Regina P. Bracy, Parish, Richard L. | 10/7/2005 12:24:09 AM
Farm and grounds maintenance equipment is often exposed to rain, high humidity, fertilizer, pesticides and corrosive plant materials (such as grass clippings). The manufacturers of that equipment have taken steps to try to protect the equipment and reduce the potential for corrosion. Some steps they have taken include:
Although plain carbon steel and cast iron are still the most common materials in farm and grounds maintenance equipment, there is increasing use of alloy steel, stainless steel and plated steel in critical areas. Adding chromium, nickel, copper or phosphorus to steel can improve its corrosion resistance. Sometimes these materials are incorporated into the steel alloys and sometimes plated onto the surface.
Better Degreasing Before Painting
Steel comes from the mill with a coating of oil. Additional contaminants such as cutting oil and die lubricants as well as dirt can be added during the manufacturing process. These surface contaminants must be removed before the steel is painted. Manufacturers have installed improved equipment to better clean the steel.
Better Paint Preparation Coatings
Paint will bind to steel much better if the cleaned metal is coated with a base material such as iron or zinc phosphate. These materials provide some corrosion resistance themselves and also allow a much stronger bond by the paint. These phosphatizing processes are used on automobile bodies and are now being adopted on some farm and grounds maintenance equipment. Other conversion coatings are used on small parts such as fasteners to reduce corrosion of those parts.
Paints themselves have been improved. Alkyd enamel used to be the predominant paint for farm and grounds maintenance equipment, but the major manufacturers are now switching to epoxy primers, acrylic and urethane liquid topcoats, and polyester, epoxy or urethane powder coatings. All of these help provide better corrosion resistance, longer paint life and better shine retention.
Better Application Methods
Although sprayed or dipped liquid paint is still common, some manufacturers are switching their high-end products to alternate processes such as powder coating and e-coating. In powder coating, the prepared parts are grounded while electrically charged dry coating particles are sprayed on. The electric charge causes the particles to stick to the parts and to wrap around corners and into difficult areas. The dry-coated parts are then baked so the polymer particles can melt, flow and bond to the part yielding a very corrosion-resistant coating. In e-coating, the parts are dipped into a charged tank of coating material. Once again, the electric charge helps the paint reach difficult areas and bond well.
Better Test Standards
The standards for evaluating paint quality and corrosion resistance have improved over the years. One of the basic tests is the salt spray test in which test parts or test panels are scratched and then exposed to a spray of salt water. Better coatings resist rusting and paint blistering from the scratch for a longer period. Panels may also be exposed to a cycle of salt spray followed by high humidity. Painted panels may be subjected to mandrel bend or impact tests to measure paint adhesion and resistance to cracking and peeling. Painted panels are tested for ultraviolet light deterioration by exposure to direct sunlight, typically in a southern state. The acceptance standards for these tests have been raised so that current coatings last longer.
More Use of Plastics
Manufacturers are increasing their use of plastic for body panels as well as functional parts. Plastic does not rust or corrode. The color can be molded in so that scratches are less likely to show. New materials and processes such as sheet molding compound (SMC) and reaction-injection molding (RIM) as well as larger presses for injection molding allow production of large, complex tractor and equipment parts with good surface quality. It should be noted that plastic is not always a better choice and does not always imply higher quality. Plastic can be more durable in the short term, but it is subject to embrittlement and cracking over a period of years. Plastic used judiciously and appropriately can improve the life of equipment, but indiscriminant use of plastic can reduce product reliability and durability.
Most of these improvements are found on tractors, expensive equipment such as combines and quality grounds maintenance equipment. These improvements may not be found on lesser implements or on equipment produced by short-line manufacturers, some of whom just spray or dip a coat of alkyd enamel on their products with little or no surface preparation.