Laboratory Disk Grinder, Replacement Grinding Disk and Use of a Grinding Disk

Abstract

The present disclosure relates to a laboratory wheel grinder and a method for plane grinding a lower side of specimens, in particular mounted specimens, as well as a replacement grinding disc for the laboratory wheel grinder and the use of a grinding disc in a laboratory wheel grinder, wherein the grinding disc is divided into a peripheral annular first surface and a central second surface arranged within the peripheral annular first surface wherein the upper surface of the carrier disc is covered with the abrasive only in the peripheral annular first surface so as to form a grinding peripheral annular first surface and a passive central second surface.

Claims

1. Laboratory wheel grinder with a rotating grinding disc for the plane grinding of a lower side of mounted specimens, comprising: a device housing with a grinding disc mounting plate and a drive motor, by means of which the grinding disc mounting plate can be set in rotation, a grinding disc having a carrier disc and an abrasive bonded with a bonding agent on an upper surface of the carrier disc, wherein the carrier disc of the grinding disc has an upper surface and a lower surface, and wherein the lower surface of the grinding disc can be detachably mounted on the grinding disc mounting plate, wherein the grinding disc is divided into a peripheral annular first surface and a central second surface disposed within the peripheral annular first surface, wherein the upper surface of the carrier disc is coated with the bonded abrasive only in the peripheral annular first surface to form a grinding peripheral annular first surface and a passive central second surface.

2. Laboratory wheel grinder according to claim 1, wherein the abrasive means are formed by abrasive grit and, in the cross section of the grinding disc, the abrasive grit in the grinding peripheral annular first surface defines a common annular abrasive first surface of the grinding disc and the carrier disc of the grinding disc in the passive central second surface forms a central non-abrasive second surface of the grinding disc, and wherein, in a fresh unused condition of the grinding disc, the common annular grinding first surface of the grinding disc is higher than the central non-grinding second surface of the grinding disc.

3. Laboratory wheel grinder according to claim 2, wherein the difference in height between the common annular abrasive first surface and the central non-abrasive second surface ranges from 50 μm to 5 mm.

4. Laboratory wheel grinder according to claim 1, wherein the abrasive is formed by abrasive grit and, in the grinding peripheral annular first surface, the abrasive grit is bonded with the bonding agent in a plurality of layers, on the upper surface of the carrier disc.

5. Laboratory wheel grinder according to claim 4, wherein the abrasive layer is multi-layered and is self-sharpening in such a way that dull abrasive grit breaks out during the grinding process and fresh abrasive grit, emerges from an underlying layer to the surface.

6. Laboratory wheel grinder according to claim 1, wherein the abrasive is formed by abrasive grit and, in the grinding peripheral annular first surface, is printed with a bonding agent in a predefined pattern.

7. Laboratory wheel grinder according to claim 1, wherein the grinding disc is round and/or has an outer diameter of between 100 mm and 500 mm.

8. Laboratory wheel grinder according to claim 1, wherein the grinding peripheral annular first surface has an inner diameter D_i and an outer diameter D_a, wherein half of the difference between the inner diameter D_i and the outer diameter D_a corresponds to the radial width B_r of the grinding peripheral annular first surface and is between 240 mm and 20 mm.

9. Laboratory wheel grinder according to claim 1, wherein the grinding peripheral annular first surface has an inner diameter D_i and an outer diameter D_a, wherein the inner diameter D_i has a range of between 20 mm and 450 mm, and the outer diameter D_a has a range of between 100 mm and 500 mm.

10. Laboratory wheel grinder according to claim 1, wherein the carrier disc comprises a metal sheet or a plastic sheet, and/or wherein the abrasive consists of diamond particles.

11. Laboratory wheel grinder according to claim 1, wherein the grinding disc can be fastened with the lower side on the grinding disc mounting in a removably adhering manner.

12. Laboratory wheel grinder according to claim 1, wherein the device housing comprises a collection tray for cooling liquid and grinding abrasion, with the grinding disc mounting plate rotating in the collection tray.

13. Laboratory wheel grinder according to claim 1, wherein one or more specimens are inserted into a specimen holder and pressed against the grinding disc, and wherein, in addition to the rotation of the grinding disc, the specimen holder rotates with the specimen or specimens during the grinding operation, and an edge region of the specimen or specimens extends radially inward beyond the grinding peripheral annular first surface during the rotation of the grinding disc and the specimen holder.

14. Laboratory wheel grinder according to claim 1, wherein the laboratory wheel grinder comprises a device head with a piston for fastening a specimen holder, with which one or more specimens inserted in the specimen holder are pressed onto the grinding disc with a predefined pressure force, and wherein the specimen holder is rotatable in order to simultaneously bring about a rotation of the specimen holder during the grinding process in addition to the rotation of the grinding disc, wherein the axes of rotation the grinding disc and of the specimen holder extend in a parallel offset manner.

15. Laboratory wheel grinder according to claim 1, wherein the grinding peripheral annular first surface has an inner diameter D_i and an outer diameter D_a, and wherein half of the difference between the inner diameter D_i and the outer diameter D_a defines the radial width B_r of the grinding peripheral annular first surface, and i) in the case of an individual specimen, the radial width B_r of the grinding peripheral annular first surface is selected such that the diameter of the specimen protrudes internally beyond the inner diameter D_i, due to a radial displacement of the rotating specimen during the grinding process, or ii) in the case of a specimen holder with a plurality of inserted specimens, the totality of the specimens defines an overall outer diameter D_g relative to the rotation of the specimen holder, and the radial width B_r of the grinding peripheral annular first surface is selected such that the overall outer diameter D_g projects internally beyond the inner diameter D_i, due to a radial displacement of the rotating specimen during the grinding operation.

16. Method for the plane grinding of a lower side of mounted specimens with a rotating grinding disc or with the laboratory wheel grinder wherein: a grinding disc having a carrier disc and an abrasive bonded with a bonding agent on an upper surface of the carrier disc is used, and wherein the carrier disc of the grinding disc has an upper surface and a lower surface, wherein the grinding disc is larger than the specimen to be ground, wherein the grinding disc is divided into a peripheral annular first surface and a central second surface arranged within the peripheral annular first surface, the upper surface of the carrier disc being covered with the abrasive only in the peripheral annular first surface so as to form a grinding peripheral annular first surface and a passive central second surface, wherein one or more specimens are inserted into a specimen holder and pressed against the grinding disc, and wherein, in addition to the rotation of the grinding disc, the specimen holder rotates with the specimen or specimens during the grinding operation and, during the rotation during the grinding operation, edge portions of the specimen or specimens extend inwardly beyond the grinding peripheral annular first surface and into the passive central second surface.

17. Replacement grinding disc consisting of a carrier disc and abrasive grit bonded to the carrier disc with a bonding agent, prepared for use in the laboratory wheel grinder for the plane grinding of a lower side of mounted specimens according to claim 1, wherein the grinding disc considerably larger than the specimen to be plane-ground, wherein the carrier disc of the grinding disc has an upper side and a lower side, and wherein the carrier disc can be detachably adhered with the lower side to a grinding disc mounting plate of the laboratory wheel grinder, and wherein the grinding disc is divided into a peripheral annular first surface and a central second surface arranged within the peripheral annular first surface, wherein the upper surface of the carrier disc is coated with the abrasive grit as abrasive only in the peripheral annular first surface, so that a grinding peripheral annular first surface and a passive central second surface are formed.

18. Use of the replacement grinding disc according to claim 17 in the laboratory wheel grinder according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In the drawings:

[0048] FIG. 1 is a three-dimensional representation of an embodiment of the laboratory wheel grinder,

[0049] FIG. 2 is an enlarged representation of the grinding disc and specimen holder from FIG. 1,

[0050] FIG. 3 is a cross section through a mounted specimen,

[0051] FIG. 4 provides a top view of a grinding disc with the specimen holder from FIG. 2,

[0052] FIG. 5 is a cross section along the line 5-5 in FIG. 4,

[0053] FIG. 6 is a detail enlargement of region A from FIG. 5,

[0054] FIG. 7 is another embodiment of the laboratory wheel grinder,

[0055] FIG. 8 is a schematic cross-sectional representation through the specimen holder and grinding disc of FIG. 7,

[0056] FIG. 9 is a three-dimensional representation through the device head of FIG. 7 without the device head housing,

[0057] FIG. 10 is a vertical section through the device head of FIG. 9,

[0058] FIG. 11 is a cross-sectional representation of the uneven wear of a conventional grinding disc.

DETAILED DESCRIPTION OF THE INVENTION

[0059] With reference to FIG. 1, the laboratory wheel grinder 10 has a device housing 12, in the present example a an upright housing that is to be placed on a laboratory bench. Above the device housing 12 is a device head 14, in the present example designed as a cantilever arm, which extends over the grinding disc or grinding wheel 16. The grinding disc 16 rotates in a collection pan 18 in the device housing 12. A rotating piston or pressing shaft 20 extends downwardly from the device head 14, and a specimen holder 24, in the present example in the form of a plate, with a connecting pin 26 (FIG. 2) is attached to the lower end 22 of the piston 20. In the present example, six mounted metallographic specimens 30 are inserted into the specimen holder 24 or specimen receptacle. The embodiment shown uses a central contact pressure. Alternatively, it is also possible to work with an individual contact pressure, in which case each of the specimens 30 is pressed against the grinding disc with their own pressing stem and is not clamped axially in the specimen holder 24 in a fixed manner (not shown).

[0060] The specimen holder 24 and the six mounted specimens or mounted samples 30 inserted therein rotate about the axis of rotation AK of the piston 20 or the connecting pin 26. As a result, the six mounted specimens 30 describe a circular motion about the axis AK and thereby define a total outer circumference 31 with a total outer diameter D_g of about 130 mm in the present example (FIG. 4).

[0061] In order to grind the specimens 30, the grinding disc 16 now rotates about the grinding disc axis AS on the one hand, and the specimen holder 24 rotates about the axis AK of the piston 20 on the other hand, with the axis AK of rotation of the specimen holder running laterally parallel to the axis AS of rotation of the grinding disc (FIG. 4, 5). In particular, the total circumference 31 is outside the grinding disc axis AS, which is advantageous, because the circumferential speed of the grinding disc is zero at its own axis of rotation AS.

[0062] There is a contact pressure mechanism, for example with a linear guide 78 (FIG. 9, 10) in the exemplary device head 14 with a central contact pressure, which presses the specimen holder 24 with the mounted specimens 30 against the grinding disc 16 in the same direction at a predefined pressing force F during the counter-rotation or rotation of the grinding disc 16 and the specimen holder 24, in order to effect the grinding process of the lower sides 30a of the specimens by abrasion by means of the abrasive layer of grinding or abrasive grit on the upper side 16b of the grinding disc.

[0063] With reference to FIG. 3, the specimen 30 is a mounted specimen or embedded sample that consists of the actual specimen material 32 to be examined, e.g. a piece of a metallic test object, e.g. for a later performance of a hardness test or microstructure analyses with a microscope, and a cylindrical block of plastic embedding or mounting material in which the specimen material 32 is embedded or mounted. In particular, the specimen material 32 is mounted in the plastic block 34 to be more manageable. In the present example, the plastic block consists of two different plastics 34a, 34b for cost optimization purposes. Bakelite, epoxy resins, thermosets, thermoplastics or acrylic resins for transparent mounting are used as mounting materials, for example.

[0064] In FIG. 4, the grinding disc 16 is divided into a peripheral annular region 42 and a central region 44 arranged in the peripheral annular region. The grinding disc is covered with abrasive material only in the peripheral annular region 44, in the present example with hexagonal abrasive grit. In the central inner region, the abrasive 46 is omitted so that an annular separation line 48 separates the peripheral annular region 42 with abrasive from the central inner region 44 without abrasive. In other words, the abrasive layer 47 is annular in shape and there is no grit in the central inner region 44. The distance between the axes of rotation AK and AS is now selected so that the overall circumferential line 31 of the mounted specimens 30 intersects with the separation line 48 between the peripheral annular region 42 and the central inner region 44, i.e., with the inner diameter D_i of the annular abrasive layer 47. In other words, as the grinding disc 16 and the specimen holder 24 rotate, the mounted specimens 30 travel inwardly beyond the peripheral annular region 42 with abrasive material into the inner region 44 without abrasive material. As a result, there is no location on the grinding disc 16 with abrasive material is not traversed by the mounted specimens 30, thus ensuring a uniform wear of the abrasive material.

[0065] The same is true at the outer edge 16c of the grinding disc 16, because the radial offset between the axes AK and AS is such that the specimens 30 also extend outward beyond the outer edge 16c of the grinding disc 16.

[0066] In the present example, abrasive material 46 is applied to the grinding disc 16 in a hexagonal pattern, although this is not mandatory. Other coating patterns are possible as well. Both the coating pattern and the annular shape of the abrasive layer can be produced in one step by means of screen printing. Using the screen-printing process, the bonding agent with the abrasive grit is printed as a powder on the surface of the grinding disc 16, in the present example directly onto a metal sheet, which forms the rigid carrier wheel 62, so that the abrasive grit is locally mounted in the bonding agent on the grinding disc 16 where desired. However, the carrier disc 62 screen printing may also comprise a textile intermediate layer (not shown) on which the abrasive grit is bonded.

[0067] FIGS. 5 and 6 show in even greater detail how the specimen 30, which is currently located on the inside, passes over the peripheral annular region 42 with abrasive material or across the separation line 48 inwards into the inner region 44 of the grinding disc 16 without abrasive material. Due to the fact that the specimen holder 24 rotates in addition to the grinding disc 16, it is nevertheless ensured that all specimens 30 are also ground plane at their periphery 30c, just not at the very moment when they enter the inner region 44 or the circular lack of abrasive at the center of the annular abrasive layer 47.

[0068] In other words, the grinding disc 16 is not completely covered with the abrasive 46 over its entire surface, but only annularly on the outside. Because the specimens 30 always maintain a minimum distance from the axis AS of the grinding disc 16 during the double rotation in the grinding process, a minimum peripheral speed of the abrasive relative to the specimens 30 is maintained in any rotational position. Because the specimens 30 to be ground extend on the inside beyond the peripheral annular region 42 with abrasive, both the abrasive 46 in the peripheral annular region 42 and the lower side 30a of the specimen 30 are ground plane, eliminating the need to remove the grinding disc 16. This initially saves the user the time required to pull off the specimen. However, as an added benefit, the cost of the abrasive 46 may be reduced as well, because the grinding disc 16 requires less abrasive 46.

[0069] If the inner region 44 were also covered with abrasive material, as is typically the case in the prior art, no abrasive material would be removed in the region around the axis of rotation AS of the grinding disc 16, which resulted in a non-planar wear behavior of the grinding disc. Therefore, the grinding disc had to be removed from time to time to make it planar again. Otherwise, uneven wear resulted in a certain transition at a radius r_s of the grinding disc where the overall circumference 31 ends at the center, which meant that the specimens 30 in the edge region 30c tended to round off during the grinding process and were not plane. FIG. 11 shows this rounding problem 33 as it occurred with traditional grinders or grinding discs.

[0070] Returning to the embodiment of the invention shown in FIG. 1-6, the grinding peripheral annular region 42 has an outer diameter D_a and an inner diameter D_i, in this example the outer diameter D_a=300 mm and the inner diameter D_i=50 mm. These dimensions are adapted to the specimen holder 24 shown in FIG. 4 in the form of a specimen mounting plate, which clamps six mounted specimens 30 in an annular arrangement about the axis AK and which itself has a diameter of 140 mm. In the present example, the specimens 30 have a diameter of 40 mm and the total outer diameter D_g of the overall circumference 31 is approximately D_g=130 mm. The overlapping region or exceeding region 43 of the specimens 30 into the passive inner region 44 is therefore a few millimeters in this example.

[0071] However, the principle of the annular configuration of the actively grinding surface 42 of the grinding disc 16 is not limited to specimen holders 24 with a plurality of specimens 30, but can also be used when grinding an individual specimen 30. In this regard, reference is made to FIGS. 7 to 10, which show a laboratory wheel grinder 10′ having a device head 14 that serves a plurality of grinding stations 15 each with its own grinding disc 16. In this example, the device head 14 is attached to the housing 12 so as to be displaceable along the direction 52 in order to be able to alternately operate a plurality of grinding stations 15. Each grinding disc 16 rotates in its own collection tray 18 in this example. The laboratory plate grinder 10′ also has two separate polishing stations 54.

[0072] In FIG. 8, each grinding station 15 has a grinding disc mounting plate 58, which may be formed, for example, as a stable metal plate. The grinding disc mounting plate 58 is rotated about the axis AS by a grinding disc drive 60. The grinding disc 16 is detachably adhered to the grinding disc mounting plate 58, for example by means of a magnetic holder, although other adhesion techniques are possible as well.

[0073] The grinding disc 16, in turn, has a stiff carrier disc 62 and the abrasive material 46 bonded to the carrier disc 62 in the form of abrasive grit of a specific grit size mounted in the bonding agent, thereby forming the abrasive layer 47. In this case, the abrasive grit is applied to the carrier disc in multiple layers to form a self-sharpening grinding disc 16. For this purpose, the abrasive grit is printed as a powder onto the grinding disc 16, in this example directly onto the upper surface 62b of the carrier disc 62, for example by means of a screen-printing process with a synthetic resin bonding agent. Depending on the grit size, this means that approximately 3 to 100 layers of abrasive grit may be bound in the bonding agent on the carrier disc 62. The thickness of the abrasive layer 47 thus produced is about 0.2 mm to 1 mm, depending on the grinding disc 16. By means of the screen-printing process, a desired abrasive pattern, e.g. hexagonal, as shown in FIG. 2, and the separation into the peripheral annular region 42 with abrasive and the inner region 44 without abrasive can be produced in one step. As a result of the separation into the peripheral annular region 42 with abrasive material and the inner region 44 without abrasive material, a step 64 is formed at the annular separation line 48 between the peripheral annular region 42 with abrasive material and the inner region 44 without abrasive material, the height of said step corresponding to the thickness of the abrasive material layer 47, i.e. is, for example, approximately 0.2 mm to 1 mm. The step 64, which runs downward from the peripheral annular region 42 into the inner region 44, ensures that even if the abrasive 46 in the peripheral annular region 42 is significantly worn, the specimen 30 still has a sufficient axial distance from the upper surface 62b of the carrier disc 62 and, in particular, that no undesirable step can occur upward from the peripheral annular region 42 into the inner region 44, as is the case with conventional grinding discs when the abrasive in the central region of the grinding disc is not worn off by the specimen or specimens. Therefore, a regular removal in order to render the grinding disc plane again can be dispensed with. The lower surface 62a of the carrier disc 62 is adhered to the upper surface 58b of the grinding disc mounting plate 58.

[0074] In the example shown in FIGS. 7 to 10, the specimen holder 24 is configured as a specimen gripper 72. The specimen gripper 72 has three gripper arms 74 which can automatically grip an individual specimen for automatic grinding. By means of a plurality of nozzles 76, for example, water can be automatically sprayed onto the grinding disc 16 as a coolant and/or for rinsing purposes, or diamond suspensions in various grit sizes.

[0075] Referring to FIGS. 9 and 10, the device head 14 has a linear drive mechanism 78 by means of which the specimen holder 24 and thus the specimen 30 or specimens 30 are applied against the grinding disc 16 with a defined force F, with the piston 20 rotating at the same time.

[0076] It is apparent to a person skilled in the art that the embodiments described above are to be understood as exemplary and that the invention is not limited to these, but can be varied in a number of ways without departing from the scope of protection of the claims. Furthermore, it is apparent that the features, whether they are disclosed in the description, the claims, the figures or otherwise, also individually define essential components of the invention, even if they are described together with other features. All features disclosed in connection with the laboratory wheel grinder, the method, the replacement grinding disc and the use are, of course, also considered disclosed for the objects of the respective other categories, and the features of one embodiment are also considered disclosed for another embodiment. In the present case, this applies in particular to the two embodiments in FIG. 1-6 on the one hand and FIG. 7-10 on the other.