The apparatus of hot pressing
The sample processed by the ‘twin-screw extrusion’ method is shaped into a dump bell type by the hot pressing process. The apparatus for this process is shown in the following figure 2.
Figure 2: The real figure of apparatus for hot pressing[1]
Generally, the apparatus of hot pressing includes some core equipment, such as the upper and lower plate, base plate, heating cooling plate and the heat insulating plate[2], and so on. Besides, the machining model is also an important part for the confectioning of the solid polymer mixture of PLA and PBS, as well as a container for the solid/molten mixture. A possible example of the apparatus is shown in the following figure:
Figure 3: The component schematic diagram of the apparatus[3]
Besides, in some cases where there is a need for high accuracy and sensitivity, the temperature and pressure sensors may be utilized. It depends on the operating conditions.
References
[1] The hot pressing apparatus: Modification of PLA. Retrieved from xtm888.skxox.com/
[2] Zhang Z Z, Qiu J Z. Development of hot-press molding machine based on polymer micro-nano manufacturing technology [J]. Manufacturing automation,2017,39(02):106-108.
[3] Budakci, Mehmet & Sonmez, Budakci, Mehmet & Sonmez, Abdullah & Pelit, Hüseyin. (2015). Effects of Thermomechanical
Densification and Heat Treatment on Density and Brinell Hardness of Scots Pine (Pinus sylvestris L.) and Eastern Beech (Fagus orientalis L.). Bioresources. 10. 3097-3111.10.15376/biores. 10.2.3097-3111.
[4]What are the Environmental Effects of Plastic Injection Moulding? Retrieved from https://lerablog.org/business/industry/what-are-the-environmental-effects-of-plastic-injection-moulding/
[5]Hendrik Schäfer, Claudia Pretschuh, Oliver Brüggemann, Reduction of cycle times in injection molding of PLA through bio-based nucleating agents, European Polymer Journal, Volume 115, 2019, Pages 6-11, ISSN 0014-3057.
The principle and experimental conditions of hot pressing
In the hot pressing process, the machining model is firstly preheated for 20 minutes at about 190 degrees Celsius, and then the mixed specimen is injected into the model after which the model is fixed on the heating plate with the pressure of 15MPa for approximately 20 minutes. Control the melting temperature and time of the sample, so as to achieve hardening and cooling after melting, and then take out the finished model with the sample. This process can be clarified by the following flow chart:
The 'preheating' procedure is important in this process. because it is the pre-operational step before the mixture comes to meet a molten state, where it can form and harden.
Another method--Injection moulding
There is another manufacturing method to produce the resultant sample, which is known as injection moulding. It is an approach to give the end-product which is easier for operating. The following figure indicates the relevant apparatus:
Figure 4:The apparatus of injection moulding[4].
The basic operation procedure of this method is as follows: At a certain temperature, the fully molten plastic material is stirred by a screw rod and injected into the mould cavity with high pressure. After cooling and curing, the moulded product is obtained[5].