The business of recycling scrap tires is evolving. Until more recently, most processors performed just primary reduction – reducing whole scrap tires to various size strips of rough shred. But rough tire shred is co-mingled waste – a blend of rubber, steel wire and synthetic fiber. In some cases, over 25% of the weight of the tire can be steel wire and non-rubber content. Removing the steel and non-rubber components creates a host of new market opportunities for reclaimed rubber.

Markets such as rubber mats, sports and recreational playing surfaces or raw materials for rubber compression molding are just a few of these newer applications. To tap these higher value-added opportunities, scrap tire processors need the right equipment to extract the steel from rubber shred. Enter…the primary rubber granulator.

In conversation, there are several terms for this product category. Trade names such as “rasper,” “grizzly” or “liberator” are often used interchangeably to describe equipment that performs the function of a primary granulator. Semantics aside, it’s the machines that strip steel wire from recycled tire rubber that are the focus of this month’s spotlight.

Choosing a primary granulator
Charlie Astafan, general manager of Columbus-McKinnon Corporation’s Sarasota, Florida operations said, “There are essentially two kinds of customers in the market for a primary rubber granulator. First, there’s the provider of higher grade TDF that needs a smaller, cleaner, more wire-free product. Other customers are typically involved in civil engineering applications.” Both are part of a growing market for higher-grade reclaimed rubber.

There are a number of points to consider when choosing the right primary granulator for your needs. Charlie Astafan points out, “We like to begin by asking a lot of questions. Questions such as what volume of tires a customer may be processing in a single shift, or 24-hour period. We also need to know what percentage of the inbound material is passenger car, truck or specialty tires, and if they plan to process mixed material or run each type separately. That tells us how large the infeed throat must be, and gives us some insight as to whether single pass or multiple pass configurations are necessary at different points in the line. There are a lot of numbers to gather,” he said.

Other points are less simple to quantify. Questions such as training, start-up and post-sale support, parts availability, warranty and brand preference come into play. Invariably, price and financing are important as well. Mr. Astafan notes, “Provided the right equipment is in place for the need, customers should be looking at the lowest total cost over time. Depreciation is an operator’s single largest expense. Given volumes and mix of material processed, it’s important to know how long a granulator will run before a rebuild may be needed. Other costs such as electricity, blade life, screens and routine maintenance will vary. All of these expenses should be considered to arrive at the best possible fit for each customer,” he added.

Due to the steel wire content of passenger car tires in particular, primary granulators can generate a lot of heat while in operation. As an optional safeguard, some manufacturers offer on-board fire detection and suppression capabilities. In conjunction with sprinklers, these options may result in cost savings on business insurance as well. According to Columbus-McKinnon Corporation, fire detection/suppression options would typically run less than 5% of the initial cost of the granulator.

How they work
In the tire recycling process, primary granulators are positioned just downstream from the shredder, or primary reducer – in some cases, several steps downstream. There’s a lot of variety in how a tire recycling line may be configured, due in large part to differing needs of the operation and its customers, and the inherent differences in available equipment. Typical set-ups include a primary reducer, a secondary shredder, a classifier to remove synthetic fibers, etc., and a primary granulator. Some operations include secondary granulators or grinders for crumb rubber production at the end of the process.

In most tire recycling operations, infeed material to the granulator ranges in size from four inch to six-inch shred. Once in the feed hopper, rubber shred enters the rotor chamber where rubber and steel separation begins. Tom Wendt, Jr., sales manager of Wendt Corporation, Tonawanda, New York said, “The granulator is a relatively low speed horizontal rotor. It turns at about 120 rpm and strips the steel wire from reclaimed rubber. It’s the special shape and relief angle of the knives that makes this process so effective.”

Balancing throughput, or infeed material with finished product is accomplished by way of more sophisticated electrical controls. “Sensors in the rotor measure the amperage draw, which reflects load on the machine,” said Tom Wendt, Jr. “As material passes through the screen and exits the rotor chamber, the amperage draw for the rotor drops and a signal is sent to the feed conveyor. That starts or speeds up material delivery to the rotor, keeping the process balanced,” he added.

Maintenance considerations
Keeping a granulator in top running condition isn’t terribly difficult. John Crowley, director of sales & marketing for Granutech-Saturn Corporation in Grand Prairie, Texas, makers of the popular “Grizzly” granulators observes, “Aside from cleaning and lubrication, it’s a matter of paying attention to blades (knives). Our machine features a combination of 10 stationary blades and 50 rotary blades. We recommend that on average, the blade gap be checked and adjusted every 40 – 60 hours of operation. It’s something that takes an experienced technician no longer than 45 minutes to do. Depending on the quality and cleanliness of the infeed material, the blade service interval can extend out as far as every 120 hours of operation.”

Granutech-Saturn further recommends that blades be rotated every other time the gap is checked and set. John Crowley continues, “There are four cutting surfaces to every blade, each with a 90 degree edge. Granulator blades are rotated to keep the cutting edges fresh and sharp. That keeps the product size consistent and keeps the quality of the output material as high as possible.”

As a simple precaution, most customers prefer to keep several sets of blades on hand. Tom Wendt, Jr. observes, “It’s not uncommon for customers to have three sets of knives – one set in use, one set on the shelf and a third set out for refurbishing.” Rotary knives wear a bit more quickly than the stationary knives. Refurbishing usually involves welding, heat-treating and quenching for hardness and durability.

Screens are another wear item that must be checked periodically and replaced as needed. Operators should be sure all screens are open, free of blockage and within tolerance to size finished product as specified.

In tire recycling, the North American market is about 10 years ahead of what’s going on in Europe. It was just July of 2003 that whole scrap tires were banned from most EU member landfills. In contrast, the U.S. processes about 80% of the scrap tires generated each year. Charlie Astafan notes, “We’ve seen a spike in export activity for tire recycling equipment during the past year. Exchange rates are favorable for many overseas customers and there’s a lot of U.S. built product going to Europe and South America right now,” he said. As more and more applications for recycled tire rubber are developed overseas, this trend is expected to continue.