Endless rope sling

Abstract

Herein disclosed is a multi-layered endless rope sling made of continuous nylon filament yarns. The endless rope sling comprises a core including a plurality of substantially concentric layers, which are consecutively braided from the nylon filament yarns in a manner to cover one with another, and a sheath including at least one substantially concentric layer which is consecutively braided from the filament yarns in a manner to cover the outermost layer of said core. A method of braiding the filament yarns into the endless rope sling is also disclosed, which comprises the steps of braiding the filament yarns into a rope of a predetermined length, bringing the leading end of said rope into contact with the trailing end, which is being braided, so as to form an endless rope, and continuing the braiding operation so as to consecutively cover one layer, which has been braided, with another which is being braided, thereby forming the multi-layered endless rope sling. In order to put the method into practice, the apparatus disclosed includes a plate structure, which is formed with an opening for continuously allowing a running endless rope under the braiding operation to pass therethrough, and to which a structural member is removably attached for allowing the manufactured endless rope sling to be taken out from the opening, and a plurality of guide rollers for guiding the running endless rope under a predetermined tension.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rope sling, and more particularly to a multi-layered endless rope sling which has its layers successively braided from continuous filament yarns. The present invention further relates to a method of and an apparatus for successively braiding continuous filament yarns into the multilayered endless rope.

2. Description of the Prior Art

When it is intended to hoist or lower heavy weights with use of a crane or hoist, it is a current practice to employ a steel wire rope. With the recent increase in the weight and volume of the article or object to be hung, the diameter and length of the wire rope has accordingly increased to invite not only considerable reduction in the fastening efficiency of the wire rope around the article but also augmentation of the operator's fatigue. With such increase, moreover, it is sometimes requested to hang an article weighing more than 100 tons. It is, however, above the present level of technology to manufacture a wire rope which can meet sufficiently the particular requirement. Because the present technology can hardly form an eye piece for a steel wire rope having a diameter exceeding about 50 mm or 60 mm. Even with the larger diameter of about 60 mm, however, the wire rope can hang at the heaviest about 100 tons when the handing angle is 0.degree. with four hanging points and with a safety factor of seven. On the other hand, the latest crane can hoist an article weighing about 600 tons, and as such being the case a demand for hanging an article of more than 100 tons does exist actually, which demand cannot be satisfied in the least in respect of the hanging wire rope.

Recently, a nylon belt sling has been developed as a promissing rival of the steel wire rope. This nylon belt sling is made of nylon filament yarns having a highly breaking or tensile strength, and can be appreciated in its easy handling without resorting to formation of the eye splice, which is concomitant with the steel wire rope. The nylon belt sling can also be appreciated in its excellent properties including excellencies in resistance to wear, flexibility, stability and shock absorbability. One of the strongest nylon belt sling available has dimensions of 200 mm width and 12 mm thickness and a breaking strength of 80 tons. Thus, the nylon belt sling of the strongest type can hoist an article of about 40 tons, if the article is hung at four points and if a safety factor of eight is assumed. When, therefore, it is intended to hoist an article of about 100 tons, then the width of the belt sling has to be about 500 mm or the thickness of the same has to be about 30 mm. The belt sling of such enlarged cross-section is not available, because the present industrial sewing machine can barely manufacture a belt of about 300 mm width or of about 20 mm thickness.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to provide a rope sling which can hang a highly heavy article.

Another object of the present invention is to provide a multi-layered endless rope sling which has its layers successively braided from continuous filament yarns.

Still another object is to provide a multi-layered endless rope sling of the above type, in which the inside layers forming a core are braided from continuous nylon filament yarns at a small braiding angle.

A further object is to provide a composite endless rope sling which includes a plurality of tightly bundled endless ropes of the above type and a sheath braided from the filament yarns to tightly cover the bundled endless ropes.

A further object is to provide a method of consecutively braiding the filament yarns into the multi-layered endless rope of the above type.

A further object is to provide an apparatus for consecutively braiding the filament yarns into the multilayered endless rope of the above type.

According a major aspect of the present invention, an endless rope sling is provided, which comprises a core including a plurality of substantially concentric layers consecutively braided from continuous filament yarns in a manner to cover one with another, and a sheath including at least one substantially concentric layer consecutively braided from the continuous filament yarns in a manner to cover the outermost layer of the core.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view showing a multi-layered endless rope sling according to the present invention;

FIG. 2 is a cut-away view showing a portion of the multi-layered endless rope sling of FIG. 1 with its layeres being stepwise cut away;

FIG. 3 is a partial section taken along the axis of the multi-layered endless rope sling of FIG. 1;

FIGS. 4 and 5 are similar to FIG. 1 but show modifications of the multi-layered endless rope sling of FIG. 1;

FIG. 6 is similar to FIG. 1 but shows a composite endless rope sling including a plurality of the multi-layered endless ropes of FIG. 1;

FIG. 7(A) is a cross-sectional view showing the composite endless rope sling of FIG. 6;

FIGS. 7(B) to 7(D) are similar to FIG. 7(A) but show the modifications of the composite endless rope sling of FIGS. 6 and 7(A);

FIG. 8 is a diagrammatical view showing the overall construction of an apparatus suitable for manufacturing the multi-layered endless rope sling of FIG. 1;

FIG. 9 is a partially cut-away top plan view showing a main body of the apparatus of FIG. 8;

FIG. 10 is a perspective view showing such a portion of the main body of FIG. 9 as is removable according to the present invention to allow the endless rope sling of FIG. 1 from an opening; and

FIG. 11 a simplified but enlarged view showing the removable portion of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to FIGS. 1 to 3, in which an endless rope sling according to the present invention is shown. Generally indicated at reference numeral 10 is one embodiment of the endless rope sling, which has its sheath terminating at such a portion as indicated at reference letter e. This termination e is fixed in position to a multi-layered core by a suitable heat treatment.

The endless rope sling 10 may be made of ten or more layers including the sheath, but, in the present embodiment, it is composed of a core having four layers 10a, 10b, 10c and 10d, and of the outermost layer or sheath 10e, for illustrative purposes only, as seen from FIGS. 2 and 3. These core-constituent layers 10a to 10d and the sheath 10e are manufactured by braiding a desired number of continuous filament yarns, which are made of a thermoplastic resin such as nylon. This braiding operation is carried out such that the layers 10e, 10d, 10c and 10b cover, respectively, the layers 10d, 10c, 10b and 10a. As shown in FIG. 2, the braiding angle of angles of inclination of the filament yarns, which constitute themselves into the inner layers 10a to 10d of the core, with respect to the axis of the rope sling 10 is much smaller than that of the filament yarns of the sheath 10e. More specifically, the former angle or angles is desirably preset about 5.degree. to 20.degree., whereas the latter about 45.degree. to 60.degree..

As to these angles of inclination, it is well known in the art that the breaking strength of a rope sling depends remarkably upon the twisting pitch of the constituent filament yarns. For example, let is be assumed that the breaking strength of steel wires assumes 100 when they are just bundled, and then the strength will be reduced to 80 to 90 when they are twisted and braided into a single steel wire rope. For a rope made of a thermoplastic synthetic resin filaments, on the other hand, the reduced strength is about 50. Taking such material reduction in the breaking strength due to the fact that the filament yarns are subjected to twisting, it is desirable that they should be inclined with respect to the axis of the rope sling as slightly as possible.

In the present invention, therefore, the filament yarns of the core-constituent layers 10a to 10d are arranged almost in parallel with the sling axis, because the breaking strength of the rope sling 10 is wholly given by the core. The braiding angle of the sheath 10e is, however, at a normal value of about 45.degree. to 60.degree. so that the undesirable sliding of the filament yarns and accordingly the resultant deformation of the rope sling 10, both of which are otherwise experienced frequently, can be prevented. With such large braiding angle, therefore, the sheath 10e cannot give rise to the tensile strength of the rope sling 10 as a whole, but can tightly retain the inner core layers 10a to 10d and is contributable to stability in shape of the rope sling 10. Although this sheath 10e may have one layer in the case where the total number of layers of the rope sling 10 is less than five as in the present embodiment, it is preferable that the sheath 10e has two layers in the case where the total number of layers exceeds five.

Indicated at reference letter s in FIG. 3 is an initial portion of the innermost layer 10a of the core, at which portion s the braiding of the present endless rope sling 10 is initiated. In more detail, the filament yarns are braided at a slight angle with each other to form the innermost layer 10a. After the braiding action has proceeded to a predetermined extent, the initial portion s is suitably inserted into and fixed to the braided portion of the innermost layer 10a to afford the same a predetermined length to the finally obtainable rope sling 10. The braiding action is then further continued with use of the continuous filament yarns so that the layer 10a may be covered with the second layer 10b. This second layer 10b is then covered with the third layer 10c, and on and on. The fourth layer 10d is finally covered with the outermost layer or sheath 10e which is braided at a relatively large angle from the continuous filament yarns. Although, in this instance, the sheath 10e has its termination e axially at the same position as the initial portion s so as to give a uniform tensile strength to the obtainable rope sling 10, it should be understood that the location of the termination e can be varied. Since, in either event, the present rope sling 10 is different from the conventional belt sling, in which two or more sheets of cloth of a thermoplastic synthetic resin filaments are placed one upon another to have their ends sewed to each other, the rope sling 10 can have a substantially uniform tensile strength.

In order to augment the tensile strength and to attain an increased frictional effect, which is important to secure hanging of a load by means of the rope sling 10, it is preferable that the rope sling 10 is subjected by the dipping method to a coating process of a synthetic resin or rubber, after the braiding action has been finished.

The endless rope sling 10 thus manufactured can be used as a sling as it is, but may be modified for strengthening purposes in a manner as shown in FIGS. 4 or 5. In a modification of FIG. 5, the rope sling 10" is made to have its central portions arranged in contact with each other such that the end portions are left in the form of eyes or hanging loops 11. The central portions are tightly covered with a thick woven fabric 12 which is adhered to each other at its edges 12a, thus forming an annular sheath 12. In another modification of FIG. 4, moreover, the rope sling 10' has its central portions tightly wound with a rope 13, which may be made of a similar material, before they are covered with the annular sheath 12.

In the following, the tensile strength of the present endless rope sling will be tabulated in respect of the results which are obtained with use of the Amsler tensile testing machine or by the actual test using a crane.

TABLE __________________________________________________________________________ Endless Rope Constituent Calculated Breaking 1/8/Safety Two Point Four Point Diameter m/Weight Filament Yarns Strength Strength Hanging Hanging Hanging (mm) (Kg) __________________________________________________________________________ 1260D .times. 10 .times. (10.08 Kg) 3 .times. 2 .times. 8 = (480 Yarns) 4.83 (tons) 6 Core Layers + 2 Sheath 58.0(tons) 43.5(tons) 5.4(tons) about 10 about 20 30 0.73 Layers (tons) (tons) 2880 Yarns / 29.0(tons) 1260D .times. 10 .times. 5 .times. 2 .times. 8 = 8.04(tons) 7 C.L. .times. 1 S.L. 116.2(tons) 87.15(tons) 10.89(tons) about 20 about 40 38 1.3 (tons) (tons) 2520D .times. 10 .times. 5 .times. 2 .times. 8 = 16.128(tons) 5 C.L. + 1 S.L. 161.28(tons) 120.96(tons) 15.12(tons) about 30 about 60 45 1.8 (tons) (tons) 1260D .times. 10 .times. 3 .times. 2 .times. 8 = 4.83(tons) 23 C.L. + 2 S.L. 222.6(tons) 166.95(tons) 20.8(tons) about 40 about 80 58 2.2 (tons) (tons) 2520D .times. 10 .times. 5 .times. 2 .times. 8 = 16.128(tons) 9 C.L. + 2 S.L. 290.3(tons) 217.7(tons) 27.2(tons) about 50 about 100 62 2.6 (tons) (tons) 2520D .times. 10 .times. 5 .times. 2 .times. 8 = 16.128(tons) about 80 about 160 14 C.L. + 2 S.L. 451.4(tons) 338.5(tons) 42.3(tons) (tons) (tons) 70 4.5 2520D .times. 10 .times. 5 .times. 2 .times. 8 = 16.128(tons) 580.6(tons) 435.4(tons) 54.4(tons) about 100 about 200 80 6.0 (tons) (tons) __________________________________________________________________________ Note: 1. The breaking strength is at 75% efficiency. 2. The strength calculation is based on the relation D/8 g, that is, the yarn has a strength of 8 g per D (denier). 3. The strength of the sheath layer or layers is not introduced into the calculation. 4. The Equation "1260D .times. 10 .times. 3 .times. 2 .times. 8 = 4.83(tons) means that ten filament yarns of 1260D are doubled, three of which are arranged together with for braiding operation with use of eight pairs of paired bobbines. 5. The two or four point hanging is carried out at a hanging angle of 0 degrees.

Turning now to FIGS. 6 and 7(A) to 7(D), generally indicated at reference numeral 20, 20', 20" and 20'" are endless rope slings of composite type, each of which includes a plurality of bundled rope slings 10 of the first embodiment and a sheath covering them. As shown in FIGS. 6 and 7(A), the composite endless rope sling 20 is composed of three bundled rope slings 10.sub.1, 10.sub.2 and 10.sub.3 and of two sheath-constituent layers 21 and 21'.

These sheath layers 21 and 21' are formed by the later-described braider according to the present invention, in which the bundled rope slings 10.sub.1 to 10.sub.3 are tightly covered with braided filament yarns to form a unitary structure. Since, in this instance, the sheath layers 21 and 21' will not aid in increase in the tensile strength of the composite rope sling 20, the braiding angle may have a normal or relatively large value. Although, moreover, the inner sheath layer 21' may desirably be dispensed with, two-layer construction is preferable with a view to ensuring tightening the rope slings 10.sub.1 to 10.sub.3 as well as maintaining the desired shape.

Then, the termination E of the outer sheath layer 21 thus braided is also fixed in position by the heat treatment. Moreover, the obtained rope sling 20 as a whole is dipped into a bath so that it is coated with a synthetic resin or rubber.

The filament yarns to be braided into the sheath may be made not only of nylon but also of such a variety of materials as are used in the filament yarns of the rope slings 10.sub.1 to 10.sub.3. In other words, the cutting strength of the sheath can be so preset by selecting a suitable material that its wear or cut can be a measure of disposal of the rope sling 20 as a whole.

In a modification, moreover, the sheath layers 21 and 21' may also be made of wound nylon ropes, that is, the three rope slings 10.sub.1 to 10.sub.3 are gathered to form a bundle, on which a nylon rope is tightly wound and then is subjected to the coating treatment.

In a still another modification, the sheath layers 21 and 21' may further include an annular sheath of thick woven fabric covering the wound rope.

With close reference to FIG. 7(A), the rope slings 10.sub.1 to 10.sub.3 are shown to be considerably separated from each other, but actually they are so closely tightened as to have their boundaries merging into each other. The composite rope sling 20' is composed of four rope slings 10.sub.1 to 10.sub.4, as shown in FIG. 7(B). The other rope slings 20" and 20'" are, on the other hand, composed of five and seven rope slings 10.sub.1 to 10.sub.5 and 10.sub.1 and 10.sub.7, respectively, as shown in FIGS. 7(C) and 7(D).

The testing results regarding the breaking strength of the present rope sling, which were conducted with use of the testing machine No. T - 687 by the Industrial Association of Cloth Rope of Aichi Prefecture in Japan, will be presented in the following.

(1)

Sling-Constituent Rope 10

Number of Rope-Constituent Yarns

1260(denier) .times. 10(doubling) .times. 3(doubling) .times. 2(paired bobbins) .times. 8(pairs) .times. 5(core layers) = 2400(yarns)

Calculated Strength of Core

24.2(ton) (where strength per denier is 8 g and strength per yarn is 10.08 kg)

Calculated Strength of Rope

48.4(ton)

Standard Strength (for Efficiency of 75%)

36.3(ton)

Diameter of Rope

29(mm)

Weight of Rope

0.64(kg)

Length of Rope

9.5(m)

Testing Results

Actual Strength: 39.4(ton) (Efficiency of 81.4%)

Elongation (for 1/3 cut):9.0(%)

(for total cut):14.5(%)

(2)

Rope Sling 20 with Three Ropes 10.sub.1 to 10.sub.3

Calculated Strength of Core

72.6(ton)

Calculated Strength of Rope Sling

145.2(ton)

Diameter of Rope Sling

54(mm)

Weight of Rope Sling

1.81(kg)

Length of Rope Sling

9.4(m)

Testing Results

Actual Strength: 112.5(ton) (Efficiency of 77.5%)

Elongation(for 1/3 cut):10.8(%)

(for total cut):16.0(%)

As is apparent from the above testing results, the actual strength of the rope having five-layer core is as high as 81.4 percent of its calculated strength, and the actual strength of the rope sling 20 having three ropes 10.sub.1 to 10.sub.3 is also as high as 77.5 percent of its calculated strength. It can also be appreciated that the elongation is considerably small for the rope 10 and the rope sling 20. Taking the progressive reduction in the strength efficiency with increase in number of the core layers into consideration, therefore, a rope sling having three or four ropes which respectively has about five core-layers is more efficient than a simple rope sling of larger diameter, which is made of much more core-layers, for a load of the same weight.

The endless rope sling 20 can hang a load of about 56 tons, if the hanging is carried out at four points and if the safety factor of 8 is adopted. This limit weight of hanging can be increased more if the filament yarns of about 2560 deniers, if the sling-constituent ropes are more than three as is shown in FIGS. 7(B) to 7(D), and/or if the rope itself has more core-layers than four.

Turning now to FIG. 8, the method of manufacturing the endless rope sling according to the present invention will be described with reference to FIG. 8, in which a braiding apparatus is generally indicated at reference numeral 30. A main body 31 of the braiding apparatus 30 includes a plate structure composed of upper and lower stationary plates 32 and 33, which are horizontally disposed at a spacing from each other. This upper plate 32 is formed with a plurality of openings which are positioned along a periphery of a circle. A plurality of specially shaped plate members are disposed in the openings of the upper plate 32 for defining inbetween two passages which are undulating radially of the circle. In the undulating passages are movably mounted a plurality of upright spindles 34, on which a plurality of bobbins 35 are mounted for feeding continuous filament yarns 36. These filament yarns 36 are braided at a braiding point 37a into an endless rope 37, as shown. For this purpose, a spindle transfer mechanism (which will be detailed later) is interposed between the upper and lower plates 32 and 33 and is engaged with the spindles 34 for successively moving the latter in the passages. In addition, a power transmission mechanism is also interposed between the upper and lower plates 32 and 33 and connected with the spindle transfer mechanism for actuating the latter.

Downstream of the braiding point 37a is a pulling pulley 38 which is operative to pull the braided rope 37 in synchronism with the angular speed of the spindles 34. The rope 37 thus pulled is guided in the form of an endless rope by guide means which is also disposed downstream of the braiding point 37a. This guide means includes a plurality of guide pulleys 39, 41, 42, 43, 44, 45, 46 and 47. More specifically, the pulling pulley 38 has a relatively large diameter and is rotatably supported by a bracket bearing which is mounted on a frame. To the end of a shaft of the pulling pulley 38 is secured a gear which is driven through a chain by a gear of a reduction gear mechanism 48. This reduction gear mechanism 48 is driven through an endless belt by a prime mover or electric motor 49.

With closer reference to FIG. 8, the method of braiding the continuous filament yarns 36 into a multi-layered endless rope sling in accordance with the present invention will be described in the following. First of all, location of the guide pulleys 42 and 43 is accomplished in dependence upon a desired length of the endless rope 37. These pulleys 42 and 43 are rotatably supported by a movable stand 51, on the bottom of which rollers 52 are rotatably mounted. These rollers 53 can run on two parallel rails 53 which extend toward the main body 31 of the braiding apparatus 30. The running operation of the stand 51 is carried out by a winch 54, which is disposed in the vicinity of the end of the rails 53, as shown at the lefthand side of FIG. 8. The guide pulleys 44 and 45 are, on the other hand, rotatably supported by a stationary stand 55. Thus, the endless rope 37 coming from the pulling pulley 38 is led through the stationary guide pulley 41 to the guide pulleys 42 and 44, as shown by a solid line 37s. The tension to be applied to the endless rope 37s can be maintained at a constant level by moving the movable stand 51 and accordingly the guide pulley 42 toward and away from a frame 57 of the main body 31.

At the next stage, the bobbins 35, on which the filament yarns 36 made of nylon and having a suitable denier selected in accordance with the desired diameter of the final rope and with the desired number of the layers are wounded, are attached to the spindles 34. Then, the leading ends of the filament yarns 36 are extracted from the respective bobbins 35 and are bundled to be tied to the trailing end of a flexible guide member or leading wire (not shown). This wire has the same length as that of the final endless rope. Then, the leading end of the wire is guided along some of the pulleys 39, 38, 41, 42 and, 44 and is fed to a suitable take-up mechanism (not shown). This take-up mechanism may preferably be disposed in the vicinity of the main body 31. The leading wire may also be manually taken up at the same speed as the pulling speed of the pulling pulley 38.

After the above preparatory steps have been completed, the main body 31 and the pulling pulley 38 are brought into operating conditions, and the take-up mechanism is concurrently started at the same speed of the pulling pulley 38. Thus, the filament yarns 36 are braided at the braiding point 37a at a predetermined braiding angle into the innermost layer of the endless rope 37, by the cooperation between the radially undulating horizontal movements of the bobbins 35 and the upward pulling operation of the pulling pulley 38, the detail of which will be described later. The rope layer thus braided is led through the guide rollers to the take-up mechanism.

When, moreover, the trailing end of the leading wire comes close to the take-up mechanism, the operations of the main body 31 and the take-up mechanism are discontinued to untie or cut the tied portion between the leading wire and the ends of the filament yarns. Then, the leading end 37e of the rope 37 is inserted into the braiding point 37a through an opening, which is formed in the plate structure of the main body 31, although not shown. After that, the braiding operation is started again to cover the innermost layer with an outer second layer of the braided filament yarns. More specifically, the braided single layer is successively subjected to the braiding action at the braiding point 37a, and is pulled by the pulling pulley 38 through the guide pulley 39. Then, the single layer is further guided to the guide pulley 47 by way of the guide pulleys 42, 44 and 46, successively in this order. The final guide pulley 47 is so disposed in the frame 57 as to guide the rope 37 upwardly to the braiding point 37a through the opening. Thus, a desired number of layers can be consecutively braided from the filament yarns 36 in a fashion to cover one with another.

In order to obtain a uniform braiding angle, it is necessary to increase the pulling speed of the pulling pulley 38 for the outer layer. As has been described, moreover, the tensile strength of a braided rope is known to depend inversely proportionately upon the inclination of the constituent filament yarns with respect to the axis of the rope. With this in mind, the braiding angle of the core layers should be as small as possible. Since, in this respect, the braiding angle is known to be determined mainly by the relation between the pulling speed of the rope and the running angular speed of the bobbines, the former speed is increased and the latter speed is decreased when the core layers are being braided. This control of speed can be automatically accomplished in the present invention by resorting to the reduction gear mechanism 48.

After a predetermined layers including at least one sheath layer have been formed, the operations of the main body 31 and the pulling pulley 38 are stopped. Then, the ends of the filament yarns 36 are cut at the braiding point 37a, and the winch 54 is actuated to move the stand 51 toward the main body 31 so as to loose the rope 37s. Then, a portion of the plate structure of the main body 4 31 is removed to allow the rope 37s to be taken out from the opening of the main body 31. After that, the rope 37s is also taken out from the pulleys 38, 39, 41, 42, 44, 46 and 47. The cut end of the outermost sheath layer is fixed in position to the next inner layer by a suitable heat treatment or the like. The endless rope thus manufactured is usually coated with a synthetic resin or rubber so as to improve its fatigue allowance and to increase its frictional force.

When it is intended to obtain a longer endless rope, on the other hand, the guide pulleys 41, 42, 45, 43 and 44 are used in this order in addition to the pulleys 38, 39, 46 and 47, as shown at two chain lines 37.sub.M. For a longer endless rope 37.sub.L, the stand 51 is moved apart from the main body 31 to a position as shown at 51', and the rope 37.sub.L being braided is made to run along the guide pulleys 41, 42', 45, 43' and 44.

The details of the present braiding apparatus, especially, the construction of the main body 31 will now be described with reference to FIGS. 9 to 11. As better seen from FIGS. 9 and 10, the plate structure is composed of two portions Aa and Ab, the latter of which can be removed from the former. The upper plate 32 of the plate structure has a generally circular shape, whereas the lower plate 33 has a generally rectangular shape excepting its removable fan-shaped portion Aa. The plate structure is formed substantially at its center with an opening 58, through which the endless rope being braided is allowed to pass. With the portion Ab being removed, the rope in the opening 58 can be taken out.

Before entering into the detailed discussion on the removable portion Ab of the plate structure, the spindle transfer mechanism and the power transmission mechanism will be described at first with reference to FIG. 9. The upper plate 32 is formed with eight openings which are positioned along a periphery of a circle (not shown). As shown, peach-shaped plate members 59 are disposed in the eight openings of the upper plate 32, thus defining inbetween two passages 61 which are undulating radially of the circle. Eight pairs of the spindles 34 carrying the bobbines 35 are arranged to run in the undulating passages 61. As shown with a portion of the upper plate 32 being removed, the power transmission mechanism includes eight spur gears 62, to which eight circular plates 63 are coaxially attached. Each of these circular plates 63 is formed with four notches, in which the feet of the spindles 34 are retained so that the spindles 34 can move in the passages 61. These paired spindles 34 can be transferred from the notches of one of the circular plates 63 to those of the other which is positioned adjacent to said one of the circular plates 63. As is well known in the art, the spur gears 62 and the circular plates 63 are driven by a prime mover or an electric motor 65 which is mounted on a platform 64. The driving power is transmitted by way of a pair of belt pulleys 66 and 66', two pairs of meshing bevel gears 67 and 68 and 67' and 68', and a pair of spur gears 69 and 69'.

To the lower plate 33, on the other hand, is fastened by means of bolts a pair of bracket bearings 71 and 71', to which a shaft 72 is journaled. This shaft 72 is connected through an arm 73 and a vertical shaft 74 to a handle 75. A lever 76 is made movable in the direction of an arrow by the action of the handle 75, and has its one end secured to the shaft 72 and the other secured to a shaft 78, which is rotatably supported by two bracket bearings 77 and 77'. To this shaft 78 is secured a pair of rocking arms 81 and 81' which can bring a clutch 79 into frictional engagement by the movement of the lever 76 so that the driving shaft (not shown) may rotate.

Indicated at reference numeral 82 is an auxiliary rectangular table which lies on the frame 57. The fan-shaped removable portion Ab can slide on the table 82 to be removed. Indicated at numeral 83 is a bracket bearing which is mounted on a table 84 for rotatably supporting the not-shown driving shaft. Indicated at numeral 85 is, on the other hand, a handle, by which the main body 31 can be manually brought into operation when the filament yarns are broken or when it is intended to repair the mechanism of the main body 31.

Turning now to FIG. 10, the removable portion Ab can be removed from the plate structure or separated from the portion Aa such that two of the peach-shaped plate members 59 are taken out integrally with the spur gears 62 and the circular plates 63. At this instant, some of the spindles 34 retained by the plate members 59 are taken out together with the removable portion Ab. Although, in this embodiment, the removable portion Ab is formed to have a fan-shape, the shape itself should not be limited to the fan shape if it can be separated with ease together with the plate members 59, the gears 62 and the circular plates 63. If desired, such a removable portion as above can be formed additionally in the portion Aa. Indicated at reference numeral 86 are feet which are fastened to the removable fan-shaped portion Ab of the lower plate 33 by means of bolts or the like.

The removable construction of the portion Ab of FIG. 10 will be described in more detail with reference to FIG. 11. To the lower edges of the stationary portion 33a of the lower plate 33, are secured a pair of plates 87 and 87' which have their facing edges left free to provide guide surfaces for the removable fan-shaped portion 33. To the upper edges of the portion 33a, on the other hand, are fastened two pairs of "L"-shaped retaining members 88 and 88' and 89 and 89' which have their free ends facing each other, as shown. The fastening of the retaining members 88, 88', 89 and 89' is performed in a removable manner with use of bolts. Since the retaining members 88, 88', 89 and 89' have their extensions free and juxtaposed to the guide plates 87 and 87', two guide passages for the removable portion 33 are formed, so that, when it is intended to take out the endless rope from the central opening 58, the portion 33 can be removed with the retaining members 88, 88', 89 and 89' being removed. The removable construction should not be limited to the above, and a modification is conceivable, in which the open edges of the stationary portion are formed with radially extending grooves whereas the free edges of the removable portion are formed with such radial protrusions as can be slidably fitted in the grooves.

Claims

What is claimed is:

1. An endless rope sling comprising:

a core including a plurality of substantially concentric layers which are consecutively braided from continuous filament yarns in a manner to cover one with another; and

a sheath including at least one substantially concentric layer which is consecutively braided from said continuous filament yarns in a manner to cover the outermost layer of said core.

2. An endless rope sling according to claim 1, wherein said at least one layer has its trailing end fixed in position to the outermost layer of said core.

3. An endless rope sling according to claim 1, wherein the braiding angle of the layers of said core with respect to the axis of the endless rope sling is so determined at a small value as to prevent material reduction in the tensile strength of the endless rope sling as a whole.

4. An endless rope sling according to claim 1, wherein the braiding angle of said at least one layer of said sheath is so determined at a considerable value as to prevent sliding of said filament yarns and deformation of the endless rope sling as a whole.

5. An endless rope sling according to claim 1, wherein said continuous filament yarns are made of a thermoplastic synthetic resin.

6. An endless rope sling according to claim 5, wherein said thermoplastic synthetic resin is selected from the group consisting of nylon, polyester synthetic resin and polyvinyl alcohol resin.

7. A composite endless rope sling comprising:

a plurality of tightly bundled endless ropes each comprising a core including a plurality of substantially concentric layers, which are consecutively braied from continuous filament yarns in a manner to cover one with another, and a sheath including at least one substantially concentric layer which is consecutively braided from said continuous filament yarns in a manner to cover the outermost layer of said core; and

a sheath including at least one layer which is braided from continuous filament yarns in a manner to cover said tightly bundled endless ropes and which has its trailing end fixed in position to its outer surface.