U.S. patent application number 11/921692 was filed with the patent office on 2009-04-30 for method for coating a cylinder sleeve.
Invention is credited to Gerhard Bucher.
Application Number | 20090110841 11/921692 |
Document ID | / |
Family ID | 36972883 |
Filed Date | 2009-04-30 |
United States Patent
Application |
20090110841 |
Kind Code |
A1 |
Bucher; Gerhard |
April 30, 2009 |
Method for coating a cylinder sleeve
Abstract
The invention relates to a method for coating a cylinder sleeve
consisting of an iron-based material. A first layer and a second
layer made of a zinc alloy are injected onto the outer surface
using a thermal injection method. A good metallic connection
between the cylinder sleeve and the cylinder crankcase, wherein the
cylinder sleeve is poured, is produced by using alloyed or
unalloyed copper for the first layer and by using a
zinc-aluminum-alloy for the second layer.
Inventors: |
Bucher; Gerhard;
(Ludwigsburg, DE) |
Correspondence
Address: |
COLLARD & ROE, P.C.
1077 NORTHERN BOULEVARD
ROSLYN
NY
11576
US
|
Family ID: |
36972883 |
Appl. No.: |
11/921692 |
Filed: |
June 16, 2006 |
PCT Filed: |
June 16, 2006 |
PCT NO: |
PCT/DE2006/001023 |
371 Date: |
December 6, 2007 |
Current U.S.
Class: |
427/456 ;
427/455 |
Current CPC
Class: |
C23C 4/08 20130101; C23C
24/04 20130101; C23C 4/129 20160101; C23C 4/02 20130101; C23C
28/021 20130101; C23C 4/131 20160101 |
Class at
Publication: |
427/456 ;
427/455 |
International
Class: |
C23C 4/08 20060101
C23C004/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 15, 2005 |
DE |
10 2005 027 828.0 |
Claims
1. Method for coating a cylinder sleeve made of an iron-based
material, whereby a first layer and a second layer of a zinc alloy
are sprayed onto the outer surface of the cylinder sleeve, using a
thermal spraying method, comprising the following method steps,
copper or a copper-based alloy is sprayed onto the outer surface of
the cylinder sleeve as a first layer, and a zinc-aluminum alloy is
sprayed onto the first layer as a second layer.
2. Method according to claim 1, wherein 99.9% copper is sprayed on
as the first layer.
3. Method according to claim 1, wherein a CuAl8 alloy is sprayed on
as the first layer.
4. Method according to claim 1, wherein a CuAl8Ni2 alloy is sprayed
on as the first layer.
5. Method according to claim 1, wherein a CuP8 alloy is sprayed on
as the first layer.
6. Method according to claim 1, wherein a CuSi3 alloy is sprayed on
as the first layer.
7. Method according to claim 1, wherein a CuZn alloy having up to
45 wt.-% zinc is sprayed on as the first layer.
8. Method according to claim 7, wherein a CuZn37 alloy is sprayed
on as the first layer.
9. Method according to claim 1, wherein the first layer has a
thickness between 60 .mu.m and 130 .mu.m.
10. Method according to claim 1, wherein a ZnAl alloy having 3 to
20 wt.-% aluminum is sprayed on as the 2.sup.nd layer.
11. Method according to claim 10, wherein a Zn85Al15 alloy is
sprayed on as the 2.sup.nd layer.
12. Method according to claim 10, wherein copper is alloyed into
the 2.sup.nd layer.
13. Method according to claim 1, wherein the cold gas spraying
method is used for spraying on the 1.sup.st and/or the 2.sup.nd
layer.
14. Use of copper or of a copper-based alloy as a first layer to be
applied to a cylinder sleeve made of gray cast iron, and use of a
zinc-aluminum alloy as the second layer to be applied to the first
layer.
Description
[0001] The invention relates to a method for coating a cylinder
sleeve, according to the preamble of claim 1.
[0002] Cylinder crankcases are usually cast from light metal,
particularly aluminum, whereby there is the need, due to the poor
tribological properties of the light metals, to cast cylinder
sleeves of an iron-based material, for example gray cast iron, into
the cylinder crankcase, as well. In this connection, problems occur
with anchoring the cylinder sleeves in the cylinder crankcase in
sufficiently firm manner, and with guaranteeing a sufficient heat
transfer between the cylinder sleeves and the cylinder crankcase.
These problems can be solved in that the outer surfaces of the
cylinder sleeves are given a rough-cast structure with undercuts.
This brings with it the result that the crosspieces between the
cylinder sleeves cast into the cylinder crankcase are very broad,
and that therefore the space requirement of the cylinder sleeves is
very great.
[0003] Within the scope of the trend in engine development, of
reducing the size of the engines while maintaining performance,
there is the need to reduce the distances between the individual
cylinder sleeves, and, at the same time, to improve the heat
removal from the combustion chamber to the cooling chambers of the
cylinder crankcase, by way of the cylinder sleeve. These problems
can be solved in that, as an alternative to a rough-cast sleeve,
cylinder sleeves made of gray cast iron having a smooth or
moderately rough outer surface and having a coating are used, which
coating assures bonding of the cylinder sleeve to the surrounding
cast material of the cylinder crankcase.
[0004] A cylinder sleeve of this type, made of gray cast iron, is
described in the patent DE 197 29 017 C2. This sleeve has a cover
layer of an AlSi alloy on its outer surface, applied using the
flame-spraying method or the arc-spraying method, which alloy
contains less than 15% silicon. An oxidation protection layer is
applied to this cover layer, consisting of a zinc alloy, whose task
it is to prevent oxidation of the AlSi layer, thereby preventing
metallic bonding of the cover layer to the surrounding cast
material of the cylinder crankcase.
[0005] It is a disadvantage, in this connection, that the AlSi
alloy already oxidizes when the cover layer is sprayed on. The
oxide skin formed in this connection adheres very firmly to the
AlSi layer. Furthermore, its melting temperature is higher than the
temperatures that can be reached during surrounding casting. It is
true that the oxide skin can be removed with a lot of effort, but
it quickly forms again after having been removed, so that even an
additionally applied protective layer of zinc or of a zinc alloy
cannot assure a metallic bond between the AlSi layer and the
surrounding cast material.
[0006] Furthermore, the expansion coefficient of the AlSi cover
layer is approximately 1.7 times as great as the heat expansion
coefficient of gray cast iron, so that tensions in the known layer
system occur in the case of temperature changes, which tensions
impair the bond between the cylinder sleeve and the cylinder
crankcase.
[0007] It is the task of the invention to avoid these disadvantages
of the state of the art, i.e. to improve the metallic bond of the
cylinder sleeve with the surrounding cast material of the cylinder
crankcase, and therefore also the heat transfer between the
cylinder sleeve and the cylinder crankcase. This task is
accomplished with the characteristics standing in the
characterizing part of the main claim.
[0008] In this connection, the advantages are obtained that the
gradation of the thermal expansion coefficients, in the layer
structure according to the invention, between the gray cast iron
sleeve, the layer system, and the surrounding casting material of
the cylinder crankcase, significantly reduces the thermally caused
tensions in the layer structure according to the invention.
Furthermore, the gradation of the melting temperatures, proceeding
from the cylinder sleeve, by way of the layer system according to
the invention, all the way to the surrounding cast material of the
cylinder crankcase, brings about partial solution, i.e.
diffusion-related partial alloying of the outer layer with the
surrounding cast material, bringing about a stable metal bond
between the cylinder sleeve and the surrounding cast material of
the cylinder crankcase. Finally, the coating consisting of the
alloys according to the invention has the advantage that its alloy
components participate in precipitation hardening in the bonding
zone.
[0009] Practical embodiments of the invention are the object of the
dependent claims.
[0010] The method according to the invention, for coating a
cylinder sleeve to be cast into a cylinder crankcase, will be
explained in greater detail below.
[0011] A cylinder sleeve that consists of an iron-based material,
which can be alloyed or unalloyed, is used for this purpose.
Preferably, the cylinder sleeve consists of gray cast iron, which
can contain either lamellar graphite, vermicular graphite, or
spherical graphite. In this connection, the gray cast iron can have
a ferrite/perlite, perlite, bainite, or austenite basic structure.
The outer surface of the cylinder sleeve can be configured to be
smooth. However, it can also have any other surface quality, all
the way to a flat rough-cast surface. Furthermore, the cylinder
sleeve can have an outer surface that has been machined by means of
cutting.
[0012] Any conventional casting methods, such as the die-casting
method, the pressure casting method, the gravity casting method, or
the low-pressure casting method, can be used for casting the
cylinder sleeve into the cylinder crankcase. The cylinder crankcase
consists of one of the usual light metal casting material, whereby
casting materials both on an aluminum basis and on a magnesium
basis can be used.
[0013] In order to assure the metallic bond of the cylinder sleeve
to the surrounding casting material of the cylinder crankcase when
the cylinder sleeve is cast into the cylinder crankcase, the outer
surface of the cylinder sleeve is coated by means of thermal
spraying. As preparation for this, it is necessary to clean the
outer surface of dirt and oxides, and subsequently to roughen it
up. Suitable methods for this are brushing and/or sandblasting.
Sandblasting with coarse corundum, i.e. with crystallized
Al.sub.2O.sub.3, is particularly suitable for this.
[0014] Immediately subsequent to this, a first layer is then
applied to the outer surface of the cylinder sleeve, by means of
thermal spraying. This first layer consists either of 99.9% copper,
a CuAl8 alloy, a CuAl8Ni2 alloy, a CuP8 alloy, a CuSi3 alloy, or a
CuZn37 alloy (brass). In this connection, a layer low in pores and
oxides, having a thickness between 60 .mu.m and 130 .mu.m, is aimed
at.
[0015] In order to make the gradation of the melting temperatures
of the layers applied to the cylinder sleeve finer, it is
advantageous to apply an additional layer of one of the
aforementioned copper alloys to a first layer consisting of pure
copper, the melting temperature of which additional layer is lower
than that of copper, but whose melting temperature is higher than
that of the material of which the outer coating, referred to as the
second layer in the following, consists.
[0016] Since wires of the stated alloys is commercially available,
the wire flame-spraying method is preferably used as a thermal
spraying method, whereby the additional spray material in wire form
is melted in the center of an acetylene-oxygen flame, and sprayed
onto the surface of the cylinder sleeve using an atomizer gas, such
as compressed air or nitrogen, for example.
[0017] The electric arc wire spraying method is also suitable,
whereby two spray additives in wire form are melted in an electric
arc and centrifuged onto the outer surface of the cylinder sleeve
by means of an atomizer gas. In this connection, there is the
possibility of melting two wires that differ in their composition
with one another, whereby the composition of the layer produced in
this manner can be varied within broad ranges. If, for example,
copper wire and zinc wire are used, there is the possibility of
applying a CuZn alloy having up to 45% zinc onto the outer surface
of the cylinder sleeve. When nitrogen or argon is used as the
atomizer gas, oxidation of the materials is prevented, to a great
extent.
[0018] One possibility for further reducing oxidation of the spray
material and the oxide content of the sprayed-on layer consists in
using the cold gas spraying method, whereby non-melted powder
particles, heated only to a few hundred degrees, are accelerated to
a velocity between 300 m/sec and 1200 m/sec, and sprayed onto the
outer surface of the cylinder sleeve. The temperature at the
contact surface increases on the basis of the impact of the powder
particles, and results in micro-welding of the powder particles to
the outer surface of the cylinder sleeve.
[0019] The high-velocity flame spraying method (HVOF spraying
method) can also be used, whereby continuous gas combustion takes
place, at high pressures, within a combustion chamber in the
central axis of which the spraying additive is supplied in powder
form. The high pressure of the fuel gas/oxygen mixture produced in
the combustion chamber produces a high particle velocity, which
leads to very dense spray layers having good adhesion
properties.
[0020] The functions of the first layer consist in assuring good
adhesion of the first layer to the gray cast iron of the cylinder
sleeve, creating good bonding prerequisites for a second layer, and
implementing a gradation of the melting temperatures, i.e. a
step-by-step transition of the melting temperatures of the gray
cast iron of the cylinder sleeve, by way of the first layer and the
second layer, all the way to the surrounding cast metal of the
cylinder crankshaft. Furthermore, in this way, a gradation of the
heat expansion coefficients is brought about, proceeding from the
cylinder sleeve, by way of the first and the second layer, all the
way to the light metal of the cylinder crankcase.
[0021] In order to avoid oxidation of the first layer, the second
layer is applied to the first layer immediately after application
of the first layer, using one of the aforementioned thermal
spraying methods. A Zn85Al15 alloy having 85% zinc and 15% aluminum
is preferably used for this purpose. In the case of this alloy,
however, the aluminum content can also vary between 3% and 20%. A
layer low in pores and oxides, having a thickness between 60 .mu.m
and 130 .mu.m, is aimed at.
[0022] The function of the second layer consists in adhering well
to the first layer. Furthermore, the AlZn alloy, having 15 wt.-%
aluminum, has a melting point of 450.degree. C., bringing about the
result that the second layer is slightly melted when the cylinder
crankcase is cast, by its surrounding cast material, thereby
assuring the metallic bond between the cylinder sleeve and the
surrounding cast material of the cylinder crankcase.
[0023] In this connection, the AlZn alloy does form a very thin
oxide layer, but this does not hinder bonding of cylinder
sleeve/crankcase. Nevertheless, it is advantageous to alloy a few
wt.-% of copper into the AlZn alloy, because in this way, formation
of the oxide layer is completely prevented, and this brings about a
further improvement of the bond between cylinder sleeve and
crankcase.
* * * * *