ConCar Variable Speed Belts 21x6 - 600 Li

ConCar Variable Speed Belts 21x6 – 600 mm inner length – DIN 7719 / ISO 1604

This ConCar Variable Speed Belts with a 21x6 profile and a 600 mm inner length, is a toothed variator belt conforming to DIN 7719 and ISO 1604. Variable Speed Belts are the mechanical alternative to frequency converters: they regulate the output speed purely through geometry, without electronics, harmonics, or an additional heat source in the control cabinet. In many woodworking, textile, and agricultural machines, this remains the more robust solution because it operates reliably even in dusty, humid, and vibration-prone environments.

This length in the drive

The inner length of 600 mm is a short version for the 21x6 profile. This means a compact center distance and a correspondingly small drive volume, but at the same time a high bending frequency. At a belt speed of 20 m/s, this equates to approximately 31.7 revolutions per second. With short belts, check whether the tapered pulleys meet the minimum running diameter specified by the manufacturer, as the bending stress has the greatest impact on service life at this point.

For design and comparison with an existing belt, the three length specifications are important because manufacturers use different reference dimensions. The inner length (Li) is 600 mm; it is measured at the inner circumference of the belt and is the standard ordering dimension in Germany. The effective length (Ld) of 630 mm refers to the neutral axis and is the dimension used in many catalogs and drive calculations. The outer length (La) of 638 mm is measured at the back of the belt. With a profile height of 6 mm, the difference between the inner and outer lengths is 38 mm, which corresponds to twice the difference in circumference across the belt height. When replacing an old belt, always compare using the same reference dimension; otherwise, you can easily be off by several centimeters.

Dimensions and specifications

• Internal length (Li): 600 mm

• Effective length (Ld): 630 mm

• External length (La): 638 mm

• Profile: 21x6 according to DIN 7719 / ISO 1604

• Top width: 21 mm

• Height: 6 mm

• Flank angle: 27°

• Construction: open-sided, toothed

• Mixture: Chloroprene (CR)

• Tensioning material: Polyester cord

• Antistatic: yes, according to ISO 9563

• Temperature range: -30 °C to +80 °C

• Belt speed: up to 30 m/s

• Weight: 0.09 kg

• Article number: G421060600

• EAN: 4059213020455

• Manufacturer: ConCar

Structure and materials

The belt consists of a chloroprene blend (CR) with an embedded polyester tensile cord. Chloroprene was deliberately chosen here: it is resistant to oil mist, ozone, UV radiation, and weathering, and retains its elasticity in a temperature range of approximately -30 to +80 degrees Celsius. The polyester cord absorbs the tensile forces and keeps elongation low over the belt's lifespan, which is particularly important in a variator because an elongated belt length directly translates into a shift in the control range.

The 27° flank angle is the crucial difference compared to a conventional V-belt, which operates at 34 to 40 degrees. The shallower angle generates less wedging effect per millimeter of radial travel, ensuring smooth belt operation across the entire pulley adjustment range and preventing binding at the end positions. Simultaneously, the large 21 mm upper width provides the necessary contact area to transmit torque solely through friction. The toothed underside reduces bending stiffness to such an extent that the belt can operate even on small effective diameters without the flanks overheating due to internal flexing.

Typical areas of application

Belts of this size are typically found in compact drives: bench drills and small lathes with continuously variable spindle speed, feed drives on band and circular saws, laboratory centrifuges and shakers, dosing and small conveyors in packaging lines, as well as garden equipment and small drives where the installation space does not allow for large pulleys.

What these applications have in common is that the rotational speed must be adjusted during operation to suit the material, batch, or demand. A Variable Speed Belts solves this problem purely mechanically, without any electronics in the drive train. This is advantageous wherever dust, moisture, vibration, or temperature would damage a frequency converter, and it remains the only economical solution for existing machines because the variator is an integral part of the machine's design.

Assembly and tension

For installation: Open the pulleys, place the belt on without tension, then adjust it to the required tension using the adjustment mechanism or the motor rocker. The belt must never be pulled over the pulley edge or pried open with a tool. After approximately 24 hours of operation, the belt will have settled; at this point, the tension should be checked a second time and adjusted if necessary. Insufficient tension leads to slippage and burns the belt edges, while excessive tension puts unnecessary stress on the bearings and tension members.

Transverse cracks on the underside indicate an insufficient bearing diameter or cold brittleness, while longitudinal cracks and frayed edges point to misalignment between the pulleys. It's worthwhile checking the alignment with a ruler or laser when changing the belt, as even a few millimeters of misalignment over a one-meter center-to-center distance can halve the belt's lifespan.

Similar names for other brands

Variable Speed Belts are standardized according to DIN 7719 and ISO 1604. A belt with a 21x6 profile and a 600 mm inner length is therefore dimensionally identical regardless of the manufacturer; no modification of the pulleys is required for replacement. This ConCar belt replaces, among others:

• OPTIBELT: VB 21x6 / VARIO POWER 21x6

• GATES: Multi-Speed ​​21x6 / Predator V Variable Speed

• CONTITECH: VARIO Speed ​​21x6 / CONTI-V VARISPEED

• MEGADYNE: VARISECT 21x6

• MITSUBOSHI: VARI-SPEED 21x6

• BANDO: Variable Speed ​​21x6

• PIX: Variable Speed ​​21x6

Delivery

The belt is supplied as a single, endless belt. Standard lengths and common profiles are available from stock; custom lengths and widths are available upon request. If you are unsure which length your drive requires, please send us the part number of your old belt or the dimensions of your pulleys, and we will check the compatibility.