US3015872A

US3015872A - Apparatus for the heat treatment of running yarns

Info

Publication number: US3015872A
Application number: US728635A
Authority: US
Inventors: Jones Clive Righton
Original assignee: British Nylon Spinners Ltd
Current assignee: British Nylon Spinners Ltd
Priority date: 1957-04-25
Filing date: 1958-04-15
Publication date: 1962-01-09
Anticipated expiration: 1979-01-09
Also published as: GB850080A; DE1410360A1; FR1204634A; CH364068A; BE567120A

Description

Jan. 9, 1962 c. R. JoNEs 3,015,872

APPARATUS FOR THE HEAT TREATMENT OF RUNNING YARNS Filed April 15, 1958 Inventor C'L/ve F/G/fro/v Q/o/vgs Attorneys @taies 3,015,872 Patented Jan. 9, 1962 3,015,872 APPARATUS EUR THE HEAT TREATMENT F RUNNING YARNS Clive Righten Jones, Ahergavenny, England, assigner to British Nylon Spinners Limited, Monmouthshire, England Filed Apr. 15, 1953, Ser. No. 728,635 Claims priority, application Great Britain Apr. 25, 1957 2 Claims. (Cl. 28-62) The present invention relates to a process and apparatus for the heat treatment of running yarns, and has particular though not exclusive reference to such a treatment with dry heat. The term ya-rn is herein used in the specication and claims to indicate single or multiiilament structures; and includes cords, whether single or plied, and whether as single ends o-r in the form of a Warp fabric, such as tyre-cord fabric.

It is often required to submit a running yarn or a plurality of such yarns to a heat treatment, as for example during stretching under tension, or during crimping processes such as those depending on deformation of the synthetic yarns by false-twisting or by passage of the yarns while hot over an edge. The etliciency of the heating apparatus may well be the governing factor in the productivity of the process concerned, as considerations of space will often prevent the heating apparatus from being more than, at the most, a few feet long, and this will limit the speed at which the yarn or yarns may be passed through the heater so that the heat treatment may be effective.

Various types of heating apparatus are known for the heat treatment of synthetic yarns, such as nylon yarns, some depending on conduction and some on radiation and convection to effect the transfer of heat `from the heating element to the yarn. One of the simpler forms of heatconduction apparatus is a curved heated-plate with which the yarn makes a suitable line contact, but this apparatus has the disadvantage that, as the heat is applied to one side of the yarn only, the average yarn temperature must always be lower than that plate surface temperature at which the laments of the yarn in contact with the pl-ate would melt or be degraded. Thus, for any particular yarn there is la clearly defined maximum temperature above which it is not safe to operate and the only way of increasing the ecacy of the apparatus is by increasingthe length of the line of contact with the yarn, which, as already stated, is usually prohibited by considerations ofrspace. A simple form of radiation apparatus comprises an airlled metal tube through the middle of which the yarn passes, the walls of the tube being 4heated by electric heating coils wrapped around them. This type of apparatus has advantages over the contact type in that all sides of the yarn can be heated simultaneously to the same amount, and in that the temperature of the heating elements can be raised well above the melting (or degrading) temperature of the yarn, at high yarn speeds, without damaging the yarn.

What is required of any heat treatment apparatus is that it should heat the yarn up to the required temperature and hold it at that temperature `for a time suicient to achieve the purpose of the treatment, e.g. the setting of the yarn if it is a yarn such as nylon which has the ability to be permanently set by hea-t in the configuration adopted by it at the time of the heat treatment. What the temperature and the time shall be in any given instance will depend on the nature of the treatment, the kind of yarn and its diameter, and the type of heating apparatus, but in every instance there will be some finite time (and corresponding distance) during which some or all parts of each successive length of the yarn passing through or in contact with the heater will be rising in temperature towards the desired, or equilibrium, temperature.

so that the yarn may be processed at greater linear speedsy for a given length of heater,

It is another object of the invention to provide a yarn heating apparatus having a plurality of heating zones in each of which the temperature distribution is substantially uniform throughout the greater part of the zone.

The present invention in one aspect comprises a process for the heat treatment of running yarns, especially continuous iila'ment yarns of synthetic thermoplastic materials, wherein yarn is drawn through a heating jacket and successive lengths of the yarn `a-re therein subjected lirstly to heat at a temperature considerably in excess of the treatment equilibrium temperature for -a time suicient to raise the temperature of the yarn substantially to the said equilibrium temperature but insuicient to damage or degrade the material of the yarn, and secondly to heat at the equilibrium temperature for a time suicient to achieve the purpose of the treatment. The invention in another aspect comprises apparatus for the heat treatment of running yarns, especially continuous filament yar-ns of synthetic thermoplastic materials, drawn therethrough comprising a thermally-insulated heating jacket having a distinct pre-heating zone and a distinct equilibrium heating zone, and having means to supply heat to the said preheating Zone land means to supply heat to the said equilibrium Zone, the `first-mentioned means being adapted to supply heat ata higher temperature than the second-mentioned means.

In order that 4the nature of the invention may become v apparent there will now be described, with reference to the accompanying drawings, one convenient apparatus, together with its mode of use, provided by and illustrative of the invention.

In the accompanying drawings:

FIGURE l is a longitudinal section of the said apparatus through the line C-C of FIGURE 2 or 3;

FIGURE 2 is a section rotated 90 clockwise through the line A-A o-f FIGURE l; and

FIGURE 3 is a section rotated 90 clockwise through the line B-B of FIGURE 1.

The apparatus essentially comprises a heating jacket 1 of rectangular cross-section some two feet in length, through a lcentral space in which two

yarns

3, 5 are passed, travelling in the direction from top to bottom of the jacket. The yarns, after attaining full running speed, are insertedY into operative position within the jacket by means of a closure member 7, shown diagrammatically in FIG- URE 1, which carries yarn-

guides

9, 11 and 13, 15 on its l upper land lower extremities respectively. As shown by the chain-dotted and the solid lines depicting member 7 in two positions, the member is capable of lateral movement so as to be able to move the yarns through a longitudinal threading slot 17 into and out of operative position Within the jacket, as it is not desired to insert the yarns until they are moving at operating speed, owing to the very high temperature of the apparatus. The jacket comprises an aluminium casing 19 dening within it two district, contiguous thermally-insulated

heating zones

21, 23, of which the former (pre-heating) zone 21 is at a considerably higher temperature than the latter (equilibrium) zone 23. The heating elements of both Zones are thermally insulated from the casing 19 by solid insulating material 25; and both ends of the jacket are thermally insulated from the atmosphere by blocks of solid insulating

material

27, 29. The two zones are thermally insulated from each other by an air-space 31 of some 1A; inch thickness between the metal end-plates of the two heatingzones.

As shown in FIGURES l and 2, the part of the apparatus defining the pre-heating zone 21 has an interconnected double J -shaped electrical heating element 33, each leg of which is brazed to a brass block 35 of U-shaped horizontal section. The element comprises an electrical resistance wire packed in a refractory insulating material inside a stainless steel tube and is adapted to produce a treatment temperature of, say, 460

C. Yarns

3, 5 run within the central air-lled space, comprising the pre-heating zone 2i, between the legs of the element 33 and are heated by radiation and by the hot air therein. As can be seen from FIGURE 2, the threading slot i7 tapers inwardly to an inside width of 1A@ inch, and the member 7 is actually shaped to fit closely within the outer part of the slot so as to complete the thermal insulation of this side of the jacket when the yarns are in operating position within it. The entrance to the narrow part of the slot is defined by two solid blocks of

insulating material

39, 41. The slot is also formed through end-block 27, as shown at 37 in FIGURE 2, and end-block 29. It is preferable if there is an air-gap of some 1/s inch Width between the outside of

blocks

39, 41 and the inside of member 7 when the latter is in the closed position, in order that the effect on the temperature of the yarn spaces within the heater of removing mem-ber 7 from the outer part of the slot shall not be too pronounced and in order that the temperature shall rise quickly and directly to the operating temperature when the yarns are inserted.

As shown in FIGURES l and 3, the part of the apparatus defining the equilibrium heating zone 23 has two

parallel metal elements

43, 45, some Mr inch thick and each containing an electric resistance wire packed in a refractory insulating material and each flanked on both sides by

brass plates

47, 49 and 51, 53 respectively. The elements are adapted to produce a treatment temperature of, say 260

C. Yarns

3, 5 run in the air-filled space comprising the equilibrium heating zone 23 between plates 49 'and 51, which are separated by i/li; inch from each other, after having been inserted through the inwardly-tapering slot 17 into operative position within the jacket. The yarns are heated by radiation from the

brass plates

49, 51 and by the hot air between them. The slot is narrowed to inch by means of blocks of solid

insulating material

55, 57. Brass plates @i9 and 51 are connected by a brass strip 59 on the side furthest from the slot.

It is regarded as being most important, for the maintenance of uniform temperature conditions throughout each zone, that heat losses, or mal-distribution, due to convection shall be minimized by good thermal insulation and by efcient distribution of heat throughout each zone. The thermal insulation is dependent, for one thing,

on the width of the threading slot 17 and on the insulating efliciency of the means 7 adopted to block the slot when the yarns are in operative position.

As can readily be understood by persons skilled in the art, the loss of heat by convection will not be so injurious when the heater is mounted horizontally as when it is mounted vertically, as in the former instance a temperature gradient will be established across the vertical diameter of the heater cross-section, i.e. at right angles to the yarn path, whereas in the latter instance, the temperature gradient will be in the direction of the yarn path. In the former instance, the temperature in the heater along the yarn path will be substantially constant; in the latter instance, not. In fact, the difference in temperature between the top and bottom of a vertically-mounted heater having a threading slot 1A: inch wide and no closure therefor may well be as great as 50%, i.e. the temperature at the bottom of the heater will be 50% less than the desired equilibrium temperature. If this is the case, of course, the heat treatment required, e.g. setting of the twist in a yarn, will not be carried out efficiently, if at all.

Eicient thermal insulation of the space containing the heating elements is necessary in the case of verticallymounted heaters for the additional reason that convection effects of the ambient atmosphere on the outside of the heater would otherwise tend to be reproduced in the heater elements themselves, also, and thus bring about a temperature gradient along the yarn path.

Accordingly, the threading slot of the heater has to be of very small width and the space surrounding the heating elements has to be lagged so as substantially to prevent the passage of heat to the exterior of the heater' which is in contact with the ambient atmosphere.

Preferably the equilibrium zone heating elements them-v selves, between which the yarn passes, are also narrowly spaced.

When, as shown, two or more yarns are passed simultaneously through the heater of the invention it is desirable to so guide them into, and hold them in place within, the heater that the yarns are disposed from one anotherY within the plane of the gap between the equilibrium heating elements, in order to avoid more than glancing contact of any of the yarns with either of the surfaces of they elements.

ln addition, the temperature of a zone of the yarnl heater in the vicinity of the yarn path is maintained at a` substantially uniform value throughout the Zone, by the arrangement whereby the heater elements are in heat-con-V ductive contact throughout all or part of their length with massive heat-conducting material, such as the brass in the form of blocks shaped to encompass or lie in contact with the said heater elements, as described with reference to the illustrative apparatus.

The massive heat-conducting material ensures that heat is rapidly conducted in the length direction of the heater; and, when such heater is mounted vertically, the effect of this continuous supply of heat by conduction to all parts of each zone of the heater, is great enough substantially to counteract the effect of the continuous loss of heat due to convection upwards along the yarn space of theA heater.

Naturally, the form of the massive heat-conducting material will depend on the size and shape of the electric heating elements required to be used in conjunction with it. The elements may be either incorporated within the heat-conducting material, or as shown, `attached or positioned in heat-conductive contact with the surface of the said material. In a vertically-mounted heater, as an aid to raising the temperature of the bottom of the heater, or a zone of the heater, to the desired temperature, the electric heating elements may have their heating effect reinforced at the bottom part by the addition of further resistance wires, or by the shaping of the elements themselves in such a way as to give additional heat in that part. For example, the elements, as in the form illustrated, are shaped like a J; or, when in coil form, the coils may be more closely spaced at the bottom than elsewhere along the length of the elements. `In these circumstances, it may be sufficient if the massive heat-conducting material incorporates or is attached to that part of the heating element where the heating effect is reinforced.

As has been referred to above, heating apparatus of the kind under consideration finds a useful application in processes for crimping running yarns by setting false twist which has been inserted in them. The specification of our U.S. application Serial No. 595,543, now Patent No. 2,93 6,567 describes, inter alia, such a process wherein `a rotating twist tube having, for example, a rubber lining or bush, inserts false twist in a yarn or yarns led through the tube and in contact with the bush on one side of the axis thereof, and the successive twisted portions of the yarn are led through a heater to set the twist therein. The present apparatus is very suitable for achieving such twist-setting in this crimping process. In one example of the use of such apparatus, denier multifilament polyhexamethylene adipamide yarn was led through a twisttube such as is described in the specification of the aforesaid U.S. application Serial No. 595,543, now Patent No. 2,936,567 to insert false twist therein, the yarn being heated in the highly twisted condition by passage through apparatus according to the present invention. Under the conditions of twist inserted in the yarn, the virtual denier of the yarn in the apparatus was approximately 150 and its linear speed owing to the amount of contraction occurring, 250 feet per minute, when the yarn was Wound up at 370 -feet per minute. In the form of apparatus used, the first zone, of 4- inches length, was heated by an electrical resistance wire to 680 C. (this being the temperature attained by a thermocouple allowed -to reach equilibrium in the air in the middle of the zone). The second Zone, of 14 inches length, was heated to 250 C. The crimped yarn so set by the illustrative apparatus Was of comparable quality to yarn produced under similar conditions but using a 3 foot elliptical reflector heater at a temperature of 380 C. (this heater having a comparable total power consumption).

In a two-zone heater of the type actually illustrated, which was used in a similar process for false-twist crimping 60 denier or 70 denier mu-ltilament yarns of polyhexamethylene adipamide, the two Zones of the heater were at 460 C. `and 260 C. respectively, with the yarns being wound up at 380 feet/minute (or 370 feet/minute for the 70 denier yarns). The lengths of the two zones were 7% inches and; 14 inches respectively.

It will, of course, be realised that whilst the apparatus as above described, brings about setting of yarn in a dry atmosphere it is possible to inject steam into one or both zones so that the setting is carried out in a humid atmosphere. Equally, the atmosphere within the apparatus may be another inert gas rather than air or steam, Furthermore, the cross-section of the apparatus need not, of course, be box-like, but may be circular or elliptical.

I claim:

1. Apparatus lfor the heat treatment of running yarns passed therethrough comprising: an elongated thermally insulated heating jacket defining within its interior at least one heating zone; said jacket having a threading slot extending longitudinally over one side and communicating with said zone, the slot being of inwardly tapered cross section; insulating block means disposed partially across said slot in transverse relationship adjacent to the inner end thereof; heat conducting material disposed within said zone and of a configuration to provide a passage for the yarn; heating means in contact with said heat conducting material; a thermally insulated closure member which is complementary in shape to said slot, said member being adapted for abutting engagement with the adjacent lateral surface of said slot when in a closed position in the apparatus while the inner surface thereof is spaced from the outside surface of Said insulating block means when in the closed position to provide an air gap therebetween, whereby a leakage path is provided during operation of the apparatus.

2. Apparatus dened in claim 1 wherein said air gap is a maximum of approximately lAz".

References Cited in the file of this patent UNITED STATES PATENTS 1,266,735 White May 21, 1918 2,204,603 Kline et al. June 18, 1940 2,211,141 Lobasso Aug, 13, 1940 2,343,351 Wedler Mar, 7, 1944 2,345,541 Scholze Mar. 28, 1944 2,688,067 Sonnino et al. Aug. 31, 1954 2,820,280 Benn Jan. 21, 1958 2,846,752 Lessig Aug. 12, 1958 2,888,733 Wegener .Tune 2, 1959 2,958,921 Gilchrist Nov. 8, 1960 FOREIGN PATENTS 546,015 Italy July 11, 1956 773,816 Great Britain May 1, 1957