Kovar
Kova alloy is a vacuum-melted iron-nickel-cobalt low expansion alloy whose chemical composition is controlled within a narrow range to ensure accurate and uniform thermal expansion properties. Extensive quality control is applied to the manufacture of this alloy to achieve uniform physical and mechanical properties for ease of deep drawing, stamping and machining.
Type Analysis
Applications
Kovar alloys have been used to make hermetic seals from harder Pyrex glass and ceramic materials.
This alloy has a wide range of applications in power tubes, microwave tubes, transistors and diodes. In integrated circuits, it has been used in flat packs and dual inline packages.
Preparation for Sealing
All degreased Kovar alloy parts must be degassed and annealed in a wet hydrogen atmosphere. At room temperature, hydrogen is bubbled through water to moisten the atmosphere. Care must be taken to avoid surface carbon pickup. The furnace must be provided with a cooling chamber with the same atmosphere.
Heating must be performed within the 1540/2010°F temperature range. The duration of the temperature should be between about 2 hours for the lowest temperature and 20 minutes for the highest temperature. The part must then be moved to a cooling zone and kept below 570°F before removal.
For metal-hard glass sealing, an oxide film of the metal part is preferred. The best oxide films are thin and close together. The coating can be prepared by heating the parts to 1200/1290°F for a time sufficient to form a dark gray to off-brown oxide.
workability
Forging
The main precautions to be observed when forging are to avoid rapid heating and immersion in the furnace. Prolonged soaking may result in surface identification due to absorption of sulfur and/or oxide penetration from the furnace atmosphere. A forging temperature of 2000/2150°F is preferred.
Coolant
It is important to control the calorific value, which is the main cause of warping. The recommended coolant is Cool Tool. Cool Tool contains a fatty ester to reduce friction in the cutting area and a refrigerant to remove heat generated by friction between the cutting tool and the work area.
Tooling
T-15 alloy such as Vanadium Aloys Company manufactured by Vasco Supreme. M-3 Type 2. Congo manufactured by Brevan, such as Van Cut Type 2 manufactured by Vanadium Alloys Company.
For machining with carbide tools, K-6, Firthie HA manufactured by Firth Sterling, or K2S manufactured by #370 Carboloy, Firthie T-04 manufactured by Firth Sterling can be used. One of the most important is that all feathers or wire edges must be removed from the tool. They must be kept in top condition through repeated inspections.
Turning
When using a steel cutting tool, try a feed of approximately 0.010" to 0.012" per revolution to achieve speeds of up to 35/FPM. Some angles of the cutting tool are:
End cutting edge angle - approx. 7°
Nose Radius - Approx. 0.005"
Side cutting edge angle - approx. 15°
Rear Rake - Approx. 8°
Side Rake - Approx. 8°
They are better than carbide tools when cutting high-speed tools, and should use a feed of approximately 0.001" per revolution. Cutting tools are recommended with approximately 7° face clearance and a tip greater than 25°.
Drilling
When drilling a 3/16" diameter hole, you can use a speed of approximately 40/FPM, for a 1/2" hole you should use a speed of approximately 0.002" to 0.0025" per revolution, and approximately 0.004" to 0.005" per revolution You can use the speed of ". The drill should be as short as possible, preferably making a thin web at that point in the conventional way. Do not grind the crankshaft by conventional methods. We suggest using heavy web-type drills with a nitride or electrolyte surface. Of course, you'll need to clean the holes frequently to remove chips, which can lead to punctures, which also helps with cooling. The drill must be grounded at an angle of the inclusion point of 118° to 120°.
Reaming
The reaming speed should be half the drill speed, but the feed should be about 3 times the drill speed. It is suggested that the land margin should be approximately 0.005" to 0.010", the chamfer should be approximately 0.005" to 0.010", and the chamfer angle should be approximately 30°. The tool should be as short as possible, with a slight face rake of about 5° to 8°.
Tapping
You should use a slightly larger tap drill than the standard drill recommended for conventional threads because tapping will likely introduce metal into the cut. On automatic machines, it is recommended to use a tap tool with two or three grooves. For taps under 3/16", two flutes are best. Grind the face hook angle from 8° to 10° and the tab should have a chamfered edge of 0.003" to 0.005". In some cases, the width of the land may be too large, so it is recommended to grind down the width of the heel, again, a nitride or electrolytic tool is recommended.
