Paperless recorders supplied by Yokogawa UK are playing a key role in improving process productivity at the Pirelli Tyres production plant on the outskirts of Carlisle in Cumbria, UK.
The recorders, fitted to mould presses which turn uncured 'green' tyres into the finished product, not only provide accurate and continually updated information on key process parameters such as temperature and pressure: they also provide, via their networking capabilities, comprehensive information to engineers and managers throughout the organisation. Pirelli's Carlisle plant, which employs about 1000 people, produces around 13 000 tyres per day, mostly destined for high-performance car makers such as Porsche, BMW and Jaguar as well as off-road and sports utility vehicles. The plant has 100 curing presses that will all eventually be converted to use the Yokogawa recorders, representing a total investment of over £150 000.
The moulding process
The moulding process involves inserting the uncured tyre into the mould, where an internal bladder is filled in several stages with superheated steam and water at high temperatures. The bladder forces the tyre into the shape of the mould, adding features such as the tread and maker's name to the previously blank 'green' tyre. The various stages of the process are controlled by a PLC, and it takes about 15 minutes (depending on the particular tyre being pressed) from start to finish to produce a tyre.
Process monitoring
Initially, monitoring of process parameters was carried out using traditional paper-based circular chart recorders, but these had a number of limitations and disadvantages. They could only act as passive monitoring devices and had no control or alarm facilities, so the press operators had to observe them continually to check if any parameter went outside preset limits. They also required manual setting, which introduced the possibility of human error. Last, but not least, they were expensive in terms of consumables like chart paper and pens - each machine costing around £700 per annum in chart paper alone. Chris Street, senior materials technologist at the Pirelli plant, was assigned the task of upgrading the monitoring and control operations for the mould presses. After looking at a number of options, he decided on the Yokogawa CX2000 paperless recorders. The main reason for his choice was that, at the time the decision was being taken, the Yokogawa products were the only instruments on the market that were fully networkable and Web-enabled. Other key factors in this choice were the improved visualisation of the process provided by the various display options, plus the ability to access additional process information as an aid to improving product quality and consistency.
Yokogawa's CX2000
The CX2000 is based on the Yokogawa DAQstation family of paperless recorders, with added PID control functions - and is particularly suited to use in temperature control applications where a single station can host up to six embedded control loops and link to up to 16 temperature controllers. Recorded data can be viewed in a variety of formats, and both Ethernet and Web interfaces are built in. In the Pirelli application, the CX2000 units are used for the direct recording of seven measured temperature and pressure parameters, with the recorders' built-in mathematical functions being used to derive an additional ten key parameters. They also accept digital inputs from the PLC so that they can verify other aspects such as cycle and load times. The ability to present data in various formats (graphs, bar charts, histograms etc.) is a powerful tool in the visualisation of the overall process, while the logging, history and analysis functions - aided by the use of MCPS software - provide a long-term insight into the quality and consistency of the production process.
Alarm functions are included for all parameters - 14 in total - and the detection of a valid alarm automatically halts the process. The system also monitors the usage of the bladders to ensure that they are replaced after the appropriate number of cycles. Measurements are taken every ten seconds, and recorded data is backed up every day using an onboard ZIP drive which also allows up- and downloading of data and set-up parameters via the Pirelli intranet.
Easy use
The units are easy to operate and set up, and automatically reset all functions such as setpoints, alarms and displays whenever a new configuration is entered. The networking capabilities of the CX2000 makes it possible for personnel throughout the plant - and even at other Pirelli plants in Italy and Germany - to have access to information and configure the system at different password-protected levels. Operators, for example, can observe different screens and alarms, while senior managers can access and change, if necessary, the complete process history in a variety of formats.
Pirelli engineers report that process capability - the function that compares the variability of a process in its relation to the setpoint and is thus a guide to accuracy and repeatability - has shown a fivefold improvement as a result of using the Yokogawa instruments.
There are also potential improvements in productivity resulting from the fact that the overall cycle time can be reduced by enhancing the process control capability and assessing the performance of each press in a totally quantifiable fashion.
"Pirelli is a world-leading brand in high-performance tyres", says Chris Street, "and the upgrading of our tyre moulding process using the Yokogawa CX2000 recorders - with their corresponding benefits in terms of productivity and cost effectiveness - is a key factor in enabling us to maintain this goal."
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