What to Know Before Sealing Copper, Aluminum, or Nickel Tubing
Pinch-off tools are used to permanently seal ductile metal tubing through a controlled cold-weld process. Instead of using heat, solder, brazing, or filler material, the tool applies force to collapse the tubing walls together and create a solid-state seal.
This process is commonly used in vacuum, refrigeration, laboratory, electronic, cryogenic, laser, and industrial applications where a clean, compact, and reliable tube closure is needed. CH Bull offers manual and hydraulic pinch-off tools, along with application support to help customers select the right tool for their tubing size, material, and sealing requirements.
What Is a Cold-Weld Seal?
A cold-weld seal is created when clean metal surfaces are pressed together with enough force to bond without heat. In a pinch-off application, the tool symmetrically collapses the tubing, cold-welds the material, and severs the tubulation in one controlled operation.
For many vacuum and high-vacuum applications, ductile metal tubulation provides a compact connection that can be sealed without adding a valve. The original CH Bull resource notes that this type of connection can be used in systems that need to be bakeable to 600°C and require only a small amount of space.
Why Preparation Matters
A successful pinch-off depends on the condition of the tubing and the tool surfaces. The inside and outside of the tubulation must be free of contamination at the weld point. The outside of the tubing should also be polished to remove oxide crystals, which can interfere with the cold-welding process.
The tubing should be annealed before the pinch-off, and the anvil inserts should be cleaned before each use. Any contamination pressed into the metal at the weld point can prevent a complete cold-welded seal.
Before the Pinch-Off
Before sealing the tubing, confirm the basics:
- The tubing material is appropriate for the process
- The tubing is clean, round, and free of corrosion
- The tubing has been properly annealed
- The correct tool size has been selected
- The anvil surfaces are clean
- A suitable high-vacuum lubricant has been applied where needed
- The tool is aligned correctly before pressure is applied
The goal is to create the right conditions before force is applied. A pinch-off is not just a squeeze — it is a controlled forming and cold-welding process.
During the Pinch-Off
During the pinch-off, pressure must be applied evenly until the tubing severs. Any interruption while the material is in a plastic state can lead to an incomplete cold weld.
This is one reason hydraulic pinch-off tools may be recommended for larger tubing, heavier-duty applications, or jobs where consistent force is especially important. CH Bull offers hydraulic pinch-off tools in GST, HAC, and JSP styles, with complete hydraulic system options using foot-operated air-powered or electrically powered pumps.
After the Pinch-Off
After the tubing is sealed, inspect the finished weld area for uniform compression and a smooth, continuous seal. Depending on the application, additional testing may be needed.
The original process guidance notes that sample tubes may be carried through the same process and checked by helium leak testing or microscopic examination for comparison. It also notes that the cold-welded stub should be protected after the pinch-off because it is delicate and sharp.
Choosing the Right Pinch-Off Tool
The right tool depends on:
- Tubing material
- Tubing diameter
- Wall thickness
- Access around the tubing
- Required tool style
- Manual or hydraulic force requirements
- Pump setup, if using a hydraulic tool
Manual pinch-off tools are generally used for smaller tubing and hand-operated applications. Hydraulic pinch-off tools are used when the application requires more force, larger tubing capacity, or a powered pump setup.
Need Help With a Pinch-Off Tool Application?
CH Bull can help review your tubing material, diameter, wall thickness, access conditions, and sealing requirements to recommend the right manual or hydraulic pinch-off tool.