Views: 27 Author: Site Editor Publish Time: 2025-06-07 Origin: Site
Difficulty in demolding rubber products is a common problem in the rubber processing industry. This issue is often caused by a combination of various factors and seriously affects production efficiency and product quality. The following will analyze the underlying causes from several key aspects.
(1)Interaction between Rubber and Mold Materials Different types of rubber, due to differences in their chemical structures and polarities, have different interactions with mold materials. For example, nitrile rubber, which contains highly polar cyano groups in its molecular structure, easily forms strong adsorption forces or chemical bonds with the surface of metal molds, leading to demolding difficulties. On the other hand, fluororubber, although having good chemical stability due to the high electronegativity of fluorine atoms in its molecules and low surface energy, may also cause demolding problems due to its adhesion to the mold.
(2)Viscosity of Rubber Before vulcanization, rubber has high viscosity, which causes it to closely adhere to the mold surface when in contact with the mold, increasing the demolding resistance. Especially in high - temperature environments, the viscosity of rubber further increases, and its adhesion to the mold becomes stronger. For instance, natural rubber has high viscosity during the initial stages of mixing and molding. If not properly handled, it can encounter obstacles during demolding.
(3)Influence of Additives In rubber formulations, additives play a crucial role, but improper use of certain additives may lead to demolding difficulties. For example, excessive use of plasticizers may make the surface of rubber products too soft, increasing the contact area and adhesion with the mold. Inappropriate types and amounts of vulcanizing agents may affect the cross - linking degree of rubber, resulting in poor demolding performance of rubber products. Additionally, some additives may migrate during the vulcanization process and accumulate at the interface between the rubber and the mold, changing the physical and chemical properties of the interface and thus increasing the demolding difficulty.
(1)Surface Roughness of the Mold The surface roughness of the mold has a significant impact on demolding. If the mold surface is rough, during the molding process of rubber products, the rubber will embed into the microscopic grooves on the mold surface, and greater friction needs to be overcome during demolding. Moreover, a rough surface may also increase the contact area between the rubber and the mold, thereby enhancing the adhesion force. Conversely, if the mold surface is too smooth, although the friction force will decrease, the adsorption force between the rubber and the mold may become dominant, which is also unfavorable for demolding. Therefore, the surface roughness of the mold needs to be controlled within an appropriate range to achieve the best demolding effect.
(2)Design of the Demolding Structure If the demolding structure of the mold is not designed reasonably, it will directly lead to demolding difficulties. For example, if the demolding taper of the mold is insufficient, the rubber product will be subject to large lateral resistance during demolding and will be difficult to remove smoothly. Or, if the position and number of the ejection mechanisms are not properly set, the ejection force cannot be applied uniformly, which may cause excessive local stress on the rubber product, resulting in deformation or even cracking and affecting demolding. In addition, for some rubber products with complex shapes, such as molds with undercuts, deep holes, etc., if the demolding mechanisms such as core - pulling and sliding blocks are not reasonably designed, the demolding process will become extremely difficult.
(3)Mold Material The choice of mold material has an important impact on demolding performance. Different mold materials have different characteristics such as surface energy and chemical stability. For example, steel is a commonly used mold material, but the surface properties of different types of steel also vary. Some steel surfaces are prone to rusting or chemical reactions, which can cause adhesion to rubber. Aluminum alloy molds, although having good thermal conductivity, have relatively low surface hardness and are prone to wear during use, affecting the demolding effect. In addition, some special mold materials, such as ceramic molds, although having advantages such as high temperature resistance and good chemical stability, may have poor compatibility with rubber, leading to demolding difficulties.
(1)Vulcanization Process Vulcanization temperature, time, and pressure are key parameters in the vulcanization process, and they have an important impact on the demolding performance of rubber products. If the vulcanization temperature is too high or the time is too long, the rubber may be over - cross - linked, causing the product to become hard and brittle, and it is prone to cracking during demolding. If the vulcanization temperature is too low or the time is too short, the cross - linking degree of the rubber is insufficient, the strength of the product is not enough, and it is prone to deformation during demolding. In addition, inappropriate vulcanization pressure may cause uneven filling of the rubber in the mold, leading to an increase in the local adhesion force between the rubber and the mold and increasing the demolding difficulty.
(2)Molding Process Parameters such as injection speed and holding time during the molding process also affect demolding. If the injection speed is too fast, the rubber may generate turbulence in the mold, resulting in the presence of bubbles or uneven density inside the product, affecting the demolding performance. If the holding time is too long, the contact time between the rubber product and the mold increases, and the adhesion force increases, which is unfavorable for demolding. In addition, in the compression molding process, improper pressurization methods may cause uneven stress on the rubber product in the mold, leading to excessive adhesion between the local part and the mold and making demolding difficult.
(3)Demolding Timing Choosing the appropriate demolding timing is crucial. If demolding is carried out too early, the rubber product has not fully cooled and solidified, and its strength is low, so it is prone to deformation during demolding. If demolding is carried out too late, the contact time between the rubber product and the mold is too long, and the adhesion force between them may further increase, also increasing the demolding difficulty. Therefore, it is necessary to precisely control the demolding timing according to factors such as the material and thickness of the rubber product and the structure of the mold to ensure smooth demolding.
