The first and best known of the above standard types is the Ewart chain (Fig. 33), which was first brought out by Mr. William D. Ewart and put on the market in America by the Link-Belt Company, of Chicago, and in Europe by the late Sir Francis Ley, Bart., then proprietor of the Ewart Chain Manufacturing Company of Derby.

The Ewart chain still has an enormous sale, on account of its great convenience and its comparatively low cost. It is a singularly ingenious form of chain, chosen not for its appearance but for its general utility. It is in fact the simplest of all chain types, and has the great merit of being very quickly detached or uncoupled. Thus it is easv to shorten or to lengthen such a chain at pleasure by removing or adding sufficient links to give the required length.

From Fig. 33 it will be seen that there is a flat or nip on one of the side bars, which permits the link to enter the hook easily in one position, but when fitted together the links cannot fall apart while in the work-I ing position with tension on the chain. Some chains are made " double-nip," that is to say with a flattened or reduced section on both of the side bars.

In a plain or driving chain there are no pins, and all the links are alike ; but it is very convenient to use a coupling link with pin in each chain, when the centres of the terminal shafts are both fixed. This coupling link avoids starting with a very slack chain.

These chains will run in either clean or dirty situations either with or without lubrication, but in the latter case the life is naturally shorter. In some situations lubrication is hardly feasible.

The subject of attachments is a very important one in connection with conveyor chains. It is practicable to cast special or attachment links of almost any form on a Ewart chain ; thus facilitating the fixing to the chain of elevator buckets, slats, and other forms of carriers. In course of time a great variety of attachment links have been designed and standardized. These are now obtainable with the same facility as plain links from manufacturer's stocks.

Malleable iron chain of the Ewart type is now commonly made in pilches ranging from 3/4-in. to 6-in., though it was formerly made up to 12-inch pitch. Light patterns of these chains are much used for textile machinery, including cotton, woollen, and hosiery machines. The medium and heavy sizes are employed largely in connection with conveyors and elevators, especially for handling sugar, grain, and other light materials, including paper pulp. These chains are also utilized for coal elevators of small capacity ; but the pin type of chain is more durable for heavy coal elevators. It is not advisable to use them at all for handling ashes, cement, and other cutting materials, the wear and tear being too severe, and a Ewart chain when badly worn cannot be repaired, but must be scrapped entirely and replaced by a new chain. The same applies to the sprocket wheels, whether whole or in halves.

There is a perplexing variety of sizes of Ewart chains to choose from, but generally speaking it is advisable to select one of the standard twelve chains, Table I., in order to ensure that renewals may be obtained from stock without delay. For each of these chains a good range of wheel patterns is available, an important practical consideration. A few of the more common standard attachment links for conveyor work are stocked for each chain, although many other attachments are also made to order.

Table I. Short List Of Ewart Conveyor Chains

In the Table shewn the test load of a chain is given as approximately one-fifth the breaking load as determined by a tensile testing machine. It is not advisable to exceed half the test load for the working tension, and the higher the rate of rotation of the smaller sprocket wheel the lower should be the working tension in order to obtain reasonable durability in working. The revolutions per minute are more important than the lineal speed of the chain in respect of wear and tear. Also the shorter the distance between the driving centres the more rapid the wear, other things being equal ; because any individual link engages more frequently with the driving wheel,

I where the principal wear on the links takes place. In conveyor work the chain should be supported either continuously or at short intervals.

As a rule an elevator chain will consist of three or more plain links to one attachment link ; but in a slat conveyor the attachments are usually continuous, there being no plain links. Attachment links for light conveyor chains cost a good deal more than plain links. The cost of plain chain ranges from about ten shillings to about forty shillings per coil of ten feet. A Ewart chain made up entirely of attachments might cost twice as much as plain chain, but attachments vary a good deal in cost according to their complexity. The extra cost is not merely a matter of so much extra weight of material as compared with the simpler plain chain ; but the attachment links are more difficult to mould, and therefore more expensive to manufacture than plain links.