Inver Grove Heights, MN – Within a wide variety of industries, the requirement to pinch-off and hermetically seal ductile metal tubulation (tubing) is a critical and necessary process when separating a device from a vacuum pumping station. Tools that can reliably perform the pinch-off (cold weld) function will produce a reliable seal that can withstand bake-out temperatures up to 600o C and eliminates the necessity of using expensive valves to perform the same process. The tube pinch-off and resulting cold welded (hermetically sealed) joint is accomplished in a single step using these effective tools. Although this pinch-off process is most commonly used in vacuum applications, they are equally effective with applications involving high or low pressure. Without question, the most important factor in achieving this cold welded joint is the tubing itself.
Pinch-off Tool Selection
Selecting the proper tool to perform the cold weld pinch-off process will depend on many factors. Some of those factors include:
- Tubulation material (OFHC Copper, Nickel, Aluminum, etc.)
- Tube O.D.
- Tube I.D.
- Clearance issues accessing the tool to the tubing being pinched-off.
- Tool angle required to access the tubulation being processed. This will determine the style, profile and angle of the pinch-off jaw required. The standard jaw angle on the scissor style tools will usually be 45o. Special jaw angles and profiles may be required to meet your requirements.
- How many tubes will be pinched-off and processed in a day, week, month, etc.?
- Has the tubing been exposed to any processes involving heat (braze, solder, bake-out) or severe cold prior to the pinch-off process?
The most effective tools for performing the pinch-off process are powered via hydraulic pumps. The pinch-off jaw closure force required to successfully pinch-off and cold weld approved tubing will be in excess of 5000 psi. In addition, the carbide pinch-off rollers that make contact with the tubing must be precision ground to insure the pinch surface is consistent and resists wear. Although there are a few hand held mechanical pinch-off tools available, the pinch-off produced by these tools are inconsistent and not dependable or repeatable. Hand tools simply can’t generate enough closure force to yield a hermetic seal on a consistent basis for highly critical applications.
Hydraulic pinch-off tools are available in a variety of sizes and styles, configured with a variety of hydraulic pumps, depending upon the application.
Handsets and pinch jaw models are available for tubes ranging from 1/16 - 1 inch diameter. Hydraulic pumps are available in either pneumatic or electric models and can be further modified for low or high volume applications. It’s important to match the correct handset and pump combinations to the job being performed.
Applications that involve the necessity to cold weld and hermetically seal tubulation are typically critical by nature. In other words, these tubes must be hermetically sealed and remain in the condition indefinitely, under a wide range of temperatures and environmental conditions. As a result, it’s imperative that both the tubing and the tool selected for the application be matched properly. When done correctly, the end result will be a cold welded joint that will remain hermetically sealed for the life of the product being produced.
For more information, please visit www.custom-products.com.
