124 Assistance for decisions: Burnt-on sand 125 Assistance for decisions: Burnt-on sand A Clay-bonded sand B Moulding plant Examine lustrous carbon production Measure active carbon in moulding sand, examine lustrous carbon producer, use material with greater lustrous carbon production; increase ignition loss in moulding sand Examine compaction Poorly compacted sections are at risk of overheating. Achieve more even compaction. Examine content of low-melting-point material Content of low-melting-point material in moulding sand promotes adherence. Examine new sand for impurities. Reduce dust content. Add new sand if necessary. C Gating and pouring practice Examine gating Excessive quantities of metal and over-rapid pouring rates cause local overheating. Achieve better distribution of metal. Examine oolitization High degree of oolitization reduces melting point. Add new sand if necessary. Check pouring temperature Excessively high temperatures promote sand adhesion. Reduce pouring temperature.
126 Assistance for decisions: Cods and edge disintegration 127 Assistance for decisions: Cods and edge disintegration A Moulding plant B Clay-bonded sand Examine stripping process Check moulding flasks for uneven stripping (most frequent cause of defect) Examine cluster content Reduce clusters. Use sand aerator. Reduce fines and bentonite contents if necessary. Examine prefilling Examine moulding plant for uneven sand filling Examine fines Reduce inert, n-ignitable fines content. Increase new sand content if necessary. Examine patterns Check mould tapers, correct if necessary Examine sand temperature Reduce sand temperature if too high. Install a sand cooler if necessary. Examine compacting pressure Examine mould hardness, reduce compacting pressure if necessary Examine moisture of used sand Pre-wetting of used sand increases plasticity and reduces the risk of cod and edge disintegration.
128 Assistance for decisions: Erosion 129 Assistance for decisions: Erosion A Clay-bonded sand Examine binder content Erosion can be expected below a critical amount of bentonite. Increase bentonite content if necessary. Examine sand temperature Severe drying occurs at high sand temperatures. Reduce sand temperature to below 40 C. Examine compactability At a compactability of less than 30 %, the bentonite is longer totally developed. If necessary, increase compactability. Examine sand grain size With coarse sand, individual grains can be torn from the mould, use finer sand Examine inert, n-active fines content Insufficient bonding of sand occurs with too high a proportion of inert fines. Examine lustrous carbon producer With low lustrous carbon production, the metal stream can tear away sand grains. Increase activity of lustrous carbon producer. Examine salt content of sand High salt content in water or sand leads to deactivation of bentonite.
130 Assistance for decisions: Erosion 131 Assistance for decisions: Explosive penetration B Moulding plant A Clay-bonded sand Examine compaction With low compaction there is insufficient bonding, sand must be more evenly distributed. Increase pressure of plant if necessary. Reduce moisture content Adjust compactability to minimum Examine degree of mulling Low degree of mulling necessitates a higher water content. Water is released at an early stage when casting. C Gating and pouring practice Examine pouring rate With too high a pouring rate, erosion occurs at overheated points. Reduce pouring rate. Examine proportion of inert fines Inert fines requires a lot of water which is rapidly released on heating. Reduce inert fines content (dust, bentonite, lustrous carbon carrier). Examine quantity of inflowing metal Excessive quantities of metal will cause overheating and erosion. Achieve better metal distribution. Reduce bentonite content Lower bentonite contents require less water. Use higher bentonite quality if necessary.
132 Assistance for decisions: Explosive penetration 133 Assistance for decisions: Lustrous carbon inclusions Examine sand grain size Higher AFS values reduce danger of explosive penetration. Use finer sand if necessary. A Resin-bonded sand Examine core binder Measure lustrous carbon production of the binder. Use binder with lower lustrous carbon production. Examine lustrous carbon producer More active lustrous carbon producers require less water. Less material usage and coke formation. Examine gas removal from cores Improve gas removal, core venting, coarser sand grain, core prints. B Moulding plant Examine compacting pressure Reduce compacting pressure. If necessary, increase uniformity of compacting. Pre-treatment of cores Dry cores. Coat cores at critical points. Addition of oxidation agents. C Gating and pouring practice Examine pouring rate Over-rapid pouring rate leads to explosive penetrations. Reduce pouring rate.
134 Assistance for decisions: Lustrous carbon inclusions 135 Assistance for decisions: Lustrous carbon inclusions B Clay-bonded sand C Moulding plant Examine lustrous carbon production in moulding sand Measure active carbon. Reduce quantity of lustrous carbon producer. Examine compaction Reduce compaction by increasing compactability or reducing compacting pressure. Examine lustrous carbon producer Use less active lustrous carbon producer if necessary. Use slower-reacting materials. D Gating and pouring practice Examine gating Turbulence leads to lustrous carbon inclusions. Strive for laminar pouring. Examine gas permeability Use coarser sand if possible. Reduce fines. Examine pouring data Higher pouring temperatures reduce the risk of lustrous carbon inclusions.
136 Assistance for decisions: Graphite degeneration 137 Assistance for decisions: Graphite degeneration A Metallurgy C Resin-bonded sand Examine residual magnesium content Adjust residual magnesium content to match gating, subversive elements, pouring temperature and casting systems. Examine sulphur content Sulphur content sometimes high due to PTS or other binding systems. Reduce quantities. Use other methods. Examine content of subversive elements Proportions of subversive elements such as antimony, lead, cadmium, titanium and, to a lesser extent, aluminium, copper and zinc must be kept low. Coat cores and moulds Seal surface by coating. Gas cant enter mould cavity. Apply coating more thickly if necessary. B Gating and pouring practice D Clay-bonded sand Check pouring temperature Reduce pouring temperature. Cool melt more rapidly. Examine formation of oxidizing gases Oxygen, carbon dioxide, water vapour react with the residual magnesium content. Reduce formation of these substances.
138 Assistance for decisions: Graphite degeneration 139 Assistance for decisions: Fissure defects A Metallurgy Examine sulphur content in moulding sand Use low-sulphur carbon carrier. Examine inflowing core sand for sulphur. Examine nitrogen content Nitrogen content of more than 100 ppm can lead to defects in grey and SG cast iron. Examine charge materials; modify as appropriate. Examine formation of hydrocarbons Use sufficient quantities of lustrous carbon producer. Increase lustrous carbon production if necessary. Check titanium content Titanium bonds nitrogen; add pure titanium if necessary. Increase titanium level to 0.03 %. Check CE value Critical CE values between 3.4 and 3.8. Increase to 3.8 if necessary.
140 Assistance for decisions: Fissure defects 141 Assistance for decisions: Fissure defects B Resin-bonded sand C Clay-bonded sand Check nitrogen content of binder Reduce or avoid nitrogen-containing binders, hardeners, admixtures. Reduce moisture content Gas absorption increases due to residual moisture. Reduce quantity of bentonite and inert dust. Examine gas formation Use low-gas binders. Reduce quantity of binder. Examine nitrogen contents Reduce nitrogen contents by adding new sand. Reduce quantity of lustrous carbon producer. Use lustrous carbon producer with low nitrogen content. Examine release of gas Improve gas removal. Venting. Coarser sand. Examine lustrous carbon producers More active lustrous carbon producers with low nitrogen content preferable. Quantity and release of gas / unit of time should be kept low. Add iron oxide Iron oxide prevents nitrogen absorption by the melt.
142 Assistance for decisions: Fissure defects 143 Assistance for decisions: Micro-cavities D Gating and pouring practice A Metallurgy Examine gating Shortened flow channels prevent gas absorption. Avoid turbulence. Examine solidification range Defect occurs only in metals with a wide solidification range. Reduce CE value. Remove low-melting-point components (in case of grey iron, phosphorus content). Check pouring temperature Faster and hotter pouring leads to improved liberation of gases. Examine gas contents Combine gases or remove by degassing B Clay-bonded sand Examine gas formation Check gasification rate and quantity of lustrous carbon producers. Reduce quantities if necessary. Check bentonite content and mould moisture, reduce if necessary.
144 Assistance for decisions: Micro-cavities 145 Assistance for decisions: Micro-cavities Examine inert content in dust Excessive dust contents bind water and reduce gas permeability. Reduce inert dust contents if necessary. Apply facing sand materials Use materials with high heat conductivity at critical points. Apply facing sand Apply chrome ore sand or other materials with good heat conductivity at critical points. D Moulding plant Examine mould stability Swelling and expansion of mould increase risk of defect. Compact mould evenly. Reduce compactability. Reduce bentonite content. C Resin-bonded sand Examine gas formation Check gasification rate and quantity of binder. Reduce quantity, use slow-reacting binder. Examine radii of moulds Increase edge radii. Reduces the risk of gas transfer points.
146 Assistance for decisions: Pitted surfaces 147 Assistance for decisions: Pitted surfaces A Clay-bonded sand B Metallurgy Check fluoride content in moulding sand Use more new sand where content is too high Examine Mg content Keep Mg content in melt as low as possible. Check water content Water content should be as low as possible. Reduce bentonite content, reduce dust content if necessary. C Gating and pouring practice Examine need for feeder consumption Use as few feeders as possible. Use insulation feeders if possible. Examine feeder material in moulding sand Remove all feeder materials. Fluoride-containing feeder residues cause surface reactions. Check pouring temperature Reduce pouring temperature
148 Assistance for decisions: Surface blowholes 149 Assistance for decisions: Surface blowholes A Resin-bonded sand B Clay-bonded sand Examine core venting Examine core prints, enlarge venting channels. Check sand moisture Reduce moisture content. Improve degree of mulling. Examine binder Examine quantities, type and gas release of the binder. Reduce. Check gas permeability Proportion of fine materials may be too high. Check inert fines, bentonite content, lustrous carbon carrier content; sand may be too fine. Examine moisture content Perform core-drying, store dry, reduce moisture absorption. Check sand temperature High sand temperature can lead to condensation of water on chaplets and cold cores. Check gas permeability of cores Use coarser core sands. Reduce fines such as Fe 2 O 3. Examine bentonite Check development rate of bentonite, inert fines etc. Use high quality bentonite.
150 Assistance for decisions: Surface blowholes 151 Assistance for decisions: Penetration A Clay-bonded sand Examine lustrous carbon carrier Replace fast-reacting products. Reduce quantities. Check sand grain size Penetration occurs above a critical pore size. Use finer sand if necessary. C Moulding plant Examine compaction Determine mould hardness, reduce compacting pressure. Examine lustrous carbon production Low lustrous carbon production promotes penetration through greater wetting of sand; measure active carbon; increase addition of carbon carrier if necessary. D Gating and pouring practice Check pouring temperature Liquidus temperature should be ticeably exceeded. Check proportion of fines Large quantities of fines reduce pore diameter. Check de-dusting, provide dust admixture, increase coke content if necessary. Check gating Avoid turbulence, optimize pouring times. Separate slags; optimize pouring pressure. Examine compactability High compactability leads to under-compacted sections. Keep compactability as low as possible. Improve flowability.
152 Assistance for decisions: Penetration 153 Assistance for decisions: Penetration B Resin-bonded sand C Moulding plant Check sand grain size Penetration occurs above a critical pore size. Use finer sand if necessary. Check compaction Make compaction more uniform. Examine deeper cods. Ensure even prefilling. Apply coatings Seal pores by applying coatings. Use thicker applications if required. Examine binding agent Highly viscous binding agents result in uncompacted core sections; use binder with low viscosity. Examine lustrous carbon producers. Binders with high lustrous carbon production preferable. D Gating and pouring practice Check gating Excessive quantities of inflowing metal cause overheating. Achieve more even and better metal distribution. Check pattern plate arrangement. Check pouring temperature Reduce pouring temperature if necessary
154 Assistance for decisions: Pinholes 155 Assistance for decisions: Pinholes A Metallurgy (ferrous metals) Check nitrogen content of melt Nitrogen content too high due to charge make-up. Reduce steel content for grey and SG cast irons. Check manganese content Manganese forms MnS slags with sulphides in the melt, which play a part in the formation of CO micro-holes. Reducing Mn content can be helpful. Check charge materials for oxides and hydroxides Use oxide-free and rust-free materials. In case of return scrap, watch for adhering feeders. B Clay-bonded sand Check nitrogen content High nitrogen contents can stem from lustrous carbon producers and, in particular, from core binders. Reduce proportion by adding new sand if necessary. Check aluminium content Reduce aluminium content; this reduces the reaction of water vapour with residual aluminium. Check moisture Reducing water content results in lower quantities of water vapour and hydrogen. Check titanium content The same applies as with aluminium. Titanium is used in melt beforehand to avoid pinholes. Hydrogen absorption increases in circulation. Check lustrous carbon carriers Increased lustrous carbon production in moulding sand causes a reducing atmosphere in mould cavity and thus diminished likelihood of initial CO micro-holes.
156 Assistance for decisions: Pinholes 157 Assistance for decisions: Surface roughness C Resin-bonded sand A Clay-bonded sand Examine nitrogen in core Urea-containing resins release nitrogen. Binders with low urea content reduce nitrogen pick-up in the melt and have a generally positive effect. Examine sand grain size Use finer sand grain if necessary. Add iron oxide Iron oxide admixtures prevent nitrogen absorption in the melt and have a generally positive effect. Examine lustrous carbon production Measure active carbon. Increase additions of carbon carrier. D Gating and pouring practice Examine lustrous carbon producer Use carbon carrier with higher lustrous carbon producing capacity. Examine gating Shortened flow channels reduce gas absorption and counteract the risk of pinholes. Examine for presence of slag Slag-free pouring reduces the risk of CO micro-holes into which N 2 and H 2 diffuse. Examine fines content Increase fines if necessary. Use lustrous carbon carrier with higher coke producing capacity.
158 Assistance for decisions: Surface roughness 159 Assistance for decisions: Sand inclusions B Moulding plant A Moulding plant Examine compaction If possible, compact evenly and more effectively. Reduce compactability. Examine mould for pressure points Separate flasks after assembling and perform visual inspection. Blow out mould flasks, fit pressure pads is necessary. Examine mould surface Improve adherence of sand at the surface. Avoid drying out. Examine pattern plates Inspect patterns for cracks and smoothness. Increase tapers and radii of patterns if necessary. Heat pattern plates; use release agent. C Gating and pouring practice Check pouring temperature Apply materials with good heat conductivity at critical points. Examine mould stripping process Examine mould flasks for even stripping. Examine possibility of cracks and disintegration. Correct if necessary. Examine core setting Check for edge crumbling when coring up and for core misalignment. Employ automatic core insertion.
160 Assistance for decisions: Sand inclusions 161 Assistance for decisions: Sand inclusions Examine mould hardness Examine prefilling, improve uniformity. Reduce mould compaction if necessary. Examine cluster formation Clustering depends on mixer types and total dust content. B Clay-bonded sand Examine compactability Increase compactability. High compactability reduces the risk of over-compaction and increases plasticity. Examine lustrous carbon producer Reduce quantity of lustrous carbon producer. Use material of higher lustrous carbon production capacity if necessary. Examine bentonite content Increase bentonite content, increase mixing times. Try to achieve better bentonite development. Improve pre-wetting. C Resin-bonded sand Examine core strength Where core breakage occurs, increase binder content as appropriate. Improve compaction. Examine inert dust content Limit proportion of dead-burnt inert fines to 2 2.5 % with 10 % activated clay. Restrict by adding new sand or bentonite if necessary.
162 Assistance for decisions: Sand inclusions 163 Assistance for decisions: Slag inclusions D Gating and pouring practice A Metallurgy Examine gating Improve distribution of gates if possible; avoid turbulence. Examine melt Examine melt for slag formation. Reduce oxygen-affinitive elements (Al, Mg, Mn). Reduce sulphur content if necessary. Examine pouring rate Reduce pouring rate if necessary. Examine iculation Examine dissolution capacity of iculant. Avoid mould iculation if necessary. Re-specify type and grain of iculant. Examine ladle lining Examine reaction of lining with the melt, particularly at metal / atmosphere interface. Use refractory mixtures. If necessary, improve drying of ladle. Examine de-slagging of ladle Avoid inflow of slag into ladle. Retain slag when pouring. Use teapot spout ladle; use slag-forming admixture if necessary. Clean ladle after pouring.
164 Assistance for decisions: Slag inclusions 165 Assistance for decisions: Slag inclusions B Gating and pouring practice Examine pouring conditions Raise temperature. Shorten pouring time. Examine bentonite content Increase bentonite content if necessary. Improve development of bentonite. Examine gating Keep pouring basin full, avoid turbulence. Use a dross filter, use strainer core. Examine lustrous carbon producer Use material that has a higher lustrous carbon production. Increase quantity if necessary. C Clay-bonded sand Examine inert dust content Do t allow inert fines content to rise above 2 % with 10 % activated clay. Add new sand.
166 Assistance for decisions: Scabbing 167 Assistance for decisions: Scabbing A Clay-bonded sand Examine bentonite content Measure wet tensile strength. If necessary, increase bentonite content or change its quality. Examine degree of chamottization Higher compressive stress occurs with a low degree of chamottization. Reduce quantity of new sand if necessary. Examine dust content Silica-containing inert fines increase compressive stress; improve sand de-dusting. Use bentonite with higher montmorillonite content. Examine water quality Poor water quality leads to over-salting. Carry out partial desalination if necessary. Examine sand grain size A high fines content increases compressive stress. Choose wider or coarser grain size distribution. B Moulding plant Examine compaction Excessive compaction results in compressive stress. Reduce compacting pressure, endeavour to achieve more uniform compaction. Increase compactability if necessary. Examine degree of mulling With low degree of mulling, pre-wetting is beneficial. Increase mixing time, carry out re-activation if necessary.
168 Assistance for decisions: Scabbing 169 Assistance for decisions: Swelling C Gating and pouring practice A Moulding plant Examine gating system Local overheating due to over-rapid metal flow promotes scab formation. Improve inflow of metal. Examine compaction Measure mould hardness. Improve sand distribution when filling. Increase compacting pressure if necessary. Examine patterns. Yes Yes Check pouring times Strive for faster pouring and shorter radiation heat exposure times. B Clay-bonded sand Check compactability Reduce compactability. Moulds become firmer, compaction more uniform. Improve flowability of sand Use products containing graphite. Compaction of sand becomes more uniform.
170 Assistance for decisions: Swelling 171 Assistance for decisions: Penetration due to chemical reaction C Resin-bonded sand A Clay-bonded sand Examine cores Cores insufficiently compacted, improve compaction. Improve hardening of cores. Examine compactability Reduce compactability. Examine sand grain size Coarse sands promote metal penetration. Use finer new sand; use finer core sand if necessary. D Metallurgy Examine graphitization pressure For grey cast iron, expansion pressure possible due to graphite formation in melt. Increase phosphorus content. Examine heat resistance of moulding sand Low-melting admixtures, impurities and a higher degree of oolitization all promote penetration due to chemical reaction. Add greater quantities of new good silica sand. Examine lustrous carbon production Lustrous carbon separates the melt from the moulding sand. Increase quantity of lustrous carbon producer. Use lustrous carbon producer with greater coke formation.
172 Assistance for decisions: Penetration due to chemical reaction 173 Assistance for decisions: Penetration due to chemical reaction B Moulding plant D Gating and pouring practice Examine compaction Measure mould hardness. Improve sand distribution before compacting. Increase compacting pressure if necessary. Examine pattern design. Check pouring temperature Reduce pouring temperature if necessary Examine gating system Improve distribution of inflowing quantities of metal. Avoid overheated areas. Avoid excessive metallostatic pressure. C Resin-bonded sand Examine cores Improve compaction of cores. Use finer core sand if necessary. Coat cores Coat cores at critical points (overheated sections and under-compacted areas).
174 Assistance for decisions: Angular blowholes 175 Assistance for decisions: Angular blowholes A Clay-bonded sand C Resin-bonded sand Investigate gas formation Reduce moisture. Reduce quantity of bentonite if necessary. Examine lustrous carbon carrier, reduce quantity if necessary. Use more active materials. Examine core sand Use coarser core sand and increase gas permeability. Examine gas permeability Use coarser sand. Reduce fines, particularly inert fines. Examine core binder Reduce quantity of binder. Use binders which release gas more slowly. D Gating and pouring practice B Moulding plant Check pouring temperature Reduce pouring temperature if necessary. Examine patterns Increase radii on edges of patterns. Examine gating system Improve secondary feeding of critical points.