Soldering Flux Paste Castolin 5000FX AG, hard solder flux, 125 g

Castolin 5000FX AG is a hard-solder flux paste supplied in a 125 g tube, formulated for use with silver and other hard brazing alloys. It is designed to remove surface oxides, promote wetting of base metals and filler materials, and support formation of reliable brazed joints. The product is intended for metal joining and repair tasks in plumbing, HVAC and light industrial applications where controlled flux application and post-process cleaning are required.

Advantages

This flux paste adheres well to vertical and overhead joints, providing localized protection against oxidation during heating and ensuring good flow of silver and hard brazing alloys. Its paste consistency allows precise application from the tube, minimising waste and over-application. After brazing, residues can be removed with appropriate cleaning agents, helping maintain joint appearance and preventing long-term corrosion when followed by correct cleaning procedures.

Suitable for

• Brazing copper and copper alloys in plumbing and refrigeration systems
• Joining components in HVAC installations and maintenance
• Light industrial repair and assembly requiring silver or hard filler metals
• Field repairs where a tube-applied flux provides convenient, localised application

Key specifications

• Form: paste in a squeezable 125 g tube for controlled application
• Compatibility: formulated for use with silver and other hard brazing alloys
• Function: oxide removal and promotion of wetting and filler flow during brazing
• Application temperature: suitable for typical hard-brazing temperature ranges (consult filler alloy data for exact values)
• Residue: requires post-brazing cleaning to remove flux residues for corrosion prevention

How to use

Prepare joint surfaces by removing loose scale, grease and heavy contaminants; ensure mating surfaces fit closely. Apply an even, thin layer of flux paste from the tube to the heated area or joint faces where the filler metal will flow. Heat the assembly evenly to the recommended brazing temperature for the chosen silver or hard alloy and apply filler metal once flux becomes active and base metal reaches proper temperature. Allow the joint to cool, then remove residual flux with suitable cleaners or solvents in accordance with safety data and manufacturer guidance.

Usage recommendations

Use appropriate personal protective equipment, work in a well-ventilated area and follow local safety regulations. Avoid excessive flux application and ensure thorough post-braze cleaning to prevent corrosion. Store the tube capped in a cool, dry place and keep away from children and untrained personnel.