Antimony Carbon vs Resin Carbon – A Case Study

We’d like to share the story of a recent mechanical seal replacement project that presented us with an unexpected challenge, and how our team worked diligently to resolve it, ensuring the smooth operation of a critical pump system.

The Assignment:

We were initially assigned to replace the mechanical seal on a boiler feed pump with a discharge pressure of 120 bars at a customer’s site. The job seemed straightforward, and after the installation of the new seal, the pump was commissioned and put into operation. However, shortly after commissioning, we noticed an unexpected issue: the pump exhibited a higher-than-normal level of leakage from the mechanical seal.

The Investigation:

With the increased leakage, we promptly visited the site to investigate the problem. After carefully inspecting the pump and the newly installed seal, we decided to remove it and bring it back to our workshop for further analysis. Surprisingly, despite extensive examination, there was no visible damage or obvious signs of failure on the mechanical seal.

The Analysis:

Back in our workshop, we conducted a detailed analysis of the mechanical seal. After ruling out alignment issues and vibrations as possible causes, we compared the new seal with another used, old mechanical seal from the customer’s workshop that was waiting to be repaired.

• The original, old seal used antimony carbon, a material known for its superior durability and wear resistance under high-pressure, high-temperature conditions.
• The newly installed seal, however, appeared to be made of resin carbon, which, while still effective in many applications, is generally softer and more prone to deformation, thermal degradation, and increased friction under the harsh operating conditions.

During our comparison, we also discovered a noticeable weight difference between the two carbon faces, with the resin carbon face weighing over 60 grams less than the antimony carbon face. This weight discrepancy further confirmed that the materials were not identical, suggesting that the resin carbon material was likely less dense and more prone to failure under the high stresses experienced in the pump.

Boiler feed pump mechanical seals are subject to high temperatures and significant axial movements and forces. These demanding conditions require seals made from materials that can maintain integrity and performance under stress. Despite no visible cracks or wear, the resin carbon likely experienced internal deformation due to its lower wear resistance and

poor thermal conductivity, causing it to lose proper compression over time. This resulted in micro gaps at the sealing interface, which allowed leakage without any physical signs of failure. The antimony carbon material, on the other hand, proved to be more thermally stable and better able to withstand the pressures, temperatures, and axial forces present in the pump, which is why the pump has now returned to normal operation with no leakage after the material swap.

The Solution:

After identifying the material incompatibility, we decided to replace the resin carbon face with an antimony carbon face, which we knew would be better suited for the application. Once reassembled, we tested the new seal thoroughly and reinstalled it on the pump.

The Outcome:

Since the replacement, the pump has been operating smoothly, with no further leakage from the mechanical seal. The use of the more appropriate antimony carbon material resolved the problem, ensuring the pump functions as intended, with optimal performance and reliability.

Below are more specific numerical values for the strength and weight differences between resin carbon and antimony carbon:

Summary of Differences:

Property	Resin Carbon	Antimony Carbon
Compressive Strength	60-80 MPa	100-150 MPa
Tensile Strength	20-30 MPa	50-70 MPa
Flexural Strength	25-40 MPa	60-90 MPa
Density (Specific Gravity)	1.60 – 1.80 g/cm³	2.00 – 2.20 g/cm³
Thermal Conductivity	30-50 W/m·K	60-100 W/m·K
Wear Rate	1.0-2.5 mm³/kWh	0.2-1.0 mm³/kWh
Max Temperature	150-200°C (302-392°F)	300-350°C (572-662°F)

These numerical differences highlight why antimony carbon is preferred for high-performance, high-pressure, and high-temperature applications. It offers significantly better mechanical strength, wear resistance, thermal conductivity, and the ability to withstand more extreme temperatures, making it a better choice for boiler feed pumps and other demanding industrial environments.