thomson consumer electronics teams up with sarnoff corporation to model their tv tube manufacturing process using maya's thermal analysis software. the result is reduced engineering costs and improved product quality.

image of a 20th century revolution

television is probably the most influential and revolutionary technology of this century. with millions of sets inhabiting living rooms all over the world, the medium has become a constant in our lives: entertaining, informing and educating us every day. it's difficult to imagine life without it.

thomson consumer electronics has been bringing us that social revolution since the 1940's. first created in their lancaster, pennsylvania facility, their rca, ge and proscan brand of television receivers and related video products, have become a household name synonymous with both quality and value. maintaining that reputation is serious business.

today the lancaster facility is thomson america's tube research center, responsible for optimizing the production of their manufacturing plants within the us. that's no small task - last year thomson manufactured over 14 million television tubes for north american and international markets.

a picture is worth

engineer dick hutzler is responsible for the stress and thermal analysis of the glass components used to manufacture tv tubes. the tubes range in size from 19" to 38" in the 4:3 aspect ratio and more recently in the 16:9 ratio for hdtv. he describes the challenge as equal parts chemistry, mechanics and manufacturability.

the picture tube is easily the largest, most expensive component of a modern television set. consequently, building a high performance tube that is safe and reliable requires sophisticated design and advanced manufacturing technology.

picture tubes, containing the electron guns and display screen, are made from two large pieces of glass called the panel and the funnel. after the appropriate chemical processing is performed to deposit a screen on the panel, the pieces are joined together via solder glass and evacuated. the combination of thermal stresses used to out-gas the tube and the stresses induced by evacuation can cause the tubes to shatter. application of a tension band makes the tube safe for in-home use.

"if a tube isn't properly thermally processed we can lose the tube and all the components that are in it," says hutzler. "several sizes are often intermixed in a batch during the thermal processing, so the cycle must be capable of processing all the different sizes without breakage. and we want to do that while saving as much energy as possible."

a detailed model of a tv tube shows the panel and
funnel temperatures during processing in the frit-seal oven.

thomson and sarnoff join forces to automate the simulation process

thomson developed a plan to analyze the thermal characteristics of the tube during its manufacture. this plan included the implementation of maya's thermal software package tmg. this would reduce modeling time and allow several different thermal processing cycles to be tested in a minimum amount of time. to help implement this plan, thomson enlisted the help of the sarnoff corporation. founded in 1942, sarnoff (formerly rca laboratories) were the original developers of color television, and remain one of the world's premiere r&d facilities.

through a joint effort, the engineers at sarnoff and thomson developed and qualified the thermal simulation of the frit-seal process that is used during picture tube manufacture. this process joins the two main glass components of the picture tube, the front panel containing the screen and the rear funnel containing the electron gun. they are sealed together using solder glass, a crystallizing frit. this frit is applied to the surfaces between the panel and the funnel, then both are thermally processed on a moving belt in a lehr oven.

during this process, the glass reaches the appropriate thermal conditions, the frit first flows, crystallizes and then bonds the panel and funnel together. it is during this process that breakage can occur, either because of poor frit characteristics or un-optimized thermal characteristics in the oven. the belt ovens are several feet wide by three feet high by several hundred feet long and move tubes through thermal zones with temperatures of up to 500°c.

the tubes move at a few inches per minute passing through a carefully controlled heating cycle until the frit joins the panel and funnel. the tubes are then cooled and the panel and funnel have a permanent, air-tight frit bond.

the direct view tv picture tube assembly includes the
front panel, rear funnel, electron gun and deflection yoke.

thomson wanted to reduce breakage and eventually speed up the manufacturing process. in addition a reduction in the weight of the tube was highly desirable. john gavigan and tim davis of sarnoff, put the problem in perspective. "the manufacturing team at thomson decided that they wanted virtually no breakage during this process while increasing throughput. however, glass is a brittle material and because of the numbers of tubes being built, its behavior can only be predicted statistically. experimentally tuning this process to give almost no breakage means testing tens of thousands of bulbs over a long period of time using glass from multiple vendors."

in the frit seal process alone, more than 50 design and manufacturing parameters needed to be considered, including panel height, thickness, skirt angles, internal and external blend radii, oven zone temperatures, feed rates, heating and cooling cycles, as well as tube orientation in the oven. it would be very difficult to optimize that many parameters without being able to automate the analysis process in some way. so the thomson/sarnoff team turned to maya's tmg thermal analysis software to streamline the process.

"we built parametric models driven by simple macros," explained davis and gavigan. "the thomson engineers and designers could enter a minimum of commands and the tmg model was set up and solved."

davis especially appreciated how easily tmg lent itself to automation. "i was able to create a number of macros, then customize the user interface by adding icons to control them. clicking on one imports thomson's tube geometry files, another performs a thermal solution, and another writes out the results and does a structural solution."

several tv tubes are oriented in the frit-seal oven.
tmg models the transient heating and cooling process as the tubes
travel the length of the belt oven. tube orientation and size
affects the radiative and convective thermal process.

modeling the heating process

using tmg, thomson and sarnoff developed sophisticated transient thermal models of the frit-seal process. they created a model of the picture tubes moving through a series of radiating heat sources in the belt oven.

"this was a very complicated analysis," explains davis. "the heating in the ovens is a combination of radiation and convection, so we had to solve for models with thousands of radiating surfaces, include shadowing effects and convection. tmg's strong radiation capability was very important to us. the other thermal codes we looked at couldn't handle the radiation modeling. in addition, using traditional radiation packages like trasys combined with sinda is very inefficient."

the transient solution gave thomson a picture of how the temperature distribution in the glass changed over time. these results were then used for structural simulation, enabling them to predict the thermal stresses in the glass as it was heated and cooled. this in turn allowed a more accurate prediction of the likelihood that a tube would break.

using tmg and the automated parametric modeling tools, thomson's engineers could then make changes to their models, resolve issues quickly and converge upon an optimum design and manufacturing process.

thomson is the largest manufacturer of televison tubes in north america
and the sales leader in television, digital satellite systems, and vcrs.

saving manufacturing costs and engineering time

the result of thomson's and sarnoff's collaboration was a clearer picture of how heat propagates within the tubes throughout the thermal process. the manufacturing improvements confirmed a modified tube orientation, allowed thomson to reduce the amount of glass used in each tube, and improved heating uniformity in the oven. these changes enabled thomson to reduce their breakage and save substantial manufacturing costs.

in addition, thomson was pleased by the amount of time that tmg saved. "we're talking about months of engineering time savings," notes hutzler with satisfaction. "it can take a long time to perform these tests the traditional way. we would have had to do multiple tests in a production environment which is not cost effective. this way the majority of the experimentation was done digitally, and we were able to reach design or manufacturing decisions faster."

the tmg thermal analysis package was fully supported by maya, with training courses to get thomson and sarnoff up to speed quickly and painlessly, and hotline phone support to help them past the occasional problem. "maya is a very responsive company," says hutzler. ?they addressed our training needs, and provided solutions to difficulties as they arose along the way. we're very pleased with their support. they've been attentive to our requests and have helped us get the job done."

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images courtesy of thomson consumer electronics.