Energy Savings in Foundries through Yield Improvement and Defect Reduction in Castings

ARCHIVES of ISSN (2299-2944) Volume 18 Issue 1/2018 FOUNDRY ENGINEERING 15 – 18 DOI: 10.24425/118804 Published quarterly as the organ of the Foundry Commission of the Polish Academy of Sciences 3/1 Energy Savings in Foundries through Yield Improvement and Defect Reduction in Castings B. Chokkalingam *, V. Raja, M. Dhineshkumar, M.Priya, R. Immanual Department of Mechanical Engineering, d Department of Science and Humanities, Sri Ramakrishna Institute of Technology, Coimbatore, India * Corresponding author. E-mail address: Received 10.08.2017; accepted in revised form 09.10.2017 Abstract Energy conservation is an important step to overcome the energy crisis and prevent environmental pollution. Casting industry is a major consumer of energy among all the industries. The distribution of electrical energy consumed in all the departments of the foundry is presented. Nearly 70% of the energy is consumed especially in the melting department alone. Production of casting involves number of process variables. Even though lot of efforts has been taken to prevent defects, it occurs in the casting due to variables present in the process. This paper focuses the energy saving by improving the casting yield and by reducing the rejections. Furthermore, an analysis is made on power consumption for melting in the induction furnace to produce defective castings and improvement in the casting yield. The energy consumed to produce defective castings in all other departments is also presented. This analysis reveals that without any further investment in the foundry, it is possible to save 3248.15 kWh of energy by reducing the rejections as well as by improving the casting yield. The redesign of the feeding system and the reduced major rejection shrinkage in the body casting improved the casting yield from 56% to 72% and also the effective yield from 12.89% to 66.80%. Keywords: Energy, Casting yield, Feeding system, Defective casting, Melting 1. Introduction In today’s world of competitive global market, quality casting at minimum price is inevitable. Among the various factors contributing the total manufacturing cost, the energy cost contributes a major percentage for the foundries. The melting operation alone consumes nearly more than 70% of the total energy consumed by the foundries compared with all the other operations in the foundry. Generally, electricity cost is gradually increases hence the production cost is also increases. The manufacturing cost is also increasing everyday. For being competitive in the market, it is essential to reduce the manufacturing cost inside the foundries by means of adopting various measures. The energy saving is among the one, which can be achieved by means of increasing the casting yield, reducing scrap level, auditing plant operations, eliminating losses, monitoring the power consumption, controlling the super heating temperature as well as time, quick tapping of the metal from the furnace, use of clean foundry returns, quick control of chemical and metallurgical quality of the molten metal etc. In this paper energy saving without any capital investment was analysed by means of increasing the yield and reducing rejections for a SG iron grade 500/7 casting produced in a medium scale foundry using induction furnace [1-7]. ARCHIVES of FOUNDRY ENGINEERING Volume 18, Issue 1/2018, 15-18 15 Casting yield is defined as the ratio of the casting weight to the total metal pouring weight. It is a major factor in melting energy savings. The amount of pouring metal required to produce castings is reduced by means of increasing the casting yield. The energy savings can be easily achieved by pouring less metal into the moulds due to weight reduction in runners, less number of risers etc. The effective yield includes the casting yield and rejections of the castings. This overall improvement in the yield significantly reduces the manufacturing cost besides increase in rejection levels. It is essential for the foundries to reduce defects through process control and increase the casting yield for their survival [8]. Automobile SG 500/7 casting produced in a medium scale foundry using induction furnace was taken for yield improvement analysis. The drag and cope match plates with the existing feeding system is shown in the Fig 2a and Fig 2b respectively. Rejections in the foundry shop floor for the existing feeding system are 76.97% and the major defect was identified as shrinkage. Hence, the feeding system should be modified to reduce shrinkage defect [16-20]. 2. Methodology The electrical energy consumed for the production of castings in all the departments of the foundry is shown in fig.1. It is clear from the fig.1 that, in particular melting department alone consumes a major part of the total energy consumed by the foundry. This study focuses on the effect of yield improvement and reduced rejections on the consumption of the electrical energy alone in the melting department. [2-7]. Fig. 2a. Drag pattern - existing design Fig. 2b. Cope pattern- existing design Fig. 1. Energy distribution in foundry Foundrymen must compare themselves with others to improve their operations [8-15]. The benchmarking data for melting metals using induction furnace is given in the table1. The feeding system was redesigned with the help of literature [19-20] to improve the casting yield as well to eliminate the shrinkage defect in this body casting. After redesigning the feeding system, two risers were removed (Top riser and One side riser) and a tall tapered side riser alone used instead of two risers in the existing feeding system. The drag and cope match plates with the redesigned feeding system is shown in the Fig 3a and Fig 3b respectively. Table 1. Bench marking of cast iron with induction furnace Cast iron 650 kWh /Ton Power factor 0.98 No.of heats/lining 600 (3 shifts) 500 (2 shifts) Production of defect free castings is very difficult due to the presence of many variables in the production system. The causes for the rejection may be a combination of several factors rather than one factor. The benchmarking for foundry rejections due to foundry causes is 2%. By implementing the effective rejection control methods, foundrymen must keep their rejections within this limit. 16 Fig. 3a. Drag pattern- modified design Fig. 3b. Cope pattern modified design The cope and drag patterns with components of gating and feeding system are shown in the Fig3a and Fig 3b respectively are, 1. Pattern (Cope) 2. Riser 3. Runner 4. Well 5. Pattern (Drag) ARCHIVES of FOUNDRY ENGINEERING Volume 18, Issue 1/2018, 15 -18 The casting poured with redesigned gating and feeding systems is shown in the fig 4. Total Number of Castings Produced in Numbers Accepted Castings in Numbers Rejected Castings in Numbers Fig. 4. Casting with redesigned feeding system 3. Results and Discussion The metal is melted in a medium frequency induction furnace. The total metal melted to produce the cas (...truncated)