ANALYSIS OF THE TYPE OF ERROR IN THE STRUCTURE OF RUBBER SAMPLES

Abstract

Products made of polymer materials are obtained by turning the raw material from which it is made
under the influence of temperature and, in some cases, high pressure, into a liquid state and filling the mold cavity.
This transition is often problematic because very quickly when transitioning to the liquid state, irreversible chemical
processes begin to occur in the material, and it is necessary that the process of reverse crystallization takes a very
short time. This problem is very pronounced with products made of rubber. When making the raw mixture, a
procedure must be followed regarding the speed of mixing, the order of adding the components and the duration of
the process itself. In the case of poorly chosen mixing parameters, agglomerations may occur in the structure of the
product, which can later negatively affect the exploitation of the product itself. When the raw rubber begins to
transition into the liquid phase and fills the mold cavity, the layers that are in contact with the tool form the final
structure and shape. In case the chemical system is not balanced, i.e., speed of spilling, it may happen that the rubber
does not fill the mold cavity and a scrap is obtained. Another problem is that if the closing speed of the tool is high,
an airy structure of the material or some kind of defect in the structure may appear. Regarding this phenomenon, it
must be taken into account that the speed of spilling is always higher than the speed of closing the tool. In the case
of poor selection of vulcanization temperature and vulcanizer, certain chemical compounds may also appear that
negatively affect the properties of the product. Also, special attention must be paid to the working environment, as it
very often happens that external bodies are found in the structure of the product, which are related to mixing and
pressing procedures. The release of the material structure belongs to a special group of tests and is always
accompanied by the destruction of the product. According to the type of examination, it belongs to visual control,
and according to the degree of optical magnification, to macro and micro examinations. Eye inspection belongs to
macroscopic tests and is used to check the exterior of the product and this type of test is convenient because it is fast
and reliable. Microscopic examinations of rubber are very complex and it is complicated because rubber is not a
transparent material. Therefore, the examination of the structure is carried out on SEM (scanning electron
microscope). The preparation of the sample includes vaporization with gold, and then the samples are placed in a
special chamber where they are bombarded with electrons and the structure is observed on a monitor. Depending on
the type of error in rubber products, they can be divided into those related to material technology and those caused
by external impurities. Those related to the manufacturing technology can be different, agglomerations and various
chemical compounds can occur during mixing. While with the percentage of pressing, an airy structure may appear.
The most common errors in the structure are the appearance of foreign bodies inside the product. This problem is
overcome by clear mixing and pressing procedures, but also by automating the procedures themselves, which
reduces human error to a minimum.