A FUNDAMENTAL INVESTIGATION OF RECYCLED GLASS AS A MEDIA FOR VIBRATORY MASS FINISHING

1. A FUNDAMENTAL INVESTIGATION OF RECYCLED GLASS AS A MEDIA FOR VIBRATORY MASS FINISHING Mr. PitipongBenjarungroj Supervisor: Dr M Morgan 11thFebruary 2011

2. Content • Introduction • Aims / Objectives • Problem Outline • Experimental programme • Results

3. Introduction • Mass finishing refers to the process technologies for generating edge and surface finishes on a wide range of metallic and non-metallic materials • Common edge and surface finish requirements include: deburring, descaling, surface smoothing, edge-break, radius formation, removal of surface contaminants from heat treatment and other processes, bright finishing, pre-plate or coating surface preparation.

4. Introduction • Mass finishing is an increasingly important operation found adjacent to conventional operations eg. laser cutting, water jet and EDM operations. • Applications are wide ranging and varied in material eg: coinage, domestic artefacts/ utensils, musical instruments, automotive and aerospace components

5. IntroductionMass finishing process • Energy is imparted to the abrasive media mass via a vibratory or rotary means to impart motion to it and to cause it to act on the surfaces. [process control parameters: vibration amplitude, frequency, (rotational speed)] • Common mass finishing processes include: vibratory bowl and linear; barrel, centrifugal barrel and centrifugal disk, and rotating barrel • Fluid (compound solutions) required for lubrication (-lower frictional forces and reduce wear), aid swarf removal, cleaning, ease handling

6. IntroductionMass finishing process Vibratory Bowl Linear Vibratory Centrifugal disk Centrifugal barrel

7. IntroductionMass finishing process Centrifugal barrel - Vid http://www.youtube.com/watch?v=pQAJCCBP-gw Bowl - Vid http://www.youtube.com/watch?v=rHzik_z-1C8 Linear tumbler- Vid http://www.youtube.com/watch?v=DvECh0f6lEs :Flow is amenable to CFD –velocity profiles through 2-D planes

8. IntroductionMass finishing process • Conventional media wear – used media and debris (including bond, swarf!) sent to landfill • Frequently significant loss in media volume bond plus abrasive • Performance over time deteriorates (reduced number of cutting edges)

9. IntroductionMass finishing media • “Media” refers to the abrasive consumable elements used in mass finishing process. • The common media types include natural abrasives, synthetic random media, preformed ceramic and resin-bonded media, and metallic media. • The composition of a media determines whether it is a cutting or finishing type of media.

10. IntroductionMass finishing media • Preforms are generated from the abrasive media (eg. Al2O3, SiC) held in a bond • Resin bonds: polyester or urea-formaldehyde (generally unpleasant to work with) • Ceramic bonds – vitreous based, includes glass frit • Preforms are typically cylindrical, conical or tetrahedral in shape • Common processing stages: base materials processing; mixing; compaction; heat treatment; cleaning

11. IntroductionMass finishing media • Geometry largely depends on application

12. Vibratory Finishing Recycled Glass Media :-Innovation from Vibraglaz (UK)Ltd.

13. Introduction • The media under investigation is produced wholly from recycled glass [V-Cut]. In its raw state it is in cullet form. The cullet is cleaned of contaminants and crushed. The cullet is then sieved and subsequently graded in a manner similar to that for abrasive grains. The source of glass is varied but is in general glass scheduled for landfill and most recently is predominantly window glass.

14. Introduction • The production process is greatly simplified: - materials pre-processing is minimal - moderate mixing [media possessing varied grain size] - moderate compaction - heat treatment

15. Introduction • Production control requirements: - mould technology (and release agents) - heating rate, critical temperature (Tmax), duration at Tmax, cooling rate / quenching Each have a strong effect on media quality Secret recipe!

16. Introduction Sample V-Cut media

17. V-Cut Benefits 6 key features that distinguish it from other media: • No binder required • Significantly higher percentage of abrasive • Density: plastic media < V-Cut < ceramic media • Strong green credentials and low environmental impact • Recyclable • Lower cost

18. Media Comparision 200x magnification (CAMApp - desktop equipment) V-Cut Ceramic Plastic Note Cutting edge density

19. Media Comparision • In preliminary studies V-Cut has been shown to achieve a comparable • performance to conventional media • common metals • standard vibratory machine / process conditions • typical processing times • Performance w.r.t. :target criteria (Ra, brightness)

20. Aim / Objectives HOW?

21. Aim / Objectives • To acquire fundamental understanding of the material characteristics of the media • To obtain machining data over a range of machining conditions • Establish and compare performance of V-Cut with conventional media

22. Problems / Challenges • V-Cut Preparation Challenges • Cullet quality • Sourcing availability • Size consistency within a stated grain size (grade) • Mixture -various grades

23. Problems / Challenges • V-Cut Production Challenges • Mould material (influences temperature gradients and release) • Rate of heating temperature • Critical temperature Tmax– duration at Tmax • Rate of cooling • Release agents

24. Project objectives • Materials characterisation - Hardness - Fracture strength - Cutting edge density (undertaken at intervals tests –test the validity of piranha vs shark analogy) - Crystallographic structure (influence of grain size on crystal size? Growth?) - Crystal growth mechanism (temp – time dependency) Is it like water crystals freezing? Effect of second or multiple cookings!

25. Project objectives + = After Before

26. Early Studies

27. Materials characterisation • Why we need to know these properties? • Glass is different from others material - the mechanical properties of glass depend strongly on temperature. • In most materials the modulus increases with increasing pressure and decreases with increasing temperature. In glass the modulus increases with increasing temperature

28. Preliminary Bend Test • The results suggest an experimental error. The Modulus of elasticity values vary widely. The principle reason for the disparity in results was reasoned to be the high surface roughness of the specimens. Further tests designed to reduce these errors.

29. Preliminary Bend Test • The strength of glass strongly depends upon its surface condition. Tiny flaws(cracks) in the surface lead to weakening and failure by brittle fracture. It also becomes weaker with time under stress (fatigue). • The theoretical strength of glass is relatively high (~2.4×1010 Pa for vitreous silica and ~1.6×1010 Pa for commercial soda-lime glass), but these strengths are rarely approached in practice because of the surface flaws.

30. Preliminary Hardness Test • Due to the brittleness of the glass, it is not readily amenable to conventional mechanical testing methods; there is a tendency to spontaneous failure before any deformation mode can manifest itself in the stress/strain response. • Therefore, techniques which involve large components of hydrostatic compression to restrain fracture are required. Hence, the indentation test is currently considered the most suitable method in the study of brittle materials HV = F/A; A = d2/1.854; Therefore, HV = 1.854F/d2 Where; F =applied load D = arithmetic mean of the two diagonal d1 and d2

31. Preliminary Hardness Test • The results show a promising hardness value, with the average value of 2.23 GPa. However the inconsistency of the obtained data means that there may have been some error during the experiment. The reason behind this may be due to wide variation in the grain size. Further tests are scheduled to be completed.

32. Materials characterisation • Replication methods for surface topography assessment • -identification of cutting edge density • -insight into wear mechanism Cannot use stylus methods –stylus wear and lack of information on surface features

33. Production Process –Early studies The oven used for production of media (-premarket media) was of a general type used for ceramic components and had controlled travelling rack (determined cycle time) and temperature. Assessment of this system was undertaken with / without stacking of moulds. It was found that media quality varied widely when stacked. Thermal images where obtained of the production oven and laboratory ovens.

34. Thermal Imaging -wide variation in temperature occurs within different regions of the oven (a) (b) Direct View of Laboratory Oven interior 2-D (a) and 3-D (b) Plots of Oven interior

35. Thermal Imaging It was established that stacking was problematic and the company have chosen to design an envelope(conveyor) type oven system to accommodate single layer moulds.

36. Performance Assessment • Volumetric removal • Media Wear rate • Surface roughness , Ra (principal parameter measured) • Brightness observation • Burr removal (visual assessment) • Cycle times

37. Performance Assessment V-Cut media used in studies Liner Mass Finisher (vibratory tumbler) used in studies

38. Surface Roughness - Representative Results Region of interest for industry

39. Surface Roughness - Representative Results *** It can be noticed from the results that the Ra for Aluminium and Brass is higher than that at which the tests commenced. This is due in part to the roughing effect of the abrasive and in part to the burnished condition at which they came to machining (shown later). Furthermore, most operations with these two materials would primarily be associated with deburring and/or rounding, not surface roughness. Polishing would be undertaken with a much less aggressive media.

40. Surface Roughness Discussion media 780 is medium grade cutter / polisher Results are consistent with published data for conventional media (in-house comparative data being prepared) Limiting values indicate boundary of performance on particular material For example: If lower Ra is required with material = aluminium, then different grade (i.e. polisher) would be needed, though this would be achieved at the cost of lower material removal rate

41. Surface Roughness

42. Surface Roughness Discussion media 790 performs more as a polisher than media 780 The abrasive action of the media is evident in the early part of the graph – i.e. the cutting edges initially dig into and hence roughen the surface before finishing occurs This is not so evident with a harder material eg. MS or SS

43. Surface Roughness • Further tests are in progress on this front. • Conventional media is now available for the tests • Material range is being widened – we have a Titanium based alloy • being prepared (coupons) -Aerospace turbine blade for • comparative studies. These laboratory based tests are preparatory tests prior to scheduled in-situ company (Rolls Royce) confirmation tests

44. Brightness observation Brass before and after 10 minute of machining Brass before machining Brass after machining

45. On-going and Further Studies

46. THANK YOU FOR YOUR KIND ATTENTION