Food Machinery and Equipment | Belt Conveyor Structure, Types, and Applications
1 Belt Conveyor
Belt conveyors are widely used in continuous conveying machinery in food factories, commonly for horizontal or inclined transportation of bulk, granular, and whole materials. Many pieces of processing equipment, such as sorting lines, filling lines, continuous dryers, and continuous freezers, use belt conveyors. The structure of a belt conveyor is shown in Figure 2-1.
Figure 2-1 Belt Conveyor Structure Diagram
Buffer idler Hopper Skirt board Bend pulley Tensioning device
Tail frame , Intermediate frame , Return idler , Empty belt cleaner
(Source: Food Machinery and Equipment, 2016)
The inner core material of the belt is not resistant to friction or oxidation, requiring a protective cover rubber layer of a certain thickness. The main function of the cover rubber is to bond the plies, protect them from damage, and prevent wear from conveyed materials. The cover rubber also prevents moisture and external media from eroding. The thickness of the working surface cover layer is 3–6 mm, while the non-working surface cover layer thickness is 1–3 mm.
Rubber belt marking: Width (mm) × Number of plies × (Working surface rubber thickness + Non-working surface rubber thickness) (mm) × Length (m). Example: 800 × 8 × (6+3) × 100.
In the food industry, rubber belts can be used for loading, unloading, and conveying bulk raw and auxiliary materials and packaging items. They can also be used as conveying-type inspection tables and pretreatment conveyor belts.
(2) Plastic Belt
Made from polyvinyl chloride, it is primarily used as the traction and carrying component of belt conveyors. It is divided into solid-woven core and multi-ply core types. Solid-woven core plastic belts have simple manufacturing processes and low costs, with good performance except for relatively poor flexibility. Multi-ply core plastic belts have a strength similar to that of ordinary rubber belts and consist of a carcass and cover layers. Plastic belts offer advantages such as abrasion resistance, acid and alkali resistance, oil resistance, and corrosion resistance, making them suitable for a wide range of applications. For example, plastic belts perform significantly better than rubber belts for conveying foods with high oil content.
(3) Slat Belt (Plate Belt)
Also known as chain slat conveyors, they are formed by connecting many articulated chains (Figure 2-2). This type of slat belt needs to be installed on a specialized chain slat conveying device. The movement of the conveyed material is driven by the traction of the slat articulated chain, while the support force for the slat belt and the conveyed items is provided by guide plates fixed underneath the slats. In other words, during operation, the material and slats slide on the guide plates to complete conveying.
Figure 2-2 Slat Belt
(Slat belt structure schematic)
Slat belts are mainly used in production lines for beverages, canned goods, etc., and for conveying various food product packaging boxes. In some situations where the conveying angle is too large and friction cannot keep the material stationary relative to the belt, baffles (scrapers) of a certain height need to be added to the conveyor belt.
(4) Canvas Belt
Canvas is a relatively thick cotton or linen fabric, named for its original use in sails. Canvas conveyor belts are called canvas belts. Their characteristics include high tensile strength, good flexibility, and the ability to withstand repeated folding without fatigue. Canvas is usually joined using cotton thread and synthetic fibers, and in rare cases, with leather strips. The length of canvas belts can be adjusted according to practical production needs, making them very convenient to use.
Canvas belts are mainly used in the conveying process of dough sheets and biscuit blanks before biscuit forming, such as dough sheet lamination, shortening rolling, and biscuit forming.
(5) Wire Mesh Belt
Its features include high strength and high-temperature resistance. Because it has mesh openings, and the mesh size can be selected as needed, the length of the mesh belt can also be chosen arbitrarily. Wire mesh belts (Figure 2-3) are often used in applications that require simultaneous conveying and solid-liquid separation, such as continuous fryers, fruit and vegetable cleaning equipment, and baking equipment.
Figure 2-3 Wire Mesh Belt
(Wire mesh belt structure schematic)
(6) Chain Belt
Usually consists of metal slats fixed between chain links. The traction drive is similar to that of wire mesh belts, also driven by a pair of sprockets. Some processing equipment uses chain belts as conveying components.
(7) Steel Belt
Made primarily from stainless steel. When conveying high-temperature materials, rubber belts can release harmful substances, while steel belts do not. Therefore, steel belts are suitable for high-temperature conveying applications and are particularly well-suited to the food industry. Advantages of steel belts include: high mechanical strength, low elongation, high-temperature resistance, and resistance to damage. Steel belts also have disadvantages: first, due to their high rigidity, larger-diameter drums are required to avoid breakage; second, steel belts are sensitive to impact loads, requiring accurate installation and regular monitoring during operation; third, steel belts are expensive and are not used in general working environments.
Steel belts are mainly used in high-temperature working environments. The most typical application in food processing is the conveying device in continuous baking ovens.
2. Drive Unit
The drive unit of a belt conveyor generally includes an electric motor, reducer, drive drum (sprocket), etc. On inclined conveyors, braking devices or backstops are typically installed as well. The drive drum is generally a hollow structure, slightly longer than it is wide, to ensure effective application of driving force. The drive drum is slightly crowned (larger diameter in the middle), so during operation, greater tension is generated at the center of the conveyor belt, automatically correcting belt “misalignment”.
For general belt conveyors, the driving force is mainly applied through friction between the drive drum and the conveyor belt. Therefore, to ensure appropriate friction between the two and prevent slipping, the drive drum surface is often patterned to increase the coefficient of friction with the conveyor belt.
For chain slats, wire mesh belts, and roller conveyors, the drive unit used is a pair of chain sprockets.
3. Frame and Idler Rollers
The frame is mainly welded from channel steel, angle iron, and steel plates. It serves as the main load-bearing structure in the belt conveyor. Idler rollers primarily support the conveyor belt and the conveyed material, ensuring smooth operation. Idler rollers are divided into upper idlers (also called carrying idlers) and lower idlers (also called return idlers). Depending on the material’s flow characteristics, upper idlers typically take several forms, as shown in Figure 2-4. Generally, for materials with poor flowability or packaged items, flat idlers are used, while for large quantities of bulk materials, V-type (trough) idlers are commonly used.
Figure 2-4 Several Forms of Upper Idlers
(a) Flat single roller type (b) Flat multi-section single roller type (c) Single roller type
(d) Two-roller V-type (e) Three-roller trough V-type (f) Three-roller V-type
Figure 2-5 Adjusting Idler
(Adjusting idler structure schematic)
Adjusting idlers (Figure 2-5) is mainly used to adjust the running direction of the conveyor belt, preventing belt “misalignment”. Generally, such adjusting idlers have a baffle installed at each end to prevent the belt from slipping off.
Not all conveyor belts require idler rollers. For example, slat belts rely on frame guide plates for support and sliding, while wire mesh belts and chain belts rely on chain tracks for operation. In fact, in applications with low conveying speeds and short distances, flexible conveyor belts (such as rubber, plastic, or canvas belts) often do not use idler rollers but instead use support plates.
4. Tensioning Device
Most conveyor belts (such as rubber, plastic, and canvas belts) have a specific elongation rate. Under prolonged, significant tension, their length can increase slightly. This increase directly reduces the pressure between the conveyor belt and the drive drum, lowering friction and potentially causing the belt to slip. Therefore, actual belt conveyors are equipped with tensioning devices. Common tensioning devices mainly include counterweight type, screw type, and spring-screw type (Figure 2-6). These three forms have their own advantages. For example, the screw-type device saves space and is simple to operate, but requires frequent inspection; combining it with a spring can address this issue, but the spring’s effective range is limited, and long-term use may lead to aging and failure.
