EP2954981A1 - Grinding wheel - Google Patents

Abstract

The invention relates to a grinding wheel, comprising a circumferentially acting grinding area (2) having bonded abrasive; and with not participating in the grinding process reinforcing elements (3). According to the invention, it is provided that the reinforcing elements have at least one reinforcing disk (3) arranged on the front side, which is designed to be free of abrasive material and dressable.

Description

The invention relates to a grinding wheel having a circumferentially acting grinding area comprising bonded abrasive; and with not participating in the grinding process reinforcing elements.

Abrasive-bonded abrasive tools have abrasives embedded in a binder which together form a compact body.

The choice of suitable grinding tool depends on the task underlying the machining of the workpiece. In most cases, two machining effects are decisive: on the one hand, the removal of material with the aim of geometrical shaping and, on the other, the microstructure of the machined workpiece surface. In the majority of machining tasks, a geometric shape is to be achieved, while at the same time making demands on the workpiece surface. The criterion for the condition of the workpiece surface is usually the surface roughness R _A. and the nature and orientation of structural features.

Deviating from this, however, there are also machining tasks with grinding tools, which have the goal of producing a particular microstructure of the workpiece surface predominantly or exclusively. For example Stainless steel sheets for use in elevators or interior linings provided with a decorative line pattern, without any significant material removal takes place. Preferably fleece or brush tools are used because they have sufficient elasticity to adapt to the workpiece surface. Such tools are coated abrasives.

Also in the area of bonded grinding tools, special constructions have been developed for the surface structuring of workpieces. As a rule, however, these are not large-scale workpieces such as metal sheets, but predominantly functional parts of the mechanical engineering sector. As in the field of abrasives on documents with the nonwoven and brushing tools here is the requirement of elasticity of the grinding tool to adapt to the surface contour of the workpiece. Accordingly soft and elastic binders are used for such applications, such as rubber, silicone or 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 be done both between tips, but also without a center. In both cases, the peripheral side of the grinding wheel comes into engagement, with the axis of the workpiece and the axis of the grinding wheel parallel to each other. In order to machine the workpiece over the entire length, the grinding wheel travels in the axial direction and this usually continuously in several cycles. Although this allows a uniform processing image in the desired roughness However, the surface shows a spiral surface pattern, also called "twist". This effect can affect the functionality of the workpiece, such. As in cylinders or racks that are part of a hydraulic system and procedures by seals. The achieved roughness depths are approx. R _A <0.8 mm.

Alternatively, a similar method is feasible, but the grinding tool is not continuously moved axially, but after each intervention is separated from the workpiece, moves and then in turn comes in the sense of a "Einstechschleifens" for engagement. However, the disadvantage here is the discontinuous process with the risk of producing markings with each intervention.

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

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

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

This object is achieved in a grinding wheel mentioned above in that the reinforcing elements have at least one front side arranged reinforcing disc, which is designed to be abrasive-free and dressable.

First, some terms used in the invention are explained.

The term grinding wheel in the context of the invention designates a grinding tool with bonded abrasive, which is designed for machining surfaces with a narrow side or peripheral side. The grinding area is that volume area of the grinding wheel that contains or contains the bonded abrasive. Suitable and usable in the invention abrasives 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 particular properties of these hard abrasives (high wear resistance) are generally not taken into account because of their relatively soft binding 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 preferably circular and suitable for clamping on a rotary grinding machine, but is not limited thereto.

The grinding wheel has not on the grinding process participating reinforcing elements. These elements increase the mechanical stability of the disc and in particular reduce elastic or plastic deformation of the grinding wheel under the loads occurring during grinding, such as, for example, centrifugal forces or compressive loads. Thus, they tend to reduce the inherent tendency of the bonded 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 contact with the surface of the machined workpiece in a conventional 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 free of abrasive material and dressable. The front side means that the at least one reinforcing disk is arranged on a surface of the grinding wheel, which is not the grinding peripheral surface. In a circular grinding wheel such an end face is usually perpendicular to the intended rotation axis.

The reinforcing disk is a flat element which serves to absorb and dissipate mechanical forces and is itself not designed to participate in the grinding process. It therefore contains essentially no abrasive. This reinforcement disk is dressable trained. The meaning and technical advantages of this feature will be explained below.

A common area of use of grinding wheels acting on the peripheral side is the surface structuring of curved, for example cylindrical surfaces. Prerequisites for this, however, are a sufficient elasticity of the grinding area and a high contact pressure. In this case, in the prior art, the grinding wheel can be deformed, thereby the positive engagement with the workpiece is no longer given. On the other hand, the pressure and the associated deformation can lead to the formation of cracks and, as a consequence, to the destruction of the grinding wheel.

From obvious prior use, it is already known to reduce these undesirable effects by the use of two lateral steel discs, which are mounted together with the grinding wheel on the spindle. However, this solution of the prior art is associated with considerable disadvantages.

After machining a number of workpieces, grinding wheels must be periodically dressed to restore, in particular, the desired surface geometry of the peripheral side. However, steel discs can not be dressed together with the grinding wheel. Rather, after each dressing steel discs must be mounted with a correspondingly smaller diameter. This has the disadvantage of stockpiling and assembly work. It must also be taken into account that the steel discs are only available in certain graduations and thus can not be achieved a precisely fitting support effect. A particular advantage of the present invention is that the dressable trained reinforcing discs allow a comparable mechanical stabilization, but can be dressed together with the grinding area when dressing the grinding wheel. The necessary in the prior art disassembly / assembly of steel discs deleted.

Suitability for dressing processes is understood to mean that the geometric shape and / or the sharpness can be restored by means of a conventional dressing tool. Dressing tools of this kind include embodiments with single diamonds or diamonds-occupied moldings, but also diamond-free dressing tools with silicon carbide or corundum.

According to the invention, it is particularly preferred for the reinforcing elements to have two reinforcing disks arranged on the front side, which are designed to be free of abrasives and dressable. The more easily deformable grinding area is edged and reinforced in this way from both ends.

It is further preferred that the material of the reinforcing discs has a transverse rupture strength of at least 15 MPa, preferably at least 20 MPa, more preferably at least 25 MPa. The Shore A hardness may preferably be above 100.

To measure the transverse rupture strength, square specimens measuring 16.2 mm × 16.2 mm × 120.4 mm were subjected to a 3-point bending test. The edition consisted of two metal rollers with a distance of the support points of 80 mm, the diameter of the metal rollers was 30 mm. During delivery, the crosshead speed was 10 mm / min

As a suitable, dressable material for the reinforcing discs is basically a material based on a same or comparable binder as used for the grinding area in question. This makes it easier to machine the grinding area and the reinforcing disks in one operation with the same tool. Suitable binders may be, for example, polyurethanes, phenolic resins, glass or ceramic binders. Preferably, a filler may be provided for adjusting the desired mechanical properties and increasing the strength. It may be known mineral fillers, preference is given to hollow bodies based on minerals (microspheres). The filler content may according to the invention, for example, between 10 and 60 wt .-%, more preferably 20 and 40 wt .-% are. These upper and lower limits can be combined as desired to areas according to the invention.

It is preferred that the at least one reinforcing disk is connected to the grinding area in a planar manner. Connected surface means that this reinforcing disk, at least with a large surface area of more than 50%, but preferably a full surface enters into a frictional connection with the grinding area, for example, is glued. This laminar bond prevents the grinding wheel from being compressed toward the central axis, resulting in reduced dimensional stability in the grinding zone. Such a flat composite is not possible in the prior art in the steel discs used, since these must be dismantled for dressing and then re-assembled. The material of the grinding region preferably has a lower hardness than the material of the reinforcing disks. Preferred is a range of Shore A hardness of 20 to 97, more preferred are ranges of 20-90 or 70-85, in the machining of hardened cylindrical metallic workpieces, for example, the hardness range of 70-85 may be useful.

In a particularly preferred embodiment of the invention it is provided that the grinding area is annular and surrounds a hard core area. In this context, hard means that this core region has a greater hardness than the grinding region arranged radially outside it. In the case of the preferably circular grinding wheel, this core region can absorb and divert in particular the acceleration and centrifugal forces in the region of the bore. The core area thus has the opening or bore which serves for connection to the grinding machine. The core region may according to the invention consist of a same or similar material as the reinforcing discs.

In this preferred embodiment, a grinding wheel according to the invention thus consists of four structural elements. It is the core area, the grinding area and two reinforcing discs. 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 that the core region and the reinforcing discs are integrally formed or integrally connected to each other. Thus, it is also preferred that according to the invention the reinforcing disks extend over surface areas of the Grinding area and the core area extend and thus each area (or in the case of the core area in one piece) are connected. The combination of the reinforcing discs with both the grinding area and the core area makes it possible to carry out an effective force dissipation into the core area. A radial change in shape of the grinding area is thereby substantially prevented. Consequently, a significantly improved form fidelity of the engagement zone of the grinding area is achieved against pressure forces during the grinding process. However, it should also be noted that even when accelerating the grinding wheel to the desired working speed an elongation by centrifugal forces is significantly reduced. On the one hand, this allows the use of a binder that tends to be harder with higher grinding performance. Because the grinding area is fixed flat to the reinforcing discs, the surface geometry of the grinding area tends to be maintained even under the pressure load of an application. Because of this better dimensional accuracy, the positive connection between the workpiece and the engagement zone of the grinding area is thus ensured even with a harder binder. On the other hand, the grinding wheel according to the invention also permits the use of particularly soft binders, as may be required for grinding geometrically complicated workpieces. In this case, the grinding area can largely adapt to the workpiece contour and is stabilized by the reinforcing discs against deformation and cracking. Regardless of the binder chosen, generally higher working speeds can be achieved due to the improved strength. This improves the efficiency of the grinding process, but can also allow the creation of special speed-dependent surface structures.

According to the invention, it is further preferred for the at least one reinforcing disk to extend over at least 80%, preferably at least 90%, of the end face of the grinding area and / or core area arranged thereunder. This large-area design of the reinforcing discs allows effective stabilization and shape retention of the grinding area.

The axial thickness of the at least one reinforcing disc, preferably the common axial thickness of the two reinforcing discs, in a preferred embodiment 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 treatment. Preference is given to the surface treatment of workpieces, preferably cylindrical workpieces and / or functional parts of machines. It is preferably not a large-scale processing planer surfaces, but a comparatively small-scale machining curved such as cylindrical surfaces. Particularly preferred is the use for surface structuring. Surface structuring means that no substantial change in the shape of the surface takes place in the sense of a material removal, but merely a desired surface structure is produced.

Embodiments of the invention will now be described with reference to the single drawing showing a grinding wheel according to the invention in axial and radial views.

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 grinding area with an abrasive layer and a core area in the bore and two lateral reinforcing discs. These structural elements are first manufactured as cylindrical blanks of great length and then cut by means of 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 (Lightweight filler, Omega Minerals Germany)

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

Prefabrication of the grinding area: Recipe ingredients:

RC major 110 (Diphenylmethanediisocyanate, Bayer MaterialScience) Poly-G HQEE (Crosslinker, hydroquinine di (beta-h) ester, CVH chemistry. Distribution) Diorez 770/02 (Polyester polyol, Azelis Switzerland Chemicals) Dabco TMR 2 (Activator, quartenary ammonium salt, Air Products Chemicals) Tegostab B 8905 (Surfactant, CVH-Chemie-Vertrieb GmbH & Co. Hannover KG) Dipropylene glycol Araldit AW 116 (Solvent, CVH-Chemie-Vertrieb) (epoxy resin, Fa. Epoxidharze Andreas Weigel) Hardener HV 953 U Hardener to Alaldit AW 116, Fa. Epoxidharze Andreas Weigel) Byk-W 961 SCG F 80 (Structure improver, BYK-Chemie) (abrasive grain silicon carbide green, grain size F 80, ESK-SiC GmbH foamer (Mixture of Tegostab 8905, dipropylene glycol and water to each Weils same volume fractions) 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 for 48 hours before use. The abrasive grain SCG F 80 is preheated in the same way.

The components RC Dur 110 (1079 g), frother (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 60 s. After adding CAT1 (20 g), mix again (20 s).

In a preheated and coated with release agent metal mold with the dimensions 310 mm (diameter), 155 mm (width) and 70 mm (bore diameter) of the prefabricated and adhesive coated with (Aaraldite) core area is plugged. The exact central positioning takes place by means of a centering pin.

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

Finally, the mold is opened, the blank removed, clamped in a machining center and turned off the circumference to a dimension of 307 mm. In the same setting, a disk-shaped part of a width of 30 mm is finally cut off by means of a diamond cutting wheel.

Prefabrication of reinforcing discs:

The production of the reinforcing discs is made of the material that also used for the production of the core area has been. The description of the processing is to be applied correspondingly.

Recipe ingredients:

• 2498 g Rencast FC52 ISO
• 2498 g Rencast FC52 poly
• 2505 g microspheres ISOPHERES SG-300 B

Dimensions of the mold:

• 310 mm (diameter)
• 120 mm (width)
• 70 mm (bore diameter)

The diameter of the obtained cylindrical body is reduced in a machining center by turning to 307 mm. In the same clamping disc-shaped segments are cut by 5.2 mm width by means of a diamond cutting wheel.

Further processing:

Before further processing, the individual structural elements are checked. Criteria are dimensions, weight, density, hardness and breaking strength (support disks). Furthermore, a visual inspection for damage such as cracks, pores or inhomogeneities.

The reinforcing discs are successively glued to the core area, which are each subjected to pressure during the curing time. Finally, the grinding wheel is machined by turning the faces, the bore and the circumference to the desired degree and the to obtain desired surface structure. Finally, by dressing the corresponding profile purpose corresponding circumferential profiling is generated.

The final inspection includes tests for dimensional accuracy and imbalance as well as a test run with 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 SchleifwerkzeugesTo test the breaking strength, a further test run was carried out. For this purpose, a maximum operating speed of 40 m / s and a significantly increased safety factor of 3.5 according to the actual application were used. The safety factor is defined as follows: $${\mathrm{S}}_{\mathrm{br}}={\left({\mathrm{v}}_{\mathrm{br}}/{\mathrm{<figure-callout\; id="2"\; label="v\; s"\; filenames="imgf0001.png"\; state="\{\{state\}\}">v\; </figure-callout>}}_{\mathrm{s}}\right)}^{\mathrm{2}}$$

S _br = safety factor against breakage by centrifugal force
v _br = peripheral speed at break by centrifugal force
v _s = maximum working speed corresponding to the permissible circumferential speed of a rotating grinding tool

It follows that for a working speed of 40 m / s, assuming a safety factor of 3.5, the minimum break peripheral speed is 75 m / s.

During the test run, a peripheral speed of the test pattern 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. Reference number 1 shows the core area, which may be interspersed in whole or in part by a bore for clamping on a grinding machine. The reference numeral 2 indicates the grinding area. It can be seen that this is concavely curved on the circumference in order to be able to grind cylindrical workpieces there. The reinforcing discs have the reference numeral 3.

After prolonged use of the grinding wheel may be required from a judge. Since the reinforcing discs 3 are made of dressable material, they can easily be dressed together with the grinding area 2.

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 of the company Thielenhaus

Workpiece:

Cylinder made of 100Cr6, diameter 26 mm, length 1200 mm Pre-processed by grinding with a bonded grinding wheel of grain F80.
Rz = 2.0 - 3.0 μm
Oversize <0.01 mm

The grinding wheel we first with a Einkorndiamanten CNC-profiled with an overlap degree Ud> 4 concave profiled.

Grinding wheel and workpiece are arranged to each other such that the spindle of the grinding machine behaves perpendicular to the longitudinal axis of the workpiece. Accordingly, the grinding wheel moves during the machining of the cylindrical workpiece in its axial direction in each case as a double stroke.

After a processing step, the workpiece is rotated by 30 degrees.

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

After machining, the workpiece has a uniform, axially extending surface structure with a mean roughness Ra <0.4 μm.

Claims (14)

A grinding wheel having a circumferentially acting grinding area (2) having bonded abrasive; and with not participating in the grinding process reinforcing elements (3), characterized in that the reinforcing elements have at least one frontally arranged reinforcing disc (3), which is designed to be abrasive-free and dressable. Grinding wheel according to claim 1, characterized in that the reinforcing elements have two frontally arranged reinforcing discs (3), which are formed without abrasion and dressable. Grinding wheel according to claim 1 or 2, characterized in that the material of the reinforcing discs (3) has a transverse rupture strength of at least 15 MPa, preferably at least 20 MPa, more preferably at least 25 MPa. Grinding wheel according to one of claims 1 to 3, characterized in that the at least one reinforcing disc (3) is connected flat with the grinding area (2). Grinding wheel according to one of claims 1 to 4, characterized in that the at least one reinforcing disc (3) comprises a binder and / or fillers. Grinding wheel according to a 5, characterized in that the filler content of the reinforcing discs (3) 10 to 60 wt .-%, preferably 20 to 40 wt .-% is. Grinding wheel according to one of claims 1 to 6, characterized in that the material of the grinding region (2) has a Shore A hardness of 20 to 97. Grinding wheel according to one of claims 1 to 7, characterized in that the grinding region (2) is annular and surrounds a hard core region (1). Grinding wheel according to claim 8, characterized in that the at least one reinforcing disc (3) extends over surface regions of the grinding region (2) and the core region (1) and is thus connected in a planar manner. Grinding wheel according to one of claims 1 to 9, characterized in that the at least one reinforcing disc (3) extends over at least 80%, preferably at least 90%, of the end face of grinding area (2) and / or core area (1) arranged thereunder. Grinding wheel according to one of claims 1 to 10, characterized in that the axial thickness of the at least one reinforcing disc (3) is 10 to 30%, preferably 15 to 25% of the total thickness of the grinding wheel. Use of a grinding wheel according to one of claims 1 to 11 for surface treatment. Use according to claim 12 for the surface treatment of workpieces, preferably cylindrical workpieces and / or functional parts of machines. Use according to claim 12 or 13 for surface structuring.

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