Steel or plastic? Managers of grain facilities faced with selecting a bucket style for their elevator must consider this choice in materials.
At first glance, steel may be considered more durable while plastic is thought to be safer. But manufacturers of elevator buckets — including companies in Europe and the U.S. that primarily make steel buckets and others that specialize in plastic buckets — will argue that those perceptions are wrong. Steel is certainly durable and plastic obviously produces no sparks, but plastic is also durable and steel is a safe material when proper housekeeping measures are taken.
There is no "right" answer in the steel-versus-plastic debate, and manufacturers acknowledge it is simply a matter of preference.
"Steel or plastic buckets are a matter of opinion or choice for the individual," said Chris Motley, international sales manager for Braime Elevator Components, Ltd., Leeds, U.K.
Geography also may play a role in the choice of steel or plastic buckets. About 90% of the new elevators sold in North and South America are equipped with non-metallic buckets, while most elevators in Europe and many other parts of the world are equipped with steel buckets.
While about 70% of Braime's elevator buckets are steel, market forces required that they manufacture plastic buckets as well, Motley said. Braime's newest bucket cup is a plastic model — the Super Starco SPS, available in high density polyethylene, nylon or polyurethane.
The Super Starco is one of Braime's 18 bucket designs, each available in 26 different sizes and in a choice of steel, stainless steel or plastic. Many of it's buckets are specialized designs for specific elevator brands. Motley said the company last year sold nearly 2 million buckets.
Motley believes steel buckets have several advantages. "Steel buckets are highly durable and because they are not as thick as plastic buckets, the volume capacity may be a fraction higher," he said. Steel is slightly more expensive than plastic, but many of Braime's food customers prefer steel, Motley said, because they are on high alert to contamination.
"Steel may be a better fit when moving fine powders such as flour because plastic buckets tend to gather more static electricity," he added. Any metal slivers that may break off the bucket or the elevator and become mixed with the product will be readily detected by metal detectors, he said.
While plastic buckets may safeguard against sparks, they are not necessarily safer than metal buckets, Motley said. "I don't think you'll get dust explosions with either plastic or steel buckets," he said. "Dust explosions are most often caused by hot bearings and slipped belts where the friction of steel against rubber causes a constant heat source, which can cause surrounding materials to smolder and ignite in the presence of oxygen." Regular checks and preventive maintenance of the bucket elevator are the key to safety, he added — rarely the material used in an elevator bucket.
Sweet Manufacturing Co., a manufacturer of bucket elevators in Springfield, Ohio, U.S., makes only steel buckets for its elevators. Steel is a safe, durable material, said Christian Jordan, Sweet's international sales manager.
Sweet designed its buckets with high ends to minimize spillage. The buckets are given extra strength and rigidity with ends that extend over the front and back of the body. The die-formed ends fit into matching formed offsets at the rear of the bucket, providing a reinforced and flat belt surface.
Tapered ends give the bucket body added strength and decrease drag when filling, Jordan said, allowing discharge with less friction. Vented ends provide air relief holes for faster, cleaner discharge of any type of material, including feeds and soft stock.
Sweet also designed its buckets to nest together for shipping purposes. "It helps decrease the amount of boxes tremendously," Jordan said.
Plastic or non-metallic elevator buckets also have several advantages. Ted W. Beaty, executive vice-president of Tapco Inc., St. Louis, Missouri, U.S., said non-metallic buckets are spark-free, non-corrosive, lightweight, easy to install, gentle on the product and more cost-effective over the life of the bucket.
Tapco, which manufactures the non-metallic CC-HD style elevator bucket popular in North America, recently introduced the EuroBucket, a non-metallic version of the European-style pressed steel bucket, a style that has been used for many years.
"Because of the differences in head designs in the U.S. and Europe, and customer buying habits, we knew that to reach the European market a new line of non-metallic elevator buckets would have to be produced," Beaty said.
While the CC-HD and the European-style bucket are similar in discharge characteristics, Beaty said, there are several distinct differences.
The CC design features flat breaks on the front of the bucket, which determines discharge characteristics — straight sides for a direct trajectory of the product and high ends on the bucket to help in the filling and discharging at high speeds.
"Earlier bucket designs, some dating back to the 1800s, were of a rounded shape and did not have high ends on the buckets," Beaty said. "Those styles were not deemed to be high-speed elevator buckets."
European-style buckets feature a rounded front, low ends, tapered sides and are normally spaced closer together on the elevator belt, he said.
Beaty said Tapco's research department consulted with design engineers and spoke with users in Europe before designing its new EuroBucket. "There were several major criteria identified that needed to be addressed in the manufacturing of the new buckets," he said. "First, and most important, was the design of the bucket itself."
Consistency and uniformity were key issues, he said. By designing all of the molds at one time, Tapco eliminated the variances between shapes and each bucket is made to the same exacting specifications. "This means that any bucket manufactured by Tapco will have the same shape within the projection range, and will also be consistent between projection sizes, assuring uniform discharge characteristics," Beaty said.
The EuroBucket has thick, uniform walls to give the bucket the strength to handle the high throughput demands, and is designed to "give" or yield. This allows the bucket to bypass an obstruction in the elevator and return to its original shape, saving replacement costs.
Tapco stocks seven sizes of its EuroBucket, in polyethylene, nylon and urethane, and three more sizes are projected for delivery in July.
Maxi-Lift, Inc., Dallas, Texas, U.S., manufactures several bucket designs in polyethylene, nylon and urethane. Its distinctive orange Tiger-Tuff polyethylene bucket is ideal for high-volume grain applications, said Jim Rogers, vice-president of sales and engineering.
Maxi-Lift said the Tiger-Tuff bucket features the thickest walls of any high-speed elevator bucket. The Tiger-Tuff is engineered for durability, Rogers said, and is built specifically for maximum duty elevators with tremendous capacities or extreme workloads.
"We've increased wall thicknesses more than 25% over other plastic buckets," Rogers said. The result is extended bucket life, and a reduction in lost capacity and premature bucket failure.
Both steel and plastic offer advantages and disadvantages, so the choice isn't easy. Check with your bucket elevator manufacturer to see if a certain material works best with that particular elevator design. The rest is up to you.