Introduction

In the field of automated equipment manufacturing, polyurethane covered wheels are essential components widely used in conveyor systems, sorting equipment, AGV (Automated Guided Vehicles), and warehouse logistics systems. However, during the procurement process, many engineers and purchasing managers face a critical question: How do I select the right hardness for polyurethane covered wheels based on my equipment operating conditions?

Improper hardness selection can lead to increased noise, accelerated wear, and in severe cases, compromised equipment precision or even safety hazards. This article provides a systematic explanation of polyurethane hardness definitions, testing standards, and selection logic for various automated equipment applications, helping you make informed decisions.

I. What is Shore Hardness?

1.1 Definition of Shore Hardness

Shore Hardness is an international standard for measuring the resistance of elastic materials (such as rubber and polyurethane) to indentation. It was invented by American engineer Alfred Shore. The three most common Shore hardness scales are:

 

Type	Application Range	Reading
Shore A	Soft rubber, polyurethane elastomers	0~100
Shore D	Hard plastics, semi-rigid materials	0~100
Shore 00	Extremely soft materials (sponges, gels)	0~100

 

Polyurethane covered wheels are typically rated using Shore A hardness, ranging from 50A to 98A. A higher number indicates greater hardness.

1.2 Measuring Principle of Shore A Hardness

The Shore hardness durometer works by pressing a standardized indenter into the material surface using a spring of specified force. The hardness value is calculated based on the indentation depth. Deeper indentation means lower hardness; shallower indentation means higher hardness.

Simplified explanation: Think of Shore A hardness like pressing your finger into a cake—the deeper it goes, the softer the cake (lower hardness); if you cannot press it in, the cake is hard (higher hardness).

1.3 Shore A vs. Shore D: Don't Mix Them Up

When procuring polyurethane covered wheels, you may occasionally encounter hardness ratings in Shore D. The fundamental difference lies in the indenter shape and spring force:

•  Shore A: Rounded indenter with lighter spring force, for soft materials (most common range: 50A-90A)

•  Shore D: Conical indenter with heavier spring force, for harder materials

As a general reference: When Shore A hardness exceeds 90A, the equivalent Shore D reading is approximately 30D-40D. Therefore, if a supplier specifies Shore D hardness, verify whether it suits your actual application requirements.

II. Complete Guide to Polyurethane Covered Wheel Hardness (Shore A 60-95)

2.1 Hardness Ranges and Core Characteristics

Based on practical applications in the automated equipment industry, we categorize common Shore A hardness levels for polyurethane covered wheels as follows:

 

Hardness Range	Material Characteristics	Typical Applications	Pros & Cons
Shore A 60-70	Soft, highly elastic, excellent shock absorption	Light-duty conveyors, office automation equipment	Pros: Quiet, vibration-dampening; Cons: Relatively lower abrasion resistance
Shore A 70-80 (Most Common)	Balanced performance, moderate elasticity and wear resistance	General-purpose automated conveyors, sorting equipment	Pros: Best cost-performance ratio, wide applicability; Cons: Specialized applications may require custom solutions
Shore A 80-90	High strength, excellent wear resistance, strong load capacity	Heavy-duty conveyors, warehouse logistics, AGV	Pros: Long service life, high load capacity; Cons: Reduced vibration dampening
Shore A 90-95	Ultra-high hardness, extreme wear and cut resistance	Specialized applications, heavy machinery, outdoor equipment	Pros: Maximum abrasion resistance; Cons: Poor elasticity, higher noise

 

2.2 Why Higher Hardness Isn't Always Better

A common misconception among procurement professionals is: higher hardness means better quality polyurethane covered wheels. This is a serious selection error.

The core principle of hardness selection is: Match the hardness to the operating conditions, not to the highest numerical value.

Consequences of improper hardness selection include:

•  Excessive hardness: Increases equipment vibration and noise, accelerates wear on metal wheel hubs or bearings, may cause floor scratching

•  Insufficient hardness: Increased wheel deformation, reduced load capacity, higher rolling resistance leading to increased motor load, shortened service life

Take AGV (Automated Guided Vehicle) as an example: Using 95A hardness polyurethane wheels in high-end office buildings or hospitals—where noise requirements are extremely strict—will result in noticeable driving noise and vibration even with excellent wear resistance. Conversely, using 60A soft wheels in heavy-duty warehouse environments will quickly lead to excessive wheel deformation and insufficient load capacity.

III. Hardness Selection Guide by Equipment Type

3.1 Light-Duty Conveyor Systems (Food Packaging, Electronics Assembly)

Light-duty conveyors typically carry loads under 50kg at low speeds (usually below 1m/s), with high requirements for noise control and floor protection.

Recommended Hardness: Shore A 65-75

Selection Rationale:

•  Softer wheel surfaces effectively absorb impact forces, reducing product damage during conveying

•  Lower noise during floor contact, improving the working environment

•  Better protection for precision equipment and floor surfaces

Case Study: A food packaging company's sorting conveyor line originally used Shore A 70 polyurethane covered wheels, achieving quiet operation with a wheel service life exceeding 3 years, reducing overall maintenance costs by approximately 40%.

3.2 General Sorting Equipment (E-commerce, Express Delivery, Logistics Centers)

This equipment operates at high speeds (typically 1-3m/s), handles medium loads (50-500kg), and runs 24/7, demanding exceptional wear resistance and stability.

Recommended Hardness: Shore A 75-85

Selection Rationale:

•  This hardness range offers the optimal balance between wear resistance and elasticity

•  Capable of withstanding frictional heat buildup during high-speed operation

•  Service life typically exceeds 1-2 years, reducing downtime for replacements

Special Note: In cold northern winter environments (room temperature below 5°C/41°F), polyurethane materials become harder. It is recommended to select Shore A 80 or above, or specify cold-resistant polyurethane formulations.

3.3 Heavy-Duty Warehousing and Logistics Equipment (Automated Warehouses, Heavy Industrial Conveyors)

Heavy-duty warehousing equipment handles loads from 500kg to 5 metric tons, operates at high frequency, and often involves steel slide rails or track systems, with stringent requirements for wheel load capacity and stability.

Recommended Hardness: Shore A 85-92

Selection Rationale:

•  High hardness ensures minimal deformation under heavy loads, maintaining operational precision

•  Superior abrasion resistance for harsh conditions with debris and metal shavings

•  When paired with steel or aluminum rails, hard polyurethane layers effectively protect rails from damage

Additional Recommendation: For loads exceeding 5 tons, it is advised to incorporate reinforced wheel hub designs and double-bearing configurations.

3.4 AGV (Automated Guided Vehicles)

AGV polyurethane covered wheel hardness requirements depend on operating environment and floor conditions:

•  Indoor epoxy floors: Shore A 75-82 (balancing wear resistance with quiet operation)

•  Industrial concrete floors: Shore A 82-88 (handling floor particle abrasion)

•  Outdoor or mixed surfaces: Shore A 85-92 (maximum wear resistance required)

AGV selection also requires special attention to wheel dynamic balance precision—unbalanced wheels generate eccentric forces during high-speed operation, accelerating wheel hub bearing wear and affecting AGV navigation accuracy.

IV. Industry Application Case Studies

4.1 Case 1: E-commerce Sorting Center—The Cost of Wrong Hardness Selection

Background: A large e-commerce sorting center initially procured Shore A 65 polyurethane covered wheels, expecting quiet operation. However, after just 3 months of operation, the wheels showed severe wear with thickness loss exceeding 40%, and some wheels experienced chunking (polyurethane delamination from the metal hub).

Root Cause Analysis:

•  Sorting equipment operating speed reached 2.5m/s, classified as high-speed operation

•  Sorting lines ran continuously for over 20 hours daily under high-intensity conditions

•  65A hardness under high-frequency friction generated excessive heat, accelerating polyurethane aging and delamination

Solution: Hardness was adjusted to Shore A 80, and the bonding process was strengthened (enhanced adhesive layer and surface treatment). After adjustment, wheel service life increased from 3 months to over 18 months.

4.2 Case 2: Hospital AGV Logistics System—The Wisdom of Balanced Hardness

Background: A tertiary hospital introduced AGV logistics systems for pharmaceutical and supply delivery. The hospital had extremely high noise control requirements, with high-quality epoxy resin flooring requiring protection from any scratches.

Selection Strategy:

•  Main drive wheels: Shore A 78 (balancing wear resistance and quiet operation)

•  Idler wheels and steering wheels: Shore A 72 (prioritizing floor protection and quiet operation)

•  All wheels featuring PTFE (polytetrafluoroethylene) surface treatment to reduce friction coefficient

Results: AGV operating noise remained below 45dB with no floor scratches, and wheel service life exceeded 2 years, meeting the hospital's dual standards for environment and equipment quality.

4.3 Case 3: Automotive Parts Automated Warehouse—Heavy-Duty Application Hardness Selection

Background: Stackers in an automated warehouse needed to operate on storage rack rails with maximum load per lift reaching 3 metric tons. Rails were cold-drawn steel with stable operating speed requirements.

Selection Strategy:

•  Shore A 90 hardness polyurethane covered wheels for maximum wear resistance

•  Wheel surface designed with special grooves to enhance rail grip and water drainage

•  Metal wheel hubs made from No. 45 steel with tempering treatment to HRC 45+

Results: Stacker operational precision maintained within ±1mm, wheel service life exceeded 5 years under high-intensity operation, with significantly reduced maintenance costs.

V. Frequently Asked Questions on Hardness Selection

Q1: Do products with the same hardness rating differ between manufacturers?

Absolutely. The same Shore A 80 hardness rating from different manufacturers can vary significantly due to differences in polyurethane formulations (polyester-based vs. polyether-based), process parameters (casting temperature, curing time), and raw material quality—all affecting final product wear resistance, resilience, temperature resistance, and service life. Therefore, selection should not be based solely on hardness numbers; supplier formulation capabilities and process control levels are equally important.

Q2: Does polyurethane covered wheel hardness change with aging?

Yes. Polyurethane materials gradually undergo aging during extended use, manifesting as increased hardness (embrittlement) and reduced elasticity. Key factors affecting aging include: operating temperature (high temperatures accelerate aging), UV exposure, chemical attack from lubricants or solvents, and sustained dynamic loads. Aging rate correlates closely with product quality and operating conditions—high-quality polyurethane covered wheels age significantly slower than inferior products.

Q3: How to quickly assess polyurethane covered wheel hardness on-site?

The most reliable method is using a Shore durometer for on-site measurement. If a durometer is unavailable, a simple manual test: press the wheel surface with your hand—high-hardness wheels show virtually no deformation, while low-hardness wheels show noticeable indentation. Note: This method provides only rough assessment and cannot replace durometer measurement.

Q4: Can different hardness wheels be mixed on the same equipment?

Generally, drive wheels, idler wheels, and steering wheels on the same equipment can use different hardness configurations to achieve performance and cost balance. However, prerequisites include: all wheels must have consistent diameter (otherwise load distribution will be uneven), and the hardness combination must undergo mechanical analysis to ensure normal equipment operation and drive system service life. It is recommended to conduct hardness selection under supplier engineering guidance.

Q5: Is custom non-standard hardness (between regular hardness values) feasible?

Most reputable polyurethane covered wheel manufacturers offer non-standard hardness customization. If your application analysis requires hardness between standard values (e.g., 77A between 75A and 80A), customization is available. Note: Non-standard hardness typically has minimum order quantity requirements (MOQ), and unit price will be higher than standard inventory hardness. Confirm with your supplier in advance.

VI. Selection Decision Summary and Recommendations

6.1 Core Logic for Hardness Selection

Selection is not about choosing 'the highest hardness' but 'the most suitable hardness.' Here is a simplified selection decision logic:

6.2 Quick Reference Table for Hardness Selection

 

Equipment Type	Recommended Hardness	Key Selection Criteria	Notes
Light-duty conveyors / Office automation	Shore A 65-75	Quiet operation, floor protection	Avoid high-speed operation
General sorting / E-commerce logistics	Shore A 75-85	Balance of wear resistance and elasticity	Consider low-temperature hardness compensation
Heavy-duty warehousing / Automated warehouses	Shore A 85-92	High load capacity, maximum wear resistance	Coordinate with reinforced wheel hub design
AGV (Indoor)	Shore A 75-82	Quiet operation, floor protection	Pay attention to dynamic balance precision
Outdoor / Specialized applications	Shore A 90-95	Extreme wear resistance	Accept reduced elasticity

 

6.3 Final Recommendations for Procurement Professionals

•  Do not make procurement decisions based solely on hardness values; conduct comprehensive evaluation based on equipment operating conditions

•  Prioritize suppliers with formulation R&D capabilities and process control systems

•  Before bulk procurement, request samples for actual operating condition testing (minimum 1-2 weeks)

•  Establish supplier technical files, recording actual service life data for different batches

•  Specify hardness testing standards and acceptance methods in contracts to avoid disputes

•  For critical equipment (AGV, heavy-duty stackers), conduct technical reviews and on-site condition assessments before procurement