EP0038455B1 - Method and device for treating the surfaces of workpieces by abrasive particles - Google Patents

Abstract

1. A method for the surface treatment of workpieces by means of abrasive particles within a processing container being open at its upper side and being filled, at least partially, with a granular abrasive treating agent, which is maintained in constant vibration and circulation by pulses and wherein the workpieces are embedded and wherein the workpieces coming to lie at the surface of the filling of said processing container are blasted by means of a blasting agent stream, characterized in that the volume of said workpieces amounts to no more than 50% of the filling present within said processing container, that said blasting agent constitutes at the same time the only treating agent ; and that the blasting agent comes into the bowl via the stream of a centrifugal blasting mechanism to which the blasting agent is led in a circuit after having left the processing container and having passed a cleaning device.

Description

The invention relates to a method for the surface treatment of workpieces using abrasive particles, in an upwardly open work container which is at least partially filled with a lumpy, abrasive treatment agent in which the workpieces are embedded and in which the blasting agent jet is applied to the surface of the work containers -Filling work pieces to be blasted. The invention further relates to a device suitable for carrying out the method (DE-A-2758281).

The so-called vibratory grinding process has found wide acceptance in the technology of surface treatment. It is based on the fact that the workpieces "floating" in a bed of treatment agents are gradually deburred, rounded, ground, cleaned, descaled or rusted by sliding and rubbing on their surface. On the other hand, it is known to process workpieces using an abrasive jet, a shorter machining time being necessary because of the much higher energy of the particles. While the vibratory grinding process has the disadvantage that the workpieces have to remain in the working container for a relatively long time until the desired surface treatment has ended, the disadvantage of the second-mentioned blasting process is that, in addition to the blasted workpieces, the base, i. H. the grate, the conveyor belt and the like are hit by the blasting agent, so that these parts wear out very heavily and have to be replaced relatively often.

• 1. wenn die Werkstücke allein sich in Vibration befinden, ein unerwünscht hoher gegenseitiger Abrieb und eine hohe Lärmentwicklung eintreten, oder
• 2. wenn Hilfskörper eingesetzt werden, auch die Hilfskörper verschleißen, wobei sowohl der Abrieb als auch das Strahlmittel wieder von den Hilfskörpern getrennt werden müssen.

From DE-OS 2 758 281 it is known to carry out a surface treatment of workpieces in that a bed of workpieces, alone or together with auxiliary bodies, is kept in constant vibration and circulating motion by means of impulses, the blasting agent jet being directed against the surface of the in quaisi -free liquid bed is directed. This procedure has the disadvantage that

• 1. if the workpieces are alone in vibration, an undesirably high mutual abrasion and a high level of noise occur, or
• 2. If auxiliary bodies are used, the auxiliary bodies also wear, both the abrasion and the blasting medium having to be separated from the auxiliary bodies again.

It is therefore the task of improving the method known from DE-OS 2 758 281 so that with optimal protection of the working container and minimal noise development with a short machining time, a uniform machining of the workpieces is possible, the device used for this being easy to manufacture and the workpieces should be made of both plastic and metal.

This object is achieved in the process for the surface treatment of workpieces as cited at the beginning, in which the abrasive is also the only treatment agent, the volume of the workpieces not exceeding 50% of the bed in the working container and the abrasive in the trough over the The jet of a centrifugal blast machine arrives, to which the abrasive is fed in a circuit after being removed from the working container and passed through a cleaning device.

In contrast to the method according to the prior art, no fillers, liquids or auxiliary bodies are used, but the entire cycle of the method takes place exclusively with a single treatment agent which is also an abrasive agent. Therefore, not all possible treatment agents or agents known as fillers are suitable for this process, namely no liquids, no splintering or bursting particles, such as glass particles, or particles which abrade themselves considerably.

On the other hand, the blasting agents known from surface blasting technology, such as steel or aluminum shot, are suitable. Walnut granules or plastic beads, for example made of hard polyvinyl chloride, can also be used for plastic parts.

The average size of the abrasive or treatment agent is preferably between 0.3 and 2.5 mm. The blasting agent must be suitable for processing using a known type of centrifugal blasting machine.

• - als Arbeitsbehälter einen sogenannten Vibrotrog,
• - wobei der Strahl mithilfe eines Schleuderstrahlwerkes erzeugt wird,
• - und am Ende des Vibrotroges eine Strahlmittel-Entnahmestation mit einer nachgeschalteten Reinigungsvorrichtung vorgesehen ist.

The device for performing the method has

• - a so-called vibrotrog as working container,
• - the jet being generated using a centrifugal jet,
• - And at the end of the Vibrotroges a blasting agent removal station is provided with a downstream cleaning device.

The blasting agent jet from the centrifugal blasting unit is directed onto the surface of the work container contents. The blasting energy is so great that a thin layer of blasting medium, which lies above the embedded workpieces, is blown away. The exposed, exposed surface of the workpiece is then cleaned. According to the speed of circulation of the workpieces, they then regularly reappear on the bed surface and are captured by the beam. It is also possible to make the blasting unit movable relative to the length of the working container, so that in each case the whole row of the workpieces lying above is gripped.

• Figur 1 schematisch eine Ausführungsform der Vorrichtung in Seitenansicht;
• Figur 2 einen Schnitt A-A gemäß Figur 1.

At the end of the working container there is a blasting agent removal station which is connected to a blasting agent return and cleaning device, as are known per se from surface technology. The Ent Pick-up station also enables the level of the bed to be kept exactly constant. Further properties of the method and of a device that can be used to carry out the method are illustrated with the aid of the drawing, the figures of which show:

• Figure 1 shows schematically an embodiment of the device in side view;
• FIG. 2 shows a section AA according to FIG. 1.

In the two figures, a so-called vibrotrog 1 is shown as the main part of a device suitable for carrying out the method, which in practice is a partially closed channel which is set into vibrations with a small amplitude with the aid of a vibrating motor (not shown). For example, the Vibrotrog is 3 m long and 65 cm in diameter. The oscillation amplitude is, for example, between 1 and 5 mm, and the frequency can be, for example, 16-30 Hz. However, these dimensions are not to be understood as restrictive, but are merely intended to indicate that it is an elongated, channel-like structure with certain vibration properties. Deviating from this embodiment, an annular (toroidal) work container or one that has more square dimensions can also be used.

A funnel 3 is placed on the vibrotrog 1 on its input side 2, through which workpieces 4 and / or an initial loading of an abrasive bed 5 can be entered. The blasting media known from surface blasting technology, such as steel or aluminum shot, are used as the blasting media. Also suitable for plastic parts are walnut granules or plastic beads made of hard plastics, for example PVC, with the specified grain size. The average diameter of these blasting media known per se is between 0.3 and 2.5, also up to 3 mm, although this information should also not be understood as restricting. The size and selection of the blasting media depends on the size of the vibrotrog, the workpieces and the other units used to carry out the process. However, parts that burst when they hit, such as glass beads, are not suitable.

At the end 6 of the vibrating trough 1, a workpiece removal is attached, for example a lifting mechanism equipped with a rake (not shown). The blasting agent is drawn off downwards via a mussel slide 7 and brought into the area of a bucket elevator 9 with a transport screw 8, with which it can be conveyed upwards. The blasting agent then passes - possibly interrupted by a cleaning step - via a chute 10 into a storage container 11, from which it is metered into a centrifugal blasting unit 14 with the aid of a further mussel pusher 12. The blasting unit 14 consists of a drive turbine 15 and a downward-blasting centrifugal wheel 16 which directs a centrifugal jet 17 through an opening 18 which is cut into a cover of the vibrotrog 1. The centrifugal jet 17 strikes the surface of the contents of the working container with great energy or large individual impulses of the particles.

The workpieces lying on the surface of the blasting agent bed 5 are first blown free by a thin blasting agent layer and then blasted directly on their exposed side. The beam no longer comes into contact with the wall of the vibrotrog itself. In addition, it is practically avoided that the workpieces collide with one another inside the working container during “swimming”, causing great noise and damaging one another.

A balanced relationship between the volumes of treatment agent and workpieces largely prevents the workpieces from bumping into and damaging one another. Nevertheless, the workpiece reaches the surface by vibration - with the exposed side always changing - so that the surface treatment is guaranteed. These advantages compensate for the possible disadvantage that not all of the beam energy is directed at the workpieces, but rather a part is lost due to the impact on the treatment agent adjacent to the workpiece. It turns out, however, that by choosing the bedding material and the grain size, the workpieces can receive an increased tendency to "swim" more on the surface of the bedding, so that they can be reached there more often. In addition, the workpieces are additionally surface-processed by slide grinding. However, the shortened working time prevents the workpieces from being too rounded at the edges, which is not desirable in many cases.

The return and possible cleaning of the blasting media also enables continuous operation, since fresh, unused blasting media is fed in via the centrifugal wheel and the bedding is continuously cleaned.

The inside of the work container, i.e. H. the vibrotrog, is lined with wear-resistant plastic or rubber layers. This coating is protected from the direct impact of the abrasive by the bedding 5.

Instead of a single blasting unit 14, several can be attached over the length of the vibrotrog. It is also possible to make the vibrotrog or the blasting unit movable in the longitudinal direction, so that in each case a larger work surface can be worked on during a certain unit of time.

Further details of the method are explained using two exemplary embodiments:

example 1

Circular cast steel cover plates from 1.5 cm thick and 15 cm diameter should be deburred and descaled. They are made with steel shot, average diameter 0.5-1 mm, in volume ratio

Volume (bulk): Volume (workpieces) = 3: 1 in a vibrating trough vibrating at 23 Hz (amplitude 2 mm) and blasted from above with a centrifugal blasting unit (type Schlick) movable along the trough with the same steel shot. After about 10 minutes of work, the deburring and the removal of surface oxides was finished.

Example 2

Plastic fasteners for the construction industry in the form of rosettes with a diameter of 10 cm and a weight of 15 g each were in proportion

Volume (fill): Volume (workpieces) = 1: 1 inserted in walnut shell granulate with a denomination of 1-3 mm. The radiation treatment was carried out with the same granulate. With a vibration of 28 Hz and an amplitude of 1.5 mm, the parts were completely deburred after 7 minutes of treatment and slightly matted.

Claims (3)

1. A method for the surface treatment of workpieces by means of abrasive particles within a processing container being open at its upper side and being filled, at least partially, with a granular abrasive treating agent, which is maintained in constant vibration and circulation by pulses and wherein the workpieces are embedded and wherein the workpieces coming to lie at the surface of the filling of said processing container are blasted by means of a blasting agent stream, characterized in that the volume of said workpieces amounts to no more than 50 % of the filling present within said processing container, that said blasting agent constitutes at the same time the only treating agent ; and that the blasting agent comes into the bowl via the stream of a centrifugal blasting mechanism to which the blasting agent is led in a circuit after having left the processing container and having passed a cleaning device.

2. A method according to claim 1, characterized in that said blasting or treating agent has an average grain size of between 0.3 and 3 mm.

3. An apparatus for carrying out the method according to claims 1 or 2, wherein the processing container is a so-called vibro-bowl, characterized in that the stream is produced by means of a centrifugal blasting mechanism and that a blasting agent extraction station having a cleaning device connected subsequently thereto, is provided on said vibro-bowl.

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