Analysis of Seal Materials for Sanitary Screw Pumps
Sanitary screw pumps must meet core requirements including zero contamination, easy cleaning, high-temperature sterilization resistance and zero residue. Their sealing systems are subject to harsh processes such as CIP (Clean-in-Place) online cleaning, SIP (Sterilize-in-Place) high-temperature sterilization and acid-alkaline flushing for long periods. Improper material selection may lead to wear of rotating and stationary rings, swelling and cracking of rubber seals, corrosion failure of metal components and other defects. These issues will further cause material leakage, bacterial growth, secondary contamination and rising operation and maintenance costs, making production lines fail to meet clean production standards. Therefore, seal material selection requires comprehensive consideration of wear resistance, temperature and corrosion resistance, sanitary grade and working condition compatibility.
I. Summary of Material Selection
| Seal Material | Core Advantages | Applicable Scenarios |
|---|---|---|
| EPDM (Ethylene Propylene Diene Monomer) | Steam-resistant, good sanitary performance, cost-effective | Water-based media such as dairy products, fruit juice and pure water |
| VMQ Silicone Rubber | Ultra-high temperature resistance, high sterile grade | High-temperature sterile working conditions for pharmaceuticals and infant food |
| FKM Fluoroelastomer | Oil-resistant, alcohol-resistant, strong alkali-resistant | High-fat and alcohol-containing food media |
| PTFE (Polytetrafluoroethylene) | Strong corrosion resistance, particle resistance | Acidic, granular and corrosive materials |
| WC Tungsten Carbide | Ultra-high wear resistance, wide versatility | General friction pairs for conventional food and pharmaceutical applications |
| SiC Silicon Carbide | Low friction, high-precision wear resistance | High-end sanitary applications with frequent start-stop cycles |
| Carbon Graphite | Self-lubricating, high temperature and corrosion resistance | High-temperature working conditions with minor solid particles |
II. Analysis of Hard Materials for Seal Friction Pairs
The friction pair is the core pressure-bearing and wear-resistant component of a seal, consisting of rotating and stationary rings. It needs high strength, wear and corrosion resistance, excellent air tightness and good machinability. The mainstream materials are as follows:
1.Tungsten Carbide (WC)
It is the mainstream material widely adopted across the industry, with cobalt, chromium and titanium as main components and cobalt as the binder. The higher the cobalt content, the lower the material strength. Common grades include YG-6, YG-8 and YG-15, with hardness ranging from 87 to 89.5 HRA. Its hardness is 20 times that of high-speed steel. It features high temperature resistance, low thermal expansion coefficient, low friction coefficient and good pairing performance, suitable for most conventional conveying working conditions of food, dairy products and liquid pharmaceuticals.
2.Alloy Steel and High Silicon Iron
Heat-treated alloy steel (3Cr13, 4Cr13, etc.) boasts improved wear resistance and strength, simple machining and high cost performance, suitable for working conditions with clean water and thin slurries free of strong corrosion. High silicon iron has a hardness of 45–50 HRC and resists sulfuric acid, nitric acid and organic acids, yet it cannot withstand strong alkalis and hydrochloric acid, only applicable to acidic environments without strong alkali corrosion.
3.Silicon Carbide (SiC)
It is an advanced high-precision sealing material globally recognized, featuring an extremely low friction coefficient, excellent friction reduction and wear resistance, as well as high temperature and corrosion resistance. It is mostly paired with tungsten carbide to greatly reduce seal loss, suitable for pharmaceutical and fine food conveying with frequent start-stop cycles, minor solid particles and strict sanitary requirements.
4.Carbon Graphite Materials
A classic soft friction pair material manufactured through high-temperature calcination. Its inherent pores require impregnation modification for practical use, and it can be paired with tungsten carbide or silicon carbide. Main grades include pure carbon graphite M121 (temperature resistance up to 350°C), epoxy/furan resin-impregnated graphite (temperature resistance up to 200°C) and metal-impregnated graphite M232L (temperature resistance up to 400°C). It delivers self-lubrication, low friction, corrosion resistance and easy machining, suited for high-temperature working conditions with minor solid particles.
III. Materials for Elastic Sealing Components
Elastic components provide stable compensation pressure for seals, and their materials are selected according to actual working conditions: 1Cr18Ni9Ti and 4Cr13 stainless steel for general corrosive environments; phosphor bronze for seawater and weakly corrosive environments; 65Mn and 60Si2Mn carbon steel for room-temperature clean water environments free of corrosion; 50GV for high-temperature oil pump applications, effectively preventing seal leakage caused by corrosion and elastic attenuation.
IV. Core Selection Standards and Common Failures
Material selection covers four key dimensions: matching materials with conveyed media, selecting temperature-resistant materials compliant with CIP/SIP cleaning processes, matching material temperature tolerance with equipment operating temperature, and meeting compliance standards including FDA/3A for food and USP for pharmaceuticals.
Common failures induced by improper material selection include swelling failure of EPDM upon contact with grease, cracking of silicone rubber and subsequent material contamination when exposed to concentrated acids, material leakage due to insufficient wear resistance of ordinary PTFE, embrittlement of FKM under frequent high-temperature sterilization, and seal leakage resulting from corrosion of carbon steel springs. All these failures stem from mismatches between working conditions and selected materials.
Conclusion
Sealing systems for sanitary screw pumps require full set matching; no single material can fit all working conditions. Accurate material matching with service environments is essential. EPDM paired with tungsten carbide is preferred for conventional water-based production lines; FKM paired with silicon carbide is selected for high-fat and alcohol-containing media; silicone rubber matched with modified graphite fits high-temperature sterile pharmaceutical processes; PTFE combined with carbon graphite is adopted for corrosive and granular material applications. Omron Tech Pumps specializes in clean fluid sealing, providing highly compatible, long-service-life sealing solutions for food, pharmaceutical and daily chemical industries with a full range of compliant sealing materials and mature selection systems, ensuring stable, low-consumption and compliant clean operation of production lines.