Vertical Top-Opening PVD Vacuum Coating Machine for Colored Stainless Steel Sheets: Design, Target Materials, and Process Gases

1. Introduction to the Vertical Top-Opening PVD Coating Machine

Physical Vapor Deposition (PVD) technology has revolutionized the surface treatment of stainless steel sheets, enabling the production of high-quality colored coatings with exceptional durability, corrosion resistance, and aesthetic appeal. Among various PVD equipment configurations, the vertical top-opening vacuum coating machine stands out for its efficiency in handling large stainless steel workpieces, especially in industrial-scale production. This specialized equipment features a unique top-opening structure that requires a two-story factory layout, with the upper floor serving as the access point for loading/unloading workpieces via an overhead crane system.

The core design centers on a vertical vacuum chamber made of high-grade SUS 304 stainless steel, ensuring structural integrity and corrosion resistance in harsh industrial environments. A typical chamber measures φ2600 × H4100 mm, equipped with a double-layer cooling water jacket to maintain optimal process temperatures and prevent thermal deformation of workpieces. The top-opening mechanism eliminates spatial constraints of side-opening designs, accommodating extra-large stainless steel sheets (up to 1300 × 3100 × 3 mm per batch) or irregularly shaped components (up to 1900 × 3700 × 50 mm). The machine’s interior features a hoisting-type rotary frame enabling both revolution and rotation of workpieces, ensuring uniform coating deposition. Combined with 36 arc source holes and 4 observation windows, this dual-motion system allows precise process control and real-time film formation monitoring.

2. Two-Story Factory Layout and Overhead Crane Integration

The vertical top-opening design mandates a two-story factory configuration to maximize operational efficiency and safety. The ground floor houses the PVD machine’s main body, including the vacuum chamber, pumping system, power supply units, and cooling infrastructure. The upper floor (typically 4.5 to 5 meters high) functions as a maintenance and loading platform for accessing and operating the vacuum chamber’s top cover. This layout leverages vertical space to overcome horizontal floor area limitations, suiting manufacturers with space constraints while facilitating large workpiece handling.

A critical component is the 5–10 ton overhead crane (beam crane) installed on the second floor, responsible for three key operations: opening/closing the vacuum chamber’s top cover, loading/unloading workpieces onto the rotary frame, and maintaining arc sources and internal components. Integrated with precision positioning technology, the crane ensures alignment between the workpiece carousel and vacuum chamber, minimizing contamination or damage risks. Safety features include anti-sway mechanisms, emergency stop controls, and load sensors to prevent overloading, complying with industrial safety standards.

The two-story layout optimizes workflow efficiency: while coating proceeds on the ground floor, the upper floor can prepare the next workpiece batch, reducing downtime. Additionally, the elevated platform provides safe, convenient access for maintenance tasks such as target replacement, chamber cleaning, and system inspections.

3. Target Materials for Colored Stainless Steel Coatings

Coating color is primarily determined by target material selection and its chemical reaction with process gases. Below is a detailed overview of commonly used targets and their corresponding colors, mechanisms, and applications:

3.1 Titanium (Ti) Targets

Titanium targets offer versatile color options through reactions with nitrogen, oxygen, and carbon-containing gases:

• Natural Stainless Steel Finish: Achieved via non-reactive sputtering in pure argon. A 50–100 nm thin titanium film preserves the substrate’s natural appearance while enhancing corrosion resistance and surface smoothness, suitable for kitchen appliances and architectural handrails.
• Gold: Formed by reactive sputtering in a nitrogen-rich atmosphere (N₂:Ar ≈ 3:7), producing Titanium Nitride (TiN). TiN’s electronic band structure selectively reflects yellow light, yielding a vivid golden hue with a hardness of up to 2000 HV. Ideal for decorative and functional applications like jewelry and elevator panels.
• Rose Gold: Created by adding methane (CH₄) to the nitrogen-argon mixture (N₂:CH₄:Ar ≈ 2:1:7), forming Titanium Carbonitride (TiCN). Carbon content regulates hue—higher concentrations deepen the rose shade. TiCN offers superior wear resistance for high-traffic surfaces.
• Coffee Brown: Optimized TiCN process with a higher carbon-to-nitrogen ratio (N₂:CH₄:Ar ≈ 1:2:7) and 200–300 nm coating thickness. Increased carbon incorporation creates a warm coffee brown hue (from light tan to deep espresso), popular in high-end furniture and automotive interior trim.
• Black: Produced in a mixed atmosphere of nitrogen, methane, and oxygen (N₂:CH₄:O₂:Ar ≈ 2:3:1:14), forming Titanium Carbonitride Oxide (TiCNO). This dense, amorphous coating absorbs over 95% of visible light, delivering a matte black finish with exceptional scratch resistance for consumer electronics.

3.2 Zirconium (Zr) Targets

Zirconium targets excel in durable, scratch-resistant coatings:

• Gold: Zirconium Nitride (ZrN) formed by sputtering in nitrogen (N₂:Ar ≈ 2:8) offers a warmer, softer golden shade than TiN. Superior corrosion resistance suits outdoor applications like building facades and marine hardware.
• Black: Zirconium Carbonitride (ZrCN) produced in a nitrogen-methane atmosphere (N₂:CH₄:Ar ≈ 1:3:16) delivers a deep jet-black finish. High carbon content (30–40 atomic%) enhances hardness (up to 2200 HV) for smartphone frames and industrial components.

3.3 Chromium (Cr) Targets

Chromium targets produce stable neutral and earthy tones:

• Blue: Chromium Oxide (Cr₂O₃) formed by reactive sputtering in oxygen (O₂:Ar ≈ 3:7) with 150–200 nm thickness. Light interference creates a vibrant blue hue—thinner films yield sky blue, thicker layers deep navy. Excellent UV resistance suits outdoor signage and automotive trim.
• Black: Chromium Nitride Carbide (CrCN) from a nitrogen-methane mixture (N₂:CH₄:Ar ≈ 2:2:16) offers a matte black finish with high chemical resistance, ideal for food processing equipment and bathroom fixtures.

3.4 Stainless Steel Targets

Cost-effective options for specific colors:

• Natural Stainless Steel Finish: Non-reactive sputtering in pure argon produces a coating matching the substrate composition, preserving the natural look for large-scale architectural projects.
• Blue: Reactive sputtering in nitrogen (N₂:Ar ≈ 4:6) forms Stainless Steel Nitride (FeCrN), delivering a deep blue hue with exceptional adhesion and color stability for commercial building facades.

4. Process Gases in PVD Coating

PVD processes rely on inert gases for sputtering and reactive gases for compound formation. Precise control of gas purity, flow rate, and partial pressure ensures consistent color and performance:

4.1 Inert Gases: Argon (Ar)

Argon (99.999%+ purity) serves as the primary sputtering medium, with its atomic weight (39.95 g/mol) ideal for dislodging target atoms. Flow rates range from 50–200 sccm, with chamber pressure maintained at 10⁻² to 10 Pa. For natural stainless steel finishes, pure argon (100–150 sccm) is used.

4.2 Reactive Gases

• Nitrogen (N₂): Forms nitride coatings (TiN, ZrN, FeCrN) with gold, rose gold, or blue hues. Flow rates: 30–70 sccm; purity ≥ 99.998%.
• Oxygen (O₂): Produces oxide coatings (TiO₂, Cr₂O₃) with blue or iridescent colors. Flow rates: 20–60 sccm; purity ≥ 99.998%.
• Carbon-Containing Gases: Methane (CH₄, 10–50 sccm) and acetylene (C₂H₂) introduce carbon for carbonitride coatings (TiCN, ZrCN). Methane offers stability; acetylene deepens black tones.

4.3 Gas Control Systems

Precision gas control systems (mass flow controllers, pressure transducers) integrate with PLC units, enabling storage of color-specific recipes (up to 50 profiles) for one-touch operation. Purification filters remove moisture, oil, and particulates, ensuring consistent process conditions.

5. Key Technical Specifications and Operational Advantages

• Workpiece Capacity: Up to 3 sheets (1300 × 3100 × 3 mm) per batch; dual fixture rotary frame.
• Vacuum Performance: Ultimate pressure 5.0 × 10⁻⁴ Pa; leak rate 0⁻³ Pa·L/s.
• Coating Cycle: 3–6 hours per batch (3 hours for natural finish; 5–6 hours for brown/black).
• Color Precision: Repeatability ΔE 0 (CIE Lab); real-time optical monitoring.
• Automation: Manual/semi-automatic/fully automatic modes; touchscreen interface.
• Energy Efficiency: 15–20% lower consumption than conventional side-opening machines.

6. Applications and Industry Impact

Widely used across industries:

• Architecture: Facades, curtain walls, door/window frames (gold, blue, natural finish).
• Home Appliances: Refrigerator panels, kitchen hardware (natural finish, black, rose gold).
• Automotive: Interior/exterior trim, wheel rims (black, coffee brown, rose gold).
• Consumer Electronics: Smartphone/laptop casings (black, blue, rose gold).
• Furniture: Cabinet handles, lighting fixtures (coffee brown, gold, blue).

The machine supports sustainable manufacturing with hexavalent chromium-free coatings, enhancing product differentiation through versatile color options.