Fixed caster and swivel caster

Abstract：This article is aimed at fixed casters and swivel casters, and makes a detailed introduction to the three points of characteristics of wheel distribution of turnover vehicles, calculation of casters' load and safety factor and impact of ground and speed on casters, so that we can better understand the details of SHENPAI casters.

1. Characteristics of rolling vehicle wheel distribution:

Casters can be called fixed casters and swivel casters. Fixed caster bracket with a single wheel, can only move in a straight line. Swivel caster is a 360 degree steering bracket with a single wheel, can move in any direction at will.

In the installation of caster wheel, usually with 4, choose 2 fixed casters and 2 swivel casters, so as to ensure the control of the straight line and steering movement of the vehicle with wheels. If it is matched with 4 swivel casters, it is not easy to control the straight line running of the vehicle; With 4 fixed casters, can only run in a straight line. In other special cases, the number of casters needs to be increased because the turnover vehicle itself is too long; Or special structure requirements, reduce the number of distribution wheels.

In order to properly match swivel caster and fixed caster, the following main factors should be considered when selecting caster swivel caster:

1、 Wheel Material: Corresponding to different environmental requirements, the selection of suitable materials. Hard materials damage the ground, soft materials mute effect is good, can effectively protect the ground. Special environment, such as high temperature, need to choose high temperature materials;

2、 Single caster wheel weight: the selected caster wheel weight should be greater than the maximum required carrying capacity;

3、 Wheel diameter: The larger the wheel, the higher the passability when facing obstacles, so it is more labor-saving;

4、 Steering: hard and narrow wheels are easier to turn than soft and wide wheels.  At the same time, the rotation radius is an important parameter of wheel rotation. If the rotation radius is too short, it will increase the steering difficulty, while if the rotation radius is too large, it will lead to the shaking and shorten the life of the wheel.

5、  Driving flexibility: Influence caster wheel driving factor of flexibility with stents of the structure and the selection of steel, the size of the wheel, wheel type, bearing, wheel driving the greater flexibility, the better, hard on the smooth ground, narrow wheel than flat soft wheels and effort, but on the uneven ground soft wheels and effort, and better protect the equipment and avoid vibration.

二、Load calculation and safety factor:

To calculate how much weight a single caster wheel needs to carry, you need to know the dead weight of the transport equipment, the maximum load of the transport equipment, and the number of caster wheels you plan to install.

The weight carried by a single caster wheel is calculated as follows:

T=Load capacity required for a single caster wheel

E=Dead weight of transportation equipment

Z=Maximum loading pattern

n=Plan to install caster wheels on several castles

s=Safety factor

The safety factor S of fixed casters and swivel casters will be affected by speed, wheel diameter and obstacle height. Considering that the standard operating conditions (smooth ground, uniform speed, uniform load distribution, straight line, environmental temperature of 15 ° C -- 30 ° C deviates from the actual operating conditions, it can be divided into four categories:

1.   Manual conveying in indoor area (obstacle height < 5% of wheel diameter): Safety factor: 1.0 to 1.5

2.  Manual conveying in outdoor area (obstacle height > 5% of wheel diameter): safety factor: 1.5 to 2.2

3.   Motorized conveying in indoor area (obstacle height < 5% of wheel diameter): safety factor: 1.4 to 2.0

4.   Motorized conveying in outdoor area: safety factor: 2.0 to 3.0

Points to note: The bearing weight should be calculated according to the caster wheel's bearing weight at the maximum supporting point. The concrete supporting point of fixed caster and swivel caster is shown in the figure, and P2 is the heaviest supporting point.

1. 三、Effects of ground and speed on fixed casters & swivel casters

Different materials apply to different ground environments, a variety of complex ground will affect the service life of fixed casters and swivel casters, such as: meet the mute ground rubber wheel, in the use of iron filings on the ground, will be injured, shorten the service life of casters. In order to avoid the impact of the ground environment on the caster wheel’s life, the selection can refer to the following basic performance table of materials, if you have special requirements, you can choose special material formula according to the requirements.

Swivel caster and fixed caster usually design speed standard is 4km/h, light load and soft wheel design speed standard is 3.2km/h, the actual use is higher than the design speed, caster wheel’s load performance will be reduced correspondingly, at the same time will shorten the caster life, easy to cause wheel damage, falling off and other phenomenon. Such as: for traction, speed of 5km/h (design speed of 4km/h), castor wheel load 500KG performance will be reduced to 350KG, and should not be too high frequency for a long time running (easy to fall off damage, reduce life). High speed running performance requirements, need to use suitable high speed material caster wheels and bearings.