A solid understanding of material properties is essential for any mechanical engineer or designer. This guide covers commonly used metals and non-metals in industrial manufacturing — from structural steel to engineering plastics — with practical insights on their applications, surface treatments, and limitations.
Metal Materials
- Q235 Mild Steel
The most widely used structural steel in mechanical design. Cost: ~$1.00 USD/kg (approx. 7 RMB) — highly cost-effective.
Key considerations: Prone to rust; surface treatment is typically required. For non-critical frames, baking paint is commonly applied. For high-precision base plates where dimensional stability is critical, chrome plating is recommended to maintain accuracy while providing corrosion resistance.
- Q345 High-Strength Steel
Offers superior load-bearing capacity compared to Q235, making it suitable for heavy-load frames and structural components. Surface treatment recommendations are similar to those for Q235.
- 45# Medium Carbon Steel
A versatile medium-carbon steel with good strength and wear resistance. Commonly used for shafts, connecting rods, support components, gears, and other load-bearing parts. Typical surface finishes include blackening (oxide coating) and chrome plating.
- 40Cr Alloy Steel
A higher-cost alloy steel offering excellent strength and toughness under heavy loads. While less common in light-duty non-standard machinery, it is ideal for heavy-duty gears, transmission shafts, and high-stress components where fatigue resistance is critical.
- 6061 Aluminum Alloy
Widely used for lightweight structural applications. While it can significantly reduce overall equipment weight, the cost is substantially higher than steel. Best applied selectively — for moving components where reduced inertia improves dynamic performance — rather than for entire machine frames.
- 7075 Aluminum Alloy
Aircraft-grade aluminum. Used where maximum strength-to-weight ratio is required — ideal for aerospace, high-performance automotive, and precision motion systems.
- SUS201 Stainless Steel (China Domestic Grade)
Often referred to as “rust-resistant iron” rather than true stainless steel — it will rust under certain conditions. Suitable for low-corrosion environments where appearance is not critical. Visual inspection with chemical testing can distinguish it from higher grades. Note: SUS201 is an austenitic stainless steel and is magnetic (can become non-magnetic after high-temperature treatment — do not rely on magnet testing for identification).
- SUS304 Stainless Steel (Food Grade)
The standard food-grade stainless steel — safe for direct food contact. Offers excellent resistance to acids, alkalis, and salts. Not recommended for seawater environments, as chloride ions will cause pitting and corrosion.
- SUS316 Stainless Steel (Medical Grade)
Superior corrosion resistance across acids, alkalis, and salts — with excellent high-temperature stability. Suitable for marine and seawater applications. The 316L variant has reduced carbon content, offering improved weldability while maintaining corrosion resistance.
- SKD11 Tool Steel
A high-carbon, high-chromium tool steel with exceptional wear resistance and hardness after heat treatment. Ideal for cold-press tooling, stamping dies, and high-wear structural components in forming equipment.
- S136 Tool Steel (Corrosion-Resistant)
Premium mold steel offering excellent corrosion resistance. Commonly used in injection molds, stamping tools, and components for food and medical equipment — where cleanliness and corrosion resistance are essential.
- High-Speed Steel (HSS) — “White Steel”
Specialized for cutting tools such as blades, shear knives, and trimming tools (e.g., mask machine cutters, sprue cutters). Offers:
· High hardness and wear resistance
· Excellent toughness and impact resistance
· Red hardness — maintains hardness at elevated temperatures (even when the blade glows red during high-speed cutting)
Non-Metal Materials
PTFE (Polytetrafluoroethylene)
Known as Teflon or “Plastic King.” Key properties: virtually chemically inert, extreme temperature resistance (-180°C to 260°C), ultra-low friction coefficient, non-stick, and wear-resistant. Ideal for guide rails, bearing pads, and wear strips in corrosive or high-temp environments.
Phenolic Resin (Bakelite / PF)
Excellent mechanical properties, non-absorbent, and electrically insulating — comparable to wood in insulation performance (hence the name “electric wood”). Widely used in fixtures, jigs, and tooling plates where mechanical stability and insulation are required.
Nylon (PA)
Heat-resistant, with a very low friction coefficient. Absorbs moisture, which can affect dimensional stability. Easy to machine. Commonly used for lightweight structural components, gears, bearings, and guide parts — where strength and low friction are needed.
POM (Polyoxymethylene / Acetal)
Also known as “Steel” or Delrin. Extremely low friction coefficient, excellent mechanical strength, and no moisture absorption. Similar to nylon but with lower heat resistance. Used for lightweight panels, bearings, gears, and precision components — especially in applications where dimensional stability is critical.
PU (Polyurethane / Urethane Rubber)
Combines moderate strength and rigidity with elastomeric flexibility. Commonly used in mechanical design for shock absorption, cushioning, bumpers, and impact-resistant components.
PMMA (Acrylic / Perspex)
Clear, lightweight, impact-resistant material — safer than glass. Easily machined and fabricated. If shattered, it forms dull fragments (not sharp shards like glass). Ideal for machine guards, protective covers, viewing windows, and enclosures.
Silicone
Heat-resistant, non-stick, electrically insulating, and chemically inert. Food and medical-grade variants available. Applications include conveyor belts, suction cups, soft grippers, protective tips, and cushioning components — where a soft, non-marring surface is required.
PVC (Polyvinyl Chloride)
Low-cost and widely available in flexible (soft) and rigid (sheet) forms. Good chemical resistance but poor heat stability — not suitable for high-temperature environments. In mechanical design, used for corrosion-resistant conveyor belts, tooling plates, guide rails, and protective liners.
