EP3575435B1 - Plasma spray method for coating a cylinder a cylinder liner of a cylinder crankcase of a reciprocating piston combustion engine - Google Patents

Description

field of the invention

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

Out of WO 2017/202852 A1 A coating method for coating a curved surface, a thermal coating and a cylinder with a thermal coating are known. In this case, particular reference is made to the use of powdered coating material using a thermal spray device, in particular a plasma spray device or HVOF spray device with a burner that rotates on a burner shaft about a shaft axis at a predetermined rotation frequency, wherein the coating jet for applying a coating to the curved surface is directed at least partially radially away from the shaft axis towards the curved surface. Reference is made to the use of increased rotation frequencies above 200 revolutions per minute (rpm), in particular up to 800 rpm or even more, wherein the feed rate of the powdered coating material is to be "suitably increased" accordingly. In this regard, the aforementioned publication 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.

The US 5 080 056 A discloses a method for plasma coating cylinder bores with a high rotation rate of the plasma torch of 800 rpm, whereby an axial feed rate of approximately 4.2 mm/s is expressly specified. However, the above-mentioned publication does not address the question of the preferred spray material feed rate.

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

The US 9 885 311 B1 discloses a similar process and addresses the problem of reducing the heat input into the crankcase caused by the coating process. In this regard, it particularly points to an advantageous relationship between the rotation frequency and the axial feed of the burner. In particular, 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 residence time of the burner and thus the applied layer thickness constant. In other words, the US 9 885 311 B1 a linear relationship, the extrapolation of which leads to feed rates of well below 25 mm/s at rotation frequencies of well above 500 rpm.

The 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.

An interesting article with regard to the general background can be found at 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 .

In the manufacture of cylinder crankcases for reciprocating piston 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 layer in the area of the cylinder bore, e.g. a protective layer applied by plasma spraying. A positive side effect of the coating is not only an increase in the robustness of the cylinder bore, but also a significantly reduced friction in the area of the piston group (and thus also a reduction in CO2 emissions) as well as positive effects on corrosive media. Coating processes known from the state of the art are powder plasma spraying (APS process), wire spraying processes, such as plasma transferred wire arc (PTWA/RSW) coating processes, arc wire spraying (LDS) and high-velocity flame spraying (HVOF spraying).

Before thermally coating cylinder bores in crankcases made of aluminum and sometimes also of gray cast iron, a roughening process is carried out to clamp the coating, i.e. to improve the adhesion of the coating, or is necessary so that the coating can be applied at all. This roughening process is carried out by blasting processes using corundum and water (medium-pressure/high-pressure water jets), laser beam roughening or roughening with a geometrically defined cutting edge.

When using powder plasma spraying (APS process), increased oxide formation occurs at inhomogeneities caused by the roughening process mentioned above if a process control according to a coating process known from the state of the art with, for example, 4 double cycles is selected. This can lead to oxide lines forming in the coating parallel to the surface. The oxide lines in turn cause reduced layer stability and can lead to the oxides breaking out and subsequently to micro-grooving of the cylinder running surface, particularly if the oxides/oxide lines are present on the surface of the coating (cylinder running surface) after final honing. If the oxides/oxide lines on the surface are stressed by the honing process, this can lead to increased breakouts of these oxides and thus to an increased pore area proportion of the running surface. This can cause increased oil consumption and thus correspondingly lead to increased particle emissions. A further disadvantage of the method known from the prior art is that it requires a relatively long time for the coating process.

task

The invention is based on the object of providing a coating process by means of which the formation of oxides is limited or oxide lines in the layer formation and thus negative influences due to oxide breakouts and micro-grooving - particularly caused by such oxide breakouts or existing due to a high oxide lineage - are avoided.

explanation of the invention

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 connection with the dependent claims.

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 at least partially applied 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.

By means of extensive empirical test series and by including modified plant technology, it was determined that with the above-mentioned parameter ranges, all of which must be fulfilled in accordance with a), b) and c) in order to achieve the advantages according to the invention, the formation of oxides can be reduced and the resulting oxide rows can be drastically reduced. This makes it possible to achieve a particularly homogeneous surface that is largely free of undesirable micro-grooving, which is caused by increased oxide formation and high oxide rows. In addition, a high rotation speed can be used during the process and thus the desired coating can be applied in a shorter time than with the processes known to date from the state of the art. With regard to the rotation speed of the burner technology, values between 600-700 rpm have proven to be optimal. Values between 630 rpm and 770 rpm are preferred, values between 640 rpm and 660 rpm are particularly preferred. Particularly good results were achieved with rotation speeds of 650 rpm.

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

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. In addition, reference is made to the even narrower value ranges between 52 and 60 mm/s and more preferably between 54 and 58 mm/s.

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

A steel layer or a ceramic layer is preferably applied as a 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% by mass (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 the results known from the previous state of the art.

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

Regardless of the above, a ceramic layer is preferably applied in conjunction with a previous roughening process and the previous application of an adhesion-promoting layer. A nickel-aluminum layer, a bronze layer or a low-alloy steel layer are particularly suitable as an adhesion-promoting layer. The thickness of an adhesion-promoting layer is preferably less than 100 µm, preferably less than 60 µm and particularly preferably a maximum of 40 µm.

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 small proportions of satellites is particularly preferred.

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 by means of a steel powder which contains 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 proportion by weight of 1.0 to 1.3. With regard to the proportion of manganese, particular reference is made to a proportion by weight of 1.2 to 1.6. With regard to the proportion by weight of chromium, particular reference is made to a value range of 1.2 to 1.6. With regard to the proportion by weight of nickel, particular reference is made to the value range of less than 0.5. With regard to the proportion by weight of oxygen, particular reference is made to values of less than 0.2. With regard to the proportion by weight of nitrogen, particular reference is made to the value range of less than 0.5. The value ranges mentioned above preferably apply cumulatively, ie linked to one another in this combination.

A particularly high-quality coating is obtained 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 in weight percent of steel powder with a grain size of less than 42 µm is preferably a maximum of 90 percent. 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.

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, the coating can also be applied using a protective gas or in a vacuum in a plasma spraying process according to the invention. In this case, the costs of carrying out the process are higher, but in individual cases a qualitatively significantly better coating result can be achieved, i.e. in particular a coating can be achieved that has a lower oxide content or has a lower oxide row density.

The plasma spraying process according to the invention is particularly advantageous if, before applying the coating, at least one radiant roughening process is carried out using corundum and/or water, using laser beam roughening or using roughening with a geometrically defined cutting edge. In this case, the adhesion of the coating to be applied and at the same time the durability of the resulting coating is increased.

Further practical embodiments of the invention are described below in connection with the drawings.

Short description of the drawings

Figur 1:

eine Querschnittsdarstellung eines Ausschnitts einer Zylinderlaufbahn mit einer Beschichtung,

Figur 2:

einen Blick auf eine Oberfläche einer Beschichtung einer Zylinderlaufbahn gemäß Stand der Technik,

Figur 3:

einen Querschnitt durch eine mit einem erfindungsgemäßen Verfahren hergestellte Beschichtung auf einer Zylinderlaufbahn und

Figur 4:

eine vergrößerte Darstellung des Ausschnitts gemäß Figur 3.

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 cylinder bore coating according to the state of the 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

Figure 1 shows 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 have formed during the application of the coating 12 by means of a plasma spraying process.

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, which are formed by black dots that are arranged approximately in a row. This is the oxide line structure mentioned at the beginning.

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.

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 increased quality in that oxide lines are no longer visible. In addition, 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 in Figure 1 is shown.

list of reference symbols

10

aluminum base body

12

coating

14

cylinder crankcase

16

surface

18

cylinder bore

20

black area (oxide)

22a-d

oxide lines

Claims (11)

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 and c) 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.

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