Finite Element Analysis of a Curing Press With Focus on Tightness of the Vulcanizing Chamber
Authors: Keckstein Tomas , Jirasko Jakub , Kottner Radek 
Published: February 2017

A curing press is used in the final phase of tire manufacture. A tire semi product is placed into the curing press mold and a specific pressure and temperature gives it its final shape and final mechanical properties. There are many types of curing presses; this particular press is mechanical and the pressing force is exerted by an eccentric mechanism. The size of this press allows production of tires for trucks and medium-sized tractors.

The basic demands placed on this type of press include tightness of the parts which are exposed to pressure from the heating medium. This paper mainly focuses on the tightness of the vulcanizing chamber and the tightness of the mold in which the semi product of the tire is inserted. Leakage of the vulcanizing chamber may cause leakage of the heating medium which could result in injury to the machine operator. Leakage of the mold causes an overflow of rubber into the parting plane, which may result in the production of rejects. To ensure the tightness of both these components, it is necessary to create sufficient pressure between the individual components. The value of the compressive force depends on the setting of the overlap of these parts, which depends on the stiffness of the individual parts and on the force exerted from the pressure of the heating medium that acts on these parts.

Finite element method (FEM) analysis of this problem was performed using Abaqus software. A computational model of the curing press was created for this numerical analysis. The geometry of the press is symmetrical and the load is centric, therefore, only half of the press was modelled. The aim of this analysis was to find the most suitable settings for the overlap of the mold (independent variable) and the overlap of the chamber (dependent variable) which ensure the smallest possible leakage of the mold and an uninterrupted contact surface between the sealing and the upper part of the chamber.

The sealing of the chamber is made from rubber which was modelled for the analysis as a five term generalized Mooney-Rivlin model, also known as the James-Green-Simpson model. This model assumes hyperelastic behavior with incompressibility. The insulating plates are made of a particulate composite which was considered to be linear with isotropic properties. For strength evaluation of the composite materials, all individual components of the stress tensor were investigated according to the maximum stress criterion. Hook’s law was considered to be valid for all the metallic materials. The Von Mises criterion was used to evaluate the strength of the metallic materials. The geometry of the press was discretized using 3D linear elements with 8 nodes and with reduced integration (C3D8R). The geometry of the rubber sealing was discretized using hybrid 3D linear elements with 8 nodes and with reduced integration (C3D8RH). The overall number of elements was approximately 97,000.

Calculation model enabled to compute the best overlap setting of the chamber and the mold. This setting ensures their tightness. Effect of the setting to a stress in a press was also studied and the values of the stress were in a permitted range.