1. Overview

CAC406C is a continuous-cast tin-lead bronze defined under Japanese Industrial Standard JIS H5121 (former designation BC6C), belonging to the Cu–Sn–Zn–Pb family and commonly called “5-5-5 bronze”. Its nominal composition is Cu balance, Sn 4–6%, Zn 4–6%, Pb 4–6%. As a casing wear ring (also referred to as a casing ring or wear ring) in centrifugal pumps, the alloy is selected where a renewable, corrosion-resistant, anti-galling component is required at the clearance between the rotating impeller and the stationary casing.

In centrifugal pump design, the wear ring is a deliberately renewable part: when clearance grows through service, the ring is replaced rather than the more costly impeller or casing. CAC406C offers a balanced combination of low-friction running, resistance to water and seawater corrosion, low galling tendency against steel or cast iron, straightforward machinability for repair, and a hardness lower than the mating rotating part — which suits the sacrificial role.

2. Material Identity and Standard Cross-Reference

CAC406C is the continuous-cast version of CAC406. The designation logic: JIS H5120 covers sand/gravity castings (CAC406); JIS H5121 covers continuous castings (CAC406C, suffix C = Continuous). The former JIS designation was BC6 / BC6C. International equivalents are listed below.

3. Chemical Composition and Mechanical Properties

4. Application: Casing Wear Ring in Centrifugal Pumps

Wear rings are a renewable, closely machined pair of annular components that establish a controlled clearance between the rotating impeller and the stationary casing to limit internal fluid bypass. By position they are classified as:

• Casing wear ring — fixed in the pump casing or cover (the subject of this guide);
• Impeller wear ring — mounted on the impeller suction-eye outside diameter, rotating with the impeller;
• In multi-stage pumps, a ring pair exists at each stage; some designs also use a rear wear ring with balance holes to manage axial thrust.

Schematic — single-stage centrifugal pump with casing ring

SuctionDischargeCasing (cast iron / cast steel)CAC406C wear ring (stationary)Impeller (stainless steel / bronze)Clearance ≈ 0.1–0.5 mm: throttles bypass, builds Lomakin film stiffness

5. Why CAC406C — Property to Duty Mapping

Typical material pairing (consistent with common pump construction):

6. Anti-Galling Pairing and Hardness Differential

The principal failure risk for metal wear rings is galling / seizure: similar-hardness metals in contact under load or thermal growth can cold-weld, leading to binding or severe damage. API 610 is the widely referenced design basis:

This favours CAC406C:

• CAC406C hardness is about 85 HB; mating cast iron casing (~150–200 HB) or stainless impeller (304/316, work-hardened above that) readily meet the ≥50 BHN difference;
• Bronze against iron/steel is a dissimilar-metal pair with low adhesion tendency, and it does not readily seize on transient contact;
• In practice, a duplex or austenitic stainless impeller ring paired with a stainless casing ring (same material) is a combination prone to galling; a bronze casing ring or a surface-hardened rotating ring is used to open the hardness gap.

7. Clearance Standards and Maintenance

7.1 Minimum diametral clearance (API 610 guide, metal rings)

Clearance is defined diametrally — the difference between the stationary ring inside diameter and the rotating ring outside diameter (the running clearance is half of this). API minimum values:

CAC406C casing rings are common on medium to large centrifugal pumps (ring OD up to several hundred millimetres). Apply the OEM drawing or the API table; for service temperature above 260°C or high-galling materials, add 125 µm.

7.2 Replacement trigger (2× rule)

• General rule: Plan replacement when measured diametral clearance reaches about twice the new-build (or drawing) value;
• Clean-water / municipal / HVAC pumps: some manufacturers use a 40% increase over original clearance as the trigger;
• Beyond the threshold, the Lomakin film stiffness is lost → added radial load, shaft deflection, and mechanical seal face separation. Each doubling of clearance typically corresponds to roughly 3–5 efficiency points lost (low-specific-speed, high-head pumps are more sensitive).

8. Industry Application Matrix

CAC406C casing wear rings are applied where the media is clean or mildly corrosive and the speed is moderate. They are not suited to media carrying abrasive solids (slurry, mineral tailings), where ring life is short.

9. Material Specification Notes

1. State the standard clearly: CAC406C per JIS H5121 (continuous cast); for a cast component write CAC406 per JIS H5120.
2. Request a material test report (MTR / EN 10204 3.1) and verify measured Cu/Sn/Zn/Pb composition and tensile / hardness values.
3. Approve C83600 / CC491K / ZCuSn5Pb5Zn5 / LG2 as equivalent substitutions only with a note that composition and mechanical properties are comparable.
4. Confirm the mating impeller / casing hardness to maintain the ≥50 BHN difference; if the impeller is 316 or similar austenitic stainless, avoid a same-material casing ring and use CAC406C (dissimilar metal) or harden the rotating ring.
5. Define the duty within the pump’s allowable pressure upper limit and speed upper limit, and verify fluid compatibility before specifying CAC406C.
6. Apply the OEM drawing or API 610 minimum diametral clearance; secure the ring by press fit plus locking pin / set screw / tack weld to prevent movement in service.
7. Specify working-face finish approximately Ra 0.8–1.6 μm; continuous-cast CAC406C bar or tube stock is suitable for bore finishing.