XPAR Vision is a firm believer that the current performance of the glass container industry has not yet reached its limit. Weight reduction, waste reduction and zero defects production are now possible by using the company’s equipment. In a series of exclusive articles for Glass Worldwide, Paul Schreuders shares the results of implementing the company’s technologies and how it helps the glass industry.
In Part six of this series, the Blank side Temperature Control (BTC) system was introduced. The system (figure 1) is capable of measuring the temperature of essential parts at the blank side:
- Blank moulds
- Neck rings
This part of the series focuses (again) on temperature as one of the most important parameters of the glass forming process and on the technique of setting up the measurement device in order to achieve the best results.
Temperature is one of most important parameters of the glass forming process because as everybody knows, the viscosity of the glass, which determines the quality of the bottle or jar, is highly dependent on glass temperature. The glass temperature is dependent on the heat exchange between the gob and blank mould material.
To control the temperature of the glass, the temperature of the blank moulds, neck ring and plungers have to be controlled within a few degrees Celsius. To obtain good control, one must have a good measurement of the temperature. This sounds obvious but in practice, good temperature measurement is rather difficult.
Time and position
In Part six of this series, it was stipulated that in order to give reliable and precise results, the measurement of temperature on exactly the same position and at exactly the same time is of the utmost importance (fig. 2).
The first difficulty is time. The temperature of the moulds, neck rings and especially plunger are continuously changing according to the phase of the glass forming process, eg a plunger cools down in a few milliseconds (one thousands of a second). So the temperature always has to be measured on the same time with the accuracy of a millisecond.
Another challenge is the position. The temperature of the blanks moulds, plunger and neck ring is very position dependent. The temperature on the top of the blank mould is different to the temperature inside of the blank and the temperature on the top of the plunger is completely different to the temperature near the cooling holes of the plunger. The BTC fulfils fully this necessary precondition for measuring the temperature of the mould material. With the BTC, the user can have the free choice on which positions of the mould, plunger, neck ring and parison to measure and a free choice on which time the measurement of the temperature takes place.
There is no such thing as free lunch! Because of the many possibilities and choices of the BTC, initially the setup time was quite long. Customers, as always under severe time pressure after a job change to get the glass forming running, were complaining about the long setup time of the BTC and asked XPAR Vision for improvements to this aspect of the BTC.
“When one section is set up, why can I not copy all the parameters to the other sections?” was the general remark from customers. Although this sounds very logical and looks like it can be performed easily, in practice this was impossible: In order to achieve the high measurement accuracy, the transport rail needs to be mounted with extremely high accuracy. This is not practical, will be time-consuming and the installation costs will be too high.
To give a feeling for accuracy, the transport rail with a length of 7m and a weight of several hundred kilos must have position accuracy of a few tens of millimeters over 7m! If not, there is always a small deviation of the sensor position for every section, which had to be corrected by the user manually at the setup of the temperature measuring points.
Always sensitive to suggestions from customers, XPAR Vision developed a solution: During installation of the BTC, the system will be calibrated against the IS machine for every small deviation of each cavity. Adding the blank mould dimensions to the setup is needed to give the system the dedicated offsets for each product (figure 3).
The result is astonishing; the user has to set up the BTC only for one cavity (not section!) and can copy the positions of measurements including the timing to every other cavity of the IS machine (figures 4 and 5).
This approach reduces the set up time for new jobs to just 15 minutes and results in all measurement points at exactly the same position. As a result, the accuracy of set up and thus of measurements is highest. And this is very important, as the BTC is used increasingly in automated control loops: The elimination of sensor deviations due to position errors will take out the differences from the measurements in the blank mould and ensures the same effect on bottles or jars. With the latest automated set up, the level of accuracy is at its highest.