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Graphic element Research > Growth > Research projects > Measurements & testing projects > Detecting air bubbles in ceramics production
Graphic element Detecting air bubbles in ceramics production
    16-11-2000
 

In today's highly competitive marketplaces, manufacturers are under constant pressure to cut costs while at the same time increasing productivity. Under such conditions, a fundamental priority must be the minimisation of losses due to faulty production. A case in point: manufacturers in the ceramics industry have long known that entrained air bubbles in ceramic casting slips are a major cause of production losses. From wash basins, water closets and bidets, tableware and decorativeware to high-tech items, air bubbles can produce faults in ceramic products which can be costly or impossible to repair.

Bubbles in slurries
Most of the ceramic products we come across in our daily lives are produced through slip casting, wherein a slip or slurry material (a thick suspension of clay in water) is poured into a cast, allowed to set and then fired. Air entrained into the slip in the form of bubbles can eventually lead to cracking or to 'pinhole' defects in the decorative glaze. Before this project was undertaken, a reliable and convenient means of identifying and eliminating air bubble contamination in slip systems did not exist. The state of the art in air bubble detection involved the use of compressibility tests where liquid materials are compressed and the resulting measurements compared with measurements from materials of known composition. No such tests were particularly well adapted to ceramics applications and none of them could be used on flowing slips.
Ultrasonic detection

The BUBBLES project brought together industrial, research and academic partners from four European countries with the common aim of delivering an on-line air detection system for use on flowing casting slips. Intermediate objectives included, first, the establishment of basic concepts behind the operation of such a detection system. Secondly, a prototype instrument had to be designed and manufactured. Thirdly, extensive field tests had to be conducted.

According to Dr Graham Small, project co-ordinator at CERAM Research in the UK, the detection system was to be based on newly developed ultrasonic techniques. Extensive laboratory trials carried out by the Institute of Sound and Vibration Research (ISVR) at Southampton University in the UK identified the appropriate frequencies and signal processing methods to detect bubbles in liquids under both static and flowing conditions. These same methods were then successfully applied vis-à-vis a slip flowing through a pipeline using special sensors attached to the outside of the pipe.

A compact prototype detection unit was designed and produced by the SME electronics manufacturer Pulsar16 for use in practical trials to be carried out by CERAM at working ceramics factories. Under most conditions, the prototype detected air bubbles reliably. It was effective when used both on metal and plastic pipeline systems and, importantly, the new system was considerably more convenient than previous testing methods.

  Effective diagnostic tool

Dr Small says the new device can be fitted easily and quickly to existing pipeline systems. Attached to the outside of the existing pipes, it can immediately provide data about total air content and with further, more sophisticated data processing software it can give information on the size distribution of bubbles in the casting slip. During the field trials the system proved well-suited for use as a diagnostic tool. Air entrainment can be caused by a number of factors: too tight corners causing turbulence; poor or improper valve settings; improper process order, etc. In short - poor design or operating practices are to blame. One or more BUBBLE devices can be set up at different locations in a pipeline system so as to pinpoint weak spots where bubbles are formed. Monitoring could also be established on a semi-permanent basis and the system set to automatically signal an alarm when excessive air is present. Operation requires a minimum of disruption, maintenance and user intervention.

The new system was launched commercially at the Ceramitec exhibition in Munich in October of 2000. The main targets are ceramics manufacturers, as well as builders of new factories where project partners hope their system will quickly be taken on as standard equipment. The European ceramics industry as a whole stands to achieve substantial improvements in productivity, reductions in losses and consequent savings through the use of this system.

  Strengthening partnerships

Qualceram in Ireland and Koninklijke Sphinx in Holland are end-user sanitaryware manufacturers; Bidasoa in Spain and Bridgewater Pottery in the UK are end-user tableware manufacturers; Pulsar16, also in the UK, is an electronics supply company; CERAM Research in the UK is an application research group; and the University of Southampton performed technical research.

As with many such projects, there were major challenges in holding the consortium together and ensuring that all objectives were met on time and within budget. As project co-ordinator, Dr Small says there were several occasions when for various reasons the project could have been abandoned. But strength and determination brought it to a very successful conclusion. Says Small, "We got there. We have a good product and all are happy."

   
Bubbles in slurries
Ultrasonic detection
Effective diagnostic tool
Strengthening partnerships
   

Key data

Research into effective online detection systems under the Measurement and testing generic activity is bringing about significant improvements in production processes, as revealed in the European ceramics industry.

Project: BUBBLES - Development of a Continuous On-line ultrasonic Technique for the Detection of Air Bubbles in Casting Slips (Slurries) (Project number: SMT4-CT97-5507)

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