Food equipment manufacturers face numerous challenges – meeting the industry’s demands for productivity, cleanliness and conformity to agency standards (FDA, USDA, 3A, etc.) – all while trying to keep costs down. Using high performance engineering plastics to replace metal parts is one often overlooked way to achieve these goals.
Advantages of Engineering Plastics
Today’s engineering plastics offer equipment manufacturers many advantages over metals, including:
• longer part life
• less wear on mating parts
• reduced weight and noise
• corrosion resistance
• thermal & electrical insulating properties
• reduced cost
Plastics are non-abrasive when mated to a metal part or another plastic. This means that the plastic part does not wear at the mating surface, and it does not cause wear on the metal part. In some cases, plastic can outlast metal by as much as 7 to 10 times in a wear or bearing application. Plastic is also less likely to slough contaminating slivers, particles or dust into the process as can often happen with metal-to-metal interfaces. In addition, some plastics can be internally lubricated with FDA-compliant lubricants, eliminating the cost and maintenance time associated with using external greases or oils to lubricate parts.
Certain types of plastic also offer excellent chemical and corrosion resistance. Some food processors have resorted to using expensive exotic metals to handle corrosive environments when some of the least expensive plastics offer the same outstanding chemical resistance. This property can be especially important if the equipment utilizes Clean-In-Place (CIP) processes. In recent years, as bacterial contamination has become a greater concern to the industry, concentration levels in CIP solutions have increased, sometimes to very high levels. These higher concentration levels may cause problems for existing plastic parts. If you notice chalking, expansion or cracking in plastic parts used in your CIP operations, you may want to consider upgrading inadequate plastic materials to high performance engineering plastics that offer better resistance to chemicals. In addition, some of the newer engineering plastics better resist stains. This keeps equipment looking cleaner, which makes FDA inspectors happy. Certain plastics today are even available with built-in antimicrobial properties.
Engineering plastics also offer excellent strength while reducing overall weight. As an example, A36 steel has a relative strength-to-weight ratio of 1. Nylon has a ratio of 2.27 and Techator has a ratio of 2.78, higher even than the ratio of aluminum at 2.41. Lighter weight moving parts require less energy to be moved, allowing downsizing of related materials and hydraulics. This can potentially improve the speed, accuracy and power consumption of the machine, providing higher productivity at lower operational costs. The overall weight reduction also reduces the shipping cost of the machinery, and in the case of mobile equipment, makes the equipment easier and safer to move or lift.
Engineering plastics are easier to fabricate than metals and produce less wear on the machinist’s tooling. The resultant longer cutting tool life produces a cost savings. Plastics are very cost effective to cut to size and weld, especially in comparison to exotic metals and stainless steel.
Engineering plastics also provide electrical isolation not possible with metal parts. Non-FDA-compliant materials such as Vespel, for example, can perform in continuous temperatures from cryogenic to 550° F with excursions to 900° F and higher. High performance engineering plastics can also operate in some very demanding bearing applications without lubrication. Metal parts can be very difficult to lubricate in these types of applications. Plastics also do an excellent job of dampening or reducing noise in a manufacturing facility, often a top priority for safety directors.
Finally, with the rising cost of metals, particularly steel, engineering plastics can provide a cost-effective solution to replace metals in many applications.
Which Plastic Is Right For You?
With plastics offering so many advantages, why don’t more equipment designers specify engineering plastics? Many engineers are not as well versed in plastics technology as they are in metal and may not be aware that an engineering plastic exists that can solve their problem. Another difficulty is the vast array of engineering plastics available today. Selecting the correct plastic for an application can be intimidating to manufacturers. Many may also not be aware of the numerous FDA and 3A compliant plastics that are available today. A good plastics distributor can be a useful partner in helping to choose the best plastic for your application.
The first thing to consider when selecting an engineering plastic is the component’s ultimate role in the manufacturing process. Engineering plastics are commonly described as either thermoplastic (meltable) or thermoset (non-meltable). Thermoplastics are generally divided into two major categories, amorphous and semi-crystalline. Amorphous plastics consist of chains of polymers with random molecules in a generally shapeless arrangement that appears under the microscope very much like a pile of cooked spaghetti. In semi-crystalline plastics, these random molecules begin to form partially ordered shapes. As a result of these differences in chemical structure, amorphous plastics in general tend to be transparent and heat formable. Semi-crystalline plastics are opaque, typically not thermoformable, and offer better bearing properties (friction and wear) and better fatigue resistance under repeated loading. Amorphous plastics are used for structural applications, while semi-crystalline plastics can be used for both structural and for bearing and wear applications.
A second key consideration is the application temperature. What temperatures will the plastics be exposed to and will the exposure be continuous or in cycles? The answer to this question significantly narrows the field of viable plastics for the application.
There are numerous other areas to consider when providing complete information to your plastics distributor to aid in selecting an engineering plastic:
Mechanical Properties – For structural applications, what stress or load will be applied? Will the stress be compression, tensile or flexural? Is the load continuous or cyclic? For bearing and wear applications, consider the speeds applied, the load on the bearing, and the need for lubrication. In all cases, will any materials impact on the plastic?
Chemical Properties – What chemicals are involved in the process? What are the temperature and concentration levels of the chemicals?
Electrical Properties – Does the part need to be used as an insulator? Many food processing applications involve powders such as sugar or flour. Static charges build up on the surface of some plastics, effectively clogging or impeding flow. FDA-compliant static-dissipative plastics are available for use in these cases.
Physical Properties – What shape is needed to create your part: rod, sheet, or tube? What size? Is color important?
The advantages offered by engineering plastics far outweigh the difficulties in the selection process, particularly if you work with a plastics distributor who understands the products and your applications. Recent innovations in plastic technologies have led to a group of new engineering plastics that offer the design engineer practical, cost-competitive alternatives to traditional metal substrates.