PLASMA SPRAY METHOD FOR COATING A CYLINDER RUNNING OF A CYLINDER CRANKCASE OF A PULL-ROTATING PISTON ENGINE

Description

Field of the invention

[0001] The invention relates to a plasma spraying method for coating a cylinder bore of a cylinder crankcase of a reciprocating piston internal combustion engine. State of the art

[0002] WO 2017 / 202852 A1 discloses a coating method for coating a curved surface, a thermal coating, and a cylinder with a thermal coating. Particular reference is made to the use of powdered coating material using a thermal spraying device, in particular a plasma spraying device or HVOF spraying device with a torch that rotates on a torch shaft about a shaft axis at a predetermined rotational frequency, wherein the coating jet for applying a coating to the curved surface is directed at least partially radially away from the shaft axis toward the curved surface. Reference is made to the use of increased rotational frequencies above 200 revolutions per minute (rpm), in particular up to 800 rpm or even more, with the feed rate of the powdered coating material being "suitably increased" accordingly.In this regard, the cited document discloses a linear dependence of rotation frequency and feed rate, with the parameter combinations 200 rpm - 25 g / min, 400 rpm - 50 g / min, 600 rpm - 75 g / min and 800 rpm - 100 g / min being specifically mentioned.

[0003] US Pat. No. 5,080,056 A also discloses a method for plasma coating cylinder bores with a high plasma torch rotation rate of 800 rpm, explicitly specifying an axial feed rate of approximately 4.2 mm / s. However, the aforementioned document does not address the question of the preferred spray material feed rate.

[0004] The document WO 2017 / 202852 A1 does not refer to the feed rate during the coating process and does not address the so-called oxide lineation of the coating to be achieved.

[0005] US 9 885 311 B1 discloses a similar method and addresses the problem of reducing the heat input into the crankcase caused by the coating process. In this regard, it particularly points to a relationship between the rotation frequency and the axial feed of the burner that should be advantageously maintained. Specifically, at high rotation frequencies above 500 rpm, the axial feed should be reduced to values ​​between 16 and 25 mm / s in order to keep the burner dwell time and thus the applied coating thickness constant. In other words, US 9 885 311 B1 also discloses a linear relationship, the extrapolation of which leads to feed values ​​of significantly less than 25 mm / s at rotation frequencies significantly above 500 rpm.

[0006] DE 10 2008 053 ​​642 A1 also discloses a method for cylinder liner coating and focuses primarily on the spray materials optimally used for this purpose.

[0007] An interesting article with regard to the general background can be found in Bobzin, K. et al.: "Coating Bores of Light Metal Engine Blocks with a Nonocomposite Material Using the Plasma Transfer Wire Arc Thermal Spray Process", Journal of Thermal Spray Technology, Vol. 17, No. 3, July 3, 2008 (2008-07-03), pages 344-351, XP055258217, US, ISSN:1059-9630, DOI: 10.1007 / s11666-008-9188-y .

[0008] In the production of cylinder crankcases for reciprocating internal combustion engines, there are increasing attempts to reduce the weight of the cylinder crankcases. For this purpose, cylinder crankcases made of aluminum are used, but these require a protective coating in the area of ​​the cylinder bore, e.g., one applied by plasma spraying. A positive side effect of the coating, in addition to increased robustness of the cylinder bore, is significantly reduced friction in the area of ​​the piston group (and thus also reduced CO2 emissions) as well as positive effects against corrosive media. State-of-the-art coating processes include powder plasma spraying (APS), wire spraying, such as plasma transferred wire arc (PTWA / RSW) coating processes, arc wire spraying (LDS), and high-velocity oxyfuel spraying (HVOF).

[0009] Before thermal coating of cylinder bores in aluminum and, in some cases, gray cast iron crankcases, a roughening process is performed to bond the coating, i.e., improve its adhesion. This roughening process is required for the coating to be applied at all. This roughening process is achieved by blasting processes using corundum and water (medium-pressure / high-pressure water jets), laser beam roughening, or roughening with a geometrically defined cutting edge.

[0010] When using powder plasma spraying (APS), increased oxide formation occurs at inhomogeneities caused by the aforementioned roughening process if a process control according to a coating process known from the prior art with, for example, four double cycles is selected. This can lead to oxide lines forming parallel to the surface in the coating. The oxide lines, in turn, cause reduced layer stability and, particularly if the oxides / oxide lines are present on the surface of the coating (cylinder bore) after finish honing, can lead to the oxides breaking out and subsequently to microgrooving of the cylinder bore. If the oxides / oxide lines on the surface are stressed by the honing process, this can lead to increased breakout of these oxides and thus to an increased pore area proportion of the bore surface.This can cause increased oil consumption and, consequently, increased particle emissions. Another disadvantage of the prior art process is that it requires a relatively long time for the coating process. Task

[0011] The invention is based on the object of providing a coating method by means of which the formation of oxides is limited or oxide lineages in the layer formation and thus negative influences due to oxide breakouts and microgrooving - particularly caused by such oxide breakouts or existing due to a high oxide lineage - are avoided. Description of the invention

[0012] The object is achieved according to the invention with the features of independent claim 1 and the corresponding dependent claims. Further practical embodiments and advantages of the invention are described in conjunction with the dependent claims.

[0013] According to the plasma spraying method according to the invention for coating a cylinder bore of a cylinder crankcase of a reciprocating piston internal combustion engine, the coating is applied at least partially to the cylinder bore of the cylinder crankcase using the following parameter combination: a) Rotation speed: 600 - 700 rpm, b) Spray material feed rate: 100 - 120 g / min and c) Feed rate: 24 - 75 mm / s.

[0014] Through extensive empirical test series and incorporating modified plant technology, it was determined that with the aforementioned parameter ranges, all of which must be met according to a), b), and c) in order to achieve the advantages of the invention, the formation of oxides can be reduced and the resulting oxide lineation can be drastically reduced. This makes it possible to achieve a particularly homogeneous surface that is largely free of undesirable microgrooving caused by increased oxide formation and high oxide lineation. Furthermore, a high rotation speed can be used during the process, allowing the desired coating to be applied in a shorter time than with previously known methods. With regard to the rotation speed of the burner technology, values ​​between 600 and 700 rpm have proven to be optimal.Preferred values ​​are between 630 rpm and 770 rpm, with values ​​between 640 rpm and 660 rpm being particularly preferred. Particularly good results have been achieved with rotation speeds of 650 rpm.

[0015] With regard to the spray material feed rate, the value range between 100 and 120 g / min has proven optimal. Special reference is made to the value of 110 g / min, which, especially in conjunction with the rotation speed of 650 rpm, achieved a particularly high-quality coating result for the cylinder bore.

[0016] With regard to the feed rate according to feature c), reference is made to the value range between 30 and 70 mm / s, more preferably to the value range between 40 and 65 mm / s, and particularly preferably to the value range between 50 and 65 mm / s. Furthermore, reference is made to the even narrower value ranges between 52 and 60 mm / s and more preferably between 54 and 58 mm / s.

[0017] In a practical embodiment of the plasma spraying process according to the invention, the coating is applied using 5-8 spray cycles, each in the form of double strokes. Application with 6-7 spray cycles is particularly preferred in this regard. It has been shown that the thickness and structure of a corresponding coating, in conjunction with the required processing time, is particularly high-quality and efficient in this case.

[0018] A steel layer or a ceramic layer is preferably applied as the coating. With regard to the steel layers, particular reference is made to low-alloy and high-alloy steel layers, i.e., steel layers with steels in which the sum of the alloying elements does not exceed 5 mass percent (low-alloy steels) or steels in which the average mass content of at least one alloying element is greater than or equal to 5% (high-alloy steels). The use of low-alloy steels is preferred over high-alloy steels. However, high-alloy steels also achieve results that are advantageous compared to those known from the previous state of the art.

[0019] With regard to the application of a ceramic layer, particular reference is made to layers of titanium dioxide (TiO 2 ).

[0020] Regardless of the above, a ceramic layer is preferably applied in conjunction with a prior roughening process and the prior application of an adhesion-promoting layer. A nickel-aluminum layer, a bronze layer, or a low-alloy steel layer are particularly suitable as the adhesion-promoting layer. The thickness of an adhesion-promoting layer is preferably less than 100 µm, more preferably less than 60 µm, and most preferably not more than 40 µm.

[0021] If a coating in the form of a low-alloy steel layer is to be achieved in a plasma spraying process according to the invention, this coating is preferably applied using a low-alloy steel powder. Steel powder with a predominantly spherical morphology with low satellite contents is particularly preferred.

[0022] In a further practical embodiment of a plasma spraying process according to the invention, in which a steel layer is applied as a coating, the coating is applied using a steel powder which has less than 2 wt.% carbon (C), less than 2 wt.% manganese (Mn), less than 2 wt.% chromium (Cr), less than 1 wt.% nickel (Ni), less than 1 wt.% oxygen (O 2 ) and less than 1 wt.% nitrogen (N 2 ). With regard to the proportion of carbon, particular reference is made to a wt.% proportion of 1.0 to 1.3. With regard to the proportion of manganese, particular reference is made to a proportion of 1.2 to 1.6 wt.% With regard to the weight proportion of chromium, particular reference is made to a value range of 1.2 to 1.6 wt.% With regard to the weight proportion of nickel, particular reference is made to the value range of less than 0.5 wt.%.With regard to the weight fraction of oxygen, particular reference is made to values ​​of less than 0.2 wt.%, and with regard to the weight fraction of nitrogen, particular reference is made to the value range of less than 0.5 wt.%. The above-mentioned value ranges preferably apply cumulatively, i.e., linked to one another in this combination.

[0023] A particularly high-quality coating is achieved when a steel layer is applied using a steel powder whose grain size is exclusively smaller than 60 µm and / or whose grain size is predominantly smaller than 42 µm. The proportion of steel powder with a grain size of less than 42 µm is preferably a maximum of 90 percent by weight. The proportion with a grain size of less than 26 µm is preferably a maximum of 50 percent. The proportion with a grain size of less than 16 µm is preferably a maximum of 10 percent.

[0024] In a further practical embodiment of a plasma spraying process according to the invention, the coating is applied under the influence of the atmosphere. In this case, the process is also referred to as an atmospheric plasma spraying process or APS process. One advantage of the APS process is that the use of protective gases and the associated additional costs can be dispensed with. Alternatively, however, the coating can also be applied in a plasma spraying process according to the invention using a protective gas or in a vacuum. In this case, the costs of carrying out the process are increased, but in individual cases a qualitatively significantly better coating result can be achieved, i.e. in particular a coating can be achieved which has a lower oxide content or has fewer oxide lines.

[0025] The plasma spraying process according to the invention is particularly advantageous if, prior to the application of the coating, at least one radiative roughening process is carried out using corundum and / or water, laser beam roughening, or roughening with a geometrically defined cutting edge. In this case, the adhesion of the coating to be applied is improved, while simultaneously increasing the durability of the resulting coating.

[0026] Further practical embodiments of the invention are described below in connection with the drawings. Brief description of the drawings

[0027] They show: Figure 1: a cross-sectional view of a section of a cylinder bore with a coating, Figure 2: a view of a surface of a coating of a cylinder bore according to the prior art, Figure 3: a cross-section through a coating on a cylinder bore produced by a method according to the invention and Figure 4: an enlarged view of the section according to Figure 3 . Description of preferred embodiments

[0028] Figure 1shows a section of a cylinder crankcase of a reciprocating piston internal combustion engine with a section of a cylinder bore of an aluminum base body 10 of a cylinder crankcase 14, wherein the aluminum base body 10 is provided with a coating 12 and the surface 16 facing away from the aluminum base body 10 is part of the cylinder bore 18 of the cylinder crankcase 14. The partially marked black areas 20 are oxides that formed during the application of the coating 12 by means of a plasma spraying process.

[0029] Figure 2 shows the surface 16 of the cylinder bore 18. As can be seen in the figure, individual oxide lines 22a, 22b, 22c, 22d have formed on the surface 16. These lines are formed by black dots arranged approximately in a row. This is the oxide lineation mentioned above.

[0030] Figure 3 shows a view analogous to Figure 1, wherein the coating 12 was applied by means of a plasma spraying process according to the invention.

[0031] Figure 4 shows an enlarged view of the Figure 3 As can be seen, the surface 16, which forms the cylinder bore 18 of the cylinder crankcase 14, has a significantly improved quality in that oxide lines are no longer visible. Furthermore, it can be seen that significantly fewer oxides have formed in the coating 12 than in the coating 12 according to the prior art, which Figure 1 is shown. List of reference symbols

[0032] 10Aluminum base body 12Coating 14Cylinder crankcase 16Surface 18Cylinder bore 20Black area (oxide) 22a-dOxide lines

Claims

1. Plasma spraying process for coating a cylinder barrel of a cylinder crankcase of a reciprocating piston internal combustion engine, characterized in that the coating (12) is at least partially applied to the cylinder barrel (18) of the cylinder crankcase (14) using the following parameter combination: a)rotation speed:600 - 700 revolutions / minute,b)spray material flow rate:100 - 120 grams / minute andc)feed rate:24 - 75 mm / s.

2. Plasma spraying process according to the preceding claim, characterized in that the coating (12) is applied by means of 5 - 8 spray cycles, each in the form of double strokes.

3. Plasma spraying process according to either of the preceding claims, characterized in that a steel layer or a ceramic layer is applied as the coating (12).

4. Plasma spraying process according to the preceding claim, characterized in that the coating (12) is applied by means of a low-alloy steel powder.

5. Plasma spraying process according to either of the two preceding claims, characterized in that a steel layer is applied as the coating (12) by means of a steel powder having a predominantly spherical morphology with small proportions of satellites.

6. Plasma spraying process according to any of the three preceding claims, characterized in that a steel layer is applied as the coating (12) by means of a steel powder which comprises less than 2 wt.% carbon (C), less than 2 wt.% manganese (Mn), less than 2 wt.% chromium (Cr), less than 1 wt.% nickel (Ni), less than 1 wt.% oxygen (O2) and less than 1 wt.% nitrogen (N2).

7. Plasma spraying process according to any of the four preceding claims, characterized in that a steel layer is applied by means of a steel powder of which the particle size is exclusively smaller than 60 µm and / or predominantly smaller than 42 µm.

8. Plasma spraying process according to any of the preceding claims, characterized in that the coating (12) is applied under the influence of the atmosphere.

9. Plasma spraying process according to any of the preceding claims, characterized in that the coating (12) is applied using a protective gas or in a vacuum.

10. Plasma spraying process according to any of the preceding claims, characterized in that, before applying the coating (12), at least one blasting abrasion process is carried out by means of corundum and / or water, by means of laser beam abrasion or by means of abrasion with a geometrically defined cutting edge.

11. Plasma spraying process according to any of the preceding claims, characterized in that the feed rate is 52 - 60 mm / s.