Surface Finishing & Pre-treatment

Surface Finishing & Pre-treatment Masterplan (QLQ System)

Goal: Transform raw die-castings (Zinc) and stamped parts (Iron/SS) into smooth, mirror-like surfaces ready for high-end plating.

Scope: Deburring (Deflashing), Smoothing, Fine Polishing, and Ultrasonic Cleaning.

Sourcing Strategy:

• Equipment (Tumbling Machines): [Purchase Locally / Recommended Suppliers].

• Consumables (Media/Stones): [Purchase Locally] (Ceramic, Plastic, Porcelain, Corn Cob).

• Chemical Compounds (Grinding Fluids, Polishing Pastes): [QLQ Product] (Crucial for speed and brightness).

Phase I: Process Flow & Equipment Selection

1. Zinc Alloy (Zipper Pulls, Buckles)

• Characteristics: Soft metal. Easy to deform. High requirement for surface smoothness.

• Recommended Equipment: High-G Centrifugal Disc Finisher (for speed) or Vibratory Bowl Finisher (for delicate parts).

• The 3-Step Process:

  1. Coarse Grinding (Deflashing): Removing parting lines and burrs.

  2. Fine Polishing (Smoothing): Closing surface pores and creating a semi-bright finish.

  3. Ultrasonic Degreasing: Removing polishing wax/paste residue.

2. Iron & Stainless Steel (Buttons, Rivets)

• Characteristics: Hard metal. Burrs are sharp and difficult to remove. Iron rusts easily during tumbling.

• Recommended Equipment: Rotary Barrel Tumbler (aggressive) or Vibratory Bowl.

• The Process:

  1. Heavy Deburring: Aggressive cutting.

  2. Burnishing: Using steel media to peen the surface for brightness.

Phase II: Detailed Operational SOP

Step 1: Deburring / Cutting (Rough Finishing)

• Objective: Remove die-casting flash (Zinc) or stamping burrs (Iron/SS).

• Media Selection:

  • Zinc: Resin bond cones (Plastic Media) – Gentle cutting.

  • Iron/SS: Ceramic triangles (Fast cutting).

• Chemicals:

  • [QLQ Product] Heavy-Duty Grinding Compound: Accelerates cutting and keeps media clean.

• Operational Details:

  • Ratio: 3 parts Media : 1 part Workpieces (by volume). Never overload workpieces or they will hit each other.

  • Water Level: Just covering the load (Vibratory) or 50% level (Rotary).

  • Time: 2–4 hours (depending on burr size).

  • QC Check: Visual inspection under 10x magnification. No visible parting line allowed.

Step 2: Fine Polishing / Lustering

• Objective: Turn the matte surface into a glossy, smooth surface (Ra < 0.1µm).

• Media Selection:

  • Zinc: High-density Porcelain balls (White) or Zirconia beads.

  • Iron/SS: Stainless Steel balls (Satellite/Ball mix) for burnishing.

• Chemicals:

  • [QLQ Product] High-Gloss Polishing Liquid: Provides lubrication and chemical brightening.

  • [QLQ Product] Anti-Rust Compound (For Iron only): Mandatory to prevent flash rusting during the process.

• Operational Details:

  • Time: 30–60 minutes (Centrifugal) or 2–3 hours (Vibratory).

  • Critical Note: The water must flow through continuously (Flow-through system) to flush out dirt, OR be changed every cycle. Dirty water = Dull finish.

Step 3: Drying (Optional but Recommended)

• If parts are not plated immediately, they must be dried.

• Method: Heated Vibratory Dryer using Corn Cob or Walnut Shell grit.

• Chemicals: Add [QLQ Product] Polishing Paste to the corn cob to add a final "Jewelry Wipe" effect.

Step 4: Pre-Plating Cleaning (Ultrasonic)

• Note: Even after tumbling, parts have polishing residue and microscopic dust.

• Equipment: 3-Stage Ultrasonic Cleaning Machine.

• Chemicals:

  • [QLQ Product] Ultrasonic Wax Remover: Specifically dissolves the binders in polishing compounds.

• Process:

  • Tank 1: Ultrasonic Clean (60°C, 5-10 mins).

  • Tank 2: Ultrasonic Rinse (50°C).

  • Tank 3: Pure Water Spray.

Phase III: Quality Control & Inspection Standards

Before sending parts to the plating workshop, the "QC Gate" must check:

1. The "White Cloth" Test:

   • Wipe the part with a clean white cloth after ultrasonic cleaning.

   • Pass: No black or grey residue.

   • Fail: Residue indicates poor ultrasonic cleaning $\rightarrow$ Will cause peeling in plating.

2. The "Finger Nail" Test (Deflashing):

   • Run a fingernail across the parting line/edge.

   • Pass: Smooth transition.

   • Fail: Nail catches on a burr $\rightarrow$ Will cause "High Current Density Burning" (roughness) during plating.

3. Water Break Test (Degreasing):

   • Dip part in water and remove.

   • Pass: Water film covers the surface continuously for 30 seconds.

   • Fail: Water beads up like on a waxed car $\rightarrow$ Oil is still present.

Phase IV: Expert Maintenance Tips (Preventing Common Failures)

1. Media Grading:

   • Stones/Media wear down and get smaller. Small stones can get lodged/stuck in the holes of zipper pulls or buttons.

   • Action: Screen/Sieve the media weekly to remove undersized stones.

2. Compound Concentration:

   • Using too much [QLQ Product] Polishing Liquid is wasteful; using too little causes media glazing (stones stop cutting).

   • Action: Use an automatic dosing pump (e.g., 50ml every 15 mins).

3. Iron Rusting:

   • Iron buttons can rust inside the polishing barrel if the pH drops.

   • Action: Ensure [QLQ Product] Anti-Rust Compound keeps the solution pH > 9.0.