In industrial scenarios such as powder processing, fine separation and material classification, the classifier is a key piece of equipment that determines particle size accuracy, production efficiency and product purity. The material of the classifier directly affects equipment service life, material purity, corrosion and wear resistance, and compliance. Different industries have clear and special requirements for materials due to differences in material characteristics, working conditions and hygiene standards. Choosing the wrong material will not only accelerate equipment wear and increase maintenance costs, but may also cause material contamination, reduced production capacity and even potential safety hazards. Based on the requirements of major industries including food, pharmaceutical, chemical, mining, metallurgy and new energy, this article explains the logic and practical solutions for classifier material selection.
1. Basic Properties of Common Materials for Classifiers
The parts of the classifier in direct contact with materials (classifying wheel, chamber, feed inlet, screen, pipeline, etc.) are divided into four categories, suitable for different working conditions:
- Carbon Steel (Q235, 45# Steel)
Low cost and moderate strength. Suitable for non-corrosive, low-wear and non-clean applications. Not resistant to acid and alkali, easy to rust. Not applicable to food, pharmaceutical and corrosive materials.
- Stainless Steel (304/316L/2205 Duplex Steel)
304: General-purpose, rust-proof and easy to clean, meeting conventional clean and weak corrosion requirements;
316L: Molybdenum-containing, resistant to chloride ions, acid and alkali, and damp heat, suitable for pharmaceutical, chemical and seawater environments;
2205 Duplex Steel: Excellent wear and corrosion resistance, with hardness 2–3 times that of 304, suitable for high-wear and corrosive conditions.
- Engineering Plastics (PP/PE/Nylon/PTFE)
Lightweight, anti-metal contamination, resistant to weak acid and alkali, non-sticky. Suitable for non-metallic contact and low-wear clean applications.
- Wear-resistant Ceramics (Alumina/Zirconia), Polyurethane, Wear-resistant Alloys
Ultra-high hardness and super wear resistance. Suitable for high-hardness powder, ore, sand and other highly abrasive materials, with service life far exceeding that of ordinary steel.
2. Food Industry: Hygiene, No Residue, Easy Cleaning and Compliance First
The food industry (milk powder, sugar powder, starch, condiments, grains, snack foods) has core requirements for classifiers: no heavy metal precipitation, no dead corners for easy cleaning, mildew resistance, and compliance with food-grade standards.
- Preferred Materials: 304 Stainless Steel (conventional food), 316L Stainless Steel (high-humidity, salt-containing, acidic materials)
- Key Requirements
- Internal and external mirror polishing, roughness Ra ≤ 0.8μm, non-sticky and no material accumulation;
- Welds polished and ground, no sanitary dead corners, meeting CIP/SIP online cleaning and disinfection;
- Carbon steel, ordinary paint and non-food-grade plastics are prohibited to avoid contamination from rust and harmful substances.
- Typical Applications: Sugar powder classification, starch impurity removal, milk powder particle size separation, condiment fine classification.
3. Pharmaceutical Industry: GMP Compliance, Anti-contamination and High Cleanliness
The classification of pharmaceutical APIs, intermediates, traditional Chinese medicine extracts and preparation powders must comply with GMP specifications to eliminate cross-contamination and metal residues.
- Preferred Materials: 316L Stainless Steel (mainstream), electrolytic polished 316L, PTFE coating/liner
- Core Requirements
- No precipitation or shedding of materials, no reaction with pharmaceutical ingredients;
- Clean design of the whole machine, easy disassembly and assembly, easy sterilization, meeting ISO Class 7–8 clean room requirements;
- Mirror polishing and dead-angle-free structure are preferred; porous and easily adsorptive materials are prohibited.
- Typical Applications: Fine classification of APIs, purification of traditional Chinese medicine powder, particle size control of preparation powder.
4. Chemical Industry: Acid and Alkali Corrosion Resistance and Anti-material Contamination
Most materials in the chemical industry (pigments, dyes, resins, rubber additives, daily chemical raw materials, corrosive powders) contain acid, alkali, salt and organic solvents. Corrosion protection is the top priority.
- Material Selection
- Weakly corrosive/conventional powders: 304 Stainless Steel;
- Strong acid, strong alkali, chlorine-containing, organic solvents: 316L Stainless Steel, Hastelloy, PTFE lining;
- Anti-metal contamination/sensitive chemical materials: Food-grade PP, PE plastic classifiers.
- Key Points: Avoid chemical reactions between materials and equipment, preventing equipment leakage and material scrapping caused by corrosion.
5. Mining/Sand/Building Materials Industry: Super Wear Resistance and Impact Resistance
Materials such as mining, sand, quartz sand, cement and fly ash are high in hardness and extremely abrasive. The core pain points of classifiers are fast wear, short service life and frequent maintenance.
- Preferred Materials
- Chamber/Liner: Wear-resistant ceramics, polyurethane, wear-resistant alloys;
- Classifying Wheel/Key Components: 2205 Duplex Steel, Silicon Carbide Ceramics, High Manganese Steel;
- Low-cost general applications: Carbon steel + wear-resistant coating.
- Core Requirements: High impact resistance and high wear resistance to extend service life and reduce downtime and replacement costs.
6. Metallurgy/Metal Powder Industry: Wear Resistance + Corrosion Resistance + High Precision
Metal powders (aluminum powder, titanium powder, nickel powder, tungsten powder, alloy powder) have high density and hardness, easy to wear equipment, and require iron-free contamination and high-precision classification.
- Preferred Materials: 316L Stainless Steel, ceramic coating, hard nickel alloy, zirconia ceramic parts
- Key Requirements: Prevent mixing of metal impurities, ensure powder purity and particle size accuracy, and adapt to inert gas protection conditions.
7. New Energy/Lithium Battery/Ceramics Industry: High Purity and Ultra Wear Resistance
New energy cathode materials, anode materials, ceramic powder, alumina and zirconia powders have extremely high requirements for purity and wear resistance. Slight contamination will lead to product scrapping.
- Preferred Materials: High-purity alumina/zirconia ceramics, 316L Stainless Steel, PTFE liner
- Core Requirements: No metal ion precipitation, ultra-high wear resistance, no material contamination, adapting to high-purity production standards.
8. General 5-step Judgment Method for Classifier Material Selection
- Check the Material: Whether it is corrosive, high-hardness, hygienic, or anti-metal contamination;
- Check the Environment: Normal temperature/high temperature, high humidity/dry, indoor/outdoor, coastal (chloride ions);
- Check the Standards: FDA/food grade for food, GMP for pharmaceuticals, corrosion protection specifications for chemicals;
- Check the Cost: Carbon steel for low wear and low cost, 304 for general clean use, 316L for strong corrosion, ceramics/polyurethane for high wear;
- Check the Structure: Polishing, no dead corners, easy cleaning and maintenance, adapting to production processes.
9. Summary
There is no absolute “best” material for classifiers, only the most suitable for the industry and material. Food and pharmaceuticals focus on hygiene and compliance, chemicals on corrosion protection, mining on wear resistance, new energy on high purity, and metal powders on anti-contamination and wear resistance. Correct selection can increase equipment life by 2–5 times, reduce maintenance costs, and ensure product purity and stable production.
When purchasing and customizing classifiers, be sure to clarify material properties, working conditions and industry standards to manufacturers, and prioritize models with compliant materials for parts in direct contact with materials to avoid production losses caused by improper materials.
