DE102020112078A1 - Technology for storing or conveying a granulate - Google Patents

Abstract

A hollow body (100) for storing or conveying a dielectric or electrically insulating granulate (102) is described. Inside the hollow body (100) there are electrically conductive fixtures (104) which are designed to contact a granulate surface of the granulate (102) stored or conveyed in the hollow body (100) and to dissipate an electrostatic charge from the granulate surface and / or electrostatic charge differences equalize on the surface of the granulate.

Description

The invention relates to a technique for storing or conveying a granulate. In particular, a hollow body is provided for storing or conveying a dielectric or electrically insulating granulate.

Dielectric or electrically insulating granules, for example powder for additive manufacturing, in particular for powder bed-based 3D printing processes, or for powder coating of components, are characterized by a large specific surface and low electrical conductivity of the dielectric particles (for example plastic particles) of the granules. One consequence of these material characteristics is that when the granulate moves, there is friction-induced charge shifts between the individual particles or between the particles and guide surfaces.

The resulting electrostatic charge or charge differences can or can worsen the rheology of the granulate or prevent the direct use of the granulate (for example for the additive manufacturing process). The electrostatic charge can also lead to considerable problems in the course of the process, for example when conveying or removing the granulate.

In order to ensure process-relevant properties of the granulate, for example its rheology, it is therefore customary in practice to temporarily store the granulate after the granulate has moved - for example after mixing, sieving or conveying processes. During this time, charge diffusion processes bring about a charge balance, which ultimately brings about an electrostatic homogenization of the granulate. From an economic point of view, however, this type of charge balancing is to be viewed as critical, as it considerably extends process times and ties up storage resources.

The document WO 2018/029187 A1 describes a technique for electrostatic homogenization of the granulate by means of ionizing radiation. The supply of a manufacturing device has a discharge device. The discharge device emits ionizing radiation, which electrostatically discharges the starting material. The electrostatic discharge prevents, in particular, dust particles or impurities from adhering to the surface of the starting material. In addition, a plasma source can be used to pretreat and / or sterilize the surface of the starting material. However, such a technology is expensive, maintenance-intensive and energy-intensive, since a source of ionizing radiation is required. In addition, a brittleness, a melting temperature or a viscosity of the particles (for example the plastic of the plastic particles) can be increased by the ionizing radiation.

The invention is therefore based on the object of specifying a reliable and energy-efficient technique for electrostatic homogenization of a granulate which does not, or only slightly, extends process times.

The object is achieved with the features of claim 1. Appropriate configurations and advantageous developments of the invention are specified in the dependent claims.

Embodiments of the invention are described below with partial reference to the figures.

According to one aspect, a hollow body for storing or conveying a dielectric or electrically insulating granulate comprises electrically conductive internals arranged within the hollow body. The internals are designed to contact a granulate surface of the granulate stored or conveyed in the hollow body and to derive an electrostatic charge from the granulate surface and / or to compensate for electrostatic charge differences on the granulate surface.

The electrically conductive internals can be designed to bring about an electrostatic charge balance on the surface of the granulate.

Embodiments of the hollow body can by means of the electrically conductive internals when storing the granules, for example when filling or emptying the hollow body for storing the granules, and / or when conveying the granules, for example when passing through the hollow body to convey the granules, the electrostatic charge of the granulate surface and / or compensate for the electrostatic charge differences through the contact between the granulate surface and the electrically conductive fixtures.

The granules can comprise a multiplicity of particles. A shape and / or size of the particles of the granulate can be uniform or correspond to a distribution. The granulate can be a powder, for example with particle diameters that are smaller than 100 μm.

The internals can comprise a helix or a plurality of helices, for example the internals can have the shape of one or more helical lines (preferably one inside the other). A longitudinal or symmetry axis of the helix or helices can be parallel (preferably coaxial) to a longitudinal or symmetry axis of the hollow body (for example a cylindrical tube) and / or parallel to a conveying direction (for example a direction of movement) of the granulate conveyed in the hollow body. The longitudinal or symmetry axis of the helix can be a cylinder axis, around whose lateral surface the helix winds.

By means of the helix or helices, embodiments of the hollow body can mix the granules during the conveying, filling and / or emptying according to a winding direction of the helix or helices. As a result, a larger number of particles of the granulate can come into contact with the internals in order to dissipate the electrostatic charge and / or to compensate for the electrostatic charge differences. As an alternative or in addition, the helix or helices can additionally mix the granulate, as a result of which a larger number of particles of the granulate come into contact more frequently with the electrically conductive internals.

As an alternative or in addition, the internals can comprise one or more electrically conductive (for example cylindrical) tubes. A longitudinal or symmetry axis of the tube can be parallel or coaxial to a longitudinal or symmetry axis of the hollow body and / or parallel to a conveying direction of the granulate conveyed in the hollow body. Embodiments of the hollow body can dissipate the electrostatic charge and / or compensate for differences in electrostatic charges via the inner surface of the or each tube.

As an alternative or in addition, the built-in components can comprise stick electrodes. The rod electrodes can be perpendicular to a longitudinal or symmetry axis of the hollow body, for example extending radially inward from an inner surface of a cylindrical hollow body. Alternatively or in addition, stick electrodes can extend or branch in a conveying direction of the granulate conveyed in the hollow body. As a result, a large portion of a cross section, or the entire cross section of the hollow body through an arrangement of several rod electrodes overlapping in the conveying direction, can be provided with a contact surface for discharging and / or balancing the electrostatic charge without blocking the conveyance of the granulate.

The hollow body can furthermore comprise the granulate stored or conveyed in the hollow body. The granulate can have a dielectric plastic (for example a thermoplastic) and / or an electrical insulator (for example a ceramic) or be made from it. Alternatively or in addition, a specific surface area of the granulate (for example a surface area of the particles of the granulate) can be at least 1 square meter per gram.

The hollow body can furthermore comprise an inner wall enclosing the internals. The inner wall can be designed to store or convey the granulate. For example, the granules can lie against the inner wall during storage or conveyance. For example, the inner wall can be cylindrical.

A contact area of the internals can be larger than a wall area of the inner wall for contacting the granulate surface of the granulate. Alternatively or additionally, the inner wall can be designed to contact the granulate surface and to compensate for the electrostatic charge from the granulate surface and / or electrostatic charge differences on the granulate surface. As an alternative or in addition, the inner wall can be electrically conductive and / or connect the internals in an electrically conductive manner. Embodiments of the hollow body can additionally contribute to the dissipation of the electrostatic charge and / or to the compensation of the electrostatic charge difference via the inner wall.

The internals can be electrically conductive and / or mechanically connected to the inner wall of the hollow body at a first end of the internals. For example, a second end of the internals opposite the first end can stand freely in the interior of the hollow body. As an alternative or in addition, the internals can comprise electrodes standing perpendicular to the inner wall and / or radially inwardly projecting electrodes.

The hollow body can comprise a ground connection for connecting a ground potential. The internals can be connected to the ground connection in an electrically conductive manner in order to dissipate and / or compensate for the electrostatic charge on the surface of the granulate. Embodiments can achieve the dissipation of the electrostatic charge without the use of energy (for example beyond the friction of the granulate on the internals).

The electrically conductive internals can be arranged stationary or rotating in the hollow body. For example, stationary built-in components can be reliably connected to the ground connection in an electrically conductive manner. As an alternative or in addition, the internals can rotate about an axis of rotation parallel to the conveying direction. The rotating internals can for example divert and / or compensate for the electrostatic charge in a larger cross section of the hollow body without additional friction when conveying the granulate.

The electrically conductive internals can be connected to one another in an electrically conductive manner, preferably to homogenize the electrostatic charge in the granulate. As an alternative or in addition, the built-in components can be connected in an electrically conductive manner to a ground potential.

The hollow body can have a first opening for receiving the granules and a second opening opposite the first opening in the conveying direction for dispensing the conveyed granules. The hollow body can be a pipeline or a section of a pipeline for conveying the granulate.

The conveyance of the granules can be associated with a movement, for example an internal movement or a shear flow, of the granules. Embodiments of the hollow body can prevent, compensate or dissipate the electrostatic charge which can arise, for example, due to the shear flow within the granulate or which can arise through charge separation between the granulate and a guide surface for conveying the granulate.

The invention is explained in more detail below with reference to the drawings using preferred exemplary embodiments.

• 1 eine schematische Darstellung eines Hohlkörpers zur Förderung oder Lagerung eines Granulats gemäß einem Anwendungsbeispiel in einer halbtransparenten Ansicht;
• 2 eine schematische Darstellung des Hohlkörpers gemäß einem ersten Ausführungsbeispiel in einer halbtransparenten Ansicht;
• 3 eine schematische Darstellung des Hohlkörpers gemäß einem zweiten Ausführungsbeispiel in einer halbtransparenten Ansicht;
• 4 eine schematische Darstellung des Hohlkörpers gemäß einem dritten Ausführungsbeispiel in einer halbtransparenten Ansicht;
• 5 eine schematische Darstellung des Hohlkörpers gemäß einem vierten Ausführungsbeispiel in einer halbtransparenten Ansicht und
• 6A, 6B und 6C schematische Darstellungen einer zeitlichen Sequenz des Hohlkörpers gemäß einem fünften Ausführungsbeispiel in einer halbtransparenten Ansicht.

Show it:

• 1 a schematic representation of a hollow body for conveying or storing a granulate according to an application example in a semi-transparent view;
• 2 a schematic representation of the hollow body according to a first embodiment in a semi-transparent view;
• 3 a schematic representation of the hollow body according to a second embodiment in a semi-transparent view;
• 4th a schematic representation of the hollow body according to a third embodiment in a semi-transparent view;
• 5 a schematic representation of the hollow body according to a fourth embodiment in a semi-transparent view and
• 6A , 6B and 6C schematic representations of a time sequence of the hollow body according to a fifth exemplary embodiment in a semitransparent view.

1 shows schematically an exemplary system in which an embodiment of a hollow body 100 for storing or conveying a granulate 102 can be used. The granulate can be dielectrically or electrically insulating, for example made from a dielectric solid or an electrical insulator.

The system includes a silo 110 (for example a powder silo 110 ) for storing or stocking the granulate 102 . The silo 110 stands over piping, which is used as an embodiment of the hollow body 100 for conveying the granulate in one conveying direction 108 is formed or at least partially an embodiment of the hollow body 100 for conveying the granulate in the conveying direction 108 includes, with a manufacturing facility 120 in fluid communication. The manufacturing facility 120 is designed to process the granulate, for example in additive manufacturing.

In order to achieve a rapid charge equalization within the powder, it is not sufficient, as in conventional systems, to ground the individual components for storing or conveying a granulate in the process chain. Due to the conventionally small contact areas of the granulate (for example a powder) to conductive materials and / or the low electrical conductivity of the granulate itself, charge equalization takes place only very slowly.

Only through internals is an enlargement of the contact area between the granulate (for example the powder) and the internals made of a conductive material achieved, which can significantly accelerate the charge equalization.

Against this background, the underlying technical teaching provides for the targeted introduction of additional surfaces and geometries made of conductive materials by means of the electrically conductive internals.

This allows the contact surface between the granules 102 (for example a powder) and the internals with conductive materials can be increased many times over. Electrostatic homogenization can therefore occur much earlier or more quickly.

the 2 until 5 and FIGS. 6A to 6C each show schematic views of an exemplary embodiment of a generally with reference numerals 100 designated hollow body for storing or conveying a granulate 102 . The features shown in the exemplary embodiments, in particular internals 104 , can be combined in further exemplary embodiments.

2 shows a first embodiment of the hollow body 100 . The hollow body 100 includes within the hollow body 100 arranged and electrically conductive internals 104 , which are designed to have a granulate surface of the in the hollow body 100 stored or conveyed granulate 102 and to divert an electrostatic charge from the surface of the granulate or to compensate for differences in electrostatic charges.

In the in 2 The first exemplary embodiment shown schematically comprise the hollow body 100 a tube with an inner wall 106 and the internals 104 an electrically conductive helix (for example one or more helical lines) arranged inside the pipe (preferably radially spaced from the pipe). The helix 104 can one in the conveying direction 108 include wire wound around an (imaginary) lateral surface of a cylinder. The turns of the helix can have a constant pitch.

3 shows schematically a second embodiment of the hollow body 100 . The second exemplary embodiment can be implemented on its own or as a further development of the first exemplary embodiment.

In the in 3 schematically shown second embodiment comprise the hollow body 100 and the internals 104 a double-walled pipe. An inside wall 106 of the outer tube of the hollow body 100 is preferably from a conductive inner wall of the inner tube containing the internals 104 forms, spaced.

Optionally, the distance between the outer and inner tube can be dimensioned so that part of the granulate 102 (For example, one or a few layers of the particles of the granulate) is conveyed between the outer and the inner tube.

4th shows schematically a third embodiment of the hollow body 100 . The third exemplary embodiment can be implemented on its own or as a further development of the first and / or second exemplary embodiment.

In the in 4th third exemplary embodiment shown schematically comprise the hollow body 100 a pipe and the internals 104 one is essentially in the conveying direction 108 extending stick electrode. The stick electrode splits or branches in the conveying direction 108 . The branch rod electrodes emanating from the branching of the rod electrode also extend at least in the conveying direction 108 . This allows the electrostatic charge of particles of the granulate in a larger cross section of the hollow body 100 be derived.

The rod electrode preferably branches out several times. This means that further stick electrodes can branch off from the branch stick electrodes.

5 shows schematically a fourth embodiment of the hollow body 100 . The fourth exemplary embodiment can be implemented on its own or as a further development of the first and / or second and / or third exemplary embodiment.

In the in 5 the fourth exemplary embodiment shown schematically comprise the hollow body 100 a pipe and the internals 104 conductive rods (also: stick electrodes). The rods are spaced from one another and are each perpendicular to an inner wall 106 of the pipe.

For example, are along the conveying direction 108 or in the longitudinal direction of the tube, 4 bars are arranged in groups. In each group of 4 bars, the bars are connected to the inner wall in an electrically conductive and mechanical manner at a first end of the bar. A second end opposite the first end stands free from the granulate 102 flowed through the interior of the hollow body 100 .

In each exemplary embodiment, the teaching can be technically implemented, for example, by using spirals, rods, sheets or other geometries made of electrically conductive materials as internals 104 in the hollow body 100 are arranged. The electrically conductive materials can include, for example, silver, copper, gold or precious metals. The waveguide can be designed as a pipeline, a storage container, a pump or another process component.

the 6A , 6B and 6C show schematically a time sequence of a fifth embodiment of the hollow body 100 . The fifth exemplary embodiment can be implemented on its own or as a further development of the first to fourth exemplary embodiments. In particular, each of the four above-described exemplary embodiments of the built-in 104 also be used in the fifth embodiment.

In the fifth embodiment, the internals are in a hollow body 100 for storage (preferably for stockpiling) the granulate 102 integrated. The hollow body is preferably 100 into the manufacturing facility 120 integrated.

For example, is the manufacturing facility 120 for additive manufacturing using the granulate 102 formed according to a powder bed-based 3D printing process. The granules 102 becomes from the hollow body 100 conveyed to an upper edge by means of an ascending piston during the printing process. The granulate flows through it 102 those in the hollow body 100 arranged internals 104 and is (at least partially) discharged electrostatically (preferably spark-free).

The essentially electrically neutral granulate 102 is transferred to the print bed by means of a scraper. Due to the electrostatic neutrality, the granulate spreads 102 with a uniform layer thickness (for example a monolayer) on the existing partial product. For example, a laser beam, which can be freely positioned on the printing bed via a mirror that is pivotable about two axes, can melt the next layer of granulate and thereby bond it with the existing partial product.

As was evident from the above exemplary embodiments, at least individual exemplary embodiments can realize numerous advantages. Thus, embodiments of the hollow body 100 Processing-relevant powder properties and / or a rheological properties of the granulate 102 during or after movement of the granules 102 obtain. These properties can relate to flowability, bulk density, etc. The same or further exemplary embodiments can electrostatically charge the granulate 102 prevent or reduce.

Embodiments of the hollow body 100 can rest periods and / or storage volume of the granules 102 to reduce. As an alternative or in addition, a process stability of the granulate can be used 102 be improved.

Although the invention has been described with reference to exemplary embodiments, it will be apparent to those skilled in the art that various changes can be made and equivalents used as replacements. Furthermore, many modifications can be made to adapt a particular situation or material to the teachings of the invention. Consequently, the invention is not limited to the disclosed exemplary embodiments, but rather encompasses all exemplary embodiments that fall within the scope of the appended claims.

List of reference symbols

100

Hollow body

102

granules

104

Internals

106

Inner wall

108

Conveying direction

110

silo

120

Manufacturing facility

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2018/029187 A1 [0005]

Claims (15)

Hollow body (100) for storing or conveying a dielectric or electrically insulating granulate (102), comprising: electrically conductive internals (104) arranged within the hollow body (100) which are designed to contact a granulate surface of the granulate (102) stored or conveyed in the hollow body (100) and to dissipate an electrostatic charge from the granulate surface and / or electrostatic charge differences equalize on the granulate surface. Hollow body (100) after Claim 1 , wherein the internals (104) comprise at least one helix, preferably wherein a longitudinal or symmetry axis of the helix is parallel or coaxial to a longitudinal or symmetry axis of the hollow body (100) and / or parallel to a conveying direction (108) of the in the hollow body (100 ) promoted granules (102). Hollow body (100) after Claim 1 or 2 , wherein the internals (104) comprise at least one electrically conductive tube, preferably wherein a longitudinal or symmetry axis of the tube is parallel or coaxial to a longitudinal or symmetry axis of the hollow body (100) and / or parallel to a conveying direction (108) of the in the hollow body (100) conveyed granules (102) is. Hollow body (100) according to one of the Claims 1 until 3 , wherein the internals (104) comprise rod electrodes, preferably wherein the rod electrodes are perpendicular to a longitudinal or symmetry axis of the hollow body (100) or branch in a conveying direction (108) of the granulate (102) conveyed in the hollow body (100). Hollow body (100) according to one of the Claims 1 until 4th , further comprising: the granules (102) stored or conveyed in the hollow body (100), the granules (102) having or being made from a dielectric plastic, preferably a thermoplastic, or an electrical insulator, preferably a ceramic, and / or wherein the granulate (102) has a specific surface area of at least 1 square meter per gram. Hollow body (100) according to one of the Claims 1 until 5 , further comprising: an inner wall (106) enclosing the internals (104), preferably for storing or conveying the granulate (102). Hollow body (100) after Claim 6 wherein a contact surface of the internals (104) for contacting the granulate surface of the granulate (102) is larger than a wall surface of the inner wall (106) and / or wherein the inner wall (106) is cylindrical. Hollow body (100) after Claim 6 or 7th wherein furthermore the inner wall (106) is designed to contact the granulate surface and to dissipate the electrostatic charge from the granulate surface and / or to compensate for electrostatic charge differences on the granulate surface. Hollow body (100) according to one of the Claims 6 until 8th , wherein the inner wall (106) is electrically conductive and / or connects the internals (104) in an electrically conductive manner. Hollow body (100) according to one of the Claims 6 until 9 wherein the internals (104) are electrically conductive and / or mechanically connected at a first end of the internals (104) to the inner wall (106) of the hollow body (100). Hollow body (100) according to one of the Claims 6 until 10 wherein a second end of the internals (104) opposite the first end is free in the interior of the hollow body and / or wherein the internals (104) comprise electrodes standing perpendicular to the inner wall (106) and / or radially inwardly projecting electrodes. Hollow body (100) according to one of the Claims 1 until 11 , further comprising: a ground connection for connecting a ground potential, wherein the internals (104) are electrically conductively connected to the ground connection in order to dissipate the electrostatic charge from the surface of the granulate. Hollow body (100) according to one of the Claims 1 until 12th , wherein the electrically conductive internals (104) are arranged stationary or rotating in the hollow body (100). Hollow body (100) according to one of the Claims 1 until 13th , wherein the electrically conductive internals (104) are electrically conductively connected to one another and / or are electrically conductively connected to a ground potential. Hollow body (100) according to one of the Claims 1 until 14th wherein the hollow body (100) has a first opening for receiving the granulate (102) and a second opening opposite the first opening in a conveying direction (108) for dispensing the conveyed granulate (102).

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