Glass Conditioning for High-Quality Production: The World of Glass

2. 1872 - 2006 Over 130 years of unbroken service to the Glass Industry The Group ..... ..... AT HOME IN THE WORLD OF GLASS

3. Glass conditioning for high quality production Richard SimsNikolaus Sorg GmbH & Co KG

4. Glass conditioning for container manufacture Normally consists of thermal processes - temperature reduction - thermal homogenisation Increasingly acquiring a new component - chemical homogenisation to eliminate zircon cords

5. Glass conditioning for high quality production Thermal processes generally not important - less temperature differential between entry and exit - much smaller quantities of glass Attainment of excellent chemical homogeneity extremely important

6. Chemical homogeneity

7. Glass conditioning for high quality production Elimination of chemical inhomogeneities by stirring Elimination of chemical inhomogeneities by draining Prevention of chemical inhomogeneities

8. Elimination of chemical inhomogeneities by stirring

9. Elimination of chemical inhomogeneities by stirring Chemical inhomogeneity (cord) is usually an area of differing chemical composition (= differing refractive index) We can render it invisible by equalisation of the composition - this occurs mainly by diffusion We can render it invisible by distributing it in the glass body

10. Elimination of chemical inhomogeneities by stirring To facilitate diffusion we need - a large contact area between the cord and the base glass - time Stirrers should either : - increase contact area, OR - increase time available, OR - both Contact area is increased by application of shear forces Time is increased by modifying the flow pattern

11. Spiral stirrer (blender)

12. Spiral stirrer (blender) ADVANTAGES Good vertical glass transport Little horizontal glass transport - the glass is not “pushed“ forwards Large vertical barrier area

13. Spiral stirrer (blender) Large vertical barrier area

14. Spiral stirrer (blender) ADVANTAGES Good vertical glass transport Little horizontal glass transport - the glass is not “pushed“ forwards Large vertical barrier area Residence time of the glass is increased DISADVANTAGES Low differential velocity Little actual “mixing“ effect - low shear forces

15. Paddle stirrer - various types two paddle - small two paddle - large four paddle

16. Paddle stirrer - large ADVANTAGES High differential velocity - high shear forces Good “mixing“ effect DISADVANTAGES Horizontal glass transport - glass is “pushed“ forwards

17. Paddle stirrer - large side by side in-line

18. Paddle stirrer - large ADVANTAGES High differential velocity - high shear forces Good “mixing“ effect DISADVANTAGES Horizontal glass transport - glass is “pushed“ forwards Residence time of the glass decreased

19. Rod stirrer - various types

20. Rod stirrer - typical application

21. Rod stirrer ADVANTAGES Very high differential velocity - very high shear forces Excellent “mixing“ effect DISADVANTAGES Needs vertical glass flow Metallic = platinum alloy - VERY expensive Sometimes impractical

22. Elimination of chemical inhomogeneities by stirring The combination of “mixing“ and increased residence time is necessary Stirrers and channel form must be matched Refractory stirrers wear = unstable operation BETTER results obtained with vertical flow BEST results obtained with rod stirrer in vertical channel

23. Elimination of chemical inhomogeneities by draining

24. Elimination of chemical inhomogeneities by draining If we cannot eliminate cord with stirrers it may be because it is not accessible - on or close to the surface - on or close to the bottom In such cases selective draining can solve the problem - refractory design to influence origin of drained glass - careful control of drained glass quantity

25. Surface drain

26. Surface drain Surface glass “skimmed“ off and removed by overflow drain Remaining glass of good quality Drain flow rate determined by overflow temperature

27. Bottom drain - basic principle Counter electrode Transformer CONTI-DRAIN with nozzle Thermocouple Temperature controller Thyristor unit

28. Bottom drain - details

29. Bottom drain - mathematical model

30. Bottom drain - in operation

31. Elimination of chemical inhomogeneities by draining Selective draining can often solve problems that are not accessible to stirrers A surface drain can be used to remove glass contaminated by surface volatilisation A bottom drain can be used to remove zircon-rich glass from furnace refractory corrosion Careful control of drain operation is vital for good results

32. Prevention of chemical inhomogeneities

33. Prevention of chemical inhomogeneities Chemical inhomogeneities can result from stagnant areas of glass in the forehearth channels - as a result of cold glass - as a result of poor flow patterns

34. Prevention of chemical inhomogeneities Avoid deep and wide channels Avoid sudden changes in channel width and depth Avoid flow barriers in the channels Avoid corners in the channels (as far as possible) Keep channel as short as possible

35. Prevention of chemical inhomogeneities Chemical inhomogeneities can result from stagnant areas of glass in the forehearth channels - as a result of cold glass - as a result of poor flow patterns Chemical inhomogeneities can result from surface volatilisation - for example, lead, fluorine, boron, alkalis

36. Prevention of chemical inhomogeneities Eliminate the glass bath surface

37. Prevention of chemical inhomogeneities Eliminate the glass bath surface - heating becomes a problem Indirect heating - gas or electric - forehearth is sluggish and control is difficult - forehearth is inflexible

38. Prevention of chemical inhomogeneities Eliminate the glass bath surface - heating becomes a problem Indirect heating - gas or electric - forehearth is sluggish and control is difficult - forehearth is inflexible ALTERNATIVE Non-contact cover - forehearth reaction and control are acceptable - compromise on quality

39. Prevention of chemical inhomogeneities Eliminate the glass bath surface - heating becomes a problem Indirect heating - gas or electric - forehearth is sluggish and control is difficult - forehearth is inflexible Direct heating - with electrodes - forehearth reacts well and control is good - possibility of glass quality problems from electrodes

40. Prevention of chemical inhomogeneities Eliminate the glass bath surface - heating becomes a problem Indirect heating - gas or electric - forehearth is sluggish and control is difficult - forehearth is inflexible Direct heating - with electrodes - forehearth reacts well and control is good - possibility of glass quality problems from electrodes The combination - indirect heating (gas or electric) and direct heating by electrodes gives good results with few disadvantages

41. The answer ?

43. The answer There isn't one There isn't ONE ?

44. If you want to make high quality production : Keep it as simple as possible Apply correctly designed stirrers - paddle stirrers - side-by-side - if possible in vertical channel If possible used combined indirect/direct heating Have drain facilities available

45. If you want to make high quality production : Always remember, there are 2 other major sources of glass quality problems that have not been mentioned here : - the feeder bowl - the furnace

48. 1872 - 2006 Over 130 years of unbroken service to the Glass Industry The Group ..... ..... AT HOME IN THE WORLD OF GLASS