Denim manufacturer takes control upgrades into its own hands
Mount Vernon Mills is one of largest textile mills in the United States. Our mill in Trion, GA, nestled along the Chatooga River also happens to be one of the oldest textile mills in the United States, with roots dating back to 1845.
The initial 5,000 sq ft, two-story mill had 40 employees and started by producing 5 lb bunches of yarn to sell to local merchants from wagons. Over the next 160 plus years, the mill would survive a fire in 1875, General Sherman’s march through Atlanta, bankruptcy in 1912, two world wars, the fight to get unionized, and a major flood in 1990. Through it all, the mill has continually expanded, renovated, and modified to change with the times. As a result, the mill has produced many different products over the years, including fabric used for military uniforms, crop sacks, sheeting, shirting, and even gloves.
In 1971, the decision was made to have the Trion plant produce denim. This turned out to be one of the best decisions in the mill’s history. The plant installed new equipment and rode the wave of growth in the denim industry. By 1976, the facility had more than 1,100 looms producing denim. The company continued to grow, but then faced a near disaster when the “Hundred Year Flood” hit the Trion area. After the flood, the company spent the next several years modernizing its plant with state-of-the-art machines with which to produce denim.
Today, after its latest round of renovations, the mill continues to operate using advanced equipment in more than one million square feet of manufacturing space. The denim from Mount Vernon Mills is woven and finished for sale to a many major manufacturers across the country like Wrangler and Lee. Mount Vernon is now the 3rd largest producer of denim in the United States.
Updating finishing line controls
Despite regularly keeping up with changing technologies, the company found that it was getting harder to get spare parts for control systems on some of mill’s finishing ranges and rebeamers. The age of the control systems also made it difficult to give operators the features and functions they wanted. Late in 2006, we decided to embark on upgrades for our rebeamers as well as one of our finishing lines.
The task of replacing the control system for the finishing line seemed daunting. It is a very large, multi-motor machine. All the motors have to work together and are self adjusting with dancer position sensors that send signals back to the PLC system. The PLC system automatically adjusts motor speeds to keep everything running together.
Because of the machine’s size and complexity, we first went out for bids. When the bids came back with costs that far exceeded our budget, we decided to do the project in house and source components from AutomationDirect.
To save time, we bought new back planes to bolt on the backs of the old cabinets so they could be assembled and tested before being installed in the machine. Though we initially planned on doing this in our spare time over a period of three months, we ended up getting only three weeks and having no time for testing. Electricians were finishing mounting motors and drives before I had time to complete the software setup.
Before the upgrade project, the finishing line was powered by dc drives with field regulators. We upgraded to AutomationDirect’s Durapulse ac drives and networked all the drives via Ethernet to a DL-260 DirectLogic PLC System. We selected a 15-in. C-more touch screen operator panel to replace the main operator console. We were able to procure, install, and program the entire system within the three weeks. I did all the programming of the HMI and PLC, and used AutomationDirect’s telephone technical support staff to get questions answered when we encountered problems.
The project proved to be a great success very quickly. First of all, we saved nearly $40,000 compared to the other bids. And now that our control system is largely software-based, we’re able to give the operator much more control of the machine, including setup parameters of the dry cans & dancers, line speeds, trimming capabilities, as well as some fault indication and maintenance screens. As a result, we are looking to add new functions or features as we continually refine the process for improved productivity.
On a second project, we retrofitted our old control system for a rebeamer in order to get better performance and more flexibility. The rebeamer is a speed-controlled center winder. It winds yarn from several section beams onto a single loom beam prior to weaving.
|Editor’s note: CNN conducted a profile on Mount Vernon Mill’s Trion, GA, plant less than a month after Control Engineering ‘s article and video appeared. We think you’ll find their profile of the manufacturing facility interesting as well. See it at: http://www.cnn.com/2009/US/10/30/blue.jeans.mill/index.html|
There are dozens of these machines in our facility. The original control design for the rebeamer used manual controls (pushbuttons, pilot lights, meters) on the operator station, and a dc drive to operate the spool. As with the finishing line in the first project, it was getting difficult to procure replacement parts or make any changes to the machine, operator interface, or control system.
At first, we outsourced the PLC program in our efforts to improve its performance, but we never could get the new programs to work correctly. So we scrapped the outsourcing idea and did it ourselves.
The first rebeamer project began with a plan to retrofit one of the rebeamers with a DirectLogic DL06 micro PLC, a Durapulse ac variable frequency drive, and a C-more operator interface panel. This technology combination was selected because it enabled us to put more parameters and adjustments at the operators fingertips. With our operators continually suggesting improvements to the process or machine, we are now able to act on their inputs, and use the software-based control system to streamline the process.
A key aspect of this project involved the requirement, on the rebeamer, for the speed to be adjusted as it winds up to keep the yarn at a constant velocity. I was able to establish this level of precise control without an encoder by using the DL06 micro PLC and a single proximity sensor.
|Jonathon Payton is denim mill electrical engineer, Mount Vernon Mills, Trion, GA. He can be reached at firstname.lastname@example.org .|