Cotton Weaving and Designing / 6th Edition

by John T. Taylor

FIG. 44.

Woodcroft Section Tappet.—Sect. 1, riser (heald-up); sect. 2, faller (heald-down); sect. 3, left-hand riser; sect. 4, neutral riser; sect. 5, right-hand riser; sect. 6, left-hand faller; sect. 7, neutral faller; sect. 8, right-hand faller.

Woodcroft’s Section Tappets are much used in weaving heavy goods, such as velveteens and corduroys. They are made with various numbers of sections to the round. A single tappet plate of one twelve picks to the round is given at [Fig. 43]. Sections are sometimes made in two kinds only. These are termed “risers” and “fallers,” according as they raise or depress a heald respectively. Each heald requires one plate and lever L, and as the tappets revolve, the lever L is moved up and down. When the lever L is lifted, the heald is moved downwards. A difference in the character of the shed produced by these tappets as compared with ordinary tappets will be noticed. When the lever L is lifted for two or more picks in succession, it comes down about half-way each pick. This is unavoidable in section tappets consisting only of “riser” and “faller” sections, which must join together exactly wherever inserted, thereby causing all the healds to come towards the centre of the shed after every pick. If there are twelve sections to the round, any pattern repeating on three, four, six, or twelve picks may be woven.

It is sometimes considered an objectionable feature of section tappets (as represented in [Fig. 43]) that they cause all healds to be brought level after every pick, thereby producing jerky shedding. This objection, however, has been overcome by the construction of eight distinct varieties of sections, as shown in [Fig. 44], whereby healds may remain either up or down for several picks in succession on the “open-shed” principle, as with ordinary box-plate tappets cast in one piece.

OSCILLATING TAPPETS.

Another form of shedding device, which embodies certain features of ordinary rotary tappets and dobbies, is that known as the oscillating or rocking tappet, an example of which is shown in [Fig. 45]. This type of shedding motion consists of a series of plates, B, cast with upper and lower projecting ridges, C, D, and fulcrumed on shaft A, upon which they oscillate in a manner indicated by arrows, E. A movement in either direction represents one pick. On each side of the rocking shaft A, and oscillating with the tappets, is a pattern chain, F and F′, composed of bowls and bushes threaded upon spindles, G. Pattern chains, which represent odd and even picks respectively, are rotated alternately and intermittently, one spindle for each pick, thereby causing elbow-levers H to be raised or depressed, according to whether a bowl or a bush is presented underneath them respectively. The vertical arms of H act upon loose plates, I (termed “duck-bills”), which are fulcrumed upon short studs, J. Grooves may thus be formed between either the upper or lower ridges of tappet plates, and the upper or lower edges of “duck-bills,” which grooves, by acting upon treadles K, governing healds, will operate the latter in a manner determined by the pattern chains.

FIG. 45.

Oscillating tappets are situated at one end of a loom, above the crank shaft, from which they are driven by wheel gearing and suitable connecting arms. They are chiefly employed on looms weaving fustians and similar heavy and strong fabrics.

In plain looms with under tappets, the healds are generally connected round a top roller or cone, so that when the tappet is pressing one stave down, it is also taking the other stave up. The shedding is thus positive. For weaving twills, satins, and such weaves, either spring, roller, or pulley top motions are used. Where spring tops are used, the tappet pulls the heald down, and the spring pulls it up again. Of course, the speed at which the heald moves upward will be controlled by the shape of the tappet exactly as it is in its downward stroke, but in the up stroke of the heald, the tappet is only acting negatively. With roller tops the movement is positive, as the rollers are so constructed that as one stave is taken down by the tappets another is taken up. If two staves are taken down, two will be taken up, and the tappets must be constructed so as to allow this. It is very important also that the tappets should be of the proper shape, and the exact counterpart of each other, so that any one stave is allowed to go up at exactly the same speed, and with the same amount of eccentricity in its movement, as any other stave which is being taken down by the tappets. [Fig. 46] shows the top roller arrangement for plain cloth. Straps are connected to the staves over the rollers K, K¹; so that when one stave is taken down by the tappet, the other is taken up.