EP0138848A1

EP0138848A1 - Chain wheel

Info

Publication number: EP0138848A1
Application number: EP19840900898
Authority: EP
Inventors: Simon Riber
Original assignee: PUSNES MARINE AND OFFSHORE SERVICES AS
Current assignee: PUSNES MARINE AND OFFSHORE SERVICES AS
Priority date: 1983-02-23
Filing date: 1984-02-22
Publication date: 1985-05-02
Also published as: NO156974C; NO156974B; NO830640L; WO1984003341A1

Abstract

Dans une roue à chaîne (1) ayant des dents de pignon (6) et des poches (10) pour les maillons horizontaux (2) de la chaîne et des rainures (7) pour les maillons verticaux (3), les poches sont allongées de manière à former un support (8) uniquement perpendiculairement au plan des maillons horizontaux (2) à l'extrémité opposée de la direction de traction de la chaîne, les poches ayant une forme conventionnelle dans le sens de la traction. Les poches (10) peuvent avoir une telle forme que le point tangentiel (11) avec un cercle inscrit se trouve entre le point médian (12) des maillons et le point de contact (4). Les maillons verticaux (3) de la chaîne peuvent être supportés dans le sens de la traction de la chaîne dans la région (9) où les poches (10) fusionnent avec la rainure (7).In a chain wheel (1) having pinion teeth (6) and pockets (10) for the horizontal links (2) of the chain and grooves (7) for the vertical links (3), the pockets are elongated so as to form a support (8) only perpendicular to the plane of the horizontal links (2) at the opposite end of the pulling direction of the chain, the pockets having a conventional shape in the pulling direction. The pockets (10) can have such a shape that the tangential point (11) with an inscribed circle is located between the midpoint (12) of the links and the contact point (4). The vertical links (3) of the chain can be supported in the direction of traction of the chain in the region (9) where the pockets (10) merge with the groove (7).

Description

CHAIN WHEEL .

The present invention relates to a chain wheel for heaving/ lowering a chain. The chain wheel has sprockets and pockets for the horizontal chain links and grooves for the vertical links.

A chain wheel usually has a circular groove in the middle having a U-shaped cross section at the bottom and parallel side walls extending radially until they meet the pockets for the horizontal chain links or the sprockets between two neighbouring pockets. The vertical links pass the wheel in said circular groove and has no contact with the wheel.

When the wheel is new and fits the chain, the horizontal links will be well guided in their pockets. However, the production tolerances for' anchor chains are relatively wide, so that those parts of the chain falling near the outer limits of the tolerance range do not fit very well into the chain wheel. After some use the pockets of the chain wheel will be worn. Both these factors, tolerance differences and wear, result in the chain slipping in the wheel under load, and the wear accelerates. The wear occurs at both ends of the pockets, but for a chain wheel which heaves or lowers anchor chain, the major wear is at that end of the pocket which faces the pulling direction.

For a pulling wheel most of the chain load is transmitted to the wheel from the first horizontal link being in contact with a sprocket on the chain wheel. The opposite end of said horizontal link and the remaining links in contact with the wheel have therefore little load. When the wheel rotates forward to the point where the next horizontal link is to take over the load, the angle of attack will change for the force between the horizontal link and the sprocket on the wheel. Thereby the link will tend to slip in the wheel if it has the possibility to- do so. The tendency is therefore that the link will pull itself down over the sprocket, or in other words, further down into the pocket. Thereby it

OiV.PI will also guide the next horizontal link some distance down ' on its sprocket. When the anchor chain is lowered, the tendency is the opposite. During rotation the chain pull attempts to lift the point of attack up over the sprocket, and the consecutive horizontal link will meet its sprocket higher up than normal. The result is that the chain finally overjumps. Overjumping can, however, also occur under heaving if the chain fits poorly in the wheel.

Another tendency during rotation of the wheel, when the force is about to be transmitted to a new sprocket, is that the chain force initially has an arm with respect to that point on the wheel where the force is transmitted. The correspondin moment tends to lift the horizontal link at the opposite end. During lowering such lifting of the horizontal links is particularly undesirable. The tendency is the greatest at the end of the engagement period for a sprocket. When the end of the horizontal link being remote from this sprocket is lifted, it also pulls along the horizontal link, which is to take over the chain pull, and this link will meet its sprocket higher up, with a corresponding danger of overjumping.

The object of the present invention is to provide the chain with such support that it stays in place in the wheel when loaded, and distributing the force transmission from the chain to the wheel over the largest possible area. Thus the wear will be less. Also those parts of the chain being in contact with the wheel will be better defined and one has greater certainty for the loads being as presupposed. Both the chain and the chain wheel has relatively poor ^'production tolerances and it is therefore important to ensure the best possible positioning of the chain in the wheel.

Another object is to distribute those loads which are to be transmitted from the chain to the wheel between the vertical and horizontal links, so that the load in the contact points becomes less and the additional stresses in the chain, which occur mainly as bending stresses, are reduced. ^■ These objects are obtained by making the chain pockets asymmetrical in the longitudinal direction of the chain, as stated in the main claim. The area where the force from the horizontal chain link is transmitted to the sprocket, is substantially unchanged, while the links at the opposite end have only horizontal support. Thus, length variations between the chain pocket and link will not influence the positioning of the link in the pocket. The contact point against the sprocket becomes fixed, while the variations at the opposite end will have no influence. As mentioned above, the engagement surface of the sprocket against the chain will remain substantially unchanged, but since the location of the horizontal link in the wheel is well determined, the engagement surface of the sprocket against the chain can be made to better fit the form of the chain, wherefore the specific surface pressure between the horizontal link and the wheel will be reduced. In order to counteract the tendency of lifting of the unloaded end of the horizontal link transmitting the chain force to the wheel, the pockets are given a small angle down towards the axis of the wheel, seen in the direction of the force in the chain.

In order to further reduce the surface pressure between the chain and wheel, the adjacent vertical links may also be supported at the end facing the chain force.

For the better understanding of the invention it will be described more closely, reference being had to the exemplifyin embodiments shown in the appended drawing.

Figure 1 shows a radial section through a chain wheel according to the prior art.

Figure 2 shows a section along the line A - A in Figure 1.

Figure 3 shows a radial section through a chain wheel according to the invention.

Figure 4 shows a radial section through a modification of___.

^7-r. the chain wheel in Figure 3.

Figure 1 shows a common chain wheel 1, having sprockets 6, pockets 10 and a groove 7, with the chain 2, 3 in a part of the wheel. The conditions for the chain in the wheel are good, the horizontal chain link 2 having engagement 4 against the chain wheel 1 as close as possible to the point 5 where the chain pull is transmitted along to the nearest vertical link 3. Between said contact points 4, 5, which are found ^' on both sides of each sprocket 6 on the chain wheel 1, the links 2, 3 have no other contact points. This means that the vertical links 3 have no contact with the chain wheel 1. The chain force is drawn from the contact point 5' between two chain links, and for the horizontal link 2' the contact point 4* is shown where the force by further rotation is to be transmitted to the wheel. The force will thus have an arm a, and a moment occurs attempting to lift the horizontal link 2' at the opposite end.

Figure 2 shows a section in the middle between two sprockets 6 in the chain wheel 1 in an area where the two horizontal links 2 and the vertical links 3 lie in the wheel.

Figure 3 shows a chain wheel according to the invention. The horizontal links 2 have a contact surface 4 approximately as in a common chain wheel at the pulling end, while the opposite end has a vertical support 8 in an extension of the pocket 10. The force K, giving a moment tending to lift the link 2", is correspondingly shown as in Figure 1.

In Figure 4 also the vertical links 3 are provided with support in the area 9 bordering on the pockets 10. Further¬ more, the pocket 10 is given an angle b with respect to the "tangential" embodiment shown in Figures 1 and 3. This angle shall counteract the- tendency to tipping of the horizontal links-2' as described in connection with Figure 1 and 3. The middle point 12 of the link 2' and the contact point 4 at the next engagement with the sprocket 6, are shown. In the position shown, the middle point of the link 2' is to a circle through the centre of the wheel 1, and it will be apparent that when the link 2' becomes in contact with the wheel, the tangential point 11 will lie between the middle point 12 and the contact point 4. This also results in the pitch circle Rl for the force transmitting end of the horizontal links being smaller than the pitch circle R2 for the other end of these.

When the chain is heaved or lowered, a certain movement between the chain and the wheel must be accepted. The invention reduces this movement to a minimum concurrently with increasing the contact surface transmitting the chain force to the wheel. Thus, the wear on wheel and chain is reduced. - Since positioning of the chain in the wheel is improved, the risk of the chain overjumping sprockets is also reduced.

Claims

C L I M S

1. A chain wheel (1) having sprockets (6) and pockets (10) for the horizontal chain links (2) , and grooves (7) for the vertical links (3) , characterized in that the pockets (10) at one end, as known per se, continues into sprockets (6) which transmit the chain force to the wheel and concurrently position the force transmitting end of the chain link (2) in its longitudinal direction and perpendicularly to its plane, while the other end of the pocket is not restricted by any sprocket which could act on the other end of the link in its -longitudinal direction, so that the chain is only supported perpendicularly of the plane (8) of the horizontal link (2) in the area adjacent to said other end.

2. A chain wheel according to claim 1, characterized in that the pockets (10) are given a form such that the pitch circle (Rl) of the force transmitting end of the horizontal chain links is less than the pitch circle (R2) of the other end of the horizontal links.

3. A chain wheel according to claim 1 or 2, characterized in that it comprises portions (9) for supporting of the vertical chain links (3) in the pulling direction of the chain near said other end of the horizontal links (2) .

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