With all the equipment choices available today, selecting the right dryer for your garment-printing operation shop can be a complicated proposition. You have to determine whether a dryer's performance specifications will satisfy your current production needs and be able to keep pace as your company grows. And the dryer actually has to fit on your production floor! Fortunately, dryers are available in a variety of sizes, configurations, and prices to meet the needs of all kinds of garment screen printers, from start-up businesses to high-output operations. This article discusses some of the key features to evaluate when making purchasing decisions.
Heat generated in a dryer causes ink to set and bond to the garment. Dryers are designed to deliver this heat either electrically—using infrared (IR) heat—or by way of combusted fuel gas (propane or natural gas). What's the difference? After all, heat is heat, right? Well, sort of. It's true that the 320°F necessary to cure most plastisol inks is still 320°F in an electric IR dryer or a gas-fired model, but the real difference is in how the dryers reach and maintain that temperature and apply the heat to screen-printed garments.
IR dryers use radiant heat generated by electrically powered panels or tubes to cure the printed garments. The substrate and ink film must absorb the radiant heat in order to completely cure the print. IR dryers are often favored by small- to medium-sized shops because they typically cost less to purchase and take up less floor space than gas-fired models (Figure 1).
IR dryers can be used effectively when they're carefully set up to accommodate the ink type and printed thickness, as well as garment weight and moisture content. They are used primarily with plastisol inks, which harden or cure when exposed to the proper temperature for an appropriate amount of time. To achieve a proper cure, the entire ink film, as well as the garment surface, must reach the ink's curing temperature.
Because both the garment and ink film must absorb heat in the IR dryer, it follows that a heavy sweatshirt printed with a thick ink film requires more time in the dryer than a lightweight T-shirt printed with a thin ink film. Very thick ink films and heavy garments, such as those found in some athletic-apparel applications, can act as a heat sink. In turn, a much longer dwell time is needed to achieve a full cure. Certain specialty inks can also increase dwell time in an IR dryer, as can bright whites and inks that are made with a high pigment load. Examples include gold inks, glitters, and metallics. These inks slowly absorb IR energy delivered in the form of IR radiation and can sometimes reflect the IR energy.
In addition to managing the time printed garments must remain in the oven, you also must keep an eye on moisture in your garments and the humidity in the shop. Moisture can be the biggest obstacle to a thorough cure with an IR dryer. Only when moisture is removed from the garment can the garment and ink film begin to absorb the heat necessary to cure. Some manufacturers offer integrated air-circulation systems with their IR dryers to evacuate moisture more rapidly, increase the heat-absorption rates in garments and ink films, and keep the oven chamber temperature more consistent.
Gas dryers (Figure 2) burn fuel gas to heat air, which is then moved at high velocity to cure printed garments. The hot air penetrates the print and garment, quickly driving away excess moisture and bringing the garment and ink temperatures into curing range.
Gas dryers are typically used in shops that produce high-volume jobs. They are also recommended for shops that work with water-based garment inks. These inks dry by evaporation and require both the heat and high-velocity air movement provided by a gas dryer to cure efficiently and effectively.
In gas dryers, one or more burners generate heat, and a powered blower takes in filtered air and pushes it through the burner chamber. The heated air then enters a plenum chamber and makes contact with printed garments by way of strategically placed jet nozzles or air knives that concentrate and direct the hot air. Some manufacturers offer recirculation systems to boost efficiency by keeping heated air in the dryer. A portion of the circulating air is exhausted as fresh, filtered air is introduced to the system. A few dryer models are configured so that the operator can adjust the rate of intake and exhaust to best match the application at hand. Piping the dryer's exhaust to the outside is an important part of maintaining a safe working environment for employees.
Analog controls (Figure 3) are available on both gas and electric dryers. Analog control systems can be as simple as an on-off switch and a dial that controls belt speed. The next step up is a combination of analog and digital controls. The most common setup is digital temperature control and analog belt-speed control (Figure 4). Digital control systems (Figure 5) may include alphanumeric readouts and electronically programmed temperature and belt speed, and some models come with displays and touchscreen interfaces (Figure 6).
A large IR dryer or gas dryer with either a combination of analog/digital or completely digital control will help you keep up when job sizes increase (Figure 7). These types of controls tend to be more sensitive, accurate, and responsive, allowing users to carefully tune temperatures, belt speeds, and other operating parameters to effectively deal with large runs and jobs that involve more demanding inks, such as glitters, metallics, and high-density formulations. You may also find that precision controls allow you to successfully use your dryer to cure a variety of screen-printed products other than textiles (Figure 8).
The less sophisticated the controls, the more important it is that you conduct tests to determine what temperature settings and belt speeds are required to cure your prints. Use temperature probes to monitor heat levels, and perform rub and wash tests on the printed garments to ensure that the ink film is completely cured.
Dryers use conveyor belts made of stainless steel, Teflon-coated fiberglass, and other materials designed to withstand heat and wear. Belt speeds are measured in ft/min. and can be adjusted on garment dryers. The larger the range of possible belt speeds, the wider the variety of inks, garment types, and printing techniques that the dryer will support. Belt timing is important for avoiding over- or undercuring prints. This is why some dryers feature four-point tracking systems to keep belts aligned and traveling at expected speeds.
Belt width is another important consideration. You may be able to fit only one garment on a narrow belt, but a wide belt may allow you fit several garments side-by-side for higher volume production. Belts are typically available in widths from 18-86 in. A belt's height from the floor also can affect productivity. Belt heights range from about 28-36 in. You should select a height that minimizes the need to bend or overextend the body when loading and unloading the dryer.
Some manufacturers offer a split-belt conveyor system with independent controls and reverse drives. A split-belt conveyor allows users to cure dissimilar products at the same time. One belt can be set up to slowly carry heavy sweatshirts printed with a thick ink films, while the other belt can be programmed to quickly transport lightweight T-shirts with thin ink films. And when these two belts are reversible, several operators can work at the dryer at once to load and unload from both sides.
Modules and options
Not every screen-printing business is ready for a high-volume dryer today, but may need to upgrade to meet increasing demand in the future. For such shops, modular dryers are often beneficial. These machines let smaller shops start with dryers that fit their needs and later add features and functions as required. Modular components include such things as infeed and outfeed extensions, additional heating chambers and burners, and conveyor extensions.
Several options also are available to enhance a dryer's functionality. The split-belt conveyor mentioned earlier is one example. Other options include a choice of power systems (single- or three-phase power and a variety of voltage and amperage requirements), cooling sections and blower banks on the outfeed to make garment handling more comfortable, optic-sensor-based belt-tracking systems, high maximum heating temperatures and belt speeds, and more.
A lot to process
Sorting through your dryer options might seem daunting, but you can make the process a lot simpler with a careful assessment of your needs. Start by building a list of the inks you use (including manufacturers, formulations, and colors), the kinds of presses you have, and the types of garments you routinely print. Present this information to manufacturers as you hunt down the ideal dryer. They can use these details to help you select a model that will meet your existing needs and accommodate future demand.
A dryer may not be the most romantic piece of equipment in a screen shop, but it's the garment press's soul mate. If you take the time to carefully weigh your options, you'll find a companion dryer for your press that lets you maximize efficiency and quality on your production floor.
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