Sealing And Cleanliness Assurance For One Closed Flat End Tubes

Meta: Sealing and cleanliness assurance for one closed flat end tubes, covering closed end design, nitrogen purge, acid-alkali cleaning, drying and two-end sealing standard.

1. Core Industry Pain Points

The one closed flat end tubes used as refrigerant capillary are easily polluted by internal contamination, causing hidden blockage failure. Many factories wipe inner wall with woven cloth, leaving fiber residue inside the lumen. Machining oil, metal chips and dust from swaging and coiling accumulate and are not fully removed. After cleaning, tubes are exposed in open workshop and absorb moisture and floating particles again. The closed end design reduces one pollution entry, but the open end still lets in contaminants during turnover. Improper sealing with mismatched rubber plugs leads to plug drop-off and secondary pollution. Residual water vapor inside the tube reacts with refrigerant and produces corrosive acid, eroding stainless steel inner wall. These defects pass visual inspection because they are invisible from outside, and surface as delayed system failure.

2. Fundamental Working Principle

The cleaning and sealing principle of one closed flat end tubes is based on three-stage purification and isolation. Nitrogen purge uses high-speed dry nitrogen to carry loose particles out of the lumen. Acid and alkali cleaning chemically dissolves drawing oil, oxide film and machining compound. Pure water rinse removes chemical residue. Hot air drying eliminates free water to stop electrochemical corrosion. Sealing isolates the inner cavity from ambient air. The single closed end plus sealed open end forms a complete protected cavity, preventing secondary contamination before brazing and refrigerant filling. Clean inner wall also stabilizes capillary throttling and heat exchange, ensuring accurate refrigerant flow for sensor housing assembly.

3. Equipment and Category Classification

Material options: SUS304 for conventional systems; SUS316 for corrosive and high-humidity environments. Cleaning equipment includes high-purity nitrogen supply, ultrasonic acid-alkali tank, multi-stage deionized water rinse line and clean hot air drying oven. Sealing accessories cover size-matched rubber plugs and laser welding machine for permanent sealing. Machining equipment includes turning, grinding, bending, drilling and swaging for custom tube shapes. Surface treatment: polishing reduces pollutant adhesion on inner wall; outer surface can use sandblasting, anodizing or powder coating. Products certified under ISO9001:2015 and SGS.

4. Standard Operation Guide

Implement a fixed cleaning sequence. First, nitrogen purge: insert nozzle into open end, blow out loose dust and metal chips. Second, chemical cleaning: soak in formulated acid and alkali solution to dissolve stubborn contaminants, then fully rinse with pure water. Woven wiping inside the lumen is strictly forbidden. Third, hot air circulation drying until no water stain remains. Fourth, seal both ends immediately. For turnover, use matched rubber plugs; for finished pre-assembled tubes, use temporary or permanent welding seal. When brazing the capillary to filter dryer and evaporator, clean the joint and grind the end face properly, then carry out inflation test to check blockage. New capillary should be chosen slightly longer to leave adjustment margin, and pressure-tuned later according to the 1–1.2MPa window.

5. On-Site Practical Experience

The most overlooked risk is residual detergent. Insufficient rinse leaves alkaline substance inside the tube, corroding stainless steel and reacting with refrigerant. Three-stage overflow rinsing is recommended. Operators should not use cloth to wipe inner wall even though it looks cleaner; fiber residue risk is fatal. Rubber plugs must be stored in sealed clean boxes. Drying temperature needs stable control: too low leaves moisture, too high ages plugs. Clean and dirty zones in the workshop should be separated, and dedicated transfer trays used to avoid cross contamination. Closed flat end tubes are easier to keep clean than open-end tubes because of fewer entry points.

6. Conclusion and Value

Complete sealing and cleanliness assurance builds the quality baseline for one closed flat end tubes. It eliminates particulate contamination, chemical residue and moisture inside the lumen, preventing blockage and corrosion failure. This low-cost process control improves assembly yield and long-term stability of refrigeration sensor modules, avoiding after-sales losses from invisible internal defects.

7. Industry Outlook and Suggestions

The future direction is automatic closed cleaning line with dust-free feeding and auto end-sealing. Suppliers should record cleaning parameters and batch logs under ISO9001. Customers should add lumen particle residue test in incoming inspection. For high-end refrigeration projects, prefer laser welding permanent seal to eliminate plug falling risk.