Selecting a Conveyor Dryer

dryerEveryone buying a conveyor wants the most for their money. A dryer that is good for one shop or person might not be for another. There are a lot of choices to consider, and this article will describe the choices so you make the best choice for you.

Shipping Cost First, of course, is price. Price includes shipping. Domestically that is based on weight, but common carriers can double the freight rate when the

weight per cubic foot is less than 8 pounds. A conveyor typically weighs less than 8 pounds per cubic foot. However, if the legs, in-feed and out-feed sections are removed, the cubic dimension can be reduced to get within the shipping requirement to get the lowest freight rate.

The purchase price is important, but the operating cost over the life of the conveyor will be much higher. So we will want to understand all the aspects of the operating cost.

Cost of Power Dryers that are 230 volts cost less to operate than 115 volts. Nearly every building in the U.S. has 230 volts. A house, for example, has 230 volts coming into the house to operate the electric range and clothes dryer. At the breaker box the 230 volts are split into a series of circuits most of which are 115 volts. So if the conveyor dryer is going to be located in one position and not moved to events, then installing a 230 volt circuit and outlet will save money.

Small dryers that new shops would use are typically 115 or 230 single phase. However, when conveyors are larger and three phase power is available, a three phase connection can reduce the cost of power by 40%.

The issue of gas versus electric dryers always comes up. Gas dryers typically are larger dryers rather that the small dryer a start up shop would use. To evaluate the choice of gas as opposed to electricity, we should look at the cost of power. The cost varies greatly around the U.S. Many rural areas served by electric coops or municipal electric systems have very inexpensive power. The rate in areas of Northern Upstate New York is about 3 cents per kilowatt hour (KWH). In a large city like New York City the rate is close to 20 cents. So a shop in NYC might be better off buying a gas dryer, and buying the gas at the wellhead in the Southwest, and paying a wheeling charge.

There is a lot more to know to minimize power costs. Inks cure by exposure to heat. If the exposure time is longer, we probably can reduce the amount of power the heaters draw, and thus save money. That will require having a temperature control dial on the conveyor.

Curing inks is like cooking a steak on the grill. For a rare steak, we have a hot fire, and quickly flip the steak over to cook the other side also quickly. Then we end up with a cooked outside and pink inside. A well done steak is cook over a fire that is not as hot, but we leave the steak on the fire longer. Then the meat is cooked all the way through. Inks need to be well done, or they will flake or wash out, and crack.

Always check printed images by trying to pick the ink off with your fingernail and by stretching the image 100%. If the ink picks off or cracks, it is like a rare steak and needs to go back into the conveyor to complete the curing process. If you can extend the curing time and lower the heat level, you save money.

Heater vs. Belt Width A belt can be 18”, 20” 24”, 36”, 48”, 60” or possibly another width. You want a belt wide enough to lay a shirt down, but the image will be at most probably 12” or 14” wide. How wide is the heater? You will want at least 16” or 18”, but 36” will draw a lot of power that you are not using.

When you specify a belt 36” or more inches wide you could require more than one heater arranged in lanes that touch each other. So 36” could be two lanes of 18” where one lane can be turned off to conserve power. Heaters can be place in sequence in a lane with separate controls for each heater so that the electric bill incurred matches the revenue being generated.

Most T-shirts require close to one minute to cure. A light weight white garment and garments that include synthetics might be printed with a thin deposit of ink that only requires 20 seconds to cure, but a heavy tote bag printed with 400 microns of three dimensional ink might require two or two and a half minutes for a full cure. If we use a 12” x 12” image and one minute as a standard, then a heated chamber two feet long can cure two shirts per minute and 120 per hour.

To reach this expectation, I would want adjustable doors on both ends of the heated chamber to make the dryer more efficient. The distance of the heaters to the belt is important also, because heat dissipates very rapidly under the hood. You can expect the temperature at the heater elements to be at least 120 degrees higher than at the belt.

If by our calculation a two foot long hood is rated at 120 shirts/hour, then 30” equals 150 shirts, and 48 inches equals 240 shirts. This is just a gauge to compare dryers, and your actual experience will vary on a lot of factors. Belts that move more quickly also remove more heat. Heavier weight garments
require more heat. Cotton requires more heat than synthetics. White and light colored garments reflect more heat than darks. The thickness of the ink deposit and percentage of pigment in the ink affects curing time. So there are a lot of factors bearing on your actual experience, but to sort out options available in dryers, we will use the 12” x 12” image that requires one minute for a full cure.

Folding sleeves under the body of the shirt, and folding the wet side of the garment over the unprinted side reduces the size of the garment exposed to the heating panel, and makes the dryer more efficient when the space on the belt that has been freed up is used to lay down another shirt. A 60” wide belt might have row upon row of shirts with 4 shirts in each row. Those rows should be just touching the prior row so that hot shirts are removing heat at the same rate that heat is being generated under the hood of the dryer.

Money is tight in a lot of businesses. So if you buy a conveyor where the in-feed and out-feed sections can be removed, ask if additional hoods can be added later. That would allow a purchase now of a shorter dryer to save money without precluding growth in the future

Belt Speed Another way to use your power cost as efficiently as possible is to convert the numbers on your belt speed dial to seconds. Simply select a number on the dial, and put a piece of paper on the belt. Then measure the number of seconds the paper takes from when the paper enters the chamber until the paper emerges from the other end. Write down in a column the numbers that appear on your speed dial, and next to the number you had selected enter the number of seconds the paper required. Then repeat this process for every number on the dial.

When you test garments by picking and stretching the ink, and find out the belt speed and temperature setting that works for you, you can add this information to the column of figures. A four color process print on a white shirt might require 50 seconds while white ink on black 100% heavyweight shirts requires 65 seconds. By zeroing in on your experience, and recording the results, you will be able to use the conveyor more efficiently and save money.

Digital Readout and Temperature Guns Digital readouts read the temperature at the end of a long wire called a thermocouple. If that tip of the wire is close to the heater, you will see a high reading. If the tip is at the belt, the reading will be much lower, but the actual temperature of the heater never changed. The heaters put heat out at an even rate. So when the tip is close to the heater, you get the impression that the shirt is exposed to a lot of heat and the heat is constant. The temperature reading from a thermocouple tip close to the belt will jump up and down giving you the false impression that there is something wrong with the dryer.

The truth is that a thermocouple in either location is not exactly accurate, but rather an indication. The digital display with the thermocouple close to the heater will tell you if the condition being measured is consistent. Then we just want to make sure that condition produces garments that pass the stretch and pick tests.

The guns read surface temperature, and do not tell you if the heat has penetrated the ink film fusing the ink to the garment. The gun sees an area and reads the temperature. Move the gun closer and farther away from the target, and see if the temperature changes as the area being read by the gun changes. We don’t use a gun in our printing operation.

Vent(s) Small dryers have one vent, and large might have more than one. Heat goes up the galvanized sheet tube, and that makes the conveyor dryer less efficient. However, if you cap off the vent, you could have smoke in your shop and undesirable odors. The dyes in some shirts have an undesirable odor. The vent should provide for convection to carry the lint out of the shop.

If you have lint on flat surfaces in the shop that could be from inadequate convection, or it could be just from handling a lot of shirts. Lint that is inhaled will irritate the sinuses and give those people who are exposed headaches. So the convection of the conveyor should be studied to make sure that it is adequate, but not excessive to make the conveyor expensive to operate.

The distance from the vent to the outside world should be less than 20 feet, and any bends in the vent tube should be gradual so there is no obstruction to convection and evacuation to the lint. If the distance is greater than 20 feet, and induction fan might be required at the wall end of the vent pipe, or a fan above the vent to push the air through the tube.

Other Operating Costs Fiberglass belts (tan colored typically) that are Teflon coated will last the life to the dryer as long as they are not too tight and do not rub up against the side of the dryer. In other words, the tracking system has to work well. Nylon belts (black colored typically) will stretch from the heat, wander, rub against the side of the dryer, and have to be replaced at your expense.

Smaller dryers have adjustments at one end of the dryer so that the roller is adjusted to be parallel with the roller at the opposite end. Better and larger dryers have four point tracking which means the belt can be adjusted from both ends. That makes the process easier to get a perfect adjustment so the belt does not wander.

Maintenance Costs When we buy something new we assume it will always work, but our experience tells us we better be prepared for the worst. So what can go wrong?

Quality infra-red heating elements will last the life of the conveyor. Poorly made heating elements will de-laminate, get soft, chip, and burn out the wires. A heater that fails during your peak work period can be very aggravating. So what is the track record of the heater manufacturer? Is there a warranty, and how long? Glass tube heating elements will have to be replaced, and that will be money out of your pocket.

If you have to get under the hood to inspect or make repairs, what is involved? Some manufacturers pop rivet the hoods onto the base rail, and that makes entry for maintenance a major chore. Others bolt the hood on. How many bolts are there, and where are they? A simple question like that can make a big difference when the pressure is on to get the heater going.

Once the hood is off, how simple is the dryer to inspect and work on? Can you readily see whatever is important? Ask these questions in case this is what you have to do at 10 o’clock at night trying to meet a delivery commitment. The electrical design can be so simple that almost anyone can work on the dryer without being an electrician. Just be sure to unplug the dryer before attempting any inspection or repairs. I have seen conveyors that are so complicated that commercial electricians have no idea what is wrong with the dryer or how to fix the dryer. Then you will be talking about spending a lot of money to have the manufacturer fly in a repair person maybe in 10 days when the person is available and your business is in chaos.

Conclusion There is a lot more to the cost of a conveyor dryer than the purchase price. You might make a check list from this article of all the issues important to you so all makes and models you are considering are being measured against a common standard. That will save you from making a bad decision that costs you a lot of money.