Transport rollers with toothed-belt tangential drive

When constructing transport installations to run at high speeds, strict requirements are in place nowadays on among other things the noise level and maintainability of the installations. In order to meet these stringent requirements, N.D.W. has introduced the option of driving the conveyors using a tangential toothed belt drive.

Noise level
The special shape of the teeth on the belt and the belt's pulley make a combination that complies with the norm which we have set. Because the air caught between belt and pulley can escape silently, the noise level at a transport speed of 50 m/min. is approximately 70 dB. In comparison with a chain and sprocket transmission, for example, this noise level is exceptionally low. At the same speed, the noise level of the latter application is actually approximately 87 dB, a level that is not permissible under the current (Dutch) regulations for working conditions. According to these regulations, no-one may work without hearing protection at a noise level above 80 dB.

Test rigs
N.D.W. has constructed a range of test rigs with the aim of measuring the noise levels of various sorts of drive mechanisms at increasing speeds. The results of these tests have been included in the noise level comparison diagram.

Noise level comparison diagram
A. B. C.   D.   E.   F.	Rollers driven tangentially using a smooth belt Rollers driven tangentially using a toothed belt (load roller type 85, 86, 87, 88) Rollers driven using a round belt and axle placed transversely beneath the rollers (type 80) Rollers driven tangentially using a chain and a plastic sprocket head with normally shaped teeth (e.g. load roller type 45, 46) Rollers driven tangentially using a chain and a plastic sprocket head with pinion-wheel shaped teeth Rollers driven tangentially using a steel sprocket head with pinion-wheel shaped teeth (e.g. type 49, 50, 53, 54, 56, 58)

Choice of toothed belt
Seca HTT-8M, the seamlessly welded version.
Using a belt 25 mm wide, the maximum tension is 175 daN.
Secaflex HTD-8M, the seamlessly wrapped version.
Using a belt 25 mm wide, the maximum tension is 350 daN.

Conveyor load
Assuming that the roller resistance when using a chain-and-sprocket transmission is 10% of the load on the roller, the maximum conveyor load for the two types is as follows:
Seca HTT-8M, seamlessly welded           : 1750 daN
Secaflex HTD-8M, seamlessly wrapped  : 3500 daN

Advantages
A tangential drive beneath the rollers has a number of advantages when compared with roller-to-roller drives. These advantages include
- no alignment problems. The belt stays in place because it is held inside a polyethylene guide and held taut between two guide wheels.
- simple and quick fitting of rollers
- roller pitch is independent of size
- longer lifespan for toothed belt and pulleys because there is never more than a single tooth in contact. The load on the teeth is identical for each roller from the start through to the end of the conveyor.

Construction advice
The conveyor belt should be constructed in such a way as to let the belt run underneath the rollers. Furthermore, the guide wheels and the belt guide should for example be fixed to a U-section beam of adjustable height. If the belt is broken or worn, it can then be simply replaced just by lowering the U-section, without having to dismantle and reassemble the rollers. This method also allows the belt to be easily adjusted so that its teeth mesh with the tooth grooves of the belt's pulleys. (See also: construction diagram).

Technical data
Seca HTT-8M, seamlessly welded and Secaflex HTD-8M, seamlessly wrapped

Material Toothed belt width Traction cords Width tolerance Height tolerance Length tolerance Weight Drive pulley Teeth in contact Guide wheels Breaking strain

polyurethane elastomer 25 mm steel wire, diameter 0.9 mm 0.5 mm 0.2 mm 0.5 mm 175 g/m minimum 18 teeth minimum 6 teeth minimum diameter 120 mm 1500 daN

Maximum load on the teeth for both types of toothed belt Maximum conveyor load for Seca HTT-8M seamlessly welded Maximum conveyor load for Seca HTD-8M seamlessly wrapped

: 15 daN : 1750 daN : 3500 daN

Motor power
Rule of thumb for calculating the required motor capacity, assuming horizontal transport.

Options
The Seca HTT-8M toothed belts can be provided with a polyamide material on the teeth (PAZ) and/or back (PAR) of the belt. The advantage of PAZ is that the noise level is further reduced. PAR gives a reduction in the coefficient of friction.

Table of coefficients of friction