Bushings retain and guide shafts between moving pieces in equipment like stamping presses, molding machines, and other automated, repetitive motion components. These guiding elements help keep tooling aligned in dies, ensure smooth and consistent motion, and help reduce damage and wear over thousands of cycles.
Bushings are generally available in steel or steel with a bronze lining, either plated or sintered and solid bronze. Here, we’ll focus on three different types of bronze bushings: plated, sintered, and Ready Technology’s unique SinterLube® lining. Keep reading to learn how they work and how these three linings differ in use.
Bronze Bushings and Their Applications
A bushing is one of the components that make up a set of guiding elements that align machinery for precision motion. In stamping applications especially, bushings are used in conjunction with guide pins and optional ball bearing cages.
Basic bushings are made from machined quality alloy steel that is hardened and tempered for durability and wear resistance. They require regular lubrication, are a solid choice for medium-speed operations, and are economical. However, they cannot maintain high-speed stamping or other operations which may cause premature wear and may require frequent maintenance.
Adding a bronze lining to the inside diameter of a steel bushing improves its wear resistance and ability to hold lubricants for longer. This results in fewer breaks in production to reapply lubrication. Bronze linings can be applied by plating or sintering.
Primary manufacturing applications for bushings include:
- Metal stamping
- Plastic molding
- Automated and semi-automated metalworking machinery
- Some types of food processing equipment
Types of Bronze Bushings
All bushings start with a machined bearing, which can be made from solid bronze or steel to which a bronze lining is applied. How the bronze layer is created impacts long-term durability, performance, and productivity.
Solid Bronze Bushings
Bushings can be machined from solid bronze. They are corrosion resistant and withstand heavy loads; however, they are only suitable for low-speed operations. Because they are made entirely from solid bronze, they are often more expensive than other options. Bronze bushings require regular lubrication with grease or oil.
Graphite-Plugged Bronze Bushings
To solve the time-consuming problem of regular lubrication, bushings can be made to accept small plugs of graphite, which provide ongoing lubrication. The bushing cylinder is machined from solid bronze, and then a series of small holes are machined through the bushing at intervals. Each hole is fitted with a graphite plug, secured with adhesive. The disadvantage to this type of bushing is that above certain temperatures, the adhesive can melt, causing the plugs to dislodge and eventually extrude, which further alters the bushing diameter. High-speed stamping operations generate enough heat to cause these plugged bushings to fail. What’s more, the plugs may require replacing when bushings are reground.
Bronze Plated Bushings
Bronze plated bushings are made by placing machined steel bushings in an electroplating bath that deposits a layer of bronze on the bushing. The steel bushings must be extremely clean prior to plating to avoid defects, and the thickness of the bronze layer may change between batches as the amount of bronze in the bath is depleted. The plated layer adheres to the surface well; however, it can chip, flake, or peel away over time.
Sintered Bronze Bushings
Sintering is a powder metallurgy process in which bronze powder is applied to the inside of the bushing, then fired in a special furnace under precise temperature and atmospheric conditions. This causes the bronze layer to solidify and form a permanent, mechanical bond with the steel base. The result is a thicker layer of bronze than plating can achieve, better retention of lubricant, and a much longer service life.
SinterLube® Alloy Bushings
An innovative take on standard sintered bronze bushings is Ready’s SinterLube® technology. The difference is due to a special powdered bronze and high-lubricity alloy mixture that is used instead of plain bronze powder. Its high natural lubricity maintains optimal conditions throughout production. The sintered bronze layer is just as permanent as regular sintered bronze; however, the nature of the alloy means they require only an initial application of high-viscosity lubricant for an entire production run.
How Do They Differ in Practice?
While any of these bronze linings provide excellent wear resistance and improve service life, there are trade-offs in practical application. For example:
- Long-Term Costs. Bronze plated bushings may be less expensive initially due to the thinner layer of bronze applied; however, plating is not as durable at the intense temperatures and speeds generated during high-speed stamping operations. The nature of electroplating can also lead to variations in the lining thickness.
- Maintenance Needs. Sintered bronze bushings are porous and hold lubricant better and longer than plated alternatives. This results in fewer breaks in production to reapply lubricants. What’s more, bushings made with SinterLube® Alloy are truly self-lubricating and require only a single, initial application of lubricant at the start of production, for even greater efficiency.
- Performance Over Time. Plated bronze is a surface application that tends to chip or peel off over time, due to exposure to high temperatures and fast operational speeds. In contrast, sintering is a permanent application in which the bronze or bronze alloy layer is mechanically bonded to the bushing. Sintered options are more durable and require less maintenance over time.
Advantages of Choosing Innovative SinterLube® Bushings
For many applications, the most significant value comes from investing in Ready’s SinterLube® bushings. Some advantages include:
- Self-Lubrication. Prior to sintering, the bronze powder is blended with an alloy that was developed specifically for its excellent lubricity. One application of lubricant is all that is required during production.
- Greater Reliability than Graphite Plugs. While some bronze bushings are fitted with plugs of graphite for lubrication, these are held in place with adhesive, which can melt at high temperatures. This may cause them to dislodge, creating a mess to clean and altering the bushing’s inner diameter and guiding precision.
- Consistent Initial Geometry. SinterLube® bushings wear less and maintain their initial close fit with guide pins. This guiding accuracy helps hold tight tolerances throughout production.
- Virtually Wear-Free. Sintered bronze is a permanent layer. It is also thicker and far more durable than plated bronze. After thousands or millions of cycles, wear and tear on the bushing will be minimal.
- High-Speed Operation. SinterLube® bushings withstand high press speeds and fast cycles over 800 strokes per minute.
- High Temperature Tolerance. SinterLube® bushings remain intact and properly lubricated at high operating temperatures during molding, stamping, and similar processes.
- Cost-effective. SinterLube® bushings are more efficient to manufacture vs. a graphite plug and other types of bushings. This results in an overall manufacturing cost savings that is reflected in the customer’s final price. You’ll also save on lubricating oil because a single application lasts for the entire run.
Reliable Guiding Elements from Ready Technology
Bronze bearings are a critical component for stamping, molding, and other precision manufacturing applications. All of Ready Technology’s ball bearing pins and bushings are compatible with major ball bearing brands, and we stand behind all of our products.
Contact us to learn more about our full selection of die sets, springs, benders, cams, and accessories, or request a quote to start your order.