METHOD AND APPARATUS FOR FORMING A SLIVER

Abstract: A method and apparatus (10) for forming a sliver (30) from a fibrous web (18) leaving a carding machine and comprising: a cooperating pair of control rollers (13, 14) arranged one above the other to receive the fibrous web (18) issuing from a doffer (12); a condenser arrangement (15) downstream of the control rollers (13, 14) and comprising a cooperating pair of endless conveyor belts (16, 17) which extend generally lengthwise of the rollers (13, 14) and define a nip N located intermediate the ends of the control rollers (13, 14) which receives and condenses the web (18); and sliver-forming means (19) arranged downstream of the nip N in which the endless conveyor belts (16, 17) comprise: a) web-guiding runs (22, 23) which face the control rollers (13, 14) and which guide and condense the web (18) towards the nip N; b) return ends (24, 25); and c) rotatable return ends (26, 27) at the ends of each conveyor belt (16, 17) which have an axis of rotation (29) which extends obliquely upwards and towards the sliver-forming means (19), to provide improved gripping and guidance of the condensed web (18a) which is fed to the sliver-forming means (19).

Description: METHOD AND APPARATUS FOR FORMING A SLIVER This invention relates to a method and apparatus for forming a sliver from a web of fibres leaving a co-operating pair of substantially horizontal delivery rollers of a carding machine . A carding machine usually delivers a fibrous web to a sliver-forming device e.g. a trumpet and co-operating calender rollers, via delivery rollers and a condensing arrangement. In one example of an arrangement known from US 4501048, the condenser arrangement comprises a pair of co-operating endless conveyor belts which are spaced apart to define a sliver-forming nip between them, and in which the upper runs of the conveyor belts extend gently downwardly towards each other from their outer ends towards their inner ends adjacent to the "nip" . The upper runs of the conveyor belts therefore operate to guide and condense the web, as it issues from the delivery rollers, and towards and then through the nip. The upper runs of the belts extend substantially throughout the lengths of the delivery rollers, and by extending downwardly from their outer ends towards the nip, which is located substantially mid-way along the lengths of the delivery rollers, the web is condensed and then guided to the nip. The condensed web then moves downwardly through the nip and then is guided towards the trumpet and calender rolls. As a consequence of the guiding and condensing action applied to the web, it is caused to maintain contact with an upper arcuate portion of the lowermost of the delivery rollers, and typically the arc of contact subtends an angle of about 45° at the centre of the lower roller. However, under certain humidity conditions, the web may not become detached from the lower roller periphery until it has moved through an arc of contact as high as 90°. This can cause some loss of cohesion between the fibres of the web, by abrasion with the surface of the lowermost roller, as well as possible removal of some of the surface material on the fibrous constituents of the web. Furthermore, by virtue of the arrangement of the endless conveyor belts, the web tends to remain in contact with the surfaces of the upper runs of the conveyor belts as the web is condensed and guided towards the nip. These two factors, in the known arrangement, are liable to cause breaking of the fibrous web from time to time, and also require precise and close spacing of the leading edges of the upper runs of the conveyor belts to the periphery of the lower delivery roller for satisfactory operation. The present invention therefore seeks to provide an improved arrangement which gives better handling of the web as it issues from the delivery rollers, and also facilitates better control of application of any required draft to the web. According to one aspect of the invention there is provided an apparatus for forming a sliver from a fibrous web leaving a carding machine, said apparatus comprising: a co-operating pair of control rollers arranged one above the other to receive a fibrous web issuing from a doffer of a carding machine; a condenser arrangement downstream of the control rollers and comprising at least one endless conveyor belt which is laterally spaced from the control rollers and which extends generally lengthwise of the rollers, a nip being defined adjacent to one end of the conveyor belt and being located intermediate the ends of the rollers to receive and to condense the web after it issues from the control rollers; and sliver-forming means arranged downstream of the nip and defining a path of travel for the condensed web which issues from the nip: in which the endless conveyor belt comprises: a) a web-guiding run which faces the control rollers and which is arranged to guide and to condense the web towards the nip; b) a return run; and c) a rotatable return end at the end of the conveyor- belt adjacent to the nip, said return end having an axis of rotation which extends in a direction which is obliquely upwards and towards the sliver-forming means when viewed from one side of the path of travel of the condensed web. In a preferred arrangement, the nip is defined between a pair of endless conveyor belts, in which the axes of the facing return ends each extend obliquely upwardly and in a direction towards the sliver-forming means. However, it is within the scope of the invention for the nip to be defined between the return end of one endless conveyor belt only, and an adjacent co-operating guide surface. The angle at which the axis of each return end makes with the plane containing the path of travel of the condensed web will be determined experimentally, to provide optimum angular range, consistent with providing improved cohesion of the fibrous components of the web. One preferred angle (measured from the vertical line passing upwardly through the axis of rotation of the control rollers), is 25°. It has been found that this angle gives particular benefits in terms of very marked reduction in tendency of the fibrous web to loose cohesion. It should be understood that this angle is one example only, and that many other angles can be chosen, measured from the vertical line just mentioned, and giving rise to improved cohesion of the fibrous web, in the sense of reducing the tendency of the web to tear or break as it moves along its path of travel from the control rollers, via the nip of the endless belts, and to the sliver forming means. Furthermore, the web is effectively "plucked-off" the control rollers with no "wrap round" the control rollers and without any appreciable material remaining adhering to the surfaces of the rollers, and no "ends down". One major existing arrangement is shown in Figures 6 and 7 in which vertically extending conveyor belts are provided, semi-sliver is formed along the full width of the control rollers, and which then slides towards the nip between the two vertical arrangements of conveyor belts, and which can cause "bunching *1 of the web material and a resulting "ends down" situation if any sticky material adheres to the rollers. This disadvantage of the known arrangement is overcome by a preferred embodiment of the invention. Preferably, only a very small drafting ratio applies between the control rollers and the endless belts, and in a typical arrangement the ratio of peripheral speeds is of the order of 1.05:1. With such an arrangement, this often means in practice that the fibrous web issuing from the control rollers hardly touches the surfaces of the web-guiding runs of the conveyor belts, and therefore undergo condensing and guidance, to a major extent, via contact with the portions of the endless belts running over the facing rotary return ends of the two conveyor belts. It will be appreciated that each conveyor belt is taken around an outermost return end, and also an innermost return end, and that the innermost return ends of the two belts face each other, in order to define the "nip" between the two conveyor belts. Therefore, in that the major portion, if not all, of the condensing and guiding action on the web takes place in the nip region, and with the web effectively not making any contact, or any significant contact with the web guiding runs of the belts at all during running, the two innermost return ends effectively function as calender rollers. The rotatable return ends of the endless conveyor belt typically comprise cylindrical bodies, mounted to rotate about the obliquely upwardly extending axes as referred to above. When the angle (α) of inclination of the obliquely upwardly extending axes to the vertical is about 25°, the following technical advantages have been noted: 1) the fibrous web breaks down significantly less frequently along the path of travel between the control rollers and the nip of the conveyor belt. In fact, in tests carried out to date, breakdown of the web rarely occurs, provided that the feed supply of the fibrous web from the carding machine is near to normal. 2) The upper speed limit of the web does not appear to be critical, as long as the feed to the control rollers is maintained. With present technology, this equates to a top speed of about 400 metres per minute, which is dependent at present upon the limiting speed of the web fed to the control rollers. 3) The apparatus of the invention (and also a novel method of sliver formation) "piecens" normally. As soon as the leading end of any newly started web emerges from the nip between the control rollers, the web-guiding runs of the endless belts carry and condense the leading end of the web to the nip. At the nip, it needs no further help to go through the nip, and with a slight draft between the surface speed of the control rollers and the endless belts, e.g. 1.05 drafting ratio as referred to above, the fibrous web very quickly looses contact with the conveying runs of the belts and only becomes engaged with the belts at their inner most return ends . 4) The setting which is made between the belt edges and the control rollers also is not critical, and typically gaps of 2 to 3 millimetres (or more) can work very well. By contrast, in the known arrangement referred to in the introduction, critical control of the setting is essential, and it has to be maintained at about lmm or less for satisfactory performance. 5) Because there is no "wrap" around the lower control roller in the invention, and the path of travel between the control rollers and the nip can be kept short, and it is therefore possible to use the control rollers to function as "crush" rollers without significantly increasing "ends down" i.e. the web tearing by sticking to the control roller (line contact in the invention rather than surface contact in the known arrangement) . 6) By increasing the draft between the nip and the control rollers i.e. by increasing the "apron" speed (belt speed) relative to the control rollers, it is possible to increase the production rate of the carding machine, without increasing the entry speed of the web into the control rollers i.e. without increasing the surface speeds of the doffer and associated stripping rollers of the carding machine, which convey the web. Because drafting webs does not much influence the CV of the subsequent sliver, as opposed to roller drafting which tends to do so, the present invention provides a powerful way of achieving production increase, because, in practice, there is usually a technological limit to the speed at which the doffer can rotate without disrupting the web (within the cord) . According to a further aspect of the invention there is provided a method of forming a sliver from a fibrous web leaving a carding machine, said method comprising: feeding a fibrous web issuing from a doffer of a carding machine between a co-operating pair of control rollers arranged one above the other; guiding the web issuing from between the pair of control rollers to a condenser arrangement which comprises an endless conveyor belt which is laterally spaced from the control rollers and which extends generally lengthwise of the rollers, a nip being defined adjacent to one end of the conveyor belt and being arranged to feed and condense the web so as to pass through the nip; and causing the condensed web which issues from the nip to move on a path of travel from the nip to sliver-forming means arranged downstream of the nip; in which the endless conveyor belt is operative to guide the web issuing from the control rollers to pass through the nip and comprises; a web-guiding run which faces the control rollers and which can guide and condense the web towards the nip; a return run; and a rotatable return end at said one end of the conveyor belt and which guides the movement of the web- guiding run and the return run of the conveyor belt, the return end having an axis of rotation which extends in a direction which is obliquely upwards and towards the sliver-forming means when viewed from one side of the path of travel of the condensed web. Preferred embodiments of method and apparatus can now be described in detail, by way of example only, and with reference to the accompanying drawing in which: Figure 1 is a schematic side view of a web-condensing and sliver forming arrangement according to the invention, arranged downstream of a doffer of a cotton carding machine; Figure 2 is a plan view corresponding to part of Figure i; Figure 3 is a schematic side view of a modified arrangement in accordance with the invention; Figure 4 is a plan view corresponding to Figure 3 ; Figure 5 shows schematically an alternative arrangement of condenser arrangement using one endless conveyor belt which defines a nip at one end of the belt with a co-operating guide surface in the form of an obliquely extending roller; and Figures 6 and 7 show a known arrangement as referred to in the introduction. Referring now to Figures 1 and 4 of the drawings, there will now be described an apparatus for forming a sliver from a fibrous web leaving a carding machine, according to the invention, and also a novel method of forming such a sliver. The apparatus comprises a downstream arrangement designated generally by reference 10, and defining a path of travel for a web from a doffer 12 of the carding machine (not shown in detail) to a sliver-forming device. The doffer is shown in Figure 1 by reference 12 , and has an associated stripper roller 11, and the function of doffer 12 and stripper 11, in relation to a cotton carding machine, will be well known to those of ordinary skill in the art, and need not be described in detail herein. A co-operating pair of control or crush rollers 13 and 14, arranged one above the other, receive a fibrous web issuing from the doffer 12, and then deliver the web to a condenser arrangement arranged downstream of the control rollers 13, 14, and designated generally by reference 15. The condenser arrangement preferably comprises a co-operating pair of endless conveyor belts 16 and 17, which are laterally spaced from the control rollers 13, 14, and which extend generally lengthwise of the rollers. The conveyor belts 16, 17 are spaced apart from each other to define a nip N (see Figure 2), which is located intermediate the ends of the rollers 13, 14 (preferably substantially mid-way along the lengths of the rollers 13, 14) and which serve to receive and to condense the web 18 after it issues from the control rollers 13, 14. Sliver-forming means 19 is arranged downstream of the nip N, and in the illustrated arrangement comprises trumpet 20 and calender rolls 21, both of which are known per se . The sliver forming means 19 defines a path of travel for the condensed web, shown by reference 18a, which issues from the nip N. The endless conveyor belts 16, 17 have web-guiding runs 22 and 23 respectively which face the control rollers 13, 14 and which are arranged to guide and to condense the web 18 towards the nip N, as shown clearly in Figure 2. The conveyor belts 16 and 17 also have return runs 24 and 25 respectively, and the web-guiding runs and the return runs are formed by passage of an endless conveyor belt around a pair of outer and inner rotary return ends, shown by references 26 and 27 respectively. The two facing inner return ends 27 define the nip N therebetween. Figure 2 is a schematic plan view of the endless conveyor belts 16 and 17, but in fact each return end is formed by a cylindrical roller, one of which is shown by reference 28 in Figure 1 and which has an axis of rotation which extends in a direction which is obliquely upwards and towards the sliver- forming means 19, when viewed from one side of the path of travel of the condensed web 18a. As shown in Figure 1, the axis 29 of rotation extends upwardly and in a direction towards the means 19 at an angle α to a vertical line 30 passing through the axes of rotation of the rollers 13 and 14. In a preferred arrangement, the angle is about 25°, and this has been found to give advantageous operating performance, and in particular makes substantial reduction in the risk of the web breaking down between the control rollers 13, 14 and the belts 16 and 17. In practice, break down of the web occurs extremely rarely, provided that the feed to the rollers 13 and 14 is near to normal. A typical speed of operation can run the web at a speed of about 400 metres per minute, which is effectively the speed of the doffer surfaces. The system usually piecens automatically, in that as soon as a leading end of a newly starting web comes through the rollers 13 and 14, the web belts convey the web to the nip N, where it needs no help to go through the nip. A slight draft between the surface speed of the control or crush rollers 13 and 14 and the belts 16 and 17 is preferred, with typical figure being about 1.05, and this means that once the web is running through the system, effectively the web looses contact with the facing runs 22 and 23 of the belts. The setting S (see Figure 1) between the belt edge and the control roller is not critical, and a typical gap of 2 to 3mm works perfectly. This compares with the known arrangement referred to in the introduction, where this setting gap is critical, and has to be maintained at a lower figure of 1mm or less. Because the web 18 issues horizontally from the nip between the rollers 13 and 14, the web does not wrap itself even partly around the peripheral surface of the lower roller 14, and therefore the web path between the rollers and the nip N can be kept short. This means that the control rollers 13 and 14 can function as crush rollers, without significantly increasing "ends down" i.e. the web collapsing. (This is believed to be due to line contact of the web with the rollers in the embodiment of the invention rather than surface contact in the known arrangement) . By increasing the draft between the nip N and the control rollers i.e. by increasing the apron speed relative to the control rollers, the production rate of the entire carding machine can be increased, without increasing the entry speed of the web into the control rollers 13 and 14 i.e. without increasing the surface speeds of the doffer 11 and stripping rollers 12, which convey the web. Because drafting webs does not much influence the CV of the subsequent sliver (as opposed to roller drafting which tends to do so) , a powerful way of production increase has been provided. There is usually a technological limit to the speed at which the stripper roller can rotate without disrupting the web. The oblique angle of inclination referred to above as 25° is one preferred angle. It should be understood that other angles may be adopted, eg. in the range 10° to 50°, and selected by experiment to provide the most favourable performance in the handling of the sliver as it issues from the doffer 11 (provided there is no significant wrap around the rollers) and consistent with maintaining the cohesiveness of the fibrous components of the web. Figure 2 shows endless belts 16 and 17 which, in practice, (once the web is fully running through the system) , functions somewhat as calender rolls, via the inner most ends 27. It is believed that, in some circumstances, it may be possible, within the scope of the invention, to replace at least one of the endless conveyor belts 16 and 17 by a simple arrangement of calender rollers, replacing the return end(s) 27, but otherwise functioning in generally the same way. In. that event, some other form of guide arrangement may be provided (if required) to assist the initial guiding of the web 18 from the rollers 13 and 14 to the nip N between these calender rollers. Thus, the nip N can be defined at one end of one of the belts 16, 17, namely return end 27 and an adjacent guide surface. By way of example, Figure 5 shows nip N defined between one return end 27 of endless conveyor belt 17 and a guide roller 160, and in which the axes of the return end 27 and of roller 160 extends obliquely upwards in the same way as shown in Figure 1. The schematic illustration of an example of the invention in Figures 1 and 2 may be modified, if required, for higher speed operation, as shown in Figures 3 and 4. In some circumstances, it may be desirable to provide an additional arrangement of calender rollers and located between the conveyor belt 16, 17 and the trumpet 20. These additional rollers can be set with a predetermined space between them, typically about 0.03 inches, and can be "composition coated" to give improved gripping with the condensed web. No equipment is provided above or below the additional calender rollers, apart from a suction hood to extract dust etc. The setting of the additional rollers, and the coating, avoid need for wiper or scraper blades, and also contribute to clean running. Referring in particular to Figures 3 and 4, additional calender rollers 41 and 42 are shown, arranged one above the other, and mounted in cantilever manner on an output of a gear box 43 which provides drive to the calendar rollers. Upstream of the rollers 41 and 42, there is a trumpet arrangement 44 (snubber) , comprising a fixed half trumpet 44a and a movable half trumpet 44b which can be moved away from the fixed half trumpet to a position shown in dashed outline to admit the condensed web, and can then be returned to the position shown in full lines. A suction hood 45 is arranged above the calender rollers 41, 42, and removes dust and other contamination from the fibrous web as it moves along its path of travel to the sliver- forming means 19. The arrangement shown in Figure 3 and 4 is particularly effective, and provides surprising advantage over existing systems, which are liable to have substantial "ends down" because of dust and other contamination remaining within the system, and adversely affecting the guidance of the web as it moves from the control rollers to the sliver forming means. It is believed that the surprisingly effective cleaning which is achieved by the modified arrangement in accordance with the invention, shown in Figures 3 and 4, is due partly to the cantilever manner of mounting of the calender rollers 41 and 42, together with the provision of the suction hood 45.

Claims: CLAIMS : 1. Apparatus (10) for forming a sliver (30) from a fibrous web (18) leaving a carding machine, said apparatus comprising: a co-operating pair of control rollers (13, 14) arranged one above the other to receive a fibrous web issuing from a doffer (12) of a carding machine; a condenser arrangement (15) downstream of the control rollers (13, 14) and comprising at least one endless conveyor belt (16, 17) which is laterally spaced from the control rollers (13, 14) and which extends generally lengthwise of the rollers, a nip N being defined adjacent to one end (27) of the conveyor belt and being located intermediate the ends of the control rollers (13, 14) to receive and to condense the web (18) after it issues from the control rollers; and sliver-forming means (19) arranged downstream of the nip N and defining a path of travel for the condensed web (18a) which issues from the nip: in which the endless conveyor belt (16, 17) comprises: a) a web-guiding run (22, 23) , which faces the control rollers (13, 14) and which is arranged to guide and to condense the web (18) towards the nip N; b) a return run (24, 25); and c) a rotatable return end (26, 27) at said one end of the conveyor belt (16, 17), said return end having an axis of rotation (29) which extends in a direction which is obliquely upwards and towards the sliver-forming means (19) when viewed from one side of the path of travel of the condensed web (18a) . 2. Apparatus according to claim 1, in which the axis (29) of each return end is inclined at an angle α to a line (30) passing through the axis of rotation of the rollers (13 and 14) , which is in the range 10 to 50°, preferably about 25°. 3. Apparatus according to claim 1 or 2 , in which the nip N is defined between a pair of conveyor belts (16, 17) , or between one conveyor belt (17) and a co-operating guide (160) which is preferably a roller. 4. Apparatus according to any one of claims 1 to 3 , in which a small drafting ratio applies between the control rollers (13, 14) and the endless belts (16, 17). 5. Apparatus according to claim 4, in which the drafting ratio can be up to 1:1.50. 6. Apparatus according to any one of the preceding claims, including a pair of calender rollers (41, 42) arranged along the path of travel of the condensed web (18a) and between the conveyor belts (16, 17) and the sliver-forming means (19). 7. Apparatus according to claim 6, in which the calender rollers (41, 42) are set at a predetermined spacing from each other, and are composition coated, to improve the gripping with the condensed web (18a) , and to provide improved clean running of the apparatus. 8. Apparatus according to claim 7, including a suction hood (45) arranged above the calender rollers (41, 42). 9. Apparatus according to any one of claims 6 to 8 , in which the calender rollers 41, 42 are mounted in cantilever manner, one above the other, in the path of travel of the condensed web 18a to the sliver-forming means 19. 10. A method of forming a sliver (30) from a fibrous web (18) leaving a carding machine (11, 12), said method comprising: feeding a fibrous web (18) issuing from a doffer (12) of a carding machine between a cooperating pair of control rollers (13, 14) arranged one above the other; guiding the web issuing from between the pair of control rollers (13, 14) to a condenser arrangement which comprises an endless conveyor belt (16, 17) which is laterally spaced from the control rollers (13, 14) and which extends generally lengthwise of the rollers, a nip N being defined adjacent to one end (27) of the conveyor belt and being arranged to feed and condense uhe web so as to pass through the nip (N;) and causing the condensed web (18a) which issues from the nip N to move on a path of travel from the nip to sliver-forming means (19) arranged downstream of the nip; in which the endless conveyor belt (16, 17) is operative to guide the web issuing from the control rollers (13, 14) to pass through the nip N and comprises; a web-guiding run (22, 23) which faces the control rollers (13, 14) and which can guide and condense the web towards the nip N; a return run (24, 25); and a rotatable return end (26, 27) at said one end of the conveyor belt 16, 17 and which guides the movement of the web-guiding run (22, 23) and the return run (24, 25) of the conveyor belt (16, 17), said return end (26, 27) having an axis of rotation (29) which extends in a direction which is obliquely upwards and towards the sliver-forming means (19) when viewed from one side of the path of travel of the condensed web (18a) from the nip N to the sliver- forming means (19) . 11. A method according to claim (9), in which the arrangement of the endless conveyor belt (16, 17) is such that the web issuing from the control rollers (13, 14) passes to the nip N, during normal running, substantially without coming into contact with any appreciable portion of the web-guiding run (22, 23) of the conveyor belts (16, 17) and without remaining wrapped to the periphery of the control rollers 13, 14.

Inventors: VARGA JOHN MAXIMILIAN JULES, VARGA, JOHN, MAXIMILIAN, JULES
Applicants: CARDING SPEC CANADA, CARDING SPECIALISTS (CANADA) LIMITED
Application year: 1998
Main classification: D01G15
IPC codes: D01G15