Let’s twist again

When I first started working for the big Dutch can making company Thomassen & Drijver – Verblifa, in May 1967, I became the first full-time salesman for glass closures and, in particular, twist off caps.

At the time, glass closures were generally regarded as a negligible by-product for a can producer, and can salesmen handled from customers for glass closures. However, from the 1960s, glass jars closed with metal caps took an ever larger share of the canned food market and they could not be ignored any longer. The thinking within can makers became: ‘If you cannot beat them, join them’. Moreover, some European food processors profiled themselves with the unique selling point of having glass jar transparency.

Dutch food processor Hak for instance, today a huge vegetable processor filling exclusively in jars, started using this slogan in the 1960s: “Hak, you see what you eat”, clearly as a statement against vegetables in cans. However, like other fillers, they started with the simple non-reclosable aluminium closures called Omnia-caps, which were produced in licence from Thomas Hunter in Rugby in the United Kingdom. Another non-reclosable aluminium cap, namely the PANO-cap, in licence from Pano-Verschlluss in Itzehoe, Germany, was also created.

However, international brand owners like Hero, Unilever, Heinz and others found such an opening was not good enough and demanded re-closable twist off caps for their upmarket brands as the more consumer-friendly glass closures. Like some other can makers in Europe such as Metal Box, Schmalbach and Carnaud, we were able to fulfil these demands, as we all had signed a license agreement with the US company White Cap. The brothers Phil and William White had already invented the twist off cap in the 1920s as a more convenient alternative to the old fashioned Continuous Thread screw cap, which needed one and a half to two turns to open.

The special shape of the ‘lugs’, fitting exactly to the prescribed glass finish, enabled a short twist to open and to reclose the cap, and that meant much more consumer convenience. White Cap developed the concept into a complete system, with their own proprietary closing machines. In these machines the application of their ‘Vapour Vacuum’ operation took place, resulting in minimal residue of oxygen, crucial for the conservation of any food. Soon, White Cap added a so-called ‘dud detector’’ to check the vacuum. There were special compound types for hot-fill products, for pasteurised and retorted foods. The whole system was completed with a team of specially trained service engineers. This approach was rather revolutionary and quite successful. Licensees were only admitted when they applied the total system.

Apart from the fully developed White Cap-system with a family of licensees worldwide, there was the competing US Anchor Hocking- twist cap with licensees around the world.

The first big twist off project I handled in the 1960s was a project with Hero, the Swiss/Dutch food company. They wanted to put a new high-end marmalade line on the market and chose a proprietary new glass jar with a twist off size we could not produce in our Deventer plant. In the Hero plant we installed the special closing machine and supported the set-up of the whole filling line. The launch was a success and many other twist off projects for customers like Heinz, Unilever and Kraft followed.

Continuous twist off development

In the subsequent decades, glass jars made considerable inroads into various food and drink sub-markets and twist off caps were often the preferred closure. The market for twist off caps grew explosively in many Western countries. Only the replacement of glass bottles for beverages by PET bottles and closed with plastic closures, reduced the growth of twist off closures. Many different sizes and versions were developed, like extra-deep twist off versions, the PT closure (Press-on, Turn-off) for baby food and the Eco-Top version for example. A major innovation was the venture of the so called ‘safety button’, which allows consumers to check if there is a vacuum in the jar. In the Premier League of twist off, producers today are the international players like Silgan (which took over the complete White Cap organisation), Crown, Massilly, Tecnocap, and in the second tier, tens of smaller local twist off producers are active.

Production methods varied amongst these cap producers. Machinery suppliers like Alfons Haar, Naroska, and in particular Cantec (then still part of the company SIG, now Soudronic) tuned in on the fast growing market for twist off production machinery.

“Looking at the market growth, we decided in the 1990s to adapt some of our machines that had a proven record for the production of three-piece cans and ends and make them ready for the production of twist off caps,” said Dr. Norbert Lentz, general manager engineering at Cantec in Essen, Germany. “We engineered a complete production set-up consisting of a stamping press, the forming system and a lining system.”

For the last 20 years, the pressing of twist-off caps has remained the same according to Dr. Lentz. “I would say that we went for real high capacity production with our system, though our lines are not necessarily dedicated to one single diameter and they can be easily changed to other diameters. The press we choose, our End-O-Mat, is quite reliable and adapting it for stamping twist off caps was no big deal. It is a 50 tonnes press, capable of producing caps with a diameter between 32 and 89 mm, which can be quickly retooled and reset.

“It can be supplied for single row tooling, with zig-zag feeder and without idle strokes. At the same time, it is quite versatile in its ability to stamp various depths, from the 6.5mm depth for regular twist off caps up to as high as 20mm for the deep twist off caps that also came on the market.

“This press has a capacity of up to 1200 shells per minute. We can even supply a similar 150 tonnes press, equipped with double row tooling, with a capacity of up to 2400 shells per minute, and two back end machines. So far, we haven’t supplied that press as the market obviously doesn’t need such a huge capacity.’’

At the heart of the line

 Dr. Lentz underlines the enormous importance of stamping the right shells with the required perfect geometry. The press is really the heart of the line, responsible for 80 per cent of the cap quality.

“The next part in the line, the Cap-O-Mat, in which the further forming of the caps takes place, cannot function well without good shells. You can do little there to repair earlier faults. As such, the Cap-O-Mat itself is a proven and quite robust machine with which we have a long experience.

“We can supply the Cap-O-Mat in two versions. First the version in which we do the operations Hamming or Spin Curling and Lugging operations, and in the other version we do Pre-Curling or Rail Forming, Die Curling and Lugging. Customers make their choice based on various criteria, including the pollution of the machine by remainders of coatings.”

However, Cantec do not make the compound lining units themselves; they buy these from specialised suppliers. “In the past, we integrated compound liners from BIBRA in Barmstedt, Germany into our lines, but we are also happy to work with rotary liners from the US company CMC in Eaglewood, Colarado,” said Dr. Lentz. “Due to the demand in some countries to have PVC-free compounds in twist off caps, we want to offer that alternative as well. In that case, we prefer to integrate liners from Sacmi in Italy. They have experience with these types of machines, in particular based on the production of crown caps and screw caps. It fits in our approach that we want the best possible solutions available in our production lines.’’

An important innovation in the twist off market was the launch by Crown of their Orbit closure. It is a cap consisting of two parts of metal, a central floating panel that is vacuum sealed to the jar and an outer ring that acts as the opening and reclosing device. This new twist off cap significantly reduces the opening torque. Hak were one of the first adopters of this new closure. It will certainly not be the last innovation in the dynamic twist off market.

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