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Expansion alloy / Kovar Wire UNS:K94610 Dia:0.3mm for Glass to
Metal Sealing by ASTM F15-2004
OhmAlloy-4J29 (Expansion alloy)
(Common Name: Kovar, Nilo K, KV-1, Dilver Po, Vacon 12)
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.
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 |
Kovar properties
Kovar is a nickelobalt ferrous alloy compositionally identical to Fernico, designed to be compatible with the thermal expansion characteristics of borosilicate glass ( /K between 30 and 200 C, to ~10 10 /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 Fei alloys with these particular thermal expansion properties. Note the related particular Fei alloy Invar which exhibits minimum thermal expansion.
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.
OhmAlloy-4J29 not only has thermal expansion similar to glass, but
its nonlinear thermal expansion curve can often be made to match a
glass, thus allowing the joint to tolerate a wide temperature
range. Chemically, it bonds to glass via the intermediate oxide
layer of nickel oxide and cobalt oxide; the proportion of iron
oxide is low due to its reduction with cobalt. The bond strength is
highly dependent on the oxide layer thickness and character. The
presence of cobalt makes the oxide layer easier to melt and
dissolve in the molten glass. A grey, grey-blue or grey-brown color
indicates a good seal. A metallic color indicates lack of oxide,
while black color indicates overly oxidized metal, in both cases
leading to a weak joint.
Typical Physical properties
| Density (g/cm3) | 8.2 |
| Electrical resistivity at 20℃(Ωmm2/m) | 0.48 |
| Temperature factor of resistivity(20℃~100℃)X10-5/℃ | 3.7~3.9 |
| Curie point Tc/ ℃ | 430 |
| Elastic Modulus, E/ Gpa | 138 |
Coefficient of expansion
| θ/℃ | α1/10-6℃-1 | θ/℃ | α1/10-6℃-1 |
| 20~60 | 7.8 | 20~500 | 6.2 |
| 20~100 | 6.4 | 20~550 | 7.1 |
| 20~200 | 5.9 | 20~600 | 7.8 |
| 20~300 | 5.3 | 20~700 | 9.2 |
| 20~400 | 5.1 | 20~800 | 10.2 |
| 20~450 | 5.3 | 20~900 | 11.4 |
Thermal conductivity
| θ/℃ | 100 | 200 | 300 | 400 | 500 |
| λ/ W/(m*℃) | 20.6 | 21.5 | 22.7 | 23.7 | 25.4 |
| 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 ℃ |
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= 0.01~0.1 |
| OhmAlloy-4J29 | Bar | Dia= 8~100mm | L= 50~1000 |
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.
Package
FAQ
1. What's the minimum quantity customer can order?
If we have your size in stock, we can provide any quantity you want.
If we do not have, for spool wire, we can produce 1 spool, about 2-3kg. For coil wire, 25kg.
2. How can you pay for small sample amount?
We have account, wire transfer for sample amount also ok.
3. Customer do not have express account. How will us arrange the delivery for sample order?
Just need to provide your address information, we will check the express cost, you can arrange the express cost together with sample value.
4. What's our payment terms?
We can accept LC T/T payment terms, it also depending on delivery and total amount. Let's talk more in details after getting your detailed requirements.
5. Do you provide free samples?
If you want several meters and we have stock of your size, we can provide, customer need to bear the International express cost.
6. What's our working time?
We will give you reply through email/phone Online contact tool within 24 hours. No matter working day or holidays.
