Designing with Materials Suited to Function and Operating Environment
Material Suitability is a field of design that evaluates whether the material used for a component or structure is appropriate for its required
function, loading conditions, operating environment, manufacturing process, service life, safety requirements, and cost constraints. It may also
be described as material suitability, material-selection suitability, or material suitability for the intended conditions of use.
In mechanical design, a material is not merely the substance from which a component is made. Its strength, stiffness, hardness, toughness,
corrosion resistance, wear resistance, thermal properties, and manufacturability directly determine product performance and service life.
Even components with the same geometry can differ significantly depending on the material selected. The following characteristics may change:
Allowable load
Amount of deformation
Fatigue life
Wear rate
Susceptibility to corrosion
Usable temperature range
Cleanability and hygienic performance
Manufacturing difficulty
Maintenance interval
Product cost
Recyclability and environmental burden
Material selection should therefore not be treated as the final task of adding a material designation after the design is complete. It should be
included among the early design activities that determine function and structure.
Material Suitability begins with the following questions:
What loads will this component experience?
How much deformation is allowable?
Will repeated loading or impact occur?
Will it be exposed to water, moisture, chemicals, food, or salts?
Will friction and wear occur?
Will temperature changes affect material performance?
Can the material be welded, bent, machined, or formed?
Is it suitable for food contact or human contact?
Can it satisfy both the required service life and cost target?
Is it easy to procure and replace?
The key review elements of Material Suitability can be organized as follows:
Mechanical Properties
Environmental Resistance
Thermal Suitability
Tribological Suitability
Manufacturability
Hygiene and Safety
Compatibility
Cost and Availability
Life Cycle and Sustainability
Basic Concept of Material Suitability
Material suitability is not an assessment of whether a material is inherently superior. It is a determination of whether that material is appropriate
for a specific component under specific conditions of use.
For example, stainless steel offers excellent corrosion resistance and hygienic performance, but it is not necessarily the best material for every
component. Another material may be more appropriate because of stainless steel’s higher cost, machining difficulty, thermal conductivity, friction
behavior, or weight.
Aluminum is lightweight and highly machinable, but its use may be limited under severe wear, repeated impact, strong alkaline cleaning agents, or
high-temperature conditions.
Engineering plastics can provide low friction and excellent corrosion resistance, but creep, temperature dependence, moisture absorption, and
dimensional stability must be evaluated.
Material selection should therefore consider the following relationship:
Functional requirements + Operating environment + Manufacturing process + Expected service life + Cost constraints = Suitable material
More important than the general superiority of a material is the compatibility between the requirements and the material properties.
Starting Point for Material Selection
Before selecting a material, the role of the component and its conditions of use must be clearly defined.
Component Function
Typical functions that influence material selection include:
Supporting loads
Transmitting torque
Guiding motion
Reducing friction
Resisting wear
Sealing fluids
Conducting or insulating heat
Protecting internal equipment from external impact
Directly contacting the product
Withstanding wash water and chemicals
Conducting or insulating electricity
Absorbing structural vibration
Even for the same material, the criteria used to judge suitability will differ according to the component’s role.
Operating Conditions
Materials must be evaluated under actual operating conditions.
Major conditions include:
Maximum static load
Repeated loading
Impact loading
Vibration
Rotational speed
Sliding speed
Contact pressure
Operating temperature
Rate of temperature change
Humidity
Water and steam
Cleaning and disinfecting agents
Acids and alkalis
Salts
Food constituents
Ultraviolet radiation
Dust and foreign matter
The designer must evaluate not only normal operating conditions but also cleaning, shutdown, abnormal operation, long-term storage, and
transportation conditions.
Mechanical Properties
Mechanical properties describe how a material responds to forces and deformation.
Strength
Strength is the level of stress a material can withstand before fracture or permanent deformation occurs.
Major strength characteristics include:
Tensile strength
Yield strength
Compressive strength
Shear strength
Flexural strength
Torsional strength
Fatigue strength
When selecting a component material, the designer should not consider ultimate tensile strength alone. Allowable deformation and repeated
loading conditions in the actual design must also be taken into account.
For example, a rotating shaft may have sufficient static strength but still fail through fatigue caused by repeated bending and torsion. The shaft
material must therefore be evaluated for fatigue strength, surface condition, heat treatment, and sensitivity to stress concentration, as well as
yield strength.
Stiffness
Stiffness is resistance to deformation under load and is determined mainly by the elastic modulus and component geometry.
Even when strength is sufficient, inadequate stiffness may cause the following problems:
Shaft deflection
Guide misalignment
Changes in blade position
Increased vibration
Improper gear meshing
Reduced seal contact pressure
Variation in product dimensions
Some aluminum alloys can have strength comparable to certain steels, but their elastic modulus is lower. As a result, the same geometry may
deform more when made from aluminum.
When changing materials to reduce weight, the designer must therefore evaluate structural stiffness rather than simply comparing strength
values.
Hardness
Hardness indicates resistance to indentation, scratching, and localized plastic deformation.
Hardness is particularly important for the following components:
Bearing contact regions
Gears
Cams
Rollers
Blades
Sliding surfaces
Locating pins
Repeatedly fastened areas
Higher hardness generally improves wear resistance, but excessive hardness may increase brittleness and reduce machinability.
Surface-hardening methods such as carburizing, nitriding, and induction hardening may therefore be applied to harden the surface while
maintaining toughness in the core.
Toughness
Toughness is the ability of a material to absorb energy before fracture.
High toughness is required under impact, rapid load changes, or low-temperature conditions.
A material with insufficient toughness may perform adequately under static loading but fracture suddenly under the following conditions:
Impact loading
Dropping
Emergency stops
Stress concentration at corners
Low-temperature embrittlement
Weld defects
Repeated impact
For safety-related components and rotating parts, the balance between strength and toughness is more important than simply selecting a high-
strength material.
Ductility
Ductility is the ability of a material to undergo plastic deformation before fracture.
Highly ductile materials offer the following advantages:
Lower likelihood of sudden brittle fracture
Easier bending and forming
Ability to redistribute localized stress
Visible deformation before failure
However, excessively soft materials may be vulnerable to wear, indentation, and deformation at fastening points.
Fatigue Properties
Mechanical components can fail under repeated loads even when the stress is below the yield strength. This is known as fatigue failure.
Factors affecting fatigue include:
Magnitude of cyclic stress
Mean stress
Number of load cycles
Surface roughness
Scratches and machining marks
Notches and steps
Welded regions
Corrosion
Residual stress
Heat-treatment condition
Fatigue life must be evaluated separately for rotating shafts, springs, links, welded frame joints, and reciprocating drive components.
Environmental Resistance
A material must retain its performance in the actual operating environment.
Corrosion Resistance
Corrosion is the deterioration of a material surface through reaction with water, oxygen, chemicals, or ions.
Corrosion can cause more than an appearance problem. It may lead to the following functional degradation:
Loss of cross-sectional area
Reduction in strength
Increased surface roughness
Generation of contamination
Seizure of fastened joints
Reduced fatigue life
Damage to seal-contact surfaces
Food contamination
The following environments should be distinguished when evaluating corrosion resistance:
Normal atmosphere
High-humidity environments
Water contact
Saltwater environments
Acidic environments
Alkaline environments
Chlorine-based cleaning agents
Steam
Food constituents
Conditions in which drying after cleaning is inadequate
Stainless steel is not immune to corrosion in every environment. Pitting or crevice corrosion may occur in the presence of chlorine-based
cleaners, salts, narrow gaps, weld heat-affected zones, or regions with restricted oxygen supply.
Chemical Resistance
A material must remain chemically stable in contact with cleaning agents, lubricants, food constituents, refrigerants, and process fluids.
The following factors should be checked when evaluating chemical resistance:
Type of chemical
Concentration
Temperature
Contact time
Number of repeated exposures
Pressure
Whether residue remains after cleaning
Stress condition of the material
Plastics and elastomers may undergo the following changes when exposed to chemicals:
Swelling
Hardening
Softening
Cracking
Discoloration
Loss of strength
Dimensional change
Surface delamination
A general chemical-resistance chart should therefore not be used by itself. Actual temperature, concentration, and exposure conditions must be
reflected in the evaluation.
Moisture and Water Absorption
Some plastics and composite materials absorb moisture, causing changes in dimensions and mechanical properties.
Potential problems caused by moisture absorption include:
Dimensional increase
Reduced stiffness
Changes in electrical insulation
Changes in friction characteristics
Deviation from tolerance
Distortion and warping
When plastic is used for precision guides, gears, bushings, or locating components, dimensional changes caused by moisture absorption must
be considered.
UV and Weather Resistance
Outdoor equipment and components exposed to sunlight are affected by ultraviolet radiation, temperature variation, rain, wind, and ozone.
Ultraviolet radiation may cause the following changes in some plastics and elastomers:
Surface cracking
Embrittlement
Discoloration
Reduced strength
Reduced elasticity
For expected outdoor use, materials containing UV stabilizers, protective coatings, or metal covers should be applied.
Thermal Suitability
Temperature affects material strength, stiffness, dimensions, friction, and chemical stability.
Operating Temperature Range
A material must retain its function not only during normal operation but also under the following temperature conditions:
Low temperature before startup
Normal operating temperature
Local heating caused by friction
Wash-water temperature
Steam-cleaning temperature
Sterilization temperature
High ambient temperature
Freezing conditions
Rapid temperature changes
Plastics and elastomers can lose substantial strength and stiffness as temperature rises. At low temperatures, their brittleness may increase.
Metals also lose yield strength and fatigue strength at high temperatures, and repeated thermal cycling may cause thermal fatigue.
Thermal Expansion
Material dimensions change with temperature.
When materials with significantly different coefficients of thermal expansion are joined, the following problems may occur:
Changes in clearance
Changes in fit
Changes in fastening force
Bending and warping
Adhesive-joint delamination
Changes in seal compression
Shaft misalignment
When materials with very different thermal-expansion coefficients are used together, such as aluminum and steel or plastic and metal, the
structure must be able to accommodate their relative movement.
Thermal Conductivity
Materials with high thermal conductivity transfer heat quickly, while materials with low thermal conductivity provide insulation.
Components for which thermal conductivity is important include:
Motor mounting plates
Heat sinks
Bearing housings
Heating plates
Cooling plates
Insulating covers
Operator-contact areas
Materials with high thermal conductivity, such as aluminum or copper, may be advantageous where heat must be dissipated. Conversely,
plastics, elastomers, or insulation materials may be suitable where operator protection or heat-loss prevention is required.
Thermal-Shock Resistance
Rapid temperature changes create thermal stress because of temperature differences within the material.
Materials with low thermal-shock resistance may crack under the following conditions:
Cold-water cleaning while the part is hot
Hot-water cleaning while the part is frozen
Repeated heating and cooling
Localized heating
Geometry with abrupt thickness changes
Special care is required with ceramics, glass, and some hard materials because they are particularly sensitive to thermal shock.
Tribological Suitability
Friction, wear, and lubrication are critical for components that contact and move against one another.
Friction Characteristics
The coefficient of friction affects drive force, heat generation, noise, and wear.
Structures that require low friction include:
Sliding guides
Bushings
Seal-contact regions
Chain guides
Product-conveying surfaces
Hinges
Cam followers
Conversely, some structures require friction:
Brakes
Clamps
Friction drives
Slip-resistant surfaces
Operator platforms
Product gripping areas
The coefficient of friction should therefore not simply be minimized. It should be appropriate for the intended function.
Wear Resistance
Wear is the gradual removal or deformation of material at a contact surface.
Major wear mechanisms include:
Adhesive wear
Abrasive wear
Fatigue wear
Erosive wear
Fretting wear
Corrosive wear
Where wear is expected, the following factors should be evaluated:
Material hardness
Hardness of the mating material
Surface roughness
Contact pressure
Relative speed
Lubrication conditions
Presence of foreign particles
Temperature
Surface treatment
Seizure and galling may occur where metal slides directly against metal. In particular, similar grades of stainless steel may adhere to one another
under high contact pressure during sliding.
Possible alternatives include:
Combining dissimilar materials
Using engineering-plastic bushings
Surface hardening
Applying coatings
Lubrication
Reducing contact pressure
Changing from sliding contact to rolling contact
Lubrication Compatibility
The material must be chemically compatible with the oil or grease used for lubrication.
In food-processing machinery, even food-grade lubricants should be prevented from contacting food wherever possible.
Where lubrication is difficult, the following materials may be considered:
Self-lubricating plastics
Oil-impregnated sintered bushings
Solid-lubricant coatings
Dry-bearing materials
Composite sliding materials
Manufacturability
The selected material must be capable of being manufactured into the required geometry.
Machinability
Machinability indicates how easily a material can be processed by turning, milling, drilling, grinding, and similar operations.
Factors affecting machinability include:
Material hardness
Work hardening
Thermal conductivity
Chip formation
Tool wear
Cutting heat
Surface quality
Dimensional stability
Stainless steel can be more difficult to machine than some carbon steels because of work hardening and low thermal conductivity. Hard materials
may provide excellent wear resistance but increase machining cost.
Material selection must therefore consider not only finished-component performance but also machining time, tool life, and the supplier’s
machining capability.
Formability
Formability is important in sheet-metal bending, pressing, drawing, forging, and extrusion processes.
Formability review items include:
Elongation
Minimum bending radius
Springback
Risk of cracking
Sheet-material directionality
Thickness change after forming
Residual stress
Even the same material may have different bending characteristics depending on its heat-treatment condition and sheet orientation.
Weldability
Weldability is important in welded structures.
Factors affecting weldability include:
Carbon equivalent
Hardening of the heat-affected zone
Weld cracking
Distortion
Residual stress
Combination of filler metal and base metal
Post-weld corrosion resistance
Need for post-weld heat treatment
For stainless steel, heat tint and oxide layers should be removed after welding, and pickling or passivation should be performed where necessary.
Welds on food-contact surfaces should be continuous and smoothly finished to prevent crevices and contamination buildup.
Heat-Treatment Suitability
Heat treatment changes the strength, hardness, toughness, and wear resistance of a material.
Typical heat treatments include:
Annealing
Normalizing
Quenching
Tempering
Carburizing
Nitriding
Induction hardening
Aging
Solution heat treatment
The following issues should be evaluated when applying heat treatment:
Dimensional distortion
Cracking
Residual stress
Surface oxidation
Need for post-machining
Hardness distribution
Inspection method
Surface-Treatment Suitability
Surface treatment improves surface performance while retaining the basic properties of the substrate.
Typical surface treatments include:
Plating
Anodizing
Nitriding
Hard chromium plating
DLC coating
Ceramic coating
Painting
Powder coating
Passivation
Electropolishing
The following should be checked when selecting a surface treatment:
Adhesion to the substrate
Treatment thickness
Dimensional change
Possibility of delamination during wear
Suitability for food contact
Corrosion resistance
Repairability
Surface roughness after treatment
Hygiene and Safety
Material hygiene and safety are especially important in food, pharmaceutical, cosmetic, and human-contact equipment.
Food-Contact Suitability
Food-contact materials should satisfy the following conditions:
They do not leach substances harmful to the human body.
They do not affect the taste, odor, or color of food.
They withstand repeated cleaning and disinfection.
They do not generate corrosion products.
Their surfaces are easy to clean.
They do not crack or delaminate.
They remain stable at the operating temperature.
Plastics, elastomers, lubricants, adhesives, and coatings that may contact food must be verified as suitable grades for the intended use.
Cleanability and Surface Condition
Hygienic performance depends heavily not only on material type but also on surface condition.
A hygienic surface should have the following characteristics:
Smooth surface
Few cracks and pores
No flaking or delamination
Corrosion resistance
Stability against cleaning agents
Minimal residue after cleaning
Cast surfaces, rough welds, porous materials, and damaged coatings are more likely to retain contaminants.
Toxicity and Hazardous Substances
Components contained in the material or substances generated during processing may affect workers and users.
Items to review include:
Heavy metals
Hazardous plasticizers
Volatile substances
Machining dust
Welding fumes
Fiber dust
Hazardous coating components
High-temperature decomposition products
Material selection must consider safety not only during normal use but also during machining, welding, cutting, and disposal.
Fire Safety
Flame resistance is also important in electrical equipment, high-temperature equipment, and enclosed spaces.
Review factors include:
Ignition potential
Burning rate
Smoke generation
Toxic-gas generation
Self-extinguishing behavior
High-temperature deformation
Plastic covers, cable ducts, insulation materials, and electrical enclosures should use flame-retardant grades appropriate for their intended
applications.
Compatibility
Even if the material selected for one component is suitable by itself, an inappropriate combination with surrounding materials can cause
problems.
Galvanic Corrosion
When dissimilar metals are in contact in an electrolyte environment, a potential difference may cause galvanic corrosion.
Typical material combinations include:
Aluminum and stainless steel
Carbon steel and copper
Galvanized steel and stainless steel
Dissimilar-metal fastened joints
In environments containing moisture or wash water, the following countermeasures may be considered:
Insulating washers and bushings
Nonconductive coatings
Drainage structures
Changing the metal combination
Sealing contact surfaces
Selecting appropriate fasteners
Hardness Combination
The hardness relationship between two contacting materials affects wear behavior.
If one material is excessively hard, the mating component may wear rapidly. Conversely, if both components have similar hardness and similar
material composition, seizure may occur.
A readily replaceable component may intentionally be designed as a sacrificial wear part.
Examples include:
Replaceable bushings
Wear plates
Chain guides
Scrapers
Liners
Slide pads
Thermal-Expansion Compatibility
When materials with different coefficients of thermal expansion are rigidly fastened together, temperature changes may create internal stress or
deformation.
Where necessary, the following structures may be used:
Slotted holes
Floating mounts
Elastic fastening
Flexible adhesive layers
Expansion clearances
Structures constrained in only one direction
Adhesive and Sealant Compatibility
Adhesives and sealants do not provide the same bonding strength on every material.
Review items include:
Surface energy
Surface contamination
Oxide layers
Need for primer
Temperature
Humidity
Chemical exposure
Repeated deformation
Curing conditions
Some plastics are extremely difficult to bond. Mechanical fastening or surface treatment should therefore be considered together with adhesive
joining.
Cost and Availability
The technically highest-performing material is not always the most suitable material.
The following costs should be evaluated in addition to the raw-material price:
Raw-material cost
Machining cost
Heat-treatment cost
Surface-treatment cost
Welding cost
Inspection cost
Reject rate
Maintenance cost
Replacement cost
Disposal cost
Inventory cost
If a higher-priced material significantly extends component life, the total life-cycle cost may actually be lower.
Conversely, applying a premium material that is not functionally required may increase product cost without producing a meaningful performance
improvement.
Availability
The material must be available reliably in the required specification and quantity.
Review items include:
Domestic and international availability
Availability in standard specifications
Minimum order quantity
Lead time
Number of suppliers
Availability of material certificates
Possibility of substitute materials
Long-term supply capability
When a special material is used, alternative materials and supply risks should be evaluated during the design stage.
Standardization
Where possible, standard materials and standard plate thicknesses, bar diameters, and sheet sizes should be used.
Advantages of standardization include:
Easier purchasing
Lower unit cost
Reduced inventory
Predictable manufacturability
Stable quality
Availability of alternative suppliers
Simplified drawing management
Life Cycle and Sustainability
Material suitability must be evaluated over the entire product life cycle, not only at the time of manufacture.
Service Life
The material must maintain its function throughout the target service life.
Factors affecting service life include:
Fatigue
Corrosion
Wear
Creep
Ultraviolet exposure
Thermal aging
Chemical degradation
Repeated cleaning
Repeated assembly and disassembly
Component life is determined not only by the material itself but also by surface treatment, lubrication, maintenance, and operating conditions.
Replaceability
Materials expected to wear or degrade should preferably be incorporated into replaceable structures.
Examples include:
Replaceable liners
Removable wear plates
Replaceable bushings
Modular seals
Removable guides
Replaceable blades
The structure should allow only the low-cost consumable component to be replaced rather than requiring replacement of the entire expensive
body.
Recyclability
The following can be considered to improve recyclability:
Use of a single material
Material identification
Use of detachable fastening instead of permanent bonding
Minimization of plating and multilayer coatings
Ease of separating dissimilar materials
Restriction of hazardous substances
Permanent bonding or overmolding of different materials can make recycling more difficult.
Environmental Impact
The following environmental factors may be considered during material selection:
Production energy
Carbon emissions
Resource scarcity
Use of hazardous substances
Recyclability
Transportation weight
Product service life
Maintenance frequency
Lightweight materials may reduce transportation and drive energy, but their manufacturing energy and recyclability must also be evaluated.
Major Material Groups and Their Application Characteristics
Carbon Steel
Carbon steel is widely used in general mechanical structures because it offers a favorable balance of strength, cost, and manufacturability.
Advantages include:
High strength and stiffness
Good weldability and machinability
Low cost
Wide range of available specifications
Ability to be heat treated
Limitations include:
Susceptibility to corrosion
Need for surface treatment
Limited suitability for direct food contact
Need for maintenance in wet environments
Typical applications include:
Frames
Brackets
Shafts
Bases
Welded structures
Non-contact internal components
Alloy Steel
Alloy steel contains elements such as chromium, molybdenum, and nickel to improve strength, toughness, hardenability, and wear resistance.
Typical applications include:
Highly loaded shafts
Gears
Pins
Cams
Spindles
High-strength fastening components
Because alloy-steel performance varies significantly with heat-treatment condition, the material specification and heat-treatment state must be
specified together.
Stainless Steel
Stainless steel is widely used in food-processing machinery and wet environments because of its excellent corrosion resistance, hygienic
performance, and appearance.
Advantages include:
Excellent corrosion resistance
Cleanability
Hygienic performance
No need for painting
Good appearance
Relatively high heat resistance
Limitations include:
Higher cost
Work hardening
Machining difficulty
Welding distortion
Risk of galling
Possibility of localized corrosion in chlorine-containing environments
It is suitable for food-contact parts, areas exposed to wash water, exterior covers, hoppers, chutes, and hygienic frames.
Aluminum Alloys
Aluminum alloys have low density and excellent machinability.
Advantages include:
Low weight
Excellent machinability
Relatively high thermal conductivity
Corrosion resistance from the natural oxide film
Ability to use extruded profiles
Limitations include:
Lower stiffness than steel
Vulnerability to surface wear
High thermal expansion
Vulnerability in some alkaline environments
Possibility of reduced strength after welding
They may be applied to lightweight frames, covers, guides, heat-dissipation components, and moving parts.
Copper and Copper Alloys
Copper and copper alloys offer excellent electrical conductivity, thermal conductivity, and certain favorable friction properties.
Typical applications include:
Electrical contacts
Heat-transfer components
Bushings
Bearing materials
Brazed components
Grounding components
However, cost, weight, corrosion, and suitability for food contact must be evaluated.
Engineering Plastics
Engineering plastics are lighter than metals and often provide excellent corrosion resistance and friction characteristics.
Typical materials include:
POM
PA
UHMW-PE
PTFE
PEEK
PET
PC
PVC
Advantages include:
Low weight
Low coefficient of friction
Excellent corrosion resistance
Electrical insulation
Noise reduction
Ease of machining
Limitations include:
Low stiffness
Creep
Temperature dependence
Thermal expansion
Moisture absorption
UV degradation
Vulnerability to some chemicals
They can be used for guides, bushings, chain rails, wear plates, covers, insulating parts, and lightly loaded gears.
Rubber and Elastomers
Rubber and elastomers provide elasticity, sealing, vibration absorption, and impact cushioning.
Typical materials include:
NBR
EPDM
Silicone
FKM
TPU
TPE
Typical applications include:
Seals
Gaskets
Vibration absorbers
Roller surfaces
Anti-vibration mounts
Hoses
Grips
Temperature, chemical exposure, food contact, compression set, and aging characteristics must be evaluated.
Ceramics
Ceramics offer high hardness, wear resistance, heat resistance, and chemical stability.
Typical applications include:
High-wear components
Insulating components
Seal faces
Cutting tools
High-temperature components
Precision bearing elements
Limitations include:
Brittleness
Impact sensitivity
Machining difficulty
High cost
Risk of thermal shock
Composite Materials
Composite materials combine different materials to improve strength, low-weight performance, corrosion resistance, or damping characteristics.
Typical examples include:
CFRP
GFRP
Fiber-reinforced plastics
Metal-matrix composites
Multilayer panels
Advantages include:
High specific strength
Low weight
Ability to design directional properties
Excellent corrosion resistance
Vibration damping
Limitations include:
Anisotropy
Joining difficulty
Difficulty detecting internal damage
Recyclability limitations
High material cost
Material Suitability in Food-Processing Machinery
In food-processing machinery, materials must satisfy not only mechanical-performance requirements but also hygiene, cleaning, corrosion, food-
contact, and contamination-prevention requirements.
Food-Contact Parts
Materials used in food-contact areas should satisfy the following conditions:
They are suitable for food contact.
They do not generate corrosion products.
They do not leach toxic constituents.
Their surfaces are smooth and cleanable.
They withstand repeated cleaning and disinfection.
They do not absorb odors or flavors.
They do not crack or delaminate.
Stainless steel and food-grade engineering plastics are commonly used.
Non-Contact Wet Areas
Even if a component does not directly contact food, it requires high corrosion resistance when exposed to wash water and moisture.
Applicable materials and countermeasures include:
Stainless steel
Appropriate plating
Water-resistant coatings
Sealed structures
Drainage structures
Replaceable covers
Compatibility with Cleaning Chemicals
Food-processing machinery may be exposed to alkaline detergents, acidic cleaners, chlorine-based disinfectants, and hot water.
The following should be checked during material selection:
Cleaning-agent concentration
Operating temperature
Contact time
Cleaning frequency
Rinsing conditions
Possibility of residue in crevices
Degradation of elastomers and plastics
Prevention of Foreign-Material Generation
Neither the material itself nor its surface treatment should generate foreign matter.
Potential problems include:
Paint peeling
Plating delamination
Corrosion particles
Plastic wear particles
Rubber fragments
Welding slag
Surface cracking
Components positioned above food products require particularly strict control of surface delamination and corrosion risk.
Material Suitability Evaluation Procedure
Define the Required Function
First, define the functions that the component must perform.
Support loads
Transmit torque
Guide motion
Provide sealing
Resist wear
Resist corrosion
Provide insulation
Transfer heat
Maintain hygiene
Define the Operating Environment
Describe the actual environment to which the material will be exposed.
Temperature
Humidity
Wash water
Chemicals
Food
Salts
Ultraviolet radiation
Impact
Vibration
Friction
Repeated loading
Establish Required Material Properties
Translate the functional requirements into material properties.
Examples include:
High yield strength
High stiffness
High wear resistance
Excellent corrosion resistance
Low coefficient of friction
Low moisture absorption
Food-contact suitability
Good weldability
Low thermal expansion
Select Candidate Materials
Select multiple candidates from the relevant material groups.
Carbon steel
Alloy steel
Stainless steel
Aluminum
Copper alloys
Engineering plastics
Elastomers
Ceramics
Composite materials
Compare Candidate Materials
Compare candidate materials using the following criteria:
Functional performance
Durability
Environmental resistance
Manufacturability
Hygienic suitability
Cost
Availability
Maintainability
Recyclability
Review the Manufacturing Process
Confirm that the material is compatible with the actual production process.
Machining
Bending
Welding
Forming
Heat treatment
Surface treatment
Inspection
Assembly
Prototype and Testing
Where necessary, conduct testing under simulated actual conditions.
Test items may include:
Static-load testing
Fatigue testing
Impact testing
Wear testing
Corrosion testing
Chemical-immersion testing
Thermal-cycle testing
Cleaning testing
Food-contact testing
Dimensional-stability testing
Finalize the Material Specification
After selecting the material, the drawing or specification should include more than the material name alone. The following information should be
clearly defined:
Material standard
Material grade
Heat-treatment condition
Hardness
Surface treatment
Plate, bar, or stock condition
Surface roughness
Inspection criteria
Material-certificate requirements
Permitted substitute materials
Major Failure Modes
Inadequate Material Suitability can cause the following problems.
Insufficient Strength
The material has inadequate yield or fatigue strength, resulting in deformation or fracture.
Insufficient Stiffness
The component does not fracture, but excessive deformation reduces accuracy and function.
Brittle Fracture
The material fractures suddenly under impact or low-temperature conditions.
Excessive Wear
Contact surfaces wear rapidly, increasing play, vibration, and positional error.
Corrosion
Moisture, salts, or chemicals degrade the surface and structure.
Chemical Degradation
Plastics, elastomers, or coatings react with cleaning agents and swell, crack, or delaminate.
Thermal Deformation
Thermal expansion and reduced stiffness change clearances and positions.
Galvanic Corrosion
A combination of dissimilar metals causes one material to corrode rapidly.
Manufacturing Defects
The selected material is unsuitable for bending, welding, machining, or forming, resulting in cracking and distortion.
Hygiene Problems
Corrosion, surface delamination, porosity, or chemical degradation increases the risk of food contamination.
Excessive Cost
Using a higher-grade material than necessary increases the product price.
Procurement Problems
Long lead times and unstable supply of special materials delay production.
Material Suitability Review Checklist
Function
Is the primary function of the component clearly defined?
Does the material provide the properties required for that function?
Are strength and stiffness requirements distinguished?
Have repeated loading and impact been considered?
Are friction and wear conditions defined?
Environment
Is the operating temperature range defined?
Have exposure to water, moisture, salts, and chemicals been considered?
Are cleaning-agent concentration and temperature reflected?
Have ultraviolet radiation and outdoor conditions been considered?
Have long-term storage and transportation conditions been reviewed?
Mechanical Properties
Is the yield strength sufficient?
Is the fatigue strength sufficient?
Does the material provide the required stiffness?
Does it have sufficient toughness for impact?
Does it have appropriate hardness for wear areas?
Thermal Properties
Are strength and stiffness maintained at the operating temperature?
Does thermal expansion avoid adversely affecting clearance and alignment?
Have differences in thermal expansion between materials been evaluated?
Has the possibility of thermal shock been considered?
Manufacturing
Can the material be machined and formed?
Is its weldability appropriate?
Can deformation after heat treatment be controlled?
Is the surface treatment compatible with the material?
Can the supplier manufacture it repeatedly and consistently?
Hygiene and Safety
Is the material suitable for food contact?
Does it withstand repeated cleaning?
Is there no risk of harmful substances leaching out?
Is there no risk of surface delamination or foreign-material generation?
Have flame resistance and operator safety been considered?
Compatibility
Has the risk of corrosion at dissimilar-metal contacts been evaluated?
Is the friction and hardness combination with the mating material appropriate?
Is the material chemically compatible with the lubricant?
Are the adhesive and sealant compatible with the material?
Cost and Supply
Have machining and maintenance costs been considered in addition to material cost?
Is the material available in standard specifications?
Are there sufficient suppliers?
Is long-term supply possible?
Have substitute materials been defined?
Life Cycle
Will the material maintain performance throughout the target service life?
Can worn components be replaced?
Can the material be recycled and the assembly disassembled?
Is it nonhazardous at disposal?
Is the total life-cycle cost reasonable?
Conclusion
Material Suitability is not simply the task of selecting a strong material or a material that does not corrode. It is the design process of selecting the
most appropriate material by comprehensively evaluating the component’s function, loads, deformation, wear, temperature, environment,
manufacturing process, hygiene, cost, and life cycle.
A suitable material should satisfy the following conditions:
It provides the required strength and stiffness.
It withstands repeated loading and impact.
It resists corrosion and chemical degradation in the operating environment.
It is appropriate for the friction and wear conditions.
It maintains dimensions and performance at the operating temperature.
It can be machined, formed, welded, and surface treated.
It is compatible with surrounding materials and lubricants.
It satisfies hygiene and safety requirements.
It can be procured reliably.
It satisfies the product’s target service life and cost conditions.
It supports maintenance and recycling.
In mechanical design, material is both the means by which geometry is created and a core element through which function is realized. Even with
identical geometry, changing the material changes strength, deformation, service life, manufacturing method, and safety.
Material selection should therefore not be treated as an additional task at the end of the design process. It should be a core design activity that
determines structure and function.
Ultimately, the quality of Material Suitability is determined not by whether the most advanced material is used, but by whether the material most
appropriate for the required function and operating environment has been selected within reasonable cost and manufacturing constraints.