Method for shot peening a pipe inner wall of a curved workpiece having a workpiece bore, and blasting nozzle unit and blasting chamber system therefor

For the shot peening of a pipe inner wall of a curved workpiece (200) having a workpiece bore (201), use is made of a flexible blasting abrasive feed hose (10) having blasting nozzle head (20). The latter is guided through a supporting element (30) which is applied to one workpiece end (203). The blasting abrasive feed hose (10) together with the blasting nozzle head (20) is introduced into the workpiece bore (201) and advanced along a blasting treatment section therein, and subsequently retracted into the supporting element (30) again. The blasting abrasive is emitted during the advancing movement and/or during the retraction movement. A blasting nozzle unit (100) suitable for carrying out the method comprises a flexible blasting abrasive feed hose (10) and a blasting nozzle head (20) connected to the blasting abrasive feed hose (10). The blasting nozzle head (20) has a plurality of nozzle openings (21) distributed around the circumference. The outer circumference of the blasting nozzle head (21) is smaller than the inside diameter of the workpiece bore (201) in a workpiece (200) to be processed. The blasting abrasive feed hose (10) is guided in a supporting element (30) and this element (30) is guided in a displaceable manner in a stationary bearing element (40).

BACKGROUND OF THE INVENTION

The invention relates to a method for shot-peening an inner pipe wall of a curved workpiece with a workpiece borehole for carrying out the method.

By selecting pipes in place of solid bars, mass can be saved in dynamically accelerated systems. The hardening of the surfaces by means of shot-peening results in a significant increase in the carrying capacity compared to untreated pipes, in particular in case of vibration stress. The impact of the blast particles, which are especially small spherical elements, leads to the hardening of the surfaces and to a reduction in the susceptibility to stress cracking.

A method for shot blasting of pipes, and a blasting nozzle unit therefor, are known from the DE 35 27 923 A1. This treatment method has proven itself in principle. However, it is problematic that the blasting nozzle head sends out the blasting agent in one direction only. It must, therefore, constantly be rotated to achieve a uniform hardening of the surface around the inner circumference. The feed must be coordinated with the rotation to properly blast the entire surface.

Known from DE 199 22 265 B4 is another blasting nozzle that can rotate around its longitudinal axis. It is guided through a cover which covers the clear annular gap between the blasting nozzle and a pipe with a correspondingly larger diameter.

Certain workpieces have curves, as, for example, stabilizer pipes for the chassis of road and rail vehicles, or aircraft. A three-dimensional curved progression of the pipe is often necessary to bypass adjacent components and to be able to place the pipe at all in tight spaces.

In the shot-peening treatment of pipes that already have a small pipe diameter, i.e., of a maximum of 1 inch, and that include even stronger curvatures which extend over an arc of more than about 10°-20° and/or for which the radius of curvature is relatively small, especially less than ten times the inner pipe diameter, it is difficult to effect a uniform treatment of the entire inner surface. The orientation of the nozzle opening when blasting can no longer be tracked securely from the outside, because, for example, the blasting agent feed hose that has the blasting nozzle arranged at its end, is twisted. It is thus possible that the nozzle blasts only linearly into a limited circumferential area.

If the known blasting nozzle unit is inserted in such an area of curvature with narrow pipe boreholes, there is the additional risk that it gets stuck there and acts only at one point. The nozzle unit may even no longer be pushed through the entire range of curvatures.

JP 2012-179 696 A discloses a blasting nozzle with a flexible hose positioned in front of the nozzle with the nozzle openings, when viewed in the feed direction of the blasting agent.

Known according to DE 10 201 1 005 762 A1 is a blasting chamber with two doors that serve alternatively to close the chamber. Devices for receiving workpieces are provided at the inner door.

SUMMARY OF THE INVENTION

The problem addressed by the present invention is therefore to improve a method and a blasting nozzle unit of the aforementioned kind such that curved regions of a pipe with small diameters can be blasted uniformly with blasting particles from the inside.

This objective, as well as other objectives which will become apparent from the discussion that follows, are achieved, according to the present invention, by a method and apparatus in which:a) at least one end region of the blasting agent supply hose adjacent to the blasting nozzle head is guided through a support element;b) the support element and the workpiece end are placed in contact with each other;c) the blasting agent supply hose with the blasting nozzle head is inserted into the workpiece borehole and pushed forward along a blasting treatment path inside the workpiece borehole and thereafter is again retracted into the support element, whereby the blasting agent is released through the nozzle openings during the forward movement and/or during the retraction movement; andd) the support element is retracted from the workpiece end or the workpiece end is retracted from the support element.
According to the invention, the blasting agent supply hose at its end that faces away from the blasting nozzle head is connected to a rigid blasting agent supply pipe. The unit comprising the blasting agent supply hose and blasting agent supply pipe is then guided slidably inside the support element.

The blasting nozzle head is guided in the workpiece by a borehole or by an otherwise shaped channel located on the inside. It does not have to have a circular shape. The internal diameter of the inner circle is relatively small such that it cannot be treated by shot-peening using conventional methods and devices. On the other hand, it is large enough to receive a small blasting head. In addition, a certain air gap width must be present between the blasting head and the inner wall such that the blasting agent can exit and be directed at a sufficiently high speed onto the wall to achieve the desired hardening effect. According to the invention, a shot-peening treatment is made possible with an inside diameter of the workpiece borehole of one inch (approx. 25 mm) and less. With the method according to the invention, the smallest inside diameter to be treated is around 12 mm to 16 mm.

To counter the risk of jamming, a relatively short blasting nozzle head is intended to be used in order to overcome even narrow curve radii. For an inner diameter of a pipe bend of 16 mm, for example, a blasting nozzle head with a length of only about 12 mm is provided.

Although a hydraulic, pneumatic or motorized drive for the support element is possible, it is advantageous to provide a feeder unit between the support element and the bearing element that is simply formed by a spring, in particular a compression spring. The workpiece is then guided to the end of the support element and moves the same slightly back in relation to the bearing element. This also tensions the spring and creates a constant pressing force. After removing the workpiece, the spring pushes the support tube back into the original position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will now be described with reference toFIGS. 1-5of the drawings. Identical elements in the various figures are designated with the same reference numerals.

FIG. 1shows on the right side a workpiece200such as a stabilizer element of a motor vehicle chassis, for example, in the region of a curvature202. It has at least one inner borehole201. Presented next to it inFIG. 1is a blasting nozzle unit100in sectional view comprising the following essential assemblies:

A flexible blasting agent supply hose10with a blasting nozzle head20:

A support element30in which the blasting agent supply hose10is guided;

A stationary bearing element40, in which the support element30is guided slideably;

A feed unit for placing the support element30onto the end203of the workpiece200to be treated as well as

A traveling unit50to move the blasting agent supply hose10and the blasting nozzle head20relative to the workpiece200to be treated.

In the presented embodiment, the blasting agent supply hose10is connected toward the rear to a fixed blasting agent supply pipe12. This pipe, in turn, ends in a clamping device in the traveling unit50and ends there with a suitable attachment component13, to which a conventional blasting agent supply hose can be connected. The unit consisting of the blasting agent supply hose10and the blasting agent supply pipe12is supported movably inside the pipe-shaped support element30.

The position inFIG. 1corresponds to the operating position in which shot-peening is carried out on the inner wall of the pipe borehole201of the workpiece200by accelerating a suitable blasting agent, such as in particular small steel balls, via compressed air and exiting from the blasting nozzle head20to the side.

The support element30together with the flexible blasting agent supply hose10supported therein is moved toward the mouth of the workpiece200via a traveling unit. A funnel-shaped centering element31is provided to a secure and precise solid contact of the support element30to the end of the workpiece and to hold it during blasting.

The support element30, in turn, is supported by a bearing element40, which in the presented exemplary embodiment is also pipe-shaped. The bearing element40can be attached to a work chamber wall300such that the workpiece200can be treated shielded within the work chamber and exiting blasting agent can be caught. The end of the bearing element40protruding into the work chamber has a bellows43for sealing the gap between the support element30and the bearing element40.

The assemblies20,30,40that are slideably guided in each other have different fixed stops34,35,45, through which the travel paths that are possible in relation to each other are restricted. The fixed stop35at the end of the support element30is designed as an overhanging set-off at the support element30such that the support element30can be moved only in relation to the bearing element40until the fixed stop35rests on the bearing element40.

FIG. 3shows the blasting nozzle head100) according to the invention and the workpiece200in the same position as inFIG. 1in an enlarged presentation.

The bearing element40surrounds the other elements and has the bellows43for shielding at its side that faces the workpiece200.

The support element30is supported movably therein. Slide bearing elements46,47are provided in the annular gap between the bearing element40and the support element30acting at the same time as a slide bearing and as a seal. The slide bearing element46shown left inFIG. 2is defined by a washer screwed in at the end side in the bearing element40. The other bearing element36is defined by a retaining ring at the outer circumference of the support element30. At the same time, the bearing element36forms a fixed stop for a spring element44, which in turn is defined by a fixed stop45at the inner circumference of the bearing element40. The bearing element36, the compressed spring element44and the fixed stop45prevent the support element30from being pulled out to the left from the bearing element40.

In particular the elements mentioned last serve, however, as a feed unit to bring the support pipe30into a solid contact with the workpiece end203using the uncompressed spring element44that is designed as a compression spring and to hold it there while the blasting process runs. Thus no driven actuator is provided for the presented exemplary embodiment of the blasting nozzle unit100to carry out the relative movement between the bearing element40and the support element30. Rather, the workpiece is moved toward the support element30via the spring element44as soon as the traveling unit50no longer exerts a retracting force. The support element30centers itself autonomously at its end using the centering element31.

The path of the workpiece end prior to the start of the blasting treatment can be selected such that the workpiece200pushes the support element30slightly back relative to the bearing element40by a compression of the spring element44. Due to the spring force, a largely constant pressing force can be maintained during the subsequent blasting process without any additional drive. After retracting the workpiece, the spring element44rebounds entirely and brings the support element40to its original position.

The outer circumference of the blasting nozzle head12is positioned at a distance from the inner wall of the workpiece. Thus, the outer circumference is smaller than the inner circumference of the workpiece borehole201in the workpiece200to be treated, namely so much smaller that an air gap remains in-between, which allows the support element15to be moved back and forth without the same being jammed inside the workpiece borehole201.

Essential to the invention is that the blasting agent supply hose10with the blasting head has a small diameter such that it can be guided inside the workpiece borehole201without jamming and that it is guided by the support element at the beginning of blasting and then increasingly by the workpiece itself. The length of the blasting agent supply hose10is only selected such that it can be advanced to the end of the workpiece borehole201, and shown inFIGS. 1 and 3. This effectively prevents buckling of the blasting agent supply hose10.

The other regions of the length of the blasting agent supply are formed by the rigid blasting agent supply pipe12, which is also guided in the support element30and protrudes freely from the end of the same. For centered guiding inside the support element30, the support tube12has at least one annular centering element13, which can also form a fixed stop element at the same time, which rests at the end of the intended retraction path on a fixed stop element34on the inside of the support element30.

Regarding the centering element31at the support element30,FIG. 3shows that the same is designed such that the workpiece end203is located at the end of the funnel-shaped section in an indentation with a form and size that corresponds exactly to the outer circumference of the workpiece end203. At the same time, the workpiece borehole transitions flush into the borehole in the centering element30, wherein flush in the sense of the invention refers not only to the smooth transition at the same inner diameters but also a continuous, offset-free transition with conical transitions. The purpose is to avoid jumps in diameters, where the blasting nozzle head could be caught especially during the retraction movement.

The method for shot-peening an inner pipe wall of a curved workpiece200with a workpiece borehole201is explained below based on the figures.

FIG. 4shows parts of a work chamber system300with a work chamber310having a work chamber opening313. An operating panel can be seen as well. For the purpose of clarity, not shown are known assemblies for supplying the blasting agent to the blasting nozzle unit as well as for extracting the blasting agent and the dust from the work chamber and for preparing the blasting agent for renewed introduction of the blasting agent into a closed circuit.

Pivoting doors311,312are placed on both sides of the work chamber opening313, wherein the work chamber opening is not closed jointly by the doors311,312, but alternately by the one or the other door311,312. Workpiece holders are placed on the inside of the door.

In a loading position, one workpiece each is placed therein. A blasting nozzle unit100is arranged inside the work chamber310and provides a common bearing element40for four support elements30with blasting agent supply hose10and blasting nozzle head20. The ends of the support elements30point in the direction of the work chamber opening313. The blasting agent supply hoses10are retracted as far relative to the support element30as shown inFIG. 2. In this situation, the blasting nozzle head20is located fully inside the support element30. This is achieved through the movement of the travel unit50.

Now the centering funnel is entirely free. As indicated by the block arrow on the right inFIG. 2, the workpiece end203is now moved toward the centering funnel31. This occurs in the final phase of closing one of the doors311,312at the work chamber310.

The left door311is fully closed inFIG. 5. The right door, on the other hand, is free and can be populated in its workpiece holder. The position of the workpiece ends203relative to the blasting nozzle unit100in the inside of the work chamber is now shown inFIGS. 1 and 3: The workpiece end203rests in contact with the centering funnel element31at the support element30. The support element30is pushed back relative to the bearing element40, which can be seen in particular by the different positions of the collar35inFIG. 1versus the previous position according toFIG. 2. The spring element44is slightly compressed.

The actual treatment process can now begin. To this end, the travel unit50is moved toward the bearing element40and the support element30. The blasting agent supply pipe12connected therewith pushes the blasting agent supply hose10and the blasting nozzle head20forward. As soon as the workpiece end203is reached, the blasting agent is introduced and the treatment starts.

Blasting is initiated by conveying a blasting agent through the blasting agent supply hose10to the blasting nozzle head12using compressed air. Large amounts of the blasting agent are accelerated and impact the inner pipe wall. For example, air pressure of 5 to 6 bar is used to achieve a blasting agent flow of about 1 kg/min.

The blasting agent supply pipe12and the blasting agent supply hose10are then pushed further forward at a constant speed via the travel unit50until the blasting nozzle head20has reached the end position shown respectively inFIGS. 1 and 3at the other end of the workpiece200. Then starts the retraction of the blasting nozzle head20. At this time, blasting agent can continue to be blasted to enhance the treatment effect.

The blasting agent supply is interrupted as soon as the blasting nozzle head20has returned to the workpiece end203, and the blasting nozzle head20is retracted as far as shown inFIG. 2. By opening the door311, the workpiece200moves away from the support pipe30, which is returned to its original position through the spring44.

By closing the other, right door312, at which in the meantime new workpieces have been affixed, the described process can be repeated right away, while now the already treated workpieces can be removed from the open door.

There has thus been shown and described a novel method for shot peening a pipe inner wall of a curved workpiece having a workpiece bore, and a blasting nozzle unit and a blasting chamber system therefor, which fulfill all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.