By Tom Johson, Pobco, Inc.
Packaging technology & Engineering, August 1997

FOCUS. Plastics are seeing an increased role in use on packaging equipment due to their penchant for reduced friction and wear between moving component parts. There are a number of plastic materials appropriate for use on packaging machinery, each with its own attributes. It is important for packagers to know which plastic is best for a given application.

Introduction
The influence of plastics for use on packaging equipment is significant. The evolution of packaging equipment has witnessed the need and reality of harnessing increased operating speeds with a focus on precision, safety and extended equipment life
   Made of New England grown rock maple, the wooden bearings were the company's signature product for decades, sustaining the family-owned business for three generations.
   During this transition a variety of plastic materials have been called upon to perform a multiple number of tasks. The reasons for their application are many and varied. OSHA regulations regarding safety and noise have contributed to their proliferation, as have new and updated methods of controlling and transferring power and product movement.
   The major reason, however, is to reduce friction and wear between moving component parts, particularly metal-to-metal contact. Original equipment manufacturer:; and those who retrofit for specific applications are ever searching for components that provide the following advantages: self-lubrication; wear reduction (reduced friction); noise reduction; compliance with sanitary code requirements (USDA and other international food compli-ant regulations); safety; ease of installation; non-corrosive for life; overall cost reduction and customer satisfaction.

Component Types and Uses
Packaging equipment components include: guide rails, wear strips, chain/belt/cable guides, rollers, bearings, pulleys, sprockets, chains and a countless number of custom parts/profiles made from a variety of plastic materials. Transparent plastic dividers and guards are used for safety and improved aesthetics.
   Many plastic profiles are provided complete with aluminum, steel or stainless steel mating partners such as guide rails and chain guides. Much of this application centers around the linear movement of the equipment. The metal guides fitted with friction-reducing plastics are usually furnished in 10-20 ft. lengths. They are fastened in place on the sides or bottoms (beds) of packaging equipment. Their purpose is to guide products or control the direction, tension and vibration of drive-chain along the linear plane of the equipment.
   The chain usually sits and slides over plastic wear strip. The chain is usually driven by plastic sprockets or drive rollers (metal or plastic rollers fitted with sprockets). The sprockets are powered by a motor connected to a shaft on which the sprockets are fixed. Sometimes special lubricant-filled hardwood is preferred for wear strip due to its lower coefficient of friction, lower wear rate factor and greater dimensional stability.
   Products being conveyed usually sit on top of plastic table-top chain. An increasing number of manufacturers are using plastic cap-tured chain wear strip on straight and curved sections of equipment to "capture" roller and table-top chain driven along a linear plane. This allows for smoother running, quieter, safer and longer life equipment. By preventing metal-to-metal contact, the life of the chain and 'other metal components is extended. Furthermore, since the chain is "captured" it cannot waver off course.
   Many of these components also allow for a majority of the moving parts to be "hidden," making equipment more aesthetically appealing.

(Figure 1) Chain Tensioner

   In conjunction with this, components that eventually fail or wear out must be able to be retrofitted quickly, reducing downtime. One quick method for tensioning chain is the application of plastic chain tensioners. These chain tensioners are widely used to allow for maximum sprocket drive efficiency and reduced vibration (Figure 1).

Types of Plastics Used
The types of plastic materials used and information regarding their properties are listed in the Engineering Materials and Data Section. There are various reasons why certain plastics are used for particular packaging equipment applications.
   White, repro-green/black, Tube-filled and anti-static black varieties of the polymer ultra-high molecular weight polyethylene (UHMWPE) is a predominant plastic utilized. This material has excellent abrasion resistance, a low coefficient of friction and is often USDA-approved for use in the food and beverage industry.
   There are, however, other food-approved plastics that are necessary for use where speed, temperature or chemicals prevent the use of UHMWPE. Acetals (Delrins®) are often used where more rigidity is required and where heavier loads are in evidence. Acetals also stand up well to steam cleaning.
   Teflons® are used in high heat applications (up to 450°F) and/or where chemical contact requires their use. Teflons have a low coefficient of friction but do not work effectively at high speeds and heavy loads due to their inherent "softness." However, Teflons are very flexible and can be extruded into most shapes and sizes. Rulou® 641 is a Teflon-based material made with special additives to increase temperature range (up to 550°F) and to allow fur heavy loads and speeds.
   There is also a Rulon LR bearing-grade plastic for applications not requiring food compliance. It has the same excellent physical characteristics of Rulon 641, but is less expensive and more practical for some applications.
   PET -P (polyester) is required where more dimensional stability is required at 230°F maximum temperatures. It is lower in cost than Teflons and Rulons with low moisture absorption and good rigidity similar to the Acetals.
   Natural nylons are sometimes preferred due to their availability as molded bearings, washers and fasteners at low cost. Nylon items can also be easily machined. Nylons sometimes absorb too much moisture for application since their dimensional stability in water is only fair. For better wear and load characteristics, dry lubricants are added to produce Nylon MD and wet lubricants to produce Nylube. Although not officially sanctioned by the FDA and USDA food compliant regulations, these materials do find application on packaging equipment.
   Standard or custom plastic components can often be supplied as extruded, molded or machined items. Extruded and molded products are usually less expensive than machined parts when used in volume. The lengths and shapes of certain products such as wear strips, guide rails and chain guides require the extrusion method. Bearings, rollers and other round, square and spherical shapes lend themselves to molding or machining operations. Some plastic polymers cannot be extruded or molded and must be machined from rod or sheet stock.

Synergy in the System
Packaging equipment and adjacent conveyor lines are becoming more integrated. Indeed the conveying industry uses many of the same materials and components that the packaging equipment industry utilizes. Hence there needs to be, and is, synergy in the entire system of product flow. If conveying and packaging lines do not "mesh" properly, there are often components available to "fix" the problem.
   Eliminating as much downtime as possible is one of the primary goals of maintenance and engineering departments. Manufacturers of products using packaging equipment require reliable systems and reliable solutions to problems when they arise. The manufacturers of components for these systems need to operate with an eye to solving customer problems and must have insight as to what components and materials will work in a given application.

About the Author: Tom Johnson is Marketing Manager for POBCO Inc., a Worcester, MA-based manufacturer of plastic, wood and metal equipment components. He has been with POBCO for 25 years and currently manages marketing and product development in the United States and abroad.