Proper engineering design and equipment reliability are essential to a profitable aggregate processing operation; without which significant downtime and other financial losses are inevitable.
Proper engineering design and equipment reliability are essential to a profitable aggregate processing operation. Just a small interruption in production can affect a company’s bottom line. If your plant is not operational then you are not making money. A primary purpose of your equipment provider and servicer is to get you up and running no matter what brand(s) you are using – a team who are not only experts on their components but also on their competitors’ components. A team who can resolve your problems, alleviate pains, and reduce your company’s operating and maintenance expenses – increasing your R.O.I. Here is an excellent example of how our conscientious solutions team did just that.
Within one month of operation, the company observed the rotary counterflow drum mixer drifting and lunging uphill and downhill. The great force of a unit that is 11 ft. in diameter x 50 ft. long rotating with 250 HP did not just run hard against the thrust rollers (which holds the unit in either the uphill or downhill position), but impacted them hard enough to tear them loose from their hard mounts and even breaking the idlers themselves at times. Within their first 30 days of operation, this failed design caused four of the thrust rollers to rip loose – causing their entire plant to shut down.
In 2005 a major U.S. aggregate processor wanted to consolidate some of their production facilities in the Midwest and decided to go with a large 600 TPH plant. They contracted for a ‘super plant’ with a major manufacturer, who assured the customer that they could supply the plant without any major problems. Yet, appearing to only upsize one of the OEM’s existing models – without executing a thorough engineering study and comprehensive structural design analysis, a string of costly major problems began unfurling.
Operational damage to thrust rollers, tires and trunnions can often be avoided through proper plant design and precise alignment.
Since the thrust rollers sat at an elevation of 11 ft. in the air, it was very difficult, cumbersome, and concerning safety-wise to get access to them to perform damage repair and component replacement. Plant breakdowns became so predictable that the company was forced to purchase an $80,000 man-lift to provide them with sufficient access to safely change out the broken thrust rollers. Without a better solution on hand, the designated change-out crew had to work hard to reduce the change-out time down from a few days to between four to seven hours that were required to do the removals and replacements.
An $80,000 manlift had to be purchased to minimize downtime every time the thrust rollers had to be replaced. Although nice to have onsite for maintenance, that was a painful and avoidable expense.
The repetitive scenario for their multiple emergency breakdowns required calling the mobile changeout team, positioning the tools and equipment, and waiting for plant components to cool down to a safe temperature. Meanwhile, as the plant remained idle and the silos stood empty, a queue of hauling trucks would line up for blocks – waiting for their orders to be filled. Imagine the disappointment, frustration, stress and dread this repeated scenario caused the plant operators and owners!
Unscheduled plant downtime from breakdowns is expensive for plant owners and negatively impact their customers, including material haulers lined up, waiting, and delayed from performing their jobs.
Within the first two years of operation, the company called on the OEM to provide support and some warranty consideration to help lessen their financial losses. The OEM did not honor the request and indicated they would consider looking into the equipment problems as a paid service. Upon looking into the problems, they were unable to fix the root cause of the issues. The operating company was simply told they needed to learn how to operate the plant in a better manner per the written guidelines and ensure that the tires and trunnions were aligned properly. The OEM themselves could not do what they were asking the customer to do.
Throughout the next 10 years, the company experienced nothing but trouble from the OEM’s 11’ x 50’ dryer. During that time, 28 thrust rollers were sheared off, multiple tire-rigging bolts broke, numerous discharge sweep end-rings wore or broke off, and they never truly had operational control of the drum.
Hoping to remedy the situation, the company purchased new heavier duty trunnions, bearing assemblies and trunnion bases from another source, but that didn’t solve their problems. In fact, the problem became more severe. Their next step was to bring in an independent company to diagnose and resolved the issues. But that company failed to get the drum under control. Meanwhile damaged thrust rollers continued to pile up in the scrap yard behind the plant.
Unbelievable damage to thrust rollers, trunnions and tires can result from improper design. In the poorly designed system revealed in this article, 28 thrust rollers had been torn off from the uphill and downhill thrust of its dryer.
After several attempts to remedy the situation, enduring breakdowns for nine years, the company engaged us at Louisville Dryer Company (LDC) to assess and resolve their drum control problems. Following our initial onsite inspection and measurements of the relevant components, we dispatched a field team of engineers and technicians to observe the problematic dryer in operation. Following several days of inspecting, measuring, and testing, our team came to some dramatic conclusions.
Our solutions team observed that when the rotary dryer heated up and expanded, the supporting base and unitary frame heated up at a different rate. Sean Kyser, LDC Project Engineer, reports that “there was a significant difference between static non-loaded conditions vs. dynamic loaded conditions. This system had a built-in problem of deflection because it allowed movement of the trunnion and base. Thus, the dryer did not have a solid operational base of carrier roll trunnions, framework and thrust rollers.”
It was revealed that the OEM had not had this 600TPH design aggregate dryer system back when they had originally agreed to supply it. They basically had only upscaled the motor horsepower and trunnion size – without upgrading the frame, base support and thrust rollers. Such a quick manufacturing approach ignored fundamental engineering practices. Our team further determined that the OEM’s drum frame had no gusset support or enough trunnion cross-beaming to support the weight of the drum – especially when loaded.
We engineered optimal solutions and submitted our recommendations to the customer. The suggested remedy was to stabilize the dryer by constructing a monolithic concrete pier under both trunnion base assemblies. By building a foundation directly under the load-bearing of the trunnions, this method would eliminate all deflection and vibration in both the trunnion base supports and the dryer main axle beam. The customer agreed with the solution and the project was set into motion.
To stabilize the dryer, the Louisville Dryer field service team constructed monolithic concrete piers beneath the trunnions.
The customer also engaged us to build a completely new replacement rotary dryer and separate bases to be isolated on concrete foundations. The foundations were installed and adjusted to the thousandths for stability and parallel alignment with the tires.
Louisville Dryer Company provided the new replacement rotary dryer.
Ed Stump, Sr. Installer with Louisville Dryer, oversaw the change-out and commissioning of the new replacement shell while Steve Smith, LDC Sr. Field Technician, was on-site to optically align and record the elevations and slope. They oversaw the concrete pouring and inspected the grout for new piers on which to mount the trunnion bases. By transferring all the load from the drum directly into the pier, the defection and vibration was eliminated. Further accelerated trunnion and tire wear was avoided, and the recurring thrust roller/idler damage and expensive replacement problems were solved.
After everything was aligned and the trunnions set, start-up was a success. Ever since the repair/replacement solution was provided in early 2017, the drum has produced mix flawlessly and under control. The trunnion drive motor amps dropped, and stack temps are the best they have ever been. Major pains were alleviated, the owner/operator’s investment was recovered.
The Louisville Dryer replacement drum has processed over 3 million tons – with virtually no maintenance needed (other than replacing worn flight clips, which cost less than $3,000 for parts and labor). And, they’ve never had to adjust the trunnions once since our solution was implemented over five years ago. The plant superintendent reported that, “No one touches the adjustment of that dryer except Ed from Louisville Dryer.”
The aggregate processor is very pleased with the complete solution provided by Louisville Dryer Co.
To say that this customer is pleased is an understatement. Of course, the plant personnel are happy that the sound they hear now is the repetitive reliable rotation of our custom-engineering rotary drum vs. the dreaded impacts from breakdowns including the honking of truck horns, the ringing of cellphones, and the complaints from bosses.
Now the customer has two related decisions:
1. What do they do with the 28 thrust rollers which were ripped loose?
2. Should they sell the man-lift? (Operators like having it for other maintenances.)
While their return on investment cannot be calculated accurately, imagine breaking off a thrust roller with five empty silos, trucks and paving crews standing by on a 6,000-ton day – 28 times!
That situation should never have happened. We at Louisville Dryer Company will do whatever it takes to get you up and running for the long term – at the Lowest Cost Per Revolution.
Furthermore, our pleased customer reports incredibly positive results from their chain supplied by Hotmix Parts & Service. To date, the plant has processed over 4.5 million tons using that same chain!