Friction weld or seal? Choosing the joint on PET strap

PET strap, also called polyester strap, can be closed in two main ways. The strap can be welded to itself, or the overlapped ends can be held inside a metal seal or clip that is crimped with a hand tool. Both joint types are available for PET strap in May 2019. A US patent granted in April 2016, for example, describes a mobile strapping device with a tensioner and a friction welder driven by a lithium-ion battery, while seals and clips are crimped with manual tools. The useful question is not which joint is better in general, but which joint suits a particular strap, tool, load and team.

How each joint is made

Friction weld. The tool clamps the two overlapping layers of strap and moves one against the other at high speed. PAC Strapping Products’ FAQ describes battery-powered tools that tension the strap and fuse the layers with heat generated by this vibration, so no separate seal is needed. The surfaces melt, the tool holds them while they cool, and the strap becomes one piece at the overlap. Pneumatic friction-weld tools work on the same principle, and strapping machines also join plastic strap without a separate seal.

Seal joint. The two strap ends overlap inside a sheet metal seal or open clip. A sealer then deforms the seal and strap together. Signode’s explanation of seal joints distinguishes crimp joints, which deform the seal and strap without cutting and depend on friction, from notch joints, which cut into the edges to form a mechanical interlock. For plastic strap, the same page lists crimped seals or a secured buckle as joint options.

What each joint depends on

Factor	Friction weld	Seal joint
Consumable	None beyond the strap	A seal or clip for every joint
Equipment	Powered tool or machine, with charging or air supply	Manual tensioner and crimping tool
Key settings	Weld time, pressure and cooling before load	Seal profile, crimp position and number of crimps
Matching	Strap grade and surface suited to the tool	Seal width, thickness and profile matched to the strap and tool
Inspection	Look for a complete, even weld across the strap width	Check seal position, crimp depth and that both strap ends are captured
Working without power	Not possible	Possible

Neither column is free of risk. A weld made with the wrong settings or on unsuitable strap can look complete and still separate under load. A seal of the right nominal width but the wrong profile can be crimped neatly and slip.

Joint performance is a system property

The PAC FAQ defines joint efficiency as the strength of the sealed joint relative to the break strength of the strap. That definition is the key to comparing joints honestly: a joint normally holds less than the strap it closes, and its strength belongs to the combination of strap, joint and tool, not to the joint method alone.

So treat any general figure quoted for a joint method with care, because it was obtained on someone else’s strap and tool. Ask instead for evidence on your own combination:

• The strap reference, nominal width, thickness and surface.
• The joint method, with the tool model and its settings, or the seal profile and sealer.
• The test basis used and how many joints were tested.

If a supplier cannot tell you which strap and tool a quoted joint value applies to, the number cannot be used to compare offers.

When each joint makes sense

Friction welds suit stations that strap PET in steady volumes, where a consistent strap grade is used and operators benefit from a tool that tensions, welds and cuts in one cycle. Removing a consumable also removes one more item to stock, count and match.

Seal joints remain the practical choice where there is no reliable charging routine or power supply, where volumes are low or irregular, where several strap grades are in use, and for repairs at receiving or in the yard. They also suit sites that already own manual tensioners and sealers in good condition.

Some sites use both: welded joints on the main line and sealed joints at repair and manual stations. That works well if each station has the right consumables and nobody mixes clips from one strap width into another.

Trial before you switch

1. Fix the strap. Use the production strap for the trial, not a sample from another supplier.
2. Record settings. For welds, record tool model and settings; for seals, record seal reference and sealer.
3. Inspect every joint in the trial. Note incomplete welds, misplaced seals and strap damage.
4. Load test where it matters. Agree the method and acceptance requirement before testing, not after.
5. Write the result into the specification. The approved joint, tool and consumable become part of the packing instruction. The sample approval guide shows how to record what was accepted.

If your stations close PET strap with crimped joints, the sheet metal clips range lists nominal widths and sheet thickness; clip, strap and crimping tool still need to be checked together. Share the strap and tool details through the enquiry page when you request an offer.