FIELD

[0001 ] The present invention relates to sealing. In particular, the present invention relates to a sealing of a drive shaft.

BACKGROUND

[0002] In the field of additive manufacturing an additive manufacturing apparatus is also called a 3D-printer. In 3D-printing objects or workpieces are built/created/gener ated by subsequent depositing layers (beads) of material onto each other. This mate rial may be plastic material and in particular, the depositing process may be the FDM or FFF process. The material supplied to the 3D-printer may be filament or granulated material.

[0003] The 3D-printer usually comprises a printhead that moves in three dimensions. Also, there are 3D-printers that comprise printhead that move in two dimensions and a printbed (the surface or structure on/to which the workpiece(s) are created) that moves in the third dimension. Also, there are printheads that are mounted to a con ventional industrial robot such that the printhead can realize complex trajectories. The printhead generally comprises an extruder to apply the material to build up the work- piece.

[0004] In the field of FDM or FFF printing, the printhead conventionally may comprise an extruder comprising a hotend and a material feed unit. The material feed unit sup plies build material (the material from which the workpiece is built) to the hotend. Said build material is heated up to its melting temperature within said hotend and extruded through a nozzle that is connected to the hotend. The extruded build material forms a deposited strand that in turn forms one layer of the workpiece being built. An outlet opening of the nozzle (material outlet) has usually a circular cross section, however, other shapes are possible. The heated and plastic-state material leaves the print head/the nozzle trough said outlet opening to build up the workpiece(s). The extruder may use any known technology such as screw extruders, gear pumps, tube liquefiers or any combination of these.

[0005] In the field of gear pumps usually one of the gears is driven from the outside of the gear pump to drive a meshing idle gear. This drive usually is realized by a rotat ing drive shaft being connected to the drive gear or driven gear on one end and to e.g. a motor on the other end. Since said drive shaft has to pass from the inside of the gear pump and thus a pressurized and/or high temperature environment to the outside where usually the motor is located, there has to be a sealing such that the medium being pumped and thus pressurized with the gear pump cannot spill out of the gear pump along the drive shaft. Conventional sealings are for example glands or shaft sealing rings or a labyrinth seals a combination thereof. However, these sealings are not 100% tight and/or costly and/or difficult to manufacture or integrate in the respec tive unit.

SUMMARY

[0006] It is thus the object of the present application to provide a shaft sealing and sealing arrangement according to the appended independent claims to overcome the above inconveniences. Selected embodiments are comprised in the dependent claims. Each of which, alone or in any combination with the other dependent claims, can rep resent an embodiment of the present application. The advantage of a shaft sealing and sealing arrangement according to the appended independent claims is that the sealing can be adjusted to different materials and thus operating conditions of the gear pump (e.g. different temperatures and different pressures because of different materials be ing pumped). Further, the shaft sealing and sealing arrangement may have no parts that are in contact with the rotating drive shaft and is thus almost non-wearing.

[0007] According to one aspect of the present application a shaft sealing assembly comprises a sleeve and a cooling section. The sleeve has a pump end and a motor end and the cooling section is coupled with the sleeve between these ends. This cou pling may be a thermal and/or mechanical coupling. This design may have the ad vantage that the cooling section cools the sleeve and if the shaft sealing assembly is operatively coupled to a gear pump of any sort, a pressurized and/or hot material within the sleeve may be cooled and thus the viscosity of the material is increased. This may result in a self-sealing quality of the shaft sealing assembly since material with a lower viscosity and/or higher temperature cannot pass the cooled-down material having a higher viscosity. The sleeve may be connected to another part in a conventional man ner e.g. threaded into the housing of a gear pump and this connection may be sealed with a conventional seal. The sleeve and/or the cooling section may have a coupling structure (e.g. a thread) to be connected to a housing of e.g. a pump. However, the shaft sealing assembly may be integral part of the housing. The dimensions of the cooling section may be chosen according to the individual application. For example, if a relatively big temperature drop has to be realized then the cooling section will be bigger then in case of a smaller temperature drop is needed.

[0008] According to another aspect of the present application the cooling section of the shaft sealing assembly comprises at least one cooling fin. This may have the ad vantage that the surface of the cooling section is increase and more heat can be emit ted or dissipated.

[0009] According to another aspect of the present application the at least one cooling fin may change at least one of its dimensions (e.g. width, heigh, etc.) over its length and/or comprises at least one hole and/or groove. This may have the advantage that the surface of the at least one cooling fin is enlarged and heat can be dissipated better.

[0010] According to another aspect of the present application the at least one cooling fin is orientated parallel to the cooling section. This may have the advantage that hot air may escape upwards and a convection may be established.

[001 1 ] According to another aspect of the present application the cooling section or the at least one cooling fin of the shaft sealing assembly comprises a porous material. This may have the advantage that the surface of the cooling section is increased, and more heat can be emitted or dissipated.

[0012] According to another aspect of the present application a shaft sealing assem bly comprises the cooling section made from a different material than the sleeve. This may have the advantage that for each application the most fitting material can be cho sen. This may be a wear resistant steel alloy for the sleeve and a metal or a ceramic with increased heat conducting capabilities for the cooling section.

[0013] According to another aspect of the present application the cooling section may be made from one of the following materials: bronze, cooper, brass, ceramic. This may have the advantage that the cooling section has increased heat dissipating capabilities and may additionally manufactured easily.

[0014] According to another aspect of the present application the cooling section of the shaft sealing assembly comprises at least one active cooling element. This may have the advantage that the cooling capacity can be increased. This may have an advantage in an application of the shaft sealing assembly in which e.g. due to space restraints the cooling section needs to be small. The cooling element may be any of known cooling elements such as a fan or a Peltier element or a combination thereof.

[0015] According to another aspect of the present application the shaft sealing as sembly further comprises a temperature sensor operatively coupled to the sleeve. This may have the advantage that data can be harvested, and it e.g. can be controlled if the shaft sealing assembly is operating in an allowable temperature range for an individual material. Also, the temperature sensor may be operatively coupled to an active cooling element via a control unit such that the active cooling element can be controlled de pendent on the temperature of the sleeve and thus dependent on the temperature of the material in the sleeve. Hence, the temperature of the material may be kept in an ideal range such the shaft sealing assembly exhibits its self-sealing quality even for different materials with different relations between their temperature and their viscosity. It may be of advantage if the temperature sensor is located in the vicinity of the cooling section such as to control the influence of the cooling section on the sleeve.

[0016] According to another aspect of the present application the cooling section of the shaft sealing assembly may further comprise at least one fluid channel. This may have the advantage that heat from the sleeve and/or the cooling section may be trans ported away by a cooling fluid e.g. water. Also, any other cooling fluid is possible. There may be the case that the shaft sealing assembly is used in a technical environment in which already a cooling fluid / cooling system is present, then the shaft sealing assem bly may be adopted there to. It is also possible to couple an evaporator to the cooling section. There may be also an expansion valve upstream of the evaporator. The ex pansion valve may be controllable. The data of the above temperature sensor may be used to control the flow of fluid through the at least one fluid channel. A control unit operatively coupled to and control the temperature sensor and a valve and/ or a fluid pump regulating the flow of fluid through the at least one fluid channel and/or the evap orator dependent on the data of the temperature sensor.

[0017] According to another aspect of the present application the shaft sealing as sembly further comprises a sealing element located in the area of the motor end. This may have the advantage that in case of failure of malfunction of the shaft sealing as sembly the sealing element may seal any leakage. This increases the reliability of the shaft sealing assembly.

[0018] According to a further aspect of the present application a shaft sealing arrange ment comprises a draft shaft and a shaft sealing assembly according to any of the above aspects. The drive shaft is located rotatable within the sleeve. This arrangement may have the advantage that any material that flows along the drive shaft e.g. for pres sure differences and/ or due to gravity, will be cooled-down in the area of the cooling section and thus the viscosity of the material will be increased. This may result in a self-sealing quality of the shaft sealing arrangement.

[0019] According to a further aspect of the present application a 3D-printhead com prises a shaft sealing assembly or a shaft sealing arrangement according to any of the above aspects. This may have the advantage that the reliability of the 3D-printhead may be increased. This may further have the independent advantage that the 3D-print- head may be miniaturized. The shaft sealing assembly of a shaft sealing arrangement according to any of the above aspects may be applied to an 3D-printing-extruder that utilises a gear pump extruding plastic material as build material. If the drive shaft of said 3D-printing-extruder rotates the hot and pressurized material surrounding the ro tating drive shaft wanting to escape/spill towards the motor end due to the pressure difference, can be cooled and its viscosity increased such that the material itself clogs the space between the sleeve and the drive shaft and thus sealing off the pump end from the motor end. Due to friction caused by the rotating drive shaft, the clogged material in the area of the cooling section within the sleeve has a low viscosity in the vicinity of the rotating drive shaft that allows the drive shaft to rotate. However, this vicinity is too small that material would spill since generated heat is instantaneously dissipated by the cooling section. Moreover, usually the plastic build material is a poor conductor of heat which increases the aforementioned sealing effect.

[0020] According to a further aspect of the present application a gear pump extruder comprises a shaft sealing assembly or a shaft sealing arrangement according to any of the above aspects wherein the sleeve is located around a drive shaft of the gear pump.

[0021 ] Further to the fact that only a 3D-printhead or a gear pump was described above, the present application may be applied to any application in which a rotating shaft needs to be sealed and wherein the medium to be sealed of at least partially surrounding the rotating shaft changes its viscosity due to a temperature difference. This may for example be at least one of viscous materials pumps, thermoplastics melt pumps, melt pump-based extruders, melt pump-based extruders for additive manufac turing.

[0022] The heat dissipating capability of the cooling section is dependent on different influence factor that separately may be chosen. This may be the material of sleeve and/or cooling section, the number, size and orientation of cooling fins, the size of the cooling section, holes/grooves in the fins, etc. They all may be freely combined as needed and/or desired.

[0023] Each of the above aspects is to be considered an invention on its own. The aspects can be combined freely with each other and each feature not described as being dependent on another feature may also be freely combined with each other. BRIEF DESCRIPTION OF THE FIGURES

[0024] Further advantages and features of the present disclosure will be apparent from the appended figure. The figure is of merely informing purpose and not of limiting character. The figure schematically describes embodiments of the present application. Hence, the appended figures cannot be considered limiting for e.g. the dimensions of the present disclosure. Same reference signs refer to parts/components/elements hav ing the same or similar function. For the sake of brevity only the respective differences will be described in view of the previous descriptions.

[0025] Figure 1 shows a perspective cross sectional view of an embodiment of the present application.

[0026] Figure 2 shows a perspective cross sectional view of another embodiment of the present application.

[0027] Figure 3 shows a perspective cross sectional view of another embodiment of the present application.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] Referring to figure 1 a perspective cross sectional view of an embodiment of a shaft sealing arrangement 30 with a shaft assembly 10 of the present application is depicted. The shaft sealing arrangement 30 comprises the shaft assembly 10, having a sleeve 1 1 , a cooling section 12, a sealing element 17 and a drive shaft 20 being inserted into the sleeve 1 1 . The drive shaft 20 is rotatably lodged to the sleeve 1 1 . The sleeve 1 1 has a motor end M and a pump end P. In fig. 1 a gear of a gear pump is connected to the drive shaft further along the drive shaft 20 away from the pump end P of the sleeve 20. A motor (not shown) is operatively coupled to the drive shaft 20 away from the motor end M. In this embodiment the cooling section 12 is a unitary member with the sleeve 1 1 and further comprises several cooling fins 13. The cooling fins are arranged perpendicular to an extension of the drive shaft 20 or sleeve 1 1. [0029] The shaft sealing arrangement 30 depicted in fig. 1 further comprises the seal ing element 17 in the area of the motor end M of the sleeve 1 1 . If material pumped by the gear pump is pushed along the drive shaft 20 due to pressure differences, the hot and pressurized material reaches the region of the sleeve 1 1 where the cooling section 12 with its cooling fins 13 is located. The heat of the material is transferred to the sleeve 1 1 and from there to the cooling section 12 and dissipated by the cooling fins 13. As described above the loss of heat in the material increases its viscosity resulting a con trolled clogging of the gap between the drive shaft 20 and the sleeve 1 1 . Consequently, material having a lower viscosity cannot push the cooled material further along the drive shaft 20 from the pump end P towards the motor end M. In case there is a e.g. a pressure spike or sort of a malfunction there is the sealing element 17 at the motor end M of the sleeve 1 1 as a backup and sealing off an outside of the shaft assembly 10 from an inside (i.e. the pump end P).

[0030] Referring to fig. 2 depicts another perspective cross sectional view of another embodiment of a shaft sealing arrangement 30 of the present application. Here, the sleeve 1 1 and the cooling section 12 are separate elements that may be made from different materials. Also, the cooling fins 13 in this embodiment are differently orien tated in view of the embodiment depicted in fig. 1 . The cooling fins 13 in the embodi ment depicted in fig. 1 are orientated parallel to an extension of the drive shaft 20. Further the cooling fins 13 comprise holes 14 to increase their surface in order to in crease the capability of heat dissipation. Further, the cooling fin 13 comprises a groove 15 that also increases the surface of the regarding fin. Holes 14 and groove 15 can be freely arranged. Further, the groove 15 may be a groove not passing through the cool ing fin 13 or alternatively may pass through the cooling fin 13.

[0031 ] Referring to fig. 3 depicts yet another perspective cross sectional view of an other embodiment of a shaft sealing arrangement 30 of the present application. Here, the cooling section 12 is also a separate element from the sleeve 1 1 . However, in this embodiment the cooling section 12 is made from a porous material. The shaft sealing arrangement 30 further comprises a temperature sensor 35 in the vicinity of the cooling section. The temperature sensor 35 senses the temperature of the sleeve 1 1 to which it is coupled. Further, the cooling section comprises a fluid channel 40. Through this channel it is possible to circulate a fluid to better control the heat dissipation e.g. using data provided by the temperature sensor 35.

[0032] The features of the above embodiments may freely be combined. For example, all forms and orientations of cooling fins as well as the porous material may be com bined with holes 14, grooves 15 or fluid channels. The temperature sensor 35 may be added to any shaft sealing arrangement 30 optionally. The sleeve 1 1 and the cooling section 12 may or may not be unitary. In the appended figures the sleeve 1 1 is depicted longer than the cooling section 12 (with respect to the extension of the drive shaft 20), however, the sleeve 1 1 and the cooling section 12 may have the same length.

List of reference signs

10 shaft assembly

11 sleeve

12 cooling section

13 cooling fin

14 hole

15 groove

17 sealing element

20 drive shaft

30 shaft sealing arrangement 35 temperature sensor

40 fluid channel

P pump end

M motor end