Special sleepers on curves: Cast iron “pot” sleepers are suitable only up to what maximum degree of curve?

Introduction / Context:
Pot sleepers (special cast iron units) were historically used in certain yards and low-speed track. Their suitability on curves is limited due to geometry and fastening constraints. Knowing the limit helps prevent excessive gauge widening and fastener stress.

Given Data / Assumptions:

• Legacy or secondary track applications for pot sleepers.
• Degree of curve is used as curvature measure (degree = angle subtended by a 30.5 m chord in some systems; conceptually, higher degree means tighter curve).
• Acceptable lateral forces and flange clearances assumed.

Concept / Approach:
Due to their geometry, pot sleepers provide limited ability to accommodate sharp curvature without overstressing fittings or compromising gauge and cant. Hence, a conservative cap on their use is set at about 4° to ensure safe wheel guidance and manageable maintenance.

Step-by-Step Solution:
1) Recognize limitations of pot sleeper assemblies on sharp curves.2) Apply the customary limit adopted in practice: ≤ 4°.3) Beyond this, adopt more suitable sleeper/fastening systems (e.g., concrete or timber with elastic fastenings).

Verification / Alternative check:
Legacy track standards restricted pot sleepers on sharper curves due to maintenance and safety issues, confirming 4° as a practical upper bound.

Why Other Options Are Wrong:

• Values above 4° allow too tight curvature for the pot sleeper arrangement under typical service conditions.

Common Pitfalls:

• Using pot sleepers on mainline curves with higher speeds or heavy axle loads—leads to rapid deterioration.

Final Answer:
4°.