Roll-on-pilfer-proof (ROPP) caps are made from aluminium. The thread is formed as the cap is applied to the bottle. The rotating capping head descends onto the bottle and small wheels mould the cap to the bottle thread and tuck the break-away tamper-evident seal under the rim on the bottle.
Capping heads are made specific to each size of cap. Heads can be changed on the machine to allow the application of different sizes of cap with the same machine.
It is important to use the correct machine for your product. Different machines apply different amounts of pressure to the cap when the thread is formed. Bottles containing oils need less pressure than those containing free running liquids or carbonated products. Using the wrong machine with a carbonated product could lead to an insufficient seal forming, and gas could escape from the bottle, especially when pasteurising. We can advise on the correct machine and capping head for you.