Plasma Spray System Product

Overview

Plasma spray is the highest-temperature thermal coating method, generating a jet of ionized argon or nitrogen gas at 15000 K that can melt virtually any material—metals, ceramics, and composites alike. Unlike flame spray or arc spray, which rely on fuel combustion or electric arc between consumables, plasma spray uses a transferred arc: a DC arc struck between a tungsten cathode (inside the torch) and a copper anode nozzle, ionizing the plasma gas that flows through the arc zone. The result is a dense, energetic plasma stream exiting at supersonic velocity (Mach 4+), capable of melting and accelerating even refractory ceramic powders with minimal vaporization or decomposition. Plasma spray is the first choice for aerospace thermal barriers, biomedical coatings, and extreme-wear repair where coating integrity and density matter most.

The Torch Assembly is the core technology. A tungsten rod cathode (3.2 mm diameter) is held at high negative potential within the Torch Body. Argon or nitrogen gas enters through the Primary Gas Inlet at 2–5 bar, flowing around the cathode. When the Power Supply applies high voltage (80 V strike voltage), an arc jumps from the cathode to the Copper Anode Nozzle—a copper electrode with a 6 mm constrictor bore. This arc ionizes the gas, converting it to plasma (a fourth state of matter, with free electrons and ions). The flowing gas, already ionized by the arc, becomes thermally and electrically conductive; the arc current (60–100 A) flows through the plasma column, heating it to 15000 K.

As plasma exits the 6 mm nozzle bore, isentropic expansion accelerates it to Mach 4+ velocity (over 2000 m/s). The plasma jet is dense with energy; it can melt ceramic powders, metals, and even tungsten and rhenium without vaporizing or decomposing them. The Powder Feeder injects feedstock into the carrier gas stream, which transports powder particles into the plasma jet via the Injection Probe. Powder particles melt in milliseconds and are accelerated outward in the plasma slipstream, arriving at the workpiece surface at 200–400 m/s as molten spheres that solidify on impact.

The Gas Console independently regulates two gas flows: primary plasma gas (flowing through the torch) and secondary carrier gas (transporting powder). The Primary Regulator maintains 2–5 bar primary gas, while the Secondary Regulator maintains 1–3 bar carrier gas. Two Primary Flowmeter and Carrier Flowmeter rotameters display real-time flow rates so the operator can set repeatable spray conditions. Solenoid valves—Primary Gas Solenoid and Secondary Solenoid—shut off both flows on command, allowing instant plasma extinction.

The Power Supply maintains a stable, constant-current arc at 60–100 A. A 600 V three-phase mains input feeds the Power Transformer (10 kVA, 600→80 V step-down). The Rectifier Module full-wave bridge converts secondary AC to DC. The Filter Inductor (100 mH) and Snubber Capacitor (1500 µF) smooth ripple to <3%. An Arc Stabilizer Circuit feedback loop compares torch voltage (via a Arc Voltage Monitor sensor) to a reference setpoint and adjusts supply impedance to hold current within ±5%. This constant-current regulation is critical: as plasma temperature and velocity are directly proportional to arc current, stable current ensures repeatable coating properties.

The Powder Feeder delivers powder at 10–30 g/min into the carrier gas stream. A gravity-fed Powder Hopper (5 L capacity) supplies powder to a rotating Metering Wheel, a grooved disk feeder calibrated to 20 g/min at full speed. A small Powder Feeder Motor (24 V DC, 100 W) drives the wheel at 0–500 rpm via PWM control from the Control Unit. Powder drops onto the wheel grooves, is scooped up, and deposited into a carrier gas inlet that feeds powder into the torch. A Flow Damper accumulator removes pulsation, ensuring smooth powder delivery. The copper Injection Probe (inserted axially into the torch) directs powder particles into the hottest part of the plasma jet for efficient melting.

Thermal management is essential because the torch dissipates 15–20 kW of arc power. The Water Jacket surrounding the torch body, along with the Copper Anode Nozzle (which takes most of the arc strike), must be continuously cooled. The Cooling Unit circulates demineralized water at 20–30 L/min through the torch and power supply transformer. A Water Chiller (8 kW refrigerated unit) maintains inlet water at 20°C, and a Temperature Controller proportional thermostat valve blends chiller output with return water to hold temperature within ±2°C. Without adequate cooling, the tungsten cathode erodes rapidly and the copper nozzle can melt or oxidize, raising maintenance costs and reducing run time.

The Control Unit orchestrates the entire system. An Microcontroller executes startup logic: verify cooling water is flowing, establish the plasma jet by energizing the Primary Gas Solenoid and striking the arc via the power supply, then ramp the Powder PWM Control motor to steady-state powder feed rate. The MCU monitors arc current via a Current Sensor hall-effect device and arc voltage via the Arc Voltage Monitor divider. If arc voltage diverges from the controlled band (indicating arc loss or nozzle erosion), the system shuts down to prevent unstable spray. A Bare PCB main control board routes all signals and executes safety logic: no powder can be injected until the arc is stable, and no arc can be maintained if cooling water stops flowing.

All utilities connect via the Hose & Cable Bundle. Power comes from two 25 mm² Power Cable welding cables. Primary and secondary gases flow through color-coded stainless Primary Gas Hose and Carrier Gas Hose hoses. Cooling water enters and exits via Water Inlet Hose and Water Return Hose quick-disconnects. A shielded Control Harness carries feedback and PWM command signals.

In aerospace and power generation, plasma spray coats high-temperature components with ceramic thermal barriers (YSZ, CaSZ) 0.2–0.5 mm thick. These coatings reduce blade temperature by 200–400°C, allowing higher turbine inlet temperatures and greater efficiency. Biomedical manufacturers use plasma spray to apply hydroxyapatite coatings on titanium implants, improving osseointegration. Industrial repair shops apply tungsten-carbide and cobalt-nickel-chromium dense coatings to pump seals, turbine rotors, and critical wear surfaces. The high density and strong substrate bond make plasma spray coatings superior to flame or arc spray in high-stress, high-temperature environments.

How it works

1. Mains power (600 V 3-phase) energizes the Power Supply: the Power Transformer steps down to 80 V secondary, the Rectifier Module converts to DC, and the Filter Inductor and Snubber Capacitor filter ripple.
2. The operator opens the Primary Regulator and Secondary Regulator, adjusting primary and secondary gas pressures to 3 bar and 2 bar respectively via manual hand wheels.
3. The Control Unit MCU verifies cooling water is flowing (via flow sensor feedback), then energizes the Primary Gas Solenoid to send ionization gas into the Torch Assembly.
4. Gas flows around the tungsten Tungsten Cathode and enters the Copper Anode Nozzle arc chamber. The power supply applies 80 V strike voltage; an arc jumps from cathode to anode, ionizing the argon gas into plasma at 15000 K.
5. The arc is immediately transferred to a transferred-arc mode: the Arc Stabilizer Circuit feedback loop compares Arc Voltage Monitor output to a reference, adjusting supply current to maintain 60–100 A constant current.
6. Ionized plasma gas (now electrically conductive) flows through the Copper Anode Nozzle arc column and exits as a Mach 4+ jet at 2000+ m/s, reaching 8000 K at the nozzle exit (cooler than core but still molten).
7. Meanwhile, the Powder Feeder Motor (controlled by Powder PWM Control PWM) spins the Metering Wheel feeder. Powder drops from the Powder Hopper onto the spinning grooves.
8. The Secondary Solenoid energizes, sending carrier gas (1–3 bar) through the Carrier Gas Hose into the Flow Damper and then into the powder feeder inlet. Scooped powder particles are picked up and transported into the carrier gas stream.
9. Powder enters the Injection Probe, a copper rod inserted axially into the torch, and is injected into the hottest central region of the plasma jet.
10. Powder particles melt instantly in the 15000 K plasma and are accelerated outward, traveling 80–150 mm through the air to the workpiece surface at 200–400 m/s.
11. Molten droplets solidify on impact, forming a dense, mechanically and metallurgically bonded coating (much stronger than flame or arc spray coatings due to the ultraviolet melting and solid-state diffusion).
12. Throughout operation, the Cooling Unit pumps 20–30 L/min demineralized water through the Water Jacket around the torch and through the Power Transformer, maintaining inlet temperature at 20°C via Temperature Controller.
13. The Current Sensor continuously monitors arc current; if it drifts >10% from setpoint, the MCU adjusts supply impedance to re-stabilize. The Arc Voltage Monitor sensor monitors voltage; if it diverges from controlled band, the MCU shuts down (indicating nozzle erosion or arc loss).
14. Releasing the operator trigger signal de-energizes the Primary Gas Solenoid and Secondary Solenoid, stopping gas flow and plasma formation within 50 ms.