FIELD OF THE INVENTION

The invention relates to a seal for sealing rolling elements of a bearing or for sealing linear moving elements of an actuator from environmental influence. The invention further relates to a bearing and to a method of producing the seal.

BACKGROUND ART

Additive manufacturing or more commonly called 3D printing is a known production technique in which a three-dimensional solid object is generated from a digital model. The process of additive manufacturing starts with generating the digital model via any known digital modeling methods, such as using a CAD program. Next, the digital model is divided into slices in which each slice indicates for this layer of the digital model where the printed material should be located. The individual slices are sequentially fed into an additive manufacturing tool or 3D printer which deposits the material according to the individual slices and as such generates the complete three- dimensional solid object layer by layer.

In the early days of additive manufacturing, mainly plastic materials or resins have been used as printed material for generating the three-dimensional solid object, but other processes have been developed in which also other materials, including different types of metal may be deposited in layers using this additive manufacturing technique. A major benefit of this manufacturing technique is that it allows the designer to produce virtually any three-dimensional object in a relatively simple production method. This may be especially beneficial when, for example, an initial model is required of a product or when only a limited number of products are required. A drawback of this manufacturing technique is the speed at which the three- dimensional solid objection is produced.

The use of additive manufacturing in high-quality bearings has been limited. However, United States Patent Application US 2013/0216174 discloses a method for producing a roller bearing cage using a 3D printing method. A cage base body is produced by a 3D printing method and is then coated with a thin, nanocrystalline coating. SUMMARY OF THE INVENTION

One of the objects of the invention is to provide a seal for a bearing or an actuator, which seal has location dependent properties.

A first aspect of the invention provides a seal for sealing rolling elements of a bearing or for sealing linear moving elements of an actuator from environmental influence. A second aspect of the invention provides a bearing, while a third aspect of the invention provides a method of producing the seal.

The seal in accordance with the first aspect of the invention has a seal side and an environment side, the seal comprising a first material and a second material, wherein the first material is printed via an additive manufacturing process and has different properties compared to the second material, and

wherein the first material is a hydrophobic or oleophobic material when configured on the environment side.

The inventors have realized that material properties for sealing on the seal side, that is, on the inside of the bearing (or actuator) and therefore near the rolling elements and rings (or a shaft in the case of an actuator) may advantageously be different compared to material properties at the remainder of the seal. However, it is often relatively costly or even nearly impossible to apply different materials only locally. Known methods to apply such specific material locally often require, for example, masking a part of the seal and, for example, coating only the unmasked parts with the specific material. However, such production methods are relatively labor intense and expensive and often rather inaccurate. Furthermore, the coating processes often require a specific temperature or a deposition chamber which further imposes significant limitations on the suitability of such coating solutions for constituting different parts of the seal. In a seal according to the invention in which the first material is applied via the additive manufacturing process, the first material may relatively easily be applied locally by the printing process. This reduces the labor intensive masking steps and allows depositing the first material only at the locations where it is actually required.

Using hydrophobic material for the first material when the first material, in use, is configured on the environment side contributes to keeping water and moisture away from any rolling elements and away from the inside (that is, the seal side) of the bearing to reduce corrosion of elements inside the bearing.

In an embodiment of the seal, the second material is printed via an additive manufacturing process and has different properties compared to the first material. In this embodiment, a major part of the seal may be constituted of printed material, being either the first material or the second material. Of course even further different types of printed materials may be used for producing the seal. An advantage of a seal which is produced from printed material is that it provides a high degree of freedom in the seal geometry and the possibility of placing the needed materials only where they are needed and not across the bulk of the seal. The additional freedom comes from the fact that the geometrical distribution of the elements that make up a seal is not limited as would be when using the traditional construction processes for the seal, e.g.

injection molding and casting which impose limitations related to the flow of non-molten materials into the cast as well as the passage of such materials through narrow section of the seal. Furthermore, specialized materials may be required in parts of the seal, for example, for reducing wear. Such specialized materials are often relatively expensive. Using the additive manufacturing process to apply the printed material only at the location where needed generates a significant cost reduction.

The surface of the seal may be built as part of the process to build the whole seal. This further enables to optimize or tune surface roughness, wetting, heat exchange and other performance parameters without having additional processes to control these performance parameters. All may be done in a single additive

manufacturing production step.

In an embodiment of the seal, the second material is a hydrophobic material when configured on the environment side, and the second material is an oleophilic material when configured at the seal side. So in such an embodiment, any of the first material or second material may be an oleophilic material when facing the rolling elements, and any of the first material or second material may be a hydrophobic material when facing away from the rolling elements.

In an embodiment of the seal, the seal comprises a functionally graded interface layer at one of the interfaces between the first material and the second material, and a composition of the functionally graded interface layer is configured to gradually change from the first material via a mixture of the first material and the second material to the second material. An important benefit of using functionally graded interface layers is that the bonding characteristics of the two materials is significantly improved without the need for additional bonding materials, structures or layers which may degrade the specific material characteristics required for either the first material or the second material. Coatings typically create an abrupt interphase between the bulk (base) material and the deposited layer. This interface is a weak point as it acts as stress concentrator and defines a sharp transition in terms of properties, e.g. thermal expansion, stiffness, elastic properties, chemical gradients, etc. Using an intermediate layer with intermediate properties reduces the abruptness of the properties changes but doubles the number of interfaces. A graded solution is very difficult to make in coating processes as the deposition of the two materials needs to be compatible with the coating process. However, using the additive manufacturing process in which material is deposited layer by layer in a almost pixelated fashion, mixing different materials and even gradually changing the mixing ratio layer by layer is relatively simple. There is no defined interface and it combines the best properties from the bulk and the best surface performances in a seamless solution.

In an embodiment of the seal, the first material may be a a low-friction material and/or a self-lubricating material. Such low-friction materials may enable noise reduction of the bearing comprising the seals according to the invention. Self-lubricant materials may be rather difficult to apply locally and may be rather difficult to apply in a relatively homogeneous layer. Furthermore, these self-lubricant materials are also relatively expensive. Using this additive manufacturing technique, the self-lubricating material may be applied exactly locally there where it is needed and at a layer thickness as required. This results in a good local concentration of the self-lubricant material in a cost-effective manner. Seals are constructed and designed to generate a film (or layer) of lubricant (oil) between them and another moving body. The film is built dynamically when the parts are moving relative to each other, which means that during the non-steady states (accelerations, start-ups, etc.) the film is either perturbed, destroyed or not yet created. So at these moments of acceleration or start-up of the movement most wear takes place. The ability to have self-lubricated and/or hydrophilic materials ensures lubricity at the seal lip in any condition. So adding self-lubricated materials as the first material at the contact area between the seal and any body moving relative to the seal would enhance friction performance and reduce wear.

Avoiding wear is important because wear allows contaminants (water/dust) to enter into the bearing leading to most of the life-reducing damage. From an environmental point of view, a damaged seal will leak and lead to oil/grease getting outside the intended volume and contaminate the environment.

Furthermore, some gearboxes have bearing units which are not lubricated by the same oil used to lubricate the gear wheels. So a seal according to the invention may be used to separate two different lubricants. Such a seal may have, for example, an oleophilic material facing the inside (seal side) of the bearing, and an oleophobic material facing the outside (environment side) of the bearing.

In an embodiment of the seal, the low-friction material is selected from a list comprising graphite, nano-tubes, fullerenes, C60 and other carbon structures, shearable particles, resins, specific polymers/elastomers. In an embodiment of the seal, the oleophilic material is selected from a list comprising polystyrene, silicone and its rubbers, and kapok (fiber). In a further embodiment of the seal, the self-lubricating material is selected from a list comprising graphite and nano-tubes.

In an embodiment of the seal, the second material comprises a hollow structure. A hollow structure may be used to reduce the weight of the seal.

Furthermore, the hollow structure may create space without the need for additional volume. As such, this hollow structure, for example, created during the printing of the seal in the additive manufacturing process, may now be used for other functionalities, such as the containing of lubricants or sensors or even built-in batteries.

In an embodiment of the seal, the hollow structure comprises an opening towards the rolling element. When, for example, the hollow structure is filled with lubricant, the lubricant may be delivered to the rolling elements from the hollow structure in use. The hollow structure may also comprise a sensor and the opening towards the rolling element may generate a connection to the lubricants near the rolling element and provide an indication of the quality of the lubricant near the rolling element. This may, for example, be used to monitor the condition of the bearing and only start, for example, maintenance work when really necessary - for example, resulting from parameters measured by the sensor.

In an embodiment of the seal, the hollow structure, in use, comprises a lubricant.

In an embodiment of the seal, the seal is constituted of printed material comprising the first material and the second material, and the seal is produced by printing the printed material around a building block of the bearing. Such building block may, for example, be the rolling elements or the cage, or even the inner ring, outer ring or both. Seals often have to be joined together to form a closed the seal around the bearing. At the position where the two ends of the seal are joined, the seal may have a weaker construction or wear at the rolling elements. When producing the seal according to the current embodiment, the seal is printed around the rolling elements which prevents any weakness in the construction and prevents increased local wear. Furthermore, clearance between the rolling elements, the cage and the seal are often derived from the mounting compromise which is required when the seal is built separately and mounted later. When printing the seal around the building blocks of the bearing, the clearance between the rolling elements, cage and seal may be optimized without the need for concessions with regard to mounting. The bearing in accordance with the second aspect of the invention comprises the seal according to the invention.

The method in accordance with the third aspect of the invention comprises a step of: printing the first material onto the second material via the additive manufacturing process. This printing process enables that the first material may be deposited at a location on the seal where it is required. Furthermore, the use of the additive manufacturing process allows accurate dosage of the first material, which may result in a reduction of cost.

In an embodiment of the method, the method further comprises the step of: printing the second material via the additive manufacturing process.

In an embodiment of the method, the step of printing the first material and/or the second material comprises printing the printed material around the building blocks of the bearing.

In an embodiment of the method, the additive manufacturing process is selected from a list comprising stereolithography, selective laser sintering, laminated object manufacturing, fused deposition modeling, selective binding, laser engineering net shaping, photo polymerization and selective electron beam sintering, and 3D nesting.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. In the drawings,

Fig. 1 shows a cross-sectional view of a first embodiment of a seal for a bearing according to the invention,

Fig. 2A shows a cross-sectional view of a second embodiment of the seal for a bearing according to the invention, and Fig. 2B shows a partial cross-sectional view of a third embodiment of the seal,

Fig. 3 shows a plan view of a bearing according to the invention, Fig. 4A shows a first embodiment of an additive manufacturing tool in which a liquid resin is used for applying the printed material in the additive manufacturing process,

Fig. 4B shows a second embodiment of the additive manufacturing tool in which a liquid resin is dispensed from a dispenser for applying the printed material in the additive manufacturing process, Fig. 5A shows a third embodiment of the additive manufacturing tool in which the material is granulated into small solid particles which are used for applying the printed material in the additive manufacturing process,

Fig. 5B shows a fourth embodiment of the additive manufacturing tool in which the granulated solid material is dispensed from a dispenser for applying the printed material in the additive manufacturing process, and

Fig. 6 shows a fifth embodiment of the additive manufacturing tool in which a melted plastic material is dispensed for applying the printed material in the additive manufacturing process.

It should be noted that items which have the same reference numbers in different figures, have the same structural features and the same functions, or are the same signals. Where the function and/or structure of such an item has been explained, there is no necessity for repeated explanation thereof in the detailed description.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a plan view of a first embodiment of a seal 100 for a bearing 700 (see Fig. 3) according to the invention. Such seals 100 are used in bearings 700 to protect the internal elements of the bearing 700 from environmental influences, such as moisture and water. In addition, the seals 100 are used to enclose lubricants inside the bearing 700. Such seals have a seal side, on the inside of the bearing or actuator and hence facing the rollers in a roller bearing, and an environment side, on the outside of the bearing or actuator and hence facing the environment.

The seal 100 according to the invention and as shown in Fig. 1 comprises a first material 1 10 which is deposited or printed onto a second material 120 of the seal 100, for example, at a location where, in use the rolling elements (not shown) and/or the cage (not shown) could at least occasionally contact the seal 100. Of course, the first material 1 10 may also be deposited at more positions than shown in Fig. 1 without departing from the scope of the invention.

The first material 1 10 may, for example, be a self-lubricant material or an oleophilic material for ensuring that the lubrication of the rolling elements is provided for. This first material 1 10 may be applied, for example, only at the contact surface (not indicated) between the rolling elements or cage and the seal 100.

The second material 120 may be prefabricated via any other production process, for example, an injection molding process or a casting process. In such a situation, the first material 1 10 may be printed on top of the second material 120. Alternatively, the second material 120 may also be printed via the additive

manufacturing process. When also printing the second material 120, the deposition of the first material 1 10 on the second material 120 may generate a functionally graded interface layer 230 (see Fig. 2A). The composition of such a functionally graded interface layer 230 is configured to gradually change from the first material 1 10 via a mixture of the first material 1 10 and the second material 120 to the second material 120. A benefit of such functionally graded interface layer 230 is that the bonding between the first material 1 10 and the second material 120 is relatively strong.

The second material 120 is different from the first material 1 10. For example, the first material 1 10 may be oleophilic material having a predefined wetting behavior for ensuring that sufficient lubricant is present at the interface between the seal 100 and the rolling element or cage. The second material 120 may, for example, be hydrophobic to ensure that water and moisture is banned from the seal 100 to reduce corrosion of the rolling elements and the raceways inside the bearing 300.

In an embodiment in which the second material 120 also at least partially is printed material, the second material 120 may comprise a hollow structure 350 (shown in Fig. 2B). Such a hollow structure 350 may generate additional space inside the bearing 700 without the need for more volume. Such a hollow structure 350 may be used to contain lubricant which may be deposited to the interface between the seal 100 and the rolling elements or cage via an opening 355 (again shown in Fig. 2C).

Alternatively, the hollow structure 350 may comprise other elements, such as sensors (not shown) or batteries (not shown) to feed such sensors. The inclusion of sensors in the hollow structure 350 allows measurements inside the seal 100 or bearing 700 to monitor parameters, for example, for determining maintenance needs of the bearing 700.

Alternative to the seal 100 shown in Fig. 1 , the first material 1 10 and the second material 120 may be interchanged (not shown) such that the first material 1 10 faces away from the rolling elements or cage (and is therefore located on the environment side) and the second material 120 faces the rolling elements or cage (and is therefore located on the seal side). In such an embodiment, the first material 1 10 may be hydrophobic and the second material 120 may be oleophilic.

In the embodiment of the seal 100, the seal 100 comprises a frame 140, for example, a metal frame 140. This metal frame 140 acts as a spring-fit for securing the seal 100 to a flange (not shown) of an outer ring 710 (see Fig. 3) of the bearing 700. The seal 100 shown in Fig. 1 further comprises an O-ring 160 to control a force at which the seal 100 contacts a flange (not shown) of an inner ring 720 (see Fig. 3). In use the flange of the inner ring 720 rotates relative to the seal 100.

Fig. 2A shows a cross-sectional view of a second embodiment of the seal 200 for the bearing 700 according to the invention. The seal 200 as shown in Fig. 2A also comprises the first material 210, printed on the second material 220. This second material 220 is also printed material and at the interface between the first material 210 and the second material 220 the functionally graded interface layer 230 is shown. As indicated before, the functionally graded interface layer 230 is configured to gradually change from the first material 210 via a mixture of the first material 210 and the second material 220 to the second material 220 to achieve an improved bonding between the first material 210 and the second material 220.

In the embodiment of the seal 200 shown in Fig. 2A, the seal 200 comprises a frame 240, for example, a metal frame 240 which acts as a spring-fit for securing the seal 200 to the flange (not shown) of the outer ring 710 (see Fig. 3) of the bearing 700.

Fig. 2B shows a partial cross-sectional view of a third embodiment of the seal 300 according to the invention. The seal 300 comprises a second material 320 which is printed into a metal frame 340 which acts as a spring-fit for securing the seal 300 onto the bearing (700 in Fig. 3). The seal 300 further comprises first material 310 printed on the second material 320 at a side of the seal 300 facing the rolling elements (not shown) or cage. The O-ring 360 again is present to control the force at which the seal 300 contacts the flange (not shown) of an inner ring 720 of the bearing (see Fig. 3). Printing the second material 320 onto the metal frame 340 also allows to include at some locations inside the second material 320 one or more hollow structures 350 as indicated in Fig. 2B. Such a hollow structure 350 may, in use contain a lubricant which may be released toward the rolling elements or cage via an opening 355. As indicated before, the hollow structure 350 may also comprise other elements such as a sensor (not shown) and/or a battery (not shown) or other energy storage facility - enabling to measure parameters useful to determine, for example, when the next maintenance would be due. Of course other parameters providing other intelligence about the system or condition of the bearing 700 or its building blocks may also be measured by the sensor.

Fig. 3 shows a plan view of a bearing 700 according to the invention. The bearing 700 shown in Fig. 3 is a ball-bearing 700 comprising rolling elements (hidden behind the seal 100) being spheres. The bearing 700 comprises an inner ring 720, an outer ring 710 and a cage (hidden behind the seal 100). The interior of the bearing 700 comprising the raceways of the inner ring 720 and the outer ring 710, the rolling elements and the cage are sealed from environmental influences via the seal 100 according to the embodiments of the invention.

Fig. 4A shows a first embodiment of an additive manufacturing tool 400 in which a liquid resin 450 is used for applying the printed material 460 in the additive manufacturing process. Such additive manufacturing tool 400 comprises resin container 430 comprising the liquid resin 450. Inside the resin container 430 a platform 470 is positioned which is configured to slowly move down into the resin container 430. The additive manufacturing tool 400 further comprises a laser 410 which emits a laser beam 412 having a wavelength for curing the liquid resin 450 at the locations on the printed material 460 where additional printed material 460 should be added. A re- coating bar 440 is drawn over the printed material 460 before a new layer of printed material 460 is to be applied to ensure that a thin layer of liquid resin 450 is on top of the printed material 460. Emitting using the laser 410 those parts of the thin layer of liquid resin 450 where the additional printed material 460 should be applied will locally cure the resin 450. In the embodiment as shown in Fig. 4A the laser beam 412 is reflected across the layer of liquid resin 450 using a scanning mirror 420. When in the current layer all parts that need to be cured, have been illuminated with the laser beam 412, the platform 470 lowers the printed material 460 further into the liquid resin 450 to allow the re-coating bar 460 to apply another layer of liquid resin 450 on top of the printed material 460 to continue the additive manufacturing process.

Fig. 4B shows a second embodiment of the additive manufacturing tool 401 in which a liquid resin 450 is dispensed from a dispenser 405 or print head 405 for applying the printed material 460 in the additive manufacturing process. The additive manufacturing tool 401 again comprises the resin container 430 comprising the liquid resin 450 which is fed via a feed 455 towards the print head 405. The print head 405 further comprises a print nozzle 415 from which droplets of liquid resin 450 are emitted towards the printed material 460. These droplets may fall under gravity from the print head 405 to the printed material 460 or may be ejected from the print nozzle 415 using some ejection mechanism (not shown) towards the printed material 460. The print head 405 further comprises a laser 410 emitting a laser beam 412 for immediately curing the droplet of liquid resin 450 when it hits the printed material 460 to fix the droplet of liquid resin 450 to the already printed material 460. The printed material 460 forming a solid object may be located on a platform 470.

Fig. 5A shows a third embodiment of the additive manufacturing tool 500 in which the material is granulated into small solid particles 550 which are used for applying the printed material 560 in the additive manufacturing process. Now, the additive manufacturing tool 500, also known as a Selective Laser Sintering tool 500, or SLS tool 500 comprises a granulate container 530 comprising the granulated small solid particles 550. The printed material 560 is located again on a platform 570 and is completely surrounded by the granulated small solid particles 550. Lowering the platform allows a granulate feed roller 540 to apply another layer of granulated solid particles 550 on the printed material 560. Subsequently locally applying the laser beam 512 using the laser 510 and the scanning mirror 520 will locally melt the granulated solid particles 550 and connects them with each other and with the printed material 560 to generate the next layer of the solid object to be created. Next, the platform 570 moves down further to allow a next layer of granulated solid particles 550 to be applied via the granulate feed roller 540 to continue the next layer in the additive manufacturing process.

Fig. 5B shows a fourth embodiment of the additive manufacturing tool 501 or SLS tool 501 in which the granulated solid material 550 is dispensed from a dispenser 505 or print head 505 for applying the printed material 560 in the additive manufacturing process. The additive manufacturing tool 501 again comprises the granulate container 530 comprising the granulated solid particles 550 which are fed via a feed 555 towards the print head 505. The print head 505 further comprises a print nozzle 515 from which granulated solid particles 550 are emitted towards the printed material 560. These solid particles 550 may fall under gravity from the print head 505 to the printed material 560 or may be ejected from the print nozzle 515 using some ejection mechanism (not shown) towards the printed material 560. The print head 505 further comprises a laser 510 emitting a laser beam 512 for immediately melting or sintering the solid particle 550 when it hits the printed material 560 to fix the solid particle 550 to the already printed material 560. The printed material 560 forming a solid object may be located on a platform 570.

Fig. 6 shows a fifth embodiment of the additive manufacturing tool 600 in which a melted plastic material 650 is dispensed for applying the printed material 660 in the additive manufacturing process. The additive manufacturing tool 600 shown in Fig. 6 is also known as Fused Deposition Modeling tool 600 or FDM tool 600. Now a plastic filament 630 is fed into a dispenser 610 or melter 610 via a filament feeder 640. The dispenser 610 or melter 610 comprises an extrusion nozzle 615 for melting the plastic filament 630 to form a droplet of melted plastic material 650 which is applied to the printed material 660 where it hardens and connects to the already printed material 660. The dispenser 610 may be configured and constructed to apply the droplet of melted plastic 650 to the printed material 660 under gravity or via an ejection mechanism (not shown). The additive manufacturing tool 600 further comprises a positioning system 620 for positioning the dispenser 610 across the printed material 660.

Summarizing, the invention provides a multimaterial and multifunction seal

100 for a bearing or an actuator. The invention further provides the bearing and a method of producing the seal. The seal comprises a first material 1 10 and a second material 120, the first material 110 being printed via an additive manufacturing process and having different properties compared to the second material. The first material is a hydrophobic or oleophobic material when the first material is configured on the environment side of the seal and therefore configured, in use, to face away from the rolling elements. Using such first material allows applying the first material at a location where it is actually needed.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

LISTING OF REFERENCE NUMBERS

Seal 100, 200, 300 Laser beam 412, 512

First material 1 10, 210, 310 Scanning mirror 420, 520

Second material 120, 220, 320 Resin container 430

Funct. graded layer 230 Re-coating bar 440

Metal frame 140, 240, 340 Liquid resin 450

Hollow structure 350 Feed 455, 555

Opening 355 Platform 470, 570, 670

O-ring 160, 360 SLS-tool 500, 501

Bearing 700 Granulate container 530

Outer ring 710 Granulate feed roller 540

Inner ring 720 Granulate material 550

Printed material 1 10, 210, 310, FDM-tool 600

120, 220, 320, Melter 610

140, 240, 340, Extrusion nozzle 615

460, 560, 660 Positioning constr. 620

Additive manuf. tool 400, 401 Filament 630

Print head 405, 505 Filament feeder 640

Print nozzle 415, 515 Liquid plastic 650

Laser 410, 510