EP2279279B1 - Method for preparing a surface for applying a thermally sprayed layer - Google Patents

Description

The invention relates to a method for preparing a surface on a workpiece made of metal for applying a thermally sprayed layer according to the preamble of claim 1, a hammer or impact brush for performing the method and a workpiece produced by this method.

Surfaces on workpieces made of metal for a coating by thermal spraying must be prepared accordingly. This can be done by roughening the surface. For this purpose, various methods are used industrially, such as sandblasting, high-pressure water jets, brushing, milling and similar machining processes. However, there are problems associated with these processing methods. Thus, chips and debris from the machining processes may remain in grooves and grooves on the machined surfaces and cause problems when they are covered and trapped by the coating and this layer has subsequently been honed. The grooves and grooves created by mechanical roughening have a depth of about 100 μm. This area is flat and smooth, so that the thermally sprayed layer can not adhere well at these locations.

In cases where a motor needs to be repaired during service by thermal spraying, it is necessary to machine an internal wear zone within the cylinder bore, leaving above and below this zone an area with the original smooth surface structure, for example honed , When such a cylinder bore is repaired by thermal spraying, the coating can not adhere to the honed surface. Especially for engine blocks made of aluminum alloy with cast-in cylinder liners is a repair by means of thermal spraying difficult because of the cylinder lip cross-aluminum lip and the intermediate region of the aluminum lip to be coated surface area at the cylinder liner. - Mechanical roughening leads to residual strain stresses which reduce the fatigue strength of the workpiece.

A known method is also the preparation of the surface by sandblasting with corundum particles and subsequent cleaning before the surface coating can be applied by means of thermal spraying. In addition to the comparatively complicated process step of surface cleaning, a significant disadvantage of sand blasting with corundum particles is, in particular, that the smallest corundum particles can penetrate into the surface to be coated and remain there despite intensive cleaning. Such jet particles can significantly affect the adhesive tensile strength of the coating on the previously cleaned surface after application of the surface coating.

In addition, particles of the blasting material can also adhere to surface areas of the workpiece to be coated, which are not coated and therefore have not previously been irradiated. Such blasting material particles can lead to significant problems when using the workpiece. This can for example be done on the cylinder surfaces of engines that have been processed in this form. Corundum particles that are left in or on the engine components can thus lead to significant problems and may cause a failure of the engine under certain circumstances.

To remedy this situation is out DE 198 40 117 A1 a method for machining the surface of the inside of hollow bodies in preparation for applying a thermally sprayed layer, wherein a part of the material forming the inside of the hollow body is removed and a surface having a defined structure and / or quality is produced. However, this known method has the disadvantage that no Surface profiles can be generated, which have a sawtooth effect and thus undercuts. However, since such surface structures allow decisive advantages in the adhesive tensile strength of the thermally applied coating, this represents a decisive disadvantage. In addition, no consistency in terms of surface values can be achieved by the machining process, since the machining tools are subject to a necessary wear and thus also to wear produce varying surface texture of the workpiece. In addition, the mechanical strength of the surface prepared by this method is adversely affected by chip removal.

In DE 27 12 863 A1 Furthermore, a striking tool for removing surfaces is described, which carries at one end a bunch of metallic Abtragsnadeln that oscillate in their longitudinal direction and can beat in rapid succession against a surface. Usually, such needle devices are used to remove rust or varnish from surfaces. But also in the cleaning of concrete components such needle devices are used.

The US 53633821 describes a method for preparing a surface on workpieces made of metal for the application of a thermally sprayed layer. The surface is roughened either by wire brushing or by rough mechanical processing to a certain surface roughness. However, only a few undercuts, which are necessary for the adhesive tensile strength of the thermally sprayed layer, result from this processing.

In the JP 2006 097045 A Another method for roughening a surface in preparation for a thermal coating is described. In a cylinder bore a plurality of longitudinal grooves are introduced in a first step by a round, multi-stage broach in the direction of the cylinder axis. In a second step, the tips of the longitudinal grooves are removed by a wire brush rotating parallel to the cylinder axis. This results in a surface having longitudinal grooves and between the longitudinal grooves in the circumferential direction of the cylinder brushed Umfangsriefenriefen. The brushed Umfangsriefen have a much lower roughness than the cleared longitudinal grooves. By this method, however, no undercuts in the surface, which are necessary for a good adhesion of the thermally sprayed layer.

DE 10 2006 004769 A1 discloses a method for preparing a previously mechanically roughened surface having sharp-edged ridges and depressions on metal workpieces for applying a thermally sprayed layer, wherein the ridge edges are fractured to improve adhesiveness of the subsequently applied thermally sprayed layer and / or to form undercuts be at least partially bent, characterized in that the sharp-edged ridges and depressions of the mechanically roughened surface resulting from machining are grooves.

It is an object of the present invention to overcome the above-described problems in preparing a surface on a metal workpiece for applying a thermally sprayed layer in a particular surface area.

This object is achieved with the features of claim 1. The combination of mechanical roughening and brushing leads in comparison to conventional brushing to a surface structure with properties that are very similar to a Sand or corundum or shot peening, so a bombardment with shot or other suitable blasting material is. The brush rotates in this process at a very high speed of about 3000 to 6000 revolutions per minute, whereby the impact wires transmit a high local energy to the surface of the workpiece. This leads to a plastic deformation and an increased roughness only in the machined surface area of the workpiece, wherein the sharp-edged ridges on the roughened surface to improve the adhesion of the subsequently applied thermally sprayed layer broken or at least partially bent to form undercuts. It also chips and residues from the machined surface areas are removed, which has a further improved adhesion and thus increased surface strength of the sprayed coating result.

This is especially the case when the sharp-edged ridges and depressions of the mechanically roughened surface are formed by mechanical processing grooves and impingement wires predominantly parallel to the grooves. The impact of a striking wire on the surface of a groove web formed between the grooves transmits kinetic energy, which results in plastic deformation of the surface of the groove land, whereby the material of the groove land flows into the area of at least one of the side grooves. This can also be considered as a localized curling of the groove web in the direction of the groove, whereby the undercut required for increasing the adhesion strength arises.

By the impact wires impinge parallel to the grooves, an advantageous shape of the undercuts is generated because the material of the groove webs thereby predominantly flows transversely to the grooves and thus a favorable shape of the undercuts is produced. As a predominantly parallel is to be understood here that the impact wires have a direction of movement which is predominantly parallel to the groove direction. This is z. As is the case when in a rotating brush, the axis of rotation of the brush is oriented predominantly parallel to the surface and predominantly transverse to the groove direction.

The grooves are formed as grooves in z. B. turning, drilling or milling the surface, z. B. in the mechanical machining of cylinder bores. Equivalently, the grooves can also be introduced by rolling or pressing. For the purposes of this application, all methods are suitable to produce the mechanically roughened surface having a corresponding groove structure in the Bring in the surface.

Advantageously, the grooves advantageously have a trapezoidal to rectangular cross section. In this cross-sectional shape, the necessary undercuts form very simple when the impact strikes striking in parallel deform the edges and ridges of the groove webs transversely to the groove direction. Especially with a rectangular cross-section only slight deformations of the groove web transverse to the groove direction are required to form the undercuts. When trapezoidal cross-section is advantageous that this is easy to produce, and still can be produced by the impact brushes, the necessary undercuts.

Advantageously, the impact wires have a diameter which is greater than the groove width. The groove width is the mean distance between the groove webs. In this case, the impact wires can never hit the bottom of the grooves, which would theoretically be possible in the parallel brushing, but will always impinge on at least one groove web to produce the undercut there.

The impact wires may also have a diameter which corresponds at least once to the groove spacing, preferably two to three times the groove spacing. Such impact wires will definitely hit a groove web, but can also hit two grooved webs. Due to the relatively large diameter relative to the groove spacing, a wide undercut is formed, since a large area of a groove web is plastically deformed. The groove distance is to be understood as the distance from the center of the groove to the middle of the groove or from the center of the groove center to the groove bridge center.

Advantageously, the ratio of groove depth to groove width is between 0.2 and 1, preferably between 0.5 and 0.7. The groove depth is understood to mean the average distance from the surface of the groove web to the bottom of the groove. The grooves can easily be introduced into the surface at these proportions and yet have enough depth to effect a sufficient clamping of the sprayed layer to be applied with the undercuts produced. Too deep grooves could not be filled by the spray material, with too shallow grooves, the undercuts would be ineffective, since the spray material would not get behind it.

Advantageously, the ratio of groove spacing to groove width is between 1.2 and 4, preferably between 1.8 and 2.2. The groove spacing is the average groove width plus the average width of the groove webs. Thus, groove lands and the grooves have similar widths. The widths can then be chosen so that on the one hand a good filling of the grooves is granted with the spray material, on the other hand, the width of the groove web is sufficient to firmly bind the sprayed layer to the base material.

Advantageously, the groove spacing is between 0.1 mm and 1 mm, preferably between 0.15 mm and 0.25 mm. The resulting grooves and grooved ridges are easy to manufacture, can be formed with the impact wires favorable for the undercuts, can be filled well with the spray material and have sufficient strength to hold the sprayed layer.

The combined hammer-brushing process also produces residual compressive stresses in the machined surface areas, increasing the fatigue strength of the various components. To improve the quality of workmanship and fatigue strength, the hammer or impact brush impact or torsion springs are provided with diffusion hard chromium plating containing about 53% chromium in the surface of the wires, corresponding to a Vickers hardness HV of about 1800, so that the life of the brush is so great as possible, and to avoid any contamination of steel with aluminum beams, which could otherwise lead to galvanic corrosion problems.

It is also particularly advantageous if the surface treatment, in particular in the repair of engine blocks, takes place only in the area of the worn cylinder running surfaces and the honed cylinder surfaces still present above and / or below remain unprocessed. This avoids adhesion problems for the coating which would otherwise be too thin Coating in the honed surface areas can often occur. By means of the inventive method, the areas to be coated can be processed very well without damaging or roughening the adjacent honed cylinder surface.

Thus, a thermally sprayed layer can be applied only in the area of the worn cylinder surface, which adheres very well to the engine block by the surface treatment with the brush. In particular, the inventive method is suitable for preparing a thermal sprayed coating produced by the PTWA wire-plasma spraying process.

Fig. 1

den Einsatz einer Hammer- oder Schlagbürste bei der Bearbeitung von Zylinderlaufbuchsen an Verbrennungsmotoren,

Fig. 2

eine derartige Bürste in perspektivischer Seitenansicht,

Fig. 3 und Fig. 3a

den Bürstenkörper einer derartigen Bürste in Seitenansicht mit zugehöriger Stirnansicht,

Fig. 4 und Fig. 4a

eine gegenüber Fig. 3 und Fig. 3a vergrößerte teilweise Seitenansicht des Bürstenkörpers mit zugehöriger Stirnansicht,

Fig. 5 und Fig. 5a

eine teilweise Seitenansicht des Bürstenkörpers mit einer Schnittdarstellung gemäß Schnittlinie V - V von Fig. 5,

Fig. 6 und Fig. 6a

eine Stirnansicht einer endseitigen Bürstenscheibe gemäß den vorherigen Darstellungen mit einer Schnittdarstellung gemäß Schnittlinie VI - VI von Fig. 6,

Fig. 7 und Fig. 7a

eine Seitenansicht des Bürstenkörpers mit Bürstenwelle und einer mit dem Bürstenkörper verschweißten Bürstenscheibe sowie eine zugehörige Stirnansicht,

Fig. 8

eine Seitenansicht des kompletten Bürstenkörpers mit Bürstenwelle und verschweißter Bürstenscheibe,

Fig. 9

eine weitere Ausführungsform einer Hammer- oder Schlagbürste mit einem abgewandelten Bürstenkörper in perspektivischer Ansicht,

Fig. 10

in einem vergrößerten Ausschnitt X von Fig. 9 die Ausbildung und die Arbeitsweise der Schlagdrähte von solchen Bürsten beim Bearbeiten von Oberflächen an Werkstücken nach dem erfindungsgemäßen Verfahren, während in

Fig. 11

eine weitere Ausführungsform einer Hammer- oder Schlagbürste nach Fig. 9 mit geänderten Schlagdrähten in Form von Schenkelfedern gezeigt ist, von denen eine Schenkelfeder in

Fig. 12

in perspektivischer Darstellung und in

Fig. 13 und Fig. 14

jeweils in zwei zugehörigen Längsseitenansichten wiedergegeben ist; und

Fig. 15

einen Querschnitt durch eine mit einer Spritzschicht versehenen erfinderischen Oberfläche.

Preferred embodiments of a hammer or impact brush for carrying out the method according to the invention are shown schematically in the drawing. Show it:

Fig. 1

the use of a hammer or impact brush when machining cylinder liners on internal combustion engines,

Fig. 2

Such a brush in a perspective side view,

Fig. 3 and Fig. 3a

the brush body of such a brush in side view with associated front view,

Fig. 4 and Fig. 4a

one opposite Fig. 3 and Fig. 3a enlarged partial side view of the brush body with associated front view,

Fig. 5 and Fig. 5a

a partial side view of the brush body with a sectional view along section line V - V of Fig. 5 .

Fig. 6 and Fig. 6a

an end view of an end brush disc according to the previous representations with a sectional view along section line VI - VI of Fig. 6 .

Fig. 7 and Fig. 7a

a side view of the brush body with brush shaft and a welded to the brush body brush disc and an associated end view,

Fig. 8

a side view of the complete brush body with brush shaft and welded brush disc,

Fig. 9

a further embodiment of a hammer or impact brush with a modified brush body in perspective view,

Fig. 10

in an enlarged section X of Fig. 9 the formation and operation of the impact wires of such brushes when machining surfaces on workpieces according to the inventive method, while in

Fig. 11

another embodiment of a hammer or impact brush after Fig. 9 is shown with modified impact wires in the form of torsion springs, one leg of which in

Fig. 12

in perspective and in

FIGS. 13 and 14

each reproduced in two associated longitudinal side views; and

Fig. 15

a cross section through an inventive surface provided with a sprayed layer.

The claimed method is used to prepare a previously mechanically roughened surface on a workpiece 1 made of metal by brushing for the application of a thermally sprayed layer. It is characterized in that the surface 2 to be processed on the workpiece 1 by hammer or impact brushes with a rotating hammer or impact brush 3 is processed with a plurality of radially outwardly directed impact wires 4 such that the edges of the ridges for improvement the adhesion of the subsequently applied thermally sprayed layer broken or at least partially bent to form undercuts. The brush 3 rotates at a high speed of about 3000 to 6000 revolutions per minute and is in the machining process with its axis of rotation 13 in such a constant parallel distance relative to the surface 2 of the workpiece 1 so laterally displaced that over the circumference of the brush. 3 distributed Impact wires 4 abruptly impinge with their ends 5 at an oblique angle of less than 90 ° in rapid succession on adjacent surface areas on the workpiece 1.

As in Fig. 10 and Fig. 11 is shown, the freely rotatably mounted on the brush body 7 in the direction of rotation 6 Impact wires 4 when hitting the workpiece resiliently and slide with their ends 5 along the surface to be machined to immediately lifted from the surface due to the resilient deflection and in the Continued rotation of the brush 3 against the direction of rotation 6 to be thrown back and then to return by centrifugal action in their radial orientation for a renewed surface contact.

As in Fig. 10 and Fig. 11 can also be seen, the impact wires 4 of the brush have a length such that they are pulled in the rapid rotation of the brush after its sudden impact on the surface to be machined 2 at this in the direction of rotation 6 of the brush 3 a piece along, then with the further rotation of the brush from the working surface lift again and thus stop the impact.

In all the embodiments shown, the brush 3 consists of a substantially cylindrical rotationally symmetrical brush body 7 with a plurality of axially parallel support rods 11 which are clamped over the circumference of the brush between the front side brush discs 9, 10 and a plurality of axially in the axial direction of the brush 3 next to each other arranged impact wires (4) wear.

The rotating at high speed hammer or impact brush 3 is in the embodiment of Fig. 1 to Fig. 8 from a substantially cylindrical rotationally symmetrical brush body 7 with a plurality of axially parallel longitudinal grooves 8 in which between the front side brush discs 9, 10 each axially parallel support rods 11 (FIGS. Fig. 1, Fig. 2 and Fig. 9 ) are clamped for a plurality of in the axial direction of the brush closely juxtaposed impact wires 4. The hammer or impact brush 3 shown has on the brush body 7 six evenly distributed over the circumference longitudinal grooves 8 with six support rods 11, where the punch wires 4 are freely rotatably mounted. The legs 4a, 4b of the percussion wires 4 each have the same length, and the supporting rods 11 have a round cross-section, so that the percussion wires 4 can move freely on the support rods 11 in the direction of rotation 6 of the brush back and forth. In the embodiment of FIGS. 9 and 10 are the punch wires 4 with two parallel spaced legs 4a, 4b U-shaped, so that they enclose the support rod 11 with an annular eye 4c. The impact wires 4 of the brush 3 are hard-ingrained with about 53% Cr on the wire surface and a Vickers hardness HV of at least 1800.

As in Fig. 5 and Fig. 5a is also shown, the receptacles 12 are formed for the ends of the support rods 11 on at least one brush disc 9 or 10 by means of adjustable bearing bushes 14 radially adjustable to the rotational axis 13 of the brush 3. In addition, the brush body 7 with brush discs 9, 10, Support rods 11, impact wires 4 and brush shaft 15 suitably made of a high-strength stainless steel.

In the further embodiment of a hammer or impact brush of Fig. 11 to 14 are the percussion wires 4 as leg springs formed in the axial direction of the support rods 11 closely adjacent parallel legs 4a, 4b and enclose the support rods 11 also with an annular eye 4c. When hitting the surface to be machined 2 they are bent and then spring back in the direction of a counter to the direction of rotation 6 following adjacent support rod 11.

The brush body 7 consists in this embodiment of two attached to the brush shaft 15 brush discs 9, 10, where the support rods 11 for the percussion wires or torsion springs (4) are fixed with its two ends in about the circumference of the brush body 7 also uniformly distributed receptacles 12 , Again, the receptacles 12 may be adjustable for the ends of the support rods 11 on at least one brush disc 9 or 10 by means of adjustable bearing bushes 14 radially to the axis of rotation 13 of the brush. Likewise, the brush body 7 with brush discs 9, 10, support rods 11, impact wires or torsion springs 4 and brush shaft 15 made of a high-strength stainless steel. Moreover, the materials used for the brush have the same quality as brushes Fig. 1 to Fig. 10 ,

In FIG. 15 FIG. 2 shows a cross section through an inventive surface 2 of a workpiece 1, which is provided with a spray layer 16, transversely to the grooves 17. The grooves 17 are defined at regular intervals by the groove webs 18. The grooves 17 are defined by their mean groove width B, their mean groove spacing A, the mean width S of the groove webs 18, the mean groove depth T and the mean groove web height H, the groove spacing A is the sum of groove width B and width S of the groove webs 18 and the groove depth T is equal to the groove web height H. "Middle" width or depth or height should mean here that a is formed by the cross-sectional area of a groove 17 and a groove web 18 respectively expressed by two average values.

On the surfaces 19 of the groove webs 18, the formed by the brush brushing plastic formations 20 of the groove edges 21 can be seen, whereby the undercuts 22 are formed in the grooves 17. After the grooves 17 are filled by the sprayed layer 16 a, the sprayed layer 16 is clamped together at these undercuts 22 and is thus firmly connected to the workpiece 1. It can be seen that the plastic deformations 20 occur transversely to the grooves 17 irregularly. This also applies in the longitudinal direction to the grooves 17, where the plastic deformations 20 are introduced into the groove structure more or less frequently, depending on the intensity of the brushing. Overall, this surface structure with the irregular undercuts 22 leads to a very high adhesive strength of the sprayed layer 16 on the workpiece 1.

As from the size in FIG. 15 can be seen, the grooves 17 have approximately a groove width B of 0.2 mm, a groove spacing A of 0.5 mm, so that a width S of the groove webs 18 of 0.3 mm and a groove depth S or groove web height H of 0.09 mm up. This macroscopic structure applied in a first process step has a size in the preferred magnitudes for these processes of 0.1-1 mm in width and about 0.05-0.2 mm in depth.

The introduced in the second process step by the brush plastic deformation 20 have microscopic dimensions of about 5 - 50 microns on the surface 19 of the groove webs 18. The plastically deformed surface 19 of the groove webs 18, similar to a shot peened surface, has a layer provided with residual compressive stresses.

LIST OF REFERENCE NUMBERS

1

workpiece

2

surface

3

Hammer or impact brush

4

Impact Wires - Thigh Spring

4a

Legs of trained as a leg spring percussion wires

4b

Legs of trained as a leg spring percussion wires

4c

annular eye of the percussion wires or torsion springs

5

Ends of the punch wires 4

6

Direction of rotation of the brush

7

brush body

8th

longitudinal grooves

9

brush disc

10

brush disc

11

Support rods - axles

12

Shooting for the support rods 11

13

axis of rotation

14

bushings

15

brush shaft

16

spray layer

16a

Sprayed layer in a groove

17

grooves

18

grooved ridges

19

Surfaces of the grooved webs

20

Plastic shaping of a grooved edge 21

21

groove edge

22

undercuts

Claims (9)

1. Process for preparing a previously mechanically roughened surface (2) having sharp-edged burrs and depressions on metal workpieces (1) for the application of a thermally sprayed layer, the roughened surface (2) being machined by hammer or percussion brushing using a rapidly rotating hammer or percussion brush (3) having a multiplicity of radially outwardly oriented, resilient percussion wires (4), in such a manner that the edges of the burrs are broken in order to improve the adhesion of the subsequently applied thermally sprayed layer and/or are at least partially bent over to form undercuts (22),
   where
   the sharp-edged burrs and depressions on the mechanically roughened surface (2) are grooves (17) formed by machining, and the percussion wires (4) impinge predominantly parallel to the grooves (17).
2. Process according to Claim 1,
   characterized in that
   the grooves (17) have a trapezoidal to rectangular cross section.
3. Process according to Claim 1 or 2,
   characterized in that
   the diameter of the percussion wires (4) is greater than the groove width (B).
4. Process according to one of the preceding claims,
   characterized in that
   the diameter of the percussion wires (4) corresponds to at least one times the groove spacing (A), preferably two to three times the groove spacing (A).
5. Process according to one of the preceding claims,
   characterized in that
   the ratio of groove depth (T) to groove width (B) is between 0.2 and 1, preferably between 0.5 and 0.7.
6. Process according to one of the preceding claims,
   characterized in that
   the ratio of groove spacing (A) to groove width (B) is between 1.2 and 4, preferably between 1.8 and 2.2.
7. Process according to one of the preceding claims,
   characterized in that
   the groove spacing (A) is between 0.1 mm and 1 mm, preferably between 0.15 mm and 0.25 mm.
8. Process according to one of the preceding claims,
   characterized in that
   the brush (3) rotates at a high rotational speed of about 3000 to 6000 revolutions per minute and is displaced laterally with the axis of rotation (13) thereof at such a constant parallel distance in relation to the surface (2) of the workpiece (1), and in such a manner, that the ends (5) of the percussion wires (4) distributed over the circumference of the brush (3) impinge on adjacent surface regions on the workpiece (1) in bursts at an oblique angle of less than 90° in quick succession.
9. Process according to one of the preceding claims,
   characterized in that
   the percussion wires (4) mounted so as to be freely rotatable in the direction of rotation (6) of the brush (3) are bent resiliently when they impinge on the workpiece, slide along the surface to be machined with the ends (5) thereof, are then immediately lifted off from the surface owing to the resilient bending and, when the brush (3) continues to rotate, are thrown back counter to the direction of rotation (6), in order to then return to their radial orientation for renewed surface contact as a result of the effect of centrifugal force.

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