1. Meaning of Material in Mechanical Design
In mechanical design, a material does not simply mean “the substance used to make a part.”
It is a key design factor that determines the structural strength, durability, friction behavior, hygiene, corrosion resistance, thermal deformation, machinability, assembly characteristics, maintainability, and cost of a machine.
Therefore, material selection should be reviewed together with the following questions:
Does this part carry load?
Is friction or wear generated?
Is the part exposed to water, cleaning chemicals, acids, salt, or food?
Is it used in a high-temperature or low-temperature environment?
What manufacturing process will be used: welding, cutting, bending, casting, injection molding, or machining?
Does it need to satisfy hygiene, safety, or food-contact requirements?
Should it be easy to repair or replace?
Is the balance between cost and performance appropriate?
2. Metallic Materials
Metallic materials are the most fundamental material group used in mechanical design.
They are widely used for frames, shafts, brackets, gears, bearing housings, covers, and plates because of their excellent strength, stiffness, heat resistance, machinability, weldability, and surface treatment compatibility.
2.1 Steel Materials
Steel materials are iron-based materials containing carbon and alloying elements.
They offer excellent strength relative to cost and good machinability, making them the most widely used materials in industrial machinery.
2.1.1 General Structural Steel
Representative materials:
SS400
S275
S355
ASTM A36
Main characteristics:
Low cost
Easy to cut, weld, bend, and machine
Suitable for frames, bases, brackets, and support structures
Weak against corrosion, so painting, plating, black oxide, or other surface treatments are required
Main applications:
Machine frames
Base plates
Welded structures
General brackets
Support structures
Design considerations:
Rust can occur easily, so care is required in humid, washdown, or salty environments.
It is generally not suitable for food-contact areas in food machinery.
If the painted surface is damaged, corrosion may progress quickly.
2.1.2 Carbon Steel
Representative materials:
S45C
S50C
AISI 1045
Main characteristics:
Higher strength than general structural steel
Hardness and wear resistance can be improved through heat treatment
Widely used for shafts, pins, rollers, cams, and machine elements
Weldability is lower than that of general structural steel
Main applications:
Rotating shafts
Pins
Rollers
Cams
Gear blanks
Machined mechanical parts
Design considerations:
Deformation may occur after heat treatment.
Surface treatment is required because corrosion resistance is low.
It is often not suitable for food-contact parts.
2.1.3 Alloy Steel
Representative materials:
SCM415
SCM420
SCM440
SNCM series
Main characteristics:
Contains alloying elements such as chromium, molybdenum, and nickel
Excellent strength, toughness, fatigue strength, and wear resistance
Good heat treatment characteristics
Suitable for high-load mechanical elements
Main applications:
High-strength shafts
Gears
Spindles
Bolts
Power transmission components
High-load pins
Design considerations:
More expensive than general carbon steel.
Performance varies greatly depending on heat treatment conditions.
Heat treatment and grinding processes should be considered together after machining.
2.1.4 Tool Steel
Representative materials:
SKD11
SKD61
SKH51
Main characteristics:
High hardness and excellent wear resistance
Used for dies, blades, cutting components, and friction parts
Becomes very hard after heat treatment
May be vulnerable to impact due to brittleness
Main applications:
Cutting blades
Mold components
Punches
Dies
Wear plates
High-hardness guide parts
Design considerations:
Machining after heat treatment is difficult.
Toughness must be reviewed for parts exposed to high impact loads.
For food machinery blades, stainless blade materials should also be compared.
2.2 Stainless Steel
Stainless steel is an iron-based material containing chromium and offering excellent corrosion resistance.
It is essential for food machinery, medical devices, chemical equipment, and machines used in washdown environments.
2.2.1 Austenitic Stainless Steel
Representative materials:
STS304
STS316
STS316L
Main characteristics:
Excellent corrosion resistance
Good hygienic properties
Good weldability
Non-magnetic or weakly magnetic
Susceptible to work hardening
Main applications:
Food-contact parts
Tanks
Hoppers
Covers
Frames
Parts exposed to wash water
Piping
Mixing chambers
STS304:
The most common stainless steel used in food machinery
Good balance between cost and performance
STS316:
Contains molybdenum and has better resistance to salt and acidic environments
Suitable for seawater, salt, and acidic cleaning environments
STS316L:
Low carbon content provides better corrosion resistance after welding
Suitable for hygienic piping, tanks, and welded structures
Design considerations:
More expensive than ordinary steel.
During machining, work hardening and heat generation must be controlled.
Surface roughness, weld beads, and crevice structures greatly affect hygiene.
2.2.2 Martensitic Stainless Steel
Representative materials:
STS410
STS420
SUS420J2
Main characteristics:
Hardness can be increased through heat treatment
Good wear resistance
Lower corrosion resistance than austenitic stainless steel
Used for blades, shafts, and cutting parts
Main applications:
Food cutting blades
Cutters
High-hardness shafts
Wear parts
Pump components
Design considerations:
Less suitable than STS304 or STS316 in corrosive environments.
For food-contact parts, the possibility of rust must be carefully reviewed.
Surface treatment and maintenance are important in cleaning-fluid or salt environments.
2.2.3 Ferritic Stainless Steel
Representative material:
STS430
Main characteristics:
Magnetic
Relatively low cost
Lower corrosion resistance than STS304
Used for decorative covers, exterior panels, and parts in low-corrosion environments
Main applications:
Exterior covers
Protective covers
Non-food-contact parts
Lightweight sheet metal parts
Design considerations:
Use for food-contact parts should be limited.
Weldability and corrosion resistance are lower than those of STS304.
Corrosion risk must be reviewed in washdown environments.
2.3 Non-Ferrous Metals
Non-ferrous metals are metallic materials in which iron is not the main component.
Typical examples include aluminum, copper alloys, titanium, and nickel alloys.
2.3.1 Aluminum Alloys
Representative materials:
A5052
A6061
A7075
ADC12
Main characteristics:
Lightweight
Good machinability
Good thermal conductivity
Can be anodized
Lower stiffness than steel
Main applications:
Lightweight brackets
Covers
Plates
Heat-dissipating components
Automation equipment parts
Robot components
Aluminum profile frames
A5052:
Suitable for sheet metal, bending, and cover parts
Good corrosion resistance
A6061:
Widely used for machined parts and structural components
Good balance between strength and machinability
A7075:
High-strength aluminum
Used for aerospace and high-strength lightweight parts
Expensive and relatively lower in corrosion resistance
ADC12:
Aluminum die-casting material
Suitable for complex shapes and mass production
Design considerations:
Because aluminum has a lower elastic modulus than steel, bending deformation can be larger.
Thread wear can occur easily, so inserts should be considered.
For food-contact parts, surface treatment and regulatory suitability must be reviewed.
2.3.2 Copper and Copper Alloys
Representative materials:
Pure copper
Brass
Bronze
Phosphor bronze
Main characteristics:
Excellent electrical and thermal conductivity
Good friction characteristics
Used for bushings, bearings, and electrical contacts
Some copper alloys have good wear resistance
Main applications:
Bushings
Sliding components
Electrical terminals
Heat exchange components
Worm wheels
Bearing metals
Design considerations:
Lower strength than steel.
For food-contact applications, lead content, hygiene, and corrosion risk must be reviewed.
Cost is relatively high.
2.3.3 Titanium Alloys
Representative materials:
Titanium Grade 2
Ti-6Al-4V
Main characteristics:
Lightweight and high strength
Very high corrosion resistance
Good biocompatibility
Expensive and difficult to machine
Main applications:
Aerospace components
Medical devices
Chemical equipment
High-corrosion-resistance components
Lightweight high-strength parts
Design considerations:
Material and machining costs are high.
Tool wear and heat control are important during machining.
In general industrial machinery, use is limited mainly due to cost.
3. Polymer Materials
Polymer materials include plastics, engineering plastics, rubber, and resin-based materials.
Compared with metals, they are lighter and often provide better electrical insulation, corrosion resistance, low friction, and impact absorption.
3.1 General-Purpose Plastics
Representative materials:
PE
PP
PVC
ABS
PS
Main characteristics:
Low cost
Good moldability
Lightweight
Limited strength and heat resistance
Main applications:
Covers
Handles
Protective caps
Cases
Guides
Non-structural parts
Design considerations:
Use should be limited for load-bearing structural parts.
Deformation due to temperature change can be significant.
Creep deformation may occur during long-term use.
3.2 Engineering Plastics
Engineering plastics have better strength, heat resistance, wear resistance, and dimensional stability than general-purpose plastics.
They are often used directly as mechanical components.
3.2.1 POM
Main characteristics:
Good machinability
Low coefficient of friction
Good dimensional stability
Suitable for gears, rollers, and sliders
Main applications:
Plastic gears
Rollers
Guides
Bushings
Sliding components
Jig components
Design considerations:
Low adhesive bonding performance.
Limited suitability for high-temperature environments.
For food machinery, food-contact grade suitability must be confirmed.
3.2.2 PA / Nylon
Main characteristics:
Good toughness
Good wear resistance
High impact resistance
Absorbs moisture, which can cause dimensional changes
Main applications:
Gears
Bushings
Rollers
Chain guides
Wear pads
Design considerations:
Moisture absorption can make it difficult to maintain precision dimensions.
In humid environments, dimensional change and strength reduction must be considered.
3.2.3 PC
Main characteristics:
Good transparency
High impact strength
Suitable for protective windows and safety covers
Main applications:
Transparent covers
Safety windows
Protective guards
Inspection windows
Design considerations:
May be vulnerable to certain cleaning agents or solvents.
Scratches can occur easily.
Deformation may occur in high-temperature washdown environments.
3.2.4 PTFE
Main characteristics:
Very low coefficient of friction
Excellent chemical resistance
Good non-stick properties
Good heat resistance
Main applications:
Seals
Gaskets
Sliding pads
Linings
Non-stick components
Food machinery guide parts
Design considerations:
Low stiffness and high creep tendency.
Deformation must be considered for parts under continuous load.
Compression deformation must be reviewed in fastening areas.
3.2.5 UHMW-PE
Main characteristics:
Very good wear resistance
Low coefficient of friction
Good impact absorption
Widely used in food machinery for guides, chutes, and chain rails
Main applications:
Chain guides
Conveyor rails
Sliding plates
Chute linings
Food transfer guides
Design considerations:
Weak against thermal deformation.
May not be suitable for precision dimensional parts.
Creep under long-term load must be considered.
3.3 Super Engineering Plastics
These are high-performance plastics used in high-temperature, high-load, and highly corrosive environments.
Representative materials:
PEEK
PPS
PI
PEI
Main characteristics:
High heat resistance
Excellent strength and dimensional stability
Good chemical resistance
Very expensive
Main applications:
High-temperature jigs
High-performance bushings
Insulating components
Semiconductor equipment parts
Medical device components
High-temperature mechanical parts
Design considerations:
Because the material cost is high, the application area should be clearly limited.
Dimensional accuracy may vary depending on machining conditions.
When used as a metal replacement, the difference in stiffness must be carefully reviewed.
4. Rubber and Elastic Materials
Rubber materials are used where elasticity, sealing performance, vibration absorption, and impact absorption are required.
Representative materials:
NBR
EPDM
Silicone
Viton
Urethane rubber
4.1 NBR
Main characteristics:
Good oil resistance
Widely used for general oil seals and packings
Relatively low cost
Main applications:
Oil seals
O-rings
Packings
Gaskets
Design considerations:
Weak against high temperature, ozone, and ultraviolet light.
For food-contact areas, a dedicated food-grade material must be confirmed.
4.2 EPDM
Main characteristics:
Good water resistance, ozone resistance, and weather resistance
Suitable for water, steam, and washdown environments
Weak against oil
Main applications:
Waterproof packings
Gaskets for cleaning equipment
Door seals
Outdoor exposure seals
Design considerations:
It is not recommended for oil environments.
For food machinery, food-grade suitability must be confirmed.
4.3 Silicone
Main characteristics:
Good heat and cold resistance
Stable elasticity
Widely used in food-grade and medical-grade applications
Main applications:
Food machinery packings
High-temperature seals
Tubes
Gaskets
Door packings
Design considerations:
Mechanical strength and wear resistance are not high.
It may be vulnerable to tearing.
4.4 Viton
Main characteristics:
Excellent heat resistance, chemical resistance, and oil resistance
Suitable for high-temperature, chemical, and oil environments
Main applications:
High-performance O-rings
Chemical equipment seals
High-temperature packings
Oil-resistant seals
Design considerations:
High cost.
Low-temperature elasticity may be inferior to silicone.
4.5 Urethane Rubber
Main characteristics:
Very good wear resistance
Good impact absorption
Suitable for rollers, pads, and stoppers
Main applications:
Rollers
Impact-absorbing pads
Stoppers
Wheels
Wear liners
Design considerations:
Material properties can deteriorate in high-temperature environments.
For food-contact areas, a dedicated food-grade material must be reviewed.
5. Ceramic Materials
Ceramics have higher hardness, heat resistance, wear resistance, and electrical insulation than metals or plastics.
However, they are brittle and weak against impact.
Representative materials:
Alumina
Zirconia
Silicon carbide
Silicon nitride
Main characteristics:
Very hard
Strong against wear
Stable at high temperatures
Good electrical insulation
Brittle and easily damaged by impact
Main applications:
Insulating components
High-temperature parts
Bearing balls
Nozzles
Sealing components
Wear plates
Semiconductor equipment parts
Design considerations:
Impact loads should be avoided.
Stress concentration must be reduced in threaded or fastening areas.
When assembled with metal parts, differences in thermal expansion must be considered.
6. Composite Materials
Composite materials combine two or more materials to obtain performance that is difficult to achieve with a single material.
Representative materials:
CFRP
GFRP
FRP
Metal matrix composites
Fiber-reinforced plastics
6.1 CFRP
Main characteristics:
Very lightweight and high stiffness
Good fatigue characteristics
Low thermal expansion
High cost
Main applications:
Robot arms
Aerospace components
High-speed moving structures
Precision equipment frames
Lightweight structures
Design considerations:
Impact damage can occur internally and may not be visible from the outside.
Dust control is required during machining.
Galvanic corrosion must be considered when fastening with metals.
6.2 GFRP / FRP
Main characteristics:
Good corrosion resistance
Good electrical insulation
Lighter than metal
Less expensive than CFRP
Main applications:
Covers
Tanks
Ducts
Insulating structures
Structures used in corrosive environments
Design considerations:
Dimensional accuracy may be lower than that of metals.
Fastening strength must be reviewed.
Long-term effects of ultraviolet light, moisture, and temperature must be considered.
7. Surface Treatment and Coating Materials
In mechanical design, surface properties are often more important than the base material itself.
Surface treatments and coatings are used to improve corrosion resistance, wear resistance, lubricity, hygiene, appearance, and cleanability.
7.1 Plating
Representative methods:
Zinc plating
Nickel plating
Chrome plating
Electroless nickel plating
Main purposes:
Corrosion prevention
Appearance improvement
Wear resistance improvement
Dimensional compensation
Design considerations:
For food-contact parts, the risk of plating peeling must be reviewed.
Plating thickness can affect dimensions.
Differences in plating quality at corners and inside holes must be considered.
7.2 Oxide Film Treatment
Representative methods:
Anodizing
Black oxide
Oxide film treatment
Main purposes:
Improving corrosion resistance of aluminum
Appearance improvement
Surface hardness improvement
Electrical insulation
Design considerations:
If the coating layer is damaged, the base material is exposed.
For food-contact parts, the treatment method and suitability must be confirmed.
7.3 Nitriding, Carburizing, and Induction Hardening
Main purposes:
Surface hardness improvement
Wear resistance improvement
Fatigue strength improvement
Life extension of gears, shafts, and cams
Main applications:
Gears
Shafts
Cams
Sliding components
Bearing contact areas
Design considerations:
Heat treatment deformation must be considered.
Post-processing, grinding, or dimensional correction may be required.
Balance between core toughness and surface hardness is important.
7.4 Fluororesin Coating
Representative materials:
PTFE coating
PFA coating
FEP coating
Main characteristics:
Excellent non-stick properties
Low friction
Good chemical resistance
Used for food transfer areas, chutes, and guides
Design considerations:
Coating peeling may occur.
Service life can be short in areas with sharp edges, impact, or severe friction.
In food machinery, the risk of peeled coating fragments contaminating the product must be reviewed.
8. Adhesives, Sealants, and Lubricants
In mechanical design, adhesives, sealants, and lubricants are auxiliary materials, but they have a significant effect on actual machine performance and maintainability.
8.1 Adhesives
Representative types:
Epoxy
Cyanoacrylate adhesive
Anaerobic adhesive
Structural adhesive
Main applications:
Fixing parts
Preventing screw loosening
Bonding composite materials
Bonding metal and plastic
Design considerations:
Resistance to temperature, humidity, vibration, and cleaning chemicals must be confirmed.
Use should be limited in areas requiring disassembly and maintenance.
For food machinery, food-contact suitability must be reviewed.
8.2 Sealants
Representative types:
Silicone sealant
Urethane sealant
Liquid gasket
Main applications:
Waterproofing
Oil leakage prevention
Gap sealing
Cover sealing
Design considerations:
Cleanability and hygiene must be considered.
Structures should prevent contaminants from accumulating in gaps.
Removability during disassembly and maintenance must be reviewed.
8.3 Lubricants
Representative types:
Grease
Oil
Food-grade lubricant
High-temperature lubricant
Dry lubricant
Main applications:
Bearings
Chains
Gears
Linear guides
Ball screws
Sliding components
Design considerations:
In food machinery, the use of food-grade lubricant is important.
Loss of lubricant due to wash water must be considered.
Lubrication intervals and maintenance access should be reflected in the design stage.
9. Functional Materials
Functional materials are selected not only for structural strength, but also for specific functions.
9.1 Electrical Insulating Materials
Representative materials:
POM
PTFE
PEI
PEEK
Ceramics
Epoxy glass
Main applications:
Electrical insulating plates
Sensor brackets
Terminal blocks
Insulating bushings
Electrical component protection parts
Design considerations:
Dielectric withstand voltage must be confirmed.
Insulation degradation due to humidity and contamination must be considered.
Thermal deformation and flame resistance must be reviewed.
9.2 Heat-Resistant Materials
Representative materials:
Stainless steel
Heat-resistant steel
Ceramics
PEEK
PTFE
Silicone rubber
Main applications:
Parts around heaters
High-temperature chambers
Oven equipment
Hot-air equipment
High-temperature seals
Design considerations:
Thermal expansion must be considered.
Strength reduction at high temperature must be reviewed.
Heat transfer to adjacent parts must be controlled.
9.3 Wear-Resistant Materials
Representative materials:
SKD11
Heat-treated SCM series steel
UHMW-PE
PTFE
Ceramics
Urethane
Bronze
Main applications:
Guides
Rollers
Sliders
Blades
Chain rails
Wear plates
Design considerations:
The combination with the mating material is important.
Lubrication conditions must be reviewed together.
It is preferable to design these parts as replaceable components.
9.4 Hygienic Materials
In food machinery, pharmaceutical machinery, and medical devices, hygiene is a very important material selection criterion.
Representative materials:
STS304
STS316
STS316L
Food-grade silicone
Food-grade UHMW-PE
Food-grade POM
Food-grade PTFE
Main requirements:
Must be resistant to corrosion
Must be easy to clean
Must have a smooth surface
Must have low risk of crevices, pores, or peeling
Must be safe for contact with food
Design considerations:
Food-contact and non-food-contact areas must be clearly distinguished.
Welded areas should be considered for polishing and passivation.
Paint, plating, and peelable coatings should be used carefully in food-contact areas.
Packings, gaskets, and plastic parts also require food-grade confirmation.
10. Material Selection Criteria from a Mechanical Design Perspective
When selecting materials, strength alone must not be the only consideration.
In actual design, the following items should be evaluated comprehensively.
10.1 Mechanical Properties
Items to review:
Tensile strength
Yield strength
Hardness
Elastic modulus
Fatigue strength
Impact strength
Wear characteristics
Creep characteristics
Application examples:
For frames, stiffness and weldability are important.
For shafts, fatigue strength and torsional strength are important.
For gears, surface hardness and wear resistance are important.
For guides, friction coefficient and wear resistance are important.
10.2 Chemical Properties
Items to review:
Corrosion resistance
Acid resistance
Alkali resistance
Oil resistance
Cleaning chemical resistance
Salt resistance
Application examples:
Food machinery is exposed to water, cleaning agents, salt, and fat.
Chemical equipment requires resistance to acids, alkalis, and solvents.
Outdoor equipment must consider rainwater, humidity, and ultraviolet exposure.
10.3 Thermal Properties
Items to review:
Heat resistance temperature
Coefficient of thermal expansion
Thermal conductivity
Heat deflection temperature
Low-temperature brittleness
Application examples:
Parts near heaters require heat resistance.
Precision equipment must minimize dimensional change caused by thermal expansion.
Refrigeration equipment must consider low-temperature brittleness.
10.4 Machinability and Processability
Items to review:
Machinability
Weldability
Bendability
Castability
Moldability
Grindability
Heat treatability
Application examples:
Complex shapes may require casting or injection molding.
Small-volume production is often suitable for machining.
Frames require weldability and deformation control.
Sheet metal covers require bendability and surface quality.
10.5 Assembly and Maintainability
Items to review:
Fastening stability
Thread strength
Disassembly possibility
Replaceability after wear
Surface damage risk
Cleanability
Application examples:
Wear parts should use materials and structures that are easy to replace.
Plastic parts may require threaded inserts.
Food machinery requires structures that are easy to disassemble and clean.
10.6 Cost and Availability
Items to review:
Material cost
Machining cost
Heat treatment cost
Surface treatment cost
Lead time
Availability of standard materials
Maintenance cost
Application examples:
Excessive use of high-grade materials increases product cost.
General-purpose materials should be considered first for standard parts.
High-performance materials should be selected for critical wear parts or hygienic parts.
11. Representative Material Selection Examples by Machine Part
11.1 Frames
Representative materials:
SS400
S355
STS304
Aluminum profile
Selection criteria:
Stiffness
Weldability
Cost
Corrosion environment
Hygiene requirements
General industrial machinery:
SS400 welded frame with painting
Food machinery:
STS304 or STS316 frame
Automation equipment:
Aluminum profile or machined aluminum frame
11.2 Shafts
Representative materials:
S45C
SCM440
STS304
STS420
Selection criteria:
Torsional strength
Fatigue strength
Wear resistance
Corrosion resistance
Heat treatment capability
General shafts:
S45C
High-load shafts:
SCM440
Food machinery shafts:
STS304 or STS420
11.3 Gears
Representative materials:
SCM415
SCM420
SCM440
POM
MC Nylon
Bronze
Selection criteria:
Power transmission load
Noise
Lubrication conditions
Wear
Impact load
High-load metal gears:
Carburized or heat-treated SCM series steel
Low-noise lightweight gears:
POM or Nylon
Worm wheels:
Bronze
11.4 Covers
Representative materials:
STS304
STS430
A5052
PC
ABS
Selection criteria:
Safety
Appearance
Hygiene
Transparency
Detachability
Food machinery covers:
STS304
Transparent safety covers:
PC
Lightweight covers:
Aluminum or plastic
11.5 Guides and Sliding Components
Representative materials:
UHMW-PE
POM
PTFE
Bronze
Heat-treated steel
Ceramics
Selection criteria:
Coefficient of friction
Wear resistance
Lubrication conditions
Damage to mating material
Replaceability
Food transfer guides:
Food-grade UHMW-PE
Precision sliding components:
POM, PTFE, or bronze
High-wear components:
Heat-treated steel or ceramics
11.6 Packings and Seals
Representative materials:
NBR
EPDM
Silicone
Viton
PTFE
Selection criteria:
Temperature
Pressure
Chemicals
Food-contact suitability
Elastic recovery
Food machinery packings:
Food-grade silicone
Food-grade EPDM
PTFE
Oil seals:
NBR or Viton
High-temperature seals:
Silicone or Viton
12. Material Selection Direction for Food Machinery Design
In food machinery, material selection standards are stricter than in general industrial machinery.
Materials cannot be selected based only on strength and cost. Hygiene, cleanability, corrosion resistance, and the risk of foreign material contamination must also be reviewed.
12.1 Food-Contact Areas
Recommended materials:
STS304
STS316
STS316L
Food-grade UHMW-PE
Food-grade POM
Food-grade PTFE
Food-grade silicone
Elements to avoid:
Ordinary steel with high risk of rust
Paint that may peel
Plastics without confirmed food-grade suitability
Porous materials that are difficult to clean
Surface-treated structures with many crevices
12.2 Non-Food-Contact Structural Areas
Applicable materials:
Painted SS400
STS304
Aluminum
Engineering plastics
Selection criteria:
Exposure to wash water
Machine appearance
Cost
Strength
Maintainability
Design considerations:
Even non-food-contact areas require corrosion protection if exposed to wash water and humidity.
In food production sites, stainless steel is often preferred even for exterior covers and frames.
12.3 Washdown Environments
Important factors in washdown environments:
Water resistance
Cleaning chemical resistance
Salt resistance
Surface roughness
Minimization of crevices
Weld treatment
Drainability
Recommended direction:
For food-contact parts, STS304 or higher should be considered as the basic option.
In environments with salt, acidic cleaning agents, or strong chemical cleaning, STS316 or STS316L should be considered.
Plastic guides and packings must be checked for food-grade suitability and resistance to cleaning chemicals.
13. Basic Principles of Material Selection
In mechanical design, material selection should follow the principles below.
13.1 Select Materials Based on Function
The function of the part comes first, and the material is a means to satisfy that function.
For example:
Load-bearing parts → strength and stiffness
Friction parts → wear resistance and coefficient of friction
Food-contact parts → hygiene and corrosion resistance
High-temperature parts → heat resistance and thermal expansion
Transparent covers → impact strength and transparency
13.2 Confirm Environmental Conditions First
The suitability of the same material can vary greatly depending on the operating environment.
Environmental factors to review:
Dry or wet conditions
Indoor or outdoor use
High or low temperature
Exposure to wash water
Exposure to salt
Exposure to oil
Food-contact requirements
Exposure to chemicals
13.3 Decide Together with the Manufacturing Process
Materials cannot be selected separately from the manufacturing method.
For example:
Welded structures require materials with good weldability.
Machined parts require materials with good machinability.
Sheet metal covers require bendability and surface quality.
Mass-produced parts require review of casting, injection molding, or press forming.
Precision parts require consideration of heat treatment deformation and post-processing.
13.4 Consider Maintainability and Replaceability
Machines experience wear, corrosion, and damage during use.
Therefore, material selection should consider not only service life but also replaceability.
For example:
Wear parts should use low-cost and easily replaceable materials.
Key structural parts should use long-life materials.
Food-contact wear parts should use materials with low risk of foreign material contamination.
Parts requiring cleaning should consider disassembly and surface cleanability.
14. Summary
Materials used in mechanical design can be broadly classified as follows.
Metallic materials
Used for parts where structural strength, stiffness, heat resistance, and machinability are important.Stainless steel materials
Used in food machinery and chemical equipment where corrosion resistance, hygiene, and cleanability are important.Non-ferrous metals
Used where lightweight design, thermal conductivity, electrical conductivity, or special corrosion resistance is required.Polymer materials
Used where lightweight properties, low friction, electrical insulation, and corrosion resistance are required.Rubber and elastic materials
Used where sealing, impact absorption, vibration absorption, and packing functions are required.Ceramic materials
Used where high hardness, wear resistance, electrical insulation, and high-temperature stability are required.Composite materials
Used for structures requiring lightweight, high strength, high stiffness, corrosion resistance, or special functions.Surface treatment and coating materials
Used to supplement the corrosion resistance, wear resistance, lubricity, and cleanability of the base material.
Material selection is not simply a question of “which material is stronger.”
It must be determined by considering function, load, environment, hygiene, manufacturing process, assembly, maintenance, and cost.
Especially in food machinery, food-contact conditions, cleanability, corrosion resistance, risk of foreign material contamination, and the possibility of surface coating peeling must all be reviewed.
Therefore, material should not be treated as a final selection item in mechanical design, but as a core design criterion that determines both structure and function.