Quick Answer
Conveyor belt vulcanizing can leave air bubbles when heat, pressure, joint preparation, or curing conditions are not uniform across the splice. Trapped air can form hidden voids or visible blisters that weaken the joint and increase the risk of early failure.
The HOLO company offers rubber belt vulcanizing presses with control heating and pressure systems to ensure uniform splicing. In accordance with application requirements, press design allows different belt widths and field conditions, providing assistance in stabilizing heating and pressure conditions for the curing and cooling process.
How Bubbles Form in Vulcanized Joints
In the process of conveyor belt vulcanizing, prepared splice layers should be combined in controlled conditions of heating and pressure for correct flow and curing of the material used for connection. If air is contained in layers or the pressuring process is not uniform, a bubble will form instead of elimination.
Formation of a bubble in most cases is only a symptom of a certain problem. A splice can appear normal on its periphery, while at the same time an air bubble exists inside the splice due to improper preparation, lay-up, contact or pressuring of layers.
Root Cause 1: Uneven Heating Plate Temperature
The different temperature of the platen will cause one part of the splice to be cured differently from the other part. This will have an effect on the flow and curing of the rubber in the splice.
Before a splice is made for production, check the process condition set before starting the splice. It is better to check the heating plates, sensors, blankets, and contact surfaces rather than just the controller display.
Root Cause 2: Trapped Air from Poor Preparation
Poor preparation is a common source of conveyor belt joint bubbles because contamination, uneven skiving, wrinkles, or incorrect bonding-layer placement can create spaces that pressure cannot close. Dust, moisture, or uneven tie-gum application can also interrupt contact.
The hidden failure point is often beneath the visible splice surface. Keep prepared surfaces clean and aligned, remove loose material, avoid trapped folds, and follow the belt manufacturer’s procedure for bonding materials before closing the press.
Root Cause 3: Incorrect Pressure or Time
Pressure that is too low, uneven, or applied incorrectly can leave vulcanized splice air pockets inside the joint. Excessive pressure can cause another problem by forcing bonding material away from the intended area, so increasing pressure is not automatically a fix.
Curing time must match the belt construction, compound, splice design, and validated process. Do not copy a generic cycle from another belt; confirm the required settings for the actual belt and press, then keep the process consistent.
How to Diagnose Bubbles Before Failure
Inspect the finished splice for raised areas, blisters, soft spots, edge irregularities, or unusual surface changes. If one section feels different from the surrounding belt or shows localized lifting, investigate it before returning the conveyor to service.
For recurring defects, compare the affected location with the press layout and process records. Check preparation, heating uniformity, pressure distribution, bonding-layer placement, and curing history before changing machine settings.
| Failure sign | Likely cause | First check |
|---|---|---|
| Localized blister | Trapped air or poor layer contact | Preparation and lay-up |
| Uneven surface | Heating or pressure variation | Platen condition and pressure |
| Edge lifting | Incomplete bonding or alignment issue | Joint edges and bonding layer |
| Repeated bubble in same area | Local press or heating issue | Press layout and temperature records |
Step-by-Step Fix for a Bubble-Free Splice
A reliable conveyor belt vulcanizing workflow starts by separating preparation problems from press-setting problems. Rework should follow the belt manufacturer’s splice procedure instead of simply increasing temperature or pressure.
- Prepare: Recheck cut geometry, skiving, cleanliness, alignment, and bonding-layer placement.
- Set the press: Confirm platen condition, temperature uniformity, pressure system, and sensor readings.
- Cure: Follow the validated temperature, pressure, and time for the belt construction, then cool as required before handling.
- Inspect: Check for blisters, edge lifting, uneven surfaces, or incomplete bonding before commissioning.
This sequence improves rubber belt splicing quality by giving technicians a repeatable diagnostic path. It also reduces rework because each stage can be checked before the next one begins.
Choosing a Vulcanizing Press with Uniform Heating
A reliable conveyor belt vulcanizer should provide stable heating across the splice area, controlled pressure, clear temperature monitoring, and cooling suited to the application. Uniformity matters because a press can show the correct controller temperature while local variations still create inconsistent curing conditions.
For larger field splices, frame stability, pressure-bag condition, belt-width capacity, assembly time, and transport requirements affect efficiency. HOLO’s sectional rubber conveyor belt vulcanizing press uses a thin heating-plate design and hydraulic pressure system, while its heavy-duty hot vulcanizing press provides temperature and pressure monitoring for steel-cord and fabric belts.
For steel-cord conveyor belts, the published ISO 15236-4:2004 addresses the design, dimensions, requirements, and marking of vulcanized belt joints. It is specific to steel-cord belts, so it should not be treated as a universal splicing procedure for every rubber belt.
Heavy-duty two-piece vulcanizing press for steel cord and fabric belts
Modular frame structure for fast assembly and easy transportation
Conclusion: Talk to HOLO About Vulcanizing Presses
Reliable conveyor belt vulcanizing depends on controlled preparation, heating, pressure, curing time, and cooling across the full splice. When those conditions are consistent, technicians can reduce hidden voids, repeat work, and premature joint failures.
For contractors and maintenance teams, equipment that supports uniform heating and stable pressure can improve commissioning confidence and workflow consistency. Explore HOLO products when evaluating a press for belt width, splice construction, field conditions, and production requirements.
FAQ
1. What Causes Air Bubbles in a Vulcanized Conveyor Belt Joint?
Air bubbles usually result from trapped air, poor surface preparation, uneven heating, inadequate pressure distribution, or an incorrect curing cycle. The defect should be traced to preparation and press conditions rather than treated as a surface-only problem.
2. How Can I Prevent Bubbles During Belt Vulcanizing?
Keep splice surfaces clean and aligned, verify heating and pressure uniformity, and follow the validated curing cycle for the specific belt construction. Do not change temperature or pressure blindly when a defect appears.
3. Can a Bubble in a Vulcanized Splice Be Ignored?
No. A visible bubble or blister should be assessed before commissioning because incomplete bonding or an internal void can reduce joint reliability and may worsen under operation.
