Note: Descriptions are shown in the official language in which they were submitted.
1
Hydraulic fluids containing a polyalkyl(meth)acrylate viscosity improver
for use in plastic iniection molding processes
Technical field of the Invention
The present invention relates to the use of hydraulic fluids in plastic
injection molding processes. Thereby
it was surprisingly found that the use of hydraulic fluids with the right
combination of physical parameters
like the viscosity grade, the viscosity index, the density and the dispersancy
allows for significant energy
savings in plastic injection molding processes (PIM). The PIM process is an
industrial process to
manufacture plastic parts at well controlled temperatures, pressures and cycle
times. The energy
consumption of the process became more important over the last years, however,
other parameters like
process stability and accuracy of plastic part parameters as well as machine
protection and long oil drain
intervals have to be satisfying.
Background of the Invention
Injection molding is a manufacturing process for producing parts by injecting
material into a mould at well
controlled temperatures, pressures and cycle times. Injection moulding can be
performed with a host of
materials, including metals, glasses, elastomers, confections, and most
commonly thermoplastic and
thermosetting polymers. Material for the part is fed into a heated barrel,
mixed, and forced into a mold
cavity, where it cools and hardens to the configuration of the cavity.
The power required for this process of injection molding depends on the
various movements in the molding
machine, but also varies between materials used. The book Manufacturing
Processes Reference Guide
from Robert Todd states that the power requirements depend on a material's
specific gravity, melting point,
thermal conductivity, part size, and molding rate. Injection moulding machine
is actuated by hydraulic
system, wherein the electrical energy is transformed into mechanical energy
through hydraulic energy. The
energy reaches the actuators in the form of pressure and volume flow. While
transmitting power through
hydraulic forces, a loss of energy is observed due to flow losses and
friction. In addition, the compression
of hydraulic fluid develops frictional heat, which has to be controlled for
example by cooling. Pump type and
control of that pump also contribute heavily to how efficient a molding
machine is in processing the plastic.
In the state of the art some efforts were made to save energy by modification
of the injection molding
machines. In EP 0 403 041 for example special alternating-current servo motors
for the pumps which are
connected to the hydraulic consumers are used. In US 4,020,633 a completely
new concept for the whole
hydraulic drive system of the injection molding machine is disclosed. But none
of these concepts touches
the hydraulic fluid that is used here. Therefore it must be possible to
realize additional energy savings by
optimizing these fluids.
EP 2337832 discloses a method of reducing noise generation in a hydraulic
system, comprising contacting
a hydraulic fluid comprising a polyalkyl(meth)acrylate polymer with the
hydraulic system. The hydraulic fluid
has a Viscosity Index VI of at least 130. The polyalkyl(meth)acrylate has a
molecular
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weight in the range of 10 000 to 200 000 g/nnol and is obtained by
polymerizing a mixture of olefinically
unsaturated monomers, said mixture comprising preferably 50 to 95 wt% 09 to
Cio and 1 to 30 wt% of
Ci to C8.
Target of the invention described in EP 2337832 was the reduction of noise
which is achieved by
increasing oil viscosities at higher temperatures. For this effect high
viscosities and high densities are
beneficial and the high VI of the fluids is used to increase the viscosity at
the operating temperature.
In the present invention a completely different approach is used to increase
the energy efficiency. A high
VI is used to enable a reduction of the base fluid viscosity. This reduced
viscosity in combination with a
low density of the hydraulic base fluid increases the efficiency of the
injection molding process. In
comparison to EP 2337832 it is not expected that hydraulic fluids according to
the present invention
decrease the noise level.
EP 2157159 discloses a hydraulic fluid containing, as a base oil, an ester
containing at least two ring
structures. It is described that the hydraulic fluid has low energy loss due
to compression and exhibits
excellent responsiveness when being used in a hydraulic circuit. Consequently,
the hydraulic fluid
realizes energy-saving, high-speed operation and high precision of control in
the hydraulic circuit.
EP 1987118 discloses the use of a fluid with a viscosity improving index of at
least 130 for the use in
hydraulic systems like engines or electric motors. This fluid comprises a
copolymer of Ci to C6
(meth)acrylates, 07 to 040 (meth)acrylates and optionally further with
(meth)acrylates copolymerizable
monomers in a mixture of an API group ll or III mineral oil and a
polyalphaolefine with a molecular weight
below 10,000 g/mol. It is neither shown here that such a fluid is also usable
in an injection molding
machine nor which specific composition of the fluid would be applicable in
such a machine.
However, there still exists a need to investigate further on possible
alternative hydraulic fluid
compositions to be used in a hydraulic system subject to high working
pressure, like in plastic injection
molding processes.
Object
The improvement of energy efficiency is a common object in the technical field
of injection molding.
Usually such objects are achieved by construction improvements of the unit
providing mechanical
energy of the hydraulic system. However, there is still a need for further
improvements with regard to
that object. Accordingly, the purpose of the present invention was to provide
a method for saving energy,
increase productivity, avoid heating, improve air release and avoid cavitation
over a broad temperature
operating window in a hydraulic system used in plastic injection molding
processes.
Especially was the object of the present invention to improve the performance
of a hydraulic system in
a plastic injection molding machine with energy savings of at least 5% and of
up to 10%, compared to
the performance of a machine when run with a standard fluid having a VI around
100 as recommended
3
by the producers of injection molding machines. It was also object to realize
an energy saving for single,
very energy consuming process steps of more than 10%.
Especially it was the object of the present invention to realize this energy
saving by providing a new
hydraulic fluid for the use in plastic injection molding machines.
Further objects not explicitly discussed here may become apparent herein below
from the prior art, the
description, the claims or exemplary embodiments.
Description of the Invention
The above-indicated prior art documents relating to injection molding
processes try to reduce energy
consumption, but without changing oil parameters. After an exhaustive
investigation, the inventors have
unexpectedly found that the hydraulic fluid plays a crucial role for saving
energy in plastic injection molding
processes, and in particular that some hydraulic fluid compositions adjusted
to the right physical
parameters, allow for energy savings of up to 5 % or more in the overall
plastic injection molding process
(PIM), or more than 10%, mostly up to 15% for certain step of the PIM process.
Indeed, by adjusting the
viscosity grade, the viscosity index, the density and dispersancy of the
hydraulic fluid in accordance with
the present invention, the inventors have found that a significant amount of
energy can be advantageously
saved, even by operating at high pressure conditions as it is usual in PIM
processes.
In detail, the objects discussed above have been solved by a novel method of
reducing the energy
consumption of a hydraulic system in an industrial hydraulic application,
preferably in a plastic injection
molding process or in a process comprising a hydraulic press. In this method a
hydraulic fluid is used in a
plastic injection molding process. The hydraulic fluid composition thereby
comprises (i) a
polyalkyl(meth)acrylate viscosity index improver and (ii) a base oil.
The polyalkyl(meth)acrylate viscosity index improver (i) thereby comprises at
least monomer units a) and
b) and optionally monomer units c) and/or d). Preferably the component (i) has
a weight average molecular
weight (Mw) from 20,000 to 100,000 g/mol. More preferred the molecular weight
Mw is between 30,000 and
85,000 g/mol and especially preferred between 40,000 and 70,000 g/mol. The
polydispersity index of the
polyalkyl(meth)acrylate viscosity index improver is between 1 and 4, preferred
between 1.2 and 3.0 and
most preferred between 1.5 and 2.5.
The polyalkyl(meth)acrylate viscosity index improver (i) contains 5 to 40
wt.%, preferred 7 to 30 wt.%, more
especially preferred 10 to 25 wt.% of repeating units that have been obtained
by the copolymerization of
monomers a) and 50 to 95 wt.%, preferred 60 to 93 wt.%, more especially
preferred 70 to 90 wt.% of
repeating units that have been obtained by the copolymerization of monomers
b). In a special embodiment
of the invention the amount of the compound of formula (II) is between 75 and
90 wt.%, especially preferred
between 70 and 80 wt.%.
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Monomers a) thereby are one or more ethylenically unsaturated ester compounds
of formula (I)
(I)
R3 1
R2 0
wherein R is equal to H or CH3, R1 represents a linear or branched alkyl group
with 1 to 6 carbon atoms
and R2 and R3 independently represent H or a group of the formula -COOR',
wherein R' is H or an alkyl
group with 1 to 5 carbon atoms.
Examples of component a) are, among others, (meth)acrylates, fumarates and
maleates, which derived
from saturated alcohols such as methyl (meth)acrylate, ethyl (meth)acrylate, n-
propyl (meth)acrylate,
isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate
and/or pentyl (meth)acrylate;
cycloalkyl (meth)acrylates, like cyclopentyl (meth)acrylate. Methacrylates are
even preferred over
acrylates.
Monomers b) are one or more ethylenically unsaturated ester compounds of
formula (II)
(II)
LI
R6 OR
R5 0
wherein R is equal to H or CH3, R4 represents a linear or branched alkyl group
with 7 to 15 carbon atoms
and R5and R6 independently represent H or a group of the formula -COOR",
wherein R" is H or an alkyl
group with 6 to 15 carbon atoms.
Among these are (meth)acrylates, funnarates and nnaleates that derive from
saturated alco-hols, such
as n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl (meth)acrylate,
2-tert-butylheptyl
(meth)acrylate, octyl (meth)acrylate, 3-isopropylheptyl (meth)acrylate, nonyl
(meth)acrylate, decyl
(meth)acrylate, undecyl (meth)acrylate, 5-methylundecyl (meth)acrylate,
dodecyl (meth)acrylate, 2-
methyldodecyl (meth)acrylate, tridecyl (meth)acrylate, 5-nnethyltridecyl
(meth)acrylate, tetradecyl
(meth)acrylate and/or pentadecyl (meth)acrylate.
The polyalkyl(nneth)acrylate viscosity index improver (i) may also contain
further components that are in
form of a monomer copolymerizable with at least one of the components a) and
b). These further
monomers are especially the components c) and d), with c) in a maximal
concentration of 30 wt.% and
d) in a maximal concentration of 10 wt.%.
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Monomers c) thereby represent one or more ethylenically unsaturated ester
compounds of formula (Ill)
(Ill)
R9 OR7
R8 0
wherein R is equal to H or CH3, R7represents a linear or branched alkyl group
with 16 to 30 carbon
atoms and R8 and R9 independently represent H or a group of the formula
¨COOR¨, wherein R¨ is H
or an alkyl group with 16 to 30 carbon atoms.
Examples of component c) are, among others, (nneth)acrylates, funnarates and
nnaleates, which derived
from saturated alcohols such as 2-nnethylhexadecyl (meth)acrylate, heptadecyl
(meth)acrylate, 5-
isopropylheptadecyl (meth)acrylate, 4-tert-butyloctadecyl (meth)acrylate, 5-
ethyloctadecyl
(meth)acrylate, 3-isopropyloctadecyl (meth)acrylate, octadecyl (meth)acrylate,
nonadecyl
(meth)acrylate, eicosyl (meth)acrylate, cetyleicosyl (meth)acrylate,
stearyleicosyl (meth)acrylate and/or
docosyl (meth)acrylate.
Optionally, the the polyalkyl(meth)acrylate viscosity index improver (i)
contains 5 to 20 wt.% of the
monomers a), 70 to 90 wt.% of the monomers b) and 2 to 25 wt.% of the monomers
c) in polymerized
form.
Monomers d) are at least one N-dispersant monomer. Preferred this N-dispersant
monomer is of the
R1 l(R10
R12 R13
formula (IV)
wherein R19, R11 and R12 independently are H or an alkyl group with 1 to 5
carbon atoms and R13 is either
a group C(Y)X-R14 with X = 0 or NH and Y is (=0) or (=NR15), where R15 is an
alkyl or aryl group. R14
represents a linear or branched alkyl group with 1 to 20 carbon atoms which is
substituted by a group
NR16R17, where R16 and R17 independently represent H or a linear or branched
alkyl group with 1 to 8
carbon atoms, or wherein R16 and R17 are part of a 4 to 8 membered saturated
or unsaturated ring
containing optionally one or more hetero atoms chosen from the group
consisting of nitrogen, oxygen
or sulfur, wherein said ring may be further substituted with alkyl or aryl
groups.
Alternatively R13 is a group NR18R19, wherein R18 and R19 are part of a 4 to 8
membered saturated or
unsaturated ring, containing at least one carbon atom as part of the ring
which forms a double bond to
a hetero atom chosen from the group consisting of nitrogen, oxygen or sulfur,
wherein said ring may be
further substituted with alkyl or aryl groups.
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Preferably, said dispersant monomer d) of polymer (i) is at least one monomer
selected from the group
consisting of N-vinylic monomers, (meth)acrylic esters, (meth)acrylic amides,
(meth)acrylic innides each
with N-containing, dispersing moieties in the side chain. In particular it is
preferred that the N-dispersant
monomer is at least one monomer selected from the group consisting of N-vinyl
pyrrolidone, N,N-
dimethylanninoethyl nnethacrylate and N,N-
dimethylanninopropyInnethacrylannide.
Optionally the polyalkyl(meth)acrylate viscosity index improver (i) contains 5
to 25 wt.% of the monomers
c) and 1 to 7 wt.% of the monomers d), both in polymerized form. Especially
the viscosity index improver
(i) contains 10 to 20 wt.% of the monomers c) and 2 to 5 wt.% of at least one
N- dispersant monomer d)
in polymerized form.
For this invention the base oil (ii) is selected from API group I, II, Ill or
IV base oils or a mixture thereof.
By using one of these base oils or mixtures of at least two of these base oils
together with the viscosity
index improver (VII) described above the formulated hydraulic fluid of this
invention has a fresh oil
viscosity index of at least 160, a viscosity at 40 C of 15 cSt to 51 cSt and a
density at 15 C of 800 kg/m3
to 890 kg/nn3. Especially preferred are API group IV base oils in form of
polyalphaolefin (PAO) or mixtures
of API group Ito IV base oils containing at least 50 wt.% polyalphaolefins.
Synthetic hydrocarbons, especially polyolefins are well known in the art as
API group IV base oils. These
compounds are obtainable by polymerization of alkenes, especially alkenes
having 3 to 12 carbon
atoms, like propene, 1-hexene, 1-octene, 1-decene and 1-dodecene, or mixtures
of these alkenes.
Preferred PAOs have a number average molecular weight in the range of 200 to
10000 g/nnol, more
preferably 500 to 5000 g/nnol.
In particular the hydraulic fluid composition comprises 70 to 95 wt.%, more
preferably 80 to 95 wt.% and
even more preferably 80 to 90 wt.% of the base oil (ii) selected from API
group I, II, III or IV base oils or
mixture thereof and 5 to 30 wt.%, more preferably 5 to 20 wt.% and even more
preferred 10 to 20 wt.%
of the polyalkyl(nneth)acrylate viscosity index improver (i). Especially
suitable are hydraulic fluids
corresponding to this invention having a viscosity index of at least 180,
preferred of at least 200,
especially preferred of at least 250 and a viscosity at 40 C of 15 cSt to 36
cSt, preferred between 15
cSt and 28 cSt, especially preferred between 19 cST and 28 cST. Furthermore it
is advantageous, if the
hydraulic fluid has a density at 15 C of 800 kg/nn3 to 860 kg/n3, preferred of
800 kg/m3 to 840 kg/n3.
By calculating the hydraulic fluid composition it has to be considered that
the viscosity index improver
(VII) might be added in a solvent. In a preferred embodiment of this invention
this solvent is also an API
group I, II, Ill or IV oil. It is especially preferred that this solvent is
identical to the base oil of the
composition. Independently from the solvent that is used here it has to be
calculated as part of the base
oil in the composition. Usually the VII solution that is added contains 20 to
40 wt.% solvent.
The viscosity index can be determined according to ASTM D 2270.
7
The hydraulic fluid composition according to this invention may also contain a
Dispersant-Inhibitor package
(DI package) to improve parameters like foam, corrosion, oxidation, wear and
others. This DI package may
comprise antioxidants, antifoam agents, anticorrosion agents and/or at least
one Phosphorous or Sulfur
containing antiwear agent.
Technical benefits of this invention
High VI hydraulic fluids are typically applied in mobile applications such as
excavators. In these applications
the hydraulic fluid has to deal with a broad variety of temperatures ¨very low
starting temperatures in winter
and very high temperatures under heavy load conditions. The high VI of the
fluid is required to keep the
viscosity as close as possible to the optimum. The optimum is defined by the
balance between mechanical
efficiency which requires a thin oil and volumetric efficiency which requires
a thick oil to minimize losses by
internal leakage in the pump. In regular operating conditions and especially
under heavy load conditions
volumetric efficiency becomes the dominant factor and the viscosity index
improver can greatly improve the
efficiency by increasing the viscosity of the fluid.
The injection molding application is completely different compared to an
excavator. The outside
temperature is constant, the work cycle is well defined and heavy load
conditions are avoided if possible.
For this reason the oil temperature is rather constant and high VI base fluids
are generally not used. Usually
IS046 monograde fluids are recommended by the producers of injection molding
machines.
For these reasons it would not be expected to see an advantage of high VI
fluids in an application as
injection molding, but surprisingly we found significant energy savings when
low-viscosity hydraulic fluids
with high VI were used. Completely opposed to the well-described energy
savings with high VI fluids in
excavators the efficiency increase in injection molding is largest under low
load conditions.
Surprisingly said method as defined above respectively in accordance with the
present invention not only
achieves the above-mentioned objectives, but also advantageously provides an
increased oil life time with
consequent longer drain intervals for the hydraulic system.
Furthermore, the system performance of the hydraulic system can be improved.
The expression system
performance means the work productivity being done by the hydraulic system
within a defined period of
time. Particularly, the system performance can be improved at least 5%, more
preferably at least 10%. In
preferred systems, the work cycles per hour can be improved.
Synthesis of the viscosity index improver
For the synthesis of the polyalkyl(meth)acrylate viscosity index improver (i)
the monomer mixtures
described above can be polymerized by any known method. Conventional radical
initiators can be used to
perform a classic radical polymerization. These initiators are well known in
the art. Examples for these
Date recue/date received 2021-10-22
8
radical initiators are azo initiators like 2,2'-azodiisobutyronitrile (AIBN),
2,2'-azobis(2-methylbutyronitrile)
and 1,1 azo-biscyclohexane carbonitrile; peroxide compounds, e.g. methyl ethyl
ketone peroxide, acetyl
acetone peroxide, dilauryl peroxide, tert.-butyl per-2-ethyl hexanoate, ketone
peroxide, me-thyl isobutyl
ketone peroxide, cyclohexanone peroxide, dibenzoyl peroxide, tert.-butyl per-
benzoate, tert.-butyl peroxy
isopropyl carbonate, 2,5-bis(2-ethylhexanoyl-peroxy)-2,5-dimethyl hexane,
tert.-butyl peroxy 2-ethyl
hexanoate, tert.-butyl peroxy- 3,5,5-trimethyl hexanoate, dicumene peroxide,
1,1 bis(tert. butyl peroxy)
cyclohexane, 1,1 bis(tert. butyl peroxy) 3,3,5-trimethyl cyclohexane, cumene
hydroperoxide and tert.-butyl
hydroperoxide.
Poly(meth)acrylates with a lower molecular weight can be obtained by using
chain transfer agents. This
technology is ubiquitously known and practiced in the polymer industry and is
de-scribed in Odian,
Principles of Polymerization, 1991.
Furthermore, novel polymerization techniques such as ATRP (Atom Transfer
Radical Polymerization) and
or RAFT (Reversible Addition Fragmentation Chain Transfer) can be applied to
obtain useful polymers
derived from alkyl esters. These methods are well known. The ATRP reaction
method is described, for
example, by J-S. Wang, et al., J. Am. Chem. Soc., Vol. 117, pp. 5614-5615
(1995), and by Matyjaszewski,
Macromolecules, Vol. 28, pp. 7901-7910 (1995). Moreover, the patent
applications WO 96/30421, WO
97/47661, WO 97/18247, WO 98/40415 and WO 99/10387 disclose variations of the
ATRP explained
above. The RAFT method is extensively presented in WO 98/01478, for example.
The polymerization can be carried out at normal pressure, reduced pressure or
elevated pressure. The
polymerization temperature is also not critical. However, in general it lies
in the range of -20 to 200 C,
preferably 60 to 120 C, without any limitation intended by this. The
polymerization can be carried out with
or without solvents. The term solvent is to be broadly understood here.
According to a preferred
embodiment, the polymer is obtainable by a polymerization in API Group I, ll
or III mineral oil or in API
group IV synthetic oil.
Examples
The invention is illustrated further in the following non-limiting example and
the comparative example
(reference oil). The example below serves for further explanation of preferred
embodiments according to
the present invention, but are not intended to restrict the invention. All
results are shown in Table 1 and
Table 2.
Testing and Oils
For determining the energy consumption, different test oils were compared with
a reference (ISO VG 46
monograde Castrol HyspinTM OF Top 46, VI = 100).
Date recue/date received 2021-10-22
9
The following hydraulic fluids are used:
Table 1: Hydraulic fluid formulations
Formulation KV40 KVioo VI density 15 C
[mm2/s] [mm2/s] [kg/L]
Comparative 0.85% HitecTM 521 Fresh oil: 46.6 7.6 131
0.847
Example 1 8% NexbaseTM Fill for trial: 46.6 7.6 130
3060 After trial: 46.5 7.6 130
91.15% Nexbase
3080
Comparative Aral ForbexTM SE Fresh oil: 47.2 8.2 148 0.973
Example 2 Fill for trial: 47.0 8.2 149
After trial: 46.9 8.2 149
Reference Oil Castrol Hyspin OF Fresh oil: 45.7 6.7 100 0.873
Top 46 Fill for trial: 45.7 6.7 100
After trial: 45.7 6.7 100
Example 1 5.8% PAMA-1 Fresh oil: 46.3 8.4 160 0.851
0.85% Hitec 521 Fill for trial: 46.3 8.4 160
21% Nexbase 3080 After trial: 46.1 8.3 158
72.35% Nexbase
3060
Example 2 14.2% PAMA-1 Fresh oil: 46.6 9.8 203 0.853
0.85% Hitec 521 Fill for trial: 46.2 9.7 201
17.45% Nexbase After trial: 46.0 9.6 200
3060
67.5% Nexbase
3043
Example 3 8.8 % PAMA-1 Fresh oil: 32.0 7.0 189 0.842
DI package Fill for trial: 32.1 7.0 189
Nexbase After trial: 32.3 7.0 189
3043+3060
Example 4 20% PAMA-2 Fresh oil: 25.7 7.5 285 0.831
DI package Fill for trial: 25.8 7.5 283
PA0-2 After trial: 25.7 7.4 281
The polyalkylmethacrylate viscosity index improver PAMA-1 consists of 13 wt.%
of methyl methacrylate
and 87 wt.% of C12_14 alkyl methacrylates (M ,N= 52,000 g/mol, PDI = 2.1),
dissolved in highly refined mineral
oil.
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The polyalkylmethacrylate viscosity index improver PAMA-2 consists of 10 wt.%
of methyl methacrylate
and 90 wt.% of 012-15 alkyl methacrylates = 58,000 g/mol, PDI = 2.0),
dissolved in highly refined mineral
oil.
Properties Method
Kinematic viscosity at 40 C, mm2/s ASTM 0445
Kinematic viscosity at 100 C, mm2/s ASTM 0445
VI ASTM 02270
Density at 15 C, kg/L ASTM 01298
The injection molding machine that was used to create the data was Krauss
Maffei KM 80/380 CX. The
energy consumption of the hydraulic pump was calculated by measuring voltage
and current of the pump
motor with external test equipment (measuring amplifier MX 840 PAKAP; element
for voltage recording MX
403 B, 1000V; both from Hottinger Baldwin Messtechnik GmbH). Before testing
the system was flushed
with the hydraulic fluid to be used and the oil parameters were checked to
ensure that the previous oil was
properly purged and no mixing with previous oils occurred. Table 1 shows
viscometric data for fresh oils,
oil fill for trial and for the oil collected after the trial.
During testing, molding cycles were run with a PLEXIGLAS -molding compound
which was, in cycle A,
covered with CoverForm Reactive-Liquid cf300A monomer mixture.
The evaluation of data has focussed on process steps without polymer to avoid
any influence of polymer
properties on the results.
Brief description of the drawings
Figure 1: Description of a typical injection molding cycle
The cycle begins when the mold closes (Step 1), followed by building up a
pressure (Step 2a) which is
required to keep the mold closed during injection. After moving the extruder
to the mold (Step 2b), material
is injected (Step 3) and a working pressure is maintained to compensate
material shrinkage during molding
(Step 4). Optionally, the work piece can be coated with a CoverForm process
step (Step 4.1, applied in
Cycle A). The extruder is moved back when the cooling phase has started (Steps
5 and 6). At the end of
the cooling phase the mold is opened (Step 7) and the work piece can be
removed (Step 8).
Table 2 shows the differences in energy consumption (savings are negative
values) found for cycle A, cycle
B and an evaluation of Step 1 and Step 2 taken from cycle A data.
Cycle A: Step 1 + Step 2 (2a+2b) + Step 4.1 + Step 7 + Step 8
Cycle B: Step 1 + Step 2 (2a+2b) + Step 7 + Step 8
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11
Within this cycle, Steps 1, 2, 4.1, 7 and 8 are independent of the material
which is injected. Consequently,
the energy savings are independent on the plastic material properties.
The coating step 4.1 is optional and part of the CoverForm process. Cycle A
(with coating) and cycle B
(without coating) evaluate the influence of this step on energy savings.
Table 2: Differences in energy consumption with investigated hydraulic
fluids
Comparative Comparative Ex 1 Ex 2 Ex 3
Ex 4
Ex 1 Ex 2
A energy consumption versus reference oil
Cycle A 3.6 -4.9 -7.5 -6.7
Cycle B 2.5 5.1 -5.4 -7.9 -5.2 -9.5
Step 1 + Step 2 2.1 -7.0 -8.6 -5.7
Cycle A: process steps which are material independent, with
CoverForm process step
Cycle B: process steps which are material independent, without
CoverForm process step
Step 1 + Step 2: fully material independent steps before material injection
On the basis of the above results, it is clearly demonstrated that physical
parameters of the base oil in
combination with a viscosity index improver in accordance with the present
invention are crucial in order to
observe energy savings in an hydraulic system used under the high pressure
conditions of a plastic injection
molding process.
Although illustrated and described herein with reference to certain specific
embodiments, the present
invention is nevertheless not intended to be limited to the details shown.
Rather, various modifications may
be made in the details within the scope of the claims.
Date recue/date received 2021-10-22
