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Power Transmission Distributors Association is...

the leading association for the power transmission/motion control industrial distribution channel, bringing together distributors and manufacturers.

Tech Tip: Conveyors & Components

Enhance your employees’ product and industry knowledge with PTDA’s Tech Tips. This library of online tips, hints and techniques may be used to educate new and current employees on power transmission/motion control (PT/MC) products, technologies and concepts and serve as reference and reminder for more experienced staff. Tech Tips are based on the expertise of PTDA member companies and content from PTDA’s Power Transmission Handbook®, the definitive resource and training tool on PT/MC products.

Visit the full library  of Tech Tips for additional products.

Where are winged tail pulleys utilized and how do they work?

Winged tail pulleys are constructed with individual wings or fins that act as the outside diameter of the pulley and make non-continuous contact with the underside of the conveyor belt as it articulates around the tail section of a conveyor system. The wings on the pulley create vibration in the belt. The voids in the diameter due to the wings allow material build up on the underside of the belt to dislodge into the voids and fall away. In cases where continuous contact is desired, a spiral winged pulley is specified. 

What design rules have been developed to overcome many of the issues associated with inclined screw conveyors?

1. Limit the use of standard screw conveyor components to inclines of 15 deg. or less. 
2. Use close clearance between trough and screw. The close clearance will limit the amount of material fallback.
3. Increase the speed of the screw conveyor. The increased speed with aid in pushing the material up the 
4. Shorten the pitch of the screw flight. As previously mentioned, the screw becomes more efficient as the pitch
is shortened. Screw speed must be increased to compensate for the shorter screw flight pitch.
5. Eliminate intermediate hanger bearings. Hanger bearings can be an obstruction to the flow of material and
should be eliminated. 
6. Use tubular housings. Standard U-troughs allow material to fall backwards over the top of the rotating screw.
Tubular housings contain the material and increase conveying efficiency.

What are the characteristics of construction used for open track and enclosed track overhead conveyors?

Both open and enclosed track overhead conveyors are used in washing, painting, and other processes. They differ from power and free conveyors in that they are continuously moving and are lighter duty with a lower capacity per trolley. Both the chain and transport trolleys are enclosed in a single track. 

Open-track conveyors consist of a track or channel beam rail on or between which trolleys travel linked by a chain or cable. Each trolley runs on open, sealed, or fitting-lubricated bearings. Some of these conveyors use spot or spray lubrication systems to automatically lubricate the trolley bearings. 

Enclosed track overhead conveyors have a track that largely surrounds the chain and trolleys with a bottom slot for the trolley load fixture. These are often lubricated by brushes or spray lubrication. 

What are the two different methods used to manufacture screw conveyor flighting?

1. One method is by forming a flat bar into a continuous helix. Flighting formed by this method is called helicoid flighting. Helicoid flighting provides a continuous one-piece construction with a work-hardened, smooth finish.
2. The second method is by cutting out disks from flat plate and forming each disk into a helix of approximately one revolution. Flighting formed by this method is called sectional flighting. A continuous helix is made by joining a number of sectional flights together, typically by welding. 

What is Fretting Corrosion?  How and where does it occur?

Fretting is considered a form of wear which occurs under small cyclic movements of two mating metal components. In this wear mechanism, metal adhesion and transfer occur under sliding and vibration. For instance, as shown in below image, a hollow bore of gearbox connected to the solid conveyor shaft could see fretting under small, repeated sliding motion (Axial, radial and/or circumferential). As a result, the metal particles separate in the
form of powder (Hemitite). This powder is also known as ‘iron oxide’ debris.

What are the characteristics of of cut screw flights, cut and folded screw flights, regular screw flights with mixing paddles and ribbon screw flights?

Screw conveyors can mix various materials together by utilizing special modifications to the flighting. Cut screw flights have special notches for moderate mixing of bulk materials, and they can be used for breaking up lumps. Cut and folded screw flights have a tab formed or welded on the cut screw flight for lifting and aggressively mixing bulk materials. The folded tab improves aeration and agitation of bulk materials. Regular screw flighting with mixing paddles have fixed or adjustable paddles that can be located every 90 deg. around the diameter of the center pipe. The paddles are used to retard the flow of material and provide moderate mixing. Mixing action can be controlled by adjusting the angle of the paddles on the center pipe. Ribbon-screw flighting consists of helical ribbon flighting attached to the center pipe using round bars or integral legs that are part of the ribbon design. Ribbon screws are used for mixing sticky or viscous materials or where the materials tend to adhere to the flighting in the corner where the flight meets the center pipe. 

What are some important considerations when selecting PT components for conveyors used in food and beverage processing applications?

In food and beverage applications, the type of product as well as the environment it will be in will determine the type of conveying system used and the characteristics of the components selected to build the conveying systems. There are many factors to take into consideration including temperature, the use of chemicals, water and airflow requirements, deliberate and incidental contact with food products, and product sensitivity/product damage. In many cases, mechanical components must meet USDA and FDA requirements, especially where there is direct contact with the product.

What are some common conveyor belt materials and factors that must be considered when selecting appropriate material for an application?

The main materials conveyor belts are made of include rubber, thermoplastics, metal, fabric and leather. The belt material must be selected based on various factors including, but not limited to, temperature, moisture, chemicals, load, and/or impact.

What is the difference in construction and function between a roller bed and slider bed belt conveyor?

Slider bed conveyors possess a solid polished surface, on which the conveyor belt slips during product conveyance. These conveyors are influenced by product weight variations, which create increasing or decreasing drag on the belt due to belt / slider bed friction.  Roller bed conveyors possess free-running or driven rollers, rather than the solid slider surface.  Roller bed conveyors can carry greater weights with less belt drag.

What are some considerations for equipment used in food and beverage processing?

Some considerations include; ambient operating temperatures, chemical exposure, water or airflow requirements, noise, electrostatic generation/environments, the presence of moisture or steam, product sensitivity to damage, and FDA or international food contact safety requirements.

Right and Left Hand Screws

A conveyor screw is either left hand or right hand depending on the form of the helix. The hand of the screw is easily determined by looking at the end of the screw.  If the helix wraps around the pipe in a counter-clockwise direction, or to your left (same as left hand threads on a bolt), this is arbitrarily termed a LEFT hand screw.  If the helix wraps around the pipe in a clockwise direction, or to your right, (same as right hand threads on a bolt), this is arbitrarily termed a RIGHT hand screw.  When the material flow in a screw is in the direction away from the end being viewed, a RIGHT hand screw will turn counter clockwise and a LEFT hand screw will turn clockwise.

Helpful Belt Tracking Hints

Cleanliness is vital to good belt tracking.  Any build up of material on pulleys and rolls can easily destroy the “perpendicularity" of the pulley or roll face.  Essentially foreign matter creates a new roll or pulley face, which adversely affects belt tracking.  Likewise, cleanliness is essential to proper slider bed belt tracking and any buildup of foreign materials (or roughened portioned of the slider bed face) can easily throw a belt off-center, as this will cause a differential of wrap tensions across the width of the belt.  This can seriously affect tracking.

Belt Conveyor Take-Ups

Take-ups are required on all belt conveyors to compensate for changes in belt length and to maintain belt tension.  Take-up devices may be located at any point along the return after the drive or at the tail pulley.  The most desirable location is immediately adjacent to the drive on the slack belt side.  Take-ups should be designed to provide a movement of at least one percent of the conveyor length between end pulleys with a minimum travel of two inches.

Products Conveyed in Unit Handling vs. Bulk Handling Conveyor Systems

Unit handling conveyors transport “discrete” products—products which are either varied or consistent in size and weight.  This differs from bulk materials, which are materials measured more by “flow”; by volume or mass per time.  More often, bulk materials are dirty, dusty, corrosive or lumpy.  They can be either wet or dry.

The information provided in Tech Tips is not meant to be all-encompassing, but rather to draw attention to and provide information about the particular subjects covered. All suggestions and recommendations contained in Tech Tips are based upon information that is believed to be accurate to the best of the experience and knowledge of PTDA’s contributing members, but are made without guarantee or representation as to results. PTDA and Tech Tip contributors expressly disclaim any warranties or guaranties, express or implied, as to the accuracy or completeness of any information published in Tech Tips, and disclaims and makes no warranty that the information in Tech Tips will fulfill any of your particular purposes or needs. PTDA and Tech Tip contributors disclaim liability for any personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on Tech Tips.
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