Applying modular plastic conveyor belts
Key concepts These belts handle corrosion, tracking, and sanitation problems. Speed, impact resistance, application temperature, and required life help determine the proper belt design.
These belts handle corrosion, tracking, and sanitation problems.
Speed, impact resistance, application temperature, and required life help determine the proper belt design.
Most modular plastic belts are made from polypropylene, polyethylene, or acetal thermoplastics.
Product conveyance is a necessity in virtually every manufacturing plant. No matter what the industry, raw materials are brought into the plant, products in process are transported from one operation to the next, and scrap is taken away. Further processing and packaging require even more conveyance.
There are a number of conveyor options: rollers, air transport, liquid tubes, chains, and belts. Within the most common belt conveyor category, the material choice includes steel, wire mesh, rubber, PVC, fabric, and modular plastic.
The modular plastic conveyor belt was invented about 25-yr ago to resolve conveyance problems in the shrimp processing industry. The original product was designed to deal with corrosion, belt tracking, and sanitation problems. Further technological advances enable processors to convey products with better efficiency and less maintenance.
Examining the system
Designing modular plastic conveyor belts is quite complex. Engineers first examine the application to understand the customer's requirements and conveyance objectives. Is the processor trying to convey delicate product gently, or is there a heavy, robust item to move from one operation to another? Does the application require high or low friction conveyance? Are there any special abrasive or load characteristics in the application?
Belt speeds, impact resistance, application temperature, required belt life, and other special considerations also play a critical role in the initial design.
Manufacturing uses plastic pellets injection-molded into modules to create a belt. Modules are assembled into interlocking patterns and joined by hinge rods. Depending on the style, a typical 2-ft 3 50-ft belt uses 600—4000 modules.
Positive drives increase efficiency and maximize torque transmitting capabilities, while the belts are driven by plastic or metal sprockets instead of friction rollers. Sprockets have square bores and are driven by matching square shafts (round bore sprockets are available for special applications).
Square shafts transmit torque without the need for troublesome keys and keyways, and accommodate the lateral expansion differences of the plastic belt material and metal shafts. Typically, only one sprocket per shaft is retained in the drive system. Other sprockets are allowed to float, moving along the shaft as the belt expands or contracts. Thus, the sprockets are always transmitting torque.
Belt materials are available in several versions, with polypropylene, polyethylene, and acetal thermoplastics being the most common.
Polypropylene has good chemical resistance to many acids, bases, salts, and alcohols. It is a relatively strong material, with superior fatigue resistance (in normal use). However, it is not appropriate for low-temperature applications where it becomes somewhat brittle. Polypropylene is available in flame-retardant and UV-resistant versions.
Polyethylene is better in lower temperatures and has high impact strength and flexibility.
Acetal thermoplastics, which are considerably stronger than the other two, have a good balance of mechanical, thermal, and chemical properties. Acetals also tend to have a much lower coefficient of friction.
There are also a number of other specialty materials used for specific types of applications. The "Belt materials and their characteristics" table on the next page presents data for some of the specialty materials, as well as the three primary ones.
Typically, modular plastic conveyor belts are identified by "Series" and "Style." Each numbered belt series is grouped by sprocket style. Belt style refers to the surface configuration of the belt.
For example, a belt series may be available in as many as nine different styles: flush grid, open grid, raised rib, flat top, perforated flat top, live transfer belts, mold-to-width chains with and without tracking tabs, and friction top. All these belt styles run on the same set of Series 900 sprockets, which are available in multiple pitch diameters, multiple bore sizes, and square or round bore styles.
— Edited by Ron Holzhauer, Managing Editor, 630-320-7139, firstname.lastname@example.org
&HEADLINE>Cans big on plastic&/HEADLINE>
The can manufacturing industry is a major proponent of modular plastic conveyor belting. About 20-yr ago, almost all conveyance in a two-piece beverage can plant was high-speed, single-file cable. Modular plastic conveyor belting allowed the industry to transport in mass, slowing down can movement and reducing the potential for spoilage, while still maintaining line throughput.
About 7-yr ago, another innovation in conveyance technology allowed two-piece beverage can manufacturers to further increase their efficiencies through self-clearing transfers. While the industry had already converted from older forms of conveyance technology to modular plastic conveyor belting, they were still experiencing problems with mass transfer of decorated cans. Larger pitch belts require the use of 6-in. and wider dead plates between conveyors. These dead plates sometimes stranded the small footprint beverage cans, which required processors to manually clear the line to prevent label mixups.
A minipitch belt capable of operating around a nosebar solved the problem by allowing for narrow, "self-clearing" dead plates. This belt saved hours of labor previously used to clear the lines and reduced their risk of label mixups.
Another recent innovation in can industry conveyor belt technology is a low-friction, flame-retardant material. With safety issues always a concern and insurance premiums rising, many can plants are converting to flame-retardant belting. This green belting has a V-0 rating (does not sustain a flame) and a low coefficient of friction, making it an easy retrofit from acetal belts.
Belt materials and their characteristics<table ID = 'id4726462-65-table' CELLSPACING = '0' CELLPADDING = '3' BORDER = '1' STYLE = 'background-color: #FFFFFF'><tbody ID = 'id4726473-65-tbody'><tr ID = 'id4726475-65-tr'><td ID = 'id4726477-65-td' VALIGN = 'top' STYLE = 'background-color: #F8F2E6'></td></tr><tr ID = 'id4726485-67-tr'>MaterialTemperatureSpecific gravityFeatures</tr><tr ID = 'id4726515-76-tr'><td ID = 'id4726517-76-td'>
Polypropylene</td><td ID = 'id4726524-78-td'>
34—220 F</td><td ID = 'id4726530-80-td'>
0.90</td><td ID = 'id4726537-82-td'>
Resistant to many acids, salts, bases, and alcohols
Good mix of mechanical properties, moderate strength, lightweight, and superior fatigue resistance
Strong in normal use; may be brittle at low temperatures</td></tr><tr ID = 'id4726553-87-tr'><td ID = 'id4726555-87-td'>
Polyethylene</td><td ID = 'id4726562-89-td'>
-100—150 F</td><td ID = 'id4726568-91-td'>
0.95</td><td ID = 'id4726575-93-td'>
Resistant to many acids, bases, and hydrocarbons
Superior high-impact strength and flexibility
Excellent product release</td></tr><tr ID = 'id4727264-98-tr'><td ID = 'id4727266-98-td'>
Acetal</td><td ID = 'id4727272-100-td'>
-50—200 F</td><td ID = 'id4727279-102-td'>
1.40</td><td ID = 'id4727285-104-td'>
Strong; good fatigue endurance and resilience
Low coefficient of friction
Relatively impact resistant; hard material that is also cut and scratch resistant</td></tr><tr ID = 'id4727300-109-tr'><td ID = 'id4727302-109-td'>
Electrically conductive acetal</td><td ID = 'id4727308-111-td'>
-50—200 F</td><td ID = 'id4727315-113-td'>
1.40</td><td ID = 'id4727321-115-td'>
General characteristics are similar to regular acetal (with somewhat reduced mechanical properties)
Resistance of 60,000 Ohms/square effectively dissipates static electricity build up</td></tr><tr ID = 'id4727333-119-tr'><td ID = 'id4727336-119-td'>
Anti-static acetal</td><td ID = 'id4727342-121-td'>
-50—200 F</td><td ID = 'id4727348-123-td'>
1.40</td><td ID = 'id4727355-125-td'>
Same mechanical properties as regular acetal, moderate static electricity dissipation capabilities (enough for less demanding applications)</td></tr><tr ID = 'id4727364-128-tr'><td ID = 'id4727366-128-td'>
Flame-retardant thermoplastic polyester</td><td ID = 'id4727372-130-td'>
-50—200 F</td><td ID = 'id4727378-132-td'>
1.25</td><td ID = 'id4727385-134-td'>
Will not sustain a flame; material is V-0 Rated (UL94 @ 1/32 in.)</td></tr><tr ID = 'id4727393-137-tr'><td ID = 'id4727395-137-td'>
Impact-resistant nylon</td><td ID = 'id4727402-139-td'>
-50—150 F</td><td ID = 'id4727408-141-td'>
1.13</td><td ID = 'id4727414-143-td'>
Strong; high impact and fatigue resistance
Not recommended for wet applications
More susceptible to cuts and gouges than acetal</td></tr><tr ID = 'id4727429-148-tr'><td ID = 'id4727431-148-td'>
Heat-resistant nylon (FDA)</td><td ID = 'id4727438-150-td'>
Continuous to 240 F; intermittent to 270 F</td><td ID = 'id4727445-152-td'>
1.13</td><td ID = 'id4727451-154-td'>
Heat resistant for areas where conveyor is exposed to high temperatures
UL94 flammability rating of V-2
Belts will tend to expand with water and heat</td></tr><tr ID = 'id4727466-159-tr'><td ID = 'id4727468-159-td'>
Heat-resistant nylon (non FDA)</td><td ID = 'id4727475-161-td'>
Continuous to 310 F; intermittent to 360 F</td><td ID = 'id4727482-163-td'>
1.13</td><td ID = 'id4727488-165-td'>
Same as FDA heat-resistant nylon</td></tr></tbody></table>
Sales engineers are willing to answer technical questions concerning this article. They are available at 800-535-8848. The company's web site is www.intralox.com.
For more information related to this subject, see the "Material handling" channel at www.plantengineering.com