WO2012052162A1

WO2012052162A1 - Process and apparatus for the surface treatment of an object

Info

Publication number: WO2012052162A1
Application number: PCT/EP2011/005235
Authority: WO
Inventors: Eduard Reisacher; Horst Buck
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2010-10-18
Filing date: 2011-10-18
Publication date: 2012-04-26
Also published as: EP2629927A1; DE102010048777A1; DE102010048777B4

Abstract

The invention relates to a process and an apparatus for the surface treatment of an object, in particular for blasting and/or shot peening, wherein at least one jet of blasting shot is produced, and the object is kept in a state of suspension by the at least one jet and the surface of the object is thereby treated by the at least one jet.

Description

Method and device for surface treatment of an object

The invention relates to a method and a device for surface treatment of an object, in particular for blasting and / or beam hardening, wherein at least one beam of blasting agent is generated, and the object is kept in a levitated state by the at least one beam, and the Surface of the object is treated by the at least one beam.

Blasting and blasting are well established methods of surface engineering. They include u.a. the shot peening and the shot peening process.

By blasting, it is possible to generate compressive residual stresses in a surface of an object in a targeted manner and thus the edge layer strength of the object be increased. The methods can be used for workpieces of all solid materials, in particular for metallic and brittle-hard materials.

DE 196 52 872 A1, for example, discloses a method for increasing the surface layer strength on surfaces of workpieces made of brittle-hard materials, wherein the workpiece surface is brought into contact with a tool in a narrowly limited surface area, which plastically deforms the surface area and thereby within the Workpiece generated near-surface residual compressive stresses.

DE 10 2006 046 263 describes a method for increasing the fracture toughness of the surface layer of a carbide cutting edge of a drill by means of a shot peening method, wherein the shot peening beam is directed at least over a partial region of the cemented carbide cutting edge.

It is desirable in blasting processes to achieve as even as possible a degree of coverage of the surface, that is, to expose the surface as uniformly as possible to the blasting treatment. In prior art methods, mechanical support is always needed to position the workpiece. If the workpiece is only partially treated, such a holder is not disturbing. A complete treatment of the workpiece is hereby difficult.

Object of the present invention is therefore to provide a method by which the surface of an object is completely and uniformly treatable. It is also the task to create an appropriate specify the method by which the procedure is feasible.

This object is achieved by the method for surface treatment of an object according to claim 1 and the device for surface treatment of an object according to claim 12. The respective dependent claims indicate advantageous developments of the method and apparatus according to the invention.

According to the invention it has been recognized that a particularly uniform and complete treatment of a surface of an object is possible if it can be dispensed with a holder for holding the object.

In the method according to the invention for the surface treatment of an object, therefore, at least one beam of a blasting medium is produced and the object whose

Surface to be treated, held by the at least one beam in a limbo. The surface of the object is treated by the at least one beam. The method according to the invention can thus be regarded as a blasting method and in particular embodied as a beam hardening method. The fact that the object is kept in a floating state, can be dispensed with a holder for the object.

According to the invention, use is made of the fact that the beam exerts a force on the object. By means of this force, the effect of the weight of the object is compensated so that the object is held in a floating state, ie a state in which the Fallbe ^¬ motion of the object due to the weight force by the force effect of the at least one beam is compensated. Advantageously, the object in this state is not in contact with fixed devices, such as holding devices or guiding devices. However, it is possible that the object is guided in at least one degree of freedom also by contact with a guide device, such as a rail or spiral. In a preferred embodiment, the object floats in a jet of blasting agent, which is directed We ^¬ sentlichen vertically upwards, that is the direction against gravity. The object is preferably substantially spherical or round in this embodiment. Preferably, the

Beam here a divergent course, its cross section perpendicular to the direction of movement of the blasting medium in the beam center is thus greater with increasing distance from the jet generating nozzle. Preferably, the cross-section is in this case circular or elliptical We ^¬ sentlichen, so that the beam is cone-shaped.

The object can float freely in the conical beam. By aerodynamic effects on the

Object is the position of the object near the cone axis, that is stabilized near the center of the cone. The object can be introduced into the vertical beam by placing it directly on a nozzle emitting the jet before turning on the beam, and then turning on the beam. As the pressure increases, the ball is lifted with increasing jet flow so that it finally floats freely on the exiting abrasive. The to radiating object can also be introduced directly into the existing beam, for example via a mechanical feed, such as a roller rail or a robot arm.

In all embodiments of the present invention, the distance of the ball from the exit nozzle or nozzles may be adjusted by appropriate choice of the jet stream pressure, carrier stream flow, and / or appropriate choice of nozzle geometry.

Different jet conditions can be achieved by adjusting the nozzle geometry, the pressure, the grit transported through the jet, and the distance between the nozzle (s) and the object.

The beam used in the invention preferably comprises a blasting agent that is transported by a carrier ^¬ medium. The carrier medium advantageously gas or liquid in question. In this case, gases can be, for example, air, nitrogen or other gases adapted to the corresponding use. As a liquid, for example, water comes into question. Blasting agents may include metal beads, sand, ceramic materials such as zirconia, glass, hard metal and / or nutshells (preferably for cleaning jets). As already described, is the object to be treated whose upper ^¬ surface, preferably spherical or a sphere. In this case, the object can be kept particularly stable in the beam, in particular if only one beam is used which, as described above, is directed essentially vertically upwards. For example, the sphere may be a zirconia Be ball bearing ball.

In an advantageous embodiment of the method according to the invention, as described, a jet of the blasting medium can be generated, which is directed essentially vertically upwards and in which the object is introduced. In this case, in addition, at least one stream of the carrier medium and / or one jet of the blasting medium can be generated, by which the object is stabilized in the vertical jet and / or moved in a targeted manner. Those nozzles which generate the additional streams of the carrier medium or additional jets of the blast medium preferably emit the object from other directions than from below, so that they exert lateral forces on the object

Exercise object.

By slight asymmetries in the particle stream or by asymmetries in the surface of the radiating object such as a ball, alternating torques to the floating object exerted by Aerody ^¬ namic effects that change to time ^¬ lead to the rotations of the object. With a sufficiently long beam time, this results in an isotropic distribution of the axes of rotation, so that the surface of the object is uniformly irradiated. By suitable design of the nozzle generating the jet, such asymmetries in the particle flow can also be deliberately provided, but in general the effect also results in rotationally symmetrical nozzles and rotationally symmetric beams.

As a result of the continuous addition of a blasting medium into the flow of the carrier medium, as is the case with the customary pressure blast method, the desired effect of the surface treatment, for example the Effect of shot peening or solidification blasting, the suspended object achieved. The self-stabilizing effect of the jet on the position of the ball is not impaired by the addition of a suitable amount of blasting agent.

A particularly homogeneous treatment of the surface of the object results according to the invention in that surface areas which were already influenced by the blasting material during the blasting process and thus were roughened somewhat more usually compared to not yet or not completely treated surface areas, a slightly increased friction in the stream Experienced. As a result of the resulting asymmetrical torques on the object, it is aligned with the beam direction in such a way that surface areas which were previously unirradiated are preferably aligned downward, opposite the stream of jet material. As a result, a uniform beam and thus even coverage of the entire object surface is achieved virtually automatically. This effect, in turn, is particularly advantageous in the case of spherical objects which float in a beam pointing vertically upwards.

The inventive method is particularly advantageous designed as a pressure jet method with air. But it can also be used or configured as a pressurized liquid jets or cleaning jets.

The method can be advantageously controlled by the pressure of the carrier medium flow, the choice of the nozzle and the choice of the blasting medium.

By controlling the pressure, the velocity of the carrier stream and the entrained jet stream Wells set. This can be done for example by a pressure reducer.

Due to the design of the nozzle (diameter, length of the nozzle tube), the shape of the beam cone can be controlled.

The amount of blast media per time can be controlled by the size of the outlet opening of the blasting medium reservoir. The total amount of blasting agent per treatment is preferably adjusted by an appropriate stocking.

It is also possible dynamic control of the off ^¬ outlet opening by an electrical and / or pneumatic setting of the outlet opening.

For the simultaneous blasting of many objects, preferably the number of objects corresponding to a large number of outlet nozzles are arranged in a grid on a horizontal plane in accordance with the method described above in such a way that a gas flow pad with a correspondingly large number of locally self-stabilizing beam positions is produced for many balls.

In a further advantageous embodiment, a guide device may be provided by means of which the object or objects in the beam are durable, but in particular allows a free rotation of the object. Such a guide device may, for example, be a spiral whose spiral axis coincides with an outflow seal of the blasting medium. The object can move in the direction of the beam direction inside this spiral and can rotate freely, but is limited in its movement to the interior of the spiral. This can be beneficial Spiral at its end remote from the nozzle have a conclusion, for example in the form of a portion of the spiral forming wire, which is bent over the opening of the spiral at the nozzle end remote. Advantageously, the spiral can be attached to the nozzle.

The use of the method according to the invention can be detected, for example, by means of X-ray-induced residual stress analyzes, which can detect the presence of high residual stresses in the surface of objects, as typically produced by shot peening. By means of light or electron microscopic analyzes, the impacts of the particles of the blasting agent on the surface of the object can be detected.

The method according to the invention can be used particularly advantageously for ball bearings, in particular when using balls as blasting media, in order to increase their service life and load capacity. The OF INVENTION ^¬ dung modern method is also well for uniform cleaning and / or polishing of objects, more preferably balls, of all solid materials once set zbar.

The invention also provides an apparatus for surface treatment of an object, which has at least one nozzle, with which at least one jet of a blasting medium can be generated such that the object to be treated is held in a floating state by the at least one blast and there ^¬ at the surface of the Object is treated by the at least one beam. Particularly preferably, the method described above can be carried out with the device. The method according to the invention makes it possible to treat workpieces, particularly preferably spherical workpieces, uniformly over the entire surface and, in particular, to realize the advantages of shot blasting methods.

In the following, the method according to the invention will be explained by way of example with reference to a figure.

It shows

Figure 1 shows a device according to the invention, with which the inventive method is feasible, and

2 shows a nozzle with an attached spiral for guiding the object to be treated in the beam.

The figure shows the basic structure of a pre ^¬ direction, with which the inventive method is feasible. In this case, the surface of an object 1, which is spherical in the example shown, treated by means of a blasting agent jet 2, which is emitted through an outlet nozzle 3. The outlet nozzle 3 has here a circular From ^¬ trittsoffnung, whereby the blasting abrasive jet 2 is cone-shaped. The ball 1 floats in the beam 2, since this exerts a force on the ball 1 by the flow resistance of the ball 1 in the beam 2, which is directed against the weight of the ball 1 opposite. By aerodynamic effects, the ball 1 is stabilized near the cone axis of the beam 2. The beam 2 is formed here as a single beam, which is substantially perpendicular to the top is directed. It can be provided to further stabilize the object 1 and other nozzles, the streams of the carrier medium or rays of the

Generate abrasive that can exert lateral forces on the object 1 and this further stabilize or move specifically.

It is also possible for a plurality of outlet nozzles 3, such as those shown here to be arranged next to one another, preferably in such a way that their outlet openings lie in one plane. In this case, these nozzles 3 may preferably be arranged in an equidistant grid. In this way, a surface, as a pad of the blasting agent, can be produced, on which the object can be moved in the horizontal direction.

In the example shown, the ball 1 can be introduced directly into the existing jet 2 or placed on the nozzle 3 before switching on the jet 2 and then raised by switching on the jet 2. In the example shown, object 1 floats freely. But it is also possible to provide Vorrich ^¬ obligations that guide the object. However, this pre ^¬ directions should not festhal ^¬ th the object, so that each area of the surface of the Ob ^¬ jektes 1 in the sphere of influence of the beam 2 bewe ^¬ gen can and will treated by it.

The jet 2 is in the case shown an air flow with a blasting agent such as beads or sand.

To generate the jet, the device has a supply line for compressed air 4 as a carrier medium and a device for supplying the blasting medium 5. The blasting medium is introduced into the compressed air. brought, so that a beam of the blasting medium 2 is formed.

In an exemplary implementation of the method according to the invention, a jet nozzle 3 was used whose opening had a diameter of 8 mm. In this case, air was used as the carrier medium, which was fed to the nozzle at a pressure of 2 bar. As a blasting agent here 4 kg of hard metal balls with a diameter of 0.65 mm (HMG0.65) were used, as are commercially available. A spherical object, here a ball bearing ball made of steel with a diameter of 15 mm, was irradiated for 20 minutes. In this case, a distance between the nozzle 2 and the object 1 of 10 cm was set.

The treated sphere was then characterized by X-ray residual stress analysis. The detector used was a scintillation counter and a D5000 diffractometer. The use ^¬ te radiation was Cr-Κ and the elasticity constants E-modulus and Poisson's ratio (Poissonkonstante) were used 210 MPa and 0.28.

Although the exact radiographic constants (modulus of elasticity and transverse number) can be determined metrologically. Usually, however, the macroscopic elasticity constants are used from the data sheets of the material manufacturers. The difference is usually small, especially in the present case of the steel material used.

The residual stress analysis was carried out as described, for example, in Hauck, V.: "Structural and Residual Stress Analysis by Non-destructive Methods", Elsevier (1997), p. 344 et seq., P. 596 et seq., P. 605 et seq., And Spieß, L ., Teichert, G .: "Modern X-ray diffraction", Vieweg + Teubner, GWV Fachverlage GmbH (2009), 2nd edition, Chapter 10. The following results were obtained: For a non-irradiated polished comparison ball at a measuring point 1 in 0 ° - For a compressive residual stress of -633 MPa ± 37 MPa, a compressive residual stress of -1542 MPa ± 72 MPa was obtained at a measuring point 1 in the 0 ° direction for a sphere irradiated by the method according to the invention as described above ° direction resulted in a

Residual compressive stress of -1680 MPa ± 79 MPa, at the measuring ^¬ point 2 in 45 ° direction, a compressive stress of -1493 MPa ± 68 MPa and at measuring point 2, a compressive stress of -1508 MPa resulted in 90 ° direction ± 83 MPa.

By irradiation by means of the method according to the invention, therefore, a significant increase in the intrinsic pressure was achieved by about 920 MPa to an average of -1555 MPa.

Within the scope of measuring accuracy, the height of the compressive residual stress generated at the different measuring points, ie at measuring point 1 and measuring point 2, and also in different directions at a measuring point is the same. So it was a plane isotropic Druckei- genspannungszustand at every point of the surface, it aims ^¬.

FIG. 2 shows an example of a nozzle 3 with a guide device 6 or stabilizing device 6 for the ball 1 which floats in the air flow. The stabilizing device 6 is in this case designed as a spiral which is wound around an outlet direction of the jet out of the nozzle 3. At its end facing away from the nozzle 3, the stabilizing device 6 has a conclusion 7, which closes the opening of the spiral 6 facing away from the nozzle 3, so that the ball can not be pushed out of the stabilizing device 6 by the jet. The stabilizing device 6 thus prevents the ball 1 from escaping laterally or upwards from the air flow during a momentarily excessive deflection. The rotation of the ball is not hindered by the device, however, so that nevertheless a uniform machining of the spherical surface, ie, especially in the shot peening process, a uniform degree of coverage can be achieved. For other ball diameter or another jet printing, the device can be adjusted accordingly ^¬ speaking.

Claims

claims

Process for the surface treatment of at least one object,

wherein at least one beam of a blasting medium is generated,

and the object is held in a floating state by the at least one beam, and the surface of the object is treated by the at least one beam.

Method according to the preceding claim, characterized in that exactly one jet of the blasting medium is generated, which is directed vertically in the vertical plane, and the object is held in limbo by the one jet.

Method according to one of the preceding claims,

characterized in that the object is spherical or is a sphere.

Method according to one of the preceding claims,

characterized in that the at least one jet is conical, wherein preferably the conical jet is directed vertically upwards.

Method according to one of the preceding claims,

characterized in that the object is introduced into the beam by the object at switched off beam is placed on a jet-generating nozzle and then the beam is turned on.

Method according to one of the preceding claims,

characterized in that the object is introduced into the existing beam, preferably by means of a mechanical feeding device.

Method according to one of the preceding claims, wherein the at least one object is guided by a guide device in the beam, which limits the movement of the object to a cylindrical area about a beam axis, wherein preferably the guide device is a spiral wound around the beam axis.

Method according to one of the preceding claims,

characterized in that the jet has at least one gas, air or liquid as a carrier medium, which transports the blasting agent.

Method according to one of the preceding claims,

characterized in that a jet of the blasting agent is generated, which is directed substantially vertically upwards and in addition at least one stream of the carrier medium and / or a jet of the blasting agent for stabilizing the object is generated substantially vertically upwardly directed beam. Method according to one of the preceding claims,

characterized in that a plurality of beams of the blasting agent is generated, wherein the beams are generated in a grid, preferably with mutually parallel beam directions, so that the at least one object above the, preferably total, spanned by the grid surface in suspension is and will be treated.

Method according to the preceding claim, characterized in that the object is moved over the surface spanned by the grid and is held continuously in suspension.

Device for surface treatment of an object with

at least one nozzle, with which at least one jet of a blasting medium can be generated in such a way that the object to be treated is kept in a floating state by the at least one blast, and the surface of the object is treated by the at least one blast.

Device according to the preceding claim, characterized in that with the device, a method according to one of claims 1 to 11 is feasible.