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Technical Information

Rolling Resistance

Scaffold CastorRolling resistance determines the effort necessary to move the equipment from rest and to keep it rolling. If a wheel, so hard that it will not flatten under load, rolls on an absolutely flat hard surface, perfect rolling is possible. The nearer you get to this ideal, the lower the rolling resistance becomes.
In view of this, the first choice should be hard tread wheels but the average floor is far from smooth and clean and is often littered with small particles of some description.
Once the wheels are rolling they will pass over these small items with no problem, but if the equipment starts from rest with minor obstructions, such as swarf, in front of the wheels then the starting effort includes that necessary to lift the equipment to the height of the obstructions. In cases where hard wheels are used on soft floors such as carpeting, or even asphalt, the surface deformation causes the wheels to sit in small ruts and extra effort is needed to overcome such resistance. Resilient wheels move more easily over obstructions as they deform and roll over them instead of climbing. On the other hand, as a tyre flattens under load, an area instead of a line is always in contact with the floor and resistance to rolling is greater.
Individual characteristics of our wheels will be found elsewhere in this catalogue but, because of the wide variations in floor conditions, hardnesses, wheel diameters, tread profiles, etc., it is not practical to give rolling resistance figures in the tables. We will always be pleased to advise when given the necessary information, but the only accurate assessment is one based on the user making his own tests.

Load Capacities

We do not give load capacities for ‘ideal working conditions’ as these rarely exist. Capacities given in this catalogue are based on normal working conditions on reasonably level floors free from grooves, breaks, door sills, lift entrances and other hazards. They are also based on a maximum speed of 4km/h unless
otherwise stated.
Although Revvo Wheels and Castors have high capacity reserves, we recommend the use of the following formula to determine the load capacity:

weight of transport equipment + load
three

For uneven floors, this should be divided by three as, often, only three wheels have contact with the floor on a 4-wheel trolley.

Castor and Wheel Lubrication

We recommend regular greasing of all nipples with a lithium based grease of the type used on car axles. Where nipples are not provided a few drops of light machine oil should be used.

Finish

Revvo’s standard finish for pressed steel castors is bright zinc electro-plating to BS1706. Wheels and fabricated castors are paint sprayed to a high finish. Other finishes can be supplied to special order, subject to economical batches.

Castor and Wheel Selection

The following factors all have a bearing on which wheel or castor is suitable for a particular application, including the performance to be expected.

Loading

Apart from the gross weight of the load and equipment, an allowance should be made for uneven distribution of weight as this often results in one wheel carrying more than the rest.  Mechanical towing can also impose severe shock loading.

Floor conditions

Rough uneven floors often go unnoticed but they cause severe overloading in some cases simply because one wheel leaves the ground and the load is thrust upon the remainder.  Impact loads due to kerbs and holes in the floor also cause problems.

Motive power

If a truck moved by hand meets an obstruction, it becomes harder to push and the truck slows down, takes an easier route, or the load is reduced.  All these reduce the strain on the castors as well as the person pushing.  This does not happen with mechanical towing as there is usually plenty of power in hand; This, combined with higher speed, results in considerably more castor stress.
All Revvo pressed steel castors are designed specifically for manual propulsion. As power towing of castors places increased stresses on various components, these castors are not recommended for this application. 
Fabricated castors have much higher load capacities, making them suitable for power towing. The P, X, Y and Z castors are specifically designed for power towing, but must be fitted to wheels with Ball Journal  or Taper Roller bearings only. Obstructions such as kerbs and gullies and even relatively small steps, can exert enormous impact loads which can damage a castor.
Steps such as lift sills, drain covers and joints in concrete slabs, present a particular problem if they are not approached squarely. Approaching such obstacles obliquely makes the castor turn at right angles to the obstruction instead of turning in such a way that it can climb over it, this damages the castor.
Towing trailers in train increases the problem as only one castor may have to withstand the force generated by the mass of the whole train including the tractor.
As power towing becomes more common it is often desirable to tow a number of trucks or trailers one behind another. Traditional turntable axles are often used, but are expensive and give two disadvantages.



  1.    If the turntable is at right angles to the axis of the trucks the stability is dramatically reduced.
  2.    There is a risk of jack-knifing if the trailers stop on a sharp corner.

Because of this, castors are becoming increasingly popular for this application. They work satisfactorily in these conditions providing suitable precautions are taken. ‘Cutting-in’ must be avoided, as this prevents the use of truck trains in narrow gangways. If trucks are rigidly coupled together with pin couplings at each end, they will follow the track most accurately if the distance from the fixed castor centre line to the rear coupling pin is 25-33% of the total length of the truck from front to rear coupling pins.
This can be achieved by moving the fixed castors forward.  However, this reduces the truck’s wheelbase and causes the total weight to be shared unevenly between the swivel and rear fixed castors. Therefore, it is advisable to extend the drawbar at the rear of the truck.

Floor Saving

All metal wheels will damage floors if the load is heavy.  Resilient wheels are not so easy to move but they are certainly kinder to floors. It should be remembered that the floor will cost more to repair than the price of the wheel running on it.

Directional Locks
Revvo supply directional locks across the range of heavy duty castors to fix the swivel for straight line travel. Depending on the model there are 2, 4 or 8 way D-locks.

Floor Locks

Designed to steady the equipment to which they are fitted and stop horizontal movement, floor locks are never intended to act as a jack. Any attempt to vary the fitting height from the catalogue specification will give failure and/or damage. There is some built-in resilience in the foot pad, which will allow some variations in floor level.  Nonetheless it is essential that the floor lock is fitted as closely as possible to one of the swivel castors.  Please note that the floor lock can be severely damaged if the linkage is operated whilst the trolley is moving.

Special Applications

Castors and wheels are usually fitted to equipment that is used intermittently and is often stationary for much of the time. Revvo’s products are specifically designed to operate well under such conditions.
For castors and wheels on applications such as conveyors which are run continuously, the normal load capacities do not apply as a life factor has to be introduced.  Each case should be considered individually and we will be pleased to advise on this on receipt of the relevant information.

Health And Safety at work - 1974

Revvo endeavours to ensure that all its products are safe and without risk to health when they are adequately maintained and properly used according to the recommendations in this catalogue. Specific guidance is given in the notes on this page and elsewhere in this catalogue, where appropriate.  We will always be pleased to advise on any application put before us.


Castors

Definitions and Uses - Swivel Castors

In swivel castors, the wheel and fork can rotate through a full 360 degrees, whilst the top or mounting plate remains in a fixed position.  The horizontal distance between the centreline of the swivel and the centreline of the wheel is called the offset.  When pressure is applied through the mounting plate, the offset causes the castor to swivel in line so that the wheel always trails in the opposite direction to the way in which the equipment is being moved.

Swivel Radius

Our tables give the swivel radius dimension for all swivel castors.  This shows the mounting clearance required to allow the castor to swivel without obstruction.

Fixed Castors

Fixed castors have the top plate rigidly fastened to the fork legs with the wheel in line with the fixing bolt holes. These castors do not swivel at all and the wheel can only move in two directions, forwards and backwards.

Swivel Head Seals

Swivel head seals are fitted as standard to scaffold castors and all 5,H,P,X,Y and Z series castors. They are optional on the 3 and 4 series.

Adjustment of tapered roller bearings

All castor bearings are correctly adjusted when the castor is built and should require no attention other than greasing, and then only when they are subjected to particularly arduous conditions.

Castor Combinations

2 Swivel Castors and 2 Fixed Castorstech-diag_2swiv_2fix

Providing good load capacity and manoeuvrability, this combination ensures accurate steering, even on long straight runs, making it the most practical combination for industrial use. Any trolley with this castor combination should be pushed with the fixed castors leading.
    Maximum capacity       =       load
    for each wheel                      3

4 Swivel Castorstech-diag_4swiv_0fix

As this combination gives good load capacity with exceptional manoeuvrability, it is suitable for winding runs and where sideways action is required.  It is not recommended for straight runs or ramps, as it may be hard
to guide, especially over bumpy terrain and when heavily loaded.  However, equipping two castors with directional locks makes this  arrangement very versatile and suitable for long straight runs.
    Maximum capacity    =    load
    for each wheel           3

1 Swivel Castor and 2 Fixed Castorstech-diag_1swiv_2fix

This combination provides an economical solution for lightly loaded  trolleys requiring good manoeuvrability. The trolley must be reasonably small in size and any load must be evenly distributed to ensure stability.
    Maximum Capacity    =    load
    for each wheel              2.5

3 Swivel Castorstech-diag_3swiv_0fix

This provides good load capacity with excellent manoeuvrability. However, equipment with this arrangement will
be difficult to guide on straight runs particularly over uneven ground.
This arrangement is ideal for barrel dollies and small portable machines.
    Maximum capacity    =    load
    for each wheel               2.5

4 Swivel Castors and 2 Fixed Castorstech-diag_4swiv_2fix

Centrally Pivoting
This combination provides an extremely high load capacity, with great manoeuvrability and stability.  This is ideal for very long trolleys designed to carry heavy loads - the fixed castors can be replaced by wheels mounted onto a central axle.  The unit’s base must be robust and the swivel castors are mounted to allow the trolley to pivot on the central wheels.  Therefore, 25mm of packing is required above the two fixed castors (wheels) to give alternating load support, depending on which pair of wheels is in contact with the floor.  The entire load rests on 2 central, fixed castors/wheels.
Please note that the swivel castors are subjected to
shock loads if the trolley is tipped or the load is not evenly distributed.
    Maximum capacity    =    load
    for each wheel           2          

2 Swivel Castors and 2 Fixed Castorstech-diag_2swiv_2fix(cent-piv)

Centrally Pivoting
Ideal for confined spaces, this configuration provides good load capacity with excellent manoeuvrability.  The fixed castors can be replaced by wheels which pivot the trolley centrally.  In this case, 25mm of the packing is necessary above the two fixed castors (wheels) to give alternating load support.  However, if the trolley is tipped or the load is not evenly distributed, the swivel castors are subjected to shock loads.
The entire load rests on the 2 central, fixed castors/wheels.
    Maximum capacity    =    load
    for each wheel           2


Wheels

Wheels for applications other than castors
All Revvo castor wheels are designed to have the axle supported at both ends, i.e. in a castor fork.
An axle supported at only one end (i.e. as a cantilever)
will have insufficient diameter to resist the bending moment at the full load rating.  If cantilever axles are specified by the customer, it must be his/her responsibility to choose a lower wheel rating, taking account of the working conditions and the safe stress limit for the material from which the axle is made.

Chemical resistance of wheels

The extensive range of Revvo wheels have resistance to certain chemicals and oils.  Please contact us for further information, if you have any queries.

Standards and Codes

BS.EN. ISO9000   Quality management and systems
ISO 2163   Industrial Trucks - Wheels and castors Vocabulary.
ISO 2175   Industrial wheels for non-powered equipment - Dimensions and load capacities.
ISO 2184   Industrial castors - Dimensions of top plates -
Part 1: Oblong top plates with 4 bolt holes.
ISO 3101   Wheels and castors - Triangular top plates with three fixing holes.
ISO 3102   Wheels and castors for non-powered equipment - Off-set for swivel castors.

BS.EN 12526   Vocabulary
BS.EN 12527   Castors and wheels - test methods
BS.EN 12530   Institutional castors
BS.EN 12532   Industrial castors - up to 4Km/h
BS.EN 12533   Heavy duty castors - over 4Km/h up to 16Km/h

 

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