1. Mr. Pitipong Benjarungroj
A FUNDAMENTAL INVESTIGATION OF RECYCLED GLASS AS A MEDIA FOR VIBRATORY MASS FINISHING
Mr. Pitipong Benjarungroj
Supervisor: Dr M Morgan
11th February 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. Introduction Mass 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. Introduction Mass finishing process
Vibratory Bowl
Linear Vibratory
Centrifugal disk
Centrifugal barrel

7. Introduction Mass finishing process
Centrifugal barrel - Vid
Bowl - Vid
Linear tumbler- Vid
:Flow is amenable to CFD –velocity profiles through 2-D planes

8. Introduction Mass 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. Introduction Mass 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. Introduction Mass 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. Introduction Mass 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 Mechanical Testing; Preliminary Bend Test V-Cut Bar
Preliminary Hardness Test

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 No. of Experiment Modulus of Elasticity(GPa)
Flexural strength(KPa)
1st Experiment
6.455
42.94
2nd Experiment
4.667
24.68
3rd Experiment
1.311
32.82
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
Number of crack
HV(kgf/mm2)
HV(GPa)
1st
250
2.45
2nd
211.6
2.07
3rd
192
1.86
4th
170
1.67
5th
328
3.22
6th
214
2.10
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 (a) (b) -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
Vibraglaz
(range of grades)
Media Characterization
Modelling
Performance Assessment

46. THANK YOU FOR YOUR KIND ATTENTION