MURFREESBORO, Tennessee — When it came time for the city of Murfreesboro solid waste department to replace a horizontal grinder used to process wood debris into mulch, department director Joey Smith observed demonstrations of grinders made by several manufacturers. When he wrote the bid specifications, they were a composite of the things he liked about various tub grinders. The city received several bids and ultimately officials chose a C.W. Mill Equipment Co. HogZilla tub grinder.
That was about 15 years ago. Joey was pleased with the machine’s performance and how it held up. “Most people say they get about eight years of life,” he said, from a grinder. The machine processed 50,000 tons of yard waste one year. This year the city will be close to that amount again because of a spate of storms that damaged trees.
When it finally came time to replace the tub grinder, the end result of the bidding process was a decision to purchase another HogZilla tub grinder. The new machine, a HogZilla TC-1564P, the largest tub grinder offered by C.W. Mill, arrived in August.
Joey, 57, has been working for the city since he was hired as director of the solid waste department in 2001. He previously worked for Waste Management, a national solid waste disposal business, for 14 years. “I started in the garbage, and still am,” he joked.
The city’s solid waste department provides household trash pickup for 45,000 homes. Joey oversees the work and operations of 40 employees.
Only homeowners are allowed to drop off wood debris and yard waste. The city also allows residents of neighboring Rutherford County to use the facility. Although contractors are not allowed to dispose of material at the site, Joey acknowledged that “you can’t catch everybody.” City officials are in the process of studying whether to let contractors unload wood debris at the site for a tipping fee.
The solid waste department accepts wood material up to 8 inches in diameter and up to 10 feet long. Most material falls within those parameters. The facility also accepts leaves and grass clippings.
Although homeowners generally abide by the limits on the size of material, it’s not unusual for the department to have to process larger wood debris. For example, sometimes other city departments offload wood debris from their various operations. Plus, the department makes exceptions for wood debris caused by storms, like a tornado that impacted the area in 2009. So the grinding operations may deal with much larger material and even stumps and root balls.
The department’s grinding operations are conducted on a 6-acre reinforced concrete pad that is 8 inches thick and topped with aluminum sulfate to extend the life of the surface. The quality is similar to that of a solid waste transfer station, noted Joey.
The city has offered solid waste disposal services for wood debris and yard waste since the early 1950s. The material was picked up, and burned or buried in a landfill. In the 1960s and 70s, when the limit was material only 4 inches in diameter, the department sent out employees with a small portable chipper to process material on-site at a homeowner’s location. Later it added equipment to pick up leaves during leaf season. The city invested in its first grinder, a horizontal grinder, in 1992.
The city also is under a state requirement to reduce the volume of solid waste that goes into a regional landfill. The grinding operations help the city divert wood debris that ordinarily would go to the landfill. For example, Murfreesboro collected 41,000 tons of household waste that was taken to the landfill in 2018; it also collected and processed into mulch 37,000 tons of yard waste.
When the horizontal grinder eventually needed to be replaced, Joey began researching options and eventually decided to solicit bids for a tub grinder. He was at a meeting with 35 other municipal solid waste directors and got a lot of questions about why he wanted a tub grinder instead of another horizontal grinder.
Joey’s rationale was simple. He wanted the capability to be able to grind material and take care of the city’s residents in case of a severe storm event. “I have to plan for the worst situation,” he said. “That’s why we went with the tub grinder.”
Severe storms, of course, can break off tree limbs, even blow down trees. A tub grinder is more accommodating when it comes to grinding stumps and root balls, according to Joey. Logs and limbs will lay relatively straight in the infeed of a horizontal grinder, but not a stump or root ball.
Joey wanted a grinder that could handle much larger material that would be generated from storm-damaged trees. Sure enough, a tornado struck the city on Good Friday in 2009. “We had an acre of stumps,” Joey recalled, and other wood debris.
One key feature that attracted Joey to HogZilla during the 2003 bidding process was the torque converter. “A big old transmission,” said Joey, who has familiarity with transmissions on solid waste trucks. He preferred the torque converter to machines that utilized a clutch.
“I also liked some of the safety features they had,” he added. HogZilla grinders come with a movable shield to stop material that may be ejected. “You can tell people (with a sign) not to get within 300 feet of this thing, but some resident will come right up to the sign.”
He was even asked by some other manufacturers why he chose a tub grinder instead of a horizontal grinder. “It’s just not what I needed or felt like we needed in Murfreesboro because of the limitations on certain things,” said Joey. “I know what the city’s expectations are and the residents’ expectations are if a storm comes through; they want it cleaned up and out of their yard.”
This year Murfreesboro has experienced four storms with damaging straight-line winds. Just before the new HogZilla arrived, the department had over 185,000 cubic yards of material stockpiled.
The TCII-1564P model is part of the HogZilla TC series of tub grinders, a series designed and built for high production in the harshest grinding applications.
The city bought a smaller model equipped with a knuckleboom loader and operator cab 14 years ago because officials didn’t want to spend additional money to purchase an excavator, noted Tim Wenger, vice president and sales manager for C.W. Mill. In recent years, as city officials began discussing replacing the HogZilla with a new machine, he advised them to budget for an excavator in order to invest in a larger grinder without a loader. “Anytime we have anything other than this (TC-1564P) model, we have to make concessions to the size of the grinder in order to get the loader mounted,” explained Tim.
C.W. Mill has made a number of improvements to its lineup of HogZilla grinders in recent years, noted Tim. For example, changes to the hydraulic system make it more easily accessible to perform maintenance. An optional backstop shield can be lowered hydraulically over the tub to prevent material from being thrown. “The backstop shield is the largest in the industry,” noted Tim. The Murfreesboro agency also opted for a fire suppression system on the grinder.
“They have a beautiful facility,” said Tim, referring to the solid waste department’s concrete slab. The ability to store material on the slab prevents the wood from being contaminated with wood and rocks, which wears down hammer tips.
The heart of the HogZilla TC series is the torque converter, which always allows the engine to perform at peak efficiency with multiplied torque. The engines can operate near governed speed throughout the work cycle regardless of the load requirements. The torque converter prevents lugging and needless racing of the engine while protecting it from shock and loads from torsion. The company warrantees the torque converters in its tub grinders for five years or 6,000 hours.
HogZilla TC series grinders have the biggest possible radiator pre-cleaner to help pre-filter out the most dirt and contaminants. The engine intake air is ducted from ahead of the radiator inside the pre-cleaner to capture the cleanest and coolest air. The engine exhaust assembly is configured with a special cover to keep chips out of the engine enclosure and material away from exhaust heat. Other covers, shields, and deflectors also help to protect the machine from material build up and damage.
Standard features include remote control, electronic horsepower controller, 60-degree radial stacking elevator, troughing roller conveyors and vulcanized conveyor belts, air compressor and hydraulic rod puller.
Options include mulch coloring attachment, bolt-in tire grinding package, tip and hammer variations, fire suppression, and thrown object restraint options.
C.W. Mill, which is based in Kansas, offers both electric and diesel-powered versions of tub grinders, and diesel units are available as track self-propelled machines and trailer-mounted machines; the company offers four series of trailer-mounted grinders. CW Mill also manufactures horizontal grinders as track self-propelled machines and trailer-mounted machines.
The new Hogzilla TC-1564P, powered by a Caterpillar Tier 4 C32 engine that generates approximately 1,000 hp, had been operating for about three weeks when Joey was interviewed. Like the department’s first HogZilla, it is a trailer-mounted machine that can be hauled by a semi-tractor.
“It has worked out beautifully,” said Joey. The biggest learning curve has been for running the excavator, but the operators are becoming more adept.
The new HogZilla is “a lot more sophisticated,” added Joey, and has high and low speed modes, depending on the grinding application.
“It’s hard to describe the difference between the two machines unless you’ve seen both of them,” said Joey, referring to the new grinder and the previous HogZilla. The previous self-loading grinder, with the cab and grapple, compressed the area that was available to work on and service the engine, he noted.
“The other thing we really love about this new machine is that you can get up under the engine. You can almost stand inside it, clean around the radiator, check the engine oil…The mechanics love it.” Access to fluids and filters is “very maintenance-friendly,” he added.
Joey also noted that C.W. Mill has made a number of improvements since the first HogZilla tub grinder the city purchased. “They changed the way they do some things.” For example, teflon rollers keep belts centered, and belt tensioning is simpler.
HogZilla provides about a week of training for operators and mechanics, noted Joey. The employees who would operate the machine got a few days of training, then the mechanics. After the training, they begin grinding operations under supervision of a C.W. Mill trainer. The mechanics are trained how to torque the tips and perform all the daily routine maintenance checks and procedures.
The solid waste department mechanics generally perform daily and routine maintenance, including oil changes and replacing various filters, before and after grinding. They also clean the machine, making sure no debris builds up around the tub or the conveyor belts.
C.W. Mill provides over-the-phone troubleshooting and technical support. It came in handy recently when they correctly diagnosed that a loose wire was responsible for a switch malfunction. The grinder came standard with a control panel that provides a lot of diagnostic features, noted Joey.
The city also purchased a Volvo 300 excavator to handle material and feed it to the tub grinder. Joey’s department previously had a Volvo 110A wheel loader, but he determined the excavator would be more efficient. The one machine handles and loads material into the tub grinder and also loads pickup trucks and trailers that residents bring to the yard to obtain mulch, and the excavator can perform both tasks faster, according to Joey.
The grindings are distributed free. About 20 percent go to local homeowners; the remaining 80 percent is hauled away by paper mills that use it for boiler fuel. Joey is beginning to explore the feasibility of selling the grindings to mills and other industrial users.