[Trade Journal]
Publication: Ceramic Age
Cleveland, OH, United States
vol. 82, no. 2, p. 27-28, col. 1-3
COST REDUCTION THROUGH KILN CAR ENGINEERING
By: D. Bennett
Refractories Division
The Carborundum Company
THE process of applying technical and information and practical experience to the design of kiln car superstructures, the selection of refractory materials and the construction, maintenance and usage of these cars is referred to as kiln car engineering. Its scope, in the ceramic industry, entails expenditures of approximately $50,000,000 a year for car tops, superstructures, furniture, setters, saggers, etc. On the basis of 2,000 plants, this averages $25,000 annually spent on replacement and maintenance. Obviously, the figure varies widely from plant to plant for it involves many factors including the number and size of kilns. The import, however, is that actual replacement and maintenance costs constitute a significant budget item . . . an item that often receives less attention than plant housekeeping.
Application of kiln car engineering has returned savings of from 2% to 50% . . . with 10% savings being typical where in-plant technical direction is lacking or unavailable. Most large refractory companies offer technical service in this area. Effective reduction in replacement and maintenance costs in turn reflect lower unit production cost.
Above. Girders spread load more uniformly to increase car base life.
Specific examples best illustrate how these savings are accomplished. These cases were observed by the author during ten years as a plant user and five years as a technical service engineer.
Base Design
In car design, one of the most troublesome areas is the car base (that section next to the steel frame). This usually is considered to terminate where set-out blocks, girders or other means of supporting the superstructure begin. The most common fault is breaking up of the car base and consequent loss of foundation for the sub-structure, superstructure and payload. Although the design of sub-structure has an important bearing on service life of the base, a well-designed base can contribute more to overall car performance than any other area.
At a Company where everything appeared normal cars were rebuilt about every two years. This was considered reasonable car life. However, redesigning the base structure from a system consisting of eight prefired blocks to a cast bottom lowered construction costs about 20%, cut material costs about 8% and, most important of all, increased time between rebuilds from two years to almost three years. Firing cost per pound of ware dropped almost 7%. Annual dollar savings amounted to a little less than $6,000. This was achieved by applying kiln car engineering to a serene situation.
Relationship of car sub-structure to base life Stands out in another plant’s experience. Here the car base was of good construction. The payload weight, however, was poorly distributed to the base and caused its early failure. Load on each car was almost two tons. A new system of support using full length girders that distributed the 2-ton load more uniformly increased car base life almost three times. The previous support system cost about $21 per car, the new approximately $60. Trebling life of the car base costing $104 more than paid for the $40 increase in material cost. For a $40 investment a return of over $300 was realized.
The next case involves two large tunnel kilns, approximately 330' long, that required use of over 400 kiln cars. Considerable thought had been given to the car design because there were so many cars to service. The car base design called for 8 interlocked prefired blocks of two configurations, a right and a left. The support system consisted of piers of girders upon which a deck was placed and a sagger load built up. Basic cost for the entire car approximated $350 for materials and labor. Labor per car was about $15. Both the car base blocks and the girder support systems seemed to give short life. A program was initiated wherein several new materials for these components were tried. With a change in materials, car life increased 100%. Savings amounted to approximately $25,000 per year.
Substructure on a small kiln car presents another illustration. The car deck consisted of a setting area 9" x 4½". The entire car was built up of standard 9" brick, 3" high. A change of material almost doubled car life. Savings were not particularly large since only about 30 cars were involved. Nevertheless, they were significant for the particular operation.
Superstructure Designs
Car superstructure designs are somewhat more fixed. Over long periods of time manufacturers of sanitaryware, electrical porcelains and chinaware as well as many others requiring multi-decks have experimented to find the optimum design since the structure is so costly. Users in this category are aware that, throughout the years, improved materials have helped extend service life. However, kiln car engineering often can add refinements that result in lower unit production costs.
At right. Redesigned superstructure to give increased payload. Previous
structure utilized large bulky supports that took up valuable space.
At a firm firing dinnerware on a multi-deck superstructure, increased sales required a sizable production increase. Redesign of the superstructure boosted payload 17% with no increase in kiln schedule. The approach was to decrease the number of supporting posts and increase tile size slightly. Refractory costs climbed about 10% because of shorter service life. Net savings from larger payload was about 5% in firing costs. This totalled about $4,000 per year.
Another example of superstructure refinement comes from a large sanitaryware plant. A simple redesign of the post supports allowed a 5% increase in payload. No other changes were made. Refractory costs remained unchanged. Pads on the posts were rounded and contact area reduced, permitting a few more pieces to be placed per car. Savings figures are unavailable.
Other ideas that improve superstructure performance or reduce firing cost include use of safety bars in sanitaryware kilns. They insure against a costly kiln wreck and often increase setter tile life. Another refinement is to redesign to a more flexible superstructure that can cut down on kiln furniture inventory and accommodate changes in payloads easily. Moreover, redesign for decreased weight of superstructure refractory materials can materially reduce kiln furniture cost and at the same time reduce refractory “dead weight.”
Pusher Tile Design
Kiln car engineering also comes into play in other than tunnel or large kilns. One Company had a small pusher kiln where plain pusher tile supported a small load. The schedule was fast. High tile breakage posed a problem. By cutting pusher tile size in half, Service life of the tile was almost trebled, with no decrease in payload.
Another manufacturer firing steatites had a similar cracking problem. A thinner tile materially reduced the cracking. It also increased service life and lowered unit firing cost.
One ferrite manufacturer changed from an all mullite tile to a much larger sandwich tile. The result: more payload, longer service life, and a better fired product. The same manufacturer calcined some material in a standard sagger and was encountering what was considered normal sagger loss. A redesign of the sagger into a three point support system extended service life of the saggers by almost 50%. There was no increase in refractory cost for the new design.
Below. Shelf spacing can be changed in the center section and the
entire height of the car be utilized in this design.
Many changes obviously are difficult to evaluate in dollars and cents as they relate to direct lowering of unit costs. However, most, of the time a price tag can be attached if good records are kept. Today more and more companies keep better records because they realize their value. The importance of good record keeping cannot be over-emphasized. Records not only teil where refractory dollars are going for car maintenance but allow accurate evaluation of new ideas.
