Tyre Asia April/May 2018 97
mixing line of 25,000 m3 and 30,000 m3
respectively.
For the assumed number of mixing
lines, an additional 55,000 m3 of space
is required for option 1, which would
mean an additional investment volume
of eUR 16.5 million for an assumed 300
eUR/m3 of production costs, including
ancillary costs and installations for
the reconstructed area. This results in
additional annual operating expenses
from AFA (depreciation of fixed assets)
and interest charges of eUR 880,000 (4
per cent interest, depreciation period of
30 years).
If the additional installation costs for
option 1 are added, additional costs are
estimated to be approximately eUR 1
million, assuming a 20% installation cost
based on the investment sum shown in
Table 2.
When the possibility of saving on the
mixing stages is looked at, the tandem
process brings other advantages with
it. This means that much less storage
space is needed for the mixed batches.
There are fewer transports and the
risk of confusion and consequently the
complexity expense is minimised.
If, for example, one assumes that one half
of the mixing stage can be saved in terms
of the 2.3 mixing stages, only 1.8 mixing
stages corresponding to 180,000 to/a
would be produced. Some compounds
would then have to be developed in a
single stage and remill stages would
be omitted. This scenario is certainly
considered ambitious, but it can be seen
as realistic. Based on 5.68 cents/kg,
this would result in a further saving of
2.84 million eUR/a for the pure mixing
production plus the saving of the building
area for temporary/interim storage.
These would have to be taken into
account with an annual cost of eUR 0.256
million for depreciation of fixed assets
and interest if a depreciation period of 30
years, 4 per cent imputed interest, 8 m2/t
space requirement for interim storage
[3] and 2 days storage horizon based on
the base compound requirements are
assumed. This results in a total saving
of eUR 3.095 million/a. The reduction
in investment costs for the eliminated
interim storage would be eUR 4.8 million.
Ancillary costs such as the heating
of these areas are ignored here.
consequently, this reduction in
the number of mixing stages would
render it unnecessary to provide the
corresponding mixing capacity as
this is not required at all. This would
further reduce the investment costs for
machinery and buildings, which shall not
be considered further.
In summary, it is clear that option 1
would result in significantly higher
investments. In the sample calculation,
this would be eUR 27.7 million for the
total of machinery investment, building
and installation. The annual operating
costs for option 1 are eUR 2.768 million/a
due to the higher specific mixing costs
and the need for a larger building. The
saving of half a mixing stage on average
would amount to 5.68 cents/kg of specific
mixing costs and a smaller required
building volume of 16,000 m3, an
additional potential saving of eUR 3,095
million/a. Total saving therefore should
be in the order of approximately eUR 6
million/a, as this simplified calculation
method did not evaluate all the monetary
benefits of the tandem process.Summary
In terms of quality and economy, the
tandem process shows considerable
potential for the production of final
compounds.
It presents significant benefits in
the possibility of process division in
dispersion and distribution, reducing the
mixing time or increasing throughput.
As the mixing time in the upper mixer
has to be at least 50 per cent of the
mixing time of a comparable conventional
process, the mixing time is generally
longer due to the same dwell time in the
upper and lower mixer. If the mixing
time in the upper mixer can be shortened
by only as much as 25 per cent, as the
example of the carbon black mixtures
shows, the tandem process results in a
significantly longer total mixing time.
This has a positive effect on the mixingquality, which can subsequently reduce
the number of mixing stages.Further advantages from the lower
mixer without a ram can be seen in
the better degassing performance in
reactive mixtures and the possibility
to add rework material to the lower
mixer without affecting capacity. The
underfilled lower mixer also provides
the mixture with a larger cooling
surface, resulting in lower equilibrium
temperatures which can result in shorter
reaction times in the case of reactive
mixtures when the rotor speeds are
adapted.From an economic point of view, it is
clear that not only the relative savings
potential due to the possible mixing time
reductions are relevant for the individual
mixing families, but the required absolute
mixing quantities per mixing family also
need to be considered. The absolute
savings potential is usually the greatest
despite relatively low savings in carbon
black base compounds and the final
compound quantities.
hence, the tandem process has
economic benefits which, in addition to
the depreciation and interest charges
resulting from the investments, also
depend on the amount of energy and
personnel costs when looking at the
specific mixing costs. In the case of a
comparable compound spectrum, it
is generally necessary to have fewer
tandem lines compared to conventional
mixing lines, which reduces both the
space required and the installation costs,
despite the necessary additional building
height and the higher investment costs
for a tandem line. Furthermore, the
possibility of reducing the mixing stages
opens up great potential, as there is
less need for mixing capacity, storage
requirements for the interim mixed
batches and logistical expenditure,
which reduces the complexity of the
manufacturing process. This would
lead to further advantages and benefits
in terms of capacity and required
investments.
References:
[1] http://www.dasreifenlabel.de
[2] https://rubbermachineryworld.com/
tag/dr-julius-peter/
[3] Limper, A., Kelting, U., Analyse
von Kostenstrukturen bei der
Mischungsherstellung in der
Elastomertechnik, VDI Jahrestagung
2004, Ulm (Limper, A., Kelting, U.,
Analysis of Cost Structures in Mixture
Production in Elastomer Technology,
VDI Annual Conference 2004, Ulm)
Contact: [email protected]