Conveyor drums for medium and heavy-duty conveyor systems

What is a conveyor drum?

A conveyor drum is part of a conveyor system. In this system, drums serve as a driving force, turning point and determine the shape and length of the conveyor belt.

The conveyor belt carries the material and lies like a loop around the drums and rollers. The rollers carry the belt from drum to drum. The drums play a crucial role in also guiding, straining and driving the belt. At the beginning and end of the band, belt is a drum, which also acts as the turning point of the band.

A conveyor belt goes from point A to point B and often bridges not only a distance but also height differences, we call this vertical transport. Vertical transport of bulk goods is influenced by six factors:

• The elevation height
• The length of the conveyor belt
• The elevation angle
• The material to be transported
• Capacity
• Drive power

We specialize in heavy-duty and medium duty transport of bulk goods such as sand, stone and salt. These transport systems require high transport capacities of up to 6000 tons per hour and belt speeds of up to 6 meters per second in highly polluting environments. Our conveyor drums are therefore designed to meet very high requirements in extreme conditions. In the full article “Conveyor pulleys in conveyor system for bulk goods” we tell you more about the role of a conveyor drum in a heavy duty bulk transport system.

Different types and functions of conveyor pulleys

Different types of conveyor drum pulleys have their own place and function in the conveyor system. There mainly work with five different types of drum pulleys:

• Drive drum pulley
• Return drum pulley
• Tension drum pulley
• Deflection drum pulley
• Snub drum pulley

Often the name of the type of drum pulley already gives an indication about its function, such as with the drive drum example. The drive drum drives the conveyor belt. Depending on the installation, the drum is set in motion by an electric or hydraulic drive. The friction between the drive drum and the conveyor belt causes the belt to move. The number of drive drums and the coating of the drive drum depends on the route and application of the conveyor belt.

The return drum pulley serves to increase the circumferential arc of the belt and thus the contact and the friction surface between the drive drum and the belt. If necessary, this drum is placed directly after the drive drum, in the lower part of the installation.

The turning drum pulley says it all, this drum turns the conveyor belt. This drum is placed where the belt has to change direction 180°, for example on the tail of the belt.

A tension drum pulley also serves as a turning drum pulley, with which the belt is strained. When the belt is tensioned, higher forces reflect on the drum. Therefore the tensioning drum is often made somewhat stronger. The tensioning drum pulley can also be used as a turning drum on the tail of the belt, and as a tensioning drum at any other position in the bottom part of the belt.

The deflection drum pulley is used in the lower part at places where the belt has to make a bend of a maximum of 90°, for example when the belt has to be guided through a construction.

Would you like to read more about the different types of conveyor belt drum pulleys, the applications and the interaction between drums in the entire installation? Then read the full article “Different types and functions of conveyor pulleys”

How does a drive drum operate in a conveyor belt system?

The drive drum is a hydraulically or electrically driven drum. The conveyor belt is driven by the friction that occurs between the contact surface of the drive drum body and the rubber cover of the conveyor belt. The larger this surface, the more friction.

The drive drum is placed upside down at the discharge point or on the tail, depending on the configuration and requirements of the conveyor system. In very long transport installations where high pulley power is required, several drive drums can be placed in different configurations.

Friction between the drive drum and the conveyor belt is essential in the drive of the conveyor system. To prevent external factors such as rain from making the drive drum slippery, it is coated with rubber or a combination of rubber and ceramic. This coating is profiled to drain away water to prevent aquaplaning and tire slippage.

The drum is set in motion by hydraulic or electric drive. Electric drive is the most used and consists of an electric motor with a gearbox. Hydraulic motors are powered by a pump that pumps hydraulic oil through the motor at high pressure, causing it to spin. These drives are more compact and lighter in weight, which is why they are often used in systems where weight is an important factor, such as ships and offshore installations.

In our full article “The importance of the drive pulley in a conveyor belt system” we explain the operation of a drive drum in more detail.

Conveyor drums: design & materials

Stockman’s unrivaled quality standard results in the very high reliability and long life of our drums. This way it is less likely to experience tire and construction damage, leading to less unplanned downtime which ultimately lowers maintenance costs. This quality derives from:

• Choice of material
• The dimensions we use
• 3 critical factors in our design

Stokman drums are made from normal structural steel, unless the drums will be subject to a very heavy load, or become part of an overflow with a magnetic installation. In that case, a choice can be made between structural steel with higher tensile strength, or stainless steel. We use steel for the drum shafts, tailored to the application and function of the drum, to counteract the effects of fatigue as much as possible.

A worldwide standard of 7 different diameters applies to drum diameters. We adhere to the standards as much as possible, but where necessary we also manufacture drums with a different diameter, for example due to lack of installation space or certain system requirements that must be met. The thickness of the coating depends on the load on the drum, but is available as standard in thicknesses between 10 and 30 mm. The thickness of the drum shields varies from 20 to 200 mm and depends on the type of bearings or clamping elements with which the shaft is clamped in the body.

The design of our rollers and drums act as support to the transport system and slow down the impact of the natural processes as much as possible. We speak of 3 critical points in the design of the our conveyor drums:

• Weld connection between casing and shield
• Connection between shaft and drum body
• Correct coating
• We explain each of these factors in detail in the full article: “Conveyor belt drums: design and materials”

Design and production of conveyor drums

The drums in a conveyor system are largely responsible for the correct and reliable operation of the installation. They are perhaps the most essential parts of the entire installation. A worn conveyor belt roller can be replaced relatively quickly and is also often a stored warehouse item. Not the same thing can apply for the drum and hence a non-functional drum will immediately lead to a standstill of the entire conveyor belt and possibly the entire installation. Hence when Stokman is designing a drum, we put our 100 years of experience into practice and can therefore ensure the longest possible lifespan for our products.
Our drums are custom-made and are designed and manufactured to the specific requirements of your transport system. The load on the drum determines the construction, it is influenced by 4 main factors:

• Amount of material per hour
• Speed
• Dimensions of the conveyor belt
• Delivery height

Based on this information, we calculate the required tensile forces and the total required driving force of the conveyor belt, with which we determine how many drive drums are required and where they must be placed in the installation.

The drums consist of 3 standard parts: the shell, shields and shaft. We make these 3 parts ourselves in our factory in Raamsdonksveer. The construction of Stokman drums can be divided into 4 different phases:

• Fabrication of parts and assembly of the drum body
• Finishing touches and coating the drum
• To balance
• Completion

The shell, shields and shaft are manufactured in our factory in Raamsdonksveer. The jacket and shields are then assembled with a welding robot developed by Stokman. After a drum has been welded, this standard tension arm is annealed.

When the drum body has been stress-relieved, it is tuned to the correct dimensions. If a drum needs to be coated, the surface where the coating will be placed is blasted for better adhesion. When the drum is assembled and if the coating has been inserted, the drum shaft and the drum body are joined together. The drum is then balanced to prevent unwanted vibrations during usage.

When the drum is balanced, only the finish touches remain. Our drums are preserved with anti-corrosion paint. The paint consists of several layers and can be applied in almost any RAL color. The default color we use is green. Every Stokman drum is provided with a unique identification plate, which shows the order number, the weight, the year of manufacture of the drum and possibly a warehouse code of the customer.

In the full article “Design and production of Stokman conveyor drums” we go into more detail about the design and production process of Stokman conveyor drums.

The coating of a conveyor drum

Not every conveyor drum requires coating, for example when there is less resistance and low capacity.

The main reasons for coating a drum are:

• Grip
• Wear
• Efficient use

The most important reason is the grip. A roller coated with rubber or a combination of rubber and ceramic has higher friction on the rubber conveyor belt and therefore a better grip. This minimizes the slippage of the belt.

If the conveyor drum is not coated, this will lead to uncontrolled wear on the metal drum body and lead to damage.

Controlled wear is easy to see: the rubber is subject to visible wear. By replacing the rubber (reconditioning), the drum can be protected from wear. This is an inexpensive way to preserve and extend the life of the drum.

In heavy-duty conditions, such as on ships or outdoors with a capacity of up to 6000 tons per hour, is a drum coating always required to enable efficient use.

Our four most common coatings for conveyor pulleys are:

• Mini diamond
• Big diamond
• Large diamond for drive drums (2 layers of Kevlar)
• Rubber with ceramic

The mini diamond coating is 8 mm thick and has a 20×20 mm diamond pattern. The hardness of the rubber we use is 63° Shore. This is a flexible rubber, which is therefore mainly used on smaller drums up to 400 millimeters in diameter.

The large diamond coating is 12 mm thick, with a diamond pattern of 70×50 mm, here too the hardness is 63° Shore. This coating is commonly used on a number of specific drums: the tail drum, the snub drum, the flex drum and the tension drum. These drums have to withstand heavy loads and often have a larger diameter, for example from 400 mm to 1500 mm.

Heavier peak loads can regularly occur while the drive pulleys are in use. Peak loads can cause the rubber to detach from the drum. That’s why we use the large diamond coating with two layers of Kevlar to prevent the coating from coming loose.

The 63° Shore rubber with ceramic is inlaid with ceramic plates that ensure a higher coefficient of friction. This coating is used almost exclusively on drive pulleys and tail pulleys that are difficult to access in the facility or where better grip is required due to the circumstances of the conveyor system. This coating is mainly used under the most severe conditions.

Would you like to know more about coating a conveyor belt pulley? Read the full article ” The cladding of a conveyor pulley “