Silicon carbide SiC fine powder for wear-resistant filler in PTFE-modified coatings
Silicon carbide fine powder (black/green SiC fine powder, such as 10 micron, 7micron, 5 micron ultrafine powder) can be used as a PTFE-modified wear-resistant filler. It is one of the mainstream hard ceramic fillers for industrial wear-resistant self-lubricating coatings, suitable for water-based/solvent-based PTFE composite coatings and organosilicon-PTFE high-temperature wear-resistant coatings.
I. Advantages of incorporating SiC fine powder into PTFE coatings
1. Significantly improved wear resistance and scratch resistance: Pure PTFE is soft and has extremely low hardness, making it prone to wear and detachment from the coating due to reciprocating friction and scratching by hard objects. SiC, with a Mohs hardness of 9.2, far exceeds that of white corundum and quartz, forming a rigid supporting skeleton within the coating.
– Under the same working conditions, coating wear is reduced by 70%–85%, and service life is extended by 3–5 times;
– It can resist long-term reciprocating friction from metal parts, sand, and plastic sliders, making it suitable for heavy-duty wear-resistant conditions.
2. Overcoming Inherent Shortcomings of PTFE
1. Improved Thermal Conductivity and Dissipation, Preventing Thermal Wear
Pure PTFE has extremely poor thermal conductivity (0.25 W/m·K), easily softening and failing due to frictional heat accumulation; SiC has excellent thermal conductivity, rapidly dissipating frictional heat, improving the coating’s PV limit, making it suitable for high-speed sliding seals and bearing coatings.
3. Reduced Cold Flow and Creep Resistance
Limiting PTFE molecular chain slippage, the coating is less prone to deformation, bulging, and displacement under high temperature and pressure.
4. Enhanced Coating Adhesion and Impact Resistance
Hard micro-powders form a physical anchoring structure, improving the adhesion between the coating and the metal substrate, reducing peeling and cracking from impacts.
5. Chemical Stability Matching PTFE
SiC is resistant to acids, alkalis, solvents, and high temperatures (decomposition temperature > 1800℃), compatible with PTFE’s wide-temperature corrosion resistance, preventing filler corrosion failure in acid, alkali, oil, and chemical media conditions.
6. Synergistic Effect of the Friction System
PTFE provides ultra-low friction coefficient self-lubrication, while SiC provides a wear-resistant skeleton. The soft and hard composite forms a continuous and stable transfer film, resulting in less wear on the mating parts and no severe abrasive wear fluctuations.
II. Key Points for Process Selection (For Coatings)
1. Particle Size Selection
Prioritize ultrafine SiC powders such as 28μm, 20μm, 14μm, 10μm, 7μm, 5μm:
– Coarse-grained SiC (F-series abrasives) easily causes rough coating surfaces, scratches on mating parts, and spray gun clogging;
– Silicon carbide W7-W28 particle sizes are equivalent to 600-2500 mesh, resulting in a fine and smooth coating without compromising the surface smoothness of PTFE.
2. Recommended Addition Ratio (mass fraction)
– General wear-resistant coating: 8%–15% provides optimal overall performance and the lowest wear rate;
– For heavy-duty, high-wear-resistance applications, the upper limit should not exceed 20%;
Exceeding 20% will cause two major problems:
1. Reduced PTFE content leads to significantly worse non-stickiness and self-lubrication;
2. Excessive powder makes dispersion difficult, resulting in coating sedimentation, poor spray leveling, and a tendency for pinholes and brittleness in the coating.
3. Key to Dispersion: Silane Coupling Agent Modification
SiC powder has a highly polar surface, and direct addition to PTFE emulsion/silicone resin easily leads to agglomeration and sedimentation; Using KH550/KH560/KH570 silanes for surface modification improves the compatibility of the powder with organic resins and PTFE, significantly enhancing suspension stability.
III. Application Scenarios
1. Industrial Wear-Resistant Self-Lubricating Coating
Hydraulic valve sealing surfaces, sliding bearings, gear wear-resistant coatings, and anti-stick wear-resistant layers for conveyor rollers;
2. Mold Release Wear-Resistant Coating
Rubber and plastic injection molds, die-casting molds, combining non-stick release with erosion and wear resistance;
3. High-End Non-Stick Coating for Kitchenware
Baking pans, commercial frying pans, resisting long-term scratches from metal spatulas;
4. Corrosion-Resistant and Wear-Resistant Composite Coating
Chemical equipment, mixing shafts, pump linings, resistant to media and particle erosion.
