The Basics of Food Industry Mechanical Conveyors
By Kathy Hunter
Monday, March 15, 2010
Conveyor systems are designed to move large amounts of materials at a quicker pace than, and fraction of the cost of, manual labor. Both pneumatic and mechanical conveying systems are widely used in food processing plants. This article will cover the basics of mechanical conveyors. Often called the workhorses of material handling systems, mechanical conveyors are horizontal, inclined, or vertical devices used to move or transport bulk materials from point A to point B. The term “mechanical conveyor” actually covers a wide assortment of devices, ranging from belts to trays to buckets, that can be used to move materials or products through the manufacturing process in an automated way.
Conveyors can safely transport materials from one level to another, which when done by humans could be expensive and strenuous. They can be installed almost anywhere to move loads of all shapes, sizes, and weights. In a food processing plant, conveyors can be used in a variety of ways:
• Moving raw materials into silos or other storage devices
• Transporting the same raw materials out of storage devices and into the production line for mixing, batching, and processing
• Moving the finished food product into the packaging line
• Moving the packaged products to shipping
The Conveyor Equipment Manufacturers Association (CEMA), headquartered in Naples, Florida, has defined more than 80 types of conveyors used in the process industries, and sets standards for the industry(www.cemanet.org). CEMA is the leading industry association that represents American manufacturers and designers of conveyors systems, sub-systems, and components. The association provides engineering standards, fact sheets, and specifications for design and safety for a variety of conveyor types. Although CEMA is an organization serving manufacturers of conveying systems, purchasers of the same may find the publications and fact sheets on the CEMA web site helpful with their buying decision.
Key Components and Terms
While a wide variety of conveyor types exist, each conveyor includes:
• a belt, bucket, screw, vibrating tray, tube or some other means to handle the material to be conveyed
• a drive mechanism of some sort, often an adjustable speed drive or power mechanism that enables control of the speed of the device
• a structure or stand to support the conveyor
• motor controller to start, stop, accelerate, or decelerate the conveyor drive
A basic motorized conveyor system usually consists of a belt that continuously moves over top of rotating drums or two end pulleys, or a system that is pulled by motors. The “bed” of the conveyor is that part of the conveyor upon which the load or carrying medium rests or slides while being conveyed. The term “bed” can also refer to the depth of the material being processed when conveying bulk material. A conveyor “trough”is a channel that contains the material being conveyed; it can be open or fitted with a cover. The conveyor“run” is the distance covered by the conveyor. The “maximum angle of inclination” is the maximum angle from the horizontal at which a conveyor may be inclined and still deliver a predetermined quantity of bulk material in a given time.
Sanitary Design for Food Handling
Conveyors used for food production must be designed, fabricated, constructed, and installed according to sound sanitary design principles. Mechanical conveyors, like all equipment used for food production, must meet FDA current Good Manufacturing Practices (cGMP), as described in the Code of Federal Regulations (CFR) Title 21, Subpart C, Section 110.40, calling for corrosion-resistant and smooth food contact surfaces, installation in a way that enables cleaning and inspection, and more. Mechanical conveyors used for the production of milk products are governed by the 3A Dairy Standard for mechanical conveyors, standard No. 3A 41-03, published January 4, 2008. (See www.3-a.org)
Some Common Types of Mechanical Conveyors Used in Food Plants
Belt—Belt conveyors are perhaps the most commonly used conveyor type. They are used in the food industry in both the processing and packaging of food products. The smooth continuous surface of a belt is ideal for food handling. Belts for food applications must be made of strong, durable materials such as nylon, rubber, polyester, or other materials that are acceptable for use with food products and can be cleaned. A belt conveyor consists of two or more pulleys with a continuous loop of material that rotates about them. They can be used to elevate, decline, or horizontally transport material for inspection, cooling, storing, or conveying.
Vibratory—A vibrating conveyor is a machine with a solid conveying surface that is turned up on the side to form a trough. They are used extensively in food applications where sanitation, wash down, and low maintenance are important. The trough or tray is mounted on a vibratory drive, which delivers sympathetic vibration to the trough, moving material forward. Vibratory conveyors can be multi-functional and can also be used in food plants to cool, scalp, screen, orient, and separate materials while transporting.
Screw—A screw conveyor is made of helical flight pieces that are fixed to a pipe or a solid shaft and then placed inside a U-shaped or tubular trough. As the screw rotates, material piles up in front of the flights and then the material is pushed through the trough; the screw is rotated by a motor. The trough should have openings so that any jammed material can be easily cleaned and periodic maintenance can be performed. Shaftless screw conveyors are also available for use with moist materials. Most screw conveyors used in food processing are constructed of stainless steel.
Flexible Screw—Flexible screw conveyors consist of a stainless steel or heat-treated and tempered carbon steel screw that rotates within an Ultra High Molecular Weight Polyethylene food grade tube. The term flexible means that these conveyors can curve to some extent, letting users route the conveyor around obstacles. The flexible screw conveyor is designed to be simple to install and operate and is also designed to be operated when full of material, rather than with batches or slugs of material.
Aero-mechanical conveyors (ACM)—The aero-mechanical conveyor (ACM) could also be called a “rope and disc” conveyor. The AMC consists of several evenly spaced polyurethane discs attached to a wire rope. The rope and discs travel in a continuous loop fashion at a consistently high speed within parallel steel tubes, producing an airstream that fluidizes and entrains the product in airflow until is it centrifugally ejected at the outlet. The AMC can move batches and operate at almost any angle, in straight-line fashion or rounding curves. It causes almost no degradation to the material being moved. Maintenance needs can be moderate to high, however.
Ten Key Points to Review When Selecting a Mechanical Conveying System
In order to work with a supplier to select the right type of mechanical conveyor for the application, the purchaser of a conveying system should review the following points of information:
1. What is the material to be conveyed? Review: material bulk density, particle size, characteristics such as abrasiveness, moisture content, flowability, fluidity, dustiness, flammability, explosiveness.
2. From what is the material being conveyed? (Such as silos, bulk bag, etc.)
3. To what is the material being moved? (Such as a mixer, feeder, mill, etc.)
4. How far is the material to be conveyed? Horizontally? Vertically? Route with bends?
5. At what rate/speed/throughput is the material to be conveyed, over what period of time?
6. What material condition is desired at end of the conveying route? Must the integrity of the mixture be maintained? Is it important to minimize damage to a fragile material?
7. What is the factory environment? Dusty? Hazardous? Must specific sanitary standards be met?
8. What controllers are being used and is control integration to the process line needed?
9. What routine maintenance is needed and what are the sanitary requirements for cleaning of the conveyor? Is the location accessible for maintenance and cleaning?
10. Is a product feasibility test advisable to determine the most suitable conveyor for the material concerned, the distance involved, and the throughput required?