1 hole defect
Hole defects include porosity, shrinkage, shrinkage, slag hole, sand hole, iron bean.
Porosity: the charge should be cleaned, the ferroalloy should be baked well, the ladle should be baked well during pouring; the overheating temperature and time of molten metal should be controlled by reasonable melting process, the cooling rate of castings should be accelerated, or solidified under pressure, and the gas should be precipitated; the appropriate pouring process, gating system and pouring conditions should be selected to facilitate the discharge of gas; the air permeability of the mold shell should be improved, and the exhaust hole should be added when necessary; the suitable temperature of molten metal, pouring temperature and baking temperature of the mold shell should be added; the roasting mold shell should be fully roasted; the particle size of binder and refractory should be reasonably selected.
Shrinkage: correct design of gating system to facilitate casting and sequential solidification and shrinkage; improvement of casting structure to make wall thickness as uniform as possible or increase process subsidy and cold iron; use of appropriate pouring process, such as high temperature, low temperature pouring; increase mold cooling rate, or reasonable mold formation, increase wax mold spacing and improve local heat dissipation conditions; reduce molten metal temperature during pouring and increase the height of pressure head; select smelting alloy with low shrinkage if necessary.
Shrinkage: adjust alloy composition, reduce alloy solidification range, fully deoxidize and degassing during melting and pouring to reduce the effect of gas on solidification shrinkage; improve casting structure, set pouring system reasonably, increase pressure head height and increase shrinkage capacity; select suitable pouring process, strictly control pouring temperature of molten metal; select good thermal conductivity shell material, improve cooling condition of castings and speed up cooling rate of castings; improve the position of inner gate, which is beneficial to sequential solidification.
Sand hole: keep wax and gate rod clean, prevent mold shell from falling into cavity during dewaxing, handling, storage, roasting, pouring or sand filling. Before pouring, vacuum cleaner should be used to clean the mold cavity; select suitable shell material, reasonable shell making process, strictly operate, avoid shell layer stratification; improve gating system design, avoid direct entry of refractory material into cavity and slow down the impact of molten metal on cavity surface; pay attention to pouring operation, slow down and fast before pouring, avoid severe scour of molten metal to cavity
Slag hole: strengthen charge management, adopt clean charge when smelting; use proper amount of slagging agent and deoxidizer when smelting, molten metal should have enough static time, which is beneficial to slag floating; remove slag on ladle before pouring; improve gating system design; Improve the height of ladle nozzle to shell gate cup.
Iron beans: when coating the first two layers, pay attention to the operation, to eliminate the sharp angle, corner bubble; the new coating should be static for a certain time, when adding wetting agent, should add appropriate amount of defoamer; wax mold should be degreased before coating; improve casting design, sharp angle, corner should be smooth transition.
2 schizoid defects
Cracks include: hot crack, cold crack.
Hot crack: improve casting structure, wall thickness as uniform as possible, increase casting round corner or add process bar; improve shell material or reduce shell layer number, add appropriate amount of additive, increase pouring temperature, increase shell concession; improve pouring system design; select reasonable pouring process; select materials with low thermal cracking tendency, keep furnace clean, select reasonable smelting process, add rare earth elements in appropriate amount, improve high temperature strength and plasticity of castings.
Cold crack: improve casting structure, such as uniform wall thickness, eliminate sharp angle, add process reinforcement, control cooling rate to adapt to alloy shrinkage; adopt less phosphorus furnace, adopt reasonable melting process, reduce impurity content, improve molten metal quality; When cleaning castings or removing gate, the impact force should not be too large.
3 Surface Defects of casting products
Surface defects include sand sticking, scarring, sand clamping and cold insulation.
Sanding: reasonable selection of shell materials and ensure their quality, full deoxidation, minimization of molten metal oxidation, and removal of oxide produced; control of humidity and storage time of shell storage site, use of reasonable roasting process; proper reduction of molten metal temperature and shell temperature during pouring; improvement of casting structure and heat dissipation parts; proper improvement of surface coating viscosity; proper reduction of molten metal temperature during pouring; proper reduction of pouring temperature of molded shell; proper reduction of height of pressure head.
Scarring: the coating should be fully stirred, after hanging, the air is dry well and hardened fully; reduce the density of binder in the surface coating; reduce the temperature of molten metal and shell when pouring properly, Reduce oxide in molten metal and low melting point inclusions in shell surface; improve casting structure.
Sand clamping: prevent mold shell delamination, select reasonable pouring process, reduce stress, avoid inner surface rupture of mold shell, improve casting structure, avoid large plane or concave as far as possible, design inner gate correctly, avoid local overheating; Select reasonable shell making process and strictly implement, fully harden or dry well, make coating close combination, improve shell strength.
Cold insulation: properly increase the temperature of molten metal and shell during pouring, improve the design of gating system, increase the number and position of cross section and inner gate of gating system, so as to shorten the filling time of molten metal in cavity; properly increase pouring speed, make molten metal enter cavity continuously and smoothly, and avoid the phenomenon of breaking flow; when pouring, put cover agent in the ladle in advance to prevent secondary oxidation of molten metal; make molten metal filling smoothly during pouring.
4 Defects in size, shape and weight
Dimensional shape and weight of unqualified defects include: flying wings, inadequate pouring, deformation, dislocation, Residues in the cavity, Pit, Inclusions.
Fly wing: strictly control the temperature and waxing pressure of wax material when making mould; check the parting surface carefully and clean up before making mould; improve the design of pressing type and select material reasonably; control the manufacturing quality of pressing type, Ensure the accuracy and roughness of parting surface; specify reasonable service life.
Insufficient pouring: strictly control the temperature of wax material after stirring; strictly control the injection pressure, and contact wax injection can not be interrupted; improve the pressure design to facilitate exhaust.
Deformation: reasonable selection of binders and refractories as well as paint, shell making and pouring process; control of coating ratio, viscosity and temperature, pay attention to shell coating and hanging operation; shell to prevent a certain time to dewaxing; choose a reasonable roasting process, strictly control roasting temperature and time; strengthen the regular detection and daily maintenance of roaster; shell roasting, immediately after pouring.
Dislocation: lock the live block when pressing, counteract the pressure of wax filling; determine the reasonable service life of the pressing type; select the injection pressure reasonably according to the size, shape and wax material of the wax mold.
Residues in the cavity: After the shell is hardened, it should be fully dried; select a reasonable roasting process and strictly control the roasting temperature and holding time: regularly check the roasting furnace to meet the process requirements; thoroughly clean the sprue cup before dewaxing Excess shell material on the top to avoid the shell material falling into the cavity during the dewaxing process; select a reasonable dewaxing process to strictly control the temperature and time of dewaxing; when replacing the dewaxing solution, completely remove the dewaxing The shell material at the bottom of the tank; the shell storage place should be managed in accordance with the 5s requirements, the shell should be stored upside down to prevent the shell material from falling into the cavity; be careful to avoid sprinkling the molding sand into the cavity without pouring.
Pit: Choose dry and clean charge, choose reasonable smelting process, and adopt secondary deoxidation; choose surface layer shell material reasonably; choose reasonable shell roasting process, strictly control roasting temperature and time, and eliminate residue in the cavity Make the shell white after firing; select a reasonable binder according to the material of the casting, such as silica sol binder; appropriately reduce the temperature of the molten metal and the shell during casting to speed up the cooling rate.
Inclusions: Choose clean charge, sandblasting, or shot blasting before use. Before using the alloy, it should be inspected and properly baked, and desulfurization treatment should be used if necessary; choose a reasonable melting process and pouring process, and use high temperature Use a filter screen or inert gas if necessary; deoxidize strictly during smelting to protect the surface of the molten metal. Before the molten metal is released, let it stand for 2 minutes to float the inclusions and remove them; put it in the ladle first Covering agent to prevent secondary oxidation when molten metal is poured; appropriately increase the temperature of molten metal and mold shell, which is beneficial to the floating of inclusions.
These kinds of the defect are common for steel casting manufacturers. A responsible steel casting company should demonstrate those defects and provide prevent solution for their customers. As the leader steel casting company in China, we are experienced to deal with these defects and provide perfect casting products to our customers. Our steel casting foundry is the capacity to satisfy your requirement.