DE102004006588B4 - Continuous production of profiles made of carbon material and profile produced in this way - Google Patents

Abstract

Process for the continuous production of profiles made of carbon for components in electrical and mechanical applications by means of the known process steps
- Mixing the dry carbon components and the additives with hydrocarbon-containing binder
- Burning and optionally graphitizing the green profiles and
- Editing the thus obtained profiles of carbon material
characterized in that
after the process step mixing and before the process step firing with a process step rolling compacting from a free-flowing green mixture (3), in continuous shaping a compacted profile (1) of green carbon material is produced.

Description

• – Mischen der trockenen Kohlenstoffkomponenten und der Additive mit kohlenwasserstoffhaltigem Bindemittel,
• – Brennen und gegebenenfalls Graphitieren der zunächst grünen Profile und
• – Bearbeiten der so erhaltenen Profile aus Kohlenstoffwerkstoff

The invention relates to the continuous production of profiles of carbon material for components in electrical and mechanical applications by means of the known method steps

• Mixing the dry carbon components and the additives with hydrocarbon-containing binder,
• - Burning and optionally graphitizing the first green profiles and
• - Editing the thus obtained profiles of carbon material

The Production of carbonized or graphitized carbon bodies is one since over One hundred years ago, technology dominated, industrial scale industrial scale is used and therefore sophisticated in many respects and in terms of Cost is optimized. One of the descriptions of this technique - in particular a description of the Feinkorngraphite - one finds in the small Band FEINKORNGRAPHITE by A. KINDLER in the publishing house modern industry, 1995 in the series "The Library the technique, volume 119 ".

thin-walled Components made of carbon materials become essentially in two Application areas needed: in slide valves of certain pumps and compressors as well with carbon brushes with unusual Dimensions. These thin-walled Components are machined from carbon blocks using conventional techniques those in the green production stage produced by isostatic pressing or by die pressing were. The material waste can - measured on the finished Separator or on the finished brush - two to three times the finished part. To this high material waste at avoid the processing of dense, fine grained material types, it is desirable to obtain a semi-finished product from these carbon types, the thin-walled can be produced.

In The patent literature is various green manufacturing processes for the production - even thin-walled - components or profiles consisting of carbon materials described.

In the American patent specification US 4,882,102 is a green mixture of carbon particles and low-organic compounds as a binder in the form of a comparatively low-viscosity slip to thin films or plates poured or rolled. Such films or plates are dried, cured, cut and carbonized, optionally graphitized.

It would be too possible, a slurry described in this patent continuously to pour a conveyor belt and from such a cast green body profiles of carbon manufacture.

All Green manufacturing process for profiles however, carbon, which starts from a precursor "slip", differs clearly from the invention green manufacturing process, at as a precursor a free-flowing green mixture suitable grain size is used.

In Several patents use extrusion processes as green manufacturing processes described. requirement for the extrudability of green Mixtures is their sufficient plastic deformability, so the mixture through the comparatively narrow mouthpiece of the extruder can be pressed. A sufficient plastic deformability achieved by a sufficient amount of viscous binder, by an increased processing temperature, in which the binder is low viscosity, by the addition of plasticizing additives in the green mixture, or by a Combination of these factors.

By way of example, the German Offenlegungsschrift DE 40 00 938 A1 and the American patent US 5,338,320 called.

After DE 40 00 938 A1 a green mixture is processed to a thin carbon membrane for acoustic applications. The green manufacturing process comprises the following steps: intensive homogenizing and kneading the green mixture, extruding, cutting the web-like material, the blanks to desired thicknesses, calendering, optionally finishing and firing.

To US 5,338,320 For example, a green mixture is extruded, the extruder having a slot mouthpiece whose opening has a clear width of several hundred millimeters and a clear height of only a few millimeters. The extruded sheet of green material is cut to size and, in another green working step, unilaterally profiled in a die press. This is followed by hardening and carbonation.

The group of patents describing the addition of plasticizers to the green blend includes the United States Patent US 2,761,848 and the European patent specification EP 0 933 791 , In the former case furfural or furfuryl alcohol is added to the green mixture, in the latter case PTFE is contained in the green mixture. In the latter case follows the extrusion step nor a green production step rollers.

All Green manufacturing process, which comprise the extrusion step, have as a precursor a plastic green mixture.

These plastic extruder masses with a high proportion of carbon components are subject to both consistency and composition different limitations. So the mass has a sufficiently low viscosity to get through the extruder. This must be in the Practice usually the extruder is heated to high viscosity To make masses more plastic. On the other hand, the grain is as also the friction properties of the mass a limiting factor. In addition, extruder masses contain only a few components which thermal in the extruder Reactions have. That expresses itself primarily by the limitation on the use of curing Resins that cause disorders mainly because of the excretion of condensation products (bubble and cracking) and the rapid increase in viscosity (stuck of the extruder) when cured.

Next the difficulties during But extruding are mainly downstream problems, such as about the outgassing during of carbonation promoted Cracking and poor fracture mechanics, to mention those in extruder masses with high proportion of carbon components limits both in their Consistency as well as their material composition. there are due to the antagonism between the addition of possible much low-viscosity material and its tendency to increased outgassing or thermal reaction not only of the composition of the mass itself, but also the width-thickness ratio of the extruded semi-finished product Set limits. Thus, above all, the extruding of endless Profiles made of carbon material with a large width to thickness ratio Profile cross section only when overcoming greater Difficulties possible.

In A separate group of patents describes the production of carbon tapes.

In the American patent specification US 5,326,510 It is described that a band is drawn from a pitch melt, in particular from a melt of mesophase pitch. In further steps, the pitch of this pitch band is brought into a non-fusible form and finally carbonized. The carbon tape has a width-to-thickness ratio between 10 and 1000 at an absolute thickness of 10 to 40 microns. International Patent Application No. WO 01/02632 A1 also describes drawing a pitch band from a mesophase pitch melt. In this document, the focus is on the alignment of the molecules or crystallites in the pitch melt and the resulting carbon band.

at There are none of these writings to the writings quoted above comparable green manufacturing step. The precursor for the production of a carbon band is in each case a pitch melt, the course not with the precursor of the free-flowing green mixture of suitable grain size comparable to the present application.

It Thus, in none of the cited documents is a green manufacturing process described in which for the continuous production of, too thin-walled, Profiles made of carbon materials, a dry, pourable green mixture is used.

on the other hand There is a manufacturing process, the die-pressing, in particular, the thin-walled Components are made of carbon materials, in which it is not the limitations described in terms of extrusion in the choice of materials. However, the manufacture of long components, approximately in length a meter and above, unusual strong and expensive stamping presses with appropriate dies to the associated green body to squeeze.

• – Mischen der trockenen Kohlenstoffkomponenten und der Additive mit kohlenwasserstoffhaltigem Bindemittel,
• – Brennen des zunächst grünen Formkörpers und danach gegebenenfalls Graphitieren sowie
• – Bearbeiten des so erhaltenen Profils aus Kohlenstoff.

As a boundary condition of the task it should be noted that most of the known process steps for the production of carbonized or graphitized carbon materials are retained, namely

• Mixing the dry carbon components and the additives with hydrocarbon-containing binder,
• - Burning of the first green shaped body and then optionally graphitizing and
• - Edit the profile obtained from carbon.

The The object of the invention underlying this patent application It was therefore a green manufacturing process For the continuous production of, even thin-walled, profiles made of carbon material in which it is not the one described in terms of extruding restrictions in the choice of materials and in which most of the known Process steps for the production of carbonized or graphitized carbon materials remain.

To solve the problem is after the process step mixing and before the process Step firing with a process step rolling compacting in continuous shaping produces a compacted profile of a green mixture in free-flowing form.

• • Unter einer grünen Mischung versteht man in der Kohlenstofftechnik ein Gemisch aus Trockenstoffen aus der Gruppe der Kokse, der Elektrographite, der Naturgraphite, der Ruße u. a. mit den gewünschten Kornbändern, der kohlenwasserstoffhaltigen Bindemittel und der Additive. Dabei wird insbesondere der Koks, welcher zunächst in Form von kalzinierten groben Koksstücken mit mehreren Zentimeter mittlerer Korngröße vorliegt, durch geeignete Verfahren wie Brechen, Mahlen und Sieben in geeignete kleinere Korngrößenfraktionen zerkleinert. Dieser Vorgang wird auch als Primärmahlung bezeichnet. Wenn Peche als Bindemittel eingesetzt werden, findet das Mischen bei Temperaturen oberhalb des Erweichungspunktes der Peche statt. Nach dem Mischen und Abkühlen auf Raumtemperatur liegt die grüne Mischung zunächst in schwer verarbeitbaren Schollen vor. Um diese in eine verarbeitungs- und dosierfähige Form zu bringen, werden die Schollen bevorzugt in einer Sekundärmahlung zu einer rieselfähigen Körnung mit geeigneten Korngrößen zerkleinert. Der Begriff Sekundärmahlung dient dem Fachmann zur Unterscheidung von der Primärmahlung. Die durch die Sekundärmahlung erzeugten Partikel setzen aus pechgebundenen, durch Primärmahlung vorher erzeugten, Kokspartikeln zusammen.
• • Die rieselfähige grüne Mischung wird als Vorprodukt für das erfindungsgemäße Walz-Kompaktieren eingesetzt. Die Rieselfähigkeit wird dabei gemäß DIN ISO 6186 bestimmt. Nach dieser Norm wird im allgemeinen die Rieselfähigkeit von Kunststoffen in Pulver- und Granulatform ermittelt. Dabei wird die Durchflusszeit („Rieselzeit") gemessen, die eine definierte Masse der Probe benötigt, um durch einen Trichter mit festgelegten Maßen zu rieseln. In diesem Fall wurde das normierte Messverfahren A gewählt. Dabei wird der Trichterauslass verschlossen, 150 g Probe eingefüllt und gleichzeitig mit anschließender Öffnung des Trichterauslasses eine Stoppuhr gestartet. Diese wird angehalten, sobald der Trichter leer ist. Rieselfähige grüne Mischungen im Sinne dieser Erfindung benötigen weniger als 60 s Durchflusszeit („Rieselzeit").
• • Beim Walz-Kompaktieren wird die grüne Mischung zwischen den Walzen eines Walzenpaares verdichtet. Wird die grüne Mischung dem Walzenpaar in geeigneter Weise zugeführt, so entsteht ein endloses Profil, dessen Geometrie von den Abmessungen des Walzenspalts bestimmt wird.

The terms in the following text are to be understood as:

• • A green mixture is a mixture of dry substances from the group of cokes, electrographites, natural graphites, carbon blacks, etc. with the desired grain bands, the hydrocarbon-containing binders and the additives. In particular, the coke, which is initially present in the form of calcined coarse coke pieces with several centimeters average grain size, is comminuted by suitable methods such as crushing, grinding and sieving into suitable smaller particle size fractions. This process is also referred to as primary payment. When pitches are used as the binder, mixing occurs at temperatures above the softening point of the pitches. After mixing and cooling to room temperature, the green mixture is initially present in hard to process floes. In order to bring these into a processable and meterable form, the clods are preferably comminuted in a secondary payment to a free-flowing granulation with suitable particle sizes. The term secondary payment is used by the skilled person to distinguish from the primary payment. The particles produced by the secondary payment consist of pitch-bound coke particles previously generated by primary payment.
• The free-flowing green mixture is used as a precursor for the roll compacting according to the invention. The flowability is determined according to DIN ISO 6186. According to this standard, the flowability of plastics in powder and granular form is generally determined. It measures the flow time ("trickle time") that a defined mass of sample requires to trickle through a funnel of specified dimensions, in which case the normalized measurement method A was chosen, closing the funnel outlet, filling 150 g of sample, and A stopwatch is started simultaneously with subsequent opening of the funnel outlet, which is stopped as soon as the funnel is empty.Grout-capable green mixtures in the sense of this invention require less than 60 s flow time ("trickle time").
• • In roll compacting, the green mixture is compacted between the rolls of a pair of rolls. If the green mixture is fed to the pair of rollers in a suitable manner, an endless profile is produced whose geometry is determined by the dimensions of the nip.

The continuous production of a compacted continuous profile from green Carbon material has the advantage that you do not like the die pressing in the component length is limited or as extruding on the flow processes of the plastic material and the associated limitations consideration must take.

The solution the object is achieved by the characterizing parts of claims two designed to thirteen in an advantageous manner.

The essential condition for The first compaction to a profile is that the green mixture in free-flowing Shape, preferably as a grain a secondary payment, is present. The content of hydrocarbon-containing binder of green mixture is 10 to 50% by weight. The hydrocarbon-containing binders are the common in the carbon technology Peche or synthetic resins.

For roll compacting will be a free-flowing green mixture with a particle size distribution of 10 μm up to 500 μm used.

The Roll compacting is operated in such a way that the dry, pourable Grain of green Mixture in the nip between the rolls of a pair of rolls one is exposed to high pressure. But this pressure alone is enough not sure of a secure cohesion between the individual grains of the green Mixture to achieve, especially not if the grain of a Sekundärmahlung was given to the rollers. To the viscosity of the binder involved reduce and at the same time the bond strengths between the grains too it is expedient to improve both the green Mixture up to 50 ° C preheat as well as the participating rollers to drive at temperatures of up to 50 ° C, with which other combinations of material preheating and roll temperature should not be excluded.

For roll compacting the green Mixture is used at least one pair of rollers, which has a defined set nip and two with the same but more contrary Sheath speed consists of running rollers. The axes of a such roller pair are arranged in a horizontal plane. That is convenient because in this way, the free-flowing green mixture can run into the gap of the roller pair. The pourable green mixture and the profile of the green carbon material compressed therefrom continuously conveyed essentially vertically from top to bottom.

In the case that the free-flowing green mixture, a suitable, optionally thermosetting binder and a Ausrei contains binding agent content, the process step without the process step firing directly follows the process step rolling compacting. This is possible if the free-flowing green mixture is given preheated to the compacting roller pair and / or the compacted and having a minimum strength profile is at least partially cured by hot or hot Kompaktierwalzen and optionally fully cured by a thermal aftertreatment. The process steps burning and graphitizing can be dispensed with in such material types.

If a profile compacted by rolling is carbonized, then at least one bending strength of 20 N / mm ² and at least one density of 1.6 g / cm ^{3 is} measured on this material, without the carbon material being subjected to further aftertreatment.

Around Profiles made of carbon with a high width-to-thickness ratio to are special measures required. The least amount of effort is required for slip casting, which is treated in the prior art writings. A higher effort is when extruding and pulling profiles from the melt required. There are each special Breitschlizmundstücke provide. When extruding is about it In addition, the viscosity the green Mix sensitive otherwise the extruded profile tends to, in the flow direction just behind the mouthpiece longitudinal tear. When pulling profiles from the melt, the freshly drawn melt tends due to the surface tension to get together to form a thicker strand with roundish cross-section to draw.

At the Roll compaction results in the width of the profile produced easily from the width of the rollers used in a pair of rollers and the with the green Mixture filled Width of the rolls. Depending on the set gap width of a pair of rollers and the predetermined roll width reaches the cross section of the profile from green or calcined carbon material has a ratio of width to thickness values in the range of more than two hundred to one to five hundred to one.

Not All components are best made from flat profiles. Much more are in some cases arched, corrugated or otherwise contoured - also over the length of different thickness - profiles appropriate. These Profiles can be with appropriately shaped lateral surfaces of Create rolls of a pair of rolls during roll compaction.

Examples

In a first embodiment, as solids, 53% by weight of coke, 15% by weight of graphite and 7% by weight of carbon black were mixed with 25% by weight of binder. The solids were present in a grain size of less than 500 microns and the pitch had a softening point of 80 ° C after Krämer-Sarnow. In a first mixing process, the ingredients were homogenized at room temperature and then heated to about 150 ° C. in a Bausano screw extruder. The liquid pitch then spread to the surfaces of the solids; the hot mixture was finally extruded as a profile. The hot profile was allowed to cool to room temperature and then brought to a mean grain size of 100 μm by secondary milling. This free-flowing green mixture was the precursor for roll compaction of compacted, endless profiles. Under the following conditions was condensed:
The free-flowing green mixture was placed in a hopper with adjustment over a pair of rollers, whose rolls each had a diameter of 200 mm and whose roll axes were arranged in the horizontal plane. The mantle speed of the counter-rotating rolls was 2.0 m / min. The continuous densification of the green mixture in the nip was at room temperature and the densified profile left the nip vertically from top to bottom. The nip was set to 1.50 mm.

The The result of roll compacting was a compacted, endless profile from green Carbon with a thickness of 1.70 mm.

In a second embodiment the same raw materials were used as in the first embodiment. Also, mixing, extruding and making the secondary payment were the same the first embodiment.

It the same roller mill was used. The jacket speed the opposite Rolls were 0.4 m / min. The compaction of the green mixture in the nip was carried out continuously at room temperature and the densified profile left the nip vertically from top to bottom. The nip was set to 1.90 mm.

The The result of roll compacting was a compacted, endless profile from green Carbon with a thickness of 2.10 mm.

In a third embodiment, two compacted profiles produced according to the first embodiment were placed in a pair of rollers whose roller axes were arranged in the vertical plane, the. Profiles were thus promoted horizontally. The rolling compacting was carried out under these conditions:
The rolls each had a diameter of 200 mm and the mantle speed of the counter-rotating rolls was 0.6 m / min. The two layers of material were heated to 80 ° C within one minute before entering the nip. The two layers had a total thickness of 4.50 mm before compaction and the nip was set at 3.60 mm.

The The result of roll compacting was a compacted, endless profile from green Carbon with a thickness of 3.75 mm.

By the following figure, the invention is further exemplified. It shows:

1 Scheme of a plant for the continuous production of a profile ( 1 )

Description of the figure:

The scheme of a plant for the continuous production of a profile ( 1 ) gives an overview of how the profile ( 1 ) is made of green carbon.

In a hopper ( 4 ), the free-flowing green mixture ( 3 ). By means of an adjusting device is from the hopper ( 4 ) flowing out and into the nip of the roller pair ( 5 ) entering amount of the green mixture. From the roller pair ( 5 ) the compressed profile ( 1 ).

The profile that arises essentially in the vertical direction from top to bottom ( 1 ) is easy to handle thanks to its good cohesion and can therefore be redirected by 90 °. After redirecting, the profile ( 1 ) conveyed substantially horizontally and optionally in a temperature chamber ( 6 ) at temperatures of at least 20 ° C and at most 200 ° C tempered. In the latter case, a hardened profile ( 8th ).

Claims (9)

Method for the continuous production of profiles of carbon for components in electrical and mechanical applications by means of the known method steps - mixing of the dry carbon components and the additives with hydrocarbon-containing binder - firing and optionally graphitizing the green profiles and - processing of the resulting profiles of carbon material, characterized that after the process step mixing and before the process step firing with a process step roll compacting from a free-flowing green mixture ( 3 ), in continuous shaping a compressed profile ( 1 ) is produced from green carbon material. A method according to claim 1, characterized in that the free-flowing green mixture ( 3 ) is produced as a grain by a secondary payment. A method according to claim 2, characterized in that the free-flowing green mixture ( 3 ) is used with 10 to 50 wt .-% binder. Process according to claims 1 to 3, characterized that the hydrocarbonaceous binders belong to the group of Peche or synthetic resins are used. Process according to claims 2 to 4, characterized in that the free-flowing green mixture ( 3 ) is used with a particle size distribution of 10 microns to 500 microns. Process according to claims 2 to 5, characterized that in roll compaction for Material and rolling temperatures can be chosen between room temperature and 50 ° C. Method according to one or more of claims 1 to 6, characterized in that the rolling compacting of the green mixture ( 3 ) between the rolls of at least one pair of rolls ( 5 ), which has a defined set nip and consists of two with the same but opposite mantle speed rollers running. Process according to claim 7, characterized in that the green mixture ( 3 ) and the resulting profile ( 1 ) of the green carbon material are conveyed continuously substantially vertically from top to bottom. Profile made of carbon according to one of the claims 1 to 8, characterized in that the cross section of the profile from green or burned carbon material a ratio of width to thickness in Range of more than 200: 1 to 500: 1 has.