Patent Application
20080033132
Further features and advantages of the invention are the subject of the following description and the representation of exemplary embodiments in the drawings.
Identical or functionally equivalent elements have been given the same reference numerals in all figures.
A device, shown in
A roll gap 107 with a gap width b (see
The two rollers 104 rotate in opposite directions at the same roller speed, wherein the direction of rotation of the rollers is directed such that the rolling surfaces of the rollers move downwards at the location of the roll gap 107.
The starting material in powder form to be pressed to form band-shaped lumps by means of the rollers 104 is fed to the roll gap 107 by means of a worm device 108, the vertical rotational axis 110 of which runs substantially centrally through the roll gap 107.
The worm device 108 has a pitch that decreases in the vertically downwardly directed transport direction 112 and a diameter that decreases in the transport direction 112.
The worm device 108 is arranged in a downwardly tapering storage hopper 114, which merges at its lower end into a cylindrical transport chamber 130, which terminates at the rolling surfaces of the rollers 104.
The storage hopper 114 is closed at the top except for a filling opening.
A wide-mesh grating arranged on the filling opening prevents an operator from unintentionally accessing the worm device 108.
The starting material to be pressed is fed through the upper open end of the storage hopper by means of a scoop and is apportioned to the roll gap 107 by means of the vertically arranged worm device 108.
In this case, the worm shaft extends into the wedge-like region between the rolling surfaces of the rollers 104.
To assist the feeding action of the worm device 108, the cylindrical transport chamber 130 shown in detail in
In the developed view of the peripheral wall of the transport chamber 130 shown in
Alternatively to this, a transport chamber with a smooth inner peripheral wall can also be used.
The pre-compacted and partially deaerated starting material is pressed by the rollers 104 to form the band-shaped lumps, which then pass into a screen-type mill 116 arranged below the pressing device 102.
The screen-type mill 116 shown in detail in
In the interior 120 of the screen-type mill 116 surrounded by the grinding plate 118 a rotor 122 with five blades 124, for example, rotates around a horizontal rotational axis 126.
The rotor 122 is operated at a speed in the range of approximately 60 rpm to approximately 400 rpm.
The lumps produced by means of the pressing device 102 pass through an inlet 128 into the interior 120 of the screen-type mill 116 and are ground there to a flowable powder by the rotor 122 and the grinding plate 118.
This flowable powder passes through the holes in the grinding plate 118 out of the screen-type mill 116 and is collected in a collection tank (not shown).
From the collection tank the flowable powder is passed on for its further use, e.g. for the ram extrusion of polymer workpieces.
Several examples of a method for the production of a flowable powder of a fluoropolymer from a starting material in powder form conducted by means of the above-described device 100 are described below.
The PHARMAPAKTOR L200/50 P of Hosokawa Bepex GmbH, Daimlerstrape 8, 74211 Leingarten, Germany is used as pressing device 102 in all these examples.
The Pharmapaktor is equipped with smooth rollers with a slight transverse fluting.
The pre-compaction is performed with a cylindrical/conical pre-compactor worm device.
Two longitudinal rods are welded into the compactor hopper. Grooves running in a spiral shape around the direction of passage of the starting material can be milled into the inside of the compactor chamber.
The width b of the roll gap 107 amounts to 1 cm in all examples, the length l of the roll gap 107 respectively amounting to 5 cm, so that the cross-sectional area of the roll gap 107 respectively amounts to 5 cm2.
In addition, screen mill FC 200 of Hosokawa Bepex GmbH, Daimlerstraβe 8, 74211 Leingarten, Germany is used in these examples as screen-type mill.
The finely ground PTFE powder of the type TF 1750, which is marketed by Dyneon GmbH & Co KG, Werk Gendorf, 84504 Burgkirchen, Germany, is used as starting material in powder form. This is a PTFE powder produced using the suspension polymerisation process that has been ground by means of an air jet mill to an average grain diameter of d50 of 25 μm.
The bulk density of the starting material used amounts to 370 g/l.
This starting material is fed into the storage hopper 114 by means of a scoop and conveyed into the roll gap 107 by means of the worm device 108.
The worm device 108 has the worm parameters 60; 64/100 mm, which means that the pitch of the worm device (distance from spiral to spiral) amounts to 60 mm, that the outside diameter of the worm device 108 in its lower cylindrical portion amounts to 64 mm, and that this outside diameter widens to 100 mm in the upper conical portion of the worm device 108.
This worm device 108 is operated at a worm speed of 18 rpm, a worm load current of 1.3 A and with a throughput of 110 kg/hr.
The starting material is pressed between the rollers 104 to form band-shaped lumps.
The rollers 104 are operated at a specific contact force of 3 kN/cm, a roller speed of 4 rpm and a roller load current of 3.0 A.
One of the rollers used has a concavely curved rolling surface, the other of the used rollers has a smooth-cylindrical rolling surface.
The lumps obtained are ground in the screen-type mill 116 to form a flowable powder with an average grain size of d50 of 700 μm and a bulk density of approximately 800 g/l.
The powder obtained has a good flowability and can be easily apportioned by automatic devices for further processing.
This exemplary embodiment only differs from Example 1 in that the specific contact force of the rollers is lowered to 2 kN/cm and the roller speed is increased to 6 rpm.
The throughput of the worm device is increased to 150 kg/hr in this case.
A powder with good flowability also results with this exemplary embodiment.
This exemplary embodiment differs from Example 1 in that the rollers used are provided with a corrugation profile of 6 mm open to the side.
These rollers are operated at a specific contact force of 5 kN/cm at a roller speed of 5 rpm and a roller load current of 3.0 A.
The worm device used in this exemplary embodiment has the worm parameters 60/66/120 mm, i.e. a pitch of 60 mm, and an outside diameter, which amounts to 66 mm in the cylindrical portion and widens to 120 mm in the conical portion.
This worm device is operated at a worm speed of 18 rpm with a worm load current of 1.3 A and a throughput of 130 kg/hr.
A powder with good flowability is also obtained with this exemplary embodiment.
In this exemplary embodiment the finely ground PTFE powder of the type NXT 75, which is marketed by DuPont de Nemours (Deutschland) GmbH, Bad Homburg, is used as starting material in powder form. This is a chemically modified PTFE produced using the suspension polymerisation process that has been ground by means of an air jet mill to a powder with an average grain diameter d50 of 33 μm.
The bulk density of the starting material used amounts to 440 g/l.
One of the rollers used has a concavely curved rolling surface, the other of the used rollers has a smooth-cylindrical rolling surface.
The rollers 104 are operated at a specific contact force of 3 kN/cm, a roller speed of 4 rpm and a roller load current of 3.5 A.
The worm device used has the worm parameters 60/64/100 mm, which means that the pitch of the worm device (distance from spiral to spiral) amounts to 60 mm, that the outside diameter of the worm device 108 in the lower cylindrical portion amounts to 64 mm, and that this outside diameter widens to 100 mm in the upper conical portion of the worm device 108.
This worm device is operated at a worm speed of 18 rpm, a worm load current of 1.4 A and with a throughput of 120 kg/hr.
Otherwise, this exemplary embodiment is the same as Example 1.
A powder with good flowability is also obtained with this exemplary embodiment.
This exemplary embodiment differs from Example 4 in that the rollers are operated at a specific contact force of 2 kN/cm, a roller speed of 6 rpm and a roller load current of 3.5 A.
The throughput of the worm device is increased to 170 kg/hr in this case.
A powder with good flowability is also obtained with this exemplary embodiment.
This exemplary embodiment differs from Example 4 in that the rollers used are provided with a corrugation profile of 6 mm open to the side.
These rollers are operated at a specific contact force of 5 kN/cm at a roller speed of 5 rpm and a roller load current of 3.5 A.
The worm device used has the worm parameters 60/66/120 mm, i.e. a pitch of 60 mm, and an outside diameter, which amounts to 66 mm in the cylindrical portion and widens to 120 mm in the conical portion.
This worm device is operated at a worm speed of 18 rpm with a worm load current of 1.4 A and a throughput of 145 kg/hr.
A powder with good flowability is also obtained with this exemplary embodiment.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 036 204.7 | Aug 2006 | DE | national |
