8
Remanufacturing and Advanced Machining
• Reduction of shrinkage and tightening defects and thus improvement of
product quality
• Reduction of final product mass while keeping its strength
• Reduced requirements for the nominal clapping force and power of the
related mechanisms
• Cost saving on instrumentation
In addition, the following benefits of economical production should be mentioned
(Kastner and Steinbichler, 2020):
• Dissolved gases can reduce the viscosity of polymer melts by more than
50%, leading to lower energy consumption during dosing, longer flow
lengths, and reduced injection pressures.
• Lower pressures, in combination with the absence of a packing stage, can
allow for smaller clamping units.
However, it must be considered that bubbles in the polymer melt reduce heat transfer
prolonging the cooling stage. Moreover, some blowing agents may behave like oxidants, affecting the tooling.
Nowadays, molds and their working parts may be fabricated out of aluminum and
its alloys, reducing expenses. The durability of aluminum molds is shorter than that
of steel ones, but it is sufficient to run 50 and even 100 thousands of cycles. In the
case of small lot production, e.g., for experimental purposes, tooling can be applied
based on epoxy matrix composites with metal frames and strengthening inserts.
1.2.2 Polymer foaming and Processing
There are two different methods of obtaining polymer foams from gas production
during the foaming process, namely with physical blowing agents and with chemical blowing agents. Properties of 23 groups of blowing agents and their selection,
quantity, and technology of processing for 44 polymers can be found in (Wypych,
2017). The author also evaluates the importance of foaming parameters, including
the amount of blowing agent, clamping pressure, die and mold pressure and temperature, delay time, desorption time, gas content, gas flow rate, gas injection location,
gas sorption and desorption rates, internal pressure after foaming, saturation pressure, saturation temperature, screw revolution speed, and surface tension.
Chemical blowing agents cause the formation of gas bubbles due to their decomposition to solid and gas fractions at high temperatures. The agent is mixed with the
molten polymer either prior to or during plasticization. Proportions of the chemical
blowing agents solved in the polymer may be from 0.25 up to 5% by volume, depending on chemical composition and expected foaming effects (Vovk et al., 2018). The
most important chemical blowing agents are ammonium bicarbonate (decomposition temperature 60°C), sodium bicarbonate (decomposition temperature interval
100–140°C), and sodium borohydrate (decomposition temperature 300°C). In some
cases, water can be also used as a blowing agent (Feldman, 2010).
Remanufacturing and Advanced Machining
• Reduction of shrinkage and tightening defects and thus improvement of
product quality
• Reduction of final product mass while keeping its strength
• Reduced requirements for the nominal clapping force and power of the
related mechanisms
• Cost saving on instrumentation
In addition, the following benefits of economical production should be mentioned
(Kastner and Steinbichler, 2020):
• Dissolved gases can reduce the viscosity of polymer melts by more than
50%, leading to lower energy consumption during dosing, longer flow
lengths, and reduced injection pressures.
• Lower pressures, in combination with the absence of a packing stage, can
allow for smaller clamping units.
However, it must be considered that bubbles in the polymer melt reduce heat transfer
prolonging the cooling stage. Moreover, some blowing agents may behave like oxidants, affecting the tooling.
Nowadays, molds and their working parts may be fabricated out of aluminum and
its alloys, reducing expenses. The durability of aluminum molds is shorter than that
of steel ones, but it is sufficient to run 50 and even 100 thousands of cycles. In the
case of small lot production, e.g., for experimental purposes, tooling can be applied
based on epoxy matrix composites with metal frames and strengthening inserts.
1.2.2 Polymer foaming and Processing
There are two different methods of obtaining polymer foams from gas production
during the foaming process, namely with physical blowing agents and with chemical blowing agents. Properties of 23 groups of blowing agents and their selection,
quantity, and technology of processing for 44 polymers can be found in (Wypych,
2017). The author also evaluates the importance of foaming parameters, including
the amount of blowing agent, clamping pressure, die and mold pressure and temperature, delay time, desorption time, gas content, gas flow rate, gas injection location,
gas sorption and desorption rates, internal pressure after foaming, saturation pressure, saturation temperature, screw revolution speed, and surface tension.
Chemical blowing agents cause the formation of gas bubbles due to their decomposition to solid and gas fractions at high temperatures. The agent is mixed with the
molten polymer either prior to or during plasticization. Proportions of the chemical
blowing agents solved in the polymer may be from 0.25 up to 5% by volume, depending on chemical composition and expected foaming effects (Vovk et al., 2018). The
most important chemical blowing agents are ammonium bicarbonate (decomposition temperature 60°C), sodium bicarbonate (decomposition temperature interval
100–140°C), and sodium borohydrate (decomposition temperature 300°C). In some
cases, water can be also used as a blowing agent (Feldman, 2010).