kovar bar

kovar bar 

Kovar is an important alloy used for making hermetic seals with harder pyrex glasses and ceramic materials. We are offering a wide assortment of kovar bar which finds its application in many industrial uses. Some of the applications where kovar bar is typically used include power tubes, microwave tubes, transistor and diodes. In many many integrated circuits and components kovar alloy is highly used. With below given specifications kovar bar is available.  

Physical Properties

Specific gravity.......................................8.36 Curie temperature Density °F.................................................... 815 lb/cu in............................................... 0.302 °C.................................................... 435 kg/cu m............................................... 8359 Melting Point Thermal conductivity °F.................................................. 2640 Btu-in/ft²/hr/°F...................................... 120 °C................................................. 1450 W/m-K.................................................. 17.3 Modulus of elasticity Electrical resistivity psi x 10(6) ..................................... 20 ohm-cir mil/ft......................................... 294 MPa x 10(3) .................................. 138 microhm-mm......................................... 490

Thermal Expansion Properties

The following are the average coefficient of expansion properties after annealing in hydrogen for 1 hr at 1650°F (900°C) and 15 minutes at 2010°F (1099°C) and cooled to room temperature within 1 hr. Material heat treated using this procedure should not exhibit any transformation when cooled to -112°F (-80°C) for 4 hrs. This was determined by means of metallographic examination.
Mean coefficient of thermal expansion as annealed.

Preparation for Sealing

All degreased, fabricated Kovar alloy parts should be degassed and annealed in a wet hydrogen atmosphere. Atmosphere is to be made moist by bubbling the hydrogen through water at room temperature. Care must be taken to prevent surface carbon pickup. Furnace should have a cooling chamber provided with the same atmosphere.
Heating should be conducted within the 1540/2010°F temperature range. Time at temperature should be approximately two hours for lowest temperature to 20 minutes for the highest temperature. Parts should then be transferred to the cooling zone and held until below 570°F, then removed.
An oxide film on the metallic part is preferred for metal-to-hard glass sealing. The best oxide film is thin and tightly adhering. The film can be produced by heating the parts to 1200/1290°F in regular ambient atmosphere for a time sufficient to form a dark gray to slight brown oxide.

Workability

Forging
The principal precaution to observe in forging is to heat quickly and avoid soaking in the furnace. Long soaking may result in a checked surface due to absorption of sulfur from the furnace atmosphere and/or oxide penetration. A forging temperature of 2000/2150°F is preferred.

Coolant
It is important to control heat build up, the major cause of warpage. A suggested coolant would be Cool Tool. Cool Tool contains fatty esters to reduce friction in the cutting zone and a refrigerant to remove the heat generated by friction between the cutting tool and work place.

Tooling
T-15 Alloy, such as Vasco Supreme-manufactured by Vanadium Alloys Company. M-3 Type 2, such as Van Cut Type 2-manufactured by Vanadium Alloys Company. Congo manufactured by Braeburn.
For machining with carbide tools, a K-6 manufactured by Kennemetal, Firthie HA manufactured by Firth Sterling, or #370 Carboloy could be used, or a K2S manufactured by Kennemetal, or Firthie T-04 manufactured by Firth Sterling would be satisfactory. One thing of prime importance is that all feathered or wire edges should be removed from the tools. They should be kept in excellent condition by repeated inspection.