The Best Bricks for Cupola Linings

Posted By Richard Jefferson on 14 January 2015

Posted in The Vintage Machinery Almanac

This article was originally published in Electrochemical and Metallurgical Industry Publication of April 1907. Information within this article is therefore correct as of 1907. The publication of this material aims to provide historical insight on the subject and its place in industry.

The Harbison-Walker Refractories Co. of Pittsburg, has recently issued an exceedingly interesting and useful pamphlet on the best kinds of brick for furnaces with cupola linings and on rules to be observed in laying the brick. In view of the enormous amount of experience accumulated by the Harbison-Walker Refractories Co, in many years of activity, the pamphlet should find the careful consideration of foundry superintendents. In the following we give in abstract the most important points:

There are three different classes of fire clays; soft clays, shale clays and flint clays. The soft and shale clays usually run high in silica and flint clays run high in alumina. Aluminous clays are more refractory than siliceous clays, and they can be made into tougher and stronger brick, which is more suitable for use in cupola linings.

Blocks for lining around the bottom of the cupola and for a distance of 2 feet or so above the tuyeres are made by the Harbison-Walker Co. of flint clay high in alumina with sufficient bond clay to make the brick strong and tough. From a distance of about 2 feet above the tuyeres to the charging door, the blocks are made to stand abrasion as well as heat, and they are exceedingly dense, hard and strong.

The use of high-grade material means a greater first expense for the brick, but this is many times balanced in operation by the fact that stoppages for repairs and loss of output are reduced to a minimum. The use of more expensive high-grade material is thus easily seen to represent an important source of economy.

Of course, even with high-grade material it is necessary to avoid deterioration of a lining due to careless operation. One of the sources of failure is excessive pressure of blast, causing an impinging or cutting flame, something like that from a blow-pipe, to play on the brick work. Another reason is excessive slag, or slag of a very scouring nature, which cuts out the lining rapidly. Slag should be kept as neutral as possible. Limestone and oyster shells are the slag materials in most common use.

It is quite possible that the use of chrome brick in the lower part of the lining would prove economic in the case of a cupola where firebrick cuts out very rapidly. "Chrome" brick will resist almost indefinitely the chemical action of scouring slags, and they are used in lining cupolas which burn basic materials such as dolomite and limestone, and for the bottom of soaking pit furnaces where the scouring iron slag cuts out the fire-clay brick.

The best material to be used for daubing is a plastic fire clay and silica. When properly mixed the mixture is plastic and adhesive, it does not crack, expand or contract and stands heat. The fire clay should be soaked for 24 hours or longer, as it absorbs water slowly. The use of split brick pressed into the daubing with the flat side against the lining is effective and is recommended. This, of course, decreases the amount of daubing to be used and prevents skin drying of same, also prevents breaking away from wall as soon as steam is generated behind the skin-dried surface. Split brick can be put in nearly as cheaply and quickly as a cupola can be daubed, and are almost equivalent to a new lining.

Some very useful pointers are given on brick-laying in order to get the best results as follows:

Brick should be laid in that portion of the setting for which they are intended to be used, as conditions vary in different parts of setting and brick are varied to meet conditions.

The clay used should always be of same grade as the brick that are laid with it. This is important, as one of the frequent sources of trouble is the use of inferior clay to lay brick.

Clay should be mixed to a thin soup and brick dipped in same, then rubbed to insure a brick-to-brick joint. Not more than 300 to 350 pounds of clay should be used with 1,000 bricks.

All brick-laying should be as even as possible, so as to avoid projecting brick, which could catch the flame. A perfect arch or circle over the fire will last almost indefinitely.

Heating up and cooling down slowly adds very much to the life of the brick work.

Cutting of brick should be avoided as much as possible, and regular 9-inch shapes, such as skew, arch, wedge, soap, split, key, etc., used instead of cutting 9-inch straights. A cut brick is never as good as a whole brick.

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