Looking around the tiny universe that is my hotel room in Valencia, it’s safe to say that nothing here would be possible without plastic welding. From the miniature toiletries to the pillow mints and the individually wrapped toothpicks, plastic welding is so omnipresent that trying to catalogue examples in your home is enough to make your head spin. In fact, since starting this research I’ve become a plastic-obsessed social pariah who tells people every time I spot a welded seam. I can tell you from experience that this is not casual conversation for an adult trying to make friends. To tell someone that the Wiley Encyclopedia of Packaging Technology (2009) lists fifteen separate methods for it—which can be used on everything from milk carton closures to pill bottle foil seals, raincoats, and IV fluid bag seams—does not often lead to an exchange of phone numbers.

And so, instead I will respect my allotted time and your patience by focusing on three of the juggernauts that appear in my daily life: the impulse, ultrasonic, and heated tooling methods.

Impulse Welding

On a Tuesday morning, I watch our local butcher Oscar, his pupils pinballing around in confusion, while I try to explain why I am here, in the middle of his workday, disrupting him with my haphazard Spanish. Hitting the outer orbits of my vocabulary, I proceed to call myself a writing desk and point vigorously at Oscar’s vacuum sealing machine. To his credit, the butcher remains helpful and concerned, as if he’s come across someone that appears to be drowning. This leaves me as the only one butchering anything in the establishment.

Many of the butcher shops in Madrid have the same setup: a wide vitrine of glowing goods in the front and a long counter in the back which houses various knives, slicers, and most importantly, a vacuum sealing machine, which is the reason I am pestering Oscar today. When one comes to the market to buy jamón or cecina, for example, their Oscar (or in this case their Lorenzo, Oscar’s resident jamonero), slices the pieces delicately off the mass, arranges them neatly onto a stiff piece of clear plastic, slips it into a thin plastic sleeve, and places the whole kit into a vacuum sealing machine. The machine clicks on, purrs air into the chamber for about twenty-five seconds, and then exhales it out in one big gasp while simultaneously sealing the bag hermetically closed, finishing off by slowly raising its lid with an enigmatic motion usually reserved for spaceships in sci-fi films.

The magic of this process is really in the sealing, without which no food product could be kept fresh for any extended period. These machines use a method called impulse welding, an expeditious process often integrated into small, desktop vacuum sealers. Impulse welding is a lower-tech method of plastic welding, which makes it all the easier to implement. Sheets of plastic film are sealed together by a flash of hot electricity shot through metal wires, which are sometimes hidden under a thin bar of Teflon.

As the name would suggest, most notably on the website of one component supplier, the process allows you to “follow your impulse” quite literally, since the wires do not require time to heat up and the whole sealing process takes less than a minute. This is especially convenient in a market, as Oscar and Lorenzo can service customers quickly without needing to wait for any large machinery to catch up to their formidable speed. We walk out of their shop, and I run my finger over a fresh seam. Still warm to the touch, it exhibits a thin scar from the single searing wire.

Ultrasonic Welding

The marks that plastic welding methods leave have impressions of their process, which can be picked apart like personalities. While impulse welding leaves one or two thin lines, ultrasonic welding leaves a sort of dashed mark, giving it a technical look. The process involves a tool called a horn which the machine lowers to compress and vibrate the two mating components in a hyperlocal area with such rapid speed that the surfaces making contact melt and weld together in record time. This rapid vibration can be thought of as tens of thousands of hammer hits per second, which—when coupled with the appropriate force—make the materials meld together. Ultrasonic welding is particularly desirable because it uses no surplus heat (which could potentially damage the parts) and allows for extreme precision.

Being the dominant form of plastic connection, ultrasonic welding can be seen in nearly every environment short of a cave. If you have a surgical mask with you at this moment, on close examination you will find the connection between the strap and the fabric to have a diamond stitch pattern, indicative of an ultrasonically welded connection. If you’ve had the poor luck of lugging this massive volume into a cafe, alternatively, you could now shift your eyes upward and take a look at a fellow patron who might be smoking a cigarette and notice their disposable plastic lighter which is likely finished off by ultrasonic welding since encasing butane requires an airtight seal that cannot be applied with heat. If you happen to be more reasonably reading this at your kitchen table, a glance in frankly any direction will reward you with some ultrasonic welding in the forms of chip bags, Tetra Paks, granola pouches, and even pill blister packs, all of which employ the process as evidenced by their sealing marks.

Outside of its practical applications, ultrasonic welding also makes for great advertising fodder, as demonstrated by Tironi, an ultrasonic machine supplier I found in Barcelona that proudly declares: “We vibrate with you!” The unfortunate timing of a train mechanics strike hinders a visit to their plant, but Robert, their enthusiastic Austrian sales manager, is kind enough to spend an hour on the phone with me. With the pleasantries out of the way, he talks me through the industries they service, the largest being automotive and textile, followed by the food and packaging sectors. He is well informed on his business and ready to impress upon me the technical and interesting details of ultrasonic welding (for example, that a 20kHz frequency is better for larger plastic parts which require more physical stability to be handled, while a 30kHz frequency is appropriate for smaller, more manageable ones). Robert is hurried but well-tempered, as his company is knee deep in preparations for the Fakuma plastics processing trade fair in Friedrichshafen, Germany the following week.

The company’s namesake, José Tironi, began his career at the behemoths Branson and Herrmann, some of the earliest manufacturers of ultrasonic equipment, before striking out on his own to make this family-owned enterprise. Robert explains that while for a long time the company was a one man show, it has since grown to eleven employees, two of which are Tironi’s children. This small band is behind machines that mostly weld everyday necessities like plastic car bumpers, door panels, hood liners, sun visors, and glove compartments, but their products also find their way into places one would never imagine. A rather surprising anecdote to this effect: some of their handheld ultrasonic devices are used to repair the conveyor belts that transport excrement out of suspended chicken cages in poultry factory farms. I cannot imagine a more visceral hell than having to ultrasonically mend these macabre carousels.

I am hesitant to believe that Bob Soloff, the father of ultrasonic welding, ever would have anticipated these usages. When in 1964, he accidentally welded a roll of tape together and then proceeded to drive around the United States with a home-made ultrasonic welder (a probe mounted onto a drill press stand with a timer and a pneumatic cylinder) in his car trunk, he likely didn’t expect to see his invention spread so widely. And though the first documented usage was for the odd application of attaching the roof onto a toy stagecoach, ultrasonic welding proved to be such a progressive method of joining plastics that the boundless adoption is hardly surprising. It’s often impossible to anticipate the ripples that will follow a discovery, but this is the nature of something that becomes so pervasive. As I imagine Robert, the Austrian sales manager, might put it: “It vibrates into every crevice.”

Heated Tooling Welding

Following the thread from Oscar’s stall, I reach out to several sealing machine manufacturers to get a better sense of their welding processes. I stumble and struggle through a half dozen conversations before resigning myself to a trough of YouTube videos. In recounting my troubles over chicken curry at the home of some new friends, the tipsy conversation about my weird little quest leads to a suggestion that I reach out to their family friend Borja, a jamón producer in Extremadura who likely uses welding in the packaging of his goods. Borja is patient with me over the phone and suggests that we find a time to visit his distributor’s facility in the outskirts of Madrid. With my partner Blanca in tow as reluctant translator, I make the trip out on a sunny Monday.

Borja is a bit older than I’d expected, and in a hurry. Contrary to popular belief, everyone in Spain has somewhere to be and lots of work to do, and so I can’t help but feel that my little excursion might be poking a hole in his plans. His distributor’s facility is on the first floor of an unassuming brick apartment building and we’re shuffled in through a garage door on the side. After a brief greeting and the formalities of deciding who will translate what for this friendly bumbling idiot, our tour guide Acacio issues us lab coats, hair nets, and shoe covers, before leading us to the large slop sink to wash up. I should note here that not even the lithium ion battery plants I’ve toured in Shenzhen displayed such serious security or concern for contamination. As explained to me through the game of translator telephone, the Spanish jamón industry is well regulated and highly controlled. Inspectors make stops at random, and so the conditions of the facility, both in hygiene and temperature, have to be kept well-tuned and immaculate.

Acacio walks us through the two large and extremely tidy rooms. He is one of two sons running this place with their father and the business has been in their family for four generations, having started as a small grocery in this same location. The first space is reserved for storing and drying the legs of ham, about a hundred of which are dangling on meter-long white plastic strips of hooks. In the corner are tanks of carbon dioxide and nitrogen which, as he explains, are blended in a respective 20/80 ratio and pumped into the packaging to maintain a longer shelf life for their products. I ask through Blanca whether they use ultrasonic or impulse welding methods, and am met with puzzled looks. “Heat,” he tells us, as he pulls out a black thermoplastic tray and pantomimes a film sealing to the top.

The second room contains two large machines and a younger worker who is carefully slicing pieces off the cured legs by hand. The fruits of his labor are then passed through one of these machines depending on the desired packaging. An industrial vacuum sealer—a blown-up version of the one I saw at Oscar’s a week ago, and nearly forty years old—is one choice. The other, a newer addition proudly named Taurus and made by a Spanish company called Ulma, is an automatic tray sealer. This means it’s effectively a conveyor belt that takes black plastic trays into a closed chamber, swaps their oxygenated atmosphere for the carbon dioxide and nitrogen blend, and seals them closed with a plastic film using a heated plate. This process is fairly efficient, and is demonstrated to us with empty trays, which we’re then gifted to take home as souvenirs. It’s odd to see them perfectly sealed and hollow, being presented as the final product instead of whatever they usually contain.

As we say our goodbyes and get into our welded plastic taxi, with its welded plastic bumper and its welded plastic door panels, the welded plastic radio is playing the news, a continuous bender about a volcano eruption. Thumbing the empty plastic trays, I can’t help but think that as the lava spills, it must be welding and welding and welding everything it touches, enmeshing plastic to stone to metal, making a singular mass from all these little absurd things we populate our lives with. As we drive by a grocery, I imagine steel shelves bonding to plastic packages of pasta, their molecules ceasing to tinge with any autonomy, their colors blending into the ripe red of an inferno. The moment passes and we arrive home. “What do you think we should do for dinner?” Blanca asks, as she pinches the ultrasonic seal on a bag of chips, its vibrated enclosure starting to stutter open; our plastic week welding to a close, our plastic life becoming a little more ordinary.

Commissioned for U-JOINTS – A Taxonomy of Connections, an encyclopedic publication that looks at human history through its everyday details.

Andrea Caputo
Anniina Koivu

Editorial Team:
Margherita Banchi
Marta Pezzoli

Senior Researcher:
Eleonora Castellarin

Graphic Thought Facility

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