Oil-Dripping Process in Jewelry Factories

Oil-Dripping Process in Jewelry Factories: From Technical Details to Factory Selection Guide

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Chapter 1 Overview of the Oil-Dripping Process: The Essential Unity of Low-Temperature Enamel, Baking Paint and Oil-Dripping
In the field of jewelry processing, the oil-dripping process is given a variety of names – “low-temperature enamel”, “resin baking paint”, “UV drip glue”, etc., but its core process logic is highly consistent: using special coatings to fill color blocks on the metal substrate, and forming a smooth and bright decorative layer after curing. This technology is widely used in fashion jewelry, light luxury accessories and cultural and creative products, especially suitable for creating cartoon patterns, gradient colors or imitation enamel textures.

1.1 Industry background of differences in process names
- Low-temperature enamel: borrows the coloring concept of traditional high-temperature enamel (Cloisonné), but is named because it uses resin materials that cure below 200℃;
- Baking varnish: emphasizes that the curing process requires heating (80-150℃), commonly used in metal badges and hangtags;
- Oil dripping: named because of the action of dripping liquid resin with a syringe during operation, now a common term in the industry.

Essential commonality: All are resin-based coatings + curing molding technology, the only difference is the formula system (epoxy resin/polyurethane/UV glue) and curing method (thermal curing/UV light curing).

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Chapter 2 Analysis of the entire process of oil dripping process
The oil dripping process seems simple, but it actually contains more than 20 key control points. The following is a detailed explanation of the operation steps using the standard process of an export-grade jewelry factory as an example:

2.1 Substrate pretreatment
- Metal surface milling: Use a CNC machine to process a groove with a depth of 0.3-0.5mm in the oil dripping area (Figure 1). The groove wall needs to maintain an inclination angle of 85-90° to form a natural retaining wall;
- Sandblasting: Use 120-180 mesh diamond sand to roughen the bottom of the groove to increase the adhesion of the paint (Ra value is controlled at 3.2-6.3μm);
- Degreasing and cleaning: Use an ultrasonic cleaner to pass through alkaline degreasing agent → pure water → isopropyl alcohol in turn to ensure that there are no fingerprints or oxide layers on the surface.

- Coloring process:
1. Weigh the color paste according to the Pantone C color card (Pantone Color Bridge Coated), with an error of ≤0.1g;
2. Use a planetary mixer to mix at a low speed of 500rpm for 10 minutes to avoid bubble generation;
3. Vacuum degassing treatment (-0.08MPa, 15 minutes) to ensure that the coating has no pores.

2.3 Drip and leveling
- Precision drip: Use a 0.3mm diameter dispensing needle, control the amount of glue at 0.05MPa air pressure, and fill to 90% of the groove height (reserve expansion space);
- Leveling control:
- Let the coating stand for 5 minutes to level naturally;
- If necessary, use a hot air gun at 50℃ to assist in defoaming (20cm away from the workpiece, sweep and blow for 3 seconds).

2.4 Curing and post-treatment
- Step curing (taking epoxy resin as an example):
- First stage: 40℃/1h, to make the resin initially gel;
- Second stage: 80℃/2h, completely cross-linked and hardened;
- Surface finishing:
- Manually polish the overflow with 4000 mesh sandpaper;
- Spray a nano-level transparent protective layer (thickness 5-8μm).

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Chapter 3 Five core difficulties and solutions of oil dripping process

3.1 Boundary control: How to achieve 0.1mm level precise margin
- Physical retaining wall method: Carve a 0.1mm raised edge line on the periphery of the groove (Figure 2), which is suitable for regular geometric figures;
- Surface tension method: Adjust the surface tension of the coating to 35-40mN/m, so that it automatically shrinks into a rounded corner at the edge of the groove;
- Laser cofferdam: Use ultraviolet laser to generate a micro-oxidation layer on the metal surface to form an invisible boundary.

3.2 Color difference control: from Pantone color card to mass production consistency
- Spectrum analyzer assisted color matching: control the difference between the color value (L*a*b*) of the cured coating and the standard color card within ΔE<1.5;
- Ambient light standardization: match the color in a light box with D65 light source (color temperature 6500K) to avoid color deviation on the mobile phone screen;
- Batch management: keep a standard sample block for every 500g of coating as a colorimetric benchmark for subsequent production.

3.3 Bubble elimination: prevention strategy for micron-level defects
- Vacuum drip system: complete glue injection under -0.05MPa environment;
- Centrifugal leveling technology: place the workpiece on a 200rpm rotating platform and use centrifugal force to drive out bubbles;
- Additive application: add 0.1%-0.3% BYK-A530 defoamer.

3.4 Adhesion improvement: Lifetime warranty through chemical bonding
- Primer treatment: Spray silane coupling agent (such as KH-550) to form Si-O-Me chemical bonds between metal and resin;
- Plasma activation: Treat the metal surface with atmospheric plasma to generate active hydroxyl groups (-OH);
- Thermal expansion matching: Select a resin with a CTE (thermal expansion coefficient) difference of <15% with the metal substrate (such as aluminum with epoxy resin with CTE=23ppm/℃).

3.5 Efficiency optimization: High-mix production mode
- Modular glue dripping tooling: Quickly replaceable positioning fixtures, switching styles in <5 minutes;
- UV-LED curing chain: Compress the traditional 2-hour curing process to 30 seconds;
- AI visual quality inspection: Use convolutional neural network (CNN) to automatically identify defects such as overflow and bubbles.

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Chapter 4 How to choose a professional oil-drip jewelry factory: 6 evaluation dimensions

4.1 Technical capability certification
- Required qualifications: ISO 9001 quality management system, RoHS environmental certification;
- Process verification: The factory is required to provide a color difference report of ΔE≤1.5 and adhesion cross-cut test results (ASTM D3359 standard).

4.3 Sample confirmation process
- Triple confirmation mechanism:
1. Initial sample: 3D printing model to verify structural feasibility;
2. Engineering sample: actual metal substrate to test process parameters;
3. Mass production sample: full process trial production to confirm consistency.

4.4 Mass production control system
- SPC statistical process control: key parameters such as coating thickness and color difference need to be monitored in real time CPK≥1.33;
- Traceability system: each batch of products corresponds to a complete process record (temperature/humidity/operator).

4.5 Industry reputation and cases
- Preferred choice: factories with OEM experience for brands such as Swarovski and Pandora;
- On-site factory inspection: focus on the dust-free workshop level (class 100000 or below recommended) and wastewater treatment facilities.

4.6 Cost and delivery balance
- Reasonable quotation range (reference 2024 market price):
| Process complexity | Unit price (RMB/piece) |
|—————-|——————–|
| Single color flat coating | 0.8-1.2 |
| Multi-color gradient | 2.5-4.0 |
| Enamel-like three-dimensional effect | 6.0-8.0 |

- Delivery red line: Prototyping cycle ≤ 7 days, daily production capacity of mass production orders ≥ 5,000 pieces.

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Chapter 5 Market prospects and technological innovation direction
With the application of new materials such as 3D drip glue, thermochromic pigment, fluorescent resin, etc., the oil dripping process is evolving from flat decoration to interactive smart jewelry. For example:
- Tactile feedback coating: pressure-sensitive resin can change color as the wearer touches it;
- Self-repairing coating: microcapsule technology allows scratches to be automatically repaired at 40°C;
- Environmentally friendly bioresin: a biodegradable formula made from castor oil and rosin.
The success of the oil-drip process lies in the ultimate control of “between millimeters” – 0.1mm boundary accuracy, ΔE<1.5 color tolerance, and nanometer surface flatness. Choosing a professional factory is not only about purchasing processing services, but also about introducing a proven “micron-level quality control philosophy”. When you hold that colorful jewelry in your hand, please remember: behind every perfect arc is a symphony of material science, precision machinery and craftsman experience.