If you are reading this little missive, you are likely aware that our lot in life at Saint Clair Systems is to help manufacturers master control over their fluid dispensing processes. Fortunately for us, it turns out that this is applicable across a wide range of industries.
It also turns out that virtually every application in every industry has constraints that make it unique. Nowhere is this more evident than in the manufacturing of metal cans. In fact, the simple tin can offers a comprehensive look into the analysis and development of control strategies essential in creating something that we take for granted in our everyday lives.
The History of the Humble Tin Can
According to the Can Manufacturers Institute, the tin can originated in 1810, the result of a contest sponsored in 1795 by Napoleon Bonaparte (yes, the French guy with his hand tucked in his vest) for a means of supplying provisions to his troops. Interesting, but no great surprise if you think about the number of innovations we enjoy today which resulted from the need for military conquest.
The first cans were actually made of tin-plated steel – for a number of good reasons…
First, tin was a well-understood metal – having been used in the manufacture of bronze for thousands of years. Second, it was fairly resistant to corrosion (which made it a good candidate for food packaging). Moreover, it could be easily soldered, which provided a simple means of assembly and closure.
Not a Perfect Solution…
In spite of these advantages, the original tin can designs fell far from a perfect solution. First, solder is a combination of tin and lead, which we now understand is not exactly a formulation you want in contact with your food! Second, tin is quite reactive with even mild acids – a problem if you’re trying to package anything with a tomato or citrus base. As a result, tin tends to lend a metallic taint to almost everything it comes in contact with.
Not Your Grandfather’s Tin Can
Flash forward 200+ years.
The “tin can” looks nothing like it did in Napoleon’s time.
To begin with, advances in metallurgy and forming technology have ushered in the use of new steel alloys and aluminum. And nothing is off-limits anymore. All sorts of foods and beverages, even aerosol cleaners and oils, are all fair game for packaging in today’s cans. And beyond the addition of pressurized propellant, they’re more functional than ever before. There are pull tabs and tops for easy opening; and even cans shaped like bottles with twist-off tops that make them both easy-to-open and re-sealable. But for all these outward changes, perhaps the biggest changes have come on the inside, where you can’t even see. Welding has replaced solder for seams and the ends are now attached by a hemming process that eliminates heat from the sealing process entirely. This makes it possible to package, transport and store fragile, or even flammable, materials. The possibilities are endless.
Containing Without Touching the Contents
Perhaps even more important is the lining added to isolate the metal of the can from its contents. A result of modern coating technology, this single change in process has extended the life of both the can, and its contents, finally achieving the goal set forth by Napoleon back in 1795. The coating can be roll-coated on the can stock prior to forming – a practice common in the manufacture of 3-piece food cans – or sprayed in after the forming process, as is common with 2-piece beer and beverage containers. Regardless of how it is applied, this internal coating creates an inert layer that eliminates contact between the contents and the metal shell – preventing both from degrading.
This technology extends to the sealing of the can as well. New sealant materials have been added to the rim of the can to assure an air-tight, leak-free, long-term seal when the end is hemmed onto the can body.
Enter the Need for Fluid Process Control
In order to be effective, these coatings and sealants must be applied evenly and accurately, with no voids where the contents can contact the metal shell or leak from the can. They must also be applied as a very thin coating – both to control cost, and to keep them from interfering with the forming and filling processes. With more than 130 billion cans produced for use in the US alone each year1, and most of them consumed by in the food packaging industry, the margin for error is infinitesimally small. This requires advanced fluid viscosity management to assure that these coatings and sealants are applied perfectly time-after-time-after-time. In fact, it makes can manufacturing a study in viscosity control.
This is the reason we got involved in the first place. Process viscosity control is our life. And it is the reason, over the next few months, we will be exploring the can manufacturing process in detail.
We hope you’ll join us…
Download our free Process Excellence Diagnostic to more closely evaluate the operation costs, maintenance, overall performance, and product quality of your liner process.
1 – The Can Manufacturers Institute website, History of the Can: An Interactive Timeline. http://www.cancentral.com/can-stats/history-of-the-can.