Grain & Feed Milling Technology (June/July 2001 issue)

A Case for Nonmetallic Elevator Buckets
By Ted W. Beaty, Executive Vice President and co-founder of Tapco Inc.

A light-weight nonmetallic CC style bucket

An original CC style metal bucket

The transition from metal to nonmetallic elevator buckets began, in the United States and Canada, in the late 1960s. Historically, elevator buckets were made of fabricated sheet metal. The inherent problems of metal - corrosion, heavy-weight, bending and tearing, and the potential hazard of sparking caused one astute feed manufacturer to rethink the elevator bucket.

The prime goal was to eliminate corrosion in steel buckets used in the handling of hot pellets. The first attempts solved the corrosion problem, but the choice of material used in the molding of the buckets caused other difficulties. The first buckets were made from a phenolic type of material that stopped the corrosion, but being brittle, cracked and broke under impact.

This problem was soon eliminated by making the parts from polyethylene. Once this material was proven in the field, there was no stopping the switch to nonmetallic buckets. In the early 1970s, several manufacturers started making different versions of nonmetallic buckets. This manufacturing and marketing push, along with the many advantages of modern plastics over the traditional metal used in buckets, caused a major change in how elevators were equipped in the United States and Canada.

Bucket design

Material choice aside, the most important criteria in any bucket is its design or shape. This alone determines the capacity and discharge characteristics of the bucket. Bucket shapes have evolved from the time of the early Egyptians to Leonardo da Vinci to Oliver Evans to the designers and engineers of today. Since the founding of the United States, many, many inefficient bucket designs have come and gone. In 1938, one design, that was to eclipse all others, was patented by the K. I. Willis Corporation in Illinois. That design was called the CC style. After the expiration of the patent, three other manufacturers copied that style in metal buckets.

Those four companies controlled some 75% of the bucket business at the time. In 1974, Tapco Inc. of St. Louis, Missouri became the first company to manufacture and distribute the popular CC design in nonmetallic materials. Thus, the CC style had made the transition from metal to space-age materials.

Bucket evolution

The evolution from metal to nonmetallic buckets did not happen overnight.

Being a new material, in a very conservative industry, it had to be proven.

Since the major manufacturers of the nonmetallic buckets were not makers of metal buckets, they pushed their agenda aggressively at every opportunity. Tests were run, demonstrations and seminars presented, expositions were attended, and many thousands of miles were traveled in the formative years of the nonmetallic bucket.

Most of the end users of elevator buckets could see the many advantages and were eager to make the switch. They, however, had to contend with the entrenchment of metal buckets in the mind set of the original equipment manufacturers (OEMs).

The OEMs, whose main goal, in their eyes, is to produce the most cost effective product that will still do the job for the customer, were used to working with metal buckets and could see no reason to change to the then more expensive nonmetallic parts. So the change then, came from both ends.

Astute users demanded the new buckets and perceptive elevator builders made them available. At the time of the emergence of nonmetallic buckets in the United States and Canada, about 90% of new elevators were equipped with metal buckets. Now, that percentage has changed to 90% nonmetallic, and most of the manufacturers of metal buckets have gone out of business.

Tested and proven

The design, as stated above, is paramount to performance.

Tests, many conducted by major manufacturers of elevators, proved the validity of the CC style. Most of the buckets prior to that, some dating from the 1800s, were of a rounded type with little or no height on the ends or the sides of the buckets. Tests proved that with the demand for increased speeds to produce more capacity, buckets with flat "breaks" on the front and high ends or sides would perform significantly better than the rounded slower speed buckets. Their design was more suited to industrial style buckets that traditionally ran at slow speeds.

Major advantages

Let us now touch on the some of the major advantages of nonmetallic buckets over the ones made from metals. The major advantage of any nonmetallic bucket is its ability to physically absorb impact in the elevator leg. More buckets are torn up than are worn out by the product. Bent and torn buckets can cause a myriad of problems in the elevator. Besides not carrying product, they can drag and scrape inside the casing, creating a potential sparking situation that can lead to catastrophic events. A well designed nonmetallic bucket has the built in ability to bypass an obstruction in an elevator, return to its original shape and keep on working for you. This requires strong, uniform wall thickness and the proper grade of the selected resin. The weight of the elevator bucket is significant to the cost of the total elevator. By using lighter weight buckets, that are approximately half the weight of metal buckets, the elevator manufacture can then possibly use a less heavy belt, smaller pulley shafts and bearings, and lessen the requirements for horsepower and mechanical transmission equipment.

Energy costs can also harvested by using a more efficient elevator. Modern chemistry also offers a wide choice of material resins. While metal buckets are primarily made from common cold rolled steel, with a few very expensive ones made from stainless or other exotic materials, nonmetallic buckets can be molded economically from a wide variety of materials. Currently, the most popular are high density polyethylene, nylon and polyurethane. These three materials provide a broad range of coverage against corrosion, physical damage and wear due to abrasion.

Another, but very important factor, is the ease of installation of nonmetallic buckets.

Due to their lighter weight and lack of sharp, cutting edges, they are much easier to handle when changing or retrofitting an elevator in the field. This does not affect the engineering of the elevator, but it certainly makes life easier for the men who must keep the facility running, many times 24 hours a day.

Questions and concerns

No discussion of the transition from metal buckets to nonmetallic buckets would be complete without commenting on static electricity. You cannot avoid static electricity in a nonmetallic bucket.

However, the amount of static buildup on nonmetallic buckets is deemed harmless. Extensive tests were conducted in the United States in the late 1970s by the National Grain and Feed Association, the Grain Elevator and Processing Society, the Occupational Safety and Health Administration and by many of the major grain companies themselves. Other tests were conducted in various parts of the world, most notably by the Wolfson Electrostatics Unit at the University of Southampton in England, the Physikalisch-Technische Bundesanstalt in Germany and the Laboratoires du Cerchar in France.

Conclusions were made that the main culprit was the belt and pulley assembly. Which, by its nature, it is a constant generator of static electricity. This led to requirements in the United States that all elevator belting must be static conductive and that all elevators must be grounded or earthed. Other countries around the world have now followed that lead, and are requiring the same stringent safety requirements.

The conclusion drawn by Wolfson is that they would not "feel unduly worried by plastic buckets" in an elevator application.

There is a perception that nonmetallic buckets do not have the carrying capacity of metal ones. This is a problem of design and not the material used in the manufacturing. There are many current metal buckets that do not have the capacity of nonmetallic buckets, and also the other way around. In fact, within the range of some manufacturers of both types of materials, it is possible to find discrepancies within the same size buckets.

It is very important for the user or the elevator builder to consider his design requirements and to choose the proper replacement bucket if a change is to be made.

The future of nonmetallic buckets

As this article is being written, there are new manufacturers coming into the market as well as existing manufacturers producing more and different buckets. This is good, as it gives the elevator operator and designer many options to consider. It is of vital importance, however, to consider what is being presented.

Some companies are copying classic, time proven and accepted styles and others are bringing new, unproven designs to the market. As with everything, the old is not necessarily the best, and the new is not always the solution. Are they the answer to every elevating problem? Of course not. Nonmetallic materials, from what is currently available, will not eliminate the need for metal buckets.

There will always be instances of high temperature requirements, extreme abrasive conditions and other factors that will dictate the use of metal buckets.

However, with the ongoing improvements in raw materials and manufacturing technology, that list of instances is becoming smaller everyday.

Written by: Ted W. Beaty, Executive Vice President, and cofounder of Tapco Inc., St. Louis, Missouri, U.S.A. He is a graduate of Arizona State University and has been involved with elevator buckets for thirty years. He lives in St. Louis with his wife and two cats.

Tel: +1-314-739-9191
Fax: +1-314-739-5880
Reprinted with permission of Turret West Ltd.