Metric pitch timing belts mate with same-pitch timing pulleys in power transmission systems where maintenance-of-speed ratio is an important design consideration. Metric pitch is the distance between belt teeth based on millimeters (mm).

With metric pitch timing belts, a timing pulley transmits force to the belt via evenly-spaced grooves that mate with the teeth in the belt. These same grooves and teeth prevent belt slippage.

Synchronous belt drives are highly-efficient devices. Synchronous belts come in a wide variety of materials and reinforcements. Metric pitch timing belts are also available in trapezoidal and curvilinear tooth form.

Specifications

Length, Width, and Number of Teeth - For a given pitch, a selected number of teeth will determine the belt length. Likewise, a specified belt length will determine the number of teeth for metric pitch timing belts.

Pitch is the most important consideration when searching for metric pitch timing belts. By definition, pitch is the distance from one tooth center to the adjacent tooth center.

Pitch choices for metric pitch timing belts include:

• T pitch, a metric trapezoidal pitch available in four pitch sizes: 2.5 mm, 5 mm, 10 mm, and 20 mm.
• AT pitch, a metric curvilinear pitch available in three pitch sizes: 5 mm, 10 mm and 20 mm.
• GT® pitch (Gates Rubber Company), a metric curvilinear pitch from that comes in three pitch sizes: 2 mm, 3 mm and 5 mm.
• HTD® pitch, or high torque drive pitch, is a metric curvilinear pitch developed by Uniroyal (now Gates Rubber Company). HTD pitch comes in five pitch sizes: 3 mm, 5 mm, 8 mm, 14 mm, and 20 mm.
• Super-torque, a metric curvilinear pitch available in six sizes from 2-mm pitch to 14-mm pitch.

Ultimate Tensile Strength (UTS) is the breaking strength or tension rating.

Maximum Operating Speed - Many products are rated for a maximum operating speed, dependent on material and timing belt geometry.

Types

Types of timing belts include double-sided, truly endless and open-ended.

Double-sided belts have teeth on both sides of belt.

Image credit: SKF/North America

Truly endless belts are manufactured as one closed loop; not spliced.

Image credit: MISUMI USA

Open-ended belts come in a roll and may be cut and spliced to the desired length and number of teeth.

Image credit: MISUMI USA

Materials

Materials of construction for metric pitch timing belts include:

• Neoprene
• Polyurethane
• Rubber
• Urethane

Material selection factors may include:

• Operating tension
• Environmental factors such as humidity and temperature
• Power transmission

Many metric pitch timing belts are reinforced with fibers or cables in the tension area of the belt. Reinforcement can significantly enhance the belt’s maximum operating tension. Metallic and non-metallic reinforcement fibers are available. Common materials for reinforcement also include:

• Fiberglass
• Kevlar® (DuPont)
• Polyester
• Steel

Standards

BS ISO 5296 - Synchronous belt drives - belts with pitch codes MXL, XXL, XL, L, H, XH, and XXH - metric and inch dimensions

ISO 13050 - Curvilinear thoothed synchronous belt drive systems

ISO 5295 - Synchronous belts - calculation of power rating

ISO FDIS 17396 - Synchronous belt drives - metric pitch - tooth profiles, endless and open-ended belts and pulleys

Image credit:

Belt Corporation of America