OPERATIONS AND COSTS OF FOUNDRY INDUSTRY. Any diagnostic study of the industry or a firm calls

Transcription

1 CHARTER III OPERATIONS AND COSTS OF FOUNDRY INDUSTRY Any diagnostic study of the industry or a firm calls for better understanding of the product, production process and other operational details. In measuring productivity, cost-effectiveness, and overall performance of foundry industry, it is necessary to know and understand operational details. This chapter provides an insight into the foundry product, production process and costs. Ill t

2 1.Classification of Foundriegi The foundries can be grouped as Ferrous and Non-ferrous based on the product. The product of foundry industry is "Casting". A casting is a molten metal that has been poured into a mould, on solidification it assumes the desired shape. Further, the ferrous foundries may be engaged in the manufacture of Bray Iron <GI> - low grade and high grade, Malleable Iron (MI), Spheroidal Graphite Iron (SGI), Alloy Cast Iron, Carbon Steel, Stainless Steel, Special Steel, Alloy Steel and White Chilled Iron, Compacted Graphite Cast Iron (CGI). Tracing the history of cast iron, Krishnaraj and Seshan * point out, GI was born around MI in 1720, SGI in 1947, and CGI in Non-ferrous foundries may make castings of Aluminium, Copper, Magnesium, Nickel, Cobalt, Zinc, and other unspecified nonferrous bases. 1.Krishnaraj D Seshan S. (1989) Metallurgy of Cast Iron, in Foundry Engineering Handbook P 158 III

3 2. Foundry Products The ferrous foundry products are varied. Based on the applications of castings and chemical compositions they are grouped* as: 2.1 Brey Iron : Machine tool beds, manhole covers, melting pots, motor bodies, pump castings, sewage pipes, bends, cylinder lines, piston rings, gravity die casting dies, ingot moulds, engine blocks, break drums, domestic taps and fittings, fly wheel, gating plates, plummer blocks, plastic moulds, switch gear components, flexible coupling, brake shoes. 2.2 Malleable Iron : Rear axle housing, rocker arms, conveyer chain links, insulator caps, gear cases, universal joints, pinion bearing cases, hydraulic rams, railway belt cranes, heavy duty bearing blocks, chain hoist parts, electrical conduits, driver shafts, sprockets, plumbing parts, differential carriers, truck wheel spider, shaft levers, brake shoes, hydraulic accessories, 2.3 Spheroidal Graphite Iron: Crank shaft, gear wheels, paper mill rolls, insulator components, hot rolling roll, mould boxes, cams, exhaust 1. Ibid Pp III - 3

4 manifolds, gear box housing, brake drum, propellers, pneumatic pistons, pump/turbine housing, piston ring for high power engines, connecting rods, brake drums, cylinder blocks of heavy internal combustion engines. 2.4 Compacted Graphite Iron: Ingot mould, engine base frames, crank cases, rocker arms, gear cases, clutch borders, end shields, forging press cylinders, pump bodies, bearing supports, type writer frames, hand tools, slag pots, moulding boxes, gear pinions, spray nozzles, mixer roller plates, motor bodies, pipe fittings. 3.The production process; It primarily consists of i 1) Pattern making, 2) Moulding, 3) Core making, 4) Melting and pouring, 5) Fettling and &) Inspection and quality control and 7) Dispatch. A flow chart of a typical foundry operations is presented in Figure III.1. Figure III.l A Foundry Process Flow Chart III 4

5 3.1 Pattern makingi A pattern is an exact facsimile of the product to be cast. It is made as per the design and drawings in the pattern shop. Hide range of alternative materials like wood, metal, plastic etc. could be selected for pattern depending on the surface finish requirements, number of castings required, repeat orders etc. Considerable economy could be i achieved when proper designs involving least essential specifications are made, for complicated designs and specifications increase foundry problems and costs rise. 3.2 Sand Conditioning: Sand conditioning can be considered in two stages, viz i) Controlled preparation of sand mix and ii> effective use of prepared sand mix in making of mouldings.* The natural sand is commonly used for making moulds and core in 61 foundries. The sand is mixed with clay and some additives. Thus mixed sand is manually rammed into mould boxes. Such sand mixture is cheap. But there will be more defective castings with blow holes, sand fusion, scab and sand burning and expansion defects, due to clay and moisture contents. l.vasuiani Rajan. Technology Upgradation in The Foundry Industry in West Bengal. IFJ April P 20 III 5

6 3.3 Mouldings It involves placing moulding aggregate) such as sand, clay, binders, ceramic etc. around the pattern held within a supporting frame and compressing it. On withdrawing pattern, cavity is created in the mould. On baking mould is ready for pouring molten metal. 3.4 Core making s When casting. needs interior surface, say cavity in casting, then cores are placed inside the mould cavity. The void space between the mould-cavity surface and core is what eventually becomes the casting. Cores are usually made of sand and baked before being placed within the mould. 3.5 Melting and pouring. Melting is a process of preparing molten metal for pouring into the moulds. Melting is done either in cupola or furnace. Open hearth, electric arc and induction furnaces are used greatly for steel castings. Cupola is predominantly used in grey iron castings, because it has low installation and operational cost, high output level, and ease in operations. Melting starts when cupola or furnace is fully charged. A 'charge' is a mixture of various foundry materials that III - h

7 are systematically loaded in cupola or furnace. The cupola charging starts with forming coke bed in the bottom and burning it from bottom by fire wood. Then weighted batches of pig iron, scrap, foundry returns and rejects, coke, and flux, one above another are loaded in the cupola. About 20 minute to one hour, stack is soaked, when pre-heating is done. Then blowers are started, which will allow coke to burn hot and melt metal. The molten metal and slag starts accumulating in the cupola well. So long cupola heat continues, new batch of load is added, when melting is still in progress. Now the molten metal is taken out by tapping and slagging operations. Molten metal is carried in ladles from cupola to the moulding boxes for pouring in. In case need be alloying agents, like ferro silicon, ferromanganese or silicon carbide, nickel chromium or silvery pig, may be added in the ladle before pouring in the mould. The charging of electric furnace is little different from cupola. At bottom of the electric furnace turnings or plate scrap of small sizes are loaded first. Then larger size metallic scrap, PI and foundry returns are loaded above the smaller ones at the top. There is no use of coke. Once furnace is fully charged, electric current is supplied to raise the furnace temperature for melting. Alloying agents are added in the furnace, if required. Molten metal is transferred to mould boxes mostly in ladle for pouring. To III 7

8 keep-up furnace temperature some portion of molten metal is held in the furnace and next batch of loading is done. 3.6 Fettling and finishing. On cooling, the molten metal solidifies within the mould and casts are ready. Either manually or using shakeout machinery, the castings are removed from the mould. The sand adhering to castings, inside and outside rough surface, removal of cores, runners, risers, gates and fins is the next process after shake-out, which is known as fettling. 3.7 Inspection and quality controls This is indeed a job carried before and after production of castings. Testing sand, pig iron, metallic scrap is a pre-production job. Chemical analysis, strength testing, and other quality measures are post production process. 3.8 Dispatching : It is primarily concerned with distribution of finished castings either by sending to machine shop for further machining and/or sending to the customers. Ill - 8

9 4. Layout s Keeping foundry operations in view the machineries and equipments have to be located scientifically (Figure III.2). To make one ton of castings about 5-8 tons of material need to be handled. With scientific layout it is possible to cut the cost of materials hy minimising handling and reducing wastage. Figure ITT.2 A Typical layout for a GT Foundry unit.. ' n r HAND MOULDING, MACHINE CORE POURING AND MOULDING SECTION KNOCKING POURING AND KNOCKING RAND COND- ITIONING.» Y SECURITY * R T 1 0 Foundry QUALITY FETTLING F E MATERIAL CONTROL AND T E L STORE AND MACHTNTNG 11 I A INSPECTION SHOP R c B CASTING N E STORE G -4 X I ' FINISHED CASTING DISPATCH <- Source: Gaur et. al. Technology Upgradation in Small Srale Grey Iron Foundry, IFJ Jan 1991, P. 21 T T T 9

10 3. Foundry Costt The cost of making castings consists of material, labour and overhead costs. 5.1 Material cost* The cost of material is split into basic raw materials, basic alloys, special alloys and consumables. The basic material inputs are PI, ferro metallic scrap, foundry returns and rejects. Basic alloying agents such as ferrosilicon, ferro magnanese, and inoculants are needed to form the castings. But special alloying agents, such as magnesium, nickel, copper etc. are used for attaining desired quality grade castings. Band, binders, additives, fluxes, core materials, refractories, lubricants, maintenance material, etc. are consumables, constituting the indirect material cost. The cost of these materials are taken at landed cost. The landed cost of materials include basic buying rate, sales tax, other taxes, transportation, insurance and handling charges. 5.2 Power and fuel costs It is in the form of electricity, oil, coke, gas, fire wood etc. used for moulding, core making, pattern making, melting, fettling and finishing, and general purpose. TIT - lo

11 S.3 Labour costs The cost of labour employed in making of patterns, core, moulds, and operators engaged in melting and pouring, fettling, constitutes direct. Indirect labour cost includes cost of labour engaged in handling material, maintenance, inspection and testing,etc. 3.4 Overhead costs It includes indirect material and labour, depreciation, and all other expenses of administration and sales. A.Cost ascertainment : In the ascertainment of cost of castings per ton/kg factors like capacity utilisation, spoilage, melting loss, yield rate, labour efficiency, rate of rejection on floor, machine utilisation etc. play very important role. The process of cost ascertainment begins with cost collection at both productive and service cost centers. In a foundry core making, moulding, melting and pouring, fettling and finishing constitute productive cost centers. Designs, drawings and pattern shop, quality control and inspection, maintenance, purchases and stores, administration and finance constitute service cost centers. Using departmental cost sheet (Table III.l) costs are accumulated. T 11-11

12 Table III.l Departmental Cost Compilation Sheet Cost Elements Production Departments Service Departaenti Cores Rs Moulding Rs Melting Rs Finishing Rs Pattern Rs Stores Rs Office Rs Sales Rs Materials Silica Sand Silica Sand PI, Scrap Mood,Metal Consumables Oil,Binder Additives Oil,Binder Additives Fluxes/ Desulfuring Brinders/ Cutters Binders Paints Seneral General Seneral Labour Skilled (Jhskilled Skilled Unskilled Skilled (Jhskilled Skilled Unskilled Skilled Unskilled Office Staff Office Staff Sales Staff Power 1 Fuel 0il/6as/ Electricity 0il/6as/ Electricity 0il/6as/ Coke/ Electricity Sas / Electricity Electricity Electricity Seneral lighting Seneral lighting Depreciation Core Oven Repairs! Core Shooter Maintenance Sand Mixer Compressor Furnace/ Cupola Shot Blast Hydraulic lathes/ Drilling Handling/ Equipments Expenses Misc. Misc. Misc. Misc. Misc. Misc. Misc. Misc. Total The costs so collected are used to find the cost per ton/kg of casting by using cost sheet1 as detailed in l.naik -T. G. Costing of Castings, The Management Accountant. ICWAI, Calcutta, October

13 Table III.2 Cost Sheet of Castings Order/Batch No* Quantity* Particulars Date of Commencement* Date of Completion* Amount Cost of Cores Cost of Moulds Cost of Molten Metal and pouring Cost of Shake-out,Fettling & Finishing Stores overhead Administration overhead cost Service department overheads * * * * e * * * e * * * * * ** * Gross Value of Production * * * Less Value of rejects, defectives & scraps (Valued at cost of production/market rate of scrap) * *** Total cost of production * * * Total cost of production Cost per Ton or Kg = * *** Quantity of good castings Add Expected Rate of Margin (X of ROI per ton/kg) ** Selling Rate per Ton/Kg * «11 r - 13