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How is an Aluminium ROPP cap made?

ROPP closures are made from a flat sheet of aluminium which then goes into a punching machine to give it its shape. Depending on the length of the closure it could go through several punching machines to make a pre-form known as a shell? (The shell of the closure is then side printed if required). The shell is then taken to another machine to have all the details put on it. Then another machine will insert the liner.


Closure characteristic

Retaining ring – this is at the top of the cap and is used to hold the liner inside the closure.


Strengthening ring – this to ensure the shell remains in its correct shape between manufacture to application.


Bridges – these are cuts into the side of the closures which break during the removal of the closure after application, this is the PP or pilfer proof part of the closure.


What is a compound liner in an Aluminium ROPP closure?

A compound liner is flowed into the closure, the closure is then spun pushing more of the compound to the outside edge where the seal is required. This type of compound is mainly used for carbonated products.


What is an EPE Liner in an Aluminium ROPP closure?

EPE liners are foam liners which comes ready to be inserted into the closure, the EPE liner is inserted by a machine taking the shell cap and inserting it in. The EPE liner is retained by the retaining ring.


Below is a machine inserting EPE liners into closure shells.


How are Aluminium ROPP Closures printed?

Aluminium ROPP closures can be printed using  two different processes.

The first being flat litho which means the print of the closures is printed pre-distorted.



The second is side printing which means the closure goes into a printing machine after the closure has been punch into the correct length.


How is an ROPP cap applied?…

What kind of machinery is used by our customers?

What kind of technical support might they need when switching to a new cap?

The machinery used to apply ROPP caps is called an ROPP capping machines. These machines are made by various companies mainly from Italy but also from other European Countries. Some of the names of machine manufacturers are Arol, Zalkin, Bertolaso, MBF, AVE, Rejves & Fimer.


The closures are put into a bulk hopper. The closures are then either blown by an air blower or a conveyor into the chute hopper.


When the closures are in the chute hopper they are turned the correct way by a rotary disc or by vibration they are then fed down the capper chute upside down. The closures are turned as they go through the chute so they are the correct way up to be picked up by the container as it passes through the chute pickup.



The closures are picked up from a chute by the container as it pass through the in-feed scroll, the bottle with the closures on then goes from the scroll through the inner star wheel and then into the centre star wheel.


The bottle is now in the correct position under the capping head. The capping head by way of a cam is then lowered onto the top of the bottle to apply the closure.

The ROPP closures is applied using an ROPP capping head, generally the capping head has 2  threading rollers which forms the thread on the cap from the thread on the bottle finish  at the same time the 2 tuck under rollers form the tuck under which ensures the TE (tamper evident) part of the closure.


The seal of the closure is also formed by either a flat pressure pad (generally for EPE liners) the flat pad forces the liner into the mouth of the bottle to create the seal between the closure and the bottle or a reform pressure pad generally for compound liners, the reform stretches the outside of the closure down the bottle mouth to create the seal between the closure and the bottle.


Capping heads Sometimes only have three rollers – two thread rollers and on tuck roller this is generally only used for closures under 28mm diameter.





I want to change my Aluminium ROPP closure supplier, how will this be done?

When VCL are switching a new customer from another suppliers closures to VCL closures we would first carry out a trial on the customers machine of 50 – 100 closures to see if there are any major issues. If no issues are reported then we would probably carry out an extended trial at the customer’s premises.

Adjustments that may need to be carried out will normally only be to the capping head thread rollers or tuck under rollers. If there are problems during the trials and adjustments are required the first thing to check is the setup of the capping.

The following are checks to be done; the settings will vary depending on the size/type of closure. This information will be found on the manufacturers closure spec.

  1. Check the side positions of all the rollers.
  2. Check the side pressures of all the rollers.
  3. Check the heights of all the rollers
  4. Check the head pressure is correct.
  5. Check the turret head height is correct.

It is worth noting that some bigger customer will normally have 2 suppliers so if any adjustments are made to the capping head then the other supplier’s closure should be re-tested.  If the closure being used is a compound type closure or a closure with an insert then having the correct top load pressure is also important, this pressure can be established from the closure specification.

When the closures have been applied an inspection of the thread formation and the tuck under is done, you can also carry out a torque tests to establish when un-screwing the closures the opening torque is correct to the manufacturers spec.

What is a pourer insert in an Aluminium ROPP closure?

A Pourer insert is a 2 part pre-assemble made of HDPE that is inserted into a shell of a closures and retained by the retaining ring. A special bottle neck finish is required to retain the pourer during application.


How is a plastic flat cap made?

Plastic closures are made by a process called compression or injection moulding. Compression closures are formed when a PP/PE pellet is dropped into a mould then a punch is pushed into the mould to form the pellet into the shape of the closure. Injection moulded closures a formed by injecting the PP/PE directly into a preformed shape.

How is a plastic flat cap applied?

What kind of technical support might they need when switching to a new cap?

Plastic closures are applied by a magnetic torque head that can be adjusted to give the correct application torque depending on the closures spec.

Machine parts (collets/Chucks) will be required if a customer wanted to use a different type of plastic closures. The collets are made to order for the customer’s machine to suit our closures and normally take 6 – 8 weeks to manufacture.



What is a Long-Cap?

What is a LongCap (LC) and how are they made? The LongCap is an aluminium screw cap closure and is deep-drawn from offset-printed aluminium sheets that are 0.22 to 0.24 mm thick.

The deep-drawing takes place in two steps, in case of LC 30 x 60 mm in three steps. In the process, the aluminium is stretched so much that a print design on the side would no longer be recognizable.

That’s why a special side print method, similar to that for tubes, sleeves, etc., is used. Particular attention is given to the quality of this side print, since it also serves as an advertisement later when the product is on the shelf.


What does “plunging” mean?

Plunging means that the closure is deep-drawn during the roll-on process in order to ensure a better fit or leak tightness. The photo comparison shows the advantages of a Saran-film-tin liner over a Saran liner.


Simplified Plunging Principle


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