Method and device for coating short fibers

Abstract

A method for coating short fibers, comprising: Feeding (310) a reaction gas into a non-rotating reactor (1); Introducing (315) short fibers into the reactor (1); Setting (320) the reactor (1) into an oscillation between 1 Hz and 80 Hz; Tilting (330) of the reactor (1); and Heating (340) the reactor (1) for chemical vapor deposition, wherein a substance contained in the reaction gas is separated from the reaction gas and deposited on the short fibers.

Description

[0001] The invention relates to a method and a device for coating short fibers. In particular, the invention relates to a method and a device for coating short fibers by means of chemical vapor deposition, wherein the short fibers are passed through a non-rotating, vibrating, and heated reactor, and a substance is separated from a gas in the reactor, which substance is deposited on the short fibers.

[0002] In the field of ceramic fiber composites, fibers are coated to protect them from environmental and manufacturing influences, as well as to influence their fracture behavior. For example, non-oxide fibers can be attacked by oxidation or, during a production process involving a siliconization process, by the molten silicon. Therefore, coatings of boron nitride (BN) or carbon can serve as fiber protection.

[0003] Current fiber coating processes include wet-chemical processes, such as dip coating, and dry processes, such as chemical vapor deposition (CVD). However, wet-chemical processes can result in inhomogeneous layer thicknesses. With dry processes, agglomeration increasingly occurs as fiber lengths decrease.

[0004] For example, DE 10 2019 215 044 A1 describes a method comprising a low-pressure coating system into which a particle or fiber collective is introduced. Force impacts are applied to particle or fiber agglomerates by means of pulses in a deagglomeration unit, which separate the agglomerates. The separated particles or fibers are coated in a coating zone located below the deagglomeration unit. An excitation unit can generate vibrations in the range from 0.1 Hz to 10 Hz, or in the range from 20 to 100 kHz, or 400 kHz to 5 MHz.

[0005] DE 39 22 539 C2 concerns the coating of prepregs in a reactor for CVD that is non-rotating and is neither tilted nor vibrated.

[0006] DE 198 28 843 B4 and "Coating of carbon short fibers with thin ceramic layers by chemical vapor deposition," Gerrit Hackl, Thin Solid Films, 2006, concern rotating reactors for CVD that are additionally tilted. In this process, short fibers are exposed to high frequency or microwaves.

[0007] In "Nanocoating Individual Silica Nanoparticles by Atomic Layer Deposition in a Fluidized Bed Reactor," LF Hakim, Chemical Vapor Deposition, 2005, a non-rotating reactor for CVD is described. It is oscillated at a frequency of 20 Hz and an amplitude of 3.3 mm. The reactor is not tilted, and particles are coated, not fibers.

[0008] US 2020 / 024736 A1 is directed to a non-rotating reactor vibrating at a frequency of 30 Hz to 300 Hz, which is not tilted and in which particles but no fibers are coated by CVD.

[0009] Against this background, the present invention is based on the object of providing a method and a device for coating short fibers which enable a uniform coating even of larger quantities of fibers.

[0010] This object is achieved by a method having the features of claim 1 and a device having the features of claim 7.

[0011] According to a first aspect for a better understanding of the present disclosure, a method for coating short fibers comprises supplying a reaction gas into a non-rotating reactor, introducing short fibers into the reactor, causing the reactor to oscillate between 1 Hz and 80 Hz, and heating the reactor for chemical vapor deposition, wherein a substance contained in the reaction gas is separated from the reaction gas and deposited on the short fibers.

[0012] The short fibers are thus coated in the reactor using chemical vapor deposition. Specifically, the short fibers are conveyed through a reaction zone due to the reactor's vibration. For example, the short fibers are thrown into the reaction gas stream in the reactor due to the vibration, where they disperse and are coated.

[0013] This method of conveying the short fibers through the reactor enables a uniform coating of the short fibers while significantly reducing agglomeration (compared to other conveying methods). Due in particular to the vibrations at a frequency in this range, the short fibers are atomized in the reactor and can be surrounded by the reaction gas during their flight phase. This leads to a uniform and even coating of the short fibers in the reaction zone.

[0014] A continuously supplied gas stream at the appropriate flow rate through the reactor allows the short fibers to be transported through the reaction zone and out of the reactor. This allows the fibers to be atomized in the reaction zone, where they are surrounded by the flow of reaction gas for coating and simultaneously transported further.

[0015] In the present disclosure, “short fibers” are understood to mean fibers having an (average) fiber length of less than or equal to 3 mm. This can also be a fiber mixture with different fiber lengths, where the fiber lengths are not greater than 3 mm or where the average fiber length is not greater than 3 mm. In one specific embodiment, the (average) fiber length of the short fibers is less than or equal to 2 mm, and in another specific embodiment, the (average) fiber length is less than or equal to 1 mm. For example, a short fiber can have a length of 5 to 1000 µm, preferably between 10 and 500 µm. All of these short fibers tend to form agglomerates or otherwise adhere to one another and form accumulations compared to longer fibers. Furthermore, the fibers can have diameters of 2 to 20 µm, preferably of 5 to 15 µm.

[0016] The process further includes tilting the reactor, which creates an inclined trajectory for the fibers inside the reactor. This promotes forward movement of the fibers, i.e., from a reactor inlet to a reactor outlet. This also allows for very little or no flow of reaction gas through the reactor, thus enabling smooth coating of the short fibers.

[0017] The fibers are in the flight phase and dispersed for a large portion of their residence time in the reactor. This significantly increases the accessibility of the fibers to the reaction gas compared to a bed, enabling an overall higher throughput of fibers through the reactor while maintaining a uniform coating.

[0018] In one implementation variant, setting the reactor into vibration can involve moving the reactor with an amplitude between 0.5 mm and 10 mm, preferably between 1 mm and 5 mm. This amplitude, in combination with the fiber lengths of the short fibers, enables efficient conveyance of the short fibers through the reactor.

[0019] Furthermore, causing the reactor to oscillate may comprise causing the reactor to oscillate between 10 Hz and 40 Hz.

[0020] Alternatively or additionally, a conveying speed of the short fibers in the reactor can be adjusted by the vibration of the reactor, in particular the frequency and / or amplitude, by the tilting of the reactor and / or by the gas flow.

[0021] In conventional reactors, such as a rotary kiln, the fibers fall through the reaction gas due to the rotation of the reactor. However, this results in an uneven filling of the fibers and an uneven residence time of the fibers in the reaction gas. As a result, the reaction gas cannot completely flow around the fibers and, consequently, cannot be completely coated. In the present disclosure, rotation can be omitted, thus enabling the uniform coating described above even of larger amounts of fiber.

[0022] In a further implementation variant, the process can comprise collecting the coated short fibers from the reactor in a collecting container. The collecting container can be arranged, for example, at a reactor outlet, whereby the coated short fibers fall out of the reactor at the outlet due to their conveyance through the reactor and can be collected by the collecting container. The outlet can, for example, comprise or be formed by a flexible hose. This enables continuous or semi-continuous coating of short fibers, whereby even larger quantities of coated short fibers can be produced in a simple and cost-effective manner.

[0023] In yet another implementation variant, the introduction of short fibers into the reactor can comprise connecting a container filled with uncoated short fibers to an inlet of the reactor. The connection can be made, for example, by means of a flexible hose. Furthermore, the introduction of short fibers into the reactor can comprise conveying the short fibers through a screw conveyor. The screw conveyor can, for example, be arranged in the container filled with uncoated short fibers, or an outlet of the container can be connected to a screw conveyor.

[0024] In a further implementation variant, the introduction of short fibers into the reactor and / or the collection of coated short fibers from the reactor can involve opening and closing an inlet or outlet of the reactor. For example, at least one shut-off valve can be provided at or before the inlet or at or after the outlet of the reactor, through which the corresponding supply of short fibers or removal of short fibers can be (temporarily) blocked. This allows a container with uncoated short fibers or a container with coated short fibers to be exchanged during reactor operation.

[0025] In another implementation variant, heating may involve heating the reactor to a temperature between 700 °C and 1600 °C, preferably to a temperature between 900 °C and 1400 °C. The temperature of the reactor promotes the decomposition reactions that lead to the separation of the desired substance from the reaction gas (or carrier gas).

[0026] In a further implementation variant, tilting can involve tilting the reactor to an inclination of 0° to 10°, preferably to an inclination of 0° to 5°, relative to a horizontal plane. Depending on the inclination, amplitude, frequency, and / or velocity of the reaction gas through the reactor, the throughput rate of the short fibers through the reactor can be adjusted. This adjustment of the speed of the short fibers through the reactor, in addition to the composition of the reaction gas, allows for adjustment of the layer thickness of the coating of the short fibers that can be achieved in the reactor based on the residence time of the short fibers in the reaction gas (in the reaction zone).

[0027] In yet another implementation variant, the short fibers can be carbon fibers and / or silicon carbide fibers. These fibers can be used after coating in ceramic composite materials, in particular in materials for use in high-temperature areas and / or in oxidic atmospheres. By way of example only, such ceramic composite materials can be used in rocket engines, in particular in a combustion chamber and / or thrust nozzle of the rocket engine. Likewise, the coated fibers can be used in the production of carbon fiber-reinforced silicon carbide (C f / SiC) can be used

[0028] Alternatively or additionally, the material to be deposited from the reaction gas can be carbon and / or boron nitride. This allows the short fibers to be coated with pyrolytic carbon (pyC) and / or pyrolytic boron nitride (pBN). These coatings can exhibit an orientation. This alignment leads to anisotropic properties of the coating on the fiber, especially when embedded in a ceramic matrix. These anisotropic properties are necessary for certain failure mechanisms of the ceramic fiber composite.

[0029] According to a second aspect for a better understanding of the present disclosure, an apparatus for coating short fibers comprises a non-rotating reactor, a conveyor device configured to introduce short fibers into the reactor, a means for supplying a reaction gas into the reactor, an exciting drive configured to cause the reactor to oscillate between 1 Hz and 80 Hz, and a heater configured to heat the reactor, wherein a substance contained in the reaction gas is separated from the reaction gas and deposited on the short fibers.

[0030] The device further comprises a tilting device configured to tilt the reactor. Depending on the inclination (relative to the horizontal), the trajectory of the fibers within the reactor can be adjusted, thereby adjusting the conveying speed and flow rate of the short fibers through the reactor.

[0031] The reactor can, for example, consist of a tube or comprise a tube. This tube can be made, for example, of aluminum oxide (Al2O3), silicon-silicon carbide (SiSiC), silicon nitride (Si3N4), and similar heat-resistant materials. Furthermore, the reactor can function as a hot-wall reactor, i.e., an outer side of the reactor is heated by the heater, which also heats its inner wall and transfers the heat to the reaction gas and the short fibers contained in the reactor. For example only, the reactor can have an inner diameter of less than 100 mm, preferably between 30 and 60 mm.

[0032] The means for introducing the reaction gas into the reactor can be integrated into the conveying device or implemented by a separate gas supply.

[0033] In another implementation variant, the device can further comprise a storage container in which uncoated short fibers are stored for transport by the conveyor. This enables a continuous supply of short fibers to the reactor, allowing a large quantity of short fibers to be coated in a single process step. Optionally, the conveyor can be arranged in the storage container or provided at an outlet of the storage container.

[0034] Alternatively or additionally, the device may further comprise a collecting container configured to collect coated fibers from the reactor. The collecting container may, for example, be arranged at an outlet of the reactor, so that short fibers fall out of the reactor outlet and collect in the collecting container. Of course, a (flexible) hose, a pipe, a chute, or similar element may also be provided between the reactor outlet and the collecting container, in or on which the short fibers slide into the collecting container. Likewise, a further conveying device may be provided to convey the coated short fibers from the reactor outlet to the collecting container.

[0035] In yet another implementation variant, the conveying device can comprise a screw conveyor, a conveyor belt, or similar transport element. Alternatively or additionally, the conveying device can also scatter or trickle the short fibers into a reaction gas stream before it is introduced (fed) into the reactor, so that the reaction gas stream conveys the short fibers and ultimately introduces them into the reactor.

[0036] Furthermore, the conveying device can optionally comprise a (flexible) hose, pipe, chute, or similar element that guides the short fibers into the reactor. For example, this element can be arranged between a conveyor screw and a reactor inlet.

[0037] In one implementation variant, the interior of the reactor can be sealed from its surroundings. This prevents the reaction gas from escaping from the reactor. Otherwise, exclusive atmospheres could form with the ambient oxygen. Furthermore, the reaction gas can be processed and reused if necessary after leaving the reactor. In this respect, the described device offers advantages over conventional reactors. Since the present device does not contain any rotating elements, especially the reactor, no rotating (sliding) seals are required to seal the interior of the reactor.

[0038] In a further implementation variant, the exciting drive can comprise a crankshaft drive, a piezo actuator, one or more springs, and / or a camshaft drive. For example, the reactor can be coupled to the crankshaft drive, so that rotation of the crankshaft of the crankshaft drive causes the reactor to oscillate. The stroke of the crankshaft can determine the amplitude of the oscillation. The same applies to a camshaft drive. In the case of a piezo actuator, applying an electrical voltage to the piezo element of the actuator can cause a change in the length of the actuator, which can be coupled to the reactor to generate the oscillation. One or more springs (for example, tension springs, compression springs, and / or plate springs) can be combined with any of the drives described here, whereby the oscillation frequency and / or the amplitude of the oscillation, as well as damping of the reactor, can be adjusted.

[0039] The exciting drive can be designed to cause the reactor to oscillate between 10 Hz and 40 Hz.

[0040] In another implementation variant, the device may further comprise a furnace that surrounds and thermally insulates the heater and at least parts of the reactor. For example, the furnace may comprise at least one opening through which the reactor protrudes into the furnace. The heater may be arranged inside the furnace, whereby the heat emitted by the heater acts on the outside of the reactor located there.

[0041] By way of example only, the heater may generate heat by a combustion process (for example using gas), by electricity (for example using induction or resistance heating) and / or by light (for example using a laser or flash light).

[0042] The furnace may further comprise two openings arranged substantially on opposite sides of the furnace. The reactor may thus be passed through the furnace, i.e., each end of the reactor protrudes from the respective opening on an opposite side of the furnace. The reaction zone of the reactor is thus located within the furnace, i.e., within the two openings of the furnace.

[0043] In one implementation variant, the reactor can be excited synchronously with the vibration at both ends, each of which protrudes from one of the two openings in the furnace (from the heating zone). This allows optimal vibration behavior of the reactor to be achieved.

[0044] For example, the at least one opening in the furnace can be larger than the external dimensions of the reactor at that location. This allows movement of the reactor within the furnace, particularly movement due to the vibration the reactor is subjected to. This allows the excitation drive to be located outside the furnace and does not need to be designed for the high temperatures within the furnace.

[0045] In another implementation variant, the tilting device can mount the reactor at an adjustable inclination. This inclination, in combination with the reactor's vibration, can be used to adjust the trajectory of the short fibers inside the reactor, for example, so that the short fibers are transported from a reactor inlet to a reactor outlet.

[0046] For example, the tilting device can be coupled to the exciting drive or at least form a section of the exciting drive, thus transmitting the vibration of the exciting drive to the reactor. The coupling between the tilting device and the exciting drive can be achieved via a rod, cable, support, screw connection, bolt connection, sleeve, etc. The coupling can further comprise a guide along which the reactor is moved when it is set into vibration.

[0047] In yet another implementation variant, the device may further comprise a housing that surrounds the reactor and / or the heater and / or the excitation drive and / or the tilting device. The housing may, in particular, serve to protect the components of the device arranged therein.

[0048] In another implementation variant, the device may further comprise an inlet valve configured to close a supply of short fibers upstream of an inlet of the reactor (e.g., a supply line). Alternatively or additionally, the device may further comprise an outlet valve configured to close an outlet of the reactor or a line connected thereto.

[0049] For example only, the inlet valve can be arranged at a connection between the storage container and the reactor inlet. Likewise, the outlet valve can be provided at a connection between the reactor outlet and the collection container. By closing the valve(s), the storage container and / or collection container can be replaced during operation. This allows for continuous (or semi-continuous) production of coated short fibers.

[0050] The aspects and implementation variants described above can, of course, be combined without this being explicitly described. Each of the implementation variants described is therefore optional to each implementation variant or even combinations thereof. The present disclosure is therefore not limited to the individual embodiments and variants in the described order or to a specific combination of the aspects and implementation variants.

[0051] Preferred embodiments of the invention will now be explained in more detail with reference to the accompanying schematic drawings, in which Fig. 1 schematically shows a sectional view of an apparatus for coating short fibers; and Fig. 2 schematically shows a flow diagram of a process for coating short fibers.

[0052] Fig. Figure 1 schematically shows a device for coating short fibers, which are provided, for example, in a storage container 15 of the device. For example, the storage container 15 can contain short fibers without a coating or with a coating (multiple coatings or layer systems with different substances), or at least only with a primer.

[0053] The device comprises a conveyor 10 configured to introduce short fibers into a reactor 1. The conveyor 10 may comprise a hose, a chute, a pipe, or a similar passive element. A (flexible) hose also serves to decouple the reactor from vibrations from other components of the device. Alternatively or additionally, the conveyor 10 may also be an active element, such as a screw conveyor, a conveyor belt, a blower, or the like.

[0054] The reactor 1 has an inlet 7 through which the short fibers are fed into the reactor. The reactor 1 has an interior space (or cavity) filled with a reaction gas. The reaction gas can also flow through the reactor 1 (in Fig. 1 for example from left to right).

[0055] The device further comprises a heater 3 configured to heat the reactor 1. A substance contained in the reaction gas is separated from the reaction gas and deposited on the short fibers. In other words, a chemical vapor deposition of the substance from the reaction gas and deposition on the fibers takes place.

[0056] After passing through the reaction zone of reactor 1, in particular the interior of reactor 1, the (now coated) short fibers leave reactor 1 via an outlet 8. A passive element 20 for transporting the coated fibers away, such as a hose, a chute, a pipe, or the like, can be connected to outlet 8. Alternatively or additionally, a conveying device in the form of an active element can be provided, such as a screw conveyor, a conveyor belt, a blower, a vacuum pump, or the like.

[0057] In any case, the short fibers are collected in a collecting container 25 after leaving reactor 1. The finished and coated short fibers are stored therein for further use and / or processing.

[0058] The short fibers are conveyed through reactor 1 via an exciting drive 6, which is designed to cause the reactor to vibrate. A low-frequency vibration is used, which causes the short fibers to be thrown upwards within the reactor 1 and thus disperse within the reactor 1's interior (the reaction zone). There, the fibers can be very uniformly surrounded and coated on all sides by the substance contained in the reaction gas. The vibration can, for example, have a frequency between 1 Hz and 80 Hz, preferably between 10 Hz and 40 Hz.

[0059] The exciting drive 6 can be in the form of a crankshaft drive, as in Fig. 1. Alternatively or additionally, the exciting drive 6 can also comprise a camshaft drive, a piezo actuator, and / or one or more springs.

[0060] A coupling between the reactor 1 and the exciting drive 6 can be made via a rod, a cable or a similar suspension or bearing, which is Fig. 1 is designated by reference numeral 5. The device can also achieve coupling via a tilting device configured to tilt the reactor 1. This inclination of the reactor 1, which can be between 0° and 10°, preferably between 0° and 5°, relative to a horizontal, enables a trajectory of the short fibers in the reaction zone of the reactor 1 that is directed toward the outlet 8 of the reactor 1. For example, the end of the reactor 1 with the outlet 8 can be arranged lower than its inlet 7. The tilting device 5 can be designed such that the inclination of the reactor 1 can be freely adjusted.

[0061] The excitation drive 6 can optionally be equipped with counterweights (not shown). The resulting balancing prevents or at least minimizes the transmission of vibration to the entire device, thus reducing machine vibrations.

[0062] The device may further comprise a furnace 2 that surrounds and thermally insulates the heater 3 and at least parts of the reactor 1. Thus, a high and uniform temperature can be achieved in the reaction zone of the reactor 1. To enable a continuous supply of short fibers into the reactor 1 and / or a removal of coated short fibers from the reactor 1, the furnace 2 may comprise at least one opening 4 through which the reactor 1 protrudes into or out of the furnace 2.

[0063] Furthermore, the device may comprise a housing 30 which surrounds at least the reactor 1. As in Fig. 1, the housing 30 can comprise all components of the device, with the exception of the storage container 15 and / or the collecting container 25.

[0064] Reaction gas can be introduced into reactor 1 via a gas supply line 50 (or gas feed line). Accordingly, the reaction gas can be discharged after leaving reactor 1 via a gas discharge line 55 (gas discharge line). An inlet valve 40 can be provided between storage vessel 15 and reactor 1, which hermetically seals storage vessel 15 from reactor 1 (and also from gas supply line 50). Likewise, an outlet valve 45 can be provided on the outlet side of reactor 1, which hermetically seals collection vessel 25 from reactor 1 (and also from gas discharge line 55). This allows storage vessel 15 and / or collection vessel 25 to be exchanged during operation (particularly when heater 3 is running and drive 6 is energized). The flow of reaction gas from gas supply line 50 through reactor 1 to gas discharge line 55 can be maintained.This enables continuous or semi-continuous coating of short fibers.

[0065] Fig. Figure 2 shows a schematic flow diagram of an exemplary method for coating short fibers. The method can be carried out, for example, using a device according to Fig. 1. Of course, other devices can also be used to carry out the procedure.

[0066] In a first step 310, reaction gas is fed into reactor 1. The reaction gas can be introduced into reactor 1 from a container (not shown) or a conveyor or other source, for example, via gas supply line 50.

[0067] In a further step 315, short fibers are introduced into a reactor 1. This can be achieved by simply pouring or otherwise filling the reactor 1 with short fibers. Alternatively or additionally, a continuous supply of short fibers into the reactor 1 can also be achieved via a conveyor device 10 or the like.

[0068] Steps 310 and 315 can, of course, also be performed simultaneously. For example, a stream of the reaction gas into reactor 1 can also be used to introduce the short fibers into reactor 1, for example, by blowing the short fibers into the reactor with the reaction gas.

[0069] Setting reactor 1 into vibration (step 320) causes the short fibers in reactor 1 to be thrown up and dispersed in the reaction gas. For example, reactor 1 can be set into vibration between 1 Hz and 80 Hz, preferably between 10 Hz and 40 Hz. By "whirling up" the short fibers in the reaction zone of reactor 1, and only optionally by the flow of the reaction gas through reactor 1, the short fibers are transported further within reactor 1.

[0070] This transport of the short fibers is assisted by tilting the reactor 1 in step 330. For example, an outlet 8 (end) of the reactor 1 is located lower than an inlet 7 of the reactor 1, so that the trajectory of the short fibers inside the reactor 1 tends to lead to the outlet 8 of the reactor 1. This also allows for very little or no flow of reaction gas through the reactor.

[0071] Steps 320 (oscillation) and 330 (tilting) can be combined and performed simultaneously. Alternatively, reactor 1 can be tilted first and then set into vibration.

[0072] The method further comprises heating the reactor 1 in step 340. Of course, the method can also begin with heating (step 340) the reactor 1 and the remaining steps of the method can then only be carried out once a static temperature distribution has been established in the reactor. The reactor 1 can be heated, for example from the outside, so that a substance contained in the reaction gas is separated from the reaction gas and deposited on the short fibers. For example, at temperatures between 700 °C and 1600 °C, preferably between 900 °C and 1400 °C, carbon and / or boron nitride in the pyrolytic state can be deposited on the short fibers, i.e. the short fibers can be coated therewith.

[0073] Finally, in an optional step 350, the coated short fibers are collected. This can be done, for example, using a collecting container 25 into which the coated short fibers fall and are collected after leaving reactor 1.

[0074] The parameters for the method and device described here can, of course, be used in the exemplary embodiments illustrated in the figures. The embodiments described here are merely exemplary and serve only to illustrate the present invention.

Claims

[1] A method for coating short fibers, comprising: Feeding (310) a reaction gas into a non-rotating reactor (1); Introducing (315) short fibers into the reactor (1); Setting (320) the reactor (1) into an oscillation between 1 Hz and 80 Hz; Tilting (330) of the reactor (1); and Heating (340) the reactor (1) for chemical vapor deposition, wherein a substance contained in the reaction gas is separated from the reaction gas and deposited on the short fibers. [2] Method according to claim 1, wherein the setting (320) of the reactor (1) into oscillation comprises moving the reactor (1) with an amplitude between 0.5 mm and 10 mm, preferably between 1 mm and 5 mm, and / or wherein the setting (320) of the reactor (1) into oscillation comprises setting (320) the reactor (1) into oscillation between 10 Hz and 40 Hz. [3] The method according to claim 1 or 2, further comprising: Collecting (350) the coated short fibers from the reactor (1) in a collecting container (25). [4] Method according to one of claims 1 to 3, wherein the heating (340) comprises heating the reactor (1) to a temperature between 700 °C and 1600 °C, preferably to a temperature between 900 °C and 1400 °C. [5] Method according to one of claims 1 to 4, wherein the tilting (330) comprises tilting the reactor (1) to an inclination of 0° to 10°, preferably to an inclination of 0° to 5°, relative to a horizontal. [6] Method according to one of claims 1 to 5, wherein the short fibers are carbon fibers and / or silicon carbide fibers, and / or wherein the short fibers have a fiber length of less than or equal to 3 mm, preferably less than or equal to 1 mm, further preferably a fiber length of 5 to 1000 µm, particularly preferably between 10 to 500 µm, and / or wherein the substance to be deposited from the reaction gas is carbon and / or boron nitride, and the short fibers are coated with pyrolytic carbon and / or pyrolytic boron nitride. [7] Apparatus for coating short fibers, comprising: a non-rotating reactor (1); a conveying device (10) which is designed to introduce short fibres into the reactor (1); a means for supplying a reaction gas into the reactor (1); an exciting drive (6) adapted to cause the reactor (1) to oscillate between 1 Hz and 80 Hz; a tilting device (5) adapted to tilt the reactor (1); a heater (3) configured to heat the reactor (1) for chemical vapor deposition, wherein a substance contained in the reaction gas is separated from the reaction gas and deposited on the short fibers. [8] Apparatus according to claim 7, further comprising: a storage container (15) in which uncoated short fibers are stored for conveyance by the conveyor device (10); and / or a collecting container (25) adapted to collect coated fibers from the reactor (1). [9] Apparatus according to claim 8, further comprising: an inlet valve (40) which is designed to hermetically seal the storage container (15) from the reactor (1); and / or an outlet valve (45) adapted to hermetically seal the collecting container (25) from the reactor (1). [10] Device according to one of claims 7 to 9, wherein the exciting drive (6) comprises a crankshaft drive, a piezo actuator, one or more springs and / or a camshaft drive, and / or wherein the exciting drive (6) is arranged to cause the reactor (1) to oscillate between 10 Hz and 40 Hz. [11] Device according to one of claims 7 to 10, further comprising: a furnace (2) which surrounds and thermally insulates the heater (3) and at least parts of the reactor (1), wherein the furnace (2) comprises at least one opening (4) through which the reactor (1) projects into the furnace (2). [12] Device according to one of claims 7 to 11, wherein the tilting device (5) supports the reactor (1) at an adjustable inclination, and / or wherein the tilting device (5) is coupled to the exciting drive (6) and transmits the vibration of the exciting drive (6) to the reactor (1). [13] Device according to one of claims 7 to 12, further comprising: a gas supply line (50) which is designed to guide the reaction gas to the conveying device (10) and / or to the reactor (1); and / or a gas discharge line (55) which is designed to discharge the reaction gas after leaving the reactor (1). [14] Device according to one of claims 7 to 13, further comprising: a housing (30) surrounding the reactor (1), wherein the housing (30) preferably surrounds the heater (3) and / or the exciting drive (6) and / or the tilting device (5).

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