I. Belt support
Skid plate
The belt can be supported in the following ways:

• Continuous plate support made of steel or plastics such as PE 1000. We recommend this for conveyors with heavy loads.
• Straight parallel runners made of steel or plastics. This is an inexpensive solution for applications with minimal loads. The belt wear is limited to the areas where the runners support the belt. We recommended a distance of approx. 120-150mm betwen the runners for the upper side and approx. 200mm for the return side.
• The belts is supported over the entire width by a V-shape arrangement of the runners. This spreads the wear and tear evenly and means heavy loads can be applied.
• Around the curves the belt is supported by plastic guides at the sides, for example PE 1000 or a plastic with lubricating properties, on the inner radius.

Suitable plastic runners are available from specialized dealers. The width should be approx. 30-40 mm, where by the thickness depends on the height of the screw heads.
The permissible temperature ranges, as given by the manufacturer, must also correspond to the expected operating conditions.

Thermal expansion and contraction must also be taken into consideration when mounting the support. These effects can be eliminated by slots and appropriate distancing between the runners (see the section “Effect of temperature”).

• Distance X ? 1.5 x module pitch
• Place the snub roller on the return side so that the arc of contact on the drive and idle shafts ? 180°. (This does not apply to conveyors with e ? 2 m. Rollers on the return side are not necessary here.)

Roller support
Rollers are not generally used to support the belt on the upper face. Unavoidable belt sag between the rollers as well as the chordal action of the drive unit mean the goods are tipped which can cause problems. Sometimes rollers are used for conveying bulk goods.

II. Shafts
Drive Shaft
In general, we recommend the selection of a square shaft. The main advantage of this design is that positive drive and tracking are possible without keys and keyways. This saves on additional manufacturing costs. In addition, this form facilitates the lateral movement of the sprockets in the case of temperature variations.

Occasionally round shafts with feather keys are also used for low-loaded, narrow belts.
Specially designed sprockets with bore and keyway are available.

Fastening the sprockets
Usually only 1 sprocket (as near as possible to the centre) must be fastened axially on each idle or drive shaft. The design of this sprocket enables positive tracking of the belt.

Deflection
Large belt widths and/or high tensile loads can lead to excessive deflection, preventing perfect belt-tooth engagement in the drive area. This results in uneven stress on the teeth of the sprocket, and it is possible that the sprockets do not engage properly, leading to “jumping” of the teeth when the belt is loaded. The borderline value permitted is the tooth engagement angle ?_z and depends on the shape of the gear ring and module. For the ProLink linear belts this is 1.2°.

If the borderline values are exceeded, additional intermediate bearings must be applied or a larger shaft selected.

III. Conventional conveyors
Belt sag/control of belt length
There are various causes for changes in the belt length, e.g.

• Elongation or contraction of the belt due to temperature variation
• Wear of the connecting rods as well as enlargement of the connecting rod holes in the modules after a certain “break-in time” (enlargement of holes, 0.5-mm larger holes in a 50 mm module result in an elongation of 1%).

Therefore we recommend not supporting one (or several) sections on the return side and using the resulting belt sag to compensate for the increase in length. It is important that perfect engagement between belt and sprocket is ensured.

Another effective method for compensating for belt elongation is a load-dependent take-up system (e.g. weighted roller). This should be located as closely to the drive shaft as possible since the take-up
system will ensure even tension on the return side and therefore perfect engagement between sprocket and belt.

For series 1, 3 and 7 we recommend a weighted roller, 150 mm in diameter and a weight of approx. 30 kg/m belt width.

For series 2 and 4 we recommend a weighted roller, 100 mm in diameter and a weight of approx. 15 kg/m belt width.

For series 6 we recommend a weighted roller, 100 mm in diameter and a weight of approx. 60 kg/m belt width.

IV. Reversible conveyors
Two-motor design
Advantages: Low tension on the return side, making smaller shaft loads possible Disadvantage: Increased costs due to additional motor and electronic control. For larger conveyors with relatively heavy loads, however, this system may still be the most reasonably priced.

Centre drive
For reversing operation the drive shaft must be located as close to the middle as possible. To the right and the left of the drive unit, areas with belt sag are to be provided, since these are necessary for the required belt tension. The 180° arc of contact on the drive shaft means belt and sprocket engage perfectly making reliable power transmission in both operational directions possible.

The location of the drive unit causes more stress on the shafts at the ends of the conveyor as there is effective pull on both the upper and return sides in the form of belt tension.

Alternating tail-head drive configuration
In the case of head drives the conveyor is like a conventional conveyor. It is only when conveying direction is reversed that the conveyor become tail-driven and the drive unit has to push the belt and its load. If the tension on the return side is not greater than that on the upper side it will jump sprockets.

V. Inclined conveyors
Inclined conveying
We always recommend the following:

• Only operate with a head drive, i.e. use the upper shaft as the drive shaft.
• There is always a screw-operated take-up system or a load-dependent tension take-up on the return side since tension decreases with increasing inclination (caused by the belt sag).
• If sprockets are used at upper intermediate points, the centre sprockets may not be fastened axially.
• If rollers are used at upper intermediate points, a minimum radius of approx. 80 mm is required.
• When shoe or runners are used, the radius should be as large as possible in order to keep wear to a minimum. We recommend a minimum radius of approx. 150 mm. The width of the shoe should not be smaller than 30 mm.
• If the belt is more than 600 mm wide, we recommend providing further supports on the belt surface or on the profiles on the return side.

Declined conveying
For this conveyor design, a tail drive unit is possible if there is an active load-dependent tension take-up at the lower idle shaft (e.g. gravity, spring or pneumatic). Otherwise the general recommendations given above apply here.

VI. Curve conveyors
Meshing
The teeth must mesh into the modular belting in the areas marked by the arrows.

Inner radius

Belt tension
The three usual tensioning methods are possible to create the correct belt tension:

• Screw-operated take-up system
• Gravity take-up system
• Catenary sag on the return side near the drive drum

Geometries of curves
Please consult us if you cannot construct the conveyor according to the drawings because space is restricted.

VII. Spiral conveyors
Possible conveyor designs

figure 1	figure 2
Example of declined conveying to join two production units with different heights.	For inclined conveying, the drive unit must be located at the end of the curve at the top. Make sure that the arc of contact on the drive shaft is approx. 180°. This type of design (without driven inner cage) should not have more than 2 – 3 tiers.

The main drive system is the driven inner cage, which as a rule consists of vertical rods. The curved belt is supported on the inner radius by the cage and is moved by traction between the belt and the cage. The direction of rotation of the cage determines whether the conveying is inclined or declined. The drive and tensioning unit depicted in the sketch provides the necessary belt tension. The speed of the motor must be coordinated with the speed of the cage drive. It should be possible to move the tensioning unit a distance corresponding to approx. 1% of the belt length. The belt can be supported by runners as described on page 2.

figure 3

VIII. Further information
Effect of temperature
Plastics can expand or contract significantly when temperatures fluctuate. The construction engineer must make allowances for changes in belt lengths and widths if the operating temperature is not the same as the ambient temperature.
Essentially, this affects the belt sag on the return side and the lateral clearance on the conveyor frame.

Chordal action
What is known as chordal action is typical for all sprocket-driven belts, chains etc. The rise and fall of a module during the slewing motion cause changes in the linear speed of the belt. The number of teeth on sprocket is the decisive factor for these periodic fluctuations in speed.
As the number of teeth increases, the percentual change in speed decreases. In practice this means that the largest number of teeth possible must be used if the goods are not to tip or for other reasons an even belt speed is required.

Further information:

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