EP3154745B1 - Grinding wheel - Google Patents

Description

The invention relates to a grinding wheel, with a grinding area acting in the circumferential direction, which has bound abrasive; and with reinforcing elements not participating in the grinding process according to the preamble of claim 1.

Abrasive tools with a bonded abrasive have abrasives embedded in a binder, which form a compact body when combined.

The choice of the suitable grinding tool depends on the task on which the machining of the workpiece is based. In most cases, two processing effects are decisive: on the one hand, the material removal with the aim of geometric shaping and, on the other hand, the microstructure of the processed workpiece surface. A geometrical shape is to be achieved in the majority of the machining tasks, while at the same time placing demands on the workpiece surface. The criterion for the condition of the workpiece surface is usually the roughness depth R _A. as well as the type and orientation of structural features.

Deviating from this, however, there are also machining tasks with grinding tools which are predominantly or exclusively aimed at generating a specific microstructure of the workpiece surface. For example Provide stainless steel sheets for use in lifts or interior cladding with a decorative line pattern without significant material removal. In this case, fleece or brushing tools are preferably used because they have sufficient elasticity to adapt flatly to the workpiece. Such tools are coated abrasives.

In the area of bonded grinding tools, too, special designs were developed for the surface structuring of workpieces. As a rule, however, these are not large workpieces such as sheet metal, but mainly functional parts from the mechanical engineering sector. As in the area of abrasives on underlays with the fleece and brushing tools, there is also a requirement for elasticity of the grinding tool in order to adapt to the surface contour of the workpiece. Accordingly, soft and elastic binders are used for such applications, for example rubber, silicone or even polyurethane. It is also common to incorporate elastic solids such as cork.

A common application for such tools is the machining of cylindrical workpieces. This can take place between peaks but also without centers. In both cases, the peripheral side of the grinding wheel comes into engagement, the axis of the workpiece and the axis of the grinding wheel being parallel to one another. In order to machine the workpiece over the entire length, the grinding wheel travels in the axial direction and usually continuously in several cycles. As a result, a uniform processing image in the desired roughness depth can be achieved can be achieved, however, the surface shows a spiral surface pattern, also referred to as "swirl". This effect can impair the functionality of the workpiece. B. in cylinders or racks that are part of a hydraulic system and move through seals. The roughness depths achieved are approximately R _A <0.8 mm.

Alternatively, a similar method can be carried out, but the grinding tool is not continuously moved axially, but is separated from the workpiece after each intervention, moved and then comes into engagement again in the sense of "plunge grinding". However, the discontinuous process with the risk of generating markings with each intervention is disadvantageous here.

This effect can be avoided if the circumferential side is also ground, but the grinding wheel is aligned radially to the longitudinal axis of the workpiece and moves in this direction. The grinding wheel axis always behaves perpendicular to the longitudinal axis of the workpiece. In this way, a straight, axially aligned surface structure is obtained.

Because curved surfaces are usually machined, the circumferential side is dressed according to the workpiece geometry. This makes it possible to machine almost the half-sided peripheral surface in one operation.

DE 31 38 163 A1 discloses bonded grinding tools, according to the preamble of claim 1, in particular those for plunge grinding, for example for grooves. US 3,482,355 discloses bonded abrasive tools that include an active grinding area and a non-grinding active area.

The invention is based on the object of providing a grinding wheel of the type mentioned at the outset which is suitable for grinding with the peripheral side, in particular for surface structuring, and which allows the production of high-quality surfaces with little effort.

This object is achieved by the features of claim 1.

The invention thus relates to a grinding wheel with a grinding region acting in the circumferential direction and having bound abrasive; and with reinforcing elements not participating in the grinding process, wherein the reinforcing elements have at least one reinforcing disc arranged on the end face, which is designed to be free of abrasives and can be dressed, and wherein the at least one reinforcing disc extends over at least 80% of the end face of the grinding area and core area arranged underneath, characterized in that the The grinding area is annular and the core area has a greater hardness than the grinding area arranged radially on the outside.

First, some terms used in the context of the invention are explained.

In the context of the invention, the term grinding wheel denotes a grinding tool with a bonded abrasive which is designed for machining surfaces with a narrow side or peripheral side. The grinding area is the volume area of the grinding wheel that contains or contains the bound abrasive. Suitable abrasives that can be used in the context of the invention are, for example, silicon carbide, fused and sintered corundum. Very hard abrasives such as cubic boron nitride or diamond can also be used, but the special properties of these hard abrasives (high wear resistance) are generally not effective due to the relatively soft integration into the binder.

The grinding area acts in the circumferential direction. This means that it can be brought into contact with the surface to be machined on a narrow side or peripheral side of the grinding wheel.

The grinding wheel according to the invention is circular and suitable for clamping onto a rotary grinding machine, but is not limited to this. The grinding wheel has reinforcing elements not participating in the grinding process. These elements increase the mechanical stability of the wheel and, in particular, reduce elastic or plastic deformation of the grinding wheel under the loads that occur during grinding, such as centrifugal forces or pressure loads. This often reduces the inherent tendency of the abrasives to deform under the stress of grinding. The characterization of the reinforcing elements as not participating in the grinding process means that they do not come into engagement with the surface of the machined workpiece during normal grinding.

According to the invention, it is provided that the reinforcing elements have at least one reinforcing disk arranged on the end face, which is designed to be dressing-free and without abrasives. On the end face means that the at least one reinforcing disk is arranged on a surface of the grinding wheel that is not the grinding peripheral surface. In the case of a circular grinding wheel, such an end face is generally perpendicular to the intended axis of rotation.

The reinforcing disc is a flat element that serves to absorb and dissipate mechanical forces and is itself not designed to participate in the grinding process. Accordingly, it contains essentially no abrasive. This reinforcement washer is trained to be dressable. The meaning and the technical advantages of this feature are explained below.

A frequent area of application of grinding wheels acting with the peripheral side is the surface structuring of curved, for example cylindrical surfaces. A prerequisite for this, however, is sufficient elasticity of the grinding area and a high contact pressure. The grinding wheel can be deformed in the prior art, as a result of which there is no longer a positive fit with the workpiece. On the other hand, the pressure and the associated deformation can lead to the formation of cracks and subsequently to the destruction of the grinding wheel.

From obvious prior use, it is already known to reduce these undesirable effects by using two side steel disks which are mounted on the spindle together with the grinding disk. This prior art solution is associated with considerable disadvantages.

After machining a number of workpieces, grinding wheels have to be dressed periodically, in particular to restore the desired surface geometry of the peripheral side. However, steel wheels cannot be dressed together with the grinding wheel. Rather, steel disks with a correspondingly smaller diameter must be installed after each dressing. This has the disadvantage of stockpiling and assembly effort. It must also be accepted that the steel discs are only available in certain dimensions and therefore no precisely fitting support effect can be achieved. A particular advantage of the present invention is that the dressable reinforcement disks enable comparable mechanical stabilization, but can be dressed together with the grinding area when dressing the grinding wheel. The dismantling / assembly of steel disks required in the prior art is eliminated.

Suitability for dressing processes means that the geometric shape and / or the sharpness can be restored using a conventional dressing tool. Such dressing tools include embodiments with single diamonds or moldings set with diamonds, but also diamondless dressing tools with silicon carbide or corundum.

According to the invention, it is particularly preferred that the reinforcement elements have two reinforcement disks arranged on the end face, which are designed to be dressing-free and non-abrasive. In this way, the more easily deformable grinding area is framed and reinforced from both ends.

It is further preferred that the material of the reinforcement washers has a bending strength of at least 15 MPa, preferably at least 20 MPa, more preferably at least 25 MPa. The Shore A hardness can preferably be over 100.

Square test specimens measuring 16.2 mm x 16.2 mm x 120.4 mm were subjected to a 3-point bending test to measure the bending strength. The support consisted of two metal rollers with the support points spaced apart of 80 mm, the diameter of the metal rolls was 30 mm. The crosshead speed during delivery was 10 mm / min

A suitable, dressable material for the reinforcement disks is in principle a material based on the same or comparable binder as used for the grinding area. This makes it easier to dress the grinding area and the reinforcement disks in one operation with the same tool. Suitable binders can be, for example, polyurethanes, phenolic resins, glass or ceramic binders. A filler can preferably be provided to set the desired mechanical properties and increase the strength. It can be known mineral fillers, preference is given to hollow bodies based on minerals (microspheres). According to the invention, the filler content can be, for example, between 10 and 60% by weight, more preferably 20 and 40% by weight. These upper and lower limits can be combined as desired in areas according to the invention.

It is preferred that the at least one reinforcement disk is connected to the grinding area in a planar manner. Connected across the surface means that this reinforcing disc is at least with a large area of more than 50%, but preferably over the entire area, a frictional connection with the grinding area, for example, is glued. This two-dimensional bond prevents the grinding wheel from being compressed towards the central axis, which results in reduced dimensional accuracy in the grinding zone. Such a flat connection is not possible in the prior art for the steel disks used, since these have to be dismantled for dressing and then reassembled. The material of the grinding area preferably has a lower hardness than the material of the reinforcing disks. A Shore A hardness range from 20 to 97 is preferred, ranges from 20-90 or 70-85 are further preferred. When machining hardened, cylindrical metallic workpieces, for example, the hardness range from 70-85 can be useful.

According to the invention, the grinding area is ring-shaped and surrounds a hard core area. In this context, hard means that this core area has a greater hardness than the grinding area arranged radially around it. In the case of the preferably circular grinding wheel, this core area can in particular absorb and derive the acceleration and centrifugal forces in the area of the bore. The core area thus has the opening or hole which is used for connection to the grinding machine. According to the invention, the core area can consist of the same or similar material as the reinforcing disks.

In this preferred embodiment, a grinding wheel according to the invention thus consists of four structural elements. It concerns the core area, the grinding area and two reinforcement disks. The core absorbs the described forces and driving forces in the area of the bore. In the context of the invention, it is also possible for the core region and the reinforcing disks to be formed in one piece or connected to one another in one piece. It is therefore also preferred that, according to the invention, the reinforcement disks extend over surface areas of the Extend grinding area and the core area and are thus connected to each other flat (or in one case in the case of the core area). The combination of the reinforcement disks with both the grinding area and the core area enables effective force dissipation into the core area. This essentially prevents a radial change in shape of the grinding area. As a result, a significantly improved shape accuracy of the engagement zone of the grinding area against compressive forces during the grinding process is achieved. However, it should also be noted that when the grinding wheel is accelerated to the desired working speed, expansion due to centrifugal forces is significantly reduced. On the one hand, this allows the use of a harder binder with a higher grinding capacity. Because the grinding area is fixed flat on the reinforcement discs, the surface geometry of the grinding area tends to be retained even under the pressure load of an application. Because of this better shape retention, the form fit between the workpiece and the engagement zone of the grinding area is still guaranteed with a harder binder. On the other hand, the grinding wheel according to the invention also allows the use of particularly soft binders, such as may be required for grinding geometrically complicated workpieces. In this case, the grinding area can largely adapt to the workpiece contour and is thereby stabilized against deformation and crack formation by the reinforcing disks. Regardless of the binder chosen, higher working speeds can generally be achieved due to the improved strength. This improves the efficiency of the grinding process, but can also enable the creation of special, speed-dependent surface structures.

According to the invention, it is further preferred that the at least one reinforcing disk extends over at least 80%, preferably at least 90% of the end face of the grinding area and / or core area arranged underneath. This large-area design of the reinforcement disks allows effective stabilization and shape maintenance of the grinding area.

In a preferred embodiment, the axial thickness of the at least one reinforcing disk, preferably the common axial thickness of the two reinforcing disks, is 10-30%, more preferably 15-25% of the total thickness of the grinding wheel.

Another object of the invention is the use of a grinding wheel according to the invention for surface processing. Surface processing of workpieces, preferably cylindrical workpieces and / or functional parts of machines, is preferred. It is preferably not a large-area machining of flat surfaces, but rather a comparatively small-part machining of curved surfaces, such as cylindrical surfaces. The use for surface structuring is particularly preferred. Surface structuring means that there is no substantial change in shape of the surface in the sense of material removal, but only a desired surface structure is generated.

Embodiments of the invention are described below with reference to the single drawing, which shows a grinding wheel according to the invention in an axial and radial view.

example 1

A grinding wheel according to the invention with the dimensions 300 mm (diameter) x 40 mm (width) x 76 mm (bore diameter) consists of the structural elements of the grinding area with an abrasive layer and a core area in the area of the bore, as well as two reinforcement disks on the side. These structural elements are first manufactured as cylindrical blanks of great length and then cut using a diamond cutting disc in such a way that precisely fitting, disc-shaped elements are obtained for further processing into a single tool.

Prefabrication of the core area:

Recipe ingredients: Rencast FC52 ISO (Isocyanate based on MDI, Huntsman Advanced Materials) Rencast FC52 poly (Formulated polyol, Huntsman Advanced Materials) microspheres SOPHERES SG-300 B (Light filler, Omega Minerals Germany)

740 g Rencast FC52 ISO, 740 g Rencast FC52 Poly and 762 g microspheres ISOPHERES SG-300 B are mixed homogeneously with a stirrer and into an aluminum mold coated with release agent with the dimensions 123 mm (diameter), 320 mm (length) and 70 mm (Bore diameter) cast in. After a curing time of 30 minutes, the mass is molded and separated into two sections with 155 mm each. These are then reduced to an outer diameter of 120 mm by turning and roughened in the subsequent operation for better bonding.

Prefabrication of the grinding area:

Recipe components : RC major 110 (Diphenylmethane diisocyanate, Bayer MaterialScience) Poly-G HQEE (Crosslinker, hydroquinine di (beta-h) ester, CVH chemical sales) Diorez 770/02 (Polyester polyol, Azelis Switzerland Chemicals) Dabco TMR 2 (Activator, quaternary ammonium salt, Air Products Chemicals) Tegostab B 8905 (Tensid, CVH-Chemie-Vertrieb GmbH & Co. Hannover KG) dipropylene (Solvent, CVH chemistry sales) Araldite AW 116 (Epoxy resin, company Epoxidharze Andreas Weigel) Hardener HV 953 U Hardener for Alaldit AW 116, epoxy resins Andreas Weigel) Byk-W 961 (Structure improver, BYK chemistry) SCG F 80 (Abrasive grain silicon carbide green, grit F 80, ESK-SiC GmbH foamer (Mixture of Tegostab 8905, dipropylene glycol and water each in the same proportion by volume) catalyst (Mixture of dipropylene glycol (98.04% by mass) and Dabco TMR (1.96% by mass).

Poly-G HQEE and Diorez 770/02 are mixed in a ratio of 4.76: 95.24 parts by mass and heated to 105 C 48 hours before use. The SCG F 80 abrasive grain is preheated in the same way.

The components RC-Dur 110 (1079 g), foamer (2 g), mixture Poly-G HQEE and Diorez 770/02 (3162 g), Byk-W 961 (5 g) and SCG F 80 (11859 g) become homogeneous mixed, time for this 60 s. After adding CAT1 (20g) the mixture is mixed again (20 s).

The pre-fabricated core area coated with adhesive (Aaraldit) is put into a preheated and mold-coated metal mold with the dimensions 310 mm (diameter), 155 mm (width) and 70 mm (bore diameter). The exact central positioning is carried out by means of a centering pin.

The mixture is poured in, the mold closed and heated in the oven to a temperature of 105 degrees for curing (20 minutes).

Finally, the mold is opened, the blank is removed, clamped in a machining center and turned to a circumference of 307 mm. Finally, in the same setting, a disc-shaped part with a width of 30 mm is cut off using a diamond cutting disc.

Prefabrication of the reinforcement washers:

The reinforcement washers are made from the same material used to manufacture the core area has been. The description for processing is to be applied accordingly. Recipe ingredients: 2498 g Rencast FC52 ISO 2498 g Rencast FC52 poly 2505 g microspheres ISOPHERES SG-300 B 310 mm (Diameter) 120 mm (Width) 70 mm (Bore diameter)

The diameter of the cylindrical body obtained is reduced in a machining center to 307 mm by turning. Disc-shaped segments with a width of 5.2 mm are cut in the same setting using a diamond cutting disc.

Further processing:

The individual structural elements are checked before further processing. Criteria are dimensions, weight, density, hardness and breaking strength (support disks). A visual inspection for damage such as cracks, pores or inhomogeneities is also carried out.

The reinforcement disks are glued to the core area one after the other, each of which is pressurized during the curing time. Finally, the grinding wheel is machined to the desired dimension and the size by turning the end faces, the bore and the circumference to obtain the desired surface structure. Finally, the peripheral profiling corresponding to the respective application is generated by dressing.

The final inspection includes tests for dimensional accuracy and imbalance as well as a test run at 1.2 times the maximum working speed of 40 m / s.

S_br=

Sicherheitsfaktor gegen Bruch durch Fliehkraft

v_br=

Umfangsgeschwindigkeit bei Bruch durch Fliehkraft

v_s=

Arbeitshöchstgeschwindigkeit entsprechend zulässiger Umfangsgeschwindigkeit eines rotierenden Schleifwerkzeuges

Another test run was carried out to check the breaking strength. This was based on a maximum working speed of 40 m / s and a safety factor of 3.5, which was significantly increased in accordance with the actual application. The safety factor is defined as follows: $${\mathrm{S}}_{\mathrm{br}}={\left({\mathrm{v}}_{\mathrm{br}}/{\mathrm{<figure-callout\; id="2"\; label="v\; s"\; filenames="imgf0001.png"\; state="\{\{state\}\}">v\; </figure-callout>}}_{\mathrm{s}}\right)}^2$$

S _br =

Safety factor against centrifugal breakage

v _br =

Circumferential speed in case of breakage due to centrifugal force

v _s =

Maximum working speed corresponding to the permissible peripheral speed of a rotating grinding tool

It follows that for a working speed of 40 m / s, based on a safety factor of 3.5, the minimum breaking speed is 75 m / s.

During the test run, a peripheral speed of the test samples of 75 m / s could be achieved without causing mechanical breakage or visible damage.

The grinding wheel according to the invention is shown schematically in the figure. The reference number 1 shows the core area, which can be completely or partially penetrated by a hole for clamping on a grinding machine. The reference number 2 denotes the grinding area. It can be seen that the circumference is concave in order to grind cylindrical workpieces there. The reinforcement washers have the reference number 3.

After prolonged use of the grinding wheel, dressing may be required. Since the reinforcement disks 3 are made of dressable material, they can be dressed together with the grinding area 2 without further notice.

Example 2: Tool:

Grinding wheel according to Example 1, but with the different dimensions 200 x 30 x 76.2 mm (outer diameter x width x bore diameter).

grinder:

Special machine from Thielenhaus

Workpiece:

$$\mathrm{Aufmaß}<\mathrm{0,01}\mathrm{mm}$$

Cylinder made of 100Cr6, diameter 26 mm, length 1200 mm Prepared by grinding with a bonded grinding wheel with grain size F80. $$\mathrm{March}=2.0-3.0\mathrm{microns}$$

$$\mathrm{oversize}<0.01\mathrm{mm}$$

The grinding wheel is first made with a single-grain diamond CNC-controlled with a concave degree of coverage Ud> 4.

The grinding wheel and workpiece are arranged in relation to one another such that the spindle of the grinding machine is perpendicular to the longitudinal axis of the workpiece. The grinding wheel correspondingly moves as a double stroke when machining the cylindrical workpiece in its axial direction.

After each machining step, the workpiece is rotated by 30 degrees.

The following application parameters apply to grinding: Working speed: 35 m / s Feed speed in the axial direction: 10 m / min Contact pressure of the grinding wheel 4-6 bar

After machining, the workpiece has a uniform, axially running surface structure with an average roughness Ra <0.4 µm.

Claims (13)

1. Grinding wheel, having a grinding region (2) which acts in a circumferential direction and which has bound grinding agent; and having reinforcement elements (3) which do not participate in the grinding process, wherein the reinforcement elements have at least one reinforcement disc (3) which is arranged at an end side and which is designed to be free from grinding agent and such that it can be dressed, and wherein the at least one reinforcement disc (3) extends over at least 80% of the end surface of the grinding region (2), situated therebelow, and core region (1), characterized in that the grinding region (2) is of ring-shaped form and the core region (1) has a greater hardness than the grinding region (2) arranged radially at the outside around said core region.
2. Grinding wheel according to Claim 1, characterized in that the reinforcement elements have two reinforcement discs (3) which are arranged at end sides and which are designed to be free from grinding agent and such that they can be dressed.
3. Grinding wheel according to Claim 1 or 2, characterized in that the material of the reinforcement discs (3) has a flexural fatigue strength of at least 15 MPa, preferably of at least 20 MPa, more preferably of at least 25 MPa.
4. Grinding wheel according to any of Claims 1 to 3, characterized in that the at least one reinforcement disc (3) is connected areally to the grinding region (2) .
5. Grinding wheel according to any of Claims 1 to 4, characterized in that the at least one reinforcement disc (3) has a binding agent and filler materials.
6. Grinding wheel according to Claim 5, characterized in that the filler material fraction of the reinforcement discs (3) amounts to 10 to 60 wt.%, preferably 20 to 40 wt.%.
7. Grinding wheel according to any of Claims 1 to 6, characterized in that the material of the grinding region (2) has a Shore A hardness of 20 to 97.
8. Grinding wheel according to any of Claims 1 to 7, characterized in that the at least one reinforcement disc (3) extends over surface regions of the grinding region (2) and of the core region (1) and is connected in each case areally thereto.
9. Grinding wheel according to any of Claims 1 to 8, characterized in that the at least one reinforcement disc (3) extends over at least 90% of the end surface of the grinding region (2), arranged therebelow, and core region (1).
10. Grinding wheel according to any of Claims 1 to 9, characterized in that the axial thickness of the at least one reinforcement disc (3) amounts to 10 to 30%, preferably 15 to 25%, of the total thickness of the grinding wheel.
11. Use of a grinding wheel according to any of Claims 1 to 10 for surface machining.
12. Use according to Claim 11 for the surface machining of workpieces, preferably cylindrical workpieces and/or functional parts of machines.
13. Use according to Claim 11 or 12 for surface structuring.

Images