Bismuth Brass Annealing to Prevent Cracking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bismuth brass alloys, used in manufacturing articles like plumbing fixtures, are susceptible to cracking due to the exclusion of lead and inclusion of bismuth, which affects their formability and other properties, making them unsuitable for intended end uses.
Innovation Solution
A method involving machining an extruded brass rod to form a desired shape and annealing it at a temperature no greater than 575° F./302° C. to relieve stress, with specific temperature and time conditions to limit bismuth diffusional movement and prevent cracking, maintaining the alloy's machinability and ductility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead is excluded from the brass alloy and replaced by lead-replacement elements, then the alloy can be made suitable for certain applications, but the formability and other properties are detrimentally changed
Solution Approach 1:
The patent changes the chemical composition parameters by replacing lead with bismuth (0.8-1.5 wt%) and optimizing zinc content (35-40 wt%), along with adding phosphorous (0.05-0.15 wt%). This compositional parameter change maintains reliability for plumbing applications while preserving adequate formability through the specific balance of alloying elements.
Solution Approach 2:
The patent creates a composite brass alloy system combining copper base metal with bismuth, phosphorous, and zinc elements. This composite material approach allows the alloy to exhibit both the reliability needed for lead-free plumbing applications and the formability required for manufacturing, by synergistically combining the properties of different elements.
2Reliability
If bismuth is included in the brass alloy to replace lead, then the alloy can be used in plumbing fixtures, but the alloy becomes more susceptible to cracking
Solution Approach 1:
The patent applies preliminary stress relief annealing at 575° F. (302° C.) or below after machining operations. This preliminary thermal treatment removes residual stresses from machining before the article is installed or further processed, preventing the initiation and propagation of cracks in the bismuth-containing alloy, thereby improving crack resistance while maintaining plumbing fixture suitability.
Solution Approach 2:
The patent optimizes the bismuth content parameter to 0.8-1.5 wt% and controls phosphorous at 0.05-0.15 wt%. This precise parameter control ensures adequate machinability and formability while minimizing crack susceptibility. The specific composition range balances the competing requirements of reliability for plumbing use and strength against cracking.
3Reliability
If the annealing temperature is increased to relieve stress, then the stress relief is more effective, but the diffusional movement of bismuth increases causing cracking
Solution Approach 1:
The patent precisely controls the annealing temperature parameter at 575° F. (302° C.) or below, and limits the annealing time to 90 minutes or less. This parameter optimization achieves adequate stress relief effectiveness while preventing excessive diffusional movement of bismuth that would cause cracking. The temperature-time parameter combination is specifically tuned to balance these competing requirements.
Solution Approach 2:
The patent applies partial annealing treatment rather than prolonged high-temperature annealing. By limiting the annealing to 575° F. or below for 90 minutes or less, the patent achieves sufficient stress relief for the specific application without over-annealing, which would cause excessive bismuth diffusion and cracking. This partial action approach optimizes the trade-off between stress relief and crack prevention.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively reduces the susceptibility of bismuth brass alloys to cracking, allowing their use in plumbing fixtures by controlling bismuth distribution and maintaining the alloy's properties, thus enabling the use of lead-free bismuth brass in critical applications.
Implementation Method 1
annealing the article at an annealing temperature that is no greater than 575° F./302° C. to relieve stress caused by the machining
Implementation Method 2
annealing the article at an annealing temperature, T (° F.), for an annealing time, t (minutes), to relieve stress caused by the machining
Implementation Method 3
The annealing temperature and annealing time are selected to limit diffusional movement of bismuth to reduce cracking of the plumbing fixture
Data Source
AI summary
A method of processing a bismuth brass article includes the steps of machining an extruded brass rod to form an article of a desired shape and annealing the article at an annealing temperature that is no greater than 575° F./302° C. to relieve stress caused by the machining. The extruded brass rod includes a composition, by weight percentage, that includes 58-63 of copper, 0.8-1.5 of bismuth, 0.05-0.15 of phosphorous and a remainder of zinc and any impurities.