What Is a Toothed Belt? Definition, Tooth Profiles and Selection Criteria

Toothed belt construction: four functional elements

A toothed belt is a composite, and each element carries a different load path. The teeth transmit load in shear, the tension member carries it in tension, the body compound binds the two and holds the profile, and the facing fabric or backing protects whichever surface runs against a pulley or an idler. Because each element fails differently, a belt cannot be specified by pitch code alone.

Tooth profile

Trapezoidal profiles carry load on the flank of a straight-sided tooth. Curvilinear profiles — HTD and the metric T families standardised in ISO 13050 — use a rounded tooth form that engages more of the pulley groove and distributes load over a larger tooth-root area. The consequences are measurable rather than cosmetic: higher allowable torque per unit of belt width at the same pitch, lower running noise, and greater tolerance of centre-distance error. Profile also sets backlash, which decides positional error in reversing and servo-driven axes.

Tension member

The tension member — glass fibre, aramid, carbon or steel cord — sets tensile strength and elongation at working tension. Glass fibre is the general-purpose choice, aramid raises tensile strength and reduces stretch, and carbon or steel cord gives the lowest elongation where positional accuracy over a long centre distance matters. Elongation, not tensile strength alone, is the figure that decides how much take-up travel the drive needs. ZDBELT supplies these cord options across its profile ranges, so cord type is fixed together with the pitch code rather than chosen afterwards [COMPANY CLAIM — user to confirm].

Body compound

CR (neoprene) is the classic timing-belt body compound, HNBR raises the temperature and oil ceiling above CR, and PU (polyurethane) adds abrasion and cut resistance for washdown and abrasive duty, subject to hydrolysis resistance in humid ambient. Hytrel (TPC-ET) is used where a high-modulus body is needed. Where the belt contacts food, the compound is specified by its certificate against FDA 21 CFR 177.2600 or EU 10/2011, not by family name.

Backing and jacket

The backing carries the back-side idler load; a nylon tooth fabric or jacket protects the tooth face in abrasive or oil-mist service. Back-side cover cracking is usually an idler-geometry problem rather than a compound problem, and it appears when a reverse bend runs on an idler below the minimum diameter for the pitch.

Key findings

1. Pitch sets the speed-versus-torque trade-off — pitch is the distance between tooth centrelines and defines the whole system. Short pitches (MXL, 3M) suit high-speed, low-torque drives with small pulley diameters; long pitches (8M, 14M, XH) carry high torque at low speed → the same shaft power can be transmitted with fewer, wider teeth instead of a large pulley.
2. Curvilinear profiles raise torque capacity at equal pitch — a rounded tooth engages more groove flank than a trapezoidal tooth, so load spreads over a larger root area → allowable torque per millimetre of belt width rises for the same body and cord construction. Read the value from the supplier's rating curve for the specific series, pitch and width [COMPANY CLAIM — user to confirm: ZDBELT per-pitch torque rating tables].
3. The tension member controls elongation, not the torque rating — glass fibre, aramid, carbon and steel cord differ in elongation at working tension → a drive that must hold position over a long centre distance is specified by elongation and available take-up travel, not by tensile strength alone [SOURCE REQUIRED: elongation values by cord type].
4. Tooth shear is a shear-area problem, not a rubber-hardness problem — teeth strip when transmitted torque exceeds the tooth-root shear capacity of the belt → the corrective levers are pitch and width, pulley tooth condition and the service factor applied to shock-loaded driven machines, not compound substitution [COMPANY CLAIM — user to confirm: ZDBELT tooth-shear ratings per profile and width].
5. Ratcheting indicates tension, not overload — tooth jump occurs when engagement between tooth and groove is insufficient → correct belt tension and centre distance, and inspect pulley grooves for wear, before considering a larger belt.
6. Misalignment, not load, produces most edge damage — parallel misalignment makes the belt run against the flange and fatigues the cord at the belt edge → align the pulleys and shim the driven unit before replacing the belt.
7. Minimum pulley diameter is a per-pitch constraint — each pitch code has a minimum pulley diameter and a minimum number of teeth in mesh → below those limits, cord fatigue at the tooth root and back-side cracking appear even at rated load [SOURCE REQUIRED: minimum pulley diameters by pitch code].
8. Food-contact and ATEX duty are application standards — declaring a belt antistatic does not by itself make a drive compliant with Directive 2014/34/EU; the installation must be assessed → classify the zone first, then specify a conductive belt and confirm surface resistance against the applicable limit [SOURCE REQUIRED: surface-resistance values].

Pitch codes and profiles for toothed belts

Read the table as a filter: fix the pitch code from the available pulley geometry, then take the torque and speed limits from the belt supplier's rating curve for that pitch and width.

Source: ISO 5296-1/-2 (trapezoidal pitch codes and dimensional characteristics) and ISO 13050 (metric pitch curvilinear profile systems) — pitch values are definitional to those standards. Rated torque is supplier-specific and remains [SOURCE REQUIRED] pending the manufacturer's rating table. Verify the current standard editions before publishing.

Body compound selection

Compound choice is decided by temperature, oil and chemical exposure, abrasion, and whether the belt contacts food. The table lists the dimensions to compare and leaves supplier-specific values open rather than estimating them.

Source: compound-family characteristics as published by compound suppliers; [SOURCE REQUIRED] cells to be completed from current supplier datasheets before publishing.

Failure modes and corrective action

Failure classification comes before replacement: the damage pattern identifies the root cause, and an unaddressed root cause returns on the new belt.

Source: failure-mode classification follows standard belt-drive troubleshooting practice. Confirm the root cause on site before applying corrective action.

Which should you choose?

• Choose a short-pitch curvilinear belt (3M, 5M) when the axis is high-speed and low-torque and the pulley diameter is constrained by the machine envelope.
• Choose 8M or 14M curvilinear when the driven machine is low-speed and high-torque — a mill, crusher or extruder — and a narrow belt is preferred to a large pulley.
• Choose a trapezoidal inch-profile belt (XL, L, H) when the drive already exists to ISO 5296 pulley geometry and interchangeability with installed hardware outweighs torque per millimetre of width.
• Choose aramid, carbon or steel cord when positional accuracy over a long centre distance matters, or when the available take-up travel is short.
• Choose glass-fibre cord when the application is a general industrial drive where cost and tolerance of centre-distance adjustment dominate.
• Choose a PU body when the drive sees washdown cleaning and abrasion, and confirm hydrolysis resistance for the ambient humidity.
• Choose CR or HNBR when ambient or radiated heat exceeds the PU ceiling, or when oil mist is present.
• Specify a conductive belt when the installation has been classified as an explosion-risk area and the drive assessment requires it — Directive 2014/34/EU applies to the assembly, not to the belt alone.

FAQ

Is a toothed belt the same as a timing belt?

Yes — toothed belt, timing belt and synchronous belt name the same component: an endless belt with moulded teeth that mesh with grooved pulleys and transmit torque without measurable slip. "Synchronous" is the standards-driven term, used in ISO 5296 and ISO 13050; "timing" came from automotive engine drives and stayed in industrial usage. Order and specify by pitch code, profile and width, never by name alone.

What causes tooth stripping on a toothed belt, and how do you prevent it?

Tooth stripping is a shear failure: transmitted torque has exceeded the tooth-root shear capacity of the belt. The usual contributors are an undersized pitch or width, worn or undersized pulley teeth, a jammed driven load, or shock loading the service factor did not cover. Prevention is a torque check against the belt rating, a pulley inspection, and a corrected service factor.

How do I identify whether a toothed belt has failed from wear or from misalignment?

Start with where the damage sits. Uniform tooth wear across the full width points to abrasive service or normal engagement wear. Damage concentrated on one edge, with frayed fabric and exposed cord, points to parallel misalignment or flange contact. Cracking at the tooth root points to heat or ozone ageing, and uneven wear across the width is angular misalignment.

Request a belt assessment or replacement quote

Send the belt's pitch code, tooth profile, width and cord type, plus a photograph of the failed belt, and we will quote against the drive as specified.

• Company: Dongguan Zhende Machine Equipment Co., Ltd
• WhatsApp: +86 18002849592
• E-mail: liang@zd-stool.com