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Ohmalloy Material Co.,Ltd

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Vacuum Furnace Nickel Based Alloys For Glass - To - Metal Seal Vacuum Switch Tube

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Vacuum Furnace Nickel Based Alloys For Glass - To - Metal Seal Vacuum Switch Tube

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Vacuum Furnace Nickel Based Alloys For Glass - To - Metal Seal Vacuum Switch Tube

Sealing glass elements of Vacuum switch tube

OhmAlloy-4J29 (Expansion alloy)
(Common Name: Kovar, Nilo K, KV-1, Dilver P_o,Vacon 12)

Kovar is a nickel–cobalt ferrous alloy compositionally identical to Fernico, designed to be compatible with the thermal expansion characteristics of borosilicate glass (~5 × 10−6 /K between 30 and 200 °C, to ~10 × 10−6 /K at 800 °C) in order to allow direct mechanical connections over a range of temperatures. It finds application in electroplated conductors entering glass envelopes of electronic parts such as vacuum tubes (valves), X-ray and microwave tubes and some lightbulbs.

The name Kovar is often used as a general term for Fe–Ni alloys with these particular thermal expansion properties. Note the related particular Fe–Ni alloy Invar which exhibits minimum thermal expansion.

OhmAlloy-4J29 also known as Kovar alloy. it was invented to meet the need for a reliable glass-to-metal seal, which is required in electronic devices such as light bulbs, vacuum tubes, cathode ray tubes, and in vacuum systems in chemistry and other scientific research. Most metals cannot seal to glass because their coefficient of thermal expansion is not the same as glass, so as the joint cools after fabrication the stresses due to the differential expansion rates of the glass and metal cause the joint to crack.

OhmAlloy-4J29was invented to meet the need for a reliable glass-to-metal seal, which is required in electronic devices such as light bulbs, vacuum tubes, cathode ray tubes, and in vacuum systems in chemistry and other scientific research. Most metals cannot seal to glass because their coefficient of thermal expansion is not the same as glass, so as the joint cools after fabrication the stresses due to the differential expansion rates of the glass and metal cause the joint to crack.

Mainly used in electric vacuum components and emission control, shock tube, igniting tube, glass magnetron, transistors, seal plug, relay, integrated circuits lead, chassis, brackets and other housing sealing.

Style of supply

Alloys Name	Type	Dimension
OhmAlloy-4J29	Wire	D= 0.1~8mm
OhmAlloy-4J29	Strip	W= 5~250mm	T= 0.1mm
OhmAlloy-4J29	Foil	W= 10~100mm	T= 0.01~0.1mm
OhmAlloy-4J29	Bar	Dia= 8~100mm	L= 50~1000mm

Normal composition%

Ni	28.5~29.5	Fe	Bal.	Co	16.8~17.8	Si	≤0.3
Mo	≤0.2	Cu	≤0.2	Cr	≤0.2	Mn	≤0.5
C	≤0.03	P	≤0.02	S	≤0.02

Tensile Strength, MPa

Code of condition	Condition	Wire	Strip
R	Soft	≤585	≤570
1/4I	1/4 Hard	585~725	520~630
1/2I	1/2 Hard	655~795	590~700
3/4I	3/4 Hard	725~860	600~770
I	Hard	≥850	≥700

Typical Physical properties

Density (g/cm3)	8.2
Electrical resistivity at 20(mm²/m)	0.48
Temperature factor of resistivity(20~100)X10^-5/	3.7~3.9
Curie point T_c/	430
Elastic Modulus, E/ Gpa	138

The heat treatment process
Annealing for stress relief	Heated to 470~540 and hold 1~2 h. Cold down
annealing	In vacuum heated to 750~900
Holding time	14 min~1h.
Cooling rate	No more than 10 /min cooled to 200