Comprehensive Process of Removing Flash and Burrs from Zinc Alloy Products with Liquid Nitrogen Flash Machine
In the processing of zinc alloy die-castings, the precise removal of flash and burrs is crucial for enhancing product precision and appearance quality. Liquid nitrogen cryogenic deflashing technology has become an innovative solution for metal burr treatment, leveraging its high efficiency and uniformity. This article details the standard process of using a Liquid nitrogen flash machine to remove flash from zinc alloy products, combined with Sand blasting machine and small sand blasting machine for (refined) processing.
I. Pretreatment: Dual Calibration of Workpieces and Equipment
1. Initial Inspection and Fixing of Zinc Alloy Workpieces
Flash Positioning: Identify flash distribution via 3D scanning (precision ±0.05mm), commonly found on parting surfaces, gate areas, and thread hole edges. Record burr thickness (typically 0.1-0.5mm) and hardness (zinc alloy HV 80-120).
Fixture Design: Use adjustable aluminum alloy fixtures to secure workpieces. For complex structures (e.g., bathroom handles, electronic housings), design hollow supports to ensure flash is exposed without obstruction, while avoiding adhesion risks between metal and fixtures at low temperatures.
2. Parameter Setting for Liquid nitrogen flash machine
Cryogenic Embrittlement Threshold: Set equipment temperature to -180℃ to -196℃ based on zinc alloy composition (e.g., Zamak 3 alloy), with holding time adjusted to 15-25 minutes. This induces micro-cracks (width ≥5μm) in flash areas due to thermal contraction, while maintaining mechanical properties of the main workpiece.
Spray Media Preparation: Use angular alumina sand with 0.2-0.4mm particle size (hardness HV 1800-2000), pre-screened by magnetic separation to remove iron impurities and prevent surface scratches during sandblasting.
II. Liquid Nitrogen Cryogenic Deflashing: Flash Embrittlement and Batch Removal
1. Deep Cryogenic Embrittlement Stage
Gradient Cooling: After starting the Liquid nitrogen flash machine, pre-cool workpieces at -80℃ for 5 minutes, then gradually cool to -196℃ to avoid internal stress concentration from sudden temperature changes. Control liquid nitrogen atomization particle diameter at 50-100μm to ensure uniform coverage of flash surfaces.
Temperature Field Uniformity: Monitor via infrared thermography to ensure surface temperature difference ≤3℃, particularly focusing on heat dissipation blind spots like grooves and corners. Add auxiliary liquid nitrogen nozzles if necessary to ensure consistent flash embrittlement.
2. High-Speed Sandblasting for Burr Removal
Kinetic Energy Matching: After freezing, the equipment drives alumina sand with 0.6-1.0MPa compressed air at 100-150m/s. Use "angled spraying" (30°-45°) for thin flash below 0.3mm, and vertical spraying with reciprocating motion for thick flash (>0.5mm), controlling single-pass removal at 0.1-0.2mm.
Automated Trajectory Planning: For complex curved workpieces (e.g., zinc alloy gears), generate spiral spraying paths via CNC system to ensure no flash residue in key areas like tooth roots and tips, while avoiding over-blasting that could reduce tooth profile accuracy (control tolerance ±0.02mm).
III. Sandblasting Finishing: Surface Quality Optimization
1. Coarse Sandblasting with Sand blasting machine
Batch Processing: For small-to-medium zinc alloy products (e.g., zipper heads, lock accessories), use a roller-type Sand blasting machine. Load workpieces with 0.3-0.5mm glass beads (roundness ≥95%) and perform rolling sandblasting at 40-60rpm for 8-12 minutes to remove residual micro-flash after cryogenic deflashing, reducing surface roughness from Ra 12.5μm to 3.2μm.
Process Parameters: Sandblasting pressure 0.4-0.6MPa, spraying distance 15-20cm. Adjust roller speed via frequency converter to ensure uniform sand exposure on all workpiece surfaces.
2. Fine Trimming with small sand blasting machine
Local Micro-Processing: For high-precision zinc alloy parts (e.g., aerospace connectors), use a small sand blasting machine for targeted finishing. Select 0.05-0.1mm silicon carbide sand and perform secondary sandblasting on hidden areas like thread 孔口 (hole openings) and countersunk grooves under a microscope (5-10x) to remove 0.01mm-level burrs unreachable by cryogenic deflashing.
Edge Protection: Protect sharp edges with programmable shielding devices (e.g., rubber baffles) to prevent excessive rounding from sandblasting (control R-angle increment ≤0.03mm).
IV. Post-Processing and Quality Verification
1. Cleaning and Rust Prevention
Ultrasonic Degreasing: Place workpieces in an ultrasonic tank with weak alkaline detergent (frequency 28kHz) for 5-8 minutes to remove surface oil and sand particles, then rinse 3 times with deionized water to avoid residual sand affecting subsequent electroplating.
Rust Prevention Treatment: Spray dehydrating rust-proof oil (film thickness 2-5μm) immediately after drying. For electroplated workpieces, verify rust resistance via humidity test (40℃/95%RH, 24 hours), requiring no white rust formation.
2. Full-Dimension Inspection
Visual Inspection: Under 5000lux lighting, check flash removal via visual inspection system (resolution 0.01mm), requiring no visible burrs on sealing and mating surfaces, and non-functional surface burr height ≤0.05mm.
Precision Verification: Use a coordinate measuring machine (CMM) to inspect key dimensions, such as the flatness of zinc alloy valve sealing surfaces (tolerance ±0.03mm) and thread pitch diameter (tolerance ±0.015mm), ensuring no dimensional out-of-tolerance from deflashing.
V. Process Advantages and Safety Specifications
Efficiency Improvement: A single Liquid nitrogen flash machine can process 200-500 zinc alloy workpieces per hour, increasing efficiency by 8-10 times compared to traditional manual filing, with 99%+ consistency in burr removal.
Cost Control: Liquid nitrogen consumption is about 1-2L/piece, and alumina sand can be reused 30-50 times. Combined with local finishing by small sand blasting machine, comprehensive costs are 40% lower than mechanical polishing.
Safe Operation: Wear low-temperature gloves (resistant to -200℃) and dust masks. Equipment must have oxygen concentration monitoring (alarm threshold 19.5%) to prevent asphyxiation from liquid nitrogen leakage. Ensure effective door interlocks during sandblasting.
Conclusion
From deep cryogenic embrittlement to sandblasting finishing, the zinc alloy flash treatment system composed of Liquid nitrogen flash machine, Sand blasting machine, and small sand blasting machine achieves automated and precise removal of metal burrs. This process ensures dual improvement in workpiece dimensional accuracy and surface quality through three-stage treatment: low-temperature induced flash embrittlement, kinetic energy spraying for precise removal, and sandblasting for surface optimization. It provides a reliable technical solution for precision processing in automotive components, high-end hardware, and other fields.
