus produces an airlaid nonwoven web.
Thus, it is an object of the invention to provide an apparatus and a method for the production of nonwovens which allow for a considerable increase of the production speed.
The above object is solved by the features of claims 1 and 10. According to the invention, it is provided that the conveyor belts is air-permeable, and that, at the transition region between the carding machines and the conveyor belt, an underground suction force is applied using a suction means arranged at the conveyor belts. The suction is set to be just sufficient to remove the air film generated between the nonwoven and the conveyor belt at high transport speeds while, on the other hand, the nonwoven will not be sucked too firmly against the conveyor belt. Due to the removal of the air film, no disturbances of the appearance of the nonwoven will occur, not even at speeds of the nonwoven above 150 to 200 m/min. Finally, at the output side of the apparatus, the speed of the nonwoven can be as high as 400 m/min. or more.
The solution according to the invention offers the considerable advantage invention that the nonwoven is subjected to a relatively small draft. This is favorable especially in case of high speeds of the nonwoven because already a relatively small percentage draft can result in high absolute draft values, which can cause disturbances of the structure of the nonwoven.
Preferably, it is provided that, at the transition region, a take-off roller transfers a doubled non-woven onto the conveyor belt. A doubled nonwoven has better cohesion and thus is better suited for high speeds. Because a doubled nonwoven is transferred to the conveyor belt by a sole roller, the number of transition regions is reduced. Further, doubling the nonwoven within the carding machine provides the advantage that no further intermediate conveyor belts are required, so that the overall expenditure for machinery can be reduced.
The apparatus according to the invention is particularly useful for the processing of staple fibers, i. e. polyester, polyethylene or polypropylene fibers.
The suction means exerts the suction effect on the conveyor belt in sections. Thus, it is made possible that selected portions of the conveyor belt are sucked at different intensities, depending on their current position and their distance from the transition region between the carding machine and the conveyor belt. This is facilitated also because, after the generation of an air film at the transition region between the carding machines and the conveyor belt has been prevented, only a relatively small suction force is required from then on.
Preferably, suction boxes are arranged below the conveyor belt, extending, on the one hand, over the desired width of the nonwoven and, on the other hand, at least over part of the conveyor belt in the longitudinal direction. Limiting the suction to the desired width of the nonwoven offers the advantage that a sharp, linear end edge of the nonwoven will be generated, without any control or guide means being required on the upper side of the conveyor belt.
For improved adhesion, the conveyor belts can have a structured surface on the side facing towards the nonwoven.
The vacuum generated by the suction means can be controllable in a variable manner. Thus, it is possible to adapt the underground suction to the current production speed and/or the type of the fibers being processed, or to other process parameters.
Preferably, the carding machine used comprises a main cylinder, at least two web-forming rollers engaging the main cylinder and each taking off a respective fiber web from the main cylinder, a doffing means arranged downstream of the web-forming rollers, and a take-off means from which the nonwoven is transferred to the conveyor belt. By means of a common roller, arranged upstream of the take-off means, the at least two fiber webs taken off the main cylinder by the web-forming rollers, are doubled into a nonwoven which is laid as a formed web onto the conveyor belt.
A carding machine of the above type makes it possible to perform doubling and simultaneous crosslinking of the fiber webs already within the carding machine after the web-forming rollers and before the take-off means. A further advantage resides in that, behind the doffing roller, only a sole take-off means and a sole conveyor belt are required. Thus provides for a reduction of the constructional expenditure for the production of doubled fiber webs, while allowing a improved controlling of the production process, particularly in case of light-weight fiber webs and high production speeds.
According to an preferred embodiment of the invention, it is provided that a sole doffing roller is arranged in engagement with two web-forming rollers, that the doffing roller takes over a respective fiber web from each of the two web-forming rollers and doubles the fiber webs. Doubling is carried out immediately behind the web-forming rollers so that only one doffing roller is required.
An embodiment of the invention will be explained in greater detail hereunder with reference to the Figures.
The apparatus for the production of nonwovens 1 according to the embodiments illustrated in Figs. 1 and 2, comprises two carding machines 2 with a respective feed means 3, the carding machines 2 laying the respective generated nonwoven 1 onto a common conveyor belt 4. The conveyor belt 4 is provided as an endless belt and is permeable to air to be subjected to a suction force from below. Behind the second carding machine 2, the repeatedly doubled nonwoven 1 is running into a following processing unit 14, e.g. a thermobonding means. By way of alternative to the arrangement of Figs. 1 and 2, the apparatus for the production of nonwovens 1 can be provided with one carding machine 2 only or with more than two carding machines 2.
The carding machines used can be high-speed carding machines with production speeds above 150 m/min., preferably above 200 m/min. The first carding machine 2 in the running direction of conveyor belt 4 will lay a first nonwoven 1 onto the conveyor belt 4, notably in the transition region 6 between the carding machine 2 and the conveyor belt 4. A suction means 8, consisting of a plurality of suction boxes 10 distributed along the length of conveyor belt 4, is provided to subject the transition region 6 to a suction force by means of a first suction box 10. This underground suction at the transition region 6 precludes the formation of any air film between the nonwoven 1 and the conveyor belt 4, which air film, in case of high production speeds, would at least disturbe the uniform appearance of nonwoven 1 or even cause complete destruction of nonwoven 1.
The suction box 10 located at transition region 6 can be provided with a partition wall 11 so that the suction force acting on conveyor belt 4 is increased in the transition region 6. This partition wall 11 can also be arranged to be pivoted and/or displaced in suction box 10, so that the vacuum force and the area exposed to suction can be variably controlled in an easy manner. Of course, the transition region 6 can be provided with a separate suction box 10. The position of partition wall 11 shown in Fig. 3 will automatically cause a weaker suction force acting on conveyor belt 4 behind transition region 6. Another possibility for adjustment in the transition region 6 resides in shifting a slider, extending in parallel to conveyor belt 4 and being adjustable in running direction, for variably setting the sucked area under the conveyor belt.
In the further course of conveyor belt 4, further suction boxes 10 are arranged in respective areas. As compared to the suction boxes 10 arranged in the transition regions 6, these further suction boxes 10 could be operated at a lower adjustable vacuum force. The width of the suction boxes 10 exactly corresponds to the set width of the nonwoven. In this regard, a further advantage resides in that the nonwoven 1 can be given absolutely linear, sharp lateral edges without additional measures.
Between the suction boxes 10, respective support rollers 16 are provided for supporting the conveyor belt 4:
The suction capacity of the suction boxes 10 can be variably controlled in dependence on the production speed and the type of fibers. Control can be carried out by a central processing unit. In each case, the suction is set such that the generation of an air film is prevented particularly in the transition regions 6, without sucking the nonwoven 1 onto the - if required, structured - surface of the conveyor belt 4 at an excessive force.
The second carding machine 2 in the running direction of conveyor belt 4 will produce a second non-woven 1 which, at the second transition region 6 in the running direction of the belt, is laid onto the first nonwoven 1 produced by the first carding machine 2, thus doubling the nonwoven 1. As compared to the suction box 10 arranged at the first transition region 6, the suction box 10 arranged at this second transition region 6 can be operated at a higher vacuum for compensating the pressure loss due to the first nonwoven 1. Thus, formation of an air film between the first and the second nonwovens and a resultant possible disturbance are precluded.
Preferably, the carding machine used is of the type described in DE 43 44 226 A. The carding machine schematically shown in Fig. 1 comprises a main cylinder 20 arranged in engagement with two randomizing rollers 22 which in tum engage a doffing roller 24 and will double respectively two fiber webs 50,52 on doffing roller 24. The doubled fiber web will then be transferred from doffing roller 24 to two condensing rollers 26 and, from these, to two successive take-off rollers 28. From the last take-off roller 28, the nonwoven 1 is laid onto conveyor belt 4 at transition region 6. In this regard, it is essential that the doubled nonwoven 1 is transferred onto conveyor belt 4 by a sole take-off roller 29.
Fig. 3 shows a preferred embodiment of a non-woven carding machine provided with an intake means 30 consisting of an intake trough 32 and an intake roller 34.
The subsequent licker-in device 36 comprises a licker-in roller 38 and a licker-in tambour 40. The licker-in tambour 40 is provided with two worker and stripper pairs 42.
This arrangement is followed by a transfer roller 44 for transferring the supplied fiber web 46 to main cylinder 20.
Main cylinder 20 is provided with six worker and stripper pairs 48. Behind the worker and stripper pairs when viewed in the direction of rotation, two web-forming randomizing rollers 22,23 engage main cylinder 20 successively in the direction of rotation, each of them taking off one fiber web 50,52 from main cylinder 20. A sole doffing roller 24 takes over both fiber webs 50,52 from the randomizing rollers 22,23 and doubles the webs so that a doubled fiber web 54 is transferred to the subsequent condensing means 26,27 and the take-off means 28,29 arranged behind condensing means 26,27. From take-off means 28,29, the doubled fiber web 54 reaches conveyor belt 4 in the form of a nonwoven 1.
In the above embodiment, wherein two randomizing rollers 22,23 are combined with only one doffing roller 24, the randomizing rollers can be arranged in close proximity to each other, thus leaving enough space on the periphery of main cylinder 20 for an additional worker and stripper pair 48. Such an additional worker and stripper pair 48 increases the carding performance.
The web-forming rollers 22,23, preferably provided as randomizing rollers, can have different rotational speeds or different diameters whereby the properties of the to-be-doubled fiber webs 50,52 can be influenced.
The main cylinder 20 is preferably larger than the web-forming rollers 22,23.
Preferably, also the doffing roller 24 has a larger diameter than the web-forming rollers 22,23.