Conveyor belt repair: Vulcanization, metal fasteners or cold curing?
Whether you’re a maintenance or engineering manager at a snack food plant or oversee conveyor belt repairs at a distribution center, you know even the best-designed conveyor belts may need repairs to get to a replacement window and avoid a breakdown. It’s the nature of the rigorous work conveyor systems do. But when a conveyor belt starts to show signs of wear or has a full-blown breakdown, you need to know which repair methods are available.
Understanding how to efficiently repair belts is an essential skill for any maintenance or engineering manager, ensuring your plant can return to full operating capacity. Here we’ll describe the types of conveyor belt damage and common repair methods, then explain the important distinction between food and non-food belt repair.
Types of conveyor belt damage
Though any damage to a belt is undesirable, certain types of damage are more indicative towards immediate failure than others. Strings and frays can be trimmed and the belt can continue to run, though a repair or replacement may be warranted soon. Rips, tears and fingers or metal lacing popping loose on a splice means imminent catastrophic failure.
Another way to evaluate conveyor belt damage is with a rule of thumb from the NIBA: If no more than 25% of the belt width is involved in the damage, a repair is practical. When more then 25% of the width of the belt is damaged, a full resplice or replacement is preferable.
These are the main methods used to repair a damaged belt.
Vulcanization — the use of heat, time and pressure to re-splice a belt — is the most reliable conveyor belt repair method, as it creates the highest return to original belt strength. The vulcanization technique depends on the type of belt cover material: Thermoset rubber covered or thermoplastic covered.
Thermoset rubber belt cover examples are natural rubber, SBR, neoprene and nitrile and are common in non-food applications. Thermoplastic belt covers include PVC, polyurethane and polyolefin and are used in applications with direct food contact. For more information on the difference between these belt cover materials, check out this resource from the NIBA.
To repair belts with thermoset rubber covers, low heat (around 250 degrees Fahrenheit) vulcanization and an hour cooling period is used. For thermoplastic covers, high heat vulcanization is used (325 to 375 degrees Fahrenheit) with a cool time of around six minutes.
Vulcanization is the best and most dependable repair method for its speed and reliable return to original belt strength. When a thermoset rubber covered belt is damaged, this is the first choice for maintenance managers. However, it should be noted that when there is cover damage on a food-grade belt (a.k.a. thermoplastic covered belts), the damage is almost always non-repairable for sanitation concerns; in those scenarios, replacement is the best option.
A second option for conveyor belt repair, metal fasteners are quick and easy to apply. On the downside, metal fasteners offer considerably less strength than vulcanization, and there is also potential for lacing to pop up. This can cut workers, the product, or even break off and end up in the production line — making them unsuitable to repair food-grade belts.
Metal fasteners are a good back-up repair option for non-food-grade belts and should be used only to provide a temporary solution until the belt can be vulcanized or replaced. Given their risks for safety and belt reliability, metal fasteners are not meant to act as a permanent solution.
Cold curing (cold vulcanization)
The final and least desirable repair method is cold curing (also known as cold vulcanization). The two-part cement is made up of a base compound and a curing agent. Under time and pressure, the curing agent solidifies and bonds with the surface.
Cold curing is used only when space constraints in the plant don’t allow vulcanization equipment to access the belt. This method is the least desirable, however, because you must wait 24 to 36 hours for the curing agent to set, and the cement creates a stiff, rigid surface that poses issues at transfer points. This repair method should only be utilized by maintenance managers if no other repair option is viable and immediate replacement isn’t possible.
To summarize, vulcanization is the first choice for maintenance managers for repairing belts, with metal fasteners providing a quick-fix option until there is a window of downtime for vulcanization or replacement. Cold curing or cold vulcanization is a last resort repair method.
A note on repair vs. replacement
The aforementioned repair methods are not meant to take the place of getting a new belt, though that may seem more appealing to maintenance managers than spending money on a whole new belt. But vulcanization, metal fasteners and cold curing are best used as a temporary solution until you can find a window of time to replace the belt. This saves you from the future liability of catastrophic belt failure and a hit to overall plant reliability.
As noted in the vulcanization section, there is an important distinction between repairing food-grade and non-food-grade belts. Belts conveying non-food products can be repaired with vulcanization, metal fasteners or cold curing without concerns for sanitation. But with food-grade belts, the liability of a cover repair is extremely high. The belt must be extremely clean (free of oils, contaminants and foreign materials) to resplice, and your exposure to inspection services and product recalls outweighs the benefits. With food-grade belts, replacement is the safest option.
Conveyor belt maintenance is a complex but essential part of any highly efficient plant. For more industry-approved advice from conveyor belting experts, download our Guide to Conveyor Belt Maintenance and Repair. We offer insights on conveyor belt repair, advice on troubleshooting tracking issues and a printable checklist for an improved maintenance program — freeing up your time to focus on improving plant productivity.