Outsourcing the finishing of large format graphics may be a good option for digital print suppliers that lack the capital or staff to invest in finishing equipment of their own. But the cost to acquire fundamental technologies like sewing machines and heat-seaming equipment is more affordable than ever, and many large-format graphic suppliers are finding that it’s well worth the investment. Foregoing outsourcing enables printers to have better control over pricing and scheduling—generally, better control over the finished product.
A workhorse sewing machine can be purchased for just a few thousand dollars. Most digital printers already have the skilled labor to operate stitching equipment, particularly if they’ve had previous experience in the screen printing realm.
When shopping for a sewing machine, consider the range of substrates it needs to accommodate. Most off-the-shelf solutions—even the most sophisticated and expensive models—will lack the muscle and mechanics to accommodate a diverse mix of media or the voluminous workload of the small- to mid-sized sign shop.
Industrial-grade machines with walking foots are better suited to the job, the design feeds the media through the machine, smoother and faster. Brother, Juki, Pfaff, Singer, and other sewing equipment vendors manufacture industrial-strength stitching solutions.
Things are heating up
Vinyl is in widespread use across North America at large-format print suppliers; for outdoor graphics, synthetic is the name of the game. And these types of substrates are ripe for finishing automation. While stitching, taping, and gluing may be used to sure up edges and create treatments that facilitate installation, heat-seaming provides a more efficient and faster means for achieving the same results.
Heat-seaming—or, welding—solutions come in two general types: rotary or radio-frequency (RF) heat seamers.
RF welders, which preceded their contemporary rotary counterparts, function in a stamp-like way. The media is placed between a die and base plate, where its thermoplastic coating melts and forms a seal. The die and base plate release the material and the next section of substrate is moved into place in order to repeat the process.
Based in Poland, with U.S. offices in Baltimore, Zemat manufactures "moveable, high-frequency welders" for heat-seaming large-format PVC foil products and PVC-covered fabrics commonly used in banner, tarpaulin, tent, and other outdoor applications.
Forsstrom offers a range of high-frequency welders, too, including the TD and TDW models, which the manufacturer suggests are best suited to high-volume shops producing a lot of PVC products (advertising billboards, tarps, tents, and vehicle covers).
Rotary welders are said to provide a seamless process—pun intended. This technology enables the material to be continuously fed through the machine with drive wheels. Heat may be facilitated with hot air or a heated metal wedge. Generally, it’s a faster process than that of RF welding, and an air-fed system may be faster still than systems that use the heated-wedge method.
There are advantages to both types of rotary welders. Wedge welders may use less power and offer a solution that’s less noisy than air systems. The hot-air systems, however, may provide a better, more consistent fuse. Wedge systems have been known to burn the media when the process is stopped or stalled for any reason, and when imperfect media is fed through it—a raised portion of the media’s surface, for example—the wedge may not apply even pressure. Hot-air systems are more adept at dealing with substrate irregularities.
There are also technologies on the market that may be adapted to accommodate either the wedge or hot-air process. Seamtek, Sandpoint, ID, for example, offers the SP72P Seam Sealer with puller, which may be equipped to do one or the other. Wheel speed, air or wedge temperature, and other features are controlled via a touch-screen control panel. With a 72-inch-wide throat, the system is capable of creating seams between 0.250 and 2.5 inches.
Miller Weldmaster Corporation’s 112 Cross Seamer is well-suited to grand format work—billboards, fleet graphics, building wraps, murals and more. It can be equipped with hot-air or hot-wedge heating system, depending on the customer’s requirements. For smaller large format graphics, the company recommends its T-100 DR hot-wedge welder for digital and screen-printed banners, and Miller’s C-MIT 1000 hot-air welder provides a table-top finishing solution.