DEVICE AND PROCEDURE FOR CLEANING, DEBURRING AND POLISHING PARTS IN THE MAGNETIC FIELD

The present invention is an apparatus according to claim 1 as well as a method according to claim 3.

Modem manufacturing technology processes have to meet uniform requirements of reliability, accuracy, productivity and cost-effectiveness producing the lowest possible environmental load. Cleaning, deburring and polishing processes are no exception to this rule.

There are a number of known-art methods for cleaning, deburring and polishing machine parts, with abrasive-grinding methods such as revolving-drum, vibratory, and centrifugal techniques being among the most widespread (W. König, Kö szörülés, dörzsköszörülés, tükrösítés [Grinding, honing, lapping methods], Budapest, Müszaki Könyvkiadó 1983). In all of these methods machining takes place in a special container, exploiting the disordered motion of abrasive parts or particles, with the appiication of liquid additives. Individual methods differ mainly in their productivity and the size of the parts that can be processed (see description DE 2 408 359 A).

The productivity of known methods can be increased by carrying out the machining in magnetic field, which also gives way to handling parts of non-conventional materials or geometry.

A number of methods have been suggested for abrasive grinding in magnetic field, one of which being the so called barrel deburring method. According to this method the abrasive parts and the workpieces are loaded into a revolving plastic container, with the ferromagnetic part of the barrel's contents being restrained by magnetic shoes enclosing the rotating barrel. Thus the relative velocity of workpieces and abrasive parts can be increased and machining can be made more productive. Such a method is disclosed in the document HU 204,217. A drawback of the method is that the limited diameter of the barrel restricts the size of parts that can be processed, and loading and emptying the barrel may also pose problems. The applicable rotational speed and the relative velocity of workpieces and abrasive parts is heavily affected by the magnetic field strength, which decreases if the barrel diameter is increased.

Magnetic deburring and polishing machines are nowadays produced commercially. For instance, one type of such a machine utilises plastic containers with a diameter of 160-600 mm and a height of 160-540 mm (www.earth-chain.com.tw). Magnets of the machine are located below the open-top container on a rotating table, with the ferromagnetic abrasive parts, disposed inside the stationary container, being rotated by the magnetic force exerted on them by the rotating magnets. The abrasive parts collide with the non-ferromagnetic workpieces loaded into the container, deburring and polishing them. For the operation of the machine grinding liquid is needed. The apparatus is only capable of machining non-ferromagnetic parts, and it can be problematic to sufficiently retain smaller-size parts and to provide for the necessary orientation of larger ones.

Other solutions for magnetic deburring also exist, e.g. the one by W. R. Lovness and J. F. Feldhaus (German patent, filed 02.19.1974. Maschine zum Reinigen, Schleifen und Polieren von Gegenständen), where the magnetisable abrasive parts (grains) are moved among the freely moving workpieces by a rotating magnetic field generated outside the container. According to another solution the abrasive parts are retained by suitably disposed magnetic shoes inside the rotating container, with the individually fixed workpieces being polished by the abrasive parts (T. Shinmura, E. Hatano, K. Takazawa, "Development of Spindle-Finishing Type Finishing Apparatus and Its Finishing Performance Using a Magnetic Abrasive Finishing Process," Bull. Japan Soc. of Prec. Eng., Vol. 20 No. 2, June 1986). Problems with the first method are similar to drawbacks mentioned relation above, and it should be remarked that generating a rotating magnetic field in a greater-diameter container may also be problematic. Because workpieces are retained individually, the productivity of the second solution is relatively lower, but among its advantages it has to be mentioned that it is equally capable of machining ferromagnetic and non-ferromagnetic parts (see description US-A-4 730 418).

The apparatus described in document US4730418 is suitable for cleaning, deburring and polishing parts in a magnetic field, and comprises a non-magnetic container implemented as a revolving drum, an electromagnet, an electric motor, a magnetisable rotating disc, further a table supporting the electromagnet and a ferromagnetic ring and ensuring the closing of magnetic lines of force; with the rotating disc being fitted with an upper and a bottom bearing and being driven through a belt drive by means of an electric motor; and further comprising a power supply for adjusting the stationary magnetic field generated by the electromagnet.

The aim of the present invention is therefore to provide a cleaning, deburring and polishing apparatus and method that remedies the problems encountered with devices according to the state of the art.

The ferromagnetic portion of the contents of the container is rotated by means of a magnetisable disc that is disposed inside the container (which can also be rotated in a controllable way) and is magnetised to the desired extent by means of an electromagnet generating stationary magnetic field.

Non-ferromagnetic elements in the container conform to the rotation of the container, which means that in case the container is stopped the non-ferromagnetic elements are also brought to a halt. The apparatus can be used for machining both ferromagnetic and non-ferromagnetic elements, and only environmentally friendly materials can be utilised as additional media.

The invention is based on the insight that it is preferable to adjust the relative velocity of the different parts of the contents of the container to meet requirements of changing operating conditions. This can be achieved by ensuring that the rotational speed of the rotating disc and also the magnetisation level thereof can be adjusted continuously, and by providing that the container can be braked and the rotational direction thereof can be reversed. It has also been observed that in a strong magnetic field the conventional deep groove ball bearing can be utilised as a flexible coupling element.

This finding can be useful for designing the rotating and braking means of the container of the apparatus, which may be supported in bearings on a rotating iron core. The magnetic transmission element (the magnetisable disc) may be disposed in the interior of the container, in the immediate proximity of the parts loaded thereto.

Thus, the inventive goal is achieved by providing an apparatus according to claim 1 and a method of claim 3.

Preferred embodiments of the invention are defined in the dependent claims.

One embodiment of the inventive apparatus will now be described in detail, by way of example only, with reference to the accompanying drawings, where

• Fig. 1 is the schematic view of the apparatus according to the invention, and
• Fig. 2 shows the configuration of the container of the inventive apparatus in the case where non-ferromagnetic parts are machined.

The apparatus shown in Fig. 1 consists essentially of a plastic container 5, a magnetisable rotating disc 3, a braking means 6, a rotating iron core 10, a deep groove ball bearing 4, an electromagnet 7, an electric power supply 16, a ferromagnetic table 9, a ferromagnetic ring 8, an upper bearing 11, a bottom bearing 13, an electric motor 15, a variable frequency drive unit 14, a belt drive 12, ferromagnetic parts 2 and non-ferromagnetic abrasive parts 1, with said ferromagnetic parts 2 and non-ferromagnetic abrasive parts 1 being loaded into said container 5.

If the apparatus is applied for machining non-ferromagnetic parts 17, the container 5 is loaded with ferromagnetic abrasive parts 18, as it is shown in Fig. 2.

Figures 1 and 2 show an embodiment of the inventive apparatus that is suitable for cleaning, deburring and polishing ferromagnetic or non-ferromagnetic parts of small or medium size.

The operation of the inventive apparatus will now be described in detail.

The plastic container 5 is loaded from above with ferromagnetic parts 2 or non-ferromagnetic parts 17 and, depending on whether ferromagnetic 2 or non-ferromagnetic 17 parts are to be machined, non-ferromagnetic abrasive parts 1 (made of aluminium-oxide) or ferromagnetic abrasive parts 18 (made of corrosion-resistant steel) are also loaded into the container 5. Other materials may also be loaded into the container: in case of dry machining preferably wheat or corn flour can be utilised, while in case of wet machining a conventional, preferably environmentally friendly surface-active fluid is desirable as an additive.

After the container has been filled up, a stationary magnetic field is generated by the electric power supply 16 and the electromagnet 7 and the intensity of the field is adjusted to the desired level. The path of the magnetic lines of force closes through the rotating iron core 10, the magnetisable rotating disc 3, the ferromagnetic parts 2, the ferromagnetic ring 8 and the ferromagnetic table 9. After the magnetic field has developed, the container 5 becomes flexibly joined to the rotating iron core 10 by the deep groove ball bearing 4 that consists of magnetisable parts.

To ensure that the contents of the container 5 (the parts to be machined) are distributed evenly, the container 5 is set into rotary motion by the electric motor 15 via the belt drive 12. The desired rpm n₁ can be adjusted using the variable frequency drive unit 14. Due to the centrifugal force arising because of the rotation of the container 5, the contents thereof will soon be located in the vicinity of the side walls, but no material is severed from the parts at this point. The velocity difference between work-pieces and abrasive parts which is necessary for abrasive action is brought about through the braking means 6 that is used to adjust the rpm n₂ (<n₁) of the container.

Experiments have shown us that for machining parts of certain specific shapes it can be advantageous to implement the rotating disc 3 with a non-cylindrical (e.g. cogged) perimetric configuration.

The machining process finishes after the parts have become cleaned, deburred, or polished, which can be ascertained either by (ocular) inspection or by measurement. Finished parts are removed from the container 5 in the conventional way by taking them out manually or using a vacuum device, and are separated according to a known art method (e.g. magnetic or centrifugal separation).

Fig. 2 illustrates how non-ferromagnetic work-pieces are located inside the container 5 during the operation of the inventive apparatus. In this case ferromagnetic abrasive parts 18 are applied, which rotate together with the rotating disc 3 while the rotational speed of the non-ferromagnetic parts 17 is nearly equal to the speed of the container 5.

To ensure that parts are cleaned, deburred and polished evenly it may become necessary to occasionally rearrange the contents of the container 5. That can be achieved by simply turning the magnetic field on and off automatically from time to time, or alternatively by reversing the direction of rotation of the apparatus.

Among the main advantages of the inventive apparatus it should be mentioned that the apparatus speeds up the finishing process, is cost-effective, can be controlled easily, and can be applied for machining both ferromagnetic and non-ferromagnetic parts.

1

non-ferromagnetic abrasive parts

2

ferromagnetic parts

3

rotating disc

4

deep groove ball bearing

5

container

6

braking means

7

electromagnet

8

ferromagnetic ring

9

ferromagnetic table

10

rotating magnetic core

11

upper bearing

12

belt drive

13

bottom bearing

14

variable frequency drive unit

15

electric motor

16

power supply

17

non-ferromagnetic parts

18

ferromagnetic abrasive parts