Beverage & Packaging Sealings - 3rd Edition: Crown Cap/Cork details.
Although in my last edition I promised to start this edition with #PasticClosures ; but then I had a second thought. #MetalPackaging which has always been close to my heart, certainly deserve little more coverage. Hence I am again covering #CrownCaps, before to switch to #plastics ……
It will be worth mentioning here that SACMI is the only company supplying turn-key solutions and very high speed lines (6,000 crowns per minute) to produce #crown #caps all across the globe. If you open any crown cap anywhere in the world, in all likelihood you will find that it is coming from a SACMI line. SACMI’s #Metal #packaging portfolio is quite big. Apart from Crown caps, SACMI also supplies #completelines / #turnkey #packagingsolutions to produce #AluminiumCaps and #PullRingCaps. #PullRing #closures are the latest trend in #beverageindustry and are very popular among #consumers due to the fact that unlike crown caps that require an opener, Pull-Ring cap can be opened without any opener. There is a plastic ring, molded on the side-tab of this Pull-Ring cap & a consumer can open it by inserting his/her finger into this plastic ring and pulling it. Pulling the ring results into tearing off the metal cap and hence cap loosing it’s grip and coming out of the #bottle neck. Here below is an image of Pull-Ring Cap:
Crown Evolution on the basis of sealing / Lining material: Please have a look at below images of 5 crown caps with 5 different Sealing /lining materials.
Crown Cap types depending upon dimensions: As the first industrially produced crown caps were using a sealing disc made of natural cork which were thicker (compared to PVC or PVC free liners), hence they were supposed to have more height in order to accommodate a thicker sealing cork disc. This is the reason that initial crown cap, known as “STANDARD CROWN” was blanked (cut) from a metal sheet with a larger circular area and had more height compared to their subsequent versions – short crown & intermediate crown.
In India, Intermediate crown cap is produced mainly by Oriental Containers Limited ; AMD Industries Ltd. - India ; VARUN BEVERAGES LIMITED ; Hindustan Tin Works Ltd ; and are used by all major beverages/brewery brand owners like The Coca-Cola Company PepsiCo Carlsberg Group United Breweries Ltd. . However Short crown caps are equally popular and being produced and used in other parts of the world. Standard Crown is in diminishing phase, and is hardly seen nowadays.
In Below Sketch, major dimensions of Crown-Cap are identified:
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All the main dimensions of 3 versions of Crown caps are tabulated here below:
Another important dimension missing from above table is: the material & thickness of Metal sheet. Material is steel (either Tin coated sheet, or mostly Tin-Free Steel). Tin-Free Steel is a popular choice because of it’s excellent resistance to rusting. Thickness of the metal sheet used to be 0.25 during early 1990’s but now the crown caps with similar performance are being produced out of 0.16 to 0.18mm thick sheet. Of course the sheet thickness has been reduced, but in order to have same performance; the steel temper/ hardness(double reduced steel grade) has been increased to compensate for reduced thickness.
Flange Angle is an important and critical dimension, so far as Crown Cap application is concerned at the capping line. If this flange angle is too large, then the crown crimping will be poor and crown may pop-up due to internal pressure in bottle. Vice Versa – if this angle is too small then the crimping will be too hard and can damage/chip-off the sealing lip of the bottle-neck.
Variations in Crown height, Outer diameter, irregular corrugations (of course poor quality of lithographic varnish to add here) can create problems for the crown flow in the capping hopper and chutes.
Crown Lithography, Forming & Lining process : Printed/lithographed sheets with varnish layer on top of lithography (to protect print from scratched/aberrations) & a lacquer coated on the other side, are the input material to a crown punching/forming press. Outside of the Crown cap have lithography/printing displaying the Brand logos and other statutory messaging/ information.
A fully formed crown comes out of a punching press, and goes to a lining machine for lining operation. Inside of the crown is coated with a lacquering material. This lacquer layer when heated in a lining machine, acts as an adhesive/bonding layer between metal and plastic liner. A PVC free compound is extruded, cut into round pallets and then placed into a crown in a lining machine. Plastic liners are moulded inside the crown cap itself, using crown as a die, whereas the liner profile is replicated by a forming punch/tool mounted on a rotating forming turret of lining machine. This process of liner moulding is called “In-Shell Moulding”.
Crowns coming out of a lining machine are fully inspected and ready to be packed into boxes after a proper counting.