Reprint - Renfert

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What makes a
sandblaster efficient?
Dr. Gisela Peters
Renfert GmbH • Industriegebiet • 78247 Hilzingen/Germany
or: Postfach 1109 • 78245 Hilzingen/Germany • Tel. +49 77 31 82 08-0
Fax 82 08-70 • www.renfert.com • info@renfert.com
dd S C I E N C E
Osnabrück University of Applied Sciences tests eight sandblasters for consumption and efficiency
What makes a
sandblaster efficient?
Once purchased, a sandblaster is in frequent use and hardly anyone enquires about material and labour
costs. However, the cost-effectiveness of these appliances should, blasting quality not withstanding, be a
major criterion before the laboratory owner makes such an investment. Depending on which decision is
taken, follow-up costs are involved - either to a greater or lesser extent. The Osnabrück University of
Applied Sciences provides assistance: It has closely inspected eight sandblasting units. In comprehensive
tests scientists determined blasting media consumption, the effect of the media, as well as the blasting quality. Moreover, the tests exposed information on the bonding strength between ceramic and alloy after conditioning the frameworks with each sandblaster tested.
A
re you still sandblasting or are you now saving? - This question may well be asked of
laboratories when one looks at the test
results provided by the Faculty of Engineering and
Computer Science and Dental Technology of the
Osnabrück University of Applied Sciences. The
research group surrounding Professor Dr. Ing.
Isabella-Maria Zylla not only analysed the appliances’ performance, but also asked how much blasting media is used in the process and how long the
process takes.
The principle: The investment material must be
removed completely, the oxide cleaned off and the
surface sandblasted evenly. After conditioning, the
metal-to-porcelain bond must be highly resilient
and durable – this is directly influenced by thorough
and even blasting. The appliance used in this
process must operate economically – after all, the
modern laboratory must deliver the required quality
at competitive costs and prices.
The Osnabrück University of Applied Sciences tested eight blasting units:
1. SBU 5.2 Compact by Averon, Yekaterinburg,
Russia
2. Platinum D.O.S. by Dentalfarm, Turin, Italy
3. Planetarium by Mestra, Passau, Germany and
Bilbao, Spain
4. MS3 by Omec, Muggiò, Italy
5. Basic classic and
2 dental dialogue VOLUME 9 2008 ©
6. Basic quattro IS by Renfert, Hilzingen, Germany
7. Easy Sand by Silfradent, S. Sofia, Italy
8. Sand Storm Expert by Vaniman, Fallbrook,
California, USA
Regarding consumption and blasting media effect,
the Renfert Basic classic and Basic quattro IS
proved best.
Highly desirable:
Low blasting media consumption
Initial tests showed the total blasting media consumption varies according to model (Fig. 1) and that not all
appliances are economical. Per test cycle – mean
value for 50 and 125 micron grit sizes - the Renfert
Basic classic emitted only 13.68 g of corundum. The
Basic quattro IS used even less blasting media
(7.345 g) thanks to its rapid-stop feature. Compared to
this result, the test appliances with the largest consumption used 49.69 g and up to 61.65 g despite all
units using nozzles of the same size. Each test cycle
consisted of three phases:
1. The lead-time until attaining uniform blasting
media discharge,
2. the blasting time, standardised at twenty seconds, and
3. the follow-up time until no more blasting media
exited the nozzle.
S C I E N C E dd
60 g
50 g
40 g
30 g
20 g
10 g
0g
Renfert
Basic quattro IS
Renfert
Basic classic
Averon
SBU 5.2 Compact
Silfradent
Easy Sand
Mestra
Planetarium
Omec
MS3
Vaniman
Sand Storm Expert
Dentalfarm
Platinum D.O.S.
Fig. 1 The construction makes the difference: Some microblasters use the
blasting media sparingly, others consume larger amounts.
50
45
50 µm
Schwankungen in Gramm
40
125 µm
35
30
25
20
15
10
5
0
Renfert
Basic quattro IS
Renfert
Basic classic
Averon
SBU 5.2 Compact
Dentalfarm
Platinum D.O.S.
Mestra
Planetarium
Omec
MS3
Silfradent
Easy Sand
Vaniman
Sand Storm Expert
Fig. 3 Making reproducible results easy: An even flow of material despite
varying levels in the tanks – established here for each appliance – and the
two different grit sizes.
Lead and follow-up time of blasting media varied
depending on the appliance being tested as pressure build-up and release varies with each type of
appliance. The high total consumption is in some
appliances caused by an exuberant output during
the blasting time, other designs do not immediately
curb the flow in follow-up time, thus allowing the
loss of material and valuable working time. The
Basic classic builds up the required pressure rapidly, reduces it quickly after the footswitch is released,
and proves very economic during blasting.
Uniform flow of
media enhances quality
Technicians know from experience: The level of
media in the tank influences pressure build-up and
therefore the flow of blasting media. In practical use
this means pressure fluctuations and therefore a
varying amount of material being emitted while con-
Fig. 2 Application in Dr. Rusch’s in-house lab,
Owingen, Germany: When the blasting media is
emitted in an even flow, regardless of how full the
tanks are, the technician can concentrate on the
casting and condition the surface with an even panning motion. This provides for reproducible results.
ditioning castings. But constant and even flow of
material is especially important during the blasting
time. Only in this way can the technician achieve the
required quality with even panning motions (Fig. 2)
and need not adjust his method of work according to
whether the tank is full or almost empty. Considering
this, the examiners of this study determined the
material consumption of the test appliances with
varying tank levels. Measurements were taken with
the tank at one-third full, two-thirds full, and full. Two
different grit sizes were also used. According to the
Osnabrück Test, three appliances in particular emitted an especially even flow of both fine and coarse
aluminium oxide (50 micron and 125 micron) with a
simultaneously low consumption: The Basic classic,
Basic quattro IS and the SBU 5.2 Compact (Fig. 3). In
use this means: The uniform material flow of these
appliances makes it easier for the technician to reproduce good results regardless of the level in the tank
or grit size used.
© VOLUME 9 2008 dental dialogue 3
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Fig. 4 Focussed sandblasted surface with small oxide
ring from bundled jet (“laser principle”), tests with
Renfert appliance. The top six test plates were blasted
with 0.8 nozzles, the bottom six with 1.2 nozzles.
Fig. 5 Broadly blasted surface and large oxide ring
from heavily scattered material (“flashlight principle”), comparison appliance.
Blasting media focussing
really makes a difference
“The more the merrier” – is a frequently used
expression. One can deduce from the results of the
Osnabrück tests on cleaning efficiency that this is
not the case when referring to the relationship
between blasting media consumption and its effect.
Alloy test discs coated with investment were treated
for 15 seconds by the appliances and the results
then photographed. The viewer can see from this
photo documentation that the appliances of different manufacturers produce very different blasting
patterns (Fig. 4 and 5). It is apparent that the areas
freed of investment are of varying diameter depending on the appliance, and that the oxidised transition zone between the clean surface and residual
investment – also dependent on appliance – varies
in width.
This difference in cleaning results can be attributed
to the more-or-less concentrated focus of the media
flow characteristic of each appliance. It must be
stated that sand jet focussing is important for the
cleaning results. The smaller the diameter of the jet
and the smaller the sandblasted area is, the more
grit hits the surface per unit of area (Fig. 6 to 8).
Hence, the surface is cleaned more intensely.
4 dental dialogue VOLUME 9 2008 ©
At the same time, this compact “barrage” within the
focus area ensures even surface roughness. The aim
of sandblasting is to achieve a cleaned surface with
a perfectly distributed and even impact pattern.
This best prepares the metal surface for veneering
with porcelain and avoids tension resulting from firing (Fig. 9 to 12). A completely different picture,
however, is provided by wide and uneven grit distribution. The grit may even shoot past the object and
have no effect whatsoever.
This explains the relationship between focus and
material consumption quite well. The comparison of
a test disc treated with a Renfert appliance and a
disc treated by another test candidate makes this
obvious (compare Fig. 1 and 4 to 12). The Renfert
appliance produces a well-focussed stream, keeping the flow of material low and economical. In comparison, the appliance in Fig. 5 had the third highest consumption of fine-grit material and by far the
highest consumption of coarse material during
treatment. At the same time the corresponding alloy
discs exhibit a wide blasted area caused by a wide
jet with a profuse flow of material.
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Fig. 6 to 8 Blasting media saving and effectiveness: A focussed jet prevents material
shooting past the object. Instead, more particles per unit of area hit the surface within
the designated space. Hence, the surface is cleaned more thoroughly.
Fig. 9 and 10 Uneven pattern: When the jet varies in strength and the scattering is high, there is an uneven distribution pattern of
particles on the surface. Alongside areas that are hardly hit and therefore hardly “dented”, there are other areas that are hit more
frequently and therefore increasingly indented. Other areas are “thrown up” by the impact energy.
Fig. 11 and 12 Uniform pattern: When the grit is dispersed uniformly, the particles hit the surface evenly. The surface is blasted
evenly; no tension is built up in the metal-ceramic bond.
Calculated with a narrow margin
Good blasting quality (Fig. 11 to 13) on the one
hand, low consumption on the other: These are the
demands placed on an appliance that will serve
users well in everyday laboratory work. The test
results from Osnabrück University of Applied
Sciences allow exemplary calculations to be made
showing laboratory owners the differences (Fig. 16
and Tab. 1) and to show plainly the follow-up costs
of their investment.
The consumption of various appliances for lead,
blasting, and follow-up times determined by the
Osnabrück test cycles form the basis of such exemplary calculations. In addition, one can define an
exemplary term-of-use for a blasting unit of fifteen
times-a-day for a whole year. In this way the kilogramme requirement balance can be drawn up
which is then multiplied by the material price. This
provides an overview of the operating costs for blast© VOLUME 9 2008 dental dialogue 5
dd S C I E N C E
Fig. 13 Well sandblasted casting
Fig. 14 At the Osnabrück University of Applied Sciences:
A sample being scrutinised with a microscope
Fig. 15 Students from the Faculty of Dental Technology at the Osnabrück University of Applied Sciences. Following
the surface analysis, the data is evaluated with a PC.
ing media. The exemplary calculation (Table 1) for
the Renfert Basic quattro IS adds up to close to 94.00
Euros (Fig. 16). Other manufacturers’ appliances can
increase this amount to almost 640.00 Euros and
more. The range of these amounts – as also the blasting results – is a direct outcome of appliance construction.
The Osnabrück University of Applied Sciences tests
have made consumption and quality comparisons
possible which bring to light the hidden follow-up
costs of any investment and give the laboratory
owner an important tool when making such a decision. Calculated over several years, high costs can
accumulate which can expose a seemingly lowpriced purchase as being, in fact, quite expensive.
tests came about, gives tips for laboratory owners on
purchasing a sandblasting unit, and explains what
future cooperation she would like to see between
science and industry.
600
500
In the course of these results, Dr Gisela Peters interviewed Professor Dr.-Ing. Isabella-Maria Zylla. In
this interview, Professor Dr. Zylla explains how the
6 dental dialogue VOLUME 9 2008 ©
377,58 €
400
300
200
100
A discussion with …
637,42 €
700
93,38 €
0
Renfert
Basic quattro IS
Mestra
Planetarium
Vaniman
Sand Storm Expert
Fig. 16 Blasting media consumption and costs
Total consumption: mean value between
50 and 125 µm aluminium oxide
Consumption:
mean value
during all
three process
stages in g
Sandblaster
dd
Blasting tasks per
Day
Week
Month
Year**
15x
75x
300x
3150x
Expressed in
kilograms
Cost of bla- Compared
sting materi- with best in
al p.a.*
class c) in %
a) Planetarium
29.50
443
2,213
8,850
92,925
93
377,58 €
304
b) Sand Storm Expert
49.69
745
3,727
14,907
156,524
157
637,42 €
583
7.35
110
551
2,204
23,137
23
93,38 €
-
c) Basic quattro IS
* at an assumed price of € 4.06/kg
** 10.5 months
Table 1 Blasting media consumption and costs
Dr. Gisela Peters: Professor Zylla, you have
chaired the Faculty of Engineering and Computer
Science and Dental Technology of the Osnabrück
University of Applied Sciences since its formation.
You are not only responsible for teaching, but also
for further developing the scientific know-how.
What are your main areas of research at present?
Dr.-Ing. Isabella-Maria Zylla: We are involved in
developing new and testing established materials.
Above all it is our task to carry out structural and
sub-structural tests on the materials in question.
Simultaneously, we carry out technological comparisons. For example, we examine the effect that various procedures and treatment with appliances have
on the process taking place within the materials.
?
Peters: What are your research objectives?
?
Zylla: Our focus is on applied research. We formulate the questions in order to define benchmarks for
the further application of materials and processes.
Our research is designed to answer the question
“why”. We aim to provide meaningful input for further development through clarification of the cause
– for example the cause of an error. In this context,
damage research is very informative. When a material is tried beyond its limits, we can draw conclusions about correct treatment and handling. Here,
an example: With materials new to the dental field,
such as zirconium dioxide, we ask: can the way the
material behaves be directly linked to its substructure? What is responsible for this reaction? The
knowledge gained can be used to implement
changes – this applies to manufacturing as well as
processing materials.
Peters: You now have tested sandblasting appliances with regard to their effect on metal surfaces
and their efficiency. Are you satisfied with the
results?
Zylla: I would like to remark in advance, that the
objective of sandblasting is to prepare the surface
for metal-ceramic bonding. This step, among others,
therefore determines the bonding strength. In principle, all tested appliances achieved this objective.
?
Picture Credit: Dr. Gisela Peters, Bad Homburg
All appliances fulfilled the respective standard. This
means the bond-strength was at least 25 MPa. But
from the user’s point of view, there are two further
questions: The first, when I want to work efficiently,
how high is the consumption? The second: Once I
have decided on a manufacturer, can I, the laboratory owner, be sure I have purchased a product
which will deliver reliable results even after the
guarantee period has elapsed?
Peters: As far as the application tests are concerned, the appliances tested provided differing
results. What caused these large variations?
Zylla: The features and handling of the appliances
play a role here. For example, during the tests some
appliances leaked. One model, which consequently
showed higher consumption levels, leaked from the
coupling between handpiece and nozzle; others had
poor seals between tube and tank. Consumption
also increased when the tubes were not flexible
enough and manoeuvring became unmanageable.
The technical design also influences how fast the
required blasting pressure is built up and if the unit
continues releasing material after the footswitch has
been released.
?
Peters: What advice can you give laboratories?
?
Zylla: Our tests have shown there are differences
between the appliances. Therefore, not only the purchase cost should be considered, but further criteria
should also be used to help in the decision! Enquire
about how long spare parts are guaranteed to be
available. After all, you want to use your appliance
for many years. You are well advised to enquire
about a trial appliance. In this way you can gain an
impression of the appliance under laboratory conditions. You should see and test the unit yourself.
Before purchasing an appliance, you should have
changed the nozzles and also replaced and connected a tank once. It also helps to have unscrewed the
handpiece and replaced the washer. Visit local trade
fairs and have any appliance in your final selection
demonstrated to you.
© VOLUME 9 2008 dental dialogue 7
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This is what was examined during the study:
Comparison and test of efficiency of seven different sandblasters (plus one additional test). 149 pages plus appendix.
(Carried out in 2007)
Study headed by: Professor Dr.-Ing. Isabella-Maria Zylla, Faculty of Engineering and Computer Science and Dental Technology of the Osnabrück
University of Applied Sciences.
Eight current appliances available on the worldwide market were tested:
1. SBU 5.2 Compact by Averon, Yekaterinburg, Russia
5. Basic classic and
2. Platinum D.O.S. by Dentalfarm, Turin, Italy
6. Basic quattro IS by Renfert, Hilzingen, Germany
3. Planetarium by Mestra, Passau, Germany and Bilbao, Spain 7. Easy Sand by Silfradent, S. Sofia, Italy
4. MS3 by Omec, Muggiò, Italy
8. Sand Storm Expert by Vaniman, Fallbrook, California, USA
In prelude to their examination report, the examiners list the appliance characteristics observed during use. They then contribute four experiments conceived to gain information on the appliances’ blasting efficiency.
1st Assignment: The consumption.
This was ascertained with three tank levels, differentiated through measurements on lead, blasting, and follow-up times. Whereas lead and follow-up times varied from unit to unit and were dependant on build-up and reduction of the required pressure, the blasting time was set at twenty seconds for each appliance. The level in the tanks measured one-third, two-thirds, and full. The consumption test was carried out with 50
micron and 125 micron corundum. The used material was collected and weighed after each test. This showed that different amounts of blasting media were emitted by the appliances according to their design; more or less large fluctuations were observed depending on processing
stage, tank level, and grit size.
2nd Assignment: The effect of blasting media on investment and consumption
Purpose-made investment test pieces were sandblasted at a 90° angle and a distance of 3 cm for 15 seconds; the widths and depths of
the cavities were then measured. The test setup included three tank levels and two material grit sizes, as previously explained. As in
assignment no. 1, the used material was collected and weighed after each test. This test also brought to light differing results. The consumption and the crater depth and width produced on the test piece varied with the type of appliance tested.
3rd Assignment: The blasting effect on cast and roughly devested non-precious and precious test castings.
The prepared castings were treated in a predefined manner using the test appliances and then examined under a microscope. In addition,
the used blasting material was weighed. Once again there were differences in consumption depending on the appliance used; in addition,
the blasting media jet produced cleaned areas of varying size and oxide rings of greater or lesser extent.
4th Assignment: The flexural strength of the metal-ceramic bond on alloy discs
The metal discs were prepared with the test appliances before veneering with porcelain – this was the only criterion where the test discs
differed specifically. After firing, the three-point bending test according to Schwickerath was carried out. The results show the required flexural strength of 25 MPa was achieved or even exceeded in some test series, regardless of which of the eight appliances was in use. The
examiners additionally tested the allocation on the fracture plane using a scanning electron microscope. They noticed appliance-related differences regarding bonding surface boundary between metal and ceramic.
Peters: Now you have finished the blasting unit
test, what recommendations and wishes would
you like to pass on to manufacturers?
Zylla: Precisely, I would like to encourage manufacturers to make more use of the facilities at hand in
Universities of Applied Sciences. There are many
test options available, including such tests the manufacturers may not have at their disposal - we are
?
also able to provide industry and buyer with independent results. In my opinion, this provides a great
advantage for the user and both parties benefit: The
product developer and product user.
Professor Zylla, thank you very much for the friendly interview!!
Contact address
Dr. Gisela Peters • Lohrbachstraße 8 • 61350 Bad Homburg/Germany • Fon +49 (0) 61 72 - 30 10 24
Fax +49 (0) 61 72 - 30 10 25 • Mobil +49 (0) 170 - 28 55 375 • peters.gisela@t-online.de
www.concise-text.de • www.concise-pr.de
8 dental dialogue VOLUME 9 2008 ©
Professor Dr.-Ing.
Isabella-Maria
Zylla, Faculty of
Engineering and
Computer Science
and Dental
Technology of the
Osnabrück
University of
Applied Sciences.
Picture Credits: Professor Dr. Isabella-Maria Zylla, Osnabrück, Art.No. 21-1018
Source: Zylla I-M (2007): Comparison and Examination of the Efficiency of seven different sandblasters. 149 pages (plus an additional test) order-related research, Faculty of Engineering
and Computer Science and Dental Technology of the Osnabrück University of Applied Sciences