Among various types of conveying equipment, roller conveyors have an extremely wide range of applications and an undeniable strong position. Roller conveyors are widely used in express delivery, postal services, e-commerce, airports, food and beverage, fashion, automotive, ports, coal, building materials, and various other manufacturing industries.
Goods suitable for roller conveying should have a flat, hard contact surface, such as hard cardboard boxes, flat-bottom plastic boxes, metal (steel) containers, and wooden pallets. However, when the contact surface of the goods is soft or irregular (e.g., soft packages, handbags, parts with irregular bottoms), roller conveying is not suitable. It should also be noted that if the contact surface between the goods and the rollers is too small (point contact or line contact), even if conveying is possible, it can easily damage the rollers (local wear, bushing damage, etc.), affecting the service life of the equipment, such as metal containers with a mesh-like bottom contact surface.
Selection of Roller Type:
For manual pushing or inclined free sliding, non-powered rollers should be used; when driven by an AC motor, powered conveyor rollers can be selected. Powered conveyor rollers can be divided into single-sprocket drive rollers, double-sprocket drive rollers, synchronous belt drive rollers, multi-ribbed belt drive rollers, and O-belt drive rollers, depending on the transmission method; when using electric roller drives, electric rollers and powered or non-powered rollers can be used in combination; when goods need to stop and accumulate on the conveyor line, accumulation rollers can be selected. Based on actual accumulation needs, sleeve-type accumulation rollers (with non-adjustable friction) and adjustable accumulation rollers can be selected; when goods need to make a turn, tapered rollers should be used. The taper of standard tapered rollers from different manufacturers is generally 3.6° or 2.4°, with 3.6° being the most common.
Roller Material Selection:
Different operating environments require different roller materials: Plastic parts become brittle at low temperatures and are not suitable for long-term use, so all-steel rollers should be selected in low-temperature environments; rubber-coated rollers produce a small amount of dust during use, so they cannot be used in dust-free environments; polyurethane easily absorbs external colors, so it cannot be used for conveying packaging boxes and goods with printed colors; stainless steel rollers should be selected in corrosive environments; when the conveyed object causes significant wear to the rollers, stainless steel or hard chrome-plated rollers should be used instead of galvanized rollers due to the latter's poor wear resistance and unsightly appearance after wear; rubber-coated rollers should be used when greater friction is required due to acceleration, climbing, etc., as they can also protect the goods and reduce conveying noise.
Roller Width Selection:
For straight sections of conveyor lines, the roller length W is generally selected to be 50-150mm wider than the cargo width B. For applications requiring precise positioning, a smaller width of 10-20mm can be chosen. For goods with very rigid bottoms, the cargo width can be slightly larger than the roller surface length without affecting normal conveying and safety, generally W ≥ 0.8B.
For curved sections, the roller length W is affected not only by the cargo width B but also by the cargo length L and the turning radius R. This can be calculated using the formula in the diagram below, or by rotating a rectangular conveyed object L*B around the center point as shown in the diagram below, ensuring that the conveyed object does not rub against the inner and outer guide edges of the conveyor line and has a certain margin. Finally, appropriate adjustments should be made according to the roller standards of different manufacturers.
For goods of the same width on a conveyor line with both straight and curved sections, the roller length required for the curved section will be greater than that for the straight section. Generally, the roller length of the curved section is used as the uniform roller length for the entire conveyor line. If this is not feasible, a transitional straight section can be added.
Roller Spacing Selection:
To ensure stable conveying of goods, at least three rollers must support the goods at any given time, i.e., the roller center distance T ≤ 1/3L. In practice, (1/4~1/5)L is generally used. For flexible and slender goods, the deflection of the goods must also be considered: the deflection of the goods over one roller spacing should be less than 1/500 of the roller spacing; otherwise, it will greatly increase the running resistance. At the same time, it is necessary to ensure that the load on each roller does not exceed its maximum static load (this load refers to a uniformly distributed load without impact; if there is a concentrated load, the safety factor needs to be increased).
In addition to meeting the above basic requirements, the roller spacing must also meet some other special requirements:
1) The center distance of double-chain driven rollers should conform to the formula: center distance T = n*p/2, where n is an integer and p is the chain pitch. To avoid half-link chains, the commonly used center distances are shown in the table below:
2) The center distance of synchronous belt arrangements has relatively strict limitations. The commonly used spacing and corresponding synchronous belt models are shown in the table below (recommended tolerance: +0.5/0mm):
3) The roller spacing for multi-ribbed belt drives should be selected from the table below:
4) For O-belt drives, different pre-tensioning amounts should be selected according to the recommendations of different O-belt manufacturers, generally 5%~8% (i.e., subtracting 5%~8% from the theoretical base diameter circumference as the pre-tensioning length).
5) When using turning rollers, the angle between the roller spacing for double-chain drives is recommended to be ≤5°, and the center distance for multi-ribbed belts is recommended to be 73.7mm.
Selection of installation method:
There are various roller installation methods available, including spring-loaded, internal thread, external thread, flat tenon, semi-circular flat (D-type), and pin hole. Internal thread is the most commonly used, followed by spring-loaded. Other methods are used in specific situations and are less common.
Comparison of Common Installation Methods:
1) Spring-loaded press-fit:
a. The most common installation method for non-powered rollers, offering very convenient and quick installation and removal;
b. A certain installation clearance is required between the inner width of the frame and the roller, which varies depending on the diameter, bore size, and height. Typically, a gap of 0.5~1mm is left on each side;
c. Tie rods need to be added between the frames for stability and reinforcement;
d. This loose connection method is not recommended for sprocket rollers.
2) Internal thread:
a. This is the most common installation method for powered conveyors such as sprocket rollers, connecting the roller and frame as a whole through bolts at both ends;
b. Installation and removal of the roller is relatively time-consuming;
c. The mounting holes in the frame should not be too large to minimize the height difference (gap) of the rollers after installation (generally 0.5mm; for M8, a frame hole of Φ8.5mm is recommended);
d. When using an aluminum profile frame, it is recommended to choose a "large shaft diameter, small thread" configuration to prevent the shaft from penetrating the aluminum profile after tightening.
3) Flat tenon:
a. Originating from mining trough idler roller assemblies, the ends of the round shaft core are milled flat and then inserted into the corresponding frame grooves. Installation and removal are extremely simple;
b. Lacking upward constraint, it is mostly used as a belt conveyor idler roller and is not suitable for powered conveyors such as sprockets and multi-ribbed belts.
Regarding Load and Bearing Capacity:
Load: Refers to the maximum load that a driven roller can withstand. The load is affected not only by the bearing capacity of a single roller but also by the roller installation method, transmission layout, and the driving capacity of the transmission components. In powered conveying, the load plays a decisive role.
Bearing capacity: Refers to the maximum weight that the roller can bear. The main factors affecting bearing capacity are the roller body, shaft core, and bearings, and it is determined by the weakest of these components. Generally, increasing the wall thickness only enhances the impact resistance of the roller body and does not significantly affect the bearing capacity.
