Piston spraying

The piston rod spraying technology is based on thermal spraying, which melts metal, ceramic or composite materials through a high-temperature heat source and sprays them at high speed onto the surface of the piston to form a functional coating.

Technical Principle

Thermal spraying mechanism: Using plasma spraying or supersonic spraying to heat the sprayed material (such as molybdenum, chromium based alloys, alumina ceramics) to a molten or semi molten state, and impacting the piston surface at a speed of 300-800m/s to form a layered stacked coating.

Coating characteristics: The bonding strength between the coating and the substrate can reach 40-70MPa, and the porosity can be controlled below 2% -5%, significantly improving the wear resistance, corrosion resistance, and high temperature resistance of the piston.

Typical process flow

Preprocessing:

Sandblasting roughening: White corundum sand (particle size 0.75-1.00mm) is used to sandblast the surface of the piston under a pressure of 0.5MPa, with a roughness of Ra3.2-6.3 μ m.

Cleaning and decontamination: Remove oil stains and oxide layers by degreasing solvents or air burning (150 ℃ × 120min).

Spray coating construction:

Equipment parameters: Use PQ-77A plasma spray gun, nozzle angle of 50 °, main gas flow rate of 2m ³/h, powder feeding gas flow rate of 0.6-0.8m ³/h.

Process control: Spray angle of 60 ° -70 °, distance of 100-150mm, layered spraying (single-layer thickness of 0.08-0.12mm), substrate temperature controlled below 180 ℃.

Post processing:

Precision machining: The coating is ground using a CNC grinder, with a dimensional accuracy of ± 0.01mm and a surface roughness of Ra0.4 μ m.

Sealing treatment: Penetrating epoxy resin or nickel based alloy into microporous coatings to prevent medium penetration.

Matching material selection with application scenarios

The spraying material for the piston rod needs to be accurately selected according to the working conditions (temperature, medium, load). The typical material system and application scenarios are as follows:

1. Metal materials

Molybdenum (Mo): purity ≥ 99.95%, spray coating thickness 0.25mm, suitable for high-speed internal combustion engine piston rings, friction coefficient as low as 0.05-0.09, wear resistance twice that of chrome plating.

Chromium based alloy: containing elements such as Cr, Fe, Ni, etc., with better wear resistance than chrome plating under boundary lubrication conditions, suitable for medium speed diesel engine pistons.

2. Ceramic materials

Aluminum oxide/titanium dioxide (Al ₂ O ∝ - TiO ₂): Hardness HV1500, excellent acid and alkali corrosion resistance, suitable for chemical pump pistons and valve cores.

Tungsten carbide (WC) based ceramic: porosity of 1% -3%, wear resistance three times that of chromium based alloys, but with higher cost, mainly used for the top surface of engine pistons.

3. Composite materials

Nickel based alloy (Ni-Cr-B-Si): containing carbide and boride hard phases, with a heat resistance of up to 700 ℃, suitable for exhaust valve seat rings and turbocharger pistons.