DRAFT UNIT FOR SYNTHETIC FIBERS

Abstract: The invention realizes a draft unit (1; 50) for synthetic fibers consisting of an electric motor (3) that drives the rotation of a draft cylinder (2). Said cylinder consisting of a first tubular cylindrical element (14) on which the fibers (F) to be drafted are wound, splined firmly to the protruding shaft (9) of the motor, a second tubular cylindrical element (15) positioned coaxially inside said first tubular cylindrical element (14) and having one end flanged to the front shield (6; 53) of said motor (3), an inductor (16) located on the outside of said second tubular element (15), means (36) for reading the temperature of said first tubular cylindrical element (14). The inductor (16) is composed of a foliated pack (30) splined on the outside of said second tubular element (15) and is provided with longitudinal external slots (31) which hold electric conductors (32) wound in a manner basically parallel to the longitudinal axis (4) of the inductor.

Description: DRAFT UNIT FOR SYNTHETIC FIBERS The invention concerns a draft unit that is particularly suitable for application to spinning machines for synthetic fibers. It is known that in order to produce threads of synthetic fibers, special spinning machines are used consisting of an extrusion unit for the particular polymer, which is drawn into filaments by being forced through special spinnerets. Past the spinnerets are a number of draft units arranged in sequence one after the other, that progressively draft the filaments as they come out of the spinnerets, so as to produce a thread having the required count. Each draft unit is composed mainly of an electric motor that causes a draft cylinder to rotate. The filaments that come out of the spinnerets are wound around the cylinder. Depending on the case, drafting can be hot or cold. If the filaments are drafted hot, the known technique provides for heating the draft cylinder by means of the eddy currents induced in the cylinder when it rotates within the magnetic field generated by an inductor placed inside it, that is powered with sinj-r s-phase voltage at high frequency. Some systems of the known type include a draft cylinder that is composed of a first tubular cylindrical element fastened coaxially to the outside of the motor shaft that drives its rotation, and a second tubular cylindrical element placed coaxially inside the first. The second tubular cylindrical element has one end fastened to the casing of the motor and on the outside supports an inductor wound in the form of a bobbin. When the electric motor causes the draft cylinder to rotate, the first tubular element, commonly know as a "godet", cuts the flow lines of the magnetic field created by the inductor and voltage is thereby induced inside it that makes currents circulate in a longitudinal direction, heating it. To give better magnetic properties to the godet, it is made of a steel pipe, covered on the insido with a copper jacket. Experts in the sector know that if drafting has to be done hot, the ideal conditions for drafting are when the temperature of the godet reaches a certain predetermined value, but above all if this predetermined temperature is maintained along the godet. For this reason, a sensor is inserted in the godet and, depending on the temperature reading, it sends a signal to an external control unit that, by varying the current in the inductor, tends to maintain the temperature of the godet. In draft units of the known type in which the inductor consists of a single toroid winding, some difficulty is encountered in maintaining the temperature of the godet, especially if it is very long. To overcome this problem, some manufacturers divide the winding of the inductor into several toroid windings arranged axially, one next to the other. This produces a number of bobbins, each of which affects only one part of the entire surface of the godet that is thereby ideally divided into a number of ring- like bands equal to the number of bobbins. This makes it easier to maintain the temperature in each zone by varying the current that supplies the individual bobbins and thus it is possible to maintain, over the length of the godet a temperature that more closely approximates a linear progression. In draft cylinders made as described above, to read the temperature on the surface of the godet, axial holes are drilled through it, one for each bobbin into which the inductor is divided, long enough to reach the point corresponding to the center point of the respective winding. A thermocouple is inserted in each hole and connected to a rotating transducer placed coaxially on the shaft of the motor and connected electrically to an external control unit. On the basis of the temperature read in each zone of the godet, this control unit modifies the supply conditions of the relative winding of the inductor to correct the temperature so as to maintain it as constant as possible. Draft units with the inductor wound like the known type described above have a number of drawbacks, also known. A first drawback consists of the fact that the air gap across which energy is transferred from the inductor to the godet, is limited to the two narrow ring-like bands that mark off the second tubular element on which the inductor is wound. Due to the limited surface of the annular bands, they easily become saturated and the magnetic flow produced by the inductor cannot cross the air gap any longer and is dispersed in the air. This makes it necessary to supply the inductor with higher currents that create high heat, especially in the zones around the ends of the godet, which is detrimental to the linearity of the curve of distribution of the temperature along its length. Another disadvantage is that the holes drilled axially through the thickness of the godet to house the thermocouples, are deep holes with a small diameter and therefore are expensive and difficult to drill. A further handicap consists of the act that the motor shaft has to provide an axial hole for the passage of the wires that connect each thermocouple to the transducer. It is clear, also, that the costs of producing the motor also increase. Last but not least, the rotating transducer is mounted coaxially on the motor shaft, and this increases the number of dynamic components that make up the draft unit which, in addition to increasing the manufacturing cost of the unit, conspire as well to reduce its reliability. This invention intends to overcome all the above drawbacks. It is one of the primary aims of this invention to develop a draft unit for synthetic fibers with the draft cylinder provided with an internal heating inductor that has a simpler design that the inductors that are used in drafts units of the known type. Another aim of the invention is to produce a draft unit that, with respect to the known type of draft units, makes it possible to achieve more accurate control of the temperature throughout the draft cylinder. It is another aim of the invention to produce a draft unit in which the inductor creates a more uniform and better distributed electromagnetic field in the draft cylinder than that which is found in the draft units of the known type. Another aim is that the draft unit covered by the invention be of a simpler construction than the draft units of the known type available on the market. Not the least of the aims is that the draft unit of the invention have fewer components than the known type and thus be more reliable in its operation. The aims mentioned are achieved by the invention of a draft unit for synthetic fibers that, according to the main claim, includes: - an electric motor complete with casing, front and rear shields, at least one fan unit and an impeller with protruding shaft constituting a longitudinal axis of rotation; - a draft cylinder consisting of: • a first tubular cylindrical element on which the fibers to be drafted are wound, splined firmly to said protruding shaft; • a second tubular cylindrical element positioned coaxially inside the first tubular cylindrical element and having one end flanged to the front shield of the motor; • an inductor placed outside said second tubular element; • means for reading the temperature of said first tubular cylindrical element; and is characterized in that the inductor is composed of a foliated pack splined onto the outside of said second tubular element and provided with longitudinal external slots which hold electric conductors wound in a manner substantially parallel to the longitudinal axis of rotation. According to a preferred form of construction of the invention, the means used to read the temperature of the first tubular cylindrical element on which the fibers to be drafted are wound, commonly known as a "godet", include an infrared thermocouple housed in an intermediate flange located between the second tubular element and the front shield of the motor. The sensitive end of the thermocouple faces upward toward the surface of the ring adjacent to it that forms the base of the godet and is connected electrically to an external device for reading and control of the temperature. A special conduit conveys compressed air into the space between the sensitive end of the thermocouple and the surface of the godet facing it to maintain this space free of impurities that could interfere with the reading. Advantageously, the air gap runs along the entire length of the godet with lower values than those that are found in the known products. As a consequence the draft unit that is the subject of this invention has lower energy consumption with respect to the former. The aims and advantages listed will be illustrated in greater detail during the description of the preferred forms of implementation of the invention that are given by way of illustration but should not be considered exhaustive and that refer to the enclosed tables of drawings where: - fig. 1 shows the longitudinal cross-section of the draft unit of the invention; - fig. 2 shows the longitudinal cross-section of a part of the draft unit shown in fig. 1 ; - fig. 3 shows the front view from the left of the part shown in fig. 1 ; - fig. 4 shows the longitudinal cross-section of another part of the draft unit shown in fig. 1 ; - fig. 5 shows the front view from the left of the part shown in fig. 4; - fig. 6 is an enlarged view of the cross-section of the part shown in fig. 4; - fig. 7 is an enlarged view of the longitudinal cross-section of a part of the draft unit shown in fig. 1 ; - fig. 8 shows the longitudinal cross-section of an executive variant of the draft unit of the invention; - fig. 9 shows a part of fig. 8. It can be seen that in fig. 1 the draft unit for synthetic fibers to which the invention refers, indicated as a whole with the number 1 , includes a draft cylinder, indicated as a whole with the number 2, mechanically connected to an electric motor, indicated as a whole with the number 3, by which it is made to rotate around a longitudinal axis 4 common to both. The electric motor 3, as can be seen, consists of a casing 5 with a front shield 6 and a rear shield 7, between which there is an impeller, indicated as a whole with the number 8, having a protruding shaft 9 coaxial with the longitudinal axis 4. A fan unit, indicated as a whole with the number 10, is positioned in back of the rear shield 7 and consists basically of a rotor 11 splined onto shaft 9. Behind the fan unit 10 is a terminal board 12 fastened by screws 13 to the casing 5 of the motor. The draft cylinder, indicated as a whole with the number 2, consists of a first tubular cylindrical element 14, commonly known as a "godet", on which the fibers F to be drafted are wound as they come from the spinnerets, and a second tubular cylindrical element 15 placed coaxially inside the first. The two tubular elements are separated from one another to make room for an inductor, indicated as a whole with the number 16, visible in greater detail in figures 4 and 5. As regards the first tubular cylindrical element 14, that we will call hereafter by the name of godet and that is shown also in the two enlarged views in figures 2 and 3, it can be seen that it is provided with an internal sleeve 17 equipped with a flange 18 by which it is coupled coaxially to the inside of the godet 14, when the flange 18 is positioned against a ring-shaped backing 19 made in one end of the godet. The sleeve 17 contains on the inside a first cylindrical zone 20 and a second truncated conical area 21 connected to each other by means of a backing 22 located at the point where there is a variation in the diameter, the truncated conical area 21 , in particular, has the conical part devaricating toward the motor so that it can be coupled with the corresponding end of the truncated conical part 9' of the shaft 9 of the motor 3. A unit fastening the godet 14 to the shaft 9 can be seen in fig. 1 where it is indicated as a whole with the number 23 and consists of a ring 24 that lies against the backing 22 and a threaded nut 25 that is coupled to the threaded end 9" of the shaft 9 of the motor 3. When the nut 25 is tightened, the godet 14 can be splined and fastened securely to the shaft 9 of the motor. As regards the second tubular cylindrical element 15, it will be seen that this is positioned coaxially on the outside of the sleeve 17 and has one end 26 flanged to an intermediate flange 27 by screws 28, the latter being in turn flanged to the front shield 6 of the motor by screws 29. On the outside of the second tubular cylindrical element 15, is the inductor, indicated as a whole with the number 16, which, according to the invention, consists of a foliated pack 30 splined onto the outside of said second tubular cylindrical element 15, and is provided with longitudinal external slots 31 which hold electric conductors 32 wound in a manner basically parallel to the longitudinal axis of the inductor itself. Thus, advantageously, between the foliated pack 29 and the first tubular cylindrical element 14 an air gap 33 is created that is maintained constant along the entire length of the draft cylinder making the distribution of the electromagnetic field produced by the inductor more uniform. This form of construction eliminates the problem of saturation in the air gap with the danger that the magnetic flow produced by the inductor may be dispersed in the air. The ends 34, 35 of the wound electric wires are connected to the terminal board 12 to be powered by external distribution mains. As regards reading the temperature that the godet reaches, the invention foresees the use of an infrared thermocouple, which can be seen in the enlarged view in fig. 7 where it is indicated as a whole with the number 36, that, as can be seen, is placed in a housing 37 located in the intermediate flange 27. Inside this housing 37 the thermocouple is fastened by a supporting lockring 38 with stop screw 39, so that it can be removed for maintenance or replacement. It will be noted that the infrared thermocouple 36, of a type that is known in itself, has the sensitive end 40 facing the annular surface 41 of the godet 14, which is covered by a special layer of ceramic material 42 to prevent problems of reflection. In the same housing 37 there is also, as can be seen, a pipe 43, the end of which 44 is positioned near the space 45 between the sensitive end 40 of the thermocouple and the annular surface 41 of the godet 14 of which the temperature has to be measured. Compressed air is sent through the pipe 43 in direction 46 so that it enters the air space 45 and flows outward in direction 47 passing through the opening 48 between the counterflange 27 and the godet 14. In this way the sensitive end 40 of the thermocouple is always kept clean and the air space 45 always free of any impurities that could interfere with correct reading of the temperature by the thermocouple 36. Functionally, to start the draft unit, the electric motor is powered so that the rotation of its shaft 9 makes the godet 14 splined to it rotate as well. At the same time, the inductor 16 is powered through the terminal board 12 and the wires 34, 35 of the winding 32, with appropriate single-phase voltage at high frequency in the form of a square wave. In its rotation the godet 14 cuts the flow lines of the electromagnetic field generated by the inductor 16 and becomes the site of eddy currents that heat it. The temperature is controlled by the infrared thermocouple 36 that sends an appropriate signal to an outside adjustment and control unit to which it is connected by the electrical cable 36'. The electric temperature reading and control device, not shown in the figures but of a type known in itself, regulates the amount of power supplied to the wires that constitute the winding of the inductor so as to vary the electromagnetic field generated by the inductor 16 and maintain the temperature of the godet 14. During its operation, the continuous flow of compressed air in direction 46 along the pipe 43 keeps the reading zone of the thermocouple 36 clean so as to ensure correct reading. The temperature along the godet is kept basically constant much more than is possible with a draft unit of the known type. A different version of the draft unit of this invention is shown in fig. 8, where it is indicated as a whole with the number 50. It differs from the previously described version in that it includes a cooling unit, indicated as a whole with the number 51 and visible in the overall view shown in fig. 8 and more in detail in fig. 9. This cooling unit 51 includes a ring 52 with a transversal profile in the form of an L, coupled and sealed externally on the front shield 53 to form a toroid chamber 54 on the bearing 55. It will also be noted that on the front shield 53 there is a pair of conduits 56, 57 that communicate with the toroid chamber 54 and are connected by a pipeline serving for adduction 58 and discharge 59, respectively, of a cooling fluid that comes from an external distribution unit, not shown in the figures, and that is made to circulate in the toroid chamber 54 and abate the heat produced during rotation. Preferably but not necessarily the cooling fluid will be a liquid type of coolant consisting of water with additives. It is clear that in the construction of the draft unit of the invention modifications can be made to improve its operation or make it more economical or simple to produce. It is understood, however, that any such variations in construction, as they nevertheless revolve around the idea of the solution described and claimed herein, must all be considered as protected by this invention.

Claims: CLAIMS 1 ) Draft unit (1 ; 50) for synthetic fibers consisting of: - an electric motor (3) complete with casing (5), front shield (6) and rear shield (7), at least one fan unit (10) and an impeller (8) with a protruding shaft (9) constituting a longitudinal axis (4) of rotation: - a draft cylinder (2) consisting of: • a first tubular cylindrical element (14) on which the fibers (F) to be drafted are wound, splined firmly to said protruding shaft (9); • a second tubular cylindrical element (15) positioned coaxially inside said first tubular cylindrical element (14) and having one end flanged to the front shield (6; 53) of said motor (3); • an inductor (16) located on the outside of said second tubular element (15); • means (36) for reading the temperature of said first tubular cylindrical element (14); and is characterized in that said inductor (16) is composed of a foliated pack (30) splined on the outside of said second tubular element (15) and is provided with longitudinal external slots (31 ) which hold electric conductors (32) wound in a manner basically parallel to the longitudinal axis (4) of the inductor itself. 2) Draft unit (1 ; 50) according to claim 1 ) characterized in that said means for reading the temperature include at least one thermocouple (36) the sensitive end of which (40) is turned toward the annular surface (41 ) that constitutes a base of said first tubular element (14). 3) Draft unit (1 ; 50) according to claim 2) characterized in that at least one of said thermocouples (36) is of the infrared type. 4) Draft unit (1 ; 50) according to claim 2) characterized in that said thermocouple is supported by an intermediate flange (27) fastened to said front shield (6) and placed in a housing (37) located in the intermediate flange (27) itself. 5) Draft unit (1 ; 50) according to claim 4) characterized in that in said housing (37) a conduit is inserted (43) the end of which (44) is positioned near the air space (45) between the sensitive end (40) of said thermocouple (36) and the annular surface (41 ) of said first tubular element (14). 6) Draft unit (1 ; 50) according to claim 5) characterized in that inside said pipe (43) compressed air is conveyed. 7) Draft unit (1 ; 50) according to claim 5) characterized in that said air space (45) communicates with the outside through an opening (48) made between the intermediate flange (27) and said first tubular cylindrical element (14). 8) Draft unit (1 ; 50) according to any of the claims from 2) to 5) characterized in that said annular surface (41 ) is covered with a layer of ceramic material (42). 9) Draft unit (1 ; 50) according to claim 2) characterized in that at least one of said thermocouples (36) is electrically connected to units of reading and control of the temperature located externally to said motor. 10) Draft unit (1 ; 50) according to claim 1 ) characterized in that said first tubular cylindrical element (14) is provided on the inside with a sleeve (17) that has a truncated conical zone on the inside (21 ) for coupling to the corresponding truncated conical end (9') of said shaft (9). 1 1 ) Draft unit (1 ; 50) according to claim 9) characterized in that said first tubular cylindrical element (14) is splined firmly to said shaft (9) by means of a fastening unit (23) consisting of a ring (24) that interferes against a backing (22) in the sleeve (17) and of a threaded nut (25) that contrasts against said ring (24) and that is coupled to a threaded end (9") of said shaft (9). 12) Draft unit (1 ; 50) according to claim 1 ) characterized in that said electric wires (32) are powered with single-phase voltage at high frequency in the form of a square wave. 13) Draft unit (1 ; 50) according to claim 1 ) characterized in that of including a cooling unit (51 ) consisting of a toroid chamber (54) located peripherally on the outside of said front shield (53) in which the cooling fluid circulates. 14) Draft unit (50) according to claim 13) characterized in that said toroid chamber (54) consists of a ring (52) with a transversal profile in the shape of an L coupled on the outside to said front shield (53). 15) Draft unit (50) according to claim 13) or 14) characterized in that in said front shield (53) at least two conduits have been provided (56, 57) that communicate with said toroid chamber (54) and are connected to a pipeline for adduction (58) and discharge (59) of cooling fluid.

Inventors: FARINELLO SERGIO, FARINELLO, SERGIO
Applicants: FARINELLO SERGIO, I S G E V SPA, FARINELLO, SERGIO, I.S.G.E.V. SPA
Application year: 2000
Main classification: D01D10
IPC codes: D01D10, D01H1, D01H5, D02J13, H05B6