Foseco Ferrous Foundryman''''s Handbook Part 12 doc

Filtration and the running and gating of iron castings 265 Using filters in vertically parted moulds Example 1: Grey iron brake disc casting Brake disc casting are frequently made on DISAMATIC moulding machines with vertically parted moulds. The disc castings are subsequently machined over a large part of their surface, any inclusions revealed by machining lead to both high tool wear and scrap castings. Filtration is clearly desirable but there are a number of problems of application: Mould production rates are up to 350/hour. Access to the open mould is not easy, filters must be placed by the coresetter machine to avoid slowing the mould rate. Space to locate filter prints is limited. Two systems of placing filters are possible (Fig. 17.18a,b,c). (a) (b) (c) Figure 17.18 Use of a SEDEX filter in vertically parted moulds. (a) unfiltered; (b) filter placed at base of sprue; (c) filter placed in pouring bush. 266 Foseco Ferrous Foundryman’s Handbook Figure 17.18a shows the unfiltered running system, as is usual with DISAMATIC systems, the system is pressurised, being choked at the ingates. Figure 17.18b shows the SEDEX filter placed in a ‘crush print’ at the base of the sprue. In this position, the filter can be placed using the coresetter. The choke is prior to the filter. Figure 17.18c shows the filter placed in the pouring bush, here it is possible to place it by hand after the mould has been closed. The sprue base acts as choke. The pour time is shorter with the SEDEX filter than without. Running system Pour time (s) Unfiltered, choke at ingates 6.7 SEDEX filter at base of sprue 5.6 SEDEX filter in pouring bush 6.1 Both methods of using the filter are effective in removing inclusions. Combined filter, feeder and pouring cup, the KALPUR direct pouring system The concept of direct pouring into the top of a mould cavity has long been recognised as desirable, with the potential benefits of: Improved yield Simplified sprue, gating and feeding design Reduced fettling costs. Unfortunately, it was frequently found to introduce defects due to the turbulent flow of the metal in all but the simplest of castings. In addition, the impingement of high velocity metal streams caused erosion of moulds or cores. These objections can be overcome by pouring the metal through a ceramic foam filter situated at the base of an insulating pouring/feeding sleeve, the KALPUR unit. Clean metal, free from turbulence and oxide, fills the mould cavity and readily feeds the casting through the filter. Directional solidification and casting soundness is promoted and gates and sprues made unnecessary. The impingement problem is reduced because the metal velocity is reduced as it passes through the filter (Fig. 17.19). Application to horizontally parted moulds For manual moulding and simple moulding machines, the open pouring cup shape of Fig. 17.20 can be used; an example of its use is shown in Fig. 17.21. In horizontally parted automatic moulding lines, the KALPUR type shown in Fig. 17.22 can be used as in Fig. 17.23. Filtration and the running and gating of iron castings 267 Figure 17.19 A schematic view of the cleaning and flow-smoothing effect of pouring directly through a KALPUR unit. Figure 17.24 shows a ductile iron vice base, casting weight 26 kg made on a 20/24 Hunter moulding machine. 268 Foseco Ferrous Foundryman’s Handbook φ 120 φ 90 150 φ 152 φ 125 180 Figure 17.20 Open KALPUR units for manual moulding. The units are supplied in a range of sizes. Figure 17.21 Use of the open cup KALPUR unit. φ Da φ du φ Du H Figure 17.22 KALPUR unit for horizontally parted automatic moulding lines. Filtration and the running and gating of iron castings 269 φ 30 φ 50 SEDEX-filter 150 KSE 5/8/L10 36 10 φ 55 20 Cope Floating sleeve pattern Schnitt AA Drag Figure 17.23 Use of the KALPUR unit in horizontally parted automatic moulding lines. Figure 17.24 Ductile iron vice base made on a Hunter machine using a KALPUR unit. 270 Foseco Ferrous Foundryman’s Handbook Before After KALPUR KALPUR Pour weight 34.5 kg 27.7 kg Pouring time 14 s 8 s Yield 69.3% 86.4% Total scrap 20% 0.9% Grinding time 2 min 1.5 min Application of direct pouring to vertically parted moulds Increasingly complicated grey and ductile iron automotive castings are being produced in vertical moulds for hydraulic, brake, suspension and transmission systems. Components such as conrods, hubs, brake drums, flywheels, brake discs, brake brackets and steering knuckles are now common production castings in vertical moulds. Since many of these are safety castings, they must usually be filtered. For ductile iron, feeders must also be incorporated so that sound castings can be obtained. Figure 17.25a shows a conventional pattern layout for a ductile iron car hub casting made with three castings on the pattern plate. The running (a) (b) Figure 17.25 Use of the KALPUR unit in vertically parted automatic moulding lines: (a) conventional layout; (b) using KALPUR. Filtration and the running and gating of iron castings 271 system allows mould erosion due to high metal velocity. Figure 17.25b shows a direct pouring system using a KALPUR direct pour unit at the top, and below it, a KALMIN S feeder sleeve ensuring correct feeding of the lower two castings. Casting yield increased from 61% to 78% and productivity by 33% while casting quality was improved. Figure 17.26 shows a ductile iron differential housing, casting weight 30 kg made on a DISAMATIC 2070 moulding machine. Figure 17.26 Ductile iron differential housing made on a DISAMATIC 2070 moulding machine with a KALPUR unit. Before After KALPUR KALPUR Pour weight 67 kg 44.5 kg Moulding rate 215/h 230/h Yield 44.1% 66.6% Total scrap 8.5% 1.6% Slag scrap 2.3% 0.02% Grinding time 2.67 min 1.83 min KALPUR direct pouring filter/feeder systems reduce mould and core erosion and ensure that there is hotter metal in the feeders than in the castings, giving ideal directional solidification from the casting to the feeder. Chapter 18 Filtration and the running and gating of steel castings Introduction The running and gating system carries out the following functions: Controls the flow of metal into the mould cavity at the rate needed to avoid cold metal defects in the casting Avoids turbulence of metal entering the mould Prevents slag and other inclusions from entering the mould Avoids high velocity impingement of the metal stream onto cores or mould surfaces Encourages thermal gradients within the casting which help to produce sound castings Enables the casting to be separated from the running/gating system easily. Controlling the flow of metal Ideally the gating system should control the flow of metal into the mould. If lip pouring ladles are used, this can be readily achieved since the pourer is able to match the requirements of the gating system by altering the tilt of the ladle. It is more difficult with bottom pour ladles. The flow rate from a bottom pour nozzle/stopper rod system is determined by the nozzle size and the metal height in the ladle according to the formula: t DM M M dg = 4( – ( – )) 2 11 2 √√ √ ∆ ρπ where t = pouring time (s) D = mean ladle diameter (cm) M 1 = initial weight of metal (kg) ∆M = weight poured (kg) d = nozzle diameter (cm) g = acceleration due to gravity (981 cm/s 2 ) ρ = density of liquid steel (7.7 g/ml) Filtration and the running and gating of steel castings 273 (From C.S. Blackburn and B. Blair; Gating system design for bottom pour ladles, 35th SCRATA Conference, May 1992) The flow rate varies considerably depending on the level of metal in the ladle. This is illustrated in Fig. 18.1 which shows the variation in pouring time of seven 750 kg castings from a ladle initially containing 5750 kg of steel. A gating system designed to accept the initial pouring rate of 750 kg in 18.23 seconds will not be suitable to accept the last 750 kg which is discharged from the ladle in 44.95 seconds, 2.5 times longer! Figure 18.1 The variation in pouring time of seven 750 kg castings poured from a bottom-pour ladle initially containing 5750 kg of steel. (From Blackburn C.S. and Blair B. 35th SCRATA Conference, May 1992, courtesy CDC.) Weight in Pouring ladle (kg) time (sec.) 5750 5000 18.23 4250 19.68 3500 21.48 2750 23.96 2000 27.46 1250 33.37 500 44.95 122 cm dia 91 cm 5750 kg 103 cm dia 3.8 cm dia The nozzle/stopper rod system of a bottom pour ladle is an excellent ‘on/off’ valve but ideally should not be used as a flow control valve. Attempts to use it to control flow result in breakup of the metal stream with consequent risk of reoxidation of the steel and possible erosion of the stopper rod itself. There is, however, no alternative if the gating system is to control the flow rate. A compromise must be reached for each cast. 274 Foseco Ferrous Foundryman’s Handbook Conventional running systems without filters The elements of a running/gating system for a horizontally parted mould are shown in Fig. 17.1. Pouring bush The use of conical shaped bushes which direct flow straight down the sprue is discouraged as not only will air and dross be entrained and carried down into the system, but also the high velocity of the metal stream will result in excessive turbulence in the gating system. Incorrect alignment between nozzle and pouring cup will also cause metal splashing (Fig. 18.2). A pouring bush designed as in Fig. 18.3 provides a larger target area, a shape which minimises splashing and sufficient volume to accommodate the maximum flow of metal obtained by opening the stopper rod fully thus reducing the need to throttle. The exit from the pouring bush should be radiused and match up with the sprue entrance. Figure 18.2 Simulation of metal splashing due to incorrect alignment of nozzle and pouring cup. (From Blackburn C.S. and Blair B. 35th SCRATA Conference, May 1992, Courtesy CDC.) [...]... 25 100 dia × 25 30 45 50 dia × 25 60 dia × 25 340 150 × 150 × 30 10.0 150 235 100 × l00 × 25 125 × 125 × 30 5.6 85 75 × 75 × 25 17.7 12. 2 7.8 6.4 3.8 2.9 2.0 22.5 15.6 3.0 45 55 × 55 × 25 2.5 35 398 278 180 143 90 68 45 510 353 225 128 68 53 17.7 12. 2 7.8 6.4 3.8 2.9 2.0 22.5 15.6 10.0 5.6 3.0 2.5 345 241 156 124 78 59 39 442 306 195 111 59 46 Capacity kg Capacity kg Capacity kg Flow rate kg/sec Zr/Ti... which occurs during tapping and teeming Such inclusions are essentially silicates, oxides, nitrides and sulphides, or more often complexes of these 278 Foseco Ferrous Foundryman’s Handbook It has been estimated that 1 tonne of steel contains between 1 012 and 1015 indigenous oxide inclusions Each inclusion has associated with it a localised stress field, with inclusions of the order of 20 microns capable... refractory hollow-ware is used) It is presumed that a tall runner allows slag and dross 276 Foseco Ferrous Foundryman’s Handbook Figure 18.4 Flat bottomed sump located at sprue base minimises turbulent metal flow (From Blackburn C.S and Blair B 35th SCRATA Conference, May 1992, Courtesy CDC.) to collect in the upper part of the runner The distance between sprue and the first gate should be maximised for... 22.1 15.3 9.8 8.0 4.8 3.6 2.5 28.1 19.5 12. 5 7.0 3.8 3.1 Flow rate kg/sec 517 361 234 185 117 88 59 663 458 293 166 88 68 Capacity kg CaSi/Al 22.1 15.3 9.8 8.0 4.8 3.6 2.5 28.1 19.5 12. 5 7.0 3.8 3.1 Flow rate kg/sec 7.8 14.0 111 75 × 75 × 25 3.5 2.8 4.1 9.0 10.9 442 39 59 78 124 156 241 345 150 × 150 × 30 50 dia × 25 60 dia × 25 70 dia × 25 90 dia × 25 100 dia × 25 125 dia × 30 150 dia × 30 24.8 17.1 5.3... the running system The application technique and metal temperature at pouring must be suitable for good priming of the filter STELEX ZR filters control metal flow, reducing turbulence 284 Foseco Ferrous Foundryman’s Handbook Filter capacity Metal flow rate Running system The filter must be large enough to allow the casting cavity and feeders to fill before a filter blockage mechanism takes effect The... 18.3 provide a guide to capacities that can be achieved Filtration and the running and gating of steel castings 285 STLX FP1 STLX FP7 Figure 18.10 Recommended STELEX filter prints 286 Foseco Ferrous Foundryman’s Handbook Metal flow rate The same factors that affect filter capacity affect the metal flow rate through the filter Tables 18.2 and 18.3 provide a guide to flow rates that can be achieved... one filter to a casting, special assistance from Foseco should be sought KALPUR ST direct pour unit The KALPUR ST direct pour unit combines a filter and feeder sleeve into a single unit, Fig 18.11 This unit replaces an existing feeder on a casting and then serves as a combined sprue, filter and feeder Metal is introduced into 95 120 185 265 90 dia × 25 125 dia × 30 150 dia × 30 60 70 dia × 25 100 dia... (over 90%) and a very high surface area to trap inclusions The metal takes a tortuous path through the filter effecting the removal of very Figure 18.5 STELEX ZR ceramic foam filters 280 Foseco Ferrous Foundryman’s Handbook Figure 18.6 STELEX ZR filter used in a ceramic pouring cup for investment casting small inclusions by attraction and absorption to the internal ceramic pore spaces Ceramic metal... by production foundries, where improvements in the machinability of castings produced with STELEX ZR filters and also a reduction in tool wear and machine downtime have been achieved 282 Foseco Ferrous Foundryman’s Handbook Number of oxide inclusions (No./0.15 sq mm.) 30 20 Unfiltered 10 Filtered 0 1.3 2.6 3.9 5.2 6.5 7.8 Size ( µ m) of Inclusions 9.1 10.4 Figure 18.7 Histogram comparing the cleanliness... 25 70 dia × 25 90 dia × 25 100 dia × 25 125 dia × 30 150 dia × 30 24.8 17.1 5.3 31.5 21.8 195 306 100 × l00 × 25 125 × 125 × 30 4.2 46 59 50 × 50 × 20 69 517 361 234 186 117 88 58 663 459 292 166 88 3.5 24.8 17.1 10.9 9.0 5.3 4.1 2.8 31.5 21.8 14.0 7.8 4.2 465 325 211 167 105 79 53 597 412 263 149 79 61 Capacity kg Capacity kg Capacity kg Flow rate kg/sec Zr/Ti Flow rate kg/sec Bottom pour CaSi/Al . casting weight 26 kg made on a 20/24 Hunter moulding machine. 268 Foseco Ferrous Foundryman’s Handbook φ 120 φ 90 150 φ 152 φ 125 180 Figure 17.20 Open KALPUR units for manual moulding. The. a SEDEX filter in vertically parted moulds. (a) unfiltered; (b) filter placed at base of sprue; (c) filter placed in pouring bush. 266 Foseco Ferrous Foundryman’s Handbook Figure 17.18a shows. KALPUR unit in horizontally parted automatic moulding lines. Figure 17.24 Ductile iron vice base made on a Hunter machine using a KALPUR unit. 270 Foseco Ferrous Foundryman’s Handbook Before After KALPUR