ASTM B22 Standard Specification for Bronze Castings for Bridges and Turntables

 Get Certified ASTM B22 Testing for Structural Integrity and Project Success 

The alloying elements (tin, lead, zinc, aluminum, and manganese) that affect the mechanical strength, hardness, and machinability of cast bronze alloys directly influence the life and load capacity of a bearing. ASTM B22 is a testing method that ensures the chemical composition and mechanical properties of a casting heat, before machining, are within established quality limits. Through certified components from verified laboratories, structural engineers and project authorities are given complete confidence in the safety of their components. 

The scope of ASTM B22 includes:

• Material type: Copper-alloy bronze castings, Copper alloy UNS Nos. C86300, C90500, C91100, C91300, and C93700.  
• Purpose: To establish mandatory compositional, physical, and mechanical property requirements for copper alloy castings to ensure structural reliability under high static and dynamic compressive loads. 
• Elements analyzed: Chemical composition (copper, tin, lead, zinc, iron, manganese, aluminum) and mechanical properties (tensile strength, yield strength, elongation, compressive strength, and deformation limit). 
• Method: Chemical analysis by spark-OES or wet chemistry as per applicable ASTM standard practices and mechanical testing by tension and compression testing of cast test coupons. 
• Result: Determination of chemical constituent percentages and mechanical test values compared with alloy limits. 
• Test Limitations: Applies to raw casting properties and does not otherwise apply to full non-destructive testing (e.g., ultrasonic or radiographic examination) unless as purchased. 
• Environmental conditions: Mechanical testing is carried out under standard ambient conditions in the laboratory (approximately 23 °C ± 5 °C ) with specimens prepared in an appropriate manner. 
• Applications: Highway bridge expansion bearings, railroad turntable center bearings, trunnion bearings, shear keys, and heavy structural thrust washers. 

What are the Uses of the ASTM B22 Specification?

The implementation of ASTM B22 helps the foundry metallurgist and the structural engineer to quickly verify the performance of a copper alloy for use, or for routine melt quality control or certification of materials by third parties. Furthermore, the standardized specification allows for the repetition of casting alloys between foundries and project sites. This standard:

• Aids in quality control of bronze sand casting and continuous casting.
• Computes load-bearing structural engineering calculations.
• Provides data to confirm alloy selection for anticipated compression forces and wear.
• Checks material requirements for minimum yield strength, tensile strength, and hardness.
• Helps to resolve component wear or cracking problems before they occur in the field. 

What Materials Can Be Tested Under ASTM B22? 

ASTM B22 is for heavy-duty copper-alloy castings. ASTM B22 is the standard for various materials, including high-strength manganese bronze (UNS C86300), tin bronze (UNS C90500), high-tin phosphor bronze (UNS C91100 and C91300), and high-leaded tin bronze (UNS C93700) cast into bearing plates, bushings, expansion shoes, and turntable disks. 

Why is ASTM B22 Important? 

ASTM B22 offers a standardized quality system for foundries and engineers to ensure that the casting is suitable for the application before it is put into service. Inadequate alloy selection or casting quality can lead to early galling, excessive deformation, bearing seizure, and structural failure under heavy traffic on the bridge. If impurity concentrations are not within the prescribed limits, they reduce the material’s ductility and can lead to brittle fracture under shock loading. ASTM B22 specifications ensure a bridge’s long-term serviceability without costly structural repairs and optimum metallurgical quality. 

ASTM B22  Testing Process and Data Collection

Analysts first measure the dimensions of the cut test pieces. The specimen enters the testing apparatus, where controlled tensile or compressive loading measures the bronze alloy’s deformation behavior. Calibrated load cells and extensometers maintain data accuracy, recording the yield point and ultimate breaking strength. Analysts then record chemical composition spectra and mechanical test values after test completion and archive the data for certification reporting. 

Common Challenges and Troubleshooting

Common casting testing defects are shrinkage porosity (tests) or gating defects (tests and test bars) that decrease elongation, or segregation of the cast (thick section casting). Troubleshooting activities involve optimizing the mold riser design, ensuring the proper melt degasification process, or re-sampling from areas in the casting that are sound to eliminate material defects that would impact test results.

• Laboratory documentation records the specific copper alloy UNS designation (e.g., C86300 or C90500).
• The technician decides whether the casting technique is sand casting, continuous casting, or centrifugal casting.
• The analyst records all mechanical property defects, e.g., yield test results lower than specified limits, and links them with melt chemistry or cooling rates.
• When evaluating alloy test results for project acceptance, the engineer takes into account the following factors: structural design loads, bearing pressure, and movement frequency.
• The recorded material certification is for compliance with bridge construction, foundry quality control, and structural safety sign-offs by quality engineers. 

Link to ASTM B22