|Title of Invention||
PROCEDURE FOR MELTING POLYMER GRANULES AND A MELTING ELEMENT
|Abstract||The invention relates to a method for melting a polymer granulate on a melt element to enable the melted granulates to be spun. In order to allow the granulate to melt in an energetically viable manner, without high thermal or mechanical strain, a melt element which is conically tapered towards the openings on the underside of said melt element is used. The spherical particles thereof are introduced into said openings in the form of a granulate with an average diameter of D3, having a ratio to the entrance-side diameter D1 of the opening of 2 * D3 >/= D1 >/= D3.|
PRbCEDURE FOR MELTING POLYMER GRANULES AND A MELTING ELEMENT DE$CRIPTION
Th^ invention relates to a procedure for melting polymer granules on a grate-shaped melting elerjnent and subsequently spinning the melted granules. In addition, the invention relates to a graje shaped melting element for melting granules, in particular polymer granules, preferably me^nt for melt spinning. Finally, the invention is aimed at a device for melt spinning.
Dulling melt spinning, macromolecular raw material is melted and spun, wherein the fibres are solijdified through cooling. Essentially two different melt spinning procedures are known from prafctice, specifically reprocessing the raw material with fusible grates or via extruders, wherein the!raw material is always present as granules. In the first mentioned procedure, the cylindrical grajiules exit a storage tank and get onto the fusible grate under a nitrogen atmosphere. This fusible grate can consist of adjacent tubes that are heated. The melt drips from the grate into a surhp, from which the melt is conveyed via pumping to spinnerets.
Thip process of melting by means of fusible grates, which are also referred to as grate spinnerets, caijie into use in particular in the period between 1940 and the 50's. For reasons of economic efficiency and to attain higher melting capacity, i.e., to achieve higher throughputs at spinning milt, extruders were then used for fibre manufacture. Due to higher melting efficiencies and sy^em throughputs, this so-called extruder spinning has become popular in particular for mejdium-viscous melts with an intrinsic viscosity ranging between 0.6 and 0.7.
Known from DD 44 624 A is a device for melt-spinning molded bodies according to the grate spi(ining process. A melting body intended for melting chip-shaped high polymers has boreholes shaped like a funnel on the feed side.
In jorder to melt organic compounds for manufacturing yarn, GB 719,062 proposes a plate corisisting of silver with numerous boreholes expanded on the inlet side in the shape of a funnel.
In rjecent years, increasingly stringent requirements have been placed on the quality of technical yarhs. This is to be accompanied simultaneously by cost-effective production. However, sigjiificant damage can arise during the treatment of granules, e.g.:
: - Hydrolytic damage: If too much moisture adheres to the granules, the viscosity is reduced while melting, which diminishes the strength. This damage can be avoided by drying the Granules to a residual moisture of 12 oom:
j- Oxidative damage: while melting the granules, the presence of oxygen results in an oxidation, and hence in a reduction in strength. This can be remedied having melting taking place in an inert gas atmosphere, in particular an N2 atmosphere.
- Mechanical damage: using extruders to melt the granules gives rise to shear stresses that shorten or break molecule chains;
!- Thermal damage: given excessive retention times of the melted granules, e.g., due to transport in pipes to spinnerets, a decrease in viscosity sets in, resulting in a reduction in strength.
These lengthy retention times are necessitated by more complex melt distribution systems, and the resultant, Increasingly long retention times. For this reason, ever-increasing numbers of static mi)
Th^ object of this invention is to further develop a procedure or melting element of the kind mejntioned at the outset in such a way as to largely avoid mechanical and thermal damages to the mejlted granules, so that the quality of the yarns to be fabricated can be improved.
Th^ object is achieved according to the invention in a procedure for melting polymer granules with a grate-shaped melting element by having the melting element be one having openings that corliically narrow toward the bottom side of the melting element, to which spherical particles are sufi)plied as granules with an average diameter D3 that behaves as follows relative to the inlet sidje diameter Di of the opening: 2 * D3 > Di > D3.
Actording to the invention, spherical particles are used as granules, which in particular have a residual moisture of
In cither words, the granules melt in a very short time regardless of their low thermal conductivity, wherein the invention is developed further by having a heat transfer to spherical particles with an initiial volume VA take place within the opening of the melting element in such a way that its unrjnelted residual volume VR measures roughly 0.02 VA or less than 0.02 VA when exiting the opening. The residual solid left behind in this way is then melted in the melt sump present below the! melting element.
Th^ melting element should be set to a temperature T^ that exceeds the melting temperature of thej granules by roughly 5° C to 20° C, in particular 5° C to 10° C p. This ensures that thermal darinages will be largely precluded.
A melting element for melting granules, in particular polymer granules, preferably intended for melt spinning, is characterized in that the plate-shaped melting element has openings that narrow toward its bottom side, having a diameter Di at the inlet side and a diameter of D2 at the outlet sidis with 4 * D2 Th^ melting element itself can be set to a temperature Ti exceeding the melting temperature T2 of thd granules by roughly 5° C to 20° C. In addition, the nozzle-shaped openings are to have a height h measuring roughly 1 to 3 times the inlet diameter Di.
In Edition, the invention is characterized by an arrangement for melt spinning polymer granules with a storage container for holding the granules with the storage container by means of a first cohveying aggregate, wherein the spinning location comprises a casing pressurized with inert ga$, whose top side has a metering device to which the granules can be supplied, a plate or gr^te-shaped melting element situated in the casing with truncated cone-shaped openings that narrow toward its bottom side, a sump area located in the floor-side casing to receive melted granules, a second conveying device downstream from the sump area for supplying the melt to sp nnerets, wherein the melting element is set in particular to a temperature Ti that exceeds the melting temperature T2 of the granules by roughly 5° C to 20° C.
In ]this case, the second conveying device preferably consists of two series-connected toothed wrieel-metering pumps, which can each be operated at a constant, yet variable speed. The casing-side toothed wheel-metering pump can here be operated at speed Ni, and the doWnstream toothed-wheel-metering pump can be operated at a speed of N2, with Ni Thje metering device can be controlled as a function of the fill level of the melt sump. This can talte place via nitrogen pearl level measurements or mechanical and/or electromechanical fill levj-el devices. A Mechanical or pneumatic drive can be used to activate the metering device, like a rfnetering valve.
The first conveying device leading from the storage tank to the spinning location can be a vibration conveyor pressurized with nitrogen.
Fig. 1 is a basic view of a device for melting granules;
Fig. 2 is a top view of a melting element;
Fjg.S is a cross section through the melting element according to Fig. 2;
Fjg.4 is a perspective view of an opening in the melting element according to Fig. 2; and
Fjg.5 is a basic view of an opening in the melting element according to Fig. 2 with granules nielting therein.
Ill order to largely eliminate mechanical and thermal damage while melting and spinning njacromolecular raw materials, spherical polymer granule particles, so-called pellets 12, are cJDnveyed from a storage tank 10 via first conveying devices 14, 16, 18, 20 to spinning locations 2)2, 24, 26, 28.
TJhe pellets 12 here in particular have a residual moisture of especially less than 12 ppm, pkferably less than 5 ppm, and a diameter ranging between 0.5 mm and 2 mm, wherein the ai/erage diameter depends on the dimensioning of openings 30 in a plate-shaped melting element 32 to be described in greater detail below, which in the following is referred to as a ntielting grate or only as a grate for purposes of simplification.
Conveying devices 14, 16, 18, 20 preferably involve vibration-conveying grooves pressurized with itrogen.
Since spinning locations 22, 24, 26, 28 have essentially the same structure, spinning location 22 vyill be described in greater detail. The pellets 12 travel from the vibration conveying groove 14 leasing to the spinning location and arrive at a funnel 36, which can be locked by means of a sjlider 34, and is arranged in the top area 38 of a casing 40 pressurized with nitrogen or another iijiert gas. The funnel 36 can be sealed on the casing side with a metering valve 42, so that it can rheter pellets into the casing 40 to melt the latter in the way described below.
Extfending over the cross section of the casing 40 is the plate-shaped meltincf grate 32 used to meft the pellets 12 and then drip them into a melting sump 44 in the floor area of the casing 38. Th$ metering valve 42 is controlled as a function of the amount of melt accumulated in the melting sump 44. In this case, the metering valve 40 can be operated and controlled using known methods or measuring devices, i.e., directly and mechanically via level meters arranged in the meiting sump 44. As an alternative, a differential pressure 46 of the sump level can be ascjertained by means of a so-called pearl lever measurement with nitrogen. The metering valve 12 oan itself be opened or closed via a pneumatic drive in the required scope, for example.
The melt is conveyed to a desired number of spinnerets 54, 56 from the melting sump 44 by meiins of two series-connected toothed wheel-metering pumps 48, 50 as conveying aggregates via short distribution lines 52, and hence at short retention times.
Th€! melting grate 32 has openings 30 that conically narrow toward the bottom side, which have truricated cone geometry and an inlet diameter Di and outlet diameter D2. In this case, the diaiineter Diis at most two times the diameter D3 of the unmelted pellets, while the outlet diameter D2 measures roughly 0.25 to 0.15 of the diameter D3. As a result, the melted pellets 12 do not impiede each other while passing through the opening 30, so that, despite their poor thermal coriductivity, the pellets 12 melt to a sufficient extent and relatively quickly, without the melting gra^e 32 having to be heated to an undesirably high level. The grate can Instead be set to a
tenjperature Ti exceeding the melting temperature T2 of the pellets 12 by about 5° C to 20° C.
When using PET (polyethyleneterephthalate) balls as pellets 12, which have a melting teniperature of approx. 265° C, it is sufficient for the melting grate 32 to be heated to a terrlperature 270° C to 280° C. This can be done by means of heating coils 60 running between theiopenings 30.
The height of the opening 30 itself should measure roughly 3 to 5 times the diameter D3 of the peltets 12 to be melted.
Th Th4 retention time in the sump is also minimized, wherein an optimal adjustment between the pel|ets supplied via the metering valve 42 and the melt withdrawn via the conveying device, e.g., the|toothed wheel-metering pumps 48, 50, is enabled by monitoring the sump level, in particular
via ipearl level measurement.
1. A method for melting polymer granules or pellets on a grate-shaped melting element for
subsequently spinning the melted granules, wherein the melting element is one having
\ openings that conically narrow toward the bottom side, to which spherical particles are supplied as granules with an average diameter D3 that behaves as follows relative to the inlet side diameter Di of the opening: 2 * D3 > Di > D3, wherein the method comprises the following steps:
^) conveying said granules from a storage tank through first conveying devices to spinning
b) melting said granules on said grate-shaped melting element;
d) dripping the melted granules into a melting sump; and
d) conveying the melt to a desired number of spinnerets from the melting sump.
2. ; The method according to claim 1, characterized in that the melting element is set to a ■ temperature Ti that exceeds the melting temperature T2 of the spherical particle by roughly ; 5°C to 20'C, in particular 5°C to 10°C.
3. : The method according to claim 1 or 2, characterized in that a heat transfer to the spherical
particle with an initial volume VA takes place within the opening of the melting element in such a way that its unmelted residual volume VR measures roughly 0.02 VA or less than 0.02 VA after exiting the opening.
4. ; The method according to at least one of the aforementioned claims, characterized in that
granules used have a residual moisture ppm, in particular i
5. j The method according to at least one of the aforementioned claims, characterized in that
spherical particles with a diameter of between 0.5 mm and 2.0 mm are used as the granules.
6. The method according to at least one of the aforementioned claims, characterized in that
granules with an intrinsic viscosity of between 0.75 and 1.3 are used.
7. ; A device for melt spinning polymer granules having an average diameter D3, with a storage
i tank (10) for holding the granules, at least one spinning location (22, 24, 26. 28) linked with
I the storage container by means of a first conveying aggregate (14, 16, 18, 20) with a
casing (40) pressurized with inert gas, whose top side has a metering device (42) to which the granules can be supplied, a plate or grate-shaped melting element (32) situated in the : casing with truncated cone-shaped openings (30) that conically narrow toward its bottom side and with the inlet diameter Di of the openings and the average granule diameter behaving as 2 • D3 > Di > D3, a sump area (44) located in the floor-side casing to receive melted granules, a second conveying device (48, 50) downstream from the sump area for supplying the melt to spinnerets (54, 56).
The device according to claim 11, characterized in that the melting element (32) is set to a temperature Ti exceeding the melting point T2 of the granules by about 5°C to 20°C.
The device according to one of claims 11 or 12, characterized in that the second conveying device comprises two series connected toothed wheel- metering pumps (48, 50) that each * can be operated at constant, but variable speeds (N1, N2).
The device according to claim 11 to 13, characterized in that the toothed wheel-metering pump (48) arranged on the casing side can be operated at a speed of Ni and the downstream toothed wheel-metering pump can be operated at a speed of N2 wherein Ni The device according to one of claims 11 to 14, characterized in that the metering device (42) that supplies the granules to the casing can be controlled via the melt accumulated in the melt sump (44).
The melting element (32) as claimed in claim 7, characterized for melting granules (12). in particular polymer granules having an average diameter D3, preferably intended for melt spinning, characterized in that the grate-shaped melting element (32) has truncated cone-shaped openings (30) that conically narrow toward its bottom side, and that the inlet side
j diameter Di of the opening and the average granule diameter behave as follows: 2 * D3 >
! Di > D3.
^ The melting element as claimed in claim 12, characterized in that the melting element (32) can be set to a temperature Ti exceeding the melting temperature T2 of the granules (12) by about 5°C to 20*^0.
The melting element as claimed in claim 12, characterized in that the conically tapering
opening (30) of the plate-shaped melting element (32) with the geometry of a truncated
\ cone has an inlet diameter Di and an outlet diameter D2 with 4 • D2
> Di > D3. wherein D3 is the average diameter of spherical particles (12) supplied to the ; melting element as the granules.
The melting element as claimed in claims 12 to 14, characterized in that the nozzle-shaped openings (30) have a height of roughly 1 to 5 times the inlet diameter Di-
|Indian Patent Application Number||225/CHENP/2003|
|PG Journal Number||47/2008|
|Date of Filing||06-Feb-2003|
|Name of Patentee||BUHLER AG|
|Applicant Address||CH-9240 UZWIL,|
|PCT International Classification Number||D01D1/04|
|PCT International Application Number||PCT/EP01/09876|
|PCT International Filing date||2001-08-28|