Advanced Electronic Ceramics I (2004)

Compaction: General

S. J. Glass and K. G. Ewsuk, MRS Bulletin, Dec., 24 (1997)

Pressing operation1. Filling the mold or die with powder

- free-flowing spherical granulated powder prepared by spray dryingare generally used to optimize the die filling

- typical granules ( range: ~44 to 400 µm, avg. ~100 to 200 µm)- typical granule density : 45-55%- typical die fill density before pressing: 25-35%

2. Compacting the powder to a specific size and shape- consolidation by granule rearrangement- granule deformation- increase in particle-coordination number, green density, and compactstrength

- typical compaction pressure : 35- 104 MPa3. Ejecting the compact from die

- elastic springback (the expansion of a compact upon ejection from thedie should be minimized.

Advanced Electronic Ceramics I (2004)

Spray drying

S. J. Glass and K. G. Ewsuk, MRS Bulletin, Dec., 24 (1997)

Spray drying : the process that granulates the fine primary particles intospherical secondary spheres in order to increase the flowability of thepowder via the spray of the mixture between powder, additive, andsolvent

The additive for spray drying1. Binder : strength2. Plasticizer : deformable granule3. Lubricant : reduce the frictional effect

Advanced Electronic Ceramics I (2004)

Possible problems in compaction

S. J. Glass and K. G. Ewsuk, MRS Bulletin, Dec., 24 (1997)

End capping- body with poor green strength and high springback- High die-wall friction and high pressing pressure

Ring capping- poor tolerances between the punch and die body- excessive differential springback

Lamination- poor green strength- pressing at excessively high pressures- high springback or die fraction

Vertical cracks- excessive springback

Advanced Electronic Ceramics I (2004)

Consideration of Die

S. J. Glass and K. G. Ewsuk, MRS Bulletin, Dec., 24 (1997)

Narrower diameter die usually results lower packing densitybecause the packing density at the die wall is lower than that at the bulk of the compact.

High aspect-ratio (height/diameter) are undesirablebecause the packing density can vary with height

In order to reduce the die-wall effect- Use the smaller particle or large die

recommended compact diameter and thickness1. Diameter: ~X250 of the average agglomerate size of powder2. Thickness: ~X40 of the average agglomerate size of powder

Advanced Electronic Ceramics I (2004)

Density gradients predicted by the FE compaction model in a quarter section of a 94 wt% alumina tube. The 25,4 mm long tubes were compacted uniaxially at 103.4 Mpa by: a) dual-action pressing and b) single-action pressing from the top. Density changes with color from blue to green, yellow, orange, and red.

K.G. Ewsuk et al., Am.Ceram.Soc.Bull., 80(1), 53 (2001)

Dual-action and Single-action Pressings

Advanced Electronic Ceramics I (2004)

Green-Density Gradient along the pressing axisThe density gradients through the cross section of a cylindrical powder compact of 94wt.% alumina after uniaxial pressing at 69 MPa: a) measured by ultrasound velocity measurements completed on a bisque-fired part, and b) predicted using the FE compaction model assuming a die wall friction coefficient of 0.25.

K.G. Ewsuk et al., Am.Ceram.Soc.Bull., 80(1), 53 (2001)

Advanced Electronic Ceramics I (2004)

Compaction curve

S. J. Glass and K. G. Ewsuk, MRS Bulletin, Dec., 24 (1997)

Advanced Electronic Ceramics I (2004)

Compaction: the effect of granules

S. J. Glass and K. G. Ewsuk, MRS Bulletin, Dec., 24 (1997)

Easy rearrangementNo deformation

No rearrangementdeformation at center

proper rearrangementproper deformation

Advanced Electronic Ceramics I (2004)

The properties for the granules

S. J. Glass and K. G. Ewsuk, MRS Bulletin, Dec., 24 (1997)

1. Hard enough to rearrange during die filling and low-pressure compaction2. Soft enough to completely deform under maximum pressing pressure

Advanced Electronic Ceramics I (2004)

Compaction

S. J. Glass and K. G. Ewsuk, MRS Bulletin, Dec., 24 (1997)