Materials

Structural Bearings

COSMEC XL™ bronze structural bearing materials are highly corrosion resistant and are especially adapted for adverse environments. The design unit loadings suggested are considered conservative (See Table 1).

However, in view of the extended life expectancy and the size of the structures supported, the loadings are tempered by the principles of good engineering practice. The permitted loadings on these materials, as shown in the latest AASHTO, AREMA, and any state DOT specifications, should be consulted before a final alloy choice is made.

A representative group of alloys that are most popular and are accepted as standard with many federal and state agencies, as well as leading design engineers, are shown in Table 1.

TABLE 1: COSMEC XL™ Structural Bearing Bronze Alloys

The alloys in Table 1 are listed in ascending order of load carrying capacity and are also listed in ascending order of cost. This is due to the factors of the chemical element requirements in the alloy, and/or special foundry techniques necessary in producing castings and/or a lower machinability rating.

Alloys 210 (ASTM B22 Alloy C90500) and 196 (ASTM B22 Alloy C91100) are the most frequently specified and meet the requirements of over 80% of the designs. The values for design unit loading were empirically established based on the physical properties of the alloy, laboratory tests, and long experience in the field. Ordinarily, a value intermediate in each range is used in design.

Table 2 shows other, less-used bronze alloys also available in COSMEC XL™ bearings.

TABLE 2: Other COSMEC XL™ Structural Bearing Bronze Alloys

*Cosmec Alloy 237 is a modified ASTM B22 Alloy C90500 with up to 2.5% Pb, providing the increased physical properties shown, as well as improving the natural bearing qualities of inherent lubricity, conformability, embeddability, shock resistance, and durability.

Structural bearing designs should be proportional to the size of the structure they support. Bearing size should not be reduced just to bring it up to the maximum allowable loading. Within the practical limits of available space, good design practice dictates that well-distributed conservative unit loads will offer optimum performance.

Self-Lubricating Bushings

In the design of COSMEC XL™ bushings, the variables of load, operating temperature, and environmental conditions are the major factors to be considered by the Engineer. In general, as one variable increases, other variables must decrease in inverse proportion. Remember, COSMEC XL™ bushings are NOT designed to be used as high-speed bushings.

The loading (P), where P = total load/projected bearing area, and the velocity (V), where V = surface speed/minute, are combined to determine the PV rating of a particular design. The allowable PV for a particular alloy has been developed empirically. Experimental testing, experience, and past performance results have been relied upon heavily to arrive at the allowable PV factor (See Table 3).

TABLE 3: COSMEC XL™ Bushing Bronze Alloys

*Cosmec Alloy 237 is a modified ASTM B22 Alloy C90500 with up to 2.5% Pb, providing the increased physical properties shown, as well as improving the natural bearing qualities of inherent lubricity, conformability, embeddability, shock resistance, and durability.

Ultimate performance with COSMEC XL™ self-lubricating bushings can be attained by careful consideration of load and speed characteristics. Load carrying capacity is controlled by the physical properties of the bearing alloy. The following three COSMEC XL™ alloys (315, 237, 434), shown in Table 3, provide excellent results in the vast majority of applications and offer the greatest economy in their operating range.

A list of other bronze alloys (with some of their physical properties) that are also available from Cosmec is shown in Table 4 below.

TABLE 4: OTHER COSMEC XL™ Bushing Bronze Alloys

All materials for all US bearings will be certified domestic material, manufactured and fabricated in the USA in accordance with the “Buy American” requirements for all federally funded work.

Cosmec XL™ Lubricants

COSMEC XL™ lubricants are a unique proprietary combination of active lubricating ingredients that stress their dominant desirable properties and subordinate the lesser qualities of each, much like the alloying of steels to produce particular characteristics.

COSMEC XL™ lubricants are not to be confused with so many “look-alikes,” which are composed almost entirely of graphite. COSMEC XL™ lubricants are not primarily graphite-based. A percentage of graphite may be used in some of the formulas because of its excellent anti-galling and anti-seizing qualities. However, graphite alone or in high concentration has a coefficient of friction of over 25%.

Just as no one bearing alloy will meet all service requirements, no single lubricant formula can meet the operational needs of extremes in operating media.

COSMEC XL™ lubricants are specially formulated and compounded to produce optimum performance for particular environmental and service conditions. The elements and percentages in the proprietary compounded formulas were developed through research, testing, and in-the-field performance results. All the ingredients in COSMEC XL™ lubricants have lubricating properties, including the binder material.

A list of the various lubricants and their specific classes of service is intentionally not included to avoid the improper selection for a particular operating condition. It is preferable that the operating data be supplied to Cosmec’s engineering staff for recommendations.

Cosmec Custom XL™ Lubricant is the most economical general-purpose lubricant. Custom XL™ is normally supplied in all COSMEC XL™ bearings unless the service requirements indicate that another Cosmec lubricant would provide more satisfactory results.

For unusual or severe service conditions, such as in temperatures over 200˚F (90˚C), in steam, subject to radioactivity, exposure to chemicals, oils, and solvents, specific lubricants have been developed to provide solutions where few, if any, other types of bearings or lubricants can perform at all.

Where bearings are exposed to temperature extremes, submerged in salt or highly mineralized water, or in a corrosive atmosphere, care should be exercised in the selection of the bearing alloy as well as the lubricant.

Cosmec’s engineering staff will offer recommendations on bearing applications if detailed data is submitted.