Home / News & Blog / Abrasive Blog / Causes and Solutions for Rust Stains and Black Hearts in Ceramic Abrasives
Ceramic abrasives are widely used in modern industries due to their high hardness, wear resistance, and stable performance, making them the preferred choice for processing hard materials. However, during the production or usage process, ceramic abrasives may experience quality issues such as rust stains and black hearts. These problems not only affect their appearance but also reduce the product’s performance and service life.
Rust stains usually refer to the brown-yellow or reddish-brown spots that appear on the surface of ceramic abrasives. The common causes include:
Impurities in Raw Materials Ceramic abrasives are continuously subjected to high-temperature firing during production. Prolonged high-temperature exposure leads to the absorption of surrounding oxygen, causing oxidation on the surface of the ceramic abrasives. Depending on the color change, different phenomena can occur. If the abrasive grains contain magnetic materials such as iron or other impurities, these iron impurities oxidize during the high-temperature sintering process to form iron oxide, which leads to rust stains on the surface of the abrasive.
Contamination from Production Equipment or Molds After long-term use, production equipment or molds may release iron filings or other metallic particles due to corrosion or wear. These metal contaminants can remain on the surface or inside the ceramic abrasives, forming rust stains after sintering.
“Black heart” refers to abnormal black areas or discoloration in certain local regions inside or on the surface of ceramic abrasives. The common causes of black hearts are as follows:
Insufficient Sintering Temperature. During the production of ceramic abrasives, improper control of the firing time or temperature can cause black hearts. Inadequate sintering temperature or excessive heating rate can result in the incomplete decomposition of carbonaceous residues or organic binders, with the remaining carbon forming black hearts. For example, during the firing of SiC abrasives, the decomposition of SiC and the oxidation of its by-products must occur in a balanced manner. If the oxidation process lags behind the decomposition, black hearts will form.
Carbon Impurities in Raw Materials. If the raw materials contain carbon impurities such as graphite or carbon powder, these may not be fully oxidized or removed during sintering. When carbon impurities accumulate, black spots or black hearts are more likely to appear after sintering.
Improper Control of Sintering Atmosphere. Insufficient oxygen or an overly reductive atmosphere inside the sintering furnace prevents the complete oxidation and decomposition of organic substances, leaving carbon residues that form black hearts. This situation is often accompanied by local strength reductions or performance degradation.
Appearance Quality. Rust stains and black hearts significantly reduce the visual consistency of the product, affecting the customer’s perception of its quality.
Performance Loss. Rust stains may lead to localized hardness reduction, while black hearts weaken the overall strength and wear resistance of the abrasive.
Service Life. Due to the existence of localized defects, areas with rust stains and black hearts are prone to becoming stress concentration points, which can cause premature failure of the product during use.
To address rust stains and black hearts, the following solutions are proposed:
Measures to Prevent Rust Stains
Strict Control of Raw Material Purity. Choose high-purity raw materials with low iron content or those treated to remove iron, reducing the impact of iron impurities on the product. Additionally, incorporate magnetic separation equipment during the mixing process to effectively remove metallic impurities from the raw materials.
Maintain Equipment Cleanliness. Regularly inspect the cleanliness of production equipment and molds to prevent iron filings or other contaminants from entering the production process. Thoroughly clean mold surfaces before production, and regularly maintain equipment to prevent corrosion.
Optimize Storage Conditions. Store ceramic abrasives in dry, well-ventilated environments to avoid contact with moisture or acidic and alkaline substances. Use moisture-proof packaging during storage and install dehumidifiers in storage areas.
Measures to Prevent Black Hearts
Increase Sintering Temperature and Uniformity. Properly set the sintering curve to ensure that the sintering temperature meets the requirements for the complete decomposition of binders and carbonaceous materials. By optimizing the heating rate and extending the holding time, ensure that heat is evenly distributed inside the abrasive.
Strict Control of Carbon Impurities in Raw Materials. Choose high-purity raw materials with low carbon content and pre-treat carbonaceous materials before production. Perform high-temperature pre-firing of carbon-containing raw materials to reduce their residual presence during the sintering process.
Optimize Sintering Atmosphere. Control the atmosphere inside the sintering furnace, ensuring sufficient oxygen to accelerate the complete oxidation of organic materials. Regularly check the furnace’s sealing to ensure that oxygen supply is adequate and even.
Rust stains and black hearts are common quality issues in the production of ceramic abrasives. Their causes involve raw materials, process control, equipment, and environmental factors. By optimizing raw material purity, maintaining equipment cleanliness, improving the sintering process, and enhancing storage conditions, the occurrence of rust stains and black hearts can be effectively reduced, improving both the appearance and performance of the product.
In the future, as ceramic abrasive manufacturing technology continues to advance, further improvements in process flow and quality management systems will help reduce defects and provide customers with higher-quality products.
