COATING ON VALVE SEAT SURFACES

TECHNICAL FIELD OF THE INVENTION

5 The invention relates to use of PTA coatings on valve seat surfaces, and method for manufacturing a PTA coating on valve seat surfaces. The invention also relates to combustion engine exhaust valves comprising a PTA coatings on seat surfaces.

10 BACKGROUND OF THE INVENTION

The valves relating to embodiments of the invention are used in internal combustion engines, for example in internal combustion engines of marine vessels. Engines relating to the invention are used, for example, as main propulsion engines or auxiliary engines in marine vessels or in power plants for the pro- 15 duction of heat and/or electricity.

The operation of valves in an internal combustion engine is well known in the art. Engine valve seats and contacting surface of the valve head experience severe circumstances of corrosion and wear. The valve comprises a body, a head, and a contact surface on a valve head which is adapted to periodically

20 enter into gas-sealing engagement with a valve seat or seat ring. This repetitive engagement or contact of valve head with valve seat requires gas-tight contact, because valve leakage through valve causes problems with combustion and operation of the engine: incomplete combustion, power loss, engine efficiency, compression ratio, exhaust emissions and engine and/or compo-

25 nent life.

Because the valve seats and valve contacting surfaces are under corrosive environment and subjected to continuous wear, these surfaces usually comprise a coating of hard material to counter these demands. One commonly known material for these surfaces is Stellite. The coating on the valve surfaces 30 must be high-quality to provide gas-sealing engagement, and one known and commonly used process to make coatings is Plasma transferred arc (PTA). Plasma transferred arc (PTA) welding is the mostly used method for depositing high-quality metallurgically fused deposits on relatively low cost surfaces. Medium and high hardness materials can be deposited on a variety of substrates to achieve diverse properties such as mechanical strength, wear, corrosion and creep resistance.

Prior art comprises publication US20121 18402, which discloses a gas cylinder valve has a permanent coating of a solid lubricant on at least one of its internal frictional surfaces. The solid lubricant consists of or comprises tungsten disulfide. Prior art comprises publication US2007163655, which discloses a gate valve with the at least one of the engaging faces of the gate and the seat ring can have friction-resistant coating of molybdenum disulfide on a hardened outer layer.

Prior art publication US2004043160 discloses a method for coating an article, such as gas turbine assembly, with Plasma Transferred Arc (PTA) welding.

There are however some disadvantages relating to the known prior art, such as, none of the prior art disclose a PTA coating or use of PTA coatings with solid lubricants on valve seat or valve head surfaces of an internal combustion engine. None of the prior art disclose a method for preparing a PTA coating with solid lubricants on valve seat or valve head surfaces of an internal combustion engine.

However, internal combustion engines are facing more opportunities to run with new cleaner fuels. As a result of this, exhaust valves and seat surfaces or seat rings have increasing demands related to wear resistance and corrosion which both affect to their operation.

With mentioned fuels, the high temperature contact between seat surfaces can suffer higher wear rates (dry friction wear) due to low lubricity resulting in reduced components lifetime and engine failure.

Current standard solution for valve seat surfaces consists in the use of Cobalt- based alloys, whose deposition is carried out via Plasma Transferred Arc (PTA) welding technique. New material solutions enabling lower friction be- tween the two contact surfaces can reduce this type of wear bringing consequently increased exhaust valve and valve seat lifetime.

SUMMARY OF THE INVENTION An object of the invention is to alleviate and eliminate the problems or drawbacks relating to the known prior art. Another object of the invention is to provide a high quality coating for valves and valve seat surfaces, which possesses good wear-resistant and increased lifetime. Another object of the invention is to provide economically internal combustion engines and marine vessels with increased lifetime by providing a coating for valves and valve seat surfaces with enhanced lubricating properties.

The object of the invention can be achieved by the features of independent claims. The invention relates to a PTA coating for use on valve seat or valve surfaces according to claim 1 , to an internal combustion engine valve accord- ing to claim 4, to an internal combustion engine according to claim 5, to a marine vessel according to claim 6, to a method for manufacturing a PTA coating according to claim 7 and to use of PTA coating according to claim 9.

According to an embodiment of the invention, a PTA coating for use on valve seat or valve contacting surfaces of an internal combustion engine, is prepared by Plasma-Transfer-Arc-welding (PTA) and is composite material, which comprises a metal matrix and solid lubricating particles within the metal matrix. The valve is arranged to periodically enter into gas-sealing engagement with a valve seat, so as to enable the operation of the cylinder and/or internal combustion engine. The coating deposition is carried out via Plasma Transferred Arc welding (PTA). This technique provides the necessary coating thickness and adhesion to the substrate, which together with the above-mentioned constituents allow to realise mechanically resistant system and reduce the wear.

The metal matrix advantageously is based on heat resistant ferrous or non- ferrous alloys. Heat resistant alloys relate with this invention to such metal alloys that can be used in internal combustion engines on gas exchange valves or on other parts of internal combustion engine. Advantageously the metal ma- trix is based on one of the following: nickel and its alloys and cobalt and its alloys. It is also possible that matrix is based on other hard metals.

According to an additional embodiment of the invention, the solid lubricating particles are comprised of sulphides, sulphates or fluorides. Advantageously self-lubricating particles are made of at least one of the following: CaF2, BaF2, MoS2, WS2, FeS, MnS, h-BN (hexagonal boron nitride), CeF3.

According to another embodiment of the invention, the solid lubricating particles are made of at least one of such materials as selenides and tellurides (chalcogenides) of molybdenum, tungsten, niobium, tantalum, titanium (eg. MoSe2, TaSe2, TiTe2), monochalcenides (GaS, GaSe, SnSe), chlorides of cadmium, cobalt, lead, cerium, zirconium (eg. CdCI2, CoCI2, PbCI2, CeF3, Pbl2) and also some borates (eg. Na2B4O7) or sulfates (Ag2SO4, CaSo4, BaSo4, SrSo4).

According to an additional embodiment of the invention the coating further comprises particles at least one of the following: metal boride, metal carbide, metal nitride, or metal carbonitride, to increase hardness and wear-resistance and to contribute to the lubricating action. Examples of preferred metal in the compound include tungsten, vanadium, titanium, tantalum, niobium, chromium, molybdenum, or mixtures of these metals. Advantageously the hardening par- tides can be made at least one of the following: Tungsten carbide (WC), titanium carbide (TiC), chromium carbide (Cr3C2).

According to another embodiment of the invention, a valve of an internal combustion engine comprises the said PTA coating on a contact surface of the valve head. The valve comprises a body, a head, and a contact surface on a head to be adapted to periodically enter into gas-sealing engagement with a valve seat, so as to enable the operation of the cylinder and/or internal combustion engine.

According to another embodiment of the invention, the valve seat surface comprises the said PTA coating of the present invention. One further embodiment of the invention include an internal combustion engine, which comprises said PTA coating One further embodiment of the invention includes a marine vessel, which comprises the said PTA coating on valve head or on valve seat surface of an internal combustion engine.

According to one embodiment of the invention the PTA coating is manufac- tured by a method comprising steps of:

- providing a valve seat surface or a valve head surface as a substrate

- coating the substrate with a coating material by Plasma-Transferred-Arc welding, the coating material comprising solid lubricating particles and a matrix metal based on heat resistant ferrous or non-ferrous alloys. Advantageously the metal matrix is based on one of the following: cobalt or nickel or their alloys.

Naturally the coating material is in powder form suitable for deposition by plasma transferred arc welding.

According to an additional embodiment of the invention the matrix alloy powder and solid lubricant particles are mixed to form coating material powder before being inserted into a plasma torch.

According to an additional embodiment of the invention the matrix alloy powder and solid lubricant particles are provided as a mixed slurry and deposited on a substrate and then scanned with the plasma torch. One further embodiment of the invention is to use the said PTA coating prepared by the above method in a piston engine.

One further embodiment of the invention is to use the said PTA coating prepared by the above method in a piston engine of a marine vessel.

The present invention provides an improvement to drawbacks of the prior art. The present invention also provides many advantages over the known prior art, such as:

- it enables the use of new and cleaner fuels without compromising component reliability or fuel flexibility

- Lifetime increase for exhaust valves and valve seat surface or seat rings - Reduction of operational cost

- solid lubricants provide ability to work under high loads and higher thermal stability. BRIEF DESCRIPTION OF THE DRAWINGS

Next the invention will be described in greater detail with reference to exemplary embodiments in accordance with the accompanying drawings, in which: Figures 1 a and 1 b illustrate a principle of an exemplary arrangement of PTA coating on valve and valve seat according to an advantageous embodiment of the invention,

Figure 2 illustrates an exemplary structure of the method for manufacturing a PTA coating according to an advantageous embodiment of the invention.

DETAILED DESCRIPTION

Figure 1 a and 1 b illustrate a one exemplary internal combustion engine (1 ) structure, where is cylinder head (2) comprising valves (4) arranged to periodically enter into gas-sealing engagement with a valve seat. Cylinder sleeve (6) defines main combustion area (7) with piston and valves (4). Fig 1 b illustrates more detailed arrangement and the relation of valve (4) and valve seat (5). The valve (4) head and valve seat (5) comprise a PTA coating (8) with solid lubricants.

According to embodiments of the invention the PTA coating can be arranged on valve head or valve seat or both surfaces. The example of Fig 1 b shows the PTA coating (8) on both surfaces.

Fig 2 illustrates a basic principle of PTA process, where on a substrate (9) is deposited coating material (10) by plasma arc.

The PTA coating for use on valve seat or valve contacting surfaces of an inter- nal combustion engine, is prepared by Plasma-Transfer-Arc-welding (PTA). The coating material is composite material, which comprises a metal matrix and solid lubricating particles within the metal matrix. The valve is arranged to periodically enter into gas-sealing engagement with a valve seat, so as to enable the operation of the cylinder and/or internal combustion engine. The metal matrix advantageously is based on heat resistant ferrous or non- ferrous alloys. Advantageously the metal matrix is based on one of the following: nickel and its alloys or cobalt and its alloys. It is also possible that matrix is based on other hard metals. An example of an embodiment of the invention is that the solid lubricating particles are comprised of compounds of sulphides, sulphates or fluorides. Advantageously self-lubricating particles are made of at least one of the following: CaF2, BaF2, MoS2, WS2, FeS, MnS, h-BN (hexagonal boron nitride), CeF3.

An example of an embodiment of the invention is that the solid lubricating par- tides are made of at least one of such materials as sulphides, selenides and tellurides (chalcogenides) of molybdenum, tungsten, niobium, tantalum, titanium (eg. WS2, MoSe2, TaSe2, TiTe2), monochalcenides (GaS, GaSe, SnSe), chlorides of cadmium, cobalt, lead, cerium, zirconium (eg. CdCI2, CoCI2, PbCI2, CeF3, Pbl2) and also some borates (eg. Na2B4O7) or sulfates (Ag2SO4, CaSo4, BaSo4, SrSo4).

An example of an embodiment of the invention is that the coating further comprises particles of at least one of the following: metal boride, metal carbide, metal nitride, or metal carbonitride, to increase hardness and wear-resistance and to contribute to the lubricating action. Examples of preferred metal in the compound include tungsten, vanadium, titanium, tantalum, niobium, chromium, molybdenum, or mixtures of these metals. Advantageously the hardening particles are selected from the following: Tungsten carbide (WC), titanium carbide (TiC), chromium carbide (Cr3C2).

An example of an embodiment of the invention is that the valve of an internal combustion engine comprises the said PTA coating on a contact surface of the valve head. The valve comprises a body, a head, and a contact surface on a head to be adapted to periodically enter into gas-sealing engagement with a valve seat, so as to enable the operation of the cylinder and/or internal combustion engine. A further example of an embodiment of the invention is that the valve seat surface comprises the said PTA coating of the present invention.

A further example of an embodiment of the invention include an internal combustion engine, which comprises said PTA coating A further example of an embodiment of the invention includes a marine vessel, which comprises the said PTA coating on valve head or on valve seat surface of an internal combustion engine.

A further example of one embodiment of the invention, which is that the PTA coating is manufactured by a method comprising steps of:

- providing a valve seat surface or a valve head surface as a substrate

- coating the substrate with a coating material by Plasma-Transferred-Arc welding, the coating material comprising solid lubricating particles and a matrix metal based on of one of the following: cobalt or nickel or their alloys. The coating material being in powder form suitable for deposition by plasma transferred arc welding.

A further example of an additional embodiment of the invention is that the matrix alloy powder and solid lubricant particles are mixed to form coating material powder before being inserted into a plasma torch. A further example of an additional embodiment of the invention is that the matrix alloy powder and solid lubricant particles are provided as a mixed slurry and deposited on a substrate and then scanned with the plasma torch.

One further embodiment of the invention is to use the said PTA coating prepared by the above method in an internal combustion engine of a marine ves- sel.

The invention has been explained above with reference to the aforementioned embodiments, and several advantages of the invention have been demonstrated. It is clear that the invention is not only restricted to these embodiments, but comprises all possible embodiments within the spirit and scope of the inventive thought and the following patent claims.

Reference numbers:

1 Combustion engine

2 Cylinder head 6 Cylinder sleeve Main combustion area PTA coating substrate

coating material