Plastics OEM integrates a total controls system solution

Modern production and processing machines are required to satisfy ever-increasing demands for productivity, cost effectiveness and flexibility. Shorter throughput times and faster retooling are expected norms for an efficiently-operating plant. Eliminating costly disturbances and downtime resulting from maintenance work, or the lack of it, is critical to maintaining process flow and profitability. Yet, many processing operations lack the machine controls automation that will allow them to run their machines in even a modestly efficient manner, let alone with a high level of process flexibility.

Only optimized machine concepts with innovative control technology are able to meet these demands. With the right automation, even the most complex process requirements can be implemented. Additionally, using high-availability, programmable automation control systems will reduce the risk of production failures. Although the initial cost of implementing these control systems is higher, it is marginal in comparison to the long-term savings potential.

In the plastics industry, original equipment manufacturer Thoreson-McCosh Inc. recently upgraded its controls equipment from the proprietary circuit board system it had been using on its machines for the past 25 years to a sophisticated system of micro-PLCs manufactured by Siemens. When the integration was complete, Thoreson-McCosh acquired more than just PLCs, it acquired a total plastics-industry solution. With the new system, Thoreson-McCosh reduced its engineering time and was enabled to provide its clients with more value by increasing the flexibility of its equipment. Additionally, the new system made maintenance, troubleshooting and diagnostics easier, streamlined process throughput and decreased machine downtime, while providing Thoreson-McCosh with access to high-availability parts and support.

Thoreson-McCosh is a manufacturer of auxiliary material management equipment for the plastics industry. Its standard product line consists of low-maintenance dehumidifying dryers, hot-air dryers, blending systems, individual vacuum conveying units and plant-wide vacuum conveying systems. The company also provides standard and customized products to meet specific client needs.

Thoreson-McCosh was founded in 1947 and pioneered many firsts in the process of dehumidifying resin materials. It manufactures nearly 40 different types and sizes of hot air dryers for the plastics industry.

The company’s hot-air drying and preconditioning systems are designed to remove surface moisture from non-hygroscopic plastic materials. The systems automatically provide a constant supply of pre-heated, pre-conditioned, uniformly dried material for extruder or molding machines. The patented design of the company’s hopper and diffuser combination ensures consistently uniform material dryness, exposing every particle of plastic material to an identical temperature for the same amount of time. For maximum drying efficiency, Thoreson-McCosh drying systems offer the highest air flow rates of any unit in the industry.

The company also makes a line of computerized gravimetric color blending equipment for small- and medium-duty injection molding machines, and extruder applications from 400 to 6,500 pounds per hour. Additionally, the company makes metering devices for color concentrates of resin additives, which come in a variety of sizes with models for palletized materials or free-flowing powders, as well as material loading systems designed to transfer material from a gaylord to a drying hopper.

The company’s equipment supports medical molding, electronic components and packaging.

“We did not have a PLC in use on our equipment,” says Jerry Muntz, vice president of engineering for Thoreson-McCosh. “We were using a proprietary board that we developed in the early 1980s. It had evolved over time, and we were working on its third generation when we switched over to the Siemens PLCs.

“Thoreson-McCosh is a job shop; we do a lot of customization within our product lines. Our control system was reaching its capacity, and the effort and cost to redesign it was prohibitive. We were limited in our temperature-control capabilities, and our input and outputs. We have two products that required a microprocessor control – our packing loading systems and our drying equipment. However, the capabilities that we wanted in our systems we did not include because of the R&D costs.

“We did not have any historical data capability in our system, specifically for preventive maintenance functions. The number of people able to service these types of machines has decreased a lot, particularly within the past six or seven years. As a result, we knew that we had to have more capability within our controls for maintenance and diagnostics.”

The plastic material that is put into injection molding machines contains very small amounts of water. When the pellets heat up, the water boils. If the water is not removed before the injection, a honeycomb effect will be created in the formation of the plastic. It is critical to avoid this because it degrades the integrity of the form being molded.

Engineering-grade plastic materials typically require a desiccant dryer. The Thoreson-McCosh equipment dries the pellets before they go into the injection molder. The company’s dehumidified dryer dries at a minus-40 dew point. A typical moisture level that it is trying to achieve is .02 percent. A certain temperature also must be achieved, but it is different for each type of plastic material.

The plastic material goes into a holding hopper and the dehumidifier blows extremely dry air across the hopper. The air is then passed across a desiccant so that it can dry out. The same heated and dried air is then sent back to the hopper, where it again passes over the plastic material and returns to the desiccant. The cycle is repeated over and over until the desired moisture level is achieved. This closed-loop process of reusing the same increasingly heated and dried air is different from traditional systems and extremely energy efficient, a characteristic unique to Thoreson-McCosh equipment.

Multiple hoppers are used with one dryer to allow drying and pre-drying for different materials. Multiple hoppers reduce the clean-out time between material changes. Individual hopper sizes can vary to accommodate material throughput requirements. Control of hopper temperature is achieved by a pre-heater at each hopper. This enables different materials to be dried with different drying temperatures. Modulating airflow valves regulate individual hopper airflow automatically based on customized operator setups. Multiple hopper configurations are used to eliminate the need for many small dryers, reducing floor space requirements.

“Prior to using the Siemens PLCs, Thoreson-McCosh had a homegrown circuit board with some capabilities,” says Nick Skope of Electro-Matic Products Inc. “But it wasn’t expandable, it was really designed to do only the functions that each of the company’s specific machines needed. It did not have a network capability, so it could not talk via any industrial network to another machine. The machines were not capable of much more than a stand-alone, limited process.”

Electro-Matic Products is a leader in the supply of high-technology automation components and services targeting the users and manufacturers of industrial automation equipment. As a Siemens Technology Center, it offers a broad ranges of electrical and electronic products, systems and services to industrial market customers. Its technologies range from circuit protection and energy management systems to process control, industrial software and totally integrated automation solutions.

“When we first began talking with Thoreson-McCosh about expanding the controls capabilities for its equipment line, we realized the company needed a more universally available controller that its clients could readily access,” says Skope. “One of the biggest features that Siemens brought was the ability for Thoreson-McCosh to better accommodate its existing customers, located globally, with upgrades, parts and service.”

Electro-Matic recommended Siemens SIMATIC S7-200 series of micro-programmable logic controllers for Thoreson-McCosh. This system, which can control a variety of automation applications, provides a compact design and a powerful instruction set that makes the S7-200 controllers an ideal solution for controlling small applications. Additionally, the wide variety of CPU sizes and voltages, as well as the Windows-based programming tool, provides the flexibility needed to solve automation problems. The application area of the SIMATIC S7-200 extends from the replacement of simple relays and contactors to more complex automation tasks.

Each compact S7-200 CPU unit is completely self-contained and includes the CPU, power supply and input/output points (I/O). It is capable of simple discrete control, or analog control with PID and floating-point math capability. Larger systems, with additional I/O, communications or operator interfaces requirements, can easily be configured by adding expansion modules or operator interface products.

The SIMATIC S7-200 offers real-time control with Boolean processing speeds of 0.37µs per instruction. This fast execution speed, combined with Siemens 20-kilohertz high-speed counters, interrupts and 20KHz pulse outputs, provide quick responses in demanding real-time applications.

An off-the-shelf, compact solution, the SIMATIC S7-200 is accepted around the world as a Micro-PLC standard.

“With the new PLCs, each of Thoreson-McCosh’s machines now operates independently, but it is networked with the flexibility to tie into other processes and share data between machines within an in-line process,” says Skope. “Before, its equipment operated as a stand-alone machine and did not have the capability. Now, Thoreson-McCosh can tie into the network of its customers’ processes, which could be doing a broad array of different actions. This capability makes its machine considerably more flexible and changes the whole look, feel and capability of its equipment.”

“Customized controllers, like what Thoreson-McCosh was using, are inexpensive on the front end but very costly on the back end from a maintenance standpoint,” Skope says. “The company wanted more flexibility and functionality, which this new platform provides. It is cost-effective and highly scalable. Additionally, it is something that the company can secure, along with parts and service, all over the world.”

Siemens 200 processors are able to handle very basic motion, they have high networking capability, and relatively high I/O count. They have built in I/O, but are also modular, meaning they can be built onto. They are like a larger PLC, but in a much smaller form factor. The networking capability that is available on the 200 is completely flexible.

One of the new functions Thoreson-McCosh has added with the new PLCs is time-dating information, which indicates a history of events. If there is a failure of some kind, its clients can now time-stamp it and better determine what happened through what was going on at the time. The time stamp can be used to illuminate how often this problem has occurred in a particular machine. It also enables statistical analysis of the frequency of loading. Material is being moved constantly from one machine to another.

With the previous control system, there was no ability to put a priority on one machine vs. another. This new capability makes it easier and faster for the company’s clients to locate and resolve flow problems in their plastics processing.

“The possibilities and capabilities with the new PLCs are extensive,” says Muntz. “We are continuously adding features to meet our clients’ requirements. These PLCs allow us the flexibility to enhance our facility. There is also more communications between machines. The Siemens PLCs make that possible. They enhance the flexibility of our machines. With Ethernet capability, our clients can connect our equipment to a plant-wide network system, something we could not do before. They can also monitor the equipment from anywhere they can set up a connection. Instead of having eight I/O, we can now have 100. We can expand the inputs and outputs per our clients’ requests. We also like the idea that we could purchase one, two or three of these as we need them, rather than having to buy 100 at a time. It is very cost-effective in that regard. We can minimize the amount of PLCs that we need to carry in our inventory. It is a total systems solution for us.”

About Siemens
Siemens Energy & Automation Inc. is one of Siemens’ operating companies in the United States. Headquartered in the Atlanta suburb of Alpharetta, Ga., Siemens Energy & Automation manufactures and markets one of the world’s broadest ranges of electrical and electronic products, systems and services to industrial and construction market customers. Its technologies range from circuit protection and energy management systems to process control, industrial software and totally integrated automation solutions. The company also has expertise in systems integration, technical services and turnkey industrial systems. To learn more, visit www.sea.siemens.com.