Castors and Bearings: The Science Behind the Perfect Combination

In various fields such as logistics, industrial production, and every corner of daily life, castors play a crucial role. They enable heavy objects to be moved easily, significantly improving work efficiency. However, the key to the flexible rotation and heavy-load bearing capacity of castors largely depends on the bearings inside them. Different types of castors will select different types and models of bearings according to their application scenarios and load requirements.

I. Light-duty Castors and Deep Groove Ball Bearings

(I) Application Scenarios

Light-duty castors are usually used in situations where the load is relatively light, such as office chairs, small trolleys, etc. The weight carried by these devices generally does not exceed 100 kilograms.

(II) Reasons for Selecting the Bearing

Deep groove ball bearings are the ideal choice for light-duty castors. This type of bearing has a simple structure, consisting of an inner ring, an outer ring, steel balls, and a retainer. It can bear a certain amount of radial and axial loads, and at the same time, has a relatively small frictional force, enabling the castors to rotate flexibly.

(III) Specific Models

Common deep groove ball bearing models used for light-duty castors are from the 6200 series. Taking 6204 as an example, its inner diameter is 20mm, its outer diameter is 47mm, and its width is 14mm. This model of bearing can well meet the rotation and load-bearing requirements of light-duty equipment castors such as office chairs.

(IV) Installation Knowledge

1. Preparation Work
   1. Before installing deep groove ball bearings, it is necessary to ensure that the installation environment is clean to avoid dust, impurities, etc. from entering the interior of the bearings. Meanwhile, appropriate installation tools such as a small press and sleeves should be prepared.
   2. Check the bearing installation part of the castor to ensure that its surface is smooth, without burrs or damages, so as to prevent damage to the bearings during the installation process.
2. Installation Methods
   1. Cold Installation: For deep groove ball bearings of light-duty castors, the cold installation method can usually be adopted. Align the bearing with the bearing housing of the castor and use a sleeve to gently tap the outer ring of the bearing to make it smoothly enter the bearing housing. When tapping, pay attention to applying force evenly to avoid deforming the bearing due to one-sided force.
   2. Heating Installation (Optional): If the installation is difficult, the heating installation method can also be used. Heat the bearing housing of the castor appropriately to expand its inner diameter, and then quickly place the bearing into the bearing housing. This method requires precise control of the heating temperature, and generally, the heating temperature should not exceed 100°C to prevent changes in the material properties of the bearing housing.

II. Medium-duty Castors and Tapered Roller Bearings

(I) Application Scenarios

Medium-duty castors are often used in scenarios such as supermarket trolleys and light industrial equipment, with a load range generally between 100 and 500 kilogram

(II) Reasons for Selecting the Bearing

Tapered roller bearings are widely used in medium-duty castors. This type of bearing consists of an inner ring, an outer ring, rollers, and a retainer, and its rollers are conical, enabling it to bear relatively large radial and axial loads simultaneously. In medium-duty castors, since the equipment may be subjected to forces from different directions, tapered roller bearings can well adapt to this force situation, ensuring the stable rotation and load-bearing capacity of the castors.

(III) Specific Models

In medium-duty castors, the 32000 series tapered roller bearings are more commonly used. For example, the 32008 model has an inner diameter of 40mm, an outer diameter of 68mm, and a width of 19mm, which can provide reliable support and rotation performance for medium-duty castors.

(IV) Installation Knowledge

1. Preparation Work
   1. Clean the installation site to ensure there are no debris. Prepare installation tools such as special bearing installation sleeves and presses.
   2. Check the dimensional accuracy of the tapered roller bearings and the bearing housings of the castors to ensure they match. At the same time, conduct an appearance inspection of the bearings to ensure there are no defects.
2. Installation Methods
   1. When installing tapered roller bearings, attention should be paid to their directionality. Generally, the large end of the bearing should face the direction of the axial force acting on the castor.
   2. When using a press for installation, place the bearing on the workbench of the press, make the inner ring or outer ring of the bearing contact the press head, and then slowly apply pressure to press the bearing into the bearing housing of the castor. During the pressing process, ensure that the rollers and raceways of the bearing maintain the correct positional relationship to avoid uneven force on the rollers.
   3. If there is no press, the manual installation method can also be used, but it is necessary to use a soft tool such as a copper rod to gently tap the bearing to make it enter the bearing housing. When tapping, apply force evenly along the circumference of the bearing to avoid damaging the bearing.

III. Heavy-duty Castors and Needle Roller Bearings

(I) Application Scenarios

Heavy-duty castors are mainly applied in fields such as heavy industrial production and large storage equipment, with a load capacity usually exceeding 500 kilograms, and some can even reach several tons.

(II) Reasons for Selecting the Bearing

Needle roller bearings are the preferred choice for heavy-duty castors. The needles of needle roller bearings are small in diameter and large in number, having a large radial load-bearing capacity. In heavy-duty castors, mainly radial loads are borne, and needle roller bearings can make the best use of the limited space to provide efficient load-bearing capacity, ensuring that the castors can rotate smoothly when carrying heavy objects.

(III) Specific Models

In heavy-duty castors, common needle roller bearing models are from the NA4900 series. Taking NA4906 as an example, its inner diameter is 30mm, its outer diameter is 47mm, and its width is 17mm. This bearing can exhibit excellent load-bearing and rotation performance in heavy-duty castors.

(IV) Installation Knowledge

1. Preparation Work
   1. Since needle roller bearings have high requirements for installation accuracy, the installation should be carried out in a clean environment. Prepare high-precision installation tools such as special bearing installation fixtures and micrometers for measurement and auxiliary installation.
   2. Check whether the needles of the needle roller bearings are arranged neatly, whether there are any missing or damaged ones. At the same time, conduct strict dimensional measurement and surface quality inspection on the bearing installation part of the heavy-duty castor to ensure that it meets the installation requirements.
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   1. Needle roller bearings are usually installed by the press-in method. Place the bearing on the bearing installation part of the castor, and use a special fixture or press to press the bearing into it with a uniform and slow pressure. During the pressing process, always pay attention to the arrangement of the needles to prevent them from tilting or getting stuck.
   2. For some large heavy-duty castors, it may be necessary to pre-lubricate the bearings. Before installation, apply an appropriate amount of high-temperature, high-pressure lubricating grease to the needles and the bearing housing to reduce friction and wear during the initial operation of the bearings.

In conclusion, bearings play a decisive role in the performance of castors. Different types and models of bearings match different load-bearing capacities and application scenarios of castors, ensuring that castors can work efficiently and stably in various application environments, meeting the mobile needs of people in production and life. Meanwhile, the correct bearing installation method is an important link in ensuring the normal operation of castors, and the installation process should be carried out strictly in accordance with the operation specifications.