Chain with hardened Anti-wear surfaces

Abstract

Chain link (1) comprising a metal body (2) with an elongate central space (3), the body comprising at short sides (23, 24) of the central space a curved contact surface (25, 26) for interacting with adjacent chain links. The body (2) at the contact surfaces (25, 26) is of a greater hardness than the body outside the contact surfaces through a depth Dh that is smaller than a diameter D of a cross section of the body (2).

Description

[0001] Title: Chain with hardened anti-wear surfaces

[0002] Technical Field

[0003] The disclosure relates to a chain hnk comprising a metal body with an elongate central space, the body comprising at short sides of the central space a curved contact surface for interacting with adjacent chain links. The invention furthermore relates to an assembly of a chain link connected to a cable and to a grab for loading and unloading of bulk substance from a vessel or a container, as well as a method of manufacturing a chain link.

[0004] Background Art

[0005] Such a chain hnk is known from US 5878 565 in which a closable chain link is described for quick connection and release to a cable or to a tool, such as a grab. The chain link has an opening through which a rotatable locking member can be inserted and confined in the central space where it is restrained from sliding movement in axial direction. By rotation of the locking member, it can be brought in the locked position in which it abuts against the inner surface of the central space and cannot pass through the opening. The locking member is provided with an axially slidable mechanism that can be pressed by an operator against the biasing force of a spring to engage with the locking member, for rotation of the locking member.

[0006] Summary

[0007] The known chain links are used to couple tools, like grabs, to cables for loading and unloading of bulk goods from vessels or containers and are often used under conditions of fluctuating loads and may be contacted by abrasive substances. This results in a high rate of wear of the links. It is an object of the present invention to provide a chain hnk that can take up high loads and that has reduced wear. Hereto a chain link according to the disclosure comprises a body that is at the contact surfaces of a greater hardness than the body outside the contact surfaces through a depth DR that is smaller than a diameter D of a cross section of the body.

[0008] By hardening the contact surfaces up to a limited depth, the wear resistance of the chain link can be increased while the strength that is derived from the flexible core metal of the chain link is retained. Hereby the chances of failure due to fatigue cracks under strongly varying loads are kept to a minimum.

[0009] The body of the chain link may at the contact surfaces be hardened to a depth DR that is between 5% and 25 %, preferably between 10% and 20%, most preferably about 15% of the diameter D. The relatively small depth of hardening of the contact surfaces results in increased wear resistance while maintaining a high tensile strength.

[0010] The radius of curvature of the contact surface in a side view of the chain link, at an outer position of the hardened area, is at an angle no larger than 50°, preferably about 45° with the central axis. The pulling forces may act through angles between + / - 45° with respect to the length direction of the chain link, providing wear protection for a diverse range of lifting operations.

[0011] The cross-section of the body may be substantially circular, the hardened contact surface in the cross section extending through an angle o between 160° and 300°, preferably between 170° and 270°, most preferably between 180° and 240°. By leaving a substantial part of the surface area of the link unhardened, the non-contact surface of the link can remain optimally flexible to prevent fatigue cracks from forming in the chain link surface.

[0012] The hardness of the body may be between 20 and 30 HRC, the hardness of the contact surfaces (25, 26) being between 50 and 54 HRC. By hardening the contact surfaces to a hardness of 50-54 HRC, the wear resistance is about doubled compared to the softer core material.

[0013] In an embodiment of a chain link, the central space has in a length direction a length L and in a width direction a width W, the length L being between 7 cm and 40 cm, the width W being between 2 cm and 12 cm, a cross-section of the body (2) having a diameter between 1.5 cm and 10 cm, the ratio of W / L being between 0.2 and 0.4, preferably about 0.3.

[0014] The chain link body may have a C-shape with an open area situated between opposing faces and a releasable closing member that is insertable with a locking section into the central space via the open area and having a contact part for rotation of the locking section and a transverse part engaging with the body near each of the opposing faces.

[0015] Reclosable chain links that are subject to varying loads and frequent coupling and uncoupling are provided with sufficient flexibility to have high strength whilst being effectively protected against wear along the relatively small contact areas by hardening.

[0016] The chain link may comprise 34 CrNiMo6 which results in a high tensile strength and high notch toughness, so that the link is particularly suited for handling dynamic loads.

[0017] The chain link may be comprised in an assembly of a cable connected to the chain link that in turn is connected to a grab for loading and unloading of bulk substance from a vessel or a container. The chain link may with one end be connected to the grab via a chain part or via a D link and have at its other end a chain or a rope pear socket.

[0018] A method of producing a chain link comprises:

[0019] - providing a C-shaped metal with an elongate central space extending along a central axis, the body comprising at short sides of the central space a curved contact surface for interacting with adjacent chain links, and - induction hardening of the body at the contact surfaces forming hardened areas having a hardness of 50-54 HRC through a depth DR that is smaller than a diameter D of a cross section of the body.

[0020] The method according to the disclosure may comprise placing a generally U-shaped coil having two arms and an open side around the short sides of the chain link body.

[0021] Brief Description of the Drawings

[0022] An embodiment of a chain link according to the disclosure is described in detail, by way of non-limiting example, with reference to the accompanying drawings. In the drawings:

[0023] Fig. 1 shows a cross-sectional view of a chain link according to the disclosure,

[0024] Fig. 2 shows a side view of a partly completed chain link, and

[0025] Fig. 3 shows a cross-sectional view of the chain link of fig. 2, in a plane that is perpendicular to the plane of the drawing of fig.2.

[0026] Detailed Description

[0027] Figure 1 shows a chain link 1 having a C-shaped metal body 2. The link has a central open space 3 with a length L along a central axis 34 and a width W. The link 1 has opposed faces 5, 6 bounding a passage 4 in which a closing member 7 is releasably inserted. When the closing member 7 is removed from the opening, the chain link 1 can be coupled to or released from a tool, such as a grab, via a chain part or a rope pear socket.

[0028] The closing member 7 comprises a cylindrical body 8 with flat faces 9. When the flat faces 9 are rotated in parallel with the faces 5, 6, the body 8 is of smaller width than the passage 4 so that the body 8 can be inserted into the central space 3 and locked in place by rotation. A lower journal 12 of the closing member 7 is inserted into a chamber 13 for alignment of the closing member.

[0029] A broadened head 15 of the closing member 7 engages with projections 16, 17 into recesses 18, 19 in the body 2 for securing the body 8 in a locked position and for taking up the tensile forces in the open C-shaped body 2 of the chain link 1. By compression of a spring 20, which in its expanded state keeps the cylindrical body 8 in a locked position, the body 8 can be brought into contact with a retaining member 21. Via the engaged retaining member 21, an operator can rotate the body 8 for rapid locking or release of the closing member 7.

[0030] Figure 2 shows a side view of a chain link 1 after forging and hardening. The chamber 13 and recesses 18, 19 that are shown in figure 1, still need to be formed. The chain link 1 has at the inner parts of its short sides 23, 24, hardened areas 25, 26. In the area’s 25, 26 the metal of the chain link 1 has been hardened to a hardness of 50-54 HRC up to a depth DR of 15% of the diameter D in the cross-section that is sown in figure 3. The hardening may be carried out by means of induction hardening, in which the surface of the steel link 1 is heated by inducing a magnetic field in the surface area, so that the temperature rises above the transformation temperature of the steel. The core material in the link is not hardened and retains its tensile properties at lower hardness values.

[0031] In an alternative embodiment, the surface area’s 25, 26 may be hardened by flame treatment or laser beam or electron beam treatment to heat the contact surface metal over the required depth, resulting in the required hardening and the increase in wear resistance.

[0032] As can be seen in figure 2, the bounding radii 29, 30 at the end points 27, 28 of the hardened areas 25, 26 on the inner surface 32 of the open space 3 include an angle a of + / - 45° relative to the direction of the pull force. The width Wh of the hardened contact areas 25, 26 along the central axis 34 is about 0.7 times the diameter D of the chain link 1.

[0033] As can be seen from figure 3, the hardened area 26 has a depth of hardening Dh extending from the inner surface 32, over a length of 15% of the diameter D of the cross-section, determined according to EN 10328. The hardened area 26 in the cross-sectional view of fig. 3 extends along the circumference of the chain hnk 1 through an angle 0 of just over 180 degrees. At the outer surface 33 of the chain link 1, the hardened area 26 is bounded by lines 35, 36 that include an angle Y of about 30 degrees.

[0034] In a hardening step, a generally U-shaped coil, having two arms and an open side, is placed around the short sides of the chain link body and an alternating magnetic field is induced in the metal near the surface of the body in the contact areas. Hereby the temperature of the metal is raised. After the heating step, the chain link body is cooled by applying a direct spray of water onto the body to cause hardening of the metal at and near the surface.

Claims

Claims1. Chain link (1) comprising a metal body (2) with an elongate central space (3) extending along a central axis (34), the body comprising at short sides (23, 24) of the central space a curved contact surface (25, 26) for interacting with adjacent chain links, the body (2) at the contact surfaces (25, 26) being of a greater hardness than the body outside the contact surfaces through a depth DR that is smaller than a diameter D of a cross section of the body (2),. the hardness of the body (2) being between 20 and 30 HRC, the hardness of the contact surfaces (25, 26) being between 50 and 54 HRC.

2. Chain link (1) according to claim 1, the body (2) being at the contact surfaces (25, 26) hardened to a depth DR that is between 5% and 25 %, preferably between 10% and 20%, most preferably about 15% of the diameter D.

3. Chain link (1) according to claim 1 or 2, wherein in a side view of the body (2), the radius of curvature (29, 30) of the contact surface (25, 26) at an outer position (27, 28) is at an angle no larger than 50°, preferably about 45° with the central axis (34).

4. Chain link (1) according to any of the preceding claims, the crosssection of the body (2) being substantially circular, the hardened contact surface (25, 26) in the cross section extending through an angle o between 160° and 300°, preferably between 170° and 270°, most preferably between 180° and 240°.

5. Chain link (1) according to any of the preceding claims, the central space (3) having in a length direction a length L and having in a width direction a width W, the length L being between 7 cm and 40 cm, the width W being between 2 cm and 12 cm, a cross-section of the body (2)having a diameter between 1.5 cm and 10 cm, the ratio of W / L being between 0.2 and 0.4, preferably about 0.3.

6. Chain link (1) according to any of the preceding claims, the body (2) having a C-shape with an open area (4) situated between opposing faces (5, 6) and a releasable closing member (7, 8) that is insertable with a locking section (8) into the central space (3) via the open area (4) and having a contact part (20, 21) for rotation of the locking section (8) and a transverse part (15) engaging with the body (2) near each of the opposing faces (5, 6).

7. Chain link (1) according to any of the preceding claims, the chain link comprising 34 CrNiMo6.

8. Assembly comprising a cable connected to a chain link (1) according to any of the preceding claims, the chain link connected to a grab for loading and unloading of bulk substance from a vessel or a container.

9. Method of producing a chain link (1) comprising:- providing a C-shaped metal body (2) with an elongate central space (3) extending along a central axis (34), the body comprising at short sides (23, 24) of the central space a curved contact surface (25, 26) for interacting with adjacent chain links, and- induction hardening of the body (2) at the contact surfaces (25, 26) forming hardened areas having a hardness of 50-54 HRC through a depth Dh that is smaller than a diameter D of a cross section of the body (2).

10. Method according to claim 9, the hardening at the contact surfaces (25, 26) being carried out to a depth of between 5% and 25 %, preferably between 10% and 20%, most preferably about 15% of a diameter D of a cross section of the body (2) in a plane of the length direction.

11. Method according to claim 9 or 10, comprising placing a generally U-shaped coil having two arms and an open side around the short sides of the chain link body.

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