Unitizing basics

A neatly palletized, tightly wrapped unit load is the goal of most any packaging operation. In this article, Modern offers an introduction to the range of equipment - from $800,000 automated palletizing systems to $40 handheld stretchwrappers - that can assist in achieving that goal.

By Corinne Kator, Associate Editor -- Modern Materials Handling, 10/1/2006

"The vast majority of palletizing operations are in manual mode," says Brian McNamara, president of Southworth Products. Much of that palletizing is done without any mechanical assistance or with the help of all-purpose powered lift tables. In manual palletizing, Southworth and a few other suppliers offer work positioners specifically designed to assist with palletizing.

Using calibrated springs or pneumatic devices, the pallet positioners automatically adjust the height of the pallet load, minimizing potentially harmful lifting and bending. They are also topped with turntables, so operators don't have to walk around large pallets.

The positioners hold up to 4,500 pounds and work best with uniform pallet loads. They require a lift truck for depositing and retrieving pallets and cost between $1,700 and $2,500.

This equipment tremendously reduces back injuries, says Bob Clark, vice president of sales and marketing at Bishamon Industries. But the real payback, he says, is in productivity increases up to 40%—an impressive result from an inexpensive piece of equipment that needs virtually no maintenance.

Semi-automatic palletizing machines are not widely used; however, they are popular in some niche markets—such as bags of cement mix or cases of metal fasteners—where products are heavy and difficult to manually palletize.

"The semi-automatic is for low-speed operations where you can't justify the expense of full automation but you're looking for something to prevent injury and to make some poor worker's job easier," says Dennis Alduk, sales representative for Newcastle Co.

Semi-automatic palletizers handle up to 20 cases or bags per minute and cost between $15,000 and $50,000, depending on the level of automation.

A conveyor delivers products to a semi-automatic palletizer, where an operator arranges them into a layer on a plate. The operator then presses a button and the plate retracts, allowing the layer to fall onto the pallet just below. The plate can be made of smooth metal, slippery polyethylene, rollers or even an air table for especially heavy products.

Bill Powell, president of Powell Systems, says he began offering a semi-automatic palletizer to his customers in the metal fastener industry just last year and hopes to develop a wider market for the machine. Similarly, Rick Wilkinson of Alliance Machine Systems says his company believes a wider market exists for its machine, which is now used only within the paper industry.

Conventional Automatic Palletizer

A conventional palletizer forms a layer of products on a plate, positions it above a pallet, and then retracts the plate, letting the layer drop onto the pallet.

Fully automated palletizing machines are the fastest, most efficient, most ergonomic type of palletizing equipment. They are also the most expensive. Costs range from $50,000 to $800,000, depending on the speed of the machine and the sophistication of the accumulators, conveyors and pallet dispensers that accompany it.

Two types of automatic palletizers are available: conventional palletizers and robotic palletizers.

Conventional palletizers are the best choice for many palletizing operations, says Jason Bennett, director of sales and marketing at von Gal. A basic conventional machine, says Bennett, costs less than half the price of a basic robot. Conventional palletizers also have a broader range of speeds, anywhere from 10 to 200 cases per minute.

Several varieties of conventional palletizers exist, but they all work on the same basic principle: The machine forms a layer of products on a plate, it positions the plate above the pallet, and then it retracts the plate, letting the layer descend onto the pallet. "It's a version of the old tablecloth trick," says Pat O'Connor, product manager for palletizing systems at FKI Logistex, "where you pull the cloth out and leave the dishes behind." The machine repeats the cycle until the load is complete.

Robotic Palletizer

Robotic palletizers use a jointed robot arm to pick products from a line and place them on a pallet.

Robotic palletizers

"Robots are coming on strong in the palletizing business," says O'Connor. "More and more of the low- to medium-speed applications are going robotic."

Most robotic palletizing systems simply use a jointed robot arm to pick products from a production line and place them on a pallet. The robots, which often handle several cases at a time, can complete up to 25 pick-and-place cycles per minute. An entry-level robotic system costs at least $125,000.

"Robotic systems offer several advantages," says O'Connor. Pick-and-place robotic palletizers often have a smaller footprint than conventional palletizers, he says. They can build up to four pallets from four different product lines simultaneously, making them a good choice for some smaller volume operations. Though few buyers will admit it, robots offer another advantage over conventional machines, O'Connor says, "Robots are cooler."

Suppliers of automatic palletizers have traditionally focused on making high-speed, high-cost machines for high-volume operations. But, says O'Connor, "there's been a movement recently in automatic palletizing toward lower cost machines." FKI, for example, is introducing a line of palletizers at Pack Expo this month that handles fewer than 20 cases per minute and costs about $50,000.

Changes in consumer packaging are also influencing the palletizing market. As packaging gets cheaper and less durable, says Bennet, palletizers must handle products more gently. As package sizes get smaller, says Ted Yeigh, sales manager at Columbia Machine, demand increases for faster palletizers that handle smaller cases. Yeigh says demand has increased for palletizing systems sophisticated enough to build mixed loads. An automatic palletizer can place multiple SKUs (stock keeping units) on the same load, he says, as long as the layers are about the same size.

Rotary Arm Stretchwrapper

With a rotary arm stretchwrapper, the load remains stationary as the roll of film swings around it.

"Anyone who puts anything on a wooden pallet and moves it from point A to point B needs to ensure those things stay on the pallet," says Gary Ehmka of the Arpac Group. Ehmka is the national sales manager for Infrapak, Arpac's line of stretchwrap machines. Stretchwrapping, he says, is the most cost effective way to keep pallet loads together.

Manual stretchwrapping requires little equipment—at most, a $40 film dispenser and a $3 safety knife for cutting the film. A range of equipment, however, is available for automatically or semi-automatically wrapping loads.

An operation that stretchwraps more than 15 loads per day can likely justify some level of automation based on savings in labor, back strain and film costs, says Gordon Cooper, sales manager for Vestil Manufacturing.

Because stretch film is a petroleum product, he says, film prices have doubled in recent years.

And a stretchwrap machine makes more efficient use of that film than a manual operation does. Machines with pre-stretch devices, says Ehmka, can triple the life of a roll of film. Operations wrapping 20-25 loads per day, he says, can often justify the cost of a machine with a pre-stretcher.

A semi-automatic stretchwrapper needs an operator to tie the film to the load before wrapping begins, to cut the film after wrapping is complete, and—in the simplest machines—to guide the roll of film up and down the load during wrapping. Semi-automatic machines range from about $3,500 to $15,000.

Fully automatic stretchwrapping systems attach and cut the film automatically. Most use photoelectric eyes to detect loads, so no operator is necessary. They range from $14,000 to more than $400,000. These systems, says Cooper, are best suited for routine operations where the same product comes down a conveyor line many times a day.

Two main types of stretchwrap machines are used for wrapping pallet loads. With platform- or turntable-type machines, the load spins as it is being wrapped. With rotary arm machines, the load remains stationary, and the roll of film swings around the load. Rotary arm machines are best for heavy or unstable loads, says Ehmka. They are also faster than turntable machines, he says, but cost twice as much.

With so many variables to consider, says Joe Carion, marketing manager for packaging systems at Signod, customers should ask a professional for help in selecting a machine.

Turntable Stretchwrapper

With a turntable-type stretchwrapper, the load spins as it is being wrapped by the machine and the film moves up the tower.

Trends in stretchwrapping

Due to advances in plastics technology, stretch films are getting thinner and stronger, says Carion. Newer stretchwrap machines, he says, are designed to get maximum stretch from these films.

Customers today are quicker to replace broken equipment or to upgrade older models, says Ehmka, and sales are growing in South America and Mexico, where labor is still relatively cheap. These are signs, he says, that the high price of film, rather than the potential for labor savings, is driving the market for stretchwrap machines.