Mechanical Fasteners Vs. Vulcanizing
- Published: Tuesday, 22 September 2009 08:43
Amid a global economic downturn, aggregate operations need to do everything they can to improve operating efficiencies and reduce costs. At the heart of plant operations is the conveyer systemóan excellent first checkpoint when seeking to optimize productivity.
A critical area of importance on any conveyor system is the splice, and in most aggregate operations, there are two preferred types of splicing methods: mechanical splicing, the process of joining belt ends by metal hinges or plates, and vulcanized splicing, the process of joining belt ends through heat and/or chemicals.
Understanding the pros and cons of each splicing method is extremely important when making an educated decision on which splicing method to use. What are the environmental factors that might affect the splice? Are workers up against time constraints? What are the costs associated with long conveyor downtimes? These are just some of the questions to ask when choosing between mechanical fastening and vulcanization.
The vulcanization process
Vulcanization is an involved procedure that, if done correctly by an expert, can offer a smooth splice with minimal risk of snagging, tearing, and other harmful wear to the belt. There are several different types of vulcanized splices, including stepped splices, finger splices and overlap splices, and two types of vulcanizing processes, hot and cold. Each process requires unique tools and an intimate knowledge of the rubber bonding process.
For both hot and cold vulcanization, the belt must be disassembled and each belt end properly prepared according to that particular beltís splicing recommendation. Belt preparation is crucial to ensure that the finished splice will hold and perform to its published tensile ratings.
With hot vulcanization, splices are heated and cured under pressure with a vulcanizing press. This process takes a minimum of eight hours. If a belt is retensioned and used before the splice is bonded and completely cooled, the splice will be less effective and may come apart completely, causing additional downtime.
Cold vulcanization does not employ a vulcanizing press, but rather uses a bonding agent that causes a chemical reaction to splice the two belt ends together.
When vulcanizing, several factors must be taken into account to ensure a high-quality splice. First, a vulcanized splice must be performed by an expert who is skilled and trained for the procedure and who has a thorough knowledge of solvents, bonding materials, and other cover and fill materials.
Second, the process requires a specific temperature, compression and dwell time of the equipment, in addition to a virtually moisture free work area.
Third, some types of belts may not allow for vulcanization at all. If a belt is old, dirty or unevenly worn, vulcanization is not a good option, because it wonít always cure evenly, which can result in a weaker splice.
The entire process for the vulcanized splicing of a 24-inch belt will take about eight to 11 hours, depending on working conditions. Wider belts may take longer. And because vulcanization often requires time for a specialized vulcanizing crew and equipment to be brought on site, plant operations can be shut down for half a day or more resulting in costly downtimes.
Ultimately, vulcanization may cost thousands of dollars per splice, considering material and laboróand thatís before considering the cost of downtime required to make the splice.
To summarize, use vulcanization as your splicing method when:
You have a clean belt thatís free of contaminating agents, such as oil, sand, and material fines:
- Your belt is compatible with adhesives of choice
- You have a new belt or belt without excessive wear
- You have a trusted, certified vulcanizer to perform the procedure
- The work environment is at an optimal temperature and moisture level
- You have easy access to the area you need to splice and plenty of room to work
- You have enough downtime available in your operation to allow for a properly installed vulcanized splice
An Alternative: Mechanical Fasteners
The speed and simplicity of mechanical splice installation represents major advantages over the vulcanization process. Depending on belt width and thickness, most mechanical splices can be finished in less than one hour and are installed by your own on-site crew with portable, easy-to-use installation tools. In the event that you need to make an unexpected splice, you wonít have to wait for professional assistance. Mechanical splices can also be made in restrictive environments, with no special regard for space, temperature, moisture, or contaminants. Plus, mechanical belt fasteners can be an excellent alternative given current economic pressures and budget cuts. With plants running their belts for longer periods of time, the investment in vulcanized materials and external labor may not be viable. Typically, assuming you have a two-man crew, labor and materials might run $2000 to vulcanize a belt versus around $100 for a mechanical splice.
Mechanical splicing also offers reduced belt waste and visibility of splice conditionó both of which can significantly reduce costs. Because vulcanized splices often require consumption from eight to 10 feet of belt length, conveyers may not have enough ìtake upî if more than one splice is necessary over time.
And, because a mechanical splice is visible, wear and deterioration is visibly apparent and can be taken care of prior to a complete belt failure. Vulcanized splices, in contrast, typically deteriorate from the inside out due to poor adhesion. The first sign of wear comes too late for any preventive measure, resulting in catastrophic failure and longer downtime.
Mechanical splicing and aggregate applications
As with vulcanization, there are several types of mechanical fasteners, each created for use with different belt widths, lengths, thicknesses, speeds, tensions, and cleaners. Identifying the correct fastener for your application is essential to ensuring maximum splice life and performance. Mechanical fasteners are available in two types, hinged and solid plate, and with a variety of attachment methods including rivets, bolts, and staples.
For aggregate plant applications, bolt solid plate fasteners allow for the greatest versatility. Bolt solid plate fasteners uses bolts to compress the top and bottom plates distributing splice tension evenly across the entire width of each fastener plate. For added strength and pull-out resistance, specially formed teeth penetrate deep into the belt carcass ñ without damaging the carcass fibers. Bolt solid plate fasteners use specially designed templates, punches and boring tools making it fast and easy to accurately punch holes into the belt. The installation can also be done on site using portable hand or power tools.
No matter what the belt condition, mechanical fasteners are a good choice for both new and older, worn belts. Bolt solid plate fasteners can be used on belts ranging from 3/16î to 15/16î (5 ñ 24 mm). Concerns about comparable vulcanized splice strength can also be dismissed; bolt solid plate fasteners have a long history of service on belts with mechanical fastener ratings of up to 620 P.I.W (105 kN/m). Although the bolt solid plate fastener can be used for a conventional 90 degree splice, if smaller pulley diameters are present (up to 25% smaller size than recommended for 90 degree splices) these fasteners will allow for a 45 degree splice to accommodate smaller pulleys.
In addition, bolt solid plate fasteners also provide several installation benefits in aggregate applications. Twin mounting bolts, built into each bottom plate simplifies handling and positioning beneath the belt for faster installation. A piloted bolt can also help speed installation because the piloted bolt tip cradles the nut securely in place, and simplifies installation by automatically aligning the bolt and nut threads.
Using a mechanical belt fastener is a great way to get more belt availability and reduced maintenance shifts. Mechanical fasteners are installed quickly and easily, on-site, with your own maintenance crews, usually in less than 60 minutes. The mechanical splice installation tools are easily transported to the job site and offer splice installers versatility in installation methods. Depending on the plantís available power source, mechanically attached bolt solid plate splices can be installed with as little as a basic installation tool and hammer, or with a modified electric installation tool. Vulcanizing a splice typically takes eight hours or more whereas a mechanical splice typically takes an hour. Some might ask if their operation can afford the seven extra hours in downtime it would take to vulcanize.
Mechanical fasteners can also be countersunk, by skiving the belt during the installation process so that the fastener plates are flush with the beltís cover, which eliminates interference with tight-fitting scrapers, skirtboards, and other conveyor components. Countersinking also strengthens the fastener-to-belt attachment by positioning the plates closer to the beltís load-bearing carcass fibers. The belt strength remains intact as only a portion of the top cover material is removed; the beltís vital carcass fabric is left intact.
Besides virtually eliminating fastener rip-outs, bolt solid plate splicing cuts downtime by giving maintenance crews more freedom in deciding when to replace a splice. Any splice damage or wear and tear is very visible on a mechanical splice and operators can finish a shift even with a few plates missing and not worry about belt failure.
Mechanical fastening vs. vulcanization: Get the facts
Every splicing method has its limitations and it is essential to get the facts before you decide how to splice your belt.
- Not all belts can be vulcanized.
Old and/or worn fabric belts are not well-suited to vulcanizing because the layers are weaker and will become brittle when heat is applied. In addition, older rubber belts are also poor candidates for vulcanizing, as the bondable properties of rubber deteriorate over time. Finally, vulcanizing requires additional belt length, so operations with little take-up simply may not have enough belt to work with.
- Vulcanizing requires appropriate environmental conditions.
Only clean, dry, and relatively warm conditions are suitable for vulcanizing. Chemical residue, excessive moisture and extreme temperatures can interfere with the curing of the adhesives and cause nicks and/or bubbles. These conditions, in turn, weaken the strength of the splice. In addition, vulcanizing can be extremely difficult in areas that arenít easily accessible.
- Vulcanized splices can fail without warning.
The early signs of adhesion breakdown in a vulcanized splice are nearly invisible to the naked eye. Often, operators arenít even aware that a vulcanized splice is experiencing problems until it failsñña catastrophic event that requires the immediate shut down of the line.
- Vulcanization requires a lot of downtime.
Vulcanization requires you to shut down your belt for a substantial amount of time. Not only does it take longer for the splice to cure, but vulcanizing is also at the mercy of the vulcanizerís schedule.
- Mechanical fasteners are compatible with almost any type of belt.
In addition to extendable, high stretch and worn belts, mechanical fasteners work with rubber plied belting, straight warp belting, PVC solid woven belting and they are also suitable for both temporary and permanent splices.
- Mechanical fasteners can be installed under virtually any conditions.
Unlike vulcanization, mechanical fasteners are not affected by temperature dirt, or humidity levels, so theyíre ideal for harsh environments.
- With mechanical fasteners, maintenance can be anticipated and scheduled.
Because mechanical fasteners can be visually inspected, itís simple to monitor splice performance and strength. This not only helps avoid sudden splice failures, but allows the scheduling of maintenance and repairs for the most convenient times.
- Mechanical fasteners interface seamlessly with components on a conveyor.
Many fasteners are available on the market that have low profiles allowing them to pass smoothly by cleaners and over pulleys. In addition, mechanical fasteners can be countersunk to create splices that are flush with your belt surface.
Conveyor belt and belt splice damage will always be a fact of life in most material-handling applications. Consequently, operations and maintenance personnel should have a thorough understanding of the available splicing and repair alternatives and how each method can affect the productivity and cost effectiveness of their operations.
New designs, materials, and processes are making mechanical splicing better than ever and incorporating mechanical belt fasteners into your splicing routine can provide numerous benefits for your output and bottom line. In most applications, including aggregate operations, mechanical splices offer the flexibility, economy and speed to keep material and labor costs down and avoid expensive downtime situations.
Chip Winiarski is Market Manager, Heavy Duty for Flexco, a leading manufacturer of mechanical fasteners, belt cleaners, and other maintenance tools and accessories. For more information on Flexcoís products for the aggregates industry, visit www.flexco.com and select ìAggregateî under the products tab.