Valve stem spraying

The valve stem is an important component of a valve, used for transmission. It is connected to the actuator or handle, directly driving the valve core to move or rotate underneath it, thereby achieving the opening and closing or adjustment of the valve.

The valve stem is not only a moving and load-bearing component, but also a sealing element during the opening and closing process of the valve. Simultaneously subjected to the impact and corrosion of the medium, it also generates friction with the packing. Therefore, when selecting valve stem materials, it is necessary to ensure that they have sufficient strength, good impact toughness, scratch resistance, and corrosion resistance at the specified temperature. The valve stem is a vulnerable component, and when selecting, attention should be paid to the machinability and heat treatment performance of the material.

The valve stem spraying technology is mainly based on supersonic flame spraying (HVOF). Its technical principle is to accelerate the powder material into a high-speed flame flow to 1400-1800m/s, melt or semi melt it at a high temperature of 3000 ℃, and then impact the substrate surface at high speed to form a coating with high bonding strength and density. This process has three major technical advantages: the coating bonding strength can reach over 70MPa, and the wear resistance exceeds that of electroplated hard chromium layers; The range of sprayable materials is extensive, covering nickel based alloys, carbide ceramics, aluminum oxide titanium oxide composite materials, etc; Strong process adaptability, capable of achieving surface strengthening of new parts and repairing worn workpieces.

The typical process flow includes five key steps

Pre treatment: Sandblasting or chemical cleaning is used to remove oil stains and oxide layers on the surface of the valve stem, with a roughness controlled at Ra3.2-6.3 μ m to enhance coating adhesion;

Spraying construction: Use a supersonic spray gun to spray multiple layers under argon protection, with a single layer thickness controlled between 0.08-0.12mm and an interlayer temperature not exceeding 150 ℃;

Sealing treatment: Epoxy resin or nickel based alloy is used for penetration sealing of microporous coatings to prevent medium penetration;

Precision machining: The coating is processed to a dimensional tolerance of ± 0.01mm and a surface roughness of Ra0.4 μ m using a CNC grinder;

Quality inspection: Use a scratch tester to test the critical load of the coating (≥ 40N), and conduct a 99.9999% air tightness test.

Matching material system with application scenarios

Wear resistant condition: tungsten carbide (WC) based coating, with a lifespan 5-8 times longer than traditional chrome plating process in particulate media, suitable for oil and gas extraction valves;

Corrosion environment: Using aluminum oxide titanium oxide (Al ₂ O ∝ - TiO ₂) composite coating, the corrosion resistance in acidic and alkaline media is more than 20 times that of 316 stainless steel, widely used in chemical process valves;

High temperature scenario: Zirconia (ZrO ₂) thermal barrier coating can reduce the substrate temperature by 100-150 ℃, suitable for steam valves;

Economic solution: For conventional working conditions, nickel based alloy (NiCrBSi) coating can be used, which costs only 60% of ceramic coating and can still increase the service life by three times.

Breakthroughs have been made in material substitution technology: A certain valve enterprise has achieved large-scale application with an annual output of 100000 pieces by spraying a 0.3mm thick stainless steel coating on the surface of ordinary carbon steel valve stems, replacing integral stainless steel parts and reducing single piece costs by 42%.