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Keeping Flat Screens Flat
In flat-screen products, the shadow mask, such as the one shown here, is stretched flat on
a solid metal frame. Those metal frames must also be made of low-expansion
nickel alloys.
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A low coefficient of expansion is the key to alloy frames that support the shadow masks of
flat-screen products
Nickel magazine, May 5, 2003 -- Two nickel-iron alloys, containing 36% and
42% nickel, have found a new application in the rapidly expanding market for large, flat-screen
televisions.
Their main characteristic is an extremely low coefficient of thermal expansion, and that makes these
alloys, including Imphy Ugine Precision's (IUP's) Invar(R) and Krupp Thyssen VDM's newer Pernifer(R) 42 (K94100), ideal for frames that support the shadow masks of new flat-screen products.
Here's why: The shadow mask is a grid that sits just behind the TV screen and provides picture clarity.
Its job is to direct electron beams accurately to the hundreds of thousands of dots, or pixels, on the TV
screen that convert energy from the electron beams into visible light. In conventional picture tubes, the
shadow mask is curved, along with the screen, giving it greater strength. But in a flat-screen TV, the shadow
mask must be stretched on to a solid frame to keep its shape. Under these conditions, it's essential the
material in the frame does not expand and stretch the mask, even as it is heated up to temperatures as
high as 100°C during use.
The alloy also needs to resist the heat generated by the treatment process that blackens the frame and
shadow mask to enhance picture quality. Again, a low coefficient of thermal expansion prevents the shadow
mask from stretching out of shape and then losing tension when it cools down again.
Krupp Thyssen VDM's Pernifer 42 TVR (K94100), which contains about 43% nickel plus a trace amount of precipitation-hardening
elements such as titanium and niobium, has a coefficient of thermal expansion 10 times lower than
conventional steel at temperatures of 20-100°C. The resulting material is weldable, has a tensile strength of
1,000 megapascals (MPa) and displays no creep expansion under stress. IUP's Invar, which contains about 36% nickel, has a tensile strength of 630 MPa.
"Export in Asia is growing fast," reports Sylvie Gindre, communications manager for IUP. "Today, one TV
set out of three is made in China, and we supply Invar to both the manufacturers of TV tubes and their etchers."
Every year, more than 150 million TV sets are sold around the world. Although conventional sets still
account for 96% of sales, U.S. market research firm iSuppli/Stanford Resources predicts that sales of
flat-screen TVs will reach 12 million per year by 2005.
That's a brand new market for an old workhorse like Invar, which, since its discovery more than 100 years ago, has been used
extensively in applications ranging from watches to thermostats.
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