1- RESUMO

1. ESCOLA POLITÉCNICA DA UNIVERSIDADE DE SÃO PAULO B C D A E F m a i n c r a c k i n g belt/ roll interface D B C A B belt/ wood cushion interface E F belt/ roll interface belt/ cushion interface Metalografia na Inglaterra entre o final do século XIX e início do século XX FULANO DE TAL, CICRANO DE TAL, CICLANO DE TAL, COISINHA DE JESUS, CONCHITA DE TAAL Figure 3 – Microtopographic examination of the used upper rolls. Detail of the regions with perimetric wear marks, showing the presence of indentation marks, cracking (dotted arrow) and encrusted 2 mm Si-rich particles (bold arrows). SEM-BEI. Figure 4 – Lubricant residues revealed the presence of exogenous material, such as deformed helicoidal wires (originated by the release of the stainless steel bristles of the cleaning brush).SEM-SEI. Figure 5 - Microtopographic examination of the cracked stainless steel belt. Belt / wood interface showed the presence of numerous parallel secondary cracks perpendicular to the direction of the belt movement (see large black arrow). The secondary cracks are parallel to the main crack and associated to the presence of indentation and spalling (see arrows). • Figure 6 - Macrostructural examination of the cracked stainless steel belt - longitudinal section, showing the presence of 500 mm deep 45° cracks at the belt/ roll interface (see arrows) due to contact fatigue, leading to the formation of spalling. • Figure 7 - Fractographic examination of the exposed surface of the main cracking. a) General view showing the formation of a spalling by contact fatigue (region B), followed by multiple crack nucleation (region C); b) Spalling surface; c) to f) Fatigue striation marks due to reversed bending. SEM-SEI • 3- CONCLUSÕES • The main cracking was nucleated on the belt/roll interface and that there is a clear relationship between the formation of a through thickness cracking and the presence of spalling. • The spalling was preferentially originated on the belt’s surface (bell/roll interface) by a mixed rolling/slip contact fatigue mechanism. • Conventional bending fatigue cracks were nucleated at the 600 mm deep spalling. • 4- BIBLIOGRAFIA • 1- RESUMO • The premature failure of an agglomeration machine used for the annual production of 360,000 m3 of eucalypt fiber panels was investigated to identify the cracking of stainless steel belts (126 m x 2.9 m x 3.0 mm). • These belts are used to compress a cushion composed of eucalyptus fibers and glue (see fig.1). • Figure 1 - Scheme showing the functioning of the agglomeration press, featuring the positioning of stainless steel belts and case-hardening steel rolls (responsible for the transmission of temperature and compression to the belts). • 2- INTRODUÇÃO • The press contains two stainless belts moving at a maximum velocity of 90 m/min and positioned symmetrically to “insandwich the wood cushion. • The press is composed by 82 frames, each presenting 5 hydraulic pistons. • The pressure is transmitted from the pistons to the belt by the action of numerous case-hardening steel rolls. • The belt/ roll interface is lubricated by a synthetic lubricant spray. • Figure 2 - Visual inspection of the stainless steel belt showing a transversal through-thickness cracking (see dotted area). a) belt/ roll interface; b) belt/ wood cushion interface. Arrow indicates the direction of the belt movement. CENTENÁRIO DA METALOGRAFA NO BRASIL – PMT 2402 – METALOGRAFIA E TRATAMENTO TÉRMICO – 2007 – PROF. DR. CESAR R. F. AZEVEDO