NATURAL CORDIERITE

Natural machinable cordierite stone.

Final Advanced Materials provides natural cordierite, machinable high temperature ceramic. We offer boards, rods or machined parts according to your drawings.

Natural cordierite, is a pyrophyllite rock. The ore that we have selected, features exceptional mechanical and thermal performances. After treatment at high temperature, the material acquires similar properties to those of known synthetic ceramics.span>

This material allows to solve with a remarkable implementation flexibility, problems that arise in laboratories and engineering consultants of all industries where ceramics are essential for their characteristics.

Characteristics

  • Dielectric and thermal insulating property

  • Resistance to chemical agents

  • Stability and shape accuracy

  • Heat resistance up to 1300°C

  • Excellent resistance to high vacuum (up to 10-8 torr)

Applications

  • Machining of components and toolings

  • Realisation of prototypes

  • Manufacturing of small ceramic series

  • Coil cores

  • Electrical insulator

  • Template of assembly

  • Injectors, nozzles

  • Vacuum parts

  • Thermal insulators, inductive insulators

  • Template of brazing and welding

  • Sensors

Economic alternative

The alumina silicate allows to provide a very economical alternative to the use of sintered ceramics until 1300°C :

  • To realise a part in alumina 99,7% (or other sintered ceramic) it is necessary to use a raw material which will be completely machined with the diamond grinding wheel, the raw material and machining are very expensive.

  • The raw alumina silicate can be very easily machined for a relatively low cost with the conventional tool. Subsequently, the thermal resistance is obtained after firing at 940, 1100 or 1300°C. For very tight tolerances, a recovery with the diamond grinding wheel may be necessary. The material and the acquiring process are more economical.

The alumina silicate is also an interesting alternative to Macor® according to the dimensions and machining tolerances of the part to be realised. Glass industry : for the applications where a mechanical part has to be in contact with glass and leave no trace, alumina silicate gives better results than boron nitride for a much lower cost

Chemical composition

  • SiO2 : 67,78%

  • Al2O3 : 27,83%

  • TiO2 : 0,41%

  • Fe2O3: 0,048%

  • CaO : 0,10%

  • K2O : 2,96%

  • Na2O : 0,87%

Firing procedure

To resist at more than 650°C, the parts must be prepared in the furnace by sintering. The operation will start in cold oven and the heating levels will not exceed 260°C per hour. Consider the expansion to obtain the final dimensions (approximately 2%). These levels will have to go down to 150°C per hour if the parts have a thickness of more than 12 mm. The maximum temperature will not exceed 1010°C to 1100°C, and will be held, from 30 minutes for a thickness of 6 mm to 45 minutes for a thickness of 20 mm (calculate the right value by extrapolation). We shall cool then gradually until the part will be taken out of the furnace at about 90°C.

Machining advice

This material is machined with a conventional tooling, sawing, milling, drilling, turning. It’s a Machinable Technical Ceramic, MTC, whose machinability is remarkable. The homogeneous structure of the mineral allows the use of standard tools, usually dedicated to metalworking. This feature allows it more particularly to manufacture prototypes and parts series in very tight tolerances. The following procedures will be monitored and verified frequently, as well as we’ll use and verify frequently very sharp tools : these materials are very hard and abrasive, they damage rapidly the tools edges. It is imperative to work slowly without vibration nor hurry..

Lubrification

NEVER use neither lubricants, nor cooling liquids

Sawing

with circular diamond / silicon carbide saws, speeds from 2000 to 2500 RPM, top-down.

Trimming / Filing

with ribbons covered continuously with carbide powder, speed 30 m/mn maximum

Drilling

with carbide drills, Carbolloy 883 type. Slow down speeds announced for HSS drills. Never drill in a single continuous operation, suspend and restart the drill progress. Use a hammer drill, re-sharpen every 3 to 4 holes.

Boring

  • Speed (m/mn) 2.2 to 3.8

  • Tool load (mm/dent) : 0.05

  • Depth (mm) : 4 to 5

Threading

use a diamond tool with chips recovery or use a small tool in tungsten carbide.

Tapping

High speed steel tools such as those in carbide are suitable . Prepare front holes at 70% of the final diameter. Lubricate with kerosene.

Turning

with small carbide tools, or silicon carbide grinding wheels with chips recovery

  • Cutting speed (m/mn) : 2.7 to 4.5

  • Advance (mm per turn) : 0.051 to 0.08

  • Depth (mm) : 4 to 6

Grinding

with carbide discs sealed with epoxy, at recommended speeds. Use soft discs and of well distributed grains; for important jobs, finish with hard discs and of fine grains. Lubricate with a 1% oil solution. Polish with white lead on a wedge or a soft rag..

Metalizing

For thick films, use metal inks (silver, gold and silver, platinum). For thin films, work by sputtering.

Special instructions

  • Plan the expansion from 1,8 to 2% during heating : a machined dimension of 9,8 mm will become a final dimension of 10 mm. Diameters also undergo this expansion.

  • Clean the machines thoroughly after work : Alumina silicate is abrasive in powder form.

  • Once cooked, ceramics can be remanufactured with water to a very high precision, when required by the application, by means of silicon carbide grinding wheels.

  • The parts must not exceed 12mm of thickness if we want to avoid any crack; for greater thicknesses we shall drill holes.

  • During firing, the ceramic expands, from 1,9% at 980°C to 2% at 1040°C. Beyond 1040°C, the variations are negligible and the precision can reach ± 0,05 mm.

  • We can finish grinding by softening.

  • To paste this ceramic, we shall prefer the ceramic glue Cotronics 919 from our catalog.

In case of failure

Remember to check the causes most frequently observed : the firing temperature is badly adjusted ? There is a miscalculation of the expansion? The created model presents sharp corners and «hard» transitions?

Characteristics table

MATERIALS

Alumina silicate raw

Alumina silicate 940°C

Alumina silicate 1100°C

Alumina silicate 1300°C

Physical characteristics

Density g/cm3

2.2

2.9

2.4

2.5

Porosity %

1.5 - 2

0 - 0.5

0 - 0.5

0 - 0.5

Water uptake %

1.5 - 2

1.5 - 2

0 - 0.5

0 - 0.5

Mechanical characteristics

Hardness

Mohs : 2.5

Mohs : 5.5

Mohs : 7.5

Compressive strength N/mm²

6

115

150

800

Flexural strength N/mm²

12

30

50

80

Modulus of Elasticity GPa

-

-

-

-

Thermal characteristics

Maximum No Load Temperature °C

900

1000

1100

1400

Continuous Operating Temperature °C

700

940

1100

1300

Specific Heat, 20°C J/kg.K

-

950 (1160 à

1000°C)

-

-

Coefficient of Expansion 10-6 /°K

20 - 40 °C

-

-

-

-

20 - 600 °C

-

-

2.9 - 3.6

6-8

20 - 800 °C

-

-

-

-

20 - 1000 °C

7-12

-

-

4-10

Electrical characteristics

Specific resistivity at 20°C Ohm.cm

1010

-

1012

1012

Dielectric Constant at 20°C à 1 KHz

-

-

-

6.1

Loss Tangent à 1 KHz

-

-

-

9x10-5

Dielectric strength at 20°C kV/mm

8-10

-

6-7

12-17

Chemical characteristics

Corrosion resistance at 20°C

B

B

B

B

Resistance to alkalis at 20°C

B

B

B

B

For more informations, please contact us.