Conveyor belt splicing: hot and cold vulcanised and mechanical splices, how a stepped splice is made, splice faults, and the register that finds them early
Conveyor belt splicing from the maintenance side: hot vulcanised splices for fabric and steel cord belts, cold vulcanised splices and mechanical fasteners compared, how a stepped fabric splice is set out, cut, laid up and cured, the faults that show a splice going bad, and a splice register with length measured at each inspection. With a plan and section drawing of a stepped splice.
Key takeaways
- A splice is the weakest part of a conveyor belt, and most belt failures that are not damage start at one.
- Hot vulcanised splices are the strongest and the only choice for steel cord belts. Cold vulcanised and mechanical splices trade strength for speed and simplicity.
- A fabric splice is cut in steps, one fewer than the number of plies, on a bias so it does not meet a pulley all at once.
- Square to the centreline, clean and dry, and cured for the full time: those three decide whether a vulcanised splice lasts.
- Number every splice, measure its length between fixed marks at each inspection, and record failures against it. Growth in length is the early warning.
A belt has three splices. Two of them have run for years. The third was made in the rain at the end of a long shutdown, cured for less than the full time, and is now lifting at its leading step. Nobody knows which one it is, because none of the splices are numbered, and the first sign anyone sees will be the belt parting under load.
This guide covers conveyor belt splicing from the maintenance side: hot vulcanised, cold vulcanised and mechanical splices, how a stepped fabric splice is made, the faults that show a splice going bad, and the register and inspection that find them early. It sits beside the guides to conveyor belt tracking and conveyor pulleys and lagging. The dimensions shown are illustrative. The real ones come from the belt maker's splice instructions.
Types of belt splice
The splice is chosen by the belt construction, its tension, the time and conditions available, and what a failure would cost. Steel cord belts are always hot vulcanised. Fabric belts on main conveyors are usually hot vulcanised too, with cold splices and fasteners used on lighter belts and for repairs.
| Type | How it is made | Suits and limits |
|---|---|---|
| Hot vulcanised, fabric belt | The plies are cut back in steps, bonded with uncured rubber and cured in a heated press | The strongest and smoothest fabric splice, needs a press, power, a dry site and several hours |
| Hot vulcanised, steel cord belt | The cords from each end are laid between each other in a set pattern, embedded in rubber and cured in a press | The only option for steel cord belts, laid out to the belt maker's splice design for that rating |
| Cold vulcanised | The plies are stepped as for a hot splice and bonded with a cold curing adhesive, with no press | Quicker to set up, suits lighter fabric belts, and is sensitive to humidity, cleanliness and cure time |
| Mechanical fasteners | Hinged or plate fasteners are bolted or stapled across the squared belt ends | Fast and needs little equipment, so suits repairs and short belts, but is weaker, lets fines through and is hard on scrapers |
How a stepped fabric splice is made
In a fabric belt the strength is in the plies. A stepped splice cuts each end back one ply at a time so that the plies of the two ends overlap in steps, and the load passes from ply to ply through the rubber between them. A four ply belt has three steps. The whole splice runs on a bias across the belt.
The quality of a vulcanised splice is decided before the press closes. Squareness to the centreline, clean and dry surfaces, and the right materials matter more than anything done afterwards, which is why splicing is best done under cover, by a trained crew, with time allowed in the shutdown plan.
| Step | What happens | What to watch |
|---|---|---|
| Set up | Clamp both ends, mark the belt centreline over a long length on each side, and set out the splice length and bias | A splice that is not square to the centreline makes the belt shift sideways at every pass |
| Cut the steps | Cut through one ply at a time and peel it back, one step per ply less one, without nicking the ply below | A cut into the next ply is a weak line across the splice |
| Buff and clean | Buff the exposed plies and cover edges to a clean, dry, slightly rough surface | Contamination and moisture are the usual causes of a splice that lets go |
| Lay up | Apply cement and tie gum, bring the ends together on the centrelines, and fill the cover with new rubber | Steps meet without gaps or overlaps, and the joint is no thicker than the belt |
| Cure | Close the press and hold the temperature and pressure for the time the belt thickness needs, then cool under pressure | Under cure leaves a weak bond, and opening the press hot can blister the cover |
| Finish and record | Trim, check squareness and thickness, and record the splice in the register | Each splice has a number, a position on the belt, a date, a type and a crew |
A splice that is not square to the centreline makes the belt run off at the same point every revolution. No idler adjustment fixes it.
Splice faults
Splice faults usually start small. A step edge lifts, a cover blisters, a fastener works loose, or the splice slowly lengthens as the bond creeps. Caught early, a splice can be repaired or remade in a planned stop. Missed, it parts under load, often taking structure, chutes and a long downtime with it.
| Fault | Likely cause | What it looks like |
|---|---|---|
| Step lifting or ply separation | Contamination, moisture or under cure in the bond | A ply edge lifting at the leading step, often at the belt edges first |
| Splice not square | Ends cut or joined off the belt centreline | The belt runs off at the same point every revolution, then comes back |
| Cover blisters | Trapped air or solvent, or the press opened before cooling | Raised patches on the cover over the splice |
| Splice growing in length | The bond creeping under tension, the start of failure | The distance between reference marks either side of the splice increases |
| Fastener pull out or broken plates | Fasteners worn, the wrong size for the belt, or pulleys too small for them | Missing or loose fasteners, a torn belt end behind the plates |
| Cord pull out | Low cord adhesion or a splice made short of the design length | Cords exposed or the splice lengthening on a steel cord belt |
Inspecting splices and keeping the register
A splice register turns splice condition into something that can be trended. Each splice gets a number and a position measured from a fixed mark, so it can be found on the belt, and each one has its type, date and crew recorded. Inspections on the conveyor route record its condition and length, and failures go into the maintenance log against the splice. Over time the register shows which splice types, conditions and crews last, which is the evidence for the next splicing contract.
| Task | What it involves | When |
|---|---|---|
| Splice register | Every splice numbered, its type, date, crew and distance from a fixed mark | Kept current, and updated at every new splice or belt change |
| Visual check | Steps, edges, cover and fasteners at each splice | On the conveyor route, with the belt stopped and isolated or from a safe viewing point |
| Splice length | The distance between paint marks or studs either side of each splice | Recorded each inspection, so growth shows as a trend |
| Fastener check | Fasteners tight, plates intact, the belt end behind them sound | Every inspection on a belt with mechanical splices |
| Scraper and pulley contact | Scraper blades not catching the splice, no damage from small pulleys | When scrapers are changed, and after any new splice |
| Belt and splice history | Each failure recorded against the splice and belt in the maintenance log | Reviewed when choosing splice type and contractor |
Common mistakes
- Splicing in wet or dusty conditions without cover, and curing short to make the end of a shutdown.
- Setting the splice out without a long centreline on each belt end.
- Cutting into the ply below while stepping the belt.
- Leaving mechanical fasteners in place as a permanent repair on a main belt.
- No splice numbers, so a failing splice cannot be tracked or found.
- Not measuring splice length, so growth goes unnoticed until the splice parts.
- Scrapers set so hard that they catch splices and fasteners.
Common questions
What is conveyor belt splicing?
Belt splicing is joining the two ends of a conveyor belt to make it endless, when a belt is installed, replaced in sections or repaired. The joint is either vulcanised, where the layers of the belt are bonded with rubber under heat and pressure or with a cold curing adhesive, or mechanical, where metal fasteners are fixed across the belt ends.
What is the difference between hot and cold vulcanising?
Hot vulcanising cures uncured rubber between the belt layers in a heated press, which gives the strongest bond and suits steel cord and high tension fabric belts. Cold vulcanising bonds the layers with an adhesive that cures at ambient temperature, so no press is needed, but the bond is more sensitive to humidity, cleanliness and cure time and is generally used on lighter fabric belts.
When should mechanical belt fasteners be used?
Mechanical fasteners suit short belts, lighter duties and emergency repairs, because they can be fitted quickly with simple tools and no curing time. They are weaker than a vulcanised splice, let fines through onto the return run, need pulleys large enough for the fastener size, and are hard on belt scrapers. Many sites use them to get running again and plan a vulcanised splice for the next stop.
Why is a belt splice cut on a bias?
A bias means the splice runs across the belt at an angle, so it enters a pulley gradually instead of along its whole width at once. That spreads the bending stress and the impact as the splice passes pulleys and scrapers. The bias and step lengths for a given belt come from the belt maker's splice instructions.
How do you know a belt splice is failing?
Common signs are a ply edge lifting at a step, blisters in the cover, missing or loose fasteners, and the splice growing in length. Measuring the distance between marks either side of each splice at every inspection shows growth as a trend, often before anything is visible. A belt that wanders at the same point every revolution may have a splice that is not square.
Key terms
Plain-language definitions from our glossary for the concepts this article leans on.
Standards and further reading
- ISO 15236-4:2004 Steel cord conveyor belts, part 4: vulcanized belt joints (ISO)
- Belt Conveyors for Bulk Materials, 7th edition (Conveyor Equipment Manufacturers Association (CEMA))
- AS/NZS 4024.3610:2015 Safety of machinery, conveyors, general requirements (Standards Australia)
Related case studies and tools
- Reliability engineering and asset strategy program (case study)
Related reading
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