Bourdon tube materials: which of the following is never used to manufacture Bourdon tubes for pressure gauges?

Introduction / Context:
Bourdon tubes are thin-walled, elastic metallic elements that flex with internal pressure. Material choice must provide elasticity, fatigue strength, corrosion resistance, and manufacturability into precise thin sections. Some engineering metals are unsuitable because they are brittle or cannot be formed into reliable elastic elements.

Given Data / Assumptions:

• Bourdon tubes require ductility and spring properties, not just strength.
• Commonly used alloys: phosphor bronze, beryllium copper, stainless steels, monel.
• Cast iron is brittle with poor ductility and unsuitable for thin elastic members.

Concept / Approach:
Gauge makers select alloys that can be drawn into thin curved sections and repeatedly stressed within elastic limits. Cast iron, being brittle and not amenable to such forming, cannot function safely as a Bourdon tube material. Conversely, phosphor bronze, monel, stainless steels, and beryllium copper are standard, each chosen for particular media and pressure ranges.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer datasheets and standards specify bronze, stainless, and nickel alloys for Bourdon tubes; cast iron does not appear as a viable option.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming “strong” implies “suitable”; Bourdon tubes need elastic, not brittle, behavior under cyclic load.

Final Answer:
cast iron