What are the differences in load-bearing capacity of casters made of polyurethane (PU) and nylon (PA)?

There are significant differences in load-bearing capacity of casters made of polyurethane (PU) and nylon (PA). This difference stems from the molecular structure, physical characteristics and application scenario positioning of the two materials.

 

1. Analysis of the causes of differences

 

1. Influence of physical properties of materials

 

Polyurethane (PU):

 

PU is an elastomer, and the molecular structure contains soft and hard segments. The hard segment provides strength and the soft segment provides elasticity. This structure determines that its load-bearing depends on "elastic deformation dispersing pressure", but the proportion of hard segments is limited (usually 30%-50%). After exceeding 300KG, the soft segments are prone to excessive compression, resulting in permanent deformation of the wheel surface (such as depressions and bulges), and even causing bearing offset.

 

For example: In medical scenarios, if the PU wheel is used to carry more than 300KG of heavy medical equipment (such as large X-ray carts), the middle collapse of the wheel surface may occur after 1-2 months, causing the equipment to tilt.

 

Nylon (PA):

 

Nylon is a crystalline polymer with tightly arranged molecules. The nylon used in casters is mostly reinforced nylon (adding 10%-30% glass fiber), which greatly improves the crystallinity and rigidity. Its load-bearing relies on "rigid structures that resist compression", and the molecular chain is not easily stretched or broken. Even if it is carried for a long time, the deformation rate of the wheel body is usually less than 1%, and the stability is far beyond that of the PU.

 

For example: Industrial heavy-duty trolleys (such as hospital logistics mattress transfer trucks, with a full load of about 600KG) use reinforced nylon wheels and can be used continuously for more than 1 year without obvious deformation.

 

2. Differences in application scenario positioning

 

PU wheel:

 

The original intention of the design is to balance "silence, shock absorption, medium and light load", which is mainly suitable for scenarios that are sensitive to noise and moderate load (such as nursing vehicles and office furniture in medical wards), rather than heavy load requirements. If forced to be used for heavy loading, it will accelerate aging due to material fatigue and shorten the service life to 1/3 of the normal situation.

 

Nylon wheel:

 

Positioning "heavy load, wear-resistant, harsh environment", its rigid structure sacrifices some elasticity and silentness, but it has a stronger load-bearing capacity, especially suitable for high-frequency heavy load scenarios such as industrial workshops and hospital logistics warehouses. The load-bearing performance is positively correlated with service life (it can still operate stably under heavy load).

 

2. Recommendations for load bearing selection in practical applications

 

Medium-light load scenarios (≤300KG): For example, medical monitor cart (about 100KG) and mobile infusion rack (about 50KG), PU wheel is preferred, taking into account both silent and load-bearing to avoid noise problems of nylon wheels.

 

Heavy load scenarios (>300KG): For example, heavy medical equipment transfer trucks (about 500KG), material trucks next to hospital logistics elevators, nylon wheels must be selected (especially enhanced nylon) to prevent equipment tilting and casters from breaking due to insufficient load bearing, causing safety hazards.

 

In summary, the load-bearing capacity of nylon (PA) casters far exceeds that of polyurethane (PU) casters, and they have obvious advantages in heavy load stability. When choosing, you must match according to the actual load requirements to avoid equipment failure or safety risks due to wrong material selection.