PU Timing Belts Manufacturer: Technical Audit and RFQ Checklist

Qualify a PU timing belt manufacturer with documents, not with a sample. Two belts can look identical on a bench and still come off two different processes: one moulded as a closed ring in a fixed tooth cavity, the other built from open length and joined. So ask three questions before you read a price. Which pitches and tooth profiles are moulded in-house? Is the belt endless by moulding, or jointed? And how is batch-to-batch dimensional variation recorded?

Our hard rule is blunt. A quotation that arrives without a pitch list, a written joint declaration and the inspection record from the last batch cannot be compared with any other quotation, however neatly the numbers are laid out. Price is a number attached to a specification. When the specification is missing, the number is a guess with a currency symbol in front of it.

This page is the working set we hand to sourcing teams, and there are three documents in it. A mould capability table that separates what a shop really forms in its own cavities from what it subcontracts. An RFQ field sheet with eighteen fields, so that two quotations land on the same scope. And a sample validation workflow with named approval gates, so an approved prototype does not quietly turn into a different belt in mass production. Along the way we cover profile limits, joint verification, inspection items, packing and the way commercial terms should be normalized.

We have supplied synchronous and V-belt drives to packaging, textile, glass and wood-panel integrators long enough to know where these projects break. They rarely break because the wrong belt was chosen on paper. They break because the belt that arrived was not the belt that was approved. A supplier can pass a sample and still fail a program.

01What to Audit in a PU Timing Belt Supplier

An audit is a list of evidence, not a factory tour. We have walked through clean, well-lit plants that could not produce a single dimensional record from the previous month, and we have bought excellent belts from crowded workshops that kept a handwritten but complete measurement log for every mould run. The difference between those two suppliers is not visible from the gate. It only appears when you ask for paper.

Five Domains, One Question Each

The audit covers tooling, jointing, materials, measurement and commercial handling. Each domain has a single question that exposes more than an hour of factory walking. For tooling, it is whether you can see the mould register and the mould number stamped on the belts. For jointing, it is whether the supplier will put "endless, moulded" or "jointed" in writing on the drawing. For materials, it is whether the cord and compound lots are recorded against the belt size. For measurement, it is whether a completed inspection sheet exists for a real shipment. For commercial handling, it is whether tooling cost and unit price are quoted apart, because that single line tells you whether the belt is a repeatable product or a one-off service.

Why Sample Appearance Proves Almost Nothing

A six-belt sample set costs the supplier relatively little and is easy to make carefully. Mass production is where the process shows through. We have opened sample boxes with perfect T10 pitch length and then received a first production lot running 0.4 mm per 1,000 mm long, which is enough to change centre distance and tension on a fixed-axis drive. Samples are judged at the second audit stage, once the pitch list, the joint declaration and the last-batch record have arrived.

Audit Domain	Evidence Required	Pass Criteria	Risk if Absent
Tooling and moulds	Mould register listing pitch, profile, belt width and mould number	Mould number stamped on the belt matches the register entry	A size quoted as in-house is quietly bought in, and a revision ships without notice
Jointing capability	Written statement per size: endless moulded or jointed	Declaration appears on the drawing and the inspection sheet	A welded ring sold as endless fails at an indexing position and stops a line
Cord and compound	Cord lot and PU batch linked to the belt size and date code	Lot numbers traceable from carton to mould run	A cord change alters elongation and the drive no longer holds position
Measurement system	Completed inspection sheet from a named shipment, with gauges listed	Values, gauges and limits present for every line	Tolerance drifts for months before anyone notices
Commercial structure	Tooling, unit price and MOQ quoted as separate lines	Amortization model shown for the first order quantity	Custom work is priced as a favour and becomes an annual negotiation

Two narrower angles sit next to this audit and are worth one paragraph each. If your program is designed around an automated machine builder's own drawings, the position on a timing belt manufacturer for automation project is different from a replacement market, because the volume is committed earlier and the tolerance is agreed once. If instead you need your own brand on the sleeve and the carton, that question is answered in our note on choosing a private label timing belt supplier. This page stays on capability auditing; the general capabilities of a conveyor belt manufacturer running the same plant disciplines are a useful reference for how mould, press and inspection records should be organized.

02Mould and Tooling Capability: Profiles and Pitches

Tooling is the part of a PU timing belt business that cannot be improvised. A belt is formed by casting polyurethane into a cavity whose tooth geometry is cut into a steel or aluminium master, with the cord wound on a defined pitch line before the compound sets. If the cavity does not exist, the supplier is not making the belt; the supplier is buying it. That is not automatically a problem, but the buyer has to know which of the two is being priced.

Which Pitches Are Usually Moulded In-House

The metric T and AT families and the imperial MXL, XL and L family are the workhorses, and most PU shops that build synchronous belt capacity own cavity sets for the middle of that range. Very small pitches and very wide sections are where tooling investment stops, because the mould cost per size is high and the annual volume per size is usually low. The practical audit move is simple: ask for the mould register, then pick the three sizes you actually buy and ask the supplier to point at the register line for each. If a size is not in the register, ask what happens instead, and get the answer in writing. "We will handle it" is not an answer.

A short printed list of the families and their typical operating envelopes is useful when you brief an integrator, and our own timing belt page shows how the range is organized around pitch rather than around brand names. For drives where the belt is indexed thousands of times per shift, the relationship between pitch, tooth engagement and repeatability is covered in more depth in our article on a precision drive timing belt, which is the right background before you fix a tolerance on a new size.

Pitch	Tooth Profile	Typical Market Practice	Min Pulley Teeth	What to Demand
MXL, 2.032 mm	Trapezoidal, fine	Commonly in-house, narrow widths only	10 teeth	Mould number plus the width set held for that cavity
XL, 5.080 mm	Trapezoidal	In-house at most shops	10 teeth	Confirmation that cord type is fixed per size, not per order
T5, 5.0 mm	Trapezoidal	In-house; widest selection of widths	14 teeth	Pitch length tolerance quoted in mm per 1,000 mm
AT10, 10 mm	Modified trapezoidal	Usually in-house, fewer widths	15 to 16 teeth	Tooth flank profile drawing, not just a pitch figure
8M, 8.0 mm	Curvilinear	Often in-house above a certain width only	22 to 24 teeth	State whether wide sections come from the same cavity
14M, 14 mm	Curvilinear	Frequently outsourced or formed in segments	28 to 34 teeth	Declare the forming route and who inspects it
Special or non-standard	Client-specific tooth form	New master required, tooling charged	Per drawing	Ownership of the master, and whether it stays blocked for you alone

Why the Mould Register Matters More Than the Brochure

A brochure lists what a company can sell. A mould register lists what a company can make. Those two lists are not the same, and the gap between them is where lead time and tolerance are lost. When we quote a size that exists in our own register, the mould number, the cavity condition and the last run date are all known quantities, so a delivery promise is built on a real schedule. When the size has to be brought in, we say so, because the buyer deserves to know whether the tooth geometry they are approving is ours or a third party's. Buyers should ask the identical question of every supplier in a bid, in the same words, and compare the answers line by line.

03Tooth Profile Capability Boundaries

Every profile has a lower limit on pulley teeth, and near that limit the belt stops behaving like the catalogue curve. The tooth does not fail all at once. It enters and leaves the groove at a sharper angle, so the load spreads over fewer teeth, the cord sees more bending stress per revolution, and the belt starts to run hot. A supplier who never mentions the minimum is either working far above it or has not done the arithmetic.

Reading the Boundary Instead of the Rating

Published drive tables typically quote a minimum pulley tooth count for each pitch, and those figures assume full rated power. Reduce the transmitted torque to a third of rating and a smaller pulley often becomes acceptable, which is why the correct question is not "what is the minimum" but "what is the minimum at my torque, my speed and my required life". Ask for the engagement figure for the specific drive. Two of our packaging customers moved a T5 axis from 15 teeth to 12 teeth by dropping the torque requirement, and both belts had to change cord grade at the same time, because the smaller pulley increased the bend cycles per minute by roughly 25 percent.

Tooth Profile	Typical Minimum Pulley Teeth	Where It Fits	Boundary to Watch	Audit Question
Trapezoidal T2.5 to T20	12 to 16 depending on pitch	General drives, positioning, light conveying	Tooth tip stress below the minimum count	Show the engagement calculation for this drive
Modified trapezoidal AT5 to AT20	14 to 18	Reverse-bend and high-torque indexing	Backside flatness when idlers run on the back	Is the back ground, and to what flatness figure
Curvilinear 3M to 14M	10 to 24, rising fast with pitch	Higher torque per width, quieter running	Cord degradation on small pulleys at high speed	Which cord compensates for the small pulley
GT-style modified curvilinear	Per published drive table	High-accuracy positioning on servo axes	Pulley groove must match the belt generation	Is this a moulded cavity or a licensed profile
Double-sided tooth form	Same limits apply to the smaller side	Reversing drives and serpentine layouts	Cord position tolerance becomes tighter	How is pitch line position verified on both flanks

When the drive sits at a boundary, the honest route is to compare belt families rather than to squeeze one of them. A general comparison of V-belt versus timing belt layouts is a fast way to see whether the application should use positive engagement at all, and our overview of timing belt types and pitches puts the tooth families side by side. Suppliers who also build vee sections, and can therefore quote either solution, tend to give a straighter answer here; the same is true of a conveyor belt supplier who has to justify a change of drive concept rather than a change of catalogue line.

04Jointed vs Truly Endless: How to Verify

The word endless is used loosely in this trade. A moulded ring is literally endless: polyurethane is cast into a closed cavity with no seam anywhere in the body or the cord. A jointed belt is made from an open length that is welded or spliced into a ring, and it can be a perfectly good product for low-speed conveying. It is a poor product for a synchronised drive, because the joint is a discontinuity in a cord that is supposed to carry load in tension. Under indexing torque the joint creeps, the length changes, and position drifts.

Inspection Under Light, Then Under Load

Start with the cheapest test. Hold the belt against a light and rotate it slowly, watching the flank line where the tooth meets the backing. A welded joint usually shows itself as a faint lap or a colour step, and a splice in a corded belt can show a slight bulge on the outside circumference. Nothing visible is not proof of endless construction, so add a thickness reading. Take six micrometer readings across the width on one tooth and repeat at four positions around the ring; a joint reads differently from the surrounding body, often by 0.05 to 0.15 mm. The third check is functional. Run the belt on the actual drive at working speed and listen at the lowest index rate, where a joint produces a periodic tick that a moulded ring does not have.

Supplier Claim	Verification Method	Evidence That Settles It	Red Line
"Endless, moulded ring"	Light inspection plus multi-point thickness scan	Mould number on the belt matches the declared cavity	Any visible lap line on a drive belt
"Endless by welding"	Ask for the joint location, then inspect that zone	Written joint declaration on the drawing	Joint used at an indexing or high-torque station
"Cord is continuous"	Cut one sample and count cord ends in the section	Destructive test report or a sectioned sample kept on file	Visible cord ends in the cut face
"Same performance as moulded"	Index the drive and log position drift over 500 cycles	Position deviation recorded at the same torque	Drift above your machine's positioning window
"We only ship moulded"	Order a size larger than any existing mould	Delivery of the same size from a different mould number	Length jump when the forming route changes

Where Jointed Belts Are the Right Answer

Open-end and jointed belts are legitimate where the machine cannot be dismantled and the load does not require synchronisation accuracy. Long conveyor-style PU belts in a food line are a classic case. If the drive does need tooth engagement and genuine tension-carrying cord, the joint question moves to the front of the audit, and the material choice behind that cord is worth a separate read: our note on an aramid fiber PU timing belt explains why the cord family, not the compound colour, decides whether a moulded ring holds length over a year of indexing.

05Cord and Backing Consistency Evidence

The cord is the load path and the backing is the working surface, and both drift quietly. A supplier that changes cord supplier between two production lots of the same size will not announce it, because on a bench the belt measures the same. In service, elongation at a given tension shifts, and a drive set up with 1.5 percent stretch may now need a different centre distance.

What to Record on Both Sides of the Belt

Ask for four facts about the cord: material family, construction and twist, cord diameter or linear density, and the lot certificate for the spool used. Then ask for three facts about the compound: hardness in Shore A, the base polymer type, and the colour or dye lot if colour is part of your inspection routine. For a belt that runs over backside idlers, add the backside condition, because a ground back and an as-cast back are different products even when they share a part number. The comparison between polymer families is a useful background read if you are choosing between drive solutions, and our articles on PU timing belt vs rubber timing belt and on aramid fiber vs steel cord PU timing belt cover the trade-offs in more detail than is useful here.

Element	Typical Options	Consistency Evidence to Request	Field Symptom if It Drifts
Tension cord	Steel, aramid, glass fiber, polyester	Cord lot number and pull-out force per mm of width	Length creep, position drift after retensioning
Cord position	Set by winding tension and mould step	Sectioned sample with pitch line depth measured	Tooth wear on one flank only, noise under load
Backing compound	PU 85 to 95 Shore A, food-contact grades available	Hardness reading per lot plus compound batch code	Grip loss, cracking at the tooth root, faster abrasion
Backside finish	As-cast, ground, fabric covered, coated	Flatness figure or a sectioned edge sample	Trapping on the back idler, uneven tracking
Colour and marking	Natural, green, blue, black, conductive grades	Dye lot and the marking format used on the belt back	A batch that cannot be traced back to its production run

Belts and heavy belting share this discipline, and a plant that runs both usually keeps one materials register. Where a synchronised drive feeds a main haulage line, the cord and compound controls above sit alongside the belts covered in our industrial conveyor belt material, and the same question about lot tracing applies to both product families.

06Batch Consistency: Records to Request

Consistency is a record, not a promise. Any shop can hold a tolerance for one run; the question is what the last ten runs looked like and whether anyone wrote the numbers down. Our standing request on a first order is deliberately narrow: send the inspection sheet for the previous production lot of the exact same size, with the measured values visible rather than ticked as pass or fail. A sheet of ticks tells you the inspector showed up. A sheet of numbers tells you where the process sits inside its tolerance band, which is what predicts the next lot.

The Five Metrics That Move

In our experience, five measurements explain nearly every batch complaint on a PU timing belt: pitch length, width, thickness over the tooth, hardness and the pitch line position of the cord. Pitch length is the one that hurts most, because it converts directly into centre distance and tension. Width and thickness matter most on guided drives and on belts that run through a tight slot. Hardness is a proxy for compound control, and it swings before grip or wear complaints appear. Cord position rarely moves much, but when it does, the belt wears on one flank and starts to run noisy.

Batch Record	Metric	How It Is Expressed	Deviation Band	Verdict Rule
Lot inspection sheet	Pitch length over the full ring	mm per 1,000 mm, plus total mm	Agree 0.15 to 0.30 mm per 1,000 mm on precision drives	Outside the band twice in a row means the process, not the belt, is the problem
Mould run log	Mould number and run date	Code stamped on the belt back	Any mould change declared in advance	An undeclared mould change voids the approval
Compound lot	Hardness and batch code	Shore A plus the supplier's internal lot reference	Plus or minus 3 Shore A around the approved sample	A single lot outside the band triggers a compound review
Cord lot certificate	Cord grade and spool reference	Grade code plus breaking load per cord	Supplier's own incoming limit, shared with you	A grade substitution is a change of product, not a change of lot
Traceability file	Link from carton to run	Carton label, belt marking and run record as one set	Retained for at least three years	If the set cannot be produced on request, the file is decoration

07Dimensional Inspection Items

A dimensional report is only worth reading if the gauges are named, because the same nominal can be checked three ways and return three answers. Pitch length measured over 20 teeth with a steel tape is not the same measurement as the same belt checked on a two-pulley measuring fixture under tension. Both are legitimate; they are simply not interchangeable. So the inspection plan should say which method is used, and every subsequent lot should be checked with the same one.

The Items Worth Measuring Every Time

Eight items cover the commercial risk. Pitch length and tooth flank profile are the two that decide fit and noise. Width and thickness decide whether the belt sits correctly in a groove or a guide. Concentricity and backside flatness decide whether the belt runs quietly when backside idlers are in the train. Cord position decides long-term wear symmetry, and hardness predicts compound behaviour. A supplier who measures all eight on a first article and three in routine production is being proportionate.

Inspection Item	Gauge or Fixture	Spec Basis	Typical Tolerance	Frequency
Pitch length	Two-pulley fixture under stated tension, or tape over a fixed tooth count	Drawing tooth count and pitch	0.15 to 0.30 mm per 1,000 mm	First article plus sample per lot
Tooth flank profile	Optical comparator or shadowgraph against a template	Profile master for the pitch	Visual fit to template at 10x to 20x	First article and after any mould repair
Width	Vernier caliper at three positions	Nominal width in mm	Plus or minus 0.5 mm on standard widths	Every lot
Thickness over tooth	Micrometer with a flat and a pointed anvil	Drawing section	Plus or minus 0.2 mm	Every lot
Concentricity	V-blocks with a dial indicator on two reference pulleys	Belt back reference	0.2 to 0.5 mm depending on ring size	First article, then audit sample
Backside flatness	Surface plate and dial gauge, or straight edge with feeler	Applicable only to ground or coated backs	0.1 mm over a 300 mm span	Every ground lot
Cord position	Sectioned sample under a measuring microscope	Pitch line depth from the tooth root	Plus or minus 0.2 mm	Per cord lot change
Hardness	Shore A durometer on the back, five readings	Approved sample value	Plus or minus 3 Shore A	Every compound lot

Where a plant buys belts for drives and belting for haulage from the same source, the inspection logic carries over. A rubber conveyor belt is measured on different geometry, but the principle that the method must be named and repeated is identical, and buyers who insist on it in one product family usually get it in the other.

08Mechanical Test Evidence by Standard

Test certificates have a habit of being quoted without their test conditions. A tensile figure means little unless the specimen geometry, the test speed and the conditioning are the same on both sides of a comparison. So when we send test evidence, we attach the standard, the specimen description and the actual reading, and we expect the same from anyone quoting to us.

What Each Standard Usually Covers

The table below lists the standards that turn up most often in synchronised drive discussions. Treat every row as a question rather than a specification for your own application, because the standard defines the method, not the acceptance limit. The acceptance limit is what you and the supplier agree, and it belongs in the RFQ, not in a general catalogue statement.

Standard	Test Item	What It Usually Requires	Evidence to Keep
ISO 13050	Synchronous belt geometry and tooth shear	Metric pitch families, pitch length and shear strength verification	Tooth shear figure per pitch and width
ISO 37 or ASTM D412	Tensile strength and elongation of the compound	Dumbbell specimen, stated speed and conditioning	N/mm2 and elongation at break against the approved lot
ISO 868 or ASTM D2240	Hardness	Shore A reading on a defined surface, usually five points	Reading set per compound lot
DIN 53516	Abrasion resistance	Volume loss in mm3 under a controlled abrasive path	Figure in mm3, which for common PU grades is often quoted near 90 mm3
ASTM D573	Heat ageing	Property change after a stated time at a stated temperature	Before and after hardness and tensile values
ISO 1817	Liquid resistance	Volume and hardness change after immersion in a named medium	Immersion medium, temperature and duration stated
ISO 9563	Electrical conductivity for antistatic belts	Surface resistance within the conductive range after conditioning	Resistance reading and the test atmosphere
Hydrolysis or tropical test	Wet-heat ageing of the PU	Extended exposure to warm humid air, then a check for softening or cracking	Photographs plus hardness change, since this test is often the one missing

A distributor evaluating several suppliers sees these documents constantly, which is why the fastest comparison is not the certificate list but the test conditions behind it. A conveyor belt distributor running the same check on pattern belting will recognize the pattern: the standard names the method, and only the agreed limit tells you whether the belt fits your line.

09Surface Treatment and Coating Capability

On many drives the back of the belt does a second job: it carries a product, runs against an idler, or has to shed static. That second job is bought as a treatment, and treatments are where quotations become genuinely hard to compare, because two suppliers can both write "coated" and mean different processes with different life.

Which Treatments Change the Part, Not Just the Surface

Grinding the back changes geometry and must therefore be agreed as a drawing change, not as a finish option. Adding a fabric back or a coating changes friction and wear behaviour, and an antistatic grade changes the compound itself. Ask for three things on any treated belt: the process name, the property it targets, and the inspection item that catches it. If the supplier cannot name the inspection item, the treatment is a description. Buyers who are chasing grip or cleanliness on a synchronised axis usually get further by reading our note on PU timing belt surface precision before they approve a finish.

Treatment	What It Changes	Typical Limit	Inspection Item to Agree
Back grinding	Thickness and flatness of the back	Limited stock removal before the cord is exposed	Flatness over a 300 mm span
Fabric backing	Friction and noise against back idlers	Not suitable for high indexing accuracy	Adhesion and edge fray check
PU coating for grip	Coefficient of friction on the carrying side	Adds thickness, so the section must be redrawn	Coating hardness and thickness
Antistatic grade	Surface resistance of the compound	Conductive fillers reduce some mechanical values	Resistance reading under a stated atmosphere
Food-contact compound	Cleanability and regulatory status	Applies to the whole belt, including any coating	Declaration of composition and colour code

Because coated and ground belts sit next to vee drives on the same machines, buyers often evaluate both at once. A supplier that also acts as a transmission belt manufacturer can usually tell you whether the extra surface work is solving a real problem or covering for a misaligned drive.

10RFQ Field Sheet for PU Timing Belts

An RFQ is the cheapest audit instrument you own. Ten fields, filled in properly, remove most of the ambiguity that makes two quotations incomparable, and they cost a buyer twenty minutes to complete. We send this sheet back with the quotation when a field is missing, because quoting around an unknown is how projects start badly.

The Two Fields Buyers Forget

Smallest pulley tooth count and annual volume. The first decides whether the drive is even inside the profile boundary discussed above, and the second decides whether the mould exists or has to be cut. A buyer who omits them will typically receive a price for the easiest possible interpretation of the request, and then a revised price once the drawing appears.

Field	Unit	Mandatory	Reason	Example
Pitch	mm or class code	Yes	Selects the mould	T10
Tooth count	teeth	Yes	Fixes pitch length	125
Width	mm	Yes	Sets shear capacity and cavity width	20
Smallest pulley teeth	teeth	Yes	Tests the profile boundary	18
Cord family	Grade name	Yes	Sets elongation and price	Steel cord
Torque and speed	Nm and rpm	Yes	Sizes the width and cord	14 Nm at 900 rpm
Temperature range	you C	Yes	Chooses the compound	-10 to 80
Backside duty	Description	Yes	Decides grinding or coating	Flat idler contact
Annual volume	pcs per year	Yes	Justifies tooling and MOQ	600
Inspection documents	List	Yes	Defines the acceptance file	Dimensional plus hardness

Send the filled sheet to any candidate PU timing belt supplier and compare what comes back. Where a program also covers belting, the same sheet logic applies to a wholesale conveyor belts enquiry, and a buyer visiting a conveyor belt factory should take the register question with them, because tooling lists are audited the same way in both product families.

11Sample Validation Workflow

Sampling fails for one reason more often than any other: nobody decided in advance what a sample had to prove. Our workflow has five gates, and no gate is passed on a verbal approval. Note the third row. A belt that runs well on a bench fixture has proved geometry, not field life.

Five Gates Between Enquiry and Mass Production

Stage	Deliverable	Lead Time	Approval Gate
1. Drawing review	Signed size sheet with pitch, profile, width, cord	1 to 2 days	Buyer confirms the size, in writing
2. Mould check	Mould number or a tooling quotation	2 to 5 days	Tooling cost and ownership accepted
3. Prototype run	3 to 5 belts with a dimensional report	5 to 10 days	Numbers inside the agreed band
4. Field trial	Run log with hours, index count and any drift	2 to 6 weeks	Position and wear within the window
5. Golden sample	Sealed, dated sample plus inspection file	Same week as gate 4	Both parties hold a copy before mass production

Where the drive feeds a robot or an indexing head, the field trial has to include the real motion profile, not a constant-speed run. Our note on a PU timing belt for packaging robotics shows why start-stop duty exposes cord behaviour that a steady run hides. If the same machine also uses vee drives for its slower axes, ask the V-belt manufacturer a single question during the same visit: whether the belt families were selected from the same drive data.

12First-Article Inspection and Approval

The first article is the moment the approved sample becomes a document. A signed sheet with measured values turns a golden sample into something that can be defended two years later, when the belt and the inspector have both moved on.

What Belongs on the Sheet

Item	Criterion	Signed By
Pitch length	Inside the band agreed on the size sheet	Supplier quality, buyer engineering
Endless declaration	Mould number stated, no joint permitted	Supplier production
Marking and traceability	Size code, mould number and date code legible	Supplier quality
Packing check	Same packing unit as the quotation stated	Supplier, acknowledged by buyer

13Packing, Marking and Traceability

Packing is a technical variable on polyurethane belts, not a logistics afterthought. PU absorbs moisture over time and can hydrolyse, so a belt that sits in a humid warehouse for two years inside a plain cardboard box is not the belt that was tested. Marking matters for the same reason: without a mould number and date code on the belt, an incoming check cannot connect the part to a production record.

Three Rules We Ask Suppliers to Accept

Element	Requirement	Why It Matters
Belt marking	Size code, mould number, date code on the back	Links the part to its run record
Inner packing	Poly bag or moisture barrier, belts not compressed into a coil	Protects tooth geometry and limits humidity exposure
Storage note	Cool, dry, away from direct sun, with a suggested shelf period	Prevents hydrolysis complaints on slow-moving sizes
Carton label	Size, quantity, lot and order reference	Makes an incoming batch traceable in one scan

14Capacity Boundary Questions: What the Supplier Cannot Do

The most useful half hour of a supplier audit is the one where you look for the edges. Nobody volunteers a limit, so the limits have to be asked for directly, and the phrasing should make it easy to say no. A supplier who admits a boundary early is easier to work with than one who discovers the boundary during your first production order.

Four Questions That Draw the Edge

Question	Usually Available	Needs Evaluation or Tooling
Which pitches are moulded here?	The sizes held in the register	Anything outside the register, priced as a new master
What is the longest ring you can form?	Lengths covered by existing cavity blocks	Longer rings, which may become jointed or bought in
Which special compounds can you cast?	Standard PU grades and colours	Food-contact, antistatic or high-temperature grades, often with a minimum batch
Can you hold a tolerance across a year?	Yes, with a written band and a log	Tighter than the band, which needs a capability study first

Buyers running an aftermarket program tend to ask these questions in a different order, because their sizes change with every model year. The sequencing used in an automotive timing belt sourcing checklist is a good model for that situation, since range breadth matters more there than depth on a single size.

15Price, MOQ and Lead-Time Normalization

Two quotations for the same belt are rarely the same offer. One may include tooling, one may not; one may quote a unit price at 200 pieces, the other at 2,000. Normalize before you compare, or the comparison is theatre.

The Normalization Sheet

Cost Element	How to Normalize It	Common Industry Range
Tooling	Spread across the first-year volume and state who owns the master	Charged per new size when no cavity exists
Unit price basis	Convert both offers to a price per piece at your own annual quantity	Falls with volume, with a step where the mould changes
MOQ	Ask for the minimum with the existing mould and again with a new one	Often a few hundred pieces for established sizes, higher for new tooling
Lead time	Split into tooling, production and packing, then add freight separately	Weeks rather than days on established sizes, longer for new masters

Ranges here are the ones we see quoted across the trade, and any firm figure has to be confirmed against the actual drawing and required volume. Buyers who also purchase running metres of belt should keep the same sheet in use, since a rubber timing belt wholesale guide uses the same logic, and a mixed basket is often best priced through a full product catalog rather than size by size.

16Warranty and Claim Handling

A warranty is worthless unless the split between a defect and a consumption item is written down. Most disputes we see are not about the length of the period. They are about which party owns the failure.

What a Workable Clause Looks Like

Topic	Common Industry Position	Note
Period	12 to 18 months from shipment, or a running hour figure, whichever comes first	Confirmed against the actual duty and drawing
Defect items	Tooth shear, cord pull-out and joint or splice failure inside rated load	Judged against the golden sample and the size sheet
Consumption items	Normal abrasion, chemical attack by an unstated medium, misalignment and overload	Photographs and a drive record decide the split
Remedy	Replacement or credit, with freight and inspection agreed case by case	Written into the order acknowledgement

None of this is heavy paperwork. A complete RFQ, a sealed sample, a lot log and a photograph of each incoming pallet take less time than one line stoppage, and they turn a claim from an argument into a comparison. That is the whole point of auditing a SINOCONVE timing belt supplier on paper before the first order.

17Frequently Asked Questions About PU Timing Belt Sourcing

How do I qualify a PU timing belt manufacturer?

Why not simply approve a sample and place an order? Because the sample only proves that someone can make one belt carefully. Qualify the supplier on three paper items first: a pitch and profile list, a written joint declaration, and the inspection record from the previous production lot of the same size. Add a mould register check, and the case is nearly complete.

Which pitches should a supplier mould in-house?

At minimum the T5, T10 and AT families, plus XL and L, because those carry the volume. Above 8M and 14M, it is realistic for a supplier to form wide sections in segments or to buy in a size, as long as it declares which route was used and who inspected the result.

How can I verify that a belt is truly endless?

Inspect the flank under raking light for a lap or colour step, take micrometer readings at four positions around the ring, then run the belt at the lowest index rate where a joint produces a periodic tick. Destroy one sample and count cord ends in the cut face if the duty is critical.

What batch records should I request?

The last lot's inspection sheet with actual values, the mould number and run date, the compound lot with its hardness reading, and the cord lot reference. Ask for the same set again after any claimed process change, because a supplier that changes cord grade without telling you has changed the product.

Which dimensional items matter most on a PU timing belt?

Pitch length, then tooth flank profile, then width and thickness. If the belt runs over backside idlers, add concentricity and back flatness, and on a long-life drive add cord position from a sectioned sample.

What test evidence is reasonable to expect?

A hardness reading on every compound lot, a tooth shear figure per pitch and width, tensile and elongation data against the approved compound, and abrasion volume in mm3 where wear matters, plus heat ageing data on warm or humid plants.

What should a PU timing belt RFQ contain?

Ten fields are mandatory: pitch, tooth count, width, smallest pulley teeth, cord family, torque, speed, temperature range, backside duty and annual volume. Add the inspection document list and the packing requirement, and two quotations will finally be comparable on the same scope.

How long should sample validation take?

Six to ten weeks in total on a new size. Drawing review and a mould check take under a week, the prototype run adds one to two weeks, and a field trial needs two to six weeks depending on duty cycle. Compressing the trial is the expensive shortcut.

How is MOQ normally set for custom PU timing belts?

A few hundred pieces for a size that already has a mould, and more when a new master has to be cut. Ask for the two figures separately, so the tooling decision can be made on its own merits instead of being buried in a unit price.

What capability boundaries should I test with direct questions?

Ask which pitches are held in the mould register, the longest ring that can be formed, which special compounds can be cast without a dedicated batch, and whether a tolerance band can be held across a year with a written log. The answers reveal more than any catalogue.

How should claims be handled if batch variation appears?

Separate the defect from the consumption item before discussing cost. Send photographs of the failed section, the drive record and the size sheet, then compare the belt against the sealed golden sample. Inside the agreed band and within the stated load it is a consumption item; outside the band it is a supplier issue.

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• PU Timing Belts moulded in T, AT, MXL, XL and curvilinear pitches.
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• Product Catalog for the full range in one list.

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