Soldered fittings create strong, leak-proof joints by using heat to melt solder, which then flows into the space between the pipe and the fitting, creating a bond as it cools.
Here's a more detailed breakdown of the process:
1. Preparation is Key:
- Cleaning: Both the inside of the fitting and the outside of the pipe need to be thoroughly cleaned. This usually involves using a wire brush or emery cloth to remove any oxidation, dirt, or grease. This ensures proper adhesion of the solder.
- Flux Application: A flux is applied to the cleaned surfaces. The flux serves several crucial purposes:
- It further cleans the metal surfaces by removing any remaining oxides.
- It prevents oxidation from occurring during the heating process.
- It promotes the flow of the molten solder into the joint.
2. Assembly:
- The pipe is inserted into the fitting, ensuring it's fully seated.
3. Heating:
- A heat source, typically a propane or MAPP gas torch, is applied to the fitting. The goal is to heat the fitting and the pipe evenly, bringing them to a temperature sufficient to melt the solder.
4. Soldering:
- Once the fitting is hot enough (you can test this by touching the solder to the joint – it should melt on contact with the heated metal, not just the flame), the solder is applied to the joint where the pipe and fitting meet.
- Capillary action draws the molten solder into the narrow space between the pipe and the fitting.
- The heat is removed once a complete ring of solder is visible around the joint.
5. Cooling and Cleaning:
- The joint is allowed to cool naturally. Disturbing the joint while the solder is solidifying can weaken it.
- After the joint has cooled, any remaining flux residue should be cleaned off. Many fluxes are corrosive and can damage the pipe or fitting over time.
Why Soldering Works:
- Capillary Action: The close fit between the pipe and fitting, combined with the properties of the molten solder and flux, creates capillary action. This draws the solder into the joint, ensuring a complete and strong bond.
- Metallurgical Bond: While soldering doesn't melt the base metals (pipe and fitting) like welding does, it creates a strong metallurgical bond at the surface. The solder alloys with the surface molecules of the pipe and fitting, forming an intermetallic layer.
Example:
Imagine joining two copper pipes using a copper elbow fitting. You would:
- Clean the outside of the pipes and the inside of the elbow.
- Apply flux to the cleaned surfaces.
- Insert the pipes into the elbow.
- Heat the elbow fitting with a torch.
- Touch the solder to the joint; it melts and is drawn in.
- Let it cool and clean the residue.
This results in a durable, leak-proof soldered joint.
