Bronze-Base Powder Metallurgy (PM) Bearings (Oil-Impregnated)

B438: Standard Specification for Bronze-Base Powder Metallurgy (PM) Bearings (Oil-Impregnated)

For engineers and designers relying on robust, self-lubricating components, understanding the foundational standards for material selection and performance is paramount. ASTM B438 provides this essential framework, ensuring the reliability and longevity of critical bronze-base powder metallurgy (PM) bearings. This industry-leading specification is the authoritative guide for procuring and manufacturing these vital components.

What is B438?

ASTM B438, "Standard Specification for Bronze-Base Powder Metallurgy (PM) Bearings (Oil-Impregnated)," establishes the definitive requirements for bronze-based bearings manufactured using powder metallurgy techniques and impregnated with oil for lubrication. Originating from a need to standardize materials previously covered by military specifications, its primary purpose is to ensure consistent chemical composition, physical properties, and mechanical performance for these self-lubricating bearings.

Scope & Purpose

This comprehensive standard governs the material and manufacturing requirements for porous, bronze-base PM bearings designed for self-lubricating applications. It specifically covers sleeve, flange, thrust, and spherical bearing types. The scope includes the chemical, physical, and mechanical properties of the bronze-base PM materials utilized, as well as the oil impregnation process. While it provides guidance on material designations and ordering information, it does not dictate specific bearing dimensions or detailed installation procedures, which are often found in supplementary documents or engineering drawings.

Who Must Comply?

• • Primary Audience: Materials Engineers, Design Engineers, Manufacturing Engineers, Quality Control Inspectors, and Procurement Specialists involved in specifying or acquiring self-lubricating bearings.
• • Industries Affected: Manufacturing, Automotive, Aerospace, Industrial Equipment, Machinery, and any sector requiring reliable, low-maintenance bearing solutions.
• • Compliance Nature: While primarily a voluntary industry standard, B438 is often mandated in government and military procurement contracts, making compliance essential for those sectors.
• • Enforcement: Compliance is typically ensured through buyer specifications, quality control inspections, and supplier certifications. For government contracts, relevant military or defense agencies may oversee enforcement.

Key Requirements Overview

The standard requires manufacturers to adhere to specific material compositions for various bronze-base PM bearing grades, often denoted by alphanumeric codes. Professionals must ensure that the bearings are produced through a controlled powder metallurgy process, including sintering and subsequent oil impregnation. Key provisions include defining acceptable chemical composition limits for elemental constituents and specifying minimum density and oil retention properties to guarantee self-lubricating performance. Furthermore, the standard outlines requirements for mechanical properties, such as radial crushing strength, to ensure the bearing can withstand operational loads.

Related Standards & References

ASTM B438 often works in conjunction with other ASTM standards. ASTM B439 complements B438 by covering iron-base PM bearings, offering an alternative material option. Standards like ASTM B939 (Radial Crushing Strength) and ASTM B963 (Oil Content and Porosity) provide the specific test methods to verify compliance with the requirements outlined in B438. Additionally, references to MPIF Standard 35 and ISO standards offer further insights into material properties and dimensional tolerances for PM self-lubricating bearings.