1 / 37

Casting Techniques

Che5700 陶瓷粉末處理. Casting Techniques. Slip casting (e.g. drain casting, solid casting), tape casting, gel casting, centrifugal casting, etc

dacey
Télécharger la présentation

Casting Techniques

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Che5700 陶瓷粉末處理 Casting Techniques • Slip casting (e.g. drain casting, solid casting), tape casting, gel casting, centrifugal casting, etc • Prepare proper slurry (proper viscosity), fill into mold or direct forming, dehydration (or solvent), de-molding, drying, sintering, post-fabrication, product • Can be used to get complex shape products • Uniformity of slurry: very important • Dispersion of slurry: can be judged by sediment height (an index) • anisometric particles, easy to show preferred direction, e.g. plate particle, tend to be parallel to casting surface

  2. Che5700 陶瓷粉末處理 Schematics of Slip Casting • Drain casting: dilute solution (5%), porous mole, particle adsorb on mold wall, form thin layer, pour extra solution, de-molding and other processing • Rate of dehydration affect particle packing

  3. Che5700 陶瓷粉末處理 Mechanism of Slip Casting • Flow resistance: mold and cake • Darcy law applied to get relationship between pressure drop and velocity; usually mold resistance greater than cake resistance • PT = applied pressure + suction pressure from mold • Filtration theory: sample thickness and time relation

  4. Che5700 陶瓷粉末處理 Viscosity of Slurry • viscosity too high or low: not ideal • Also slurry may have yield strength • Good stability for storage life

  5. Che5700 陶瓷粉末處理 Schematics of Solid Casting • Solid casting: concentrated slurry pour into mold, dehydration, de-molding and other processing;

  6. Che5700 陶瓷粉末處理 Strength of Product • Product strength increase gradually • Due to increasing density, strength comes from interaction between particles, with help from binder

  7. Che5700 陶瓷粉末處理 Filter Pressing • In general: slip casting rely on capillary action to remove water, filter pressing: from applied pressure, can reach higher density • Cake may be compressible: S = compressibility index • another possibility: vacuum filtering

  8. Che5700 陶瓷粉末處理 Sedimentation Casting/Centrifugal Casting • Different casting process • Sedimentation: slower rate; add centrifuge to increase rate of sendimentation • Well dispersed suspension, very slow sendimentation, can reach higher density; different particle size, different rate  different effect, i.e. may be size distribution inside the cake (sediment)  to product, poor effect  always differential shrinkage • Centrifugal casting: suitable for tube making; r2 forg as the acting force

  9. 取自TA Ring, 1996

  10. 取自TA Ring, 1996;

  11. Che5700 陶瓷粉末處理 Porous Mold Materials • Gypsum: frequently used; plaster of Paris CaSO4. .5H2O + H2O  gypsum CaSO4. 2H2O • Today’s technology: good smooth surface, high ultimate porosity, micron-sized pores, short setting time, small dimensional expansion on setting (for easy release), low cost • Often use hot water to get uniform mold • Porosity: depending on mixing, electrolyte in water, T etc. parameters • Limitations : low compressive strength when partially saturated with water  erosion; when in contact with acid or alcohol, gypsum life becomes shorter • New generations of polymer mold, with similar pore structure, high strength, corrosion resistant

  12. when making mold, too much water, low strength, greater adsorption • Taken from JS Reed, 1995; when mold drying, avoid too high temperature, will cause dehydration

  13. Che5700 陶瓷粉末處理 Dip Coating • Pull at an angle and speed to get coating; • film thickness depend on slurry rheology; for Newtonian fluid

  14. Che5700 陶瓷粉末處理 Particle Orientation Taken from TA Ring, 1996; Dip coating: shear force may cause special arrangement of particlesto minimize resistance

  15. Che5700 陶瓷粉末處理 Problems of Slip Casting Implies optimized viscosity and gelation  by proper additives; slurry rheology, casting rate, cast property, drying and burn-out rate = balance of these parameters

  16. Taken from JS Reed, 1995; case A, range of “good” cast is wider and favorable; S = soft; H = hard;

  17. Che5700 陶瓷粉末處理 Gel Casting • Refer to cases where binder (monomer) can polymerize, make system a gel; fill in a mold (of complex shape)  stimulate reaction to gelation  de-mold  thermal treatment to product • Can be used for dense product or porous product, former case: concentrated slurry to get high density packing • Linear shrinkage is about 0.5 – 1.5% • Volume of binding phase/volume of particles ~ 16% • Mold not necessary porous material, can be made of a variety of materials

  18. Che5700 陶瓷粉末處理 Control of Defects in Cast

  19. Che5700 陶瓷粉末處理 Discussions on Defects • Non-uniformity in wall thickness: due to non-uniformity from mold, non-uniformity in water adsorption or casting rate; or erosion non-uniformity in mold etc. • distortion: come from stress in green body, or differential shrinkage during drying, e.g. warping • crack: difference in adhesion between object and mold wall, differential volumetric shrinkage, especially at joint; or very large agglomerates • void: could be due to trapped air • Bubbles and pin-holes: comes from during pouring; pin-hole on the surface may come from removing excess slurry • Surface irregularity: come from irregularity on mold surface, water adsorption non-uniformity, during pouring of high viscosity slipetc. • Microscopic defects: incomplete dispersion, contamination, unadsorbed additive; etc.

  20. Che5700 陶瓷粉末處理 Tape Casting • Or called doctor blade method; often used to fabricate thin, plate-like products, such as substrate • High productivity, if continuous process, green tape first, then cut into appropriate sizes; can be multilayer “laminated” products • Appropriate viscosity is of vital importance • In general, particle size around 1 μm, or specific surface area of 2 – 5 m2/g • An-isometric particles may align preferentially during casting, to form special structure; • Tapes of Tyflon, Mylar are often used as carrier, may be coated with de-molding compound (脫模劑)for easy removal

  21. Common tape casting equipment; from JS Reed, 1995

  22. Che5700 陶瓷粉末處理 Doctor Blade • Belt moving velocity + pressure gradient  effect of motion

  23. MLCC=multilayer ceramic capacitorLTCC = low temperature co-fired ceramics Taken from TA Ring, 1996

  24. Che5700 陶瓷粉末處理 Slurry Compositions Change to water system: a common trendfor environmental reasons; need to overcome drying-shrinkage problem

  25. Che5700 陶瓷粉末處理 Additives

  26. Che5700 陶瓷粉末處理 Quantity Effects Too much lubricant, lower tensile strength; increase strain-to-failure

  27. Che5700 陶瓷粉末處理 Binder Quantity • Tape casting:Vb/Vp ~ 15 – 25% • high MW binder, can offer higher strength and toughness green body, not moving during drying (migration with solvent) • Yet binder has to be removed during calcination

  28. Che5700 陶瓷粉末處理 Tape Thickness • Pressure flow under the blade + planar laminar flow by the carrier • Thickness = f(height under blade, speed of carrier, drying shrinkage, viscosity of slurry) • Dr = (density of slurry)/(density of as-dried tape);ho cast thickness at the blade; L = length of tape • Drying stage: shrinkage mostly in the thickness; not much in the lateral direction  thus use Dr

  29. Che5700 陶瓷粉末處理 Uniformity Issue High rate and high viscosity, beneficial to product uniformity Industrial scale: 25 m long, several meters wide, 1500 mm/min speed, tape thickness: 25-1250 m are common;

  30. Che5700 陶瓷粉末處理 Drying • Drying rate ~ temperature and solvent content of the drying air; initial: solvent evaporation, drying rate about constant • Capillary force to transport liquid inside green body: mechanism during rate decreasing region • Shrinkage occurs: particle closer to each other • Binder often not moving, lubricant can move • Last item: vapor transport may be rate determining step, tape becomes more elastic • Final density ~ 55-60% of TD; 35% organics, 15% porosity

  31. Che5700 陶瓷粉末處理 Shaping and Laminating • Individual steps: scale become smaller and smaller; 0402; 0201, etc.

  32. Che5700 陶瓷粉末處理 Binder Burnout • Need certain gas permeability to allow organics to burn out and vented; • Bond strength between layers: important issue during burnout stage; • Strength related to pressure during forming, temperature and time

  33. Che5700 陶瓷粉末處理 Defects • Agglomerate inhibit sintering in that region; differential shrinkage lead to crack; bubbles & poor surface cause poor contact between layers • Difference between metal line and neighboring ceramics; gas pressure from binder burnout may cause problem

  34. Che5700 陶瓷粉末處理 Effects of Some Parameters • Effects • bubble skinning crack • More solventdecrease NA may increase • Higher temperaturedecrease increase NA • Increase solvent • evaporation rate NA increaseincrease • Faster pouring • rate NA NA NA • Air rate up NA NA increase • Inorganic NA lowerNA • Ideal slip: high solid content, low viscosity, solvent not causing skinning and trap air bubble, drying system can remove gas and rapid drying

  35. 取自JS Reed, 1995;

More Related