Free water draining:
A rubber crumb slurry containing between typically 5% to 10% solids is fed to the finishing line to “Dewatering Screen” units. These units are the vibrating conveyors that are specifically engineered for the major water reduction task with specific slope and appropriate mesh grids based on the production capacity and characteristics of the rubber.
Mechanical dewatering : (Extrusion)
By restricting the flow of rubber through the “Expeller®” die plate (hydraulic choke control), work is put into the rubber and internal barrel head pressures are effectively elevated to reach the required value for optimum crumb squeeze and moisture reduction.
Mechanical dryer: (Expansion)
The material is conveyed immediately into the feed section of the “Expander-Dryer®” barrel. The conveying section effectively begins to masticate the polymer (kneading action) which will result in a reduction in the polymer viscosity. The friction between the rotating flights and the polymer in this section will begin to gradually increase the polymer temperature.
Based on the type of the rubber and licensor procedures the mechanical expander may or may not be present in the rubber drying package.
The rubber is cut into small manageable wafers as it discharges from the die plate. The rubber is cut into small manageable wafers/crumbs as it discharges from the die plate. The milling unit can be chosen within cutting knife blades and hammer type systems. Ideally the dewatered wafers are dropped immediately into the Dryer unit feed hopper. The discharging product is now higher in solid content and will typically contain between 3% to 10% moisture based on the rubber type and production license.
The Dryer unit is generally considered to absorb the remaining volatile vapors and reach the minimum level of the moisture content while controlling the temperature of the rubber crumbs which should be the ideal condition for baling and packaging at the end of the line.
The dryer units can totally vary on the type based on the rubber type that your company produces. From Apron(Band) Dryers to Hot Box and Cold Box untis, they generally include feeding hopper units that should distribute the rubber with continuous and homogenous form, Temperature controlling Units, fans with heating medias, discharge and die plate with cutter head can be completely enclosed if needed. At the discharge point, the moisture remaining in the polymer is normally 2% or less (~0.5%) but is no longer bound in the polymer making it very easy to remove during conveying to the packaging system.
Vapor exhaust and pellet containment and conditioning:
The Dryer unit design can be equipped with vapor exhaust conditioning that will effectively contain the polymer and hot gases discharging from the Dyer. By adjusting the airflow between the heating input blower and exhaust blower to produce a negative pressure inside the Hot Box, the hot gases exploding from the polymer are effectively contained and removed from the process stream.
The ambient temperature inside of the Dryer units can be maintained at between its predefined operating range to prevent the re-condensation of the moisture vapor back into the dry polymer. The gases are then immediately exhausted off and the porous dry polymer is will be conveyed to the final stage of the rubber finishing line.
The violent conversion of liquid to gas produces a porous pellet that retains a very small amount of moisture that is then easily evaporated out of the product as it is conveyed to the packaging system.
Crumb rubber / pellet conveying:
Ideally the dry crumb will be gradually cooled as it is conveyed to the packaging system. Vibratory conveyors are most commonly used for conveying crumb rubber to help produce a more evenly cooled product, to prevent polymer “cold flow” and reduce rubber sticking to conveyor decks.
Maximum reasonable temperatures are maintained to ensure minimize bale cycling times. The moisture levels in the finished bale is normally required at 0.5% or less for most all polymer types. Some TPE grades will contain 1.0% or less in the pellet prior to baling, which meets acceptable industry standards.
To further reduce polymer sticking to the conveyor decks they are commonly coated with Teflon.
A vibrating feeder conveyor is used to feed both baling systems. The feeder is also designed with a dynamic braking device for controlled shutoff of product flow to the feeding hopper of the Bale press unit.
The Bale Press Unit:
The bale press unit is consisted of a feeding hopper which receives the ready to pack bale crumbs, the product then reaches the weighing basket that doses the product to a predefined value normally ranged between 25 to 40 kg based on your marketing strategies. The weighing system must be interlocked with the baling systems to ensure smooth operation and accurate weighments. Then the heavy duty hydraulic press with two stage hydraulic motor will come into action to produce the bales with capacity up to 240 bales/hour speed with client’s predefined dimensions. The height of the bales will vary based on the weight. The bales are ready to be packed at the last stage.
Bale Packaging Unit:
The product here will be wrapped and packed and will be monitored by check weigher and metal detector or even the dimension and defected bales can be easily identified and rejected. Finally, by aid of vacuum hoist partner or automatic robot palletizer, the bales are palletized in crates, labeled and the crate final weigh will be checked.
Finishing Line Control Systems:
The whole rubber finishing line is totally integrated with PLC based control system. The Process Automation and Factory Automation phases are generally separated in control logic system however the whole rubber finishing package is completely integrated. The control system is generally controlled through the DCS unit.
This is the end of the journey of the rubber and it is ready to be shipped to the end users.
At RAPCO, our outstanding deep engineering studies and polymer processing experience has taught us how important flexibility is for most applications. By using our solutions for mechanical dewatering and drying stages, we’re able to help manufacturers adjust moisture, viscosity porosity, temperature, and pressure of the polymer at specific points during processing, not only lowering downstream drying costs but improving the quality of the end product.
Additionally, with RAPCO’s “All-In-One” solutions, manufacturers continually struggle to stabilize the rubber reaction and stripping steps, often resulting in off-grade rubber, downtime, and even equipment failure.
Why to choose RAPCO for the Finishing Lines?
- RAPCO is flexible to provide Upgrades and Ongoing Support.
- RAPCO is able to completely to transfer the processing technology knowledge.
- RAPCO is capable of minimizing the operation bottlenecks based on removing the gap between the theoretical and operational knowledge.