Automation controllers offer benefits over proprietary boards

In the plastics industry, original equipment manufacturer (OEM) 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. With the new system, Thoreson-McCosh reduced its engineering time and was able 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 customised products to meet specific client needs.

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 preheated, preconditioned, uniformly-dried material for extruders or moulding machines. A patented design of hopper and diffuser 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 high air flow rates.

The company also makes a line of computerised gravimetric colour blending equipment for small- and medium-duty injection moulding machines, and extruder applications from 400-6500 pounds-per-hour. Additionally, the company makes metering devices for colour concentrates of resin additives, which come in a variety of sizes with models for palletised materials or free-flowing powders, as well as material loading systems designed to transfer material from a gaylord to a drying hopper.

Proprietary control board

Jerry Muntz, Vice President of Engineering for Thoreson-McCosh, states: "We did not have a PLC in use on our equipment. 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 customisation 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 inputs 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 preventative 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 moulding 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 moulding.

Drying process

Engineering plastics typically require a desiccant dryer. The Thoreson-McCosh equipment dries the pellets before they go into the injection moulder. The company's dehumidified dryer dries at a -40 dew point. A typical moisture level that it is trying to achieve is 0.02 per cent. 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 that is claimed to be unique to Thoreson-McCosh equipment.

Multiple hoppers are used with one dryer to allow drying and pre-drying for different materials. Control of hopper temperature is achieved by a pre-heater that enables different materials to be dried with different drying temperatures. Modulating airflow valves regulate individual hopper airflow automatically, based on customised operator set-ups. Multiple hopper configurations eliminate the need for many small dryers, thereby reducing floor space requirements.

Electro-Matic Products is a Siemens Technology Centre and a leading supplier of high-technology automation components and services targeting the users and manufacturers of industrial automation equipment. The company's Nick Skope comments: "When we first began talking with Thoreson-McCosh about expanding the controls capabilities for its equipment line, we realised the company needed a more universally-available controller that its clients could readily access. 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 the Siemens Simatic S7-200 series of micro-programmable logic controllers for Thoreson-McCosh. This system provides a compact design and a powerful instruction set that makes the S7-200 controllers excellent for 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.

Self-contained controller

Each compact S7-200 CPU unit is completely self-contained and includes the CPU, power supply, and inputs/outputs (I/O). It is capable of simple discrete control, or analogue control with PID, and floating-point maths 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 0.37us per instruction. This fast execution speed, combined with Siemens 20kHz high-speed counters, interrupts, and 20kHz pulse outputs, provides quick responses in demanding real-time applications.

Skope says: "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. Before, its equipment operated as a standalone 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."

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 expanded, plus they have flexible networking capability.

Kimberly Cambell-Djuric, Account Manager with Siemens, comments: "Siemens controls are pretty much the accepted standard equipment in most plastics facilities. There is a huge support network globally for plastics OEMs like Thoreson-McCosh. So they can do what they do best - which is to create the process, automate the process - and let us do what we do best, which is to provide the right solution to automate their technology.

"It is a matter of support, ensuring the equipment will do everything that it needs to do. We were there on the front-end helping Thoreson-McCosh understand exactly how to adapt the PLCs to its equipment processes. We are able to provide continuous support."

Time stamps

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. With the previous control system it was not possible to put a priority on one machine versus another. This new capability makes it easier and faster for the company's clients to locate and resolve flow problems in their plastics processing.

Muntz says: "The possibilities and capabilities with the new PLCs are extensive. 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 minimise the amount of PLCs that we need to carry in our inventory."