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.
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
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.
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.
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.
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
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.
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
of Southampton performed technical research.
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."
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
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)