SIZING.

The chief systems of sizing are slashing, dressing, ball-sizing, and hank-sizing.

The object of sizing is to strengthen the yarn by saturating it with a starchy substance, which lays the fibres, thus making it weave with less breakages. Other objects are to impart “feel” to the cloth, and to give it additional weight. For light sizing, in which the object is simply to strengthen the yarn, and not to increase its weight, only 10 to 15 per cent. is added to the weight. When 30 or 40 per cent. is added it is termed medium sizing, and for heavy sizing often 100 per cent. or more is added to the weight. The materials used for light sizing are: wheat flour, sago, farina or potato starch, rice flour or starch, maize.

Potato starch, or farina, is obtained from the tubers by reducing them to a pulp and mixing well with water. The water carries away the starch, and when allowed to stand the starch falls to the bottom of the vessel and the water can be drawn away. Farina is much used in all kinds of sizing, on account of its cheapness and the thickness of the paste it produces when boiled with water.

Sago is much used in light sizing, for which it is specially adapted. It is obtained from the pith of the sago palm, and made into flour by treating with water and drying on hot plates.

Maize is a starch obtained from the Indian corn, and is sometimes used for lightly sizing the finer counts of cotton yarns.

For light sizing it is not necessary to use anything but wheat flour, farina, or sago, and a small quantity of softening material, usually tallow or wax. Wheat flour is fermented before using by mixing it well with water (about equal weights of each) and leaving it for several weeks, occasionally stirring to keep the particles in suspension. When flour is fermented new bodies are formed, which have a powerful influence in preventing mildew. The fermenting cistern, 1 ([Fig. 22]), is usually a large vessel 8 feet by 4 feet by 4 feet, in which are two revolving “dashers,” C, to stir the flour and water when fermenting. Another similar cistern, 2, is used for storing called a “storage and diluting” cistern, into which the mixture is pumped after a few days, and left to further ferment. A force-pump, N, is used for pumping from this to the mixing cistern, 3, where the softening and weighting materials are added, after being boiled together in pan 4.

FIG. 22.

[❏
LARGER IMAGE]

Softening materials are used to render the yarn more pliable. The articles mostly used for this purpose are tallow, wax, and soap, cocoanut and palm oil.

The following mixtures are suitable for light sizing. They can be made to give a greater or less percentage, according to the specific gravity of the mixture. For testing the specific gravity or density of the liquid, the Twaddell’s hydrometer is used. This instrument registers in degrees the density of the mixture, or the amount of matter in solution.

For light sizing—

Wheat flour

280

lbs.

Tallow

„

Another mixture is—

Sago

100

lbs.

Farina

100

„

Tallow

„

Soap

„

For sizing with sago, cocoanut oil is often used as a softening material. A mixture of these two gives as good a size as anything for pure sizing.

Another mixture used for fine counts is—

Farina

100

lbs.

Wax

„

Tallow

„

1 gall. water to 1 lb. farina.

Almost every manufacturer uses different proportions of ingredients. Many use wheat flour, farina, and sago mixed in various proportions, whilst a flour and farina mixture in the proportions of 2 : 1 is considered by some to give the best results. Farina and sago are also often mixed for light sizing in the proportion of two parts farina to one part sago. Wheat flour carries through better than farina or sago, and is therefore more generally used for the heavier kinds of sizing.

Any of these mixtures may be altered as regards strength, or otherwise, by increasing or diminishing their density. If a mixture twaddles 10 degrees at a given temperature, it may be strengthened for heavier cloths or higher picks by increasing the proportion of solid matter in the mixture until it twaddles 15 degrees at the same temperature.

For adding weight to the cloth china clay is the chief ingredient used. This material is found in deposits in Devonshire and Cornwall, and is used in large quantities for the purpose of weighting and filling cloth, more especially those manufactured for export to the Eastern markets.

For what is termed “medium” sizing, viz. adding about 30 to 50 per cent. to the weight of the cloth, the following materials are used in various proportions, the proportion given being an example—

Flour

100

lbs.

Clay

to 40 lbs.

Tallow

lbs.

Chloride of magnesium

gallon.

Chloride of zinc

„

It will be noticed here that chloride of magnesium and chloride of zinc are introduced along with the china clay. Chloride of magnesium is a very powerful softener as well as a weighting material, and one of its uses is to prevent the gritty feel which the addition of clay alone would give to the cloth. It has a great affinity for water, and has thus the power of attracting moisture to the cloth in which it is used. It is this which really constitutes its softening effect.

Chloride of zinc is used to prevent mildew, which is a species of vegetable growth which often occurs in sized cloth which has been left damp, or which attracts moisture.

As chloride of magnesium attracts moisture, it is necessary to use an antiseptic which will counteract the tendency of the cloth to mildew. Chloride of zinc possesses valuable properties as an antiseptic, and therefore it is often used where chloride of magnesium is used in the size as a softening and weighting material.

If china clay is used for medium sizing without using chloride of magnesium, it is necessary to greatly increase the proportion of tallow or other softeners in the mixture. Thus, for every 100 lbs. of flour, 40 lbs. clay, and perhaps 25 lbs. tallow would be used.

Chloride of calcium has a similar effect to chloride of magnesium, but is scarcely as powerful. It is used by many in light-sizing mixtures to prevent the yarn becoming too brittle.

For heavy sizing the proportions of clay and mineral ingredients are increased. In some classes of low shirtings, over 100 per cent. is added to the weight of the yarn. The adhesive material mostly used is wheat flour, as it carries the added materials better than farina or sago; but farina is sometimes used for sizing up to 100 per cent. Sometimes two parts clay to one of flour is used for very heavy sizing. For 100 per cent. sizing about the following proportions may be used:—

Flour

100

lbs.

Clay

130

„

Tallow

„

Chloride of magnesium

gallons

Chloride of zinc

„

Colouring matters are used in size to give the yarn any desired tinge. Blue is the most common, as it neutralizes the yellowness of the cloth given in heavy sizing. Only a very small quantity is required. Sometimes yellow is used to give a brownish appearance to American yarn, making it appear more like Egyptian. Numerous other materials are used for various purposes in sizing. “Gloy” has been found useful for strengthening warps for very heavily picked cloths.

[Fig. 23] will show the principle of the slashing machine in its most usual form. The warpers’ beams are placed in the creel 1, at the back of the machine. In the diagram there are six beams, 1 to 6, so that if each one contains 500 ends there would be 3000 ends in the warp. The warp passes over roller A, and into the size-box. The small roller B in the size-box is of copper, and is called the immersion roller. The warp is passed under this, and its depth in the size mixture is regulated by it. The warp then passes between two pairs of rollers, C, D, and E, F (of which D and F are covered with flannel), to squeeze the surplus size from the yarn. The size is kept boiling in the size-box by the injection of steam. When the warp comes from the rollers E, F, it passes over a large drying cylinder, M, and, after passing almost completely round it, over a smaller cylinder, N, and then round the fan P and over guide-roller Q. The warp then passes through the dividing rods R (which divide the warp into the same portions that come from each warpers’ beam), thence over guide-roller S and tin measuring roller T, between drawing rollers U, V, and finally on to a weaver’s beam, Z. This end of the machine is called the “headstock,” and comprises the measuring mechanism, dividing rods, and winding-on arrangement.

FIG. 23.

[❏
LARGER IMAGE]

The position of the immersion roller in the size has some effect upon the amount of size retained on the warp, as by sinking the roller lower in the box the yarn will remain longer in the size, and will therefore absorb more. This roller is also mounted so that it can be lifted out of the size altogether when the machine is stopped. The larger cylinder is usually 6 feet to 7 feet diameter, and the smaller one about 4 feet diameter, and both are heated with steam.

Some machines have a revolving brush between the size-box and the cylinder. This brush is usually driven from the fan shaft, and its object is to lay the projecting fibres, and so strengthen the yarn. Brushes are only used in some fine-weaving districts, and not always there. The brush gives the threads a round, smooth feel, and prevents them sticking together. Under the brush which brushes the yarn a smaller brush is placed, running at a slower speed than the one above it; the lower brush is placed a short distance into the upper one, and serves the purpose of cleaning it as it revolves.

The marking mechanism in the slashing frame usually consists of a tin roller wheel, B ([Fig. 24]), driving the wheel D, called the “stud wheel”; a screw or worm, E, on this stud drives the bell wheel F. The marking hammer L is situated immediately above a vessel containing colouring matter, and is lifted by a cam, P, driven from the tin roller, and dropped suddenly on the warp, marking it to the required lengths.

The length between each mark is regulated by the wheels used. The tin roller wheel being the driver, if this is divided into the product of the stud wheel and bell wheel, it will give the number of revolutions of the tin roller for each mark, and this multiplied by the circumference of the roller will give the length of the mark. The formula will stand thus—

stud wheel × bell wheel × circumference of rollertin roller wheel = length of mark.

FIG. 24.

If the stud wheel contains 90 teeth, the bell wheel 45 teeth, the tin roller wheel 60, and the roller is 14·4 inches circumference, the length of the mark will be

90 × 45 × 14·460 = 972 inches

There are other marking motions in use for marking short lengths for dhooties and scarves of various kinds, some being constructed so as to mark scarves of two different lengths in succession—say one scarf is marked 2 yards long, and the next one 4, the two being repeated.

FIG. 25.

A “slow motion” arrangement is used for keeping the machine moving very slowly whilst the weaver’s beam is changed. If the machine is stopped completely, the warp becomes marked where it rests on the drying cylinders. [Fig. 25] shows the principle of this arrangement. There are three pulleys, A, B, C, on the driving shaft D. Between the fast and loose pulleys A, C, the slow motion pulley B is placed. When the belt is moved from the fast pulley to the slow motion, the wheel F is set in motion and drives another wheel, G, and this, through the bevel wheels H, J, K, M, causes the catch O to drive the ratchet wheel P on the driven cone shaft T. As the motion of the driving catch O is slower than the cone T when driven by the fast pulley, the catch O will begin to work when the strap is moved from the fast pulley to the slow motion pulley, and the speed of the machine is reduced to the point where the catch O overtakes the driven cone T.

Hot-air drying has been employed in place of cylinder drying, but is not much used. In this system of drying the warp passes from the size-box to hot-air chambers. The air is heated with steam pipes and driven through the chambers by fans. Combinations of cylinder and hot-air drying have also been used, but with little success.

In a slasher sizing machine, yarn is withdrawn from back beams and finally wound upon a weaver’s beam at a uniform pace, notwithstanding the gradually increasing diameter of the latter as it fills with yarn. It follows, therefore, that the velocity of a beam must gradually diminish from the commencement of winding. In order to meet such requirement a beam is driven negatively by means of a frictional driving motion, one of which is shown in sectional elevation in [Fig. 26]. This motion consists of a tooth wheel, A, whose sides are extended beyond its proper teeth to form inner flanges, which latter are turned at right angles to form an outer rim. Two outer flanges, B, interlock with the rims of wheel A, as shown at C, so that wheel A and flanges B always revolve at the same velocity. Enclosed within each chamber between the inner flanges of A and outer flanges B is a sheet steel disc, D, encased within two flannel washers, E, and secured to a hub which rotates on a hollow beam shaft, O, in which is cut a channel or key-bed, R. The hubs of steel discs D being furnished with a key that enters the channel R, are free to slide upon shaft O, which they rotate at the same velocity. The hub of wheel A revolves freely upon the hubs of discs D; also, the hubs of flanges B revolve freely upon shaft O; therefore, by compressing the flanges and discs together, any degree of friction, within certain limits, may be induced. Pressure is applied to the flanges by means of a vertical lever, F, fulcrumed at G, and elbow lever J fulcrumed at K. A stud, I, in lever J bears against lever F with a force that may be regulated by means of an adjustable weight, L, N. On the inner end of shaft O, which receives one of the beam gudgeons, is a disc, P, furnished with a stud or peg, Q, to which is attached a rope or strap that encircles and grips one end of the weaver’s beam, which is thereby turned. As a beam becomes filled and its velocity diminishes, the slippage between discs D and the driving flanges increases, because the velocity of the driving flanges remains undiminished.

FIG. 26.

Automatic Supply of Size to a Sizing Machine.

There are numerous devices for the purpose of ensuring a continuous and automatic supply of size to the size-box of a slasher sizing machine. One of these is represented in Figs. [27] and [28]. From the last mixing beck 3 ([Fig. 22]) size is pumped into a storage beck, 5, whence it is withdrawn and forced by a ram, N, along feed pipe Q, which is coiled within a steam-heated chamber, U. From the steam chamber it returns along pipe T, through regulating valve Z, and into the size-box, in a boiling state. Within a separate chamber of the size-box is a floating copper roller, X, connected at one end by means of rod Y to a tap which regulates the flow of size through valve Z, on the principle of a ball tap.

FIG. 27.

FIG. 28.

Scotch dressing is another system of applying size to the yarn. This is a much slower method than slashing, and is chiefly suitable for very fine yarns. In this machine the weaver’s beam is placed above an expanding reed, R ([Fig. 29]), and to prevent the ends being crowded the warper’s beams are divided, one-half the ends being placed at each end of the machine. The warp is passed through a pair of rollers, A E, the top one being very heavy. The lower roller of the pair is immersed some distance in the size, and takes the size up to the yarn. After emerging from the rollers or “squeezers,” the yarn passes through a revolving brush, B, and over a fan in a hot-air chamber, F, then through another brush, C, round a guide-roller through the expanding reed to the weaver’s beam. The opposite half of the machine is a duplicate of this. By this process the yarn is greatly strengthened. The brushing lays down all the projecting fibres, and makes the thread round, preventing any caking of the size on the threads. The production, of a machine of this kind, is much less than that of a slashing frame, as only about five beams a day can be dressed, whilst about fifteen beams could be slashed in the same time. Instead of the circular brush B, sometimes flat brushes are used. These are made to work on both sides, as shown at [Fig. 30]. The dotted lines show the movement of the brushes. The warp is brushed in the opposite direction to that in which it is moving.

FIG. 29.

FIG. 30.

FIG. 31.

Ball-warp Sizing.

[Fig. 31] is a sectional elevation of a sizing machine for ball-warps. One or more warps, A, are placed upon cones, and their yarn guided over rollers, B, C, into a large size-box, 4, containing a series of rollers, between which yarn passes until it emerges at guide-roller G, when all excess of size is removed by rollers H, I. From the squeezing rollers, yarn is conducted to a drying machine ([Fig. 32]), consisting of a series of steam-heated cylinders arranged in two vertical zigzag rows, O, N, the outer rows of which are driven from vertical shafts containing a series of bevel wheels, Z, gearing with bevel wheels Y at one end of the cylinder shafts. By this means yarn is subjected to little tension, and its elasticity is better preserved. After drying, the warps are deposited in box crates, R, to be subsequently re-balled, ready for beaming or winding on to a weaver’s beam.

FIG. 32.

FIG. 33.

[❏
LARGER IMAGE]

FIG. 34.

[❏
LARGER IMAGE]

Beaming.

Beaming machines exist in great variety, but they may be classed under the heads of (1) press beaming, and (2) tension beaming machines. An example of the first-named type, as made by Butterworth and Dickinson, Ltd., is illustrated in [Fig. 33]. If beaming is accomplished from back beams prepared by a beam warping machine, a creel or stand capable of holding several beams is situated in the rear of the headstock of the beaming machine; but if beaming is from ball-warps, yarn from the latter is passed in a circuitous manner under and over tension and guide rollers A, B, for the purpose of tautening and separating warp-ends, which are finally passed through the dents of an expending comb, C, and on to a weaver’s beam. By causing weighted levers, D, to bear upon the beam-ends during winding, a hard and compact beam is made.

A tension beaming machine of the type known as a Yorkshire dressing machine, as made by Hattersley & Sons, is shown in [Fig. 34]. Yarn from a warp, A, or from several sections of warps, is conducted under and over the bars of a tension ladder, B, thence around dividing bars, C, between tension rollers, D, and finally through a wraith or coarse reed on to a weaver’s beam, E; but if Yorkshire dressing proper is adopted, warp-ends are passed through the dents of a reed in groups of two to four, and disposed according to pattern (if any) before passing on to a weaver’s beam ready for weaving in the loom. By means of stepped speed pulleys, F, G, the velocity of a beam may be retarded at intervals, to compensate for the gradually increasing diameter of a beam, and thereby maintain a uniform rate of winding.

CHAPTER II
HAND AND POWER LOOMS

THE three principal movements in weaving are shedding, picking, and beating up the weft. By shedding is meant opening the warp threads to allow the shuttle containing the weft to pass over certain ends and under others. In the common hand loom the shed is made by the weaver operating treadles with his feet. [Fig. 35] shows the method of connecting the shafts or staves with the treadles for weaving a plain cloth. There are two treadles, A and B, placed underneath the loom, and centred at C. The stave E is connected to the treadle A through the lever G. The stave F is connected to the same treadle through the “tumbler” T and the lever M. When the treadle A is pressed down it will take the stave E down, and the stave F up. For the second pick, the stave F is connected to the treadle B through the lever H, and the stave E is connected to the same treadle through the “tumbler” R and the lever N. Therefore, when the treadle B is pressed down, it will take the stave F down and stave E up. By alternately pressing first one treadle and then the other, we get each stave up for one pick and down for the next, alternately, as required for weaving plain cloth. The levers M and N are usually called “long lams,” the levers G, H “short lams,” and the top levers R, T “tumblers.” The cords PP connect the long lams and tumblers together at the side of the loom.

FIG. 35.

In mounting this loom for weaving a three-shaft twill, three treadles are required, one treadle for each pick in the pattern. Supposing one stave to be down and two up for each pick. The stave required to be taken down for the first pick must be connected to the first treadle through a short lam, and the two staves required to be taken up must be connected to the same treadle through their long lams and tumblers. Each pick in the pattern must be gone through in this manner. A separate treadle is required for every pick in the pattern, unless the same pick is repeated, in which case one treadle will do for more than one pick. It is not advisable to break the regularity in the order of treading in order to save a treadle; but in diaper patterns and similar weaves the effect of a point draft is obtained by reversing the order of treading.

FIG. 36.

FIG. 37.

Figs. [36] and [37] show the design and cording plan respectively for a twill cloth requiring eight treadles.

FIG. 38.

The hand loom is practically obsolete in the cotton trade, but it is still extensively used in silk manufacture, where power looms, as at present constructed, are not found advantageous for weaving the finer classes of goods.

The chief shedding motions in power looms are tappets, dobbies, and jacquards.

There are various kinds of tappets, the simplest and best for plain or twill weaving being those shown at Figs. [38] and [39]. The former is the more general arrangement. In this the tappets are placed under the loom, inside the framework. In the arrangement shown at [Fig. 39] the tappets are placed outside the loom, and thus a larger amount of floor space is taken up by the latter than the former.

Outside tappets are mostly used in the Yorkshire weaving districts, and are commonly made for weaving with about eight shafts. The top levers, with “half moons,” are centred at the cross rods EE ([Fig. 39]), and the heald is lifted from both sides of the loom. The top levers are very useful for equalizing the shed, as the connection with the upright rod can be altered without difficulty.

FIG. 39.

In a power loom there are two horizontal shafts, the top shaft A ([Fig. 38]) and the bottom shaft B. The former is used for working the slay, by means of the crank C, and the connecting rod or “crank arm” D ([Fig. 38]). The bottom shaft is used for “picking,” and for this purpose it is necessary that the shaft should revolve at one-half the speed of the top or crank shaft. The toothed wheel on the bottom shaft must therefore contain twice the number of teeth in the wheel on the crank shaft which drives it. As a plain cloth contains two picks to the round, and the bottom shaft makes one revolution for two picks, the tappets are fixed to the bottom shaft. Each tappet acts upon treadle bowl E, and therefore the size of the bowl will require to be taken into consideration in shaping the tappets. For weaving plain cloth four staves are usually taken, in order to prevent overcrowding the healds on each stave, the ends being drawn through the staves in the order 1, 3, 2, 4. As the staves are fastened together in pairs, this is the same as two staves.

The kind of movement to be given to the staves is very important, especially in quick-running looms. The staves should be moving quickest when they are level, and their speed should gradually decrease as the shed opens. It is obvious that a movement of this kind will put as little strain as possible on the warp, and therefore cause the fewest breakages. The depth of the shed should only be sufficient to allow the shuttle to pass, therefore the “lift” or stroke of the heald is dependent upon the depth of the shuttle used. The shed when opened should remain open only long enough to allow the shuttle to pass through.

Example.—What lift should a tappet have to make a plain cloth, the other arrangements in the loom being as follows: Sweep of slay 5½ inches, distance of healds from cloth 8 inches, heald connected to treadle 24 inches from fulcrum, distance from fulcrum to centre of treadle bowl 16 inches, size of shuttle 1½ inch broad, 1¼ inch deep?

Assuming that the tappets are under the loom, as in [Fig. 38], the treadle bowl E is 16 inches from M, and the heald connected 24 inches from M. If slay moves back from cloth 5½″, and the shuttle is 1½″ broad and 1¼″ deep, it follows that the shed must be 1¼″ deep, or a little over, at a point 4″ from the cloth (5½-1½ = 4). Then if the heald is 8″ from cloth, the stroke of heald may be obtained—4 : 8

To obtain the proper shape of the tappets for a plain cloth, the lift or stroke of the tappets to give the required lift to the healds must be obtained. If the lift of the heald is required to be 4 inches, and the centre of the treadle bowl E ([Fig. 38]) is situated 12 inches from the fulcrum of the treadle M, the heald being connected to the treadle at, say, 18 inches from the fulcrum, the lift or stroke of the tappet will be obtained as follows:—

As 18

: 12

18 )

48 (

2⅔ lift of tappet

In some makes of looms the staves are connected to the treadles at a point between the fulcrum and the treadle bowl, the fulcrum being at the front of the loom. This necessitates a larger lift of tappet than lift of heald. The tappets in this case are very large, and are preferred by some manufacturers.

FIG. 40.

To construct a tappet for a plain cloth from the following dimensions.—Lift of tappet, 4 inches. Distance from centre of shaft to nearest point of contact with treadle bowl, 2 inches; dwell one-third of a pick. Diameter of treadle bowl, 2 inches.

At a radius of 2 inches describe the circle A ([Fig. 40]). This circle represents the distance from the centre of the shaft to the nearest point of contact with the treadle bowl.

At a radius of 3 inches describe the circle B. One inch added for radius of treadle bowl.

At a radius of 7 inches describe the circle C. Four inches added for lift.

The circle B represents the centre of the treadle bowl when the inner circle of the tappet is acting upon the bowl.

The circle C represents the centre of the bowl when pressed down by the tappet.

The pattern being a plain one, the circle must be divided into two equal parts, and each half-circle will then represent one pick. By the line DE divide the circle into two equal parts. Then, as the healds must have a pause or dwell equal to one-third pick when at the top and bottom of their stroke, divide each half-circle into three equal parts by the lines FK, GH. Divide FH and GK each into six equal parts, and divide the space between the circles B and C into the same number of unequal parts, the largest being in the middle, gradually decreasing towards the circles B and C.

From the corners of these unequal spaces, and with the radius of the treadle bowl in the compasses, describe circles representing the position of the treadle bowl at different parts of its movement.

Draw the curved line touching the extremities of the treadle bowl. This gives the outline of the tappet.

As previously stated, the movement of the heald must be quickest when the shed is nearly closed, and must gradually decrease in speed as the shed opens. The unequal spaces into which the lift of the tappet was divided give this eccentric movement to the heald. The curve of the tappet will approach nearer to a radial line as the shed closes, and the heald approaches the centre of its stroke. Referring to [Fig. 40], it will be seen that the treadle bowl is at rest from F to G and from H to K, or one-third of a pick at both the top and bottom of the stroke. Therefore the time allowed for change, or for moving the heald from top to bottom, or vice versâ, is equal to two-thirds of a pick. If a dwell equal to half a pick is required, it can be obtained by dividing the pick into four equal parts and taking the middle two parts for dwell. If two-thirds dwell is required, divide the pick into six parts and take four parts for dwell.

It is usual to give the tappet which operates the back heald a slightly larger lift than the tappet which operates the front heald. The difference required can be easily calculated. In looms with the fulcrum of the treadles at the front, and the healds connected to the treadles between the fulcrum and the treadle bowls, some of the required extra lift is obtained by connecting the back heald to the treadle at a point further from the fulcrum than the front heald is connected. In looms with the fulcrum of the treadles at the back of the loom, and the tappets acting between the heald and the fulcrum, there will be a greater difference between the size of tappets in proportion to the lift than in the former case.

Tappets for twills, and other simple weaves, having more than two picks to the round, are usually placed upon a counter-shaft, but outside tappets are usually worked loose upon the bottom shaft.

The following example will illustrate the principle of constructing twill tappets:—

Draw a tappet for a 3 up and 1 down twill. Distance from centre of shaft to nearest point of contact with treadle bowl 3 inches, lift 3 inches, bowl 2 inches diameter, dwell ½ pick.

FIG. 41.

At a radius of 3 inches describe the circle A ([Fig. 41]). At a radius of 4 inches describe the circle B (one inch added for treadle bowl). At a radius of 7 inches describe the circle C (3 inches added for lift). There being four picks in the pattern, divide the circles into four equal parts by the lines DE, FG. Then each quarter-circle represents one pick, and the tappets must be made to make one revolution for four revolutions of the crank shaft. As the dwell of the heald (when the shed is open) must be equal to half a pick, or half a revolution of the crank shaft, divide the first pick into four equal parts by the points O, L, M; make DP equal to DO, and FN equal to FM, and rule lines from P, O, M, N to the centre. The distance OM represents the half-pick dwell, and the distances OP and MN represent the half-pick which will be allowed for changing the heald from bottom to top of its stroke, and vice versâ. Divide OP and MN into six equal parts, and the lift of tappet, or the distance between the circles B and C, into six unequal parts, the largest in the middle and gradually decreasing towards the two circles. From the corners of the unequal spaces describe the small circles representing the treadle bowl at different parts of its stroke, and draw the outline of the tappet touching the extremities of these circles.

A tappet of this shape acting upon a treadle bowl two inches in diameter will take the heald down for one pick and allow it to go up for three picks. The heald will be held stationary for exactly half a pick when at the bottom of its stroke, and will begin to rise slowly, and gradually increase in speed as it approaches the centre of its stroke, and will gradually decrease in speed as it approaches the top of its stroke. The downward movement will be an exact counterpart of this. In this kind of tappet it will be noticed that the heald, when it gets to the top (if it is required up for more than one pick), remains stationary until it is required to come down. Thus the heald remains at the top while the circles revolve from N to P.

For this twill there will be four treadles, each treadle being operated by a tappet of the same shape; but the tappet operating each succeeding treadle will be placed one quarter of a revolution later than the previous one.

The size of the treadle bowl has a very appreciable effect upon the shape of the tappet, more especially when there are several picks to the round. The movement imparted to the centre of the treadle bowl will be the exact movement given to the heald as far as regards dwell and eccentricity, and as the tappet acts on the treadle bowl at a distance of 1 or 2 inches from the centre, the required amount of dwell and eccentricity must be given to the centre of the bowl, and the shape of the tappet obtained accordingly. It will be noticed at [Fig. 41], that to give a dwell of half a pick to the centre of the treadle bowl, a slightly longer dwell is on the tappet at the inner circle; and as the size of the treadle bowl increases, this hollowing out of the tappet must be increased in order to keep the dwell of the heald the same.

[Fig. 42] is a drawing of a tappet for a 3 down, 1 up, 1 down, 1 up (six to the round) twill. Centre of tappet shaft to nearest point of contact with bowl 4 inches, lift of tappet 2 inches, bowl 1½ inch diameter, dwell one-third of a pick.

FIG. 42.

To construct this tappet:—At a radius of 4 inches describe the circle A. At a radius of 4¾ inches describe the circle B. At a radius of 6¾ inches describe the circle C. As there are six picks to the round, divide the circles into six equal parts by the lines D, E, F, G, H, I. As there is one-third pick dwell, divide each pick into three equal parts, and take the middle one for dwell. Rule the lines L, M, N, O, P, Q, R, S to the centre, and divide the spaces allowed for change into six equal parts, and the distance between the circles B and C into six unequal parts, as in the previous examples. From the corners of the unequal spaces describe the circles representing the movement of the treadle bowl, and obtain the shape of the tappet accordingly. It will be noticed that at point L the treadle bowl begins to dwell, and remains stationary until it reaches the point S, when it begins to go up. The heald will thus be down for the first, second, and third picks, up for the fourth, down for the fifth, and up for the sixth.

FIG. 43.—Woodcroft’s Tappet.

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.

SIZING.

CHAPTER IIHAND AND POWER LOOMS

CHAPTER II
HAND AND POWER LOOMS