The Use of Fiberglass and Ceramic Cylinders to Support the Root Pass in C-Steel Welds with a Double-V Groove

Soldagem & Inspeção. 2015;20(3):359-366 http://dx.doi.org/10.1590/0104-9224/SI2004.05 Technical Papers The Use of Fiberglass and Ceramic Cylinders to Support the Root Pass in C-Steel Welds with a Double-V Groove Ricardo Fernandes Gurgel1, Ronaldo Pinheiro da Rocha Paranhos2* 1 2 Instituto Federal Fluminense, Campus Itaperuna, Itaperuna, RJ, Brazil. Laboratório de Materiais Avançados - LAMAV, Universidade Estadual do Norte Fluminense - UENF, Campos dos Goytacazes, RJ, Brazil. Received: 11 May, 2015 Accepted: 10 Aug., 2015 E-mails: (RFG), (RPRP) Abstract: The aim of this work is to evaluate the effectiveness of fiberglass and ceramic fiber cylinders as root-pass weld backing for a double-V groove in 16 mm-thick carbon steel. Three different cylinder diameters were tested: 4.8, 9.5 mm (fiberglass) and 6.4 mm (ceramic fiber). The welding process used was GMAW. The welding technique and the following process variables were investigated: root opening, current and travel speed. The results show that cylindrical fiberglass and ceramic fiber backings not only have excellent refractory properties, but also seal the root opening and contain the weld pool sufficiently to produce a root bead free of discontinuities and with a satisfactory shape and geometry. Working points were defined, together with a possible operating range for the welding parameters. It was concluded that cylindrical fiberglass and ceramic fiber weld backings hold great promise for use in root-pass welds in double-V grooves in applications in the naval and metallurgical industry. Keywords: Root bead; Weld backing; Fiberglass; Ceramic fiber. O Uso de Cilindros de Fibra de Vidro e Fibra Cerâmica como Material para Suporte do Passe de Raiz em Soldas de Aços C com Chanfro Duplo V Resumo: O objetivo deste trabalho é avaliar a eficiência da fibra de vidro e fibra cerâmica em formato cilíndrico como material para suporte de solda do passe de raiz em chanfro duplo V em aço carbono de 16 mm de espessura. Foram testados dois diâmetros de cilindros de fibra de vidro (4,8 e 9,5 mm) e um de fibra cerâmica (6,4 mm). O processo GMAW foi usado sendo investigadas a técnica de soldagem e as seguintes variáveis do processo: abertura de raiz, corrente e velocidade de soldagem. Os resultados mostram que os suportes de solda cilíndricos de fibra de vidro e de fibra cerâmica, além de possuir excelentes propriedades refratárias, ofereceram vedação da abertura de raiz, contendo adequadamente a poça de solda fundida, produzindo um passe de raiz isento de descontinuidades, com adequado formato e geometria do cordão. Além de pontos de trabalho, foi delineada uma possível faixa de operação para os parâmetros de soldagem. Foi concluído que os suportes de solda a base de cilindros de fibra de vidro e de fibra cerâmica apresentam excelentes perspectivas para a soldagem do passe de raiz em chanfros duplo V em aplicações na indústria naval e no setor metal-mecânico. Palavras-chave: Passe de raiz; Suporte de solda; Fibra de vidro; Fibra cerâmica. 1. Introduction Weld backing is used when complete penetration of the weld is required during the root pass or when the base metal does not have sufficient mass to provide a shield that can support the weld pool. Welding generates a large pool of molten metal that remains liquid for a relatively long time and must be supported until it has solidified completely [1]. Welding with a backing has the advantage of eliminating root gouging, which is required in conventional welding. The use of backing not only gives the bead surface a higher-quality finish, but also minimizes welding time and cost. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License which permits unrestricted non-commercial use, distribution, and reproduction in any medium provided the original work is properly cited. Although conventional ceramic backing currently used in welding operations has these advantages, because it is stiff and brittle it does not mold properly to the different weld groove shapes and is thus more suitable for straight grooves. In circumferential welds, articulated ceramic backing can only be used with diameters greater than 600 mm [2]. Gurgel et al. Fiberglass and ceramic fiber have properties and characteristics that are common to ceramic materials, suggesting that they could be suitable for use as weld backing. They have a high melting point of around 1760 °C, slightly above that of steel; they are manufactured by melting silica and do not generate gases; they are available in a wide variety of different shapes and thicknesses; they are low-cost products and can be used to produce low-cost weld backing; and they are flexible and easily molded to any surface [3,4]. Few studies of fiberglass cloth [5-7] that identified the potential of this material for use as weld backing in the welding manufacturing industry were found in the literature. The main aim of this study was to evaluate cylindrical fiberglass and ceramic fiber weld backing with different diameters during root-pass welding of butt joints with a double-V groove and identify the most suitable welding technique and process variables, as well as a possible process operating range. Only the root pass was investigated. The study is a novel one, as to the author’s knowledge there are no references in the literature to the use of fiberglass and ceramic fiber cylinders in root-pass welds in double-V grooves. In light of this, the rationale behind the study was to develop cylindrical fiberglass and ceramic fiber weld backing with excellent refractory properties, mobility and flexibility for use in root openings. 2. Materials and Methods The backings used in this study were made from woven strands of fiberglass and were cylindrical in shape with diameters of 4.8 and 9.5 mm (fiberglass) and 6.4 mm (ceramic fiber). They look like string and are shown in Figure 1. The chemical composition of the fiberglass is 52-56% SiO2, 12-16% Al2O3, 11-15% CaO, 5-10% B2O3 and 0-6% MgO, while the composition of the ceramic fiber is 53% SiO2 and 46% Al2O3. The melting point of both fibers is 1760 °C [8]. Figure 1. Cylindrical fiberglass weld backing with a diameter of 4.8 mm (a) and 9.5 mm (b) and ceramic fiber backing with a diameter of 6.4 mm (c). ASTM A36 steel plates measuring 150 × 50 × 16 mm with a double-V 90° groove and without any land were prepared, as shown in Figure 2a. The root opening was 0, 2.5 and 5.0 mm. Joints were assembled using auxiliary plates made of the same steel at each end of the joint to keep the plates in place, the root opening constant and the whole structure firm. Figure 2b shows an assembled joint ready for welding. The fiberglass and ceramic fiber backing was kept in place by pressure againt the root opening, as shown in Figure 2b. Figure 2. (a) Details of the groove used; (b) a prepared joint ready for welding. 360 Soldagem & Inspeção. 2015;20(3):359-366 The Use of (...truncated)