Heating apparatus for an advancing yarn

An apparatus for heating an advancing thermoplastic yarn led over heating ridges along a heated surface. An essential feature of the invention is that the heating ridges can be maintained at a temperature as high as that of the heating surface, in particular at a temperature sufficient for ensuring a self-cleaning effect, without damaging the yarn. If required, the heat flow on the yarn may also be regulated by adjusting the height of the heating ridges and/or by modifying the length of contact with the yarn.

BACKGROUND OF THE INVENTION 
The invention relates to a heating apparatus, in particular an elongate 
body, such as a tubular heater for heating an advancing yarn. 
Such a heating apparatus is used, for example in a false twist crimping 
machine. 
Apparatus for heating synthetic yarns in false twist crimping machines are 
known. In general, they comprise heating rails arranged in elongate 
heating chambers, which are heatable to a certain temperature, and over 
which the yarn can be guided in that it advances over yarn carriers, 
so-called ridges, so as to be heated. 
For drawing and thermosetting synthetic yarns, tubular yarn guide members 
are known. For example, DE-AS 13 03 384 describes a guide member, which is 
looped by the yarn. This yarn guide member has a rotationally symmetric 
configuration and is provided with a bead at its yarn contact end. It can 
be heated from its yarn contact end toward its yarn runoff end to 
temperatures increasing continuously from a yarn drawing temperature to a 
yarn setting temperature, and be configured and arranged such that it can 
be looped by the yarn in a steep coil. This yarn guide member is 
complicated in its structure, and requires for its manufacture a plurality 
of costly operations. In addition, it is expected not to operate with the 
reliability to be met by high-speed processes. 
In modern false twist crimping processes, the yarns advance at a 
considerable speed. The temperatures prevailing in the heating chambers 
are therefore accordingly high, which may result in damage to the yarn, 
when it contacts the heated surfaces of the heater. Furthermore, it is 
difficult to provide a uniform level of the yarn path over the heated 
surface, especially in curved heating chambers, in a simple manner, which 
ensures that the advancing yarn is heated without damage. Moreover, the 
known heating devices do not permit a modification of the predetermined 
curvature or length of a yarn path without great expenditure. 
Since such heating apparatus are also used in the treatment and processing 
of film tapes and filaments, the latter will always be included, when in 
the following reference is made to a yarn. 
A thermoplastic material for the yarn includes in particular polyamide or 
polyethylene therephthalate (PA 6, PA 6.6), but is not limited thereto. 
It is the object of the invention to provide a heating apparatus, which 
allows to operate all structural components at high temperatures, and to 
make effective use in particular of the selfcleaning effects. 
SUMMARY OF THE INVENTION 
The above and other objects and advantages of the present invention are 
achieved by the provision of a yarn heating apparatus which comprises an 
elongate heating surface, means for heating the heating surface, and yarn 
guide means comprising a plurality of yarn carriers mounted in a 
longitudinally spaced apart arrangement along the length of the heating 
surface. The yarn carriers define relatively short axial ranges which 
directly contact the yarn and thereby directly heat the yarn, and axial 
ranges between the yarn carriers which are not in contact with the yarn 
and wherein the yarn is heated by radiation. Also, the yarn carriers are 
thermally connected to the heating surface and constructed so that in 
operation they assume approximately the same temperature as that of the 
heating surface. 
By the described configuration of the yarn carriers and a close thermal 
bonding of the yarn carriers to the heating surface, it has been found 
that the heating surface and the yarn carriers may be maintained at a 
relatively high temperature during operation, preferably at a temperature 
above that necessary for self cleaning, without damaging the yarn. 
As a surprise, it has been found that a danger of burning does not exist 
for the yarn at high temperatures and thin yarns, even when, as is further 
proposed to be advantageous, the height of the yarn carriers is selected 
from about 0.1 mm to 5 mm, preferably from 0.5 mm to 3 mm. The lower limit 
is predetermined by the curvature of the heating surface and the slope of 
the helix, along which the yarn is guided, or the curvature of the heating 
surface, as well the spacing between successive yarn carriers, and must be 
selected such that the yarn does not contact the heating surface itself. 
The following should be pointed out: both the fact that yarn carriers and 
the heating surface have a particularly good heat contact, and the fact 
that the ridges have only a small height relative to the heating surface, 
represent, each for itself as well as jointly, a significant improvement 
over the state of the art. These improvements can be used with advantage 
in any type of high temperature heater, in which the yarn is advanced over 
the heating surface along a curved threadline. A particularly good heat 
contact may also be realized, when heating surface and yarn carriers are 
made integral, or by yarn guides in a highly heat conductive arrangement. 
It is also a further object of the invention to provide a yarn heating 
apparatus, which, in the presence of the aforesaid properties, permits to 
influence in addition the heat transfer to an advancing yarn in each case 
of application. This means, the invention is intended to provide likewise 
a yarn heating apparatus, which enables temperature profiles within wide 
limits in accordance with the necessary heat transfer conditions. In 
particular, the invention is to provide for a heating apparatus, which 
allows to make changes both in the curvature and in the length of the yarn 
path and surface traversed or contacted by the yarn. 
A relative movement of the yarn guides arranged at the inlet and outlet end 
of the yarn path allows to change not only the length of the yarn path, 
but a correspondingly variable width and/or height of the axial regions on 
the heating surface, which are operative as yarn carriers, permits to 
change, in a controllable manner, also the temperature profile of the heat 
transfer that is operative on the yarn. 
Yarn guide ridges that are variable in width permit to vary the dwelling 
time of a yarn on the heating surface. This means that as the heated 
surface, which is contacted by the yarn, is varied in its size, the heat 
transferred to the yarn is changed likewise. In addition, a corresponding 
variation of the contactfree zones extending between the ridges allows to 
also control the profile of the heat transfer. A further possibility of 
variation is given by height-adjustable ridges, which allow to adjust 
uniformly or variably the spacing between the heating surface per se and 
the yarn path. 
In a preferred embodiment, the heater is a tube, on which rings or disks 
are inserted for use as yarn guide ridges. The circumferential surfaces of 
these rings serve as yarn contact or yarn guide surfaces and effect the 
heat transfer to the yarn advancing thereover. Over their circumference, 
the rings may have an even or continuous or a stepwise variable width 
and/or height. The axial spacing between them may be constant and 
invariable, or it may increase or decrease or be otherwise variable in 
direction of the advancing yarn. 
It should be expressly pointed out that it is possible to adapt the heating 
surfaces, which are here illustrated by way of tubes, in their form to the 
particular requirements. Thus, it is also possible to apply the teaching 
of the invention in connection with flat or grooved heaters. 
The rings may be spaced apart from one another by grooves cut into the 
surface of the heater, or they may be arranged on the surface stationarily 
or adjustably. 
The lengths of yarn passage may be varied, in that in direction of the 
advancing yarn, directly preceding or following the heater, yarn guides 
are provided, which are adjustable in their position relative to the 
heater and/or to one another. If need arises, however, these yarn guides 
may also be provided at the inlet end and outlet end of the heater itself. 
Otherwise, with respect to exemplified forms and adjustment possibilities 
of the yarn guides reference should be made to the description. 
In particular, it should be noted that the heating apparatus of this 
invention may be operated in a temperature range, which corresponds to the 
selfcleaning temperature of the heated surface. 
In this connection, the invention avails itself of the recognition that the 
selfcleaning temperature is in the order of approximately 430.degree. C., 
and that the influencing of the heat transfer from the heated surface to 
the yarn being heated subjects the yarn to a lesser temperature of, for 
example, 350.degree. C. 
These measures are advantageous, especially when thermoplastic yarns of a 
lower denier, for example 20 deniers, advance through the heating 
apparatus of the present invention, for example, at a yarn speed of about 
1000 meters per minute. 
In practice, these measures allow to prevent the heated surface from being 
gradually covered as a result of continuously forming sediments from the 
advancing yarn. Thus, it is possible to maintain the heating conditions of 
the advancing yarn substantially constant over the entire yarn length. 
This possibility offers itself, especially when a heating apparatus is 
provided for several yarns to be heated. In this instance, during the 
cleaning phase of one of the yarn heating zones, the other yarn is allowed 
to advance continuously in its associated yarn heating zone, without it 
being possible that the selfcleaning of the first yarn heating zone 
affects the quality of the yarn that continues to advance in the second 
heating zone. 
Likewise, it may be useful to rotate or move the yarn heating zones below 
the advancing yarn at certain time intervals, so as to obtain a regular 
selfcleaning of the yarn heating zones. 
In the following, among other things, a special embodiment of the invention 
is described in more detail, which is employed as a heating apparatus for 
a false twist crimping machine. 
This heating apparatus is described in EP 0 412 429 A2. The advantage of 
this heating apparatus lies, on the one hand, in its high heating 
performance, which is transferrable to the yarn, and allows a short length 
of the heater. The other advantage is its selfcleaning effect. 
It has been found that this selfcleaning effect varies over the length of 
the heater. 
A further object of the invention with respect to this special embodiment 
consists of perfecting the known heater such that it is not necessary to 
clean the heater from caked or cracked residues of the thermoplastic yarn 
material. 
In a special embodiment of the invention, the heater may comprise an inlet 
zone, in which the yarn has only a slight or no contact with the yarn 
carriers as a result of spacing the yarn carriers widely apart from one 
another. Preferably, the inlet zone is provided with only one inlet yarn 
guide, and the outlet zone has only one outlet yarn guide. Moreover, it 
shows to be advantageous, when the inlet yarn guide remains unheated. For 
this reason, it is suggested that the inlet yarn guide has no heat contact 
with the heating surface. As a result, the yarn guide remains essentially 
unheated, so as to prevent thermoplastic material from separating. The 
yarn guide at the outlet end should, however, have a selfcleaning effect. 
It is therefore connected, preferably directly, with the heating surface, 
and arranged at the beginning of the so-called "control zone," which 
follows the inlet zone. 
The control zone is the section, in which the yarn is brought to its 
desired temperature. The control zone accommodates several yarn carriers. 
These yarn carriers are spaced apart from one another equally or variably, 
as is described in the above-referenced EP 0 412 429 A2 publication. 
The use of yarn carriers in the control zone allows to ensure that the yarn 
is guided at an exactly defined distance from the heating surface. To 
ensure moreover that in the inlet zone, the yarn does not come into 
contact with the heating surface, it is also suggested that the heating 
apparatus be provided with a stepped portion between the inlet zone and 
control zone, so that in the inlet zone, the spacing between the heating 
surface and the yarn path is greater, preferably amounts to a multiple of 
that distance which the yarn path assumes from the heating surface in the 
control zone. 
For improving the selfcleaning properties, it is further provided that the 
yarn carriers are mounted on the heating surface as ridges and have a 
highly heat-conductive contact. It may further be provided the ridges and 
the heating surface are made of one piece, i.e., that the heating surface 
consists of ridges and recesses alternating therewith. Each of these 
measures is suitable and destined to ensure that the ridges are heated to 
the same high temperature as the heating surface, i.e., to temperatures, 
which are higher than 300.degree. C. to 350.degree. C. 
The arrangement of the yarn carriers in accordance with the invention 
ensures that the yarn guides are arranged only in the zone, in which the 
selfcleaning is guaranteed on the one hand as a result of the temperature 
assumed by the yarn, and on the other hand by the heater temperature. In 
the control zone, the temperature of the heating apparatus is accurately 
controlled, preferably by a control system. The precise guidance of the 
yarn relative to the heating apparatus allows to ensure in this zone that 
the yarn assumes a predetermined desired temperature. In so doing, the 
variable widths of the yarn carriers with respect to an advancing yarn 
allow to vary the so-called dwelling time of the yarn within wide ranges, 
when the yarn carriers are movable, i.e., the contact surface between yarn 
and yarn carrier is adjusted as a function of the temperatures measured on 
the yarn or on the heater. In the inlet zone, a precise guidance of the 
yarn is not needed. In this instance, use is made of the recognition that 
in the inlet zone, the heating of the yarn occurs with great temperature 
gradients between the heating apparatus and the yarn and, therefore, an 
accurate temperature control of the yarn is neither wanted nor possible. 
The heating of the yarn in the control zone causes that, at first, the 
outer layers of the yarn assume the desired temperature. Required however 
is a uniform heating of the yarn over its entire cross section. This goal 
is achieved in that the control zone is followed by an outlet zone, in 
which the yarn carriers are again arranged widely spaced apart, or that 
they are absent. To prevent the yarn from coming into contact with the 
heating surface of the heating apparatus, it is also preferred in this 
zone that the spacing between the yarn path and the heating surface is 
greater, preferably by a multiple of the spacing which the yarn path and 
the heating surface assume in the control zone. This arrangement of the 
outlet zone ensures that, due to only a slight heat transfer,r heat losses 
are prevented, and the heat supplied in the control zone is distributed 
evenly over the entire cross section of the yarn. 
In the inlet zone, it is possible to accept a great, unsupported length of 
the yarn, since it has shown that in the inlet zone, the tendency of the 
yarn to vibrate is small. A length of 400 mm to 500 mm is possible. 
However, for limiting expenditure, the length should be increased to the 
extent that is necessary for achieving the desired preheating of the yarn. 
The outlet zone is, in any event, shorter than the inlet zone. The length 
of the outlet zone is limited preferably to 300 mm and, in particular, 
should be even smaller. 
The spacing between yarn path and heating surface in the outlet zone and in 
the inlet zone is greater, preferably by a multiple of the spacing in the 
control zone, but is preferably also limited to 5 mm, preferably 3 mm. 
Within the scope of this invention, use may be made in an especially 
advantageous manner of the fact that the contact length of the yarn 
carriers influences the heat transfer. 
The optimization of the heating effect on the yarn is highly significant 
for the quality of the yarn and its texturing in the false twist crimping 
machine. For this reason, it is suggested that the contact length of the 
yarn guides be adjustable. As a result, it is also possible to optimize 
the adjustment of the heating effect on the desired yarn speed and yarn 
diameter (denier). To accomplish this, it will be opportune to design the 
heating apparatus and yarn carriers such that the latter are exchangeable. 
To optimize the heating effect and to adapt same to the speed of the 
advancing yarn and its denier, it further suggested to be advantageous 
that the ratio of contact length of the yarn guidance to the contactfree 
length of the heating apparatus be made adjustable, in particular in the 
region of the control zone. A heating apparatus may have, for example, the 
shape of a tube, which is provided on its circumference with several 
ridges that widen axially in the circumferential direction. These ridges 
may be arranged on the circumference successively and offset from one 
another. This allows to accomplish that the yarn helically looping about 
the tube contacts the ridges, one after the other, in regions, in which 
the ridges have substantially the same length of contact. 
A further embodiment, which allows at any time an adaptation of the heating 
effect to the specific process parameters, in particular yarn denier and 
speed of advance, consists of a heater, which can be varied in its length 
by combined sections. 
In accordance with a further embodiment of this invention, it is possible 
to slip over a heating tube having a substantially smooth surface a sleeve 
or a cage, the inside diameter of which corresponds to the outside 
diameter of the heating tube, and the jacket of which contains identically 
shaped recesses extending therethrough in a line-by-line arrangement. In 
the sleeve, lines of identically shaped recesses are preferably 
diametrically opposed, with lines of differently shaped recesses extending 
preferably next to these lined-up recesses. Preferably, the lines extend 
axis parallel. Arranged between the lined-up recesses are identically 
shaped ridges corresponding to the shape of the recesses and extending 
over the circumference. The sleeve is secured on the heating tube against 
axial displacement, but may be rotated. This results on the one hand in 
the advantage that a gradual rotating of the sleeve on the tube allows to 
guide the yarn always over a clean contact point of the ridges. On the 
other hand, it is possible to heat the yarn within wide temperature ranges 
due to the different configuration of the ridges. Since in the sleeve, 
identically-shaped ridges and recesses are diametrically opposite, or 
repeat at certain angular distances, contact paths are formed for two or 
more yarns. Otherwise, the ridges extending between the lines in the axial 
direction of the sleeve have no significance for the essence of the 
invention.

In the following description of different embodiments of the invention, 
like parts are identified by like numerals. 
A heating apparatus as shown in FIG. 3 consists of a tube 1, hereafter also 
named heating tube. The heating tube 1 accommodates in its interior two 
parallel extending heating resistors or elements 6, which preferably are 
separated from one another and from the inside surface of heating tube 1 
by a suitable insulating material, such as, for example, powdered 
magnesium oxide or magnesium silicate. The heating tube 1 consists of a 
highly heat-conductive metal, such as steel or, preferably, a copper 
aluminum alloy. 
Inserted on heating tube 1 is a plurality of rings or disks 2. As shown 
individually in FIGS. 1 and 2, these disks 2 are circular and have a 
radial slot 5, the inside width of which corresponds substantially to the 
diameter of heating tube 1, and the opposite edges of which extend 
parallel to one another. The outer edge of disks 2 is spherical. Arranged 
in the one front end of disks 2 is a plurality of cavities or recesses 4, 
which are equally spaced apart from one another and from the axis of disk 
2. From the opposite front end of disk 2, a pin serving as a spacer 
extends, at a distance from the disk axis, which corresponds to the 
distance of recesses 4 from the disk axis. 
The disks 2 are placed on heating tube 1, so that pin 3 projecting from a 
disk 2 engages in a recess 4 of an adjacent disk, the disks 2 being 
inserted on the heating tube, preferably with an even angular offset from 
one another, so that the openings of slots 5 and pins 3 surround the 
heating tube in spirals, or overlie one another in a specific pattern in 
the axial direction of tube 1. To secure the rings 2 on tube 1, it is 
possible to insert into slots 5 a spring clip 10, if need be, the legs of 
which lie against the opposite slot edges, and the apex of which is in 
contact with tube 1. 
The spherical edges of disks 2 serve to guide a yarn 7, which is placed via 
an inlet yarn guide 8 against the yarn guide surface of the heating 
apparatus that is formed by the spherical edges of disks 2, and leaves the 
apparatus via an outlet yarn guide 9 that is angularly and axially offset 
from yarn guide 8. This means that yarn 7 loops about the apparatus in a 
spiral, the pitch or inclination of which is dependent on the offset of 
yarns guides 8 and 9 relative to one another. At least one of the yarn 
guides is rotatable relative to the other about the axis of heating tube 
1, so that the length of the yarn path over disks 2 can be varied by 
changing the pitch of the spiral formed by yarn 7. The yarn guides 8 and 9 
are positioned on both sides of slot 5, and the spiral of yarn 7 extends 
in the region of disks 2 outside of slots 5. 
Preferably, the disks consists of a heat-resistant and nonscaling material, 
for example, aluminum oxide or titanium oxide. To increase the abrasive 
resistance of the disk edges, same may be coated, if need be, with a 
suitable metal, and to increase their yarn-friendliness, the disk edges 
may be ground or polished. 
The embodiment of the invention, as shown in FIG. 4, consists of a heating 
tube 1, which is provided with an electric resistance heating wire 6, and 
surrounded by a plurality of rings 2. The rings 2 are fixedly connected to 
heating tube 1, for example by soldering, and they are equally spaced 
apart from one another. However, the rings 2 may also be formed by beads, 
which are formed on the tube at regular distances by upsetting. The rings 
may also be spaced apart from one another by grooves, which are machined 
out of the outer surface of heating tube 1. The radially projecting 
peripheral surface of rings 2 is spherical and of a yarn-friendly quality. 
The rings 2 serve to guide a yarn 7 at a distance over the surface of 
heated tube 1, the yarn path looping preferably spirally about tube 1. As 
schematically illustrated, at both ends of heating tube 1, yarn guides 8 
and 9 are arranged, their offset from one another defining the pitch and 
the length of the yarn path. At least one of the two yarn guides may be 
adjustable relative to the other. The means necessary to adjust this yarn 
guide are state of the art and not shown. 
The embodiment shown in FIG. 5 consists of a heating tube 1, which 
accommodates in its interior an electric resistance heating wire 6, which 
is surrounded over its entire length by a helical yarn guide 2. The 
helical yarn carrier 2 is fixedly connected to tube 1, for example, by 
soldering. Its outwardly directed surface is spherical and of a 
yarn-friendly quality, i.e., it exerts a negligible friction, if possible, 
on the yarn advancing thereover. The yarn advances in a spiral, which is 
opposite to the threads of yarn carrier 2. The yarn is threaded onto the 
helical yarn carrier 2 by means of eyelet-shaped yarn guides 8 and 9, 
which are provided on the inlet and outlet ends of heating tube 1. As in 
the above-described embodiments, it is possible to adjust yarn guides 8, 9 
relative to one another. 
A fourth embodiment of the invention is shown in FIG. 6. Likewise, this 
embodiment includes a tube 1 heated by a heating resistor 6. In this 
instance, the tube 1 is looped by a helical yarn carrier 2, which consists 
of a flexible, if possible, an elastic material. For example, the yarn 
carrier 2 may be a small metal tube with its flat surface lying against 
the heating tube 1, so that an intimate heat contact is present between 
heating tube 1 and yarn carrier 2. The connection between yarn carrier 2 
and the surface of heating tube 1 is by frictional engagement, so that the 
pitch of the yarn carrier 2 helically winding about heating tube 1 may be 
changed, in that one of its ends is displaced relative to its other on the 
surface, thereby changing the pitch and the length of the yarn carrying 
spiral. Any widenings or narrowings resulting the change in the length of 
the spiral can be adapted to the diameter of tube 1 by adjusting the 
spiral ends at the beginning of the surface of tube 1. In FIG. 6, the 
helical yarn carrier 2 is shown in solid lines in an extended position and 
in a compressed position in dash-dotted lined 2a. Any widenings or 
narrowings resulting the change in the length of the spiral can be adapted 
to the diameter of tube 1 by adjusting the spiral ends on the 
circumference of the surface of tube 1. 
In this manner, it is possible to change the length of the yarn path along 
the heating tube. Likewise, the adjustment of yarn guides 8, 9 at the 
inlet and outlet ends of the heating tube allows to change in addition the 
pitch of the path traversed by the yarn. 
The yarn contact heaters described so far offer, among other things, the 
advantages of enabling yarn paths that can be varied within wide ranges. 
Furthermore, they permit to realize variable temperature profiles over the 
lengths of a yarn path by the successive arrangement of several, 
differently heated yarn guides. 
Further shown in FIGS. 7-9 and 11-15 are heating apparatus, in which an 
inlet yarn guide 8 and an outlet yarn guide 9 are arranged at the yarn 
inlet and at the yarn outlet of heating tube 1, and in which the yarn 
guides 8, 9 and tube 1 are rotatable relative to one another in the 
circumferential direction of the tube. 
This may be realized either by rotatably arranged inlet and/or outlet yarn 
guides 8, 9 cooperating with a stationary heating tube 1, or by 
stationarily arranged inlet and/or outlet yarn guides 8, 9 cooperating 
with a heating tube 1 rotating about is longitudinal axis, or by rotatable 
inlet and/or outlet yarns guides 8, 9 cooperating with a rotatable heating 
tube 1. 
In the embodiment of FIG. 7, only outlet yarn guide 9 is rotatable relative 
to the tube, whereas inlet yarn guide 8 is stationary. 
In the embodiment of FIG. 8, the outlet yarn guide 9 formed by a notch 16 
is arranged coaxially and rotatably on the lower end of heating tube 1 and 
can be rotated relative to the tube in a range of rotation 15. 
It is obvious that when outlet yarn guide 9 is rotated relative to the 
tube, the advancing yarn 7 describes a spiral on rings 2, the geometry 
(winding, pitch) of which is dependent on the rotated position of notch 16 
in outlet yarn guide 9. 
For the sake of completeness, it should be remarked that heating tube 1 has 
an electric resistance heating, which receives a heating current via 
electric supply lines 6a. 
As is further shown in FIGS. 7-9 and 11-14, the heating apparatus may have 
at the inlet end of heating tube 1 and/or at the outlet end of heating 
tube 1, respectively an inlet zone 11 and an outlet zone 12, which occupy 
a greater radial distance from advancing yarn 7 than the surface of 
heating tube 1. 
Arranged between the inlet zone 11 and the outlet zone 12 is a control zone 
13, which has a further characteristic in the present instance. 
As can be noted to this end, among other things, from FIG. 9, the inlet 
yarn guide 8 and outlet yarn guide 9 are rotatable relative to heating 
tube 1, whereby a sector angle is formed on the surface of rings 2, which 
is covered by yarn 7 due to the range of rotation 15. As a result thereof, 
a range of possible contact surfaces forms between the yarn and the rings. 
Consequently, the yarn 7 can advance along desired points within the 
predetermined sector angle, depending on the particular rotated position 
of yarn guides 8, 9 and tube 1 relative to one another. 
In the sector angle covered by yarn 7, the rings have a width, which varies 
in circumferential direction. This means, the width B of a ring changes as 
a function of a circumferential coordinate u and by a function B(u), which 
may each time be predetermined. In this instance, the function is linear. 
Further shown in FIG. 9 is the characteristic that over the possible range 
of contact, rings 2 have a height H which varies in the circumferential 
direction. This means that the height H is a function of circumferential 
coordinate u, which is indicated accordingly at H(u). 
In the embodiment of FIG. 9, the width B of the rings increases in that 
circumferential direction, in which the height H of the rings decreases. 
One can therefore expect that as the contact time of yarn 7 on the rings 
increases, due to the increasing ring width B, the heat flow to the yarn 
increases likewise in the contactfree axial ranges between rings 2, due 
the to simultaneously decreasing spacing between yarn 7 and the tube 
surface. 
Supplementing the foregoing, FIGS. 7 and 8 show that in the sector angle 
covered by the yarn, the rings 2 may have a height varying in the 
circumferential direction, when the width of rings 2, namely, the ridge 
width does not change in the circumferential direction. 
These two embodiments of the invention may exist both in combination with 
one another and separately from one another. 
It should further be remarked that the rings may also be formed in that 
annular grooves are machined out of the tube surface, so as to leave rings 
in accordance with the invention, over which yarn 7 advances. 
In operation, heat is transferred from heating tube 1 to yarn 7, on the one 
hand, on the contact zones that are formed by rings 2 with yarn 7. 
Furthermore, heat flows to yarn 7 in the axial ranges between rings 2 that 
are not contacted by the yarn. Since the bottom of the annular grooves 
between rings 2 has a distance from the advancing yarn of only few 
millimeters, for example, starting with about 0.5 mm and increasing to 
about 3 mm, it can be assumed, in view of the heating temperature of 
heating tube 1 of about 300.degree. C. or higher, in particular 
temperatures in the order of the selfcleaning temperature, that a relevant 
flow of heat is also present in the noncontacted axial ranges. 
Consequently, the flow of heat acting as a whole on the yarn becomes a 
function of the respectively adjusted yarn path geometry with respect to 
the tube geometry, since the lengths of contact and the noncontacted axial 
ranges are, as is the ring height, dependent on the position of inlet yarn 
guide 8 or outlet yarn guide 9 relative to heating tube 1. 
Thus, it is possible to adjust the respectively transferred heat flow very 
sensitively. Already the slightest changes in the rotated positions 
relative to one another will effect noticeable improvements of the heat 
being effective as a whole on a yarn portion of a predetermined length. 
The invention avails itself of this recognition by the practical example 
applied to a false twist texturing machine, which will be described in 
more detail below. 
As is further shown in FIG. 10, several rings 2 of this invention may be 
arranged off center with respect to tube axis 17, it being advantageous to 
offset the rings relative to one another, each in pairs, by 180.degree.. 
The last-described further development of the invention offers the 
additional advantage that the heating apparatus is symmetric to tube axis 
17, thereby making it suitable for treating and processing a pair of 
advancing yarns 7.1, 7.2. 
Shown in FIG. 11 is a heating apparatus 13, which is preceded by feed rolls 
18. Subjacent heating apparatus 13, is a cooling zone, illustrated as an 
elongate cooling plate 19, as well as a false twist unit 20 and feed rolls 
21. 
As is further shown in FIG. 11, the inlet yarn guide 8 and outlet yarn 
guide 9 are adjustable relative to one another or relative to heating tube 
1 as a function of the yarn temperature measured at the outlet end of 
heating apparatus 13. To this end, a temperature sensor 22 arranged in the 
outlet region of heating tube 1 is used, which supplies an output signal, 
so as to adjust, as a function of the temperature, inlet yarn guide 8 or 
outlet yarn guide 9, each by means of a stepping motor 23. It should be 
expressly stated that the measuring signal of temperature sensor 22 may 
also be superposed by a yarn tension signal, which is generated by a 
tensiometer 24 downstream of the heating apparatus. 
Among other things, the present invention offers the significant advantage 
that it allows to adjust the respectively effective heat transfer from the 
heating apparatus to the yarn extremely sensitively in the sense of a 
process optimization, and that moreover it allows to precisely control the 
yarn temperature, so as to attain an optimal yarn quality over the entire 
yarn length. 
Shown in FIGS. 12-14 are supplemental embodiments of the invention. 
In these embodiments, without limiting the invention thereto, two yarn 
heating zones 25 are arranged on each heating apparatus 1. 
In each of yarn heating zones 25, several ridges 2 are mounted on the 
heated surface transversely to the direction of the advancing yarn, the 
height of the ridges extending beyond the heated surface by at least 0.1 
mm, however, no more than 5 millimeters. 
It is important that the height of ridges 2 above the heated surface 
amounts to no more than about 5 millimeters, so as to make use, 
individually or simultaneously, of the inventive advantages of this 
heating apparatus, in particular its selfcleaning and its sensitive 
controllability. 
In all embodiments, the yarn heating zone is curved convexly in direction 
toward the yarn, thereby making it possible to guide the yarn over the 
yarn heating zone along a spiral line. 
The tube may be constructed as a body of rotation, a section, or a segment 
of a body of rotation, so as to realize in a simple manner a yarn path 
along a spiral line. 
Within the scope of the present invention, a yarn heating zone is 
understood to be that range of the heating apparatus, which permits a 
relevant heat transfer from the heating apparatus to the yarn. 
In the embodiment of FIG. 13, this may be the yarn heating zone on the 
left, or even a single threadline, when, for example, an adjustability of 
the yarn path relative to the heated surface is not provided. 
However, as shown in FIGS. 12 and 14, as well as in the right-hand yarn 
heating zone of FIG. 13, this may also be a sector angle, in which a yarn 
can be guided relative to the heated surface. 
As is further shown to this end in FIG. 12, it is possible to design and 
construct both yarn heating zones 25a, 25b identically. In this instance, 
without limiting the invention to this variant, it is realized that the 
width B of rings 2 changes in circumferential direction. More 
specifically, in accordance with the invention, this can be of advantage, 
alone or in combination with a height H of the rings that varies in the 
circumferential direction. 
As is further shown in FIG. 13, it may also be useful to provide only one 
of the yarn heating zones with rings, the width B of which changes in 
circumferential direction, and analogously to the foregoing description, 
likewise their height H, whereas the ring width B in the other of the two 
heating zones is maintained constant. 
In this instance, it will not be necessary to provide for a relative 
adjustability between inlet yarn guides 8 or outlet yarn guide 9 and yarn 
heating zone 25, since it can be presumed that the heat transfer from the 
heated surface to yarn 7 is constant over the entire range of the yarn 
heating zone. 
However, it should be expressly stated that for certain applications, it 
may also be useful to vary the height H of the rings in circumferential 
direction, and that naturally it will then be useful to provide for a 
relative adjustability between the heated surface and the advancing yarn. 
As is shown in the embodiment of FIG. 12, it will be especially useful in 
the presence of identical yarn heating zones, when these yarn heating 
zones are associated each with a synchronously movable inlet yarn guide 8 
or outlet yarn guide 9, the yarn guides 8 or 9 being located in the end 
regions of rotatable yarn guide levers 26. 
The synchronous movability is easy to realize via a corresponding gear 
mechanism. Such a gear mechanism, however, is state of the art, and is 
therefore not described in more detail. 
In this manner, it is also easy to attain an identical yarn quality of two 
yarns advancing over the heating apparatus. 
As is shown in FIGS. 15a-e, it is possible to arrange two yarn heating 
zones 25a, 25b diametrically opposite to one another, and to arrange in 
this instance inlet yarn guides 8 or outlet yarn guides 9 on their 
respective yarn guide levers 26 such that the yarns advance over locations 
with identical operating conditions. 
It is easy to imagine that within the scope of the present invention, it 
will also be possible to change the width B of the rings in steps. This 
means that the width B is piecewise constant, and increases at certain 
circumferential coordinates stepwise, for example, from a smaller width to 
a larger width. 
The foregoing statement applies likewise to a change in height H of the 
rings. It is intended that the invention also includes a stepwise change 
in the height H in circumferential direction, so as to obtain, for 
example, ranges of the yarn path, in which a slight lateral fluctuation of 
the contact zone between the yarn and ring leaves the heat transfer 
between the heated surface and the yarn substantially unaffected. 
To this end, it may turn out to be advantageous, when rings of variable 
width and/or height are offset from one another in circumferential 
direction such that, in expectation of the possible yarn path, the 
respectively effective contact zones permit substantially identical 
contact times or yarn distances from the outer surface of the tube. 
Naturally, this applies likewise to rings, the height H of which is changed 
stepwise. 
In particular, it should be pointed out that a stepwise changing ring 
height H will be easy to realize, when rings are provided with sectors, 
each having a constant radius per sector. The zone of transition between 
two adjacent sectors of different radii will then have to be designed in a 
yarn-friendly manner, i.e., it will be necessary to round sudden or 
angular changes of the respective ring radius toward the adjacent ring 
radius in circumferential direction, so as to avoid damage to the yarn. 
As is further shown in FIGS. 15a-c, it may be useful to make the outer 
contour of rings 2, at least in sections, substantially elliptical. In 
this instance, it is also proposed to have two yarns yarn 7 advance over 
opposite locations of the ellipses. 
These locations may be opposite both with respect to the long axis and with 
respect to the short axis, as is shown in FIGS. 15a and 15b. 
One of the most effective possibilities with respect to an adjustment of 
the yarn path, however, is shown in FIG. 15c, in which one of the yarns 7 
advances exclusively within a quadrant extending between the long semiaxis 
and the short semiaxis of the ellipsis. 
As one can see, in this instance the heat transfer from heating tube 1 to 
the yarn increases or decreases continuously over the entire yarn length 
between inlet yarn guide 8 and outlet yarn guide 9. In the present 
embodiment, a very large spacing exists between the yarn at inlet yarn 
guide 8 and heating tube 1, which decreases rapidly along the yarn path in 
direction toward outlet yarn guide 9, and assumes its smallest value at 
yarn guide 9, so that the heat transfer increases continuously from inlet 
yarn guide 8 to outlet yarn guide 9. 
Thus, an extremely effective controllable heat transfer becomes possible 
over the entire length of the yarn advancing between inlet yarn guide 8 
and outlet yarn guide 9, since the entire range of ridge 2 is available 
between the minimum spacing in the region of the small semiaxis of the 
ellipsis and the maximum spacing in the region of the long semiaxis of the 
ellipsis. 
Within this possible line of yarn contact, it is therefore possible to 
expect the optimally possible heat transfer at a certain relative position 
between inlet yarn guide 8 and outlet yarn guide 9, a continuously 
increasing heat transfer from the tube to the yarn being made possible in 
this instance. 
Consequently, in this embodiment, "two opposite locations of the ellipsis" 
are understood to be two circumferential areas of the ellipsis, which are 
diametrically opposite with respect to the intersection of the long and 
the short axis of the ellipsis. 
Furthermore, FIGS. 15d and 15e show eccentrically arranged ridges 2. The 
ridges 2 are circular, the center of the circle of ridge 2 being offset 
from the center of circle of tube 1 by an eccentricity 27. 
The inlet and outlet yarn guides for each yarn are arranged separately, 
each on a yarn guide lever 26, and they are circumferentially rotatable 
with respect to the center of ring 2 in the sense of having the same 
effect on the heated yarn. 
In this manner, it is accomplished that upon an adjustment of the inlet 
yarn guides 8 or outlet yarn guides 9, the heat flow to both yarns is 
influenced to the same extent. 
As is shown additionally in FIG. 15e, which illustrates a situation 
corresponding to FIG. 15d, but rotated by 180.degree., it is thus possible 
to obtain an optimal influencing of the heat transfer from heating tube 1 
to yarn 7. 
Whereas in FIG. 15d, in the region of inlet yarn guide 8, the entering yarn 
assumes a relatively great distance from the heated surface of heating 
tube 1, while the exiting yarn is at a relatively small distance 
therefrom, the conditions are exactly inverted in the case of FIG. 15e. 
In the latter, the entering yarn is relatively strongly heated in the 
region of inlet yarn guide 8, since it assumes only a very small distance 
from the heated surface of heating tube 1, whereas the exiting yarn 
assumes a relatively great distance from the heated surface in the region 
of outlet yarn guide 9. 
More specifically, relevant with respect to the heat transfer from the 
heated surface to the yarn is not only the average spacing between the 
heated surface and the yarn along its path between the inlet and the 
outlet end of the heating apparatus, but also, as is further recognized by 
the invention, the fact that the heat transfer from the heated surface to 
the yarn increases disproportionately, as the yarn approaches the heated 
surface. 
For this reason, the rings as provided by this invention permit to operate 
the heated surface easily at selfcleaning temperatures, whereas the 
temperatures being operative on the yarn enable a heating without damage. 
Furthermore, the invention makes it possible to process filament yarns of 
different deniers, for example 20 denier and 40 denier, respectively, with 
the same heating apparatus and at the same time, provided the relative 
position between the advancing yarn and the heated surface is adjusted 
accordingly. 
This means that in heating apparatus having several yarn heating zones, it 
is also quite possible that one of the yarn heating zones is out of 
operation, while another yarn heating zone is in operation. 
Accordingly, it is possible to realize with one and the same heating 
apparatus and without changing or adjusting the temperature of the heated 
surface, different heat flows to different yarn qualities by only 
selecting the relative position between the yarn path and the heating 
apparatus. 
The following description of the Figures relates in particular to FIGS. 
16-18. Wherever the Figures require a special description, such will be 
expressly noted. 
The heating apparatus is used preferably in a false twist crimping machine. 
Such a false twist crimping machine is described, for example, in DE-PS 37 
19 050, and comprises a plurality of feed yarn packages, from which a 
plurality of yarns are unwound, heating devices, over which each yarn 
advances, cooling devices, over which each yarn advances, a false twist 
unit, which imparts to the yarn a temporary twist, as well as feed and 
delivery rolls, which withdraw the yarn from the supply packages, or from 
the false twist unit. Subsequently, each yarn is wound on a takeup 
package. The illustrated heating devices refer to the aforesaid heater, 
which is arranged in the false twist zone. 
The illustrated heating devices 30 are tubular. The yarn 7 advances first 
through an inlet yarn guide 8 and contacts then the circumference of the 
tube. The yarn is guided over the tube with an axial and with 
circumferential components by a yarn guide 9 at the outlet end. The yarn 
guide 9 is a disk rotatable about the tube axis and has a yarn guide notch 
16. FIGS. 16 and 18 show, in a simplified manner, an aligned position of 
inlet yarn guide 8 and notch 16. FIG. 17 shows--as can be applied likewise 
to the embodiment of FIG. 18--that disk 9 is rotated such that the yarn, 
as aforesaid, is guided over the tube both with an axial and with 
circumferential components, thereby describing a steep helix. The rotation 
of disk 9 allows to adjust the looping of the yarn about the tube in 
circumferential direction. The looping is synonymous with a curvature of 
the yarn. Therefore, the looping permits the yarn to totally contact the 
tube or the yarn carriers attached thereto. These yarn carriers are 
described in more detail below. 
The heating device consists of three sections, namely an inlet zone 11, a 
control zone 13, and an outlet zone 12. Above inlet zone 11, the yarn 
advances through inlet yarn guide 8, as well as a first yarn carrier 31.1 
of control zone 13. In this region, the heating surface directed to the 
yarn, i.e., the jacket of inlet zone 11, assumes from the yarn a distance 
which amounts to a multiple of the distance that the yarn assumes from the 
heating surface, i.e., the axial surface ranges of control zone 13 
extending between yarn carriers 31. The spacing between yarn guide 8 from 
the first yarn carrier 31.1 of the control zone amounts likewise to a 
multiple of the spacing of the yarn carriers in the control zone. In the 
latter zone, lengths of up to 500 mm can be accepted. The length in this 
zone is greatly dependent on the tendency to vibrations. Preferably, the 
length of inlet section 11 is selected smaller, so as to permit an 
efficient preheating of the yarn. 
The heating apparatus is heated by a resistance heater in the form of a 
heating tube 1. Indicated at 6a are the electrical supply lines of the 
resistance heater. The resistance heater is constructed as a heating 
cartridge 1, and extends over the entire length of the heating apparatus, 
i.e., over inlet zone 11, control zone 13, and outlet zone 12. 
The temperature control system of the heating apparatus comprises a 
temperature sensor, which detects the effective actual temperature of 
control zone 13. This temperature is equalized. The control zone has 
therefore a very accurate temperature control. 
Arranged in control zone 13 is a plurality of yarn carriers 31. All of 
these yarn carriers 31, including first yarn carrier 31.1 are constructed 
as ridges, which extend over the circumference of the control zone. These 
ridges have a certain predetermined distance and have a certain height 
over the remaining surface range of control zone 13. The number of the 
yarn carriers is determined by the tendency of the yarn to vibrate, as 
well as the heat transfer. The height of the ridges relative to the 
surface of the control zone is selected preferably small, and amounts at 
most to 3 mm. Preferably, it is smaller than 1.5 mm. 
The yarn advances over the outer circumference of the yarn carriers. In so 
doing, the yarn contacts the outer circumference over a certain length. 
This length is likewise decisive for the heat transfer. 
To protect the yarn, this length of contact is selected short, it being 
necessary to make a compromise with the requirements of the heat transfer. 
The axial distance of the yarn carrier influences likewise the heat 
transfer. As a whole, a ratio of contact length to spacing of yarn 
carriers of 1:5 may be applied. Preferably however, this ratio is smaller, 
in particularly smaller than 1:10. 
The distance from the heating surface, i.e., the surface of the inlet zone, 
amounts to 3 to 10 times the height of ridges 31, but is preferably less 
than 10 times. With respect to this, the illustrations in the drawing are 
not in a true scale. 
In the outlet zone, the yarn advances again over only few yarn carriers, 
namely outlet yarn carrier 31.3 of the control zone, as well as the 
aforesaid disk 9 with its yarn guide notch 16. The spacing between the 
yarn path and the surface of outlet zone 12 is again by a multiple larger 
than the height of yarn guide ridges 31 relative to the surface of the 
control zone. Also in this instance, the same rules of proportioning apply 
as to inlet zone 11. As a whole, however, the spacing of the yarn carriers 
in the outlet zone is smaller than in the inlet zone. The spacing of the 
yarn guides amounts to 300 mm and is preferably smaller. It should be 
mentioned, that in practice the illustrated heating apparatus is enclosed 
by an insulating cage, which has a slot for threading the yarn, and which 
forms a peripheral gap or passage relative to the control zone, in which 
the yarn is guided. It is also possible to heat two yarns on one heating 
apparatus by arranging one pair each of inlet yarn guides 8 and yarn guide 
notches 16 in disk 9. 
If possible, yarn guide inlet 8 has no contact with the heating apparatus, 
thus preventing yarn guide 8 from being heated. Therefore, also absent is 
a formation of sediments on yarn guide 8, which develop when the yarn is 
heated. As aforesaid, the outlet yarn guide of inlet zone 11 is the first 
yarn carrier 31.1 of control zone 13. It is a ridge as are the remaining 
yarn carriers 31.1, 31.2, 31.3 of the control zone. These ridges are 
machined out of the jacket or surface of the control zone. They are 
therefore in a highly heat-conductive contact with the heating apparatus. 
Their small height ensures that the control temperature is also present in 
the contact surfaces, thereby guaranteeing that the heater temperature, 
which is higher than 300.degree. C., and selected so high that adhering 
yarn remnants are caused to crack and burn, exists even in the contact 
surfaces of ridges 31.1, 31.2, 31.3. Therefore, these yarn carriers have 
good selfcleaning properties. 
The outlet yarn guide, i.e., disk 9 with yarn guide notch 16, is arranged 
for rotation on cartridge 1 of the heating apparatus. As a result, it is 
ensured that the temperatures in heating cartridge 1 extend likewise to 
disk 9, so that good selfcleaning effects can be expected at this end. 
A special characteristic of the embodiment of FIG. 18 is the 
circumferential configuration of the ridges serving as yarns carriers 
31.1, 31.2 and, possibly, 31.3. In the circumferential direction, the 
ridges have an increasing axial extension, the narrowest location, as one 
might note from FIG. 18, being not exactly on a surface line, but 
essentially on a line, which is substantially parallel to the contact line 
of the yarn, it being possible to change this contact line of the yarn. In 
so doing, it will be necessary to select a contact line corresponding to 
normal operating conditions. It will then be possible to rotate in FIG. 18 
about the axis of the heating apparatus not only the outlet yarn guide in 
the form of disk 9 with yarn guide notch 16, but also inlet yarn guide 8. 
This allows to shift the yarn path on the circumference of the heating 
apparatus to a range, in which the contact length of the yarn guide ridges 
31 has a desired dimension, and in which there is a desired ratio of 
contact length to unsupported guide length between the ridges. This allows 
to influence the heat transfer and, likewise, the smooth run of the yarn. 
On the other hand, a too great contact length will lead to considerable 
yarn frictions, which is undesired for the protection of the yarn. 
Shown in FIG. 19 is a blank 32 of a sleeve 33 in its unrolled state, which 
contains successively lined-up recesses 34, 35, 36, 34', 35', 36'. The 
recesses of each row are of the same shape and equally spaced apart. 
Formed between the recesses are ridges 37, 38, 39, 37', 38', and 39', 
which extend transversely to the blank and will be described in more 
detail below. The connecting ridges extending in the axial direction of 
blank 32 between each row of recesses are not relevant for the essence of 
the invention. 
As shown in FIG. 20, the blank 32 of FIG. 19 may be formed to a hollow 
cylinder and be slipped as such over a heating tube 1, the inside diameter 
of the hollow cylinder corresponding to the outside diameter of the 
heating tube. The cylinder, hereafter sleeve 33, is secured on heating 
tube 1 against axial displacement, but can be rotated about same, its 
rotation, if necessary, being dependent on the release of a blocking 
device known per se, but not illustrated in the Figure. In the illustrated 
embodiment, the recesses 34 extend in a line parallel to the axis of 
heating tube 1, and form between them equally wide ridges 37. The ridges 
37 serve as guide ridges for a yarn 7 (which other than shown in the 
Figure for the sake of simplification, advances in a spiral along the 
cylinder), and are equally wide. The fact that sleeve 33 can be rotated 
about heating tube 1, offers the possibility of having yarn 7 advance over 
the circumferentially extending range of ridges 37, each time over a clean 
place, thereby further increasing the selfcleaning effect of the ridges, 
which is given per se in accordance with the above-described temperatures. 
The line of recesses 34' shown in FIG. 19 is diametrically opposite to 
recesses 34, and serves as a yarn path for a second yarn 7'. 
Adjacent to the line of recesses 34 is a line of trapezoidal recesses 35, 
between which wedge-shaped ridges 38 extend. Diametrically opposite to 
this line is an identical arrangement of trapezoidal recesses 35' and 
wedge-shaped ridges 38'. Thus, it is possible to change the length of the 
heating surfaces being in contact with the yarn by a simple rotation of 
sleeve 33 about heating tube 1. 
Finally, the illustrated embodiment of sleeve 33 is provided with a further 
variant of lined-up recesses 36. Same are recesses that a relatively small 
in axial direction, but leave wide connecting ridges 39 between them, 
which offer as yarn guide ridges a larger heating surface to a yarn 7. 
Corresponding to the other recesses, also in the case recesses 36 a 
diametrically opposite line of recesses 36' with corresponding ridges 39' 
is provided, which form a second yarn guide path. 
The radial spacing between the surface of heating tube 1 and the surface of 
the ridges corresponds to the aforesaid dimensions, and is in a preferred 
range from 0.5 to 5 mm, preferably 0.50 to 3 mm. 
The sleeve 33 may be provided with differently shaped recesses, so as to 
meet with specific operating conditions. 
Further embodiments of the invention are shown in FIGS. 21 and 22. Common 
to these embodiments is that the tubes 1 carrying the yarn guide ridges or 
rings 2, are composed of sections. 
In the embodiment of FIG. 21, the sections consist each of a segment 1a' 
having a larger diameter and a segment 1b' having a smaller diameter, the 
latter corresponding to the inside diameter of segment 1a' with the larger 
outside diameter. Suitably, threads G are cut into the inner surface of 
segment 1a' with the larger outside diameter, and into the outer surface 
of segment 1b' with the smaller outside diameter. These threads allow to 
interconnect the individual tube sections. If need be, the screw 
connections may be secured by counternuts K, thus permitting a precise 
adjustment of the position of sections relative to one another. 
Provided on the outer circumference of each segment 1a' with the larger 
diameter is a yarn carrier 2, which may be designed and constructed in 
accordance with the above-described embodiments, but is schematically 
indicated as a simple ring 2 in FIG. 21. The ring 2 may surround segment 
1a' coaxially or, however, it may also be arranged off center. It may have 
an identical width over its entire circumference, or gradually or stepwise 
increasing widths. The outer surface of ring 2 may be interrupted by at 
least one axial groove (not shown), thus forming on tube 1 by a 
corresponding adjustment of rings 2, in addition to the spacings between 
rings 2, zones, which are not contacted by an advancing yarn 7. 
With a corresponding configuration of rings 2, this embodiment of the 
invention has the advantage that by the rotation of tube sections, 
depending on the width of the individual rings 2 and their spacing between 
one another, it becomes possible to vary yarn contact lengths and 
contactfree zones within wide ranges. 
Moreover, in the sense of the above-described embodiments, it is further 
possible to make the circumference of rings 2 eccentric to the axis of 
sections, or to provide steps over the circumference, so as to guide yarn 
7 at a variable distance from the surface of sections. Otherwise, 
reference is made to the embodiments of FIGS. 1-20. 
The embodiment shown in FIG. 22 differs from that of FIG. 21 in that it is 
provided in the place of stepped tube section, with internal and external 
sleeves 1b' and 1a' respectively, which can be screwed together by means 
of outside or inside threads and be secured in their position, if need be, 
by counternuts K. The outer sleeves 1a' are provided each on their surface 
with a ring 2 serving as a yarn carrier, the rings 2 being illustrated by 
way of example with a width that increases continuously in the axial 
direction of the tube consisting of sleeves 1b' and 1a'. 
Otherwise, the foregoing description of the other embodiments applies 
likewise to this embodiment of heating apparatus and its yarn guides 
regardless of their configuration. 
The present invention enables the optimal use of selfcleaning properties of 
a heating apparatus with a simultaneously good heating behavior, in 
particular in false twist crimping machines.