| Typical Material Structure | Injection-molded or machined polypropylene, usually unfilled or mineral-filled. | High-performance polyether ether ketone, normally injection-molded or machined; conductive grades are available. | Machined or formed aluminum alloy, often with anodized or chemically treated surfaces. | Combination of materials, commonly an aluminum frame with PP, PEEK, PPS, or other engineering-polymer contact components. |
| Density | 0.90–0.91 g/cm³ | 1.30–1.32 g/cm³ | 2.66–2.70 g/cm³ for common wrought aluminum alloys | Approximately 1.1–2.2 g/cm³, depending on the metal-to-polymer ratio |
| Relative Weight for Similar Volume | Very low; suitable where manual handling and high cassette counts are important. | Low to medium; heavier than PP but substantially lighter than aluminum. | High; may increase rack, conveyor, and operator-handling loads. | Low to medium; can be optimized by using metal only in load-bearing areas. |
| Typical Continuous Service Temperature | Approximately 80–100°C, depending on load, design, and grade. | Approximately 240–260°C for many unfilled grades. | Well above 200°C for the metal itself; surface treatment, seals, and polymer inserts may limit the assembly. | Typically 80–250°C; the lowest-rated component determines the usable temperature range. |
| Short-Term Heat Resistance | Limited. Prolonged exposure near the softening range can cause warpage under load. | Excellent; suitable for demanding thermal cycling and elevated-temperature cleaning. | Excellent; retains high stiffness at temperatures used in many cell-processing steps. | Good when the polymer inserts and joining method are selected for the process temperature. |
| Thermal Expansion Coefficient | Approximately 100–150 × 10−6/K | Approximately 45–55 × 10−6/K | Approximately 22–24 × 10−6/K | Approximately 25–80 × 10−6/K, depending on construction and material orientation |
| Dimensional Stability | Good at moderate temperatures; creep and thermal expansion should be considered for long unsupported spans. | Very good; low moisture absorption and high stiffness support tight tolerances. | Excellent; high stiffness and low thermal expansion provide stable positioning. | Very good when the design controls differential expansion between metal and polymer sections. |
| Typical Tensile Strength | Approximately 25–40 MPa, depending on grade and reinforcement. | Approximately 90–100 MPa for many unfilled grades. | Approximately 200–310 MPa for commonly used heat-treatable wrought alloys; alloy and temper are decisive. | Approximately 50–250 MPa at assembly level, depending on the load-bearing material and joint design. |
| Flexural Stiffness | Low to medium; ribs and thicker sections may be required to prevent sagging. | High for a thermoplastic; suitable for thin, rigid precision components. | Very high; well suited to long spans and high-load cassette frames. | High when aluminum carries the primary load while polymer parts protect the cells. |
| Chemical Resistance | Very good against many aqueous acids, bases, and cleaning chemicals; assess strong oxidizers and elevated-temperature exposure. | Excellent against a broad range of solvents, acids, bases, and process chemicals; verify compatibility with concentrated acids and high-temperature media. | Good against many neutral environments, but susceptible to corrosion or surface attack from strong acids, strong alkalis, chlorides, and galvanic contact. | Depends on the weakest component; polymer contact surfaces can provide chemical protection for a metal frame. |
| Moisture Absorption | Very low, generally below 0.1% after 24-hour water immersion. | Very low, generally around 0.1–0.2% after 24-hour water immersion. | No polymer-like moisture absorption; corrosion protection is required in wet or chemically aggressive environments. | Low to medium; determined mainly by the selected polymer inserts and bonded interfaces. |
| Electrical Behavior | Normally electrically insulating; static-control grades can be specified. | Normally insulating; conductive or dissipative PEEK grades are available for ESD-sensitive processes. | Electrically conductive; grounding and insulation at contact points may be required. | Can combine a grounded conductive frame with electrically isolated or ESD-controlled cell-contact surfaces. |
| Risk of Cell Scratching | Low when molded with smooth, burr-free contact surfaces; damaged or contaminated edges must be controlled. | Very low when properly finished; maintains contact geometry under heat and repeated cleaning. | Medium to high if edges, burrs, particles, or hard contact points are not controlled; protective coatings or inserts are recommended. | Low when polymer inserts isolate the cell from the metal load-bearing structure. |
| Particle and Burr Control | Generally good after proper molding and trimming; wear particles may increase under abrasive contact. | Very good; precision machining and high wear resistance support clean contact surfaces. | Requires careful deburring, edge finishing, and coating control; anodizing can improve surface durability. | Good if metal edges are enclosed or finished and polymer inserts are replaceable. |
| Wear Resistance | Moderate; suitable for standard handling but may wear faster at sliding contact points. | Excellent, especially in reinforced or wear-optimized grades. | High structural wear resistance; exposed surfaces may require treatment to reduce galling or particle generation. | High overall performance when wear-resistant polymer inserts are used at contact locations. |
| Cleanability | Easy to wash and dry; verify resistance to the selected detergents and drying temperature. | Excellent; suitable for repeated cleaning and demanding chemical sanitation. | Easy to clean, but coatings, joints, and galvanic corrosion areas require inspection. | Good; the design should prevent liquid entrapment between metal and polymer components. |
| Manufacturing Flexibility | High for high-volume injection molding; integrated ribs, guides, and locating features are economical. | Good for complex precision parts, but tooling and machining costs are higher. | Excellent for precision machining, formed frames, and modular construction; complex shapes may increase fabrication cost. | High design flexibility, but assembly, bonding, fastening, and tolerance management are more complex. |
| Typical Relative Material Cost Index | 1.0× baseline | Approximately 4–10× PP, depending on grade, form, and order volume | Approximately 1.5–3.5× PP for the material portion, depending on alloy and surface treatment | Approximately 2–6× PP for the material and basic assembly portion |
| Expected Service Life | Good for moderate-temperature handling; life decreases with high heat, heavy loads, and repeated sliding. | Very long in high-temperature, chemically aggressive, and high-cycle applications. | Very long when corrosion, coating wear, and cell-contact damage are controlled. | Very long when replaceable polymer inserts protect the frame and wear components can be serviced. |
| Best-Fit Production Conditions | High-volume handling, moderate-temperature processes, cost-sensitive lines, and lightweight manual logistics. | High-temperature processes, aggressive chemical cleaning, tight dimensional tolerances, and high-cycle precision handling. | Heavy-load automation, long unsupported spans, high rigidity requirements, and grounded handling systems. | High-throughput lines requiring a balance of rigidity, low cell contact risk, serviceability, and total cost. |
| Main Advantages | Lowest weight, low material cost, good chemical resistance, and efficient injection molding. | Highest overall polymer performance, excellent chemical and thermal resistance, and strong wear resistance. | Superior rigidity, dimensional stability, thermal conductivity, and electrical conductivity. | Combines metal stiffness with polymer protection, replaceable contact elements, and application-specific customization. |
| Main Limitations | Lower temperature capability, higher thermal expansion, and greater risk of creep under sustained load. | High material and processing cost; conductive performance requires a specified grade and validated design. | Higher weight, possible corrosion or galvanic issues, and greater risk of cell damage at unprotected contact points. | More complex procurement, assembly, tolerance control, and validation than a single-material cassette. |
| Recommended Selection Priority | Choose when cost, low weight, and moderate operating temperature are the primary requirements. | Choose when temperature, chemical exposure, wear, and dimensional precision justify a premium material. | Choose when rigidity, load capacity, grounding, and thermal stability are more important than low weight. | Choose when a balanced design is required for automated handling, cell protection, serviceability, and lifecycle value. |