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Alumina Ceramic Machining and Grinding

High Purity Alumina
San Jose Delta maintains an in-house inventory of most grades of alumina ceramics as BARS-RODS-TUBES and SHEETS. The availability of fired “grinding stock” ceramic makes the production of small quantity and prototype orders less costly and offers shorter lead-times.

For larger production quantity orders we offer isostatic or dry pressed “near-net” shapes that are fired and diamond ground to customer dimensional requirements.

SJD is often asked to combine these two manufacturing approaches resulting in a faster initial delivery and the cost benefits of production manufacturing.

Whatever your ceramic part design description is: Ceramic Support Rod, Spacer, Bushing, Standoff, Isolator, Insulator, Insert; Threaded or Epoxied, or High Temperature Fixturing, San Jose Delta has the resources to deliver your parts on time, competitively priced and "to print".


Whatever your production need; “contact us”.

Alumina Ceramic Material Properties Data

(AL2o3) Alumina Products Properties
 
Property
Units
AM-94
AM-98
AM-99.5
Specs
Al2O3 Content
%
94.6
97.59
99.43
 
Density
g / cc
3.62
3.77
3.88
ASTM-C20
Color
-
White
White
3.88
 
Crystal Size (Ave)
Microns
2.81
17
9.9
ASTM-E112
Compressive Strength @ 25 C
(kPsi)
(323)
2229
(303)
2091
(364)
2512
ASTM-C773
Tensile Strength @ 25 C
(kPsi)
MPa
(29)
200
(29)
200
(36)
248
ACMA TEST # 4
Flexural Strength @ 25 C
(kPsi)
MPa
(48)
331
(40)
276
(47)
324
ASTM-F417
Elastic Modulus @ 25 C
(Psi X 10-6)
GPa
(42)
290
(48)
331
(53)
366
ASTM-C848
Hardness : Knoop Rockwell
(Gpa) Kg/mm2
R45N
(11.7)   1196
79
(12.5)   1276
77
(14)   1428
85
ASTM-E384
ASTM-E18
Thermal Conductivity @ 25 C
(W / m-Deg K)
cal-cm / sec
-cm2-Deg C
(20.8)
.05
(28.1)
.067
(30.7)
.073
ASTM-C408
Coefficient of Thermal Expansion @ 25-1000 C
1 X 10-6 /
Deg C
7.9
8.5
8.1
ASTM-C372
Specific Heat @ 25 C
(1 / Kg-Deg K)
cal / g / Deg C
(771)
.184
(770)
.184
(761)
.182
ASTM-C372
Maximum Working Temp.
Deg C
1650
1650
1700
No Load Cond.
Volume Resitivity      @25 C                                @ 500 C                                @700 C
ohm-cm
ohm-cm
ohm-cm
1 X 10-13
3 X 10- 9
1 X 10-8
1X 10-13
8.9 X 10-9
2.2 X 10-9
1 X 10-13
1 x 10-12
6 x 10-7
ASTM-D257
Dielectric Strength        50Mils
(@ Thickness)            100Mils                                   250Mils
ac volts
per mil
--
350
223
--
340
217
--
335
213
ASTM-D149
Dielectric Constant        1Mhz 
@ 25 C                        10Mhz
                                   100Mhz
e' / eo
8.6
--
8.6
9.4
9.5
9.0
9.7
--
9.7
ASTM-D150
Dissipation Factor        1 Mhz
@ 25 C                       10 Mhz
                                   100Mhz
Tan Delta
.0004
--
--
.0003
--
--
.0003
--
--
ASTM-D150
Loss Index                   1 Mhz
@ 25 C                       10 Mhz
                                   100Mhz
--
.003
--
--
.0029
--
--
.0027
--
--
ASTM-D150
 
 
Alumina ceramics answer your need for materials that will retain their desirable physical properties in spite of adverse environmental conditions. Alumina ceramics consists of formulations ranging from 85% to 99.9% purity, and blended to meet specific requirements of strength, wear resistance, surface finish, metallizeability and electrical properties.
Alumina ceramics are unique in that they combine many of the desirable properties of metals (high strength, hardness and high temperature resistance) with those of plastics (chemical resistance and good electrical properties).
Hardness
Hardness is a good indicator of a materials' ability to withstand mechanical wear and abrasion. Alumina ceramics are among the hardest materials known-harder than tool steel or tungsten carbide. In fact, alumina ceramics are as hard as sapphire, making them excellent choices for severe-wear applications such as mill and chute linings, bearings and wear plates in addition to those applications already mentioned.
 
Compressive Strength
High alumina ceramics also have exceptional compressive strength, again with values exceeding that of tool steel. Compared to electrical insulator materials such as fused quartz or porcelain, alumina provides two to five times the compressive strength; and values far exceed those of glass, plastics and steatite. The high compressive strength of alumina, even at elevated temperatures, provides long life in structural applications, while other materials may fail due to distortion under load. Stability. Metals frequently warp or distort during machining or heat cycling. Plastics tend to flow under pressure, and sometimes upon aging. This creates problems for the designer, often necessitating compromises in design to allow for deformation or warping. The extreme hardness, modulus of elasticity and low thermal expansion of alumina ceramics means that, within the limits of their tensile and compressive strengths, they will maintain original dimensions under high load and high temperature conditions and aging. Typical room temperature modulus of elasticity values, ranging from 32 x 106 psi to 56 x 106 psi demonstrate the rigidity of aluminas. Exceptional thermal stability assures precision fits over widely varying conditions of loading, speed and vibration. This makes aluminas a good choice for applications such as mechanical seal rings, air bearings, precision valves and wire-drawing components.
 
High Temperature Characteristics
At 1000°C (orange heat) alumina ceramics retain approximately 50% of their room-temperature tensile strength, while most metals will not support their own weight at this temperature. Metals are weakened by oxidation reactions at high temperatures, but when returned to ambient temperature the mechanical strength properties of ceramics are essentially unchanged. Furthermore, with uniform heating and cooling, ceramic parts always return to original dimensions.
 
Chemical Resistance
Alumina ceramics are inert and therefore are highly resistant to chemical attack (except from fluoride or strongly basic solutions). In addition, ceramic is almost unaffected by water, solvents, salt solutions and molten salt. The corrosion resistance of high alumina ceramics is generally far superior to metals: approaching that of plastics such as fluorocarbons. However, plastics can't begin to match the strength of alumina ceramics
 
Joining
Epoxy bonding, the use of flanges, heat-shrinking metal over ceramic, and brazing to metallized surfaces; these are the most common methods of bonding ceramic-to-ceramic or ceramic-to-metal.
 
Variety Of Shapes, Sizes and Tolerances
Ceramic parts are produced using a wide variety of forming methods including pressing, casting, extruding, and injection molding. For maximum economy, parts should be designed for symmetry and simplicity; and in general, it is best to avoid or minimize sharp edges and corners, projections, threads, narrow and deep spInes, variable thicknesses, uneven cross sections, and thin walls and barriers. Ceramic can be used to manufacture micro-miniature parts as small as a pinhead to cylinders two feet in diameter and five feet long. However, maximum economy will be realized by keeping parts within reasonable limits.

General guidelines on dimensional tolerances are as follows:
Pressed as-fired parts: ±1%, not less than 0.005" (0. 13mm).
Large complex shapes and glazed surfaces:
±2%, not less than 0.012" (030mm).
Concentricity, as-fired: 1% to 0.006" (0.15mm) min. depending on tooling.
Flatness, as-fired: 0.006 in/in
(0.006mm/mm).

Closer dimensional tolerances can be achieved, if required, through special processing, grinding and other post-firing finishing techniques.
 
Special Purpose Ceramics
Most physical properties of technical ceramics are usually improved as oxide content increases; including hardness, compressive strength, dielectric strength and chemical resistance. Some characteristics of alumina ceramic such as its ability to be metallized are optimized by formulations. Some requirements, such as thermal-shock resistance are satisfied best by ceramics other than aluminas. To meet industry's broad requirements for technical ceramics, specialized ceramic formulations have been developed to meet specific design and application requirements. They include: Refractory-Alumina-mullite formulations provide the high purity and consistent physical properties required for quality insulating brick and kiln furniture. Porous alumina-When a rugged, inert material is needed for filtration, fluid flow restriction and semi-permeable membranes, porous ceramic offers a unique solution. Good mechanical strength, high working temperatures and a variety of shapes make it a versatile design material. Cordierite-In applications where rapid temperature changes are common, cordierite, with its relatively low coefficient of thermal expansion, has good ability to withstand thermal stress and shock. In addition, its high density provides good wear resistance. Zirconia-For the combination of extremely high working temperature and high resistance to thermal shock, zirconia is the answer. This material is successfully used in iron-alloy extrusion dies and in other high temperature wear applications.

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