The Ultimate Guide to Fluororubber Compound Quality Control: Problems & Fixes
This article provides a relatively detailed introduction to fluororubber, covering its applications, properties, formulations, processing, and common problems with compounds.
I. Basic Introduction to Fluororubber
Fluororubber refers to a synthetic polymer elastomer where fluorine atoms are attached to the carbon atoms of the main chain or side chains. Fluorine atoms impart excellent heat resistance, oxidation resistance, oil resistance, and corrosion resistance to the rubber, making it primarily used in the field of special sealing products.
Currently, the common main varieties of fluororubber are the ordinary binary fluororubber F26 type (copolymer of vinylidene fluoride and hexafluoropropylene) and the ternary fluororubber F246 type, corresponding to DuPont's VITON A and B. Their consumption accounts for over (90%) of the world's total fluororubber consumption.
Other special fluororubbers include the following:
Tetrafluoroethylene-propylene rubber (FEPM): A copolymer of tetrafluoroethylene and propylene. It exhibits high corrosion resistance to inorganic acids (e.g., (96%) sulfuric acid, volume change (\leq 5%)), alkalis, various bleaching agents, superheated water and steam, especially steam mixed with acids/alkalis, and phosphate-based hydraulic oils.
Peroxide-curable fluororubber: Modified by adding cure-site monomers to binary or ternary fluororubbers. Common examples include fluorinated vinyl ether rubbers, such as DuPont's VITON GLT.
Perfluoroelastomer (FFKM): Excellent low-temperature properties, high fluorine content, and superior solvent resistance.
Fluorosilicone rubber: Excellent low-temperature properties, average solvent resistance.
II. Properties of Fluororubber
Ordinary F26 type fluororubber typically has a tensile strength of (10\sim) 20MPa, elongation at break of (150% \sim 600%), tear strength of (20\sim 40\mathrm{kN / m}), poor elasticity, good wear resistance, and a density of (1.8\sim 2.1\mathrm{g / cm}^3).
F26 type can work long-term at (200℃- 250℃) and short-term around (280℃); F246 type can work long-term at (250℃).
Outstanding stability against organic liquids, fuel oils, and lubricating oils. Resistant to most inorganic acids and hydrocarbons.
Ordinary fluororubber has average resistance; FEPM is recommended for better performance.
Brittle temperature is around (-25^{\circ}C). Specialized grades like fluorosilicone offer better low-temp flexibility.
Fluororubber has excellent weathering and ozone resistance. It can be stored naturally for over 10 years and shows no cracking after more than 1 month in air with 100 PPM ozone.
High levels of halogen (fluorine) give it excellent flame retardancy; it is self-extinguishing upon removal of flame.
Excellent vacuum performance with low air diffusion rates. Better than chloroprene rubber (CR) and natural rubber.
III. Compounding and Processing of Fluororubber
Select appropriate raw rubber based on service conditions. F26/F246 for heat, FFKM for extreme heat, and FEPM for corrosive media or steam.
Fluororubber is a highly saturated fluoropolymer. Sulfur curing cannot be used. Bisphenol AF/BPP and peroxide curing are commonly used today.
Stabilizers neutralize HF released during vulcanization. Commonly used are metal oxides like (\mathrm{MgO}) and (\mathrm{Ca(OH)_2}).
Plasticizers are rarely used due to volatilization. Aids like palm wax, WS280, and 935P are used to increase flow and prevent sticking.
Enhanced cooling is essential due to poor thermal conductivity and high heat generation during mixing to prevent scorching.
Requires primary cure and an open high-temperature secondary cure (e.g., (230^{\circ}C\times 16h)) to remove low molecular weight substances.
IV. Applications of Fluororubber
Widely used in Automotive Electronics Aviation Shipbuilding and Chemical Industry. Especially used for O-rings, gaskets, and seals in fuel and transmission systems.
V. Common Problems & Solutions
1. Mold Contamination
Solutions: Increase acid acceptor dosage; add mold release aids (palm wax); treat mold surface with semi-permanent release agents.
2. Short Molding/Incomplete Fill
Solutions: Use low Mooney viscosity rubber; increase scorch time; lower temperature or increase pressure; adjust charge placement.
3. Uneven or Non-Curing
Note: Avoid acidic materials; do not use stearic acid; avoid HAF grade carbon blacks or precipitated silica; do not incorporate sulfur.
4. Scorch and Burnt Edges
Solutions: Blend with low Mooney viscosity rubber; reduce BPP or Ca(OH)₂ dosage to slow cure rate.
5. Product Tearing
Causes: Tight mold fit; rough cavity surface; high curing temperature making the compound brittle; low compound strength.
6. Product Deformation
Solutions: Ensure sufficient primary cure; use stepwise temperature increase for post-cure; select materials with appropriate viscosity.
7. Poor Dispersion
Solutions: Use small fill factor in mixers; keep rotor speed and discharge temperature low; ensure sufficient cooling and rest time.
8. Color Difference
Factors: Raw material quality; aging of color standards; contamination during mixing; temperature fluctuations during curing.