Patent Application
20110281511
The present invention relates to a resin-bonded abrasive disk in which plant seed capsules are used as pore formers, as well as a method for the production of such abrasive disks.
An abrasive disk consists essentially of abrasive grain, binder and pore space. The pore space is composed of the natural interstices which form between the abrasive grains and the pores introduced into the abrasive disk by pore formers. In addition to their formulation, the size and number of pores is also influenced by the contact pressure. Thus a small pore space forms at high pressure while a correspondingly larger pore space results from low pressure. However, a low contact pressure also produces a softer disk. In addition to pore formers, further fillers can also be used in abrasive disks. These can be abrasion-active (e.g. cooling) and thus support the grinding process or serve to stabilize (bursting strength, flexibility) the abrasive disk.
The fineness of the chips forming during the grinding process or the roughness of the material surface depends substantially on the size of the abrasive grain. Abrasive grains consist mostly of hard, brittle materials and are routinely used in a broad range of sizes. The binder material can be a resin, as in the present invention. It serves to hold together the individual abrasive grains. The pore space makes it possible, inter alia, to safely remove the material chips, but can also be used to absorb coolant. By varying the volume ratio of the individual components relative to one another, the properties of the abrasive disk can be adjusted, with the result that the desired grinding results can be achieved for every material to be treated.
Organic pore formers have thus far been used only in ceramically-bonded abrasive disks.
A ceramically-bonded abrasive disk which can be produced in a single firing step and manages without the use of a binder is described in U.S. Pat. No. 5,221,294 A. There are used as pore formers inter alia walnut shells, plastic beads or foamed organic material. A sol-gel based on boehmite crystal seeds mixed with walnut shells with an average size of 275 μm serves as starting product. This mixture is then cast into the desired shape, dried and then fired at a maximum temperature of 1300° C. The boehmite crystallizes to a-aluminium oxide. At these high temperatures the walnut shells burn without residue and therefore leave behind pores in the abrasive disk. The end-product has a porosity of approximately 40% and is sufficiently stable to be used as abrasive disk.
An abrasive disk which consists of a combination of pore formers, namely hollow aluminium-oxide beads and organic pore former as well as a sol-gel of aluminium oxide abrasive grains is described in U.S. Pat. No. 5,203,886 A. The organic pore former can be produced from nut shells, carbon, flower seeds, starch, sugar or wood particles. The organic pore former completely decomposes during firing of the abrasive disk and leaves behind open pores in the abrasive disk. The thereby achieved porosity of the abrasive disk is approximately 1 to 12% of its volume. The temperature-resistant, hollow, thin-walled aluminium oxide beads as closed pores give the abrasive disk additional porosity of up to 70% and thus provide sufficient stability. However, a problem here is that, while these closed pores can absorb coolant, they are not usually capable of removing ground chips.
DE 602 06 661 T2 describes an impregnated vitreous bonded abrasive disk which is impregnated with a sulphur-bearing organic substance as a grinding aid. This impregnant is a hydrocarbon compound with at least one carbon-sulphur bond. There may also be used as pore formers inter alia organic substances, such as nut shells, resins or wood flour which, however, may burn without residue at the indicated firing temperature of 538 to 1371° C. (1000 to 2500° F.) during the firing step.
DE 12 943 A relates to a method for the production of porous porcelain, earthenware or clay. A large number of substances, such as wood, hemp, flax, paper and grains of different types are named as pore formers. However, in the method described, these pore formers burn during the firing process. The earthenware produced according to this method is suitable inter alia for use as artificial millstones in flour mills.
DE 10 2004 035 088 A1 describes an organically bonded cut-off wheel with a functional additive. The abrasive device comprises a binder (phenolic resins, epoxy resins, imides), abrasive grain and at least one functional filler. Here, the functional filler is a metal alloy which can be chosen depending on the material to be worked. During production, a firing temperature in the range of from 150° C. to 250° C. is applied and the hardening step lasts a total of 12 to 76 hours.
DE 697 05 538 T2 describes abrasive articles and methods for their production. There are used as binders inter alia phenolic resins and epoxy resins. The abrasive grain used has a diameter of from approximately 1 μm to approximately 10 mm. These abrasive disks harden over a period of from 8 to 15 hours at temperatures of from 66 to 120° C.
DE 102 97 124 T5 describes a method for the production of a vitrified superabrasive tool in which a fritted vitreous bond composition is selected, a superabrasive grain component, a filler component with hollow bodies and the vitreous bond composition are combined, and the combined components are fired at from approximately 600 to 850° C.
The object of the present invention is to provide resin-bonded abrasive disks which have long lifetimes, do not become clogged and have a cool cut.
With an abrasive disk of the type named at the outset this object is achieved by the finished abrasive disk containing the plant seeds.
The abrasive disk consists of a mixture of abrasive grain, binder and pore former, wherein the pore formers are plant seeds and the plant seeds are not burned during production but are contained in the finished abrasive disk.
During production of the abrasive disk the plant seeds are used as organic pore formers. The plant seeds are not—as is customary in the production of ceramically-bonded abrasive disks—burned during production but remain intact and form an important component of the finished abrasive disk.
The plant seeds have several functions. As a component of the abrasive disk they have a certain supporting effect which prevents the abrasive grain from cracking prematurely. In addition to this supporting function, the plant seeds can also act as conventional pores and for example also remove the grinding chips. As the plant seeds are relatively soft they can be deformed by the mostly harder grinding chips and then remove these in the newly created pore space. It is also possible that the hot grinding chips which have temperatures of from between 1500° C. and 2000° C. burn the plant seeds during the grinding step. The resultant pore space is then comparable with that of a conventional pore and can then serve accordingly to remove the grinding chips. Additionally, during grinding of non-ferrous metals, the disk can be prevented from clogging by adding pore formers in the form of plant seeds.
An advantage of the present invention is that there are natural plant seeds in the most varied shapes and sizes, with the result that the porosity of the grinding tool can be adapted virtually at will. This is particularly important because the size of the resulting chips may vary depending on the size of the abrasive grain and depending on the condition of the workpiece.
The resin-bonded abrasive disk of the present invention consists 60 to 90 wt.-% of abrasive grain and 10 to 40 wt.-% of binder. The plant seeds may account for up to 80 wt.-% of the binder. In addition, various other known fillers may be used.
Essentially, all materials customarily used as abrasive grain are suitable as abrasive grain. These include corundum, silicon carbides, chromium oxides, cubic boron nitride, diamonds, silicon oxides, zirconium oxides, garnet and emery, as well as mixtures thereof. The abrasive grains may have different sizes in the range of from 0.5 μm to 5000 μm. The size as well as the material of the abrasive grains can be chosen depending on the workpiece to be worked. Preferably the abrasive grain has a particle size of from 105 μm to 2830 μm, more preferably of from 250 μm to 2830 μm.
In a preferred embodiment oleaginous seeds, such as e.g. rape seeds, are used. The oil contained in the plant seeds results in a lubricating effect, i.e. the oil reduces the friction of the abrasive grain during the formation of chips and thus reduces the build-up of heat during grinding. As a result, on the one hand the lifetime of the abrasive disk is increased and on the other hand the workpiece is protected against undesired hardening.
In addition to oleaginous plant seeds, poppy, clover, lupine, mustard, serradella or vetch seeds or similar plant seeds may be used.
The binder is a mixture of a synthetically produced polymeric compound and fillers. The polymeric compound may be resin which can be used in both liquid and powder form. Suitable resins are for example polyimides, phenolic resins, epoxy resins, unsaturated polyesters and the like.
The invention also relates to a method for the production of the abrasive disks according to the invention. Firstly, a pourable mixture of abrasive grain, binder and plant seeds is produced. This mixture is poured steadily into a preformed compression mould and then pressed to a previously determined volume. The moulding then undergoes a hardening programme in an oven, wherein it is exposed to temperatures of up to 250° C. The pressing and hardening of the abrasive disk may also take place in one step.
The abrasive-disk mixture is poured extremely evenly dispersed into a compression mould. Then, the moulding is pressed in a normal press, e.g. a hydraulic press, under contact pressures of from 15 to 45 N/mm2, preferably from 20 to 35 N/mm2, even more preferably of from 30 N/mm2 to produce a green preform. The pressing time can lie in the range of from 1 to 100 seconds, preferably 5-50 seconds. To increase the structural integrity of the abrasive disk, additional reinforcements (e.g. glass fibre cloth) can also be pressed in. Preferably the pressing is carried out at room temperature.
The green preform is then hardened at increased temperature. The hardening process takes place in chamber or tunnel ovens. The temperature can be automatically controlled by a programme regulator. The selection of a suitable hardening programme depends on a series of factors, such as the measurements and the structure of the disk, the proportion of filler, the proportion of resin bond and the resin properties. The temperature at which hardening takes place is chosen such that the plant seeds in the green preform do not burn.
Typically the mouldings are pre-dried firstly at temperatures of between 50° C. and 100° C. and then hardened at temperatures of up to 250° C., preferably of up to 200° C., even more preferably of up to 180° C. and in particular of up to 150° C., whereby they obtain their final shape and composition. The hardening process lasts between 5 and 40 hours, preferably between 10 and 30 hours and even more preferably 15 hours.
The production of an abrasive disk with poppy seeds is described below by way of example:
To produce the abrasive disk, firstly abrasive grain with the particle size 36 (˜500 μm) is pre-mixed in a mixer. Resol (liquid phenolic resin) is then added, whereby the abrasive grain is evenly wetted and coated with a thin resin film. When the abrasive grain is evenly wetted with resol, a mixture of powdery phenolic resin, poppy seeds and cryolite is added.
The composition of the formulation is as follows:
The mixing process is continued until the desired homogeneous consistency is achieved. The abrasive-disk mixture is to be not too dry, but dust-free and pourable. After production, the mixture is sieved off and stored for a few hours.
After the storage the pressing mixture is accurately weighed-in and conveyed into the compression mould with the help of sliders. The mixture is poured extremely evenly dispersed into the compression mould. Then the moulding is cold-pressed to produce a green preform within a few seconds in a customary press under a contact pressure of 30 N/mm2. To increase the structural integrity of the abrasive disk three woven fabrics are also pressed in.
After pressing, the produced green preform is clamped between metal disks and fired over a multi-stage hardening profile up to a temperature of 180° C. over a total of 15 hours. After the firing the finished abrasive disk is removed from between the metal plates.
The finished disk measures 125×7×22.23 mm and has an agreeably cool cut.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 006 699.3 | Jan 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/050996 | 1/28/2010 | WO | 00 | 7/28/2011 |
