Seat base for office chair

Abstract

A plastic seat base 2 for use in an office chair includes a metal connecting element 20 for connecting a pedestal 8 to the seat base. The connecting element includes an internal socket shaped to recei

Description

Field of the Invention The invention relates to a plastic seat base for use in an office chair, the seat base located between the pedestal column and the seating portion of the chair, and in particular to a seat base comprising a metal connecting element for connection of the pedestal column to the seat base. Background of the Invention Office chairs typically comprise a base provided with wheels, a rotatable column, and a seat portion and back rest mounted on the rotatable column. The rotatable column typically comprises a gas lift cylinder which allows for height adjustment of the chair. The top part of the gas lift cylinder has a conical or tapered end which is designed to fit snugly into a corresponding socket on the underside of the seat portion. This socket is usually reinforced with a metal insert to provide extra durability. An example of such a connection is described in EP2421408. In this example, the socket on the underside of the seat portion has a truncated cone shape and is provided with a flange. The socket is formed by cold-pressing a portion of sheet metal. This socket component is then co-moulded with the plastic seat base to join the two parts together. Holes in the flange enable a more effective grip between the two parts during injection moulding. A problem with this arrangement occurs at the end of the life of the chair, when it is very difficult to remove the metal component from the plastic base, meaning that neither part can be easily recycled. It would be advantageous to provide a connecting element for an office chair which is more easily separated from the seat base, allowing for easier recycling of the various parts. Summary of the Invention According to an aspect of the invention there is provided a plastic seat base for use in an office chair, the seat base including a metal connecting element for connecting a pedestal to the seat base, wherein the connecting element includes an internal socket shaped to receive an end of a pedestal and an external surface which is provided with a thread, and wherein the thread of the connecting element is embedded in the plastic of the seat base, and wherein the connecting element further comprises means for connection to a tool for applying a torque force to the connecting element in order to remove the connecting element from the seat base. The internal socket of the connecting element may have a tapered shape. The internal socket of the connecting element may have a smooth inner surface. The end of the pedestal is preferably a friction fit, or push fit into the socket of the connecting element. The pedestal preferably comprises a gas lift cylinder, allowing for the height of the office chair to be altered. The thread on the external surface of the connecting element may be a continuous thread, or it may be a discontinuous thread. The thread may be right-handed or left handed. The means for connection to a tool may comprise any means of transmitting a torque force from the tool to the connecting element. The means for connection to a tool may comprise a plurality of castellations. According to a further aspect of the invention, there is provided a metal connecting element for connecting a pedestal to a seat base forming part of an office chair, the connecting element including an internal socket shaped to receive an end of a pedestal, and an external surface which is provided with a thread, wherein the internal socket has a tapered shape and the connecting element further comprises means for connection to a tool for applying a torque force to the connecting element. According to a further aspect of the invention, there is provided a method of making a seat base for an office chair comprising the steps of: (a) providing a metal connecting element, wherein the connecting element includes an internal socket shaped to receive an end of a pedestal and an external surface which is provided with a thread; (b) inserting said connecting element into a mould shaped to replicate the form of the seat base; (c) injecting plastic material into the mould so as to incorporate the external surface of the connecting element into the plastic material; and (d) removing the co-moulded seat base and connecting element from the mould. According to a further aspect of the invention, there is provided a method for removing a connecting element from a plastic seat base as hereinbefore defined, the method comprising the steps of: (a) providing a tool for exerting a torque force on a connecting element; (b) connecting the tool to the connecting element to form a static connection between the tool and the connecting element; (c) applying a torque force to the connecting and tool in the direction of the thread on the connecting element; and (d) removing the connecting element from the plastic seat base. The metal connecting member of the invention is easily separated from a plastic seat base, allowing for separate recycling of each part. In each aspect of the invention the plastic material may be nylon (polyamide). Brief Description of the Drawings In the Drawings, which illustrate preferred examples of the invention: Figure 1 is a side view of a chair provided with a base support according to the invention; Figure 2 is an exploded perspective view of the base support of Figure 1; Figure 3a and 3b show an underneath perspective view of two different embodiments of a connecting element forming part of the base support of Figure 1; Figure 4a is a longitudinal cross-section through the base support of Figure 1 at the connecting element, and Figure 4b is an enlarged view of the part circled in Figure 4a; Figure 5 is an exploded perspective view of the base support, connecting element, and removal tool; and Figure 6 is a longitudinal cross section through the base support, connecting element, and removal tool. Detailed Description of the Preferred Embodiments Figure 1 illustrates an office chair 2 which includes a base support 2 connected to the underside of the seating portion 4 of the chair. The base support 2 includes a socket 6 for receiving the upper end of a gas strut 8. The gas strut allows a user of the chair to adjust the height of the seat, typically using a lever 10 located underneath the seat. The gas strut 8 is connected to a chair base 12 comprising a plurality of legs 14, with wheels or casters 16 attached to the ends of the legs. The base support 2 also connects to an arm assembly 20, and to the back rest 18 of the chair via a connecting arm 19. The base support is formed of plastic (typically nylon), using an injecting moulding technique. The socket 6 for receiving the end of the gas strut includes a connecting element 20 which is co-moulded with the base support, as shown in Figure 2 and 3. The connecting element is formed of metal and is hollow. Preferably, the internal hollow of the connecting element has a truncated cone shape, such that the diameter (DI) of the uppermost end is smaller than the diameter (D2) of the lower end, as shown best in Figure 4b. The external surface of the connecting element is provided with a plurality of ridges 22 arranged in the form of a thread. The thread may be a continuous spiral (as shown in Figure 3a) or it may be a discontinuous thread (as shown in Figure 3b), with gaps 23 between the ridges 22. The internal surface 24 of the connecting element may be smooth and the upper end 8a of the gas-strut is a push fit, or friction fit into the centre hollow 26 of the connecting element 20, 20’, as illustrated in Figure 5. The two parts have corresponding shapes to allow the connecting element to engage with the upper end of the gas-strut. Figure 4 illustrates the co-moulded base support 2 and connecting element 20, showing a longitudinal cross-section through the connecting element. To form the base support the connecting element is placed in a mould, then plastic is injected into the mould to form the base support. The ridges 22 forming the external thread enable an effective grip on the connecting element to be made by the plastic material during the injection moulding process. A discontinuous thread may allow a better grip of the plastic onto the metal connecting element since the plastic occupying the gap 23 formed by the discontinuity in the thread must be fractured for the base support 22 to rotate relative to the connecting element 20. As shown in Figure 4, the plastic of the base support surrounds the external surface of the connecting element 20. When the office chair is ready to be recycled the end gas strut is removed from the connecting element and a removal tool is then used to remove the metal connecting element 20 from the plastic base support. As shown in the Figures, the connecting element 20, 20’ includes a plurality of castellations 28 located towards the lower edge of the inner surface. The castellations 28 are designed to engage with a removal tool 30 which is illustrated in Figure 6. In the illustrated example, the removal tool 30 includes a substantially cylindrical part 33 which fits into the central hollow of the connecting element 20 once the end of the gas strut has been removed. The removal tool 30 also includes a plurality of protrusions 32 which are shaped and dimensioned to mate with the castellations 28 on the lower end of the connecting element. An aperture 34 on the opposite side of the tool 30 allows for the connection of a tool for providing torque, such as a lever bar 36. The removal tool 30 is inserted into the connecting element 20 such that the protrusions 32 on the removal tool 30 mate with the castellations 28 on the connecting element 20, providing a static connection between the two parts. A tool such as a lever bar 36 is then inserted into the aperture 34 on the removal tool and a torque force is applied to remove the connecting element 20 from the base portion 2 whilst reacting the force on the base portion 2, for example by holding it still, or clamping in a vice. Since the ridges 22 are in the form of a thread, the connecting element 20 can be removed by ‘unscrewing’ it from the base support 2. If the thread is a right-handed thread, then torque is applied in an anticlockwise direction to remove the connecting element. Likewise, if the thread is left-handed, then torque is applied in a clock-wise direction to remove the connecting element 20 from the plastic base support 2. The metal connecting element 20 is therefore easily removed from the plastic base support 2, allowing recycling of both parts. Where the connecting element 20 has a discontinuous thread, the plastic filling the gaps 23 in-between the ridges 22 forming the thread is fractured by turning the lever bar.

Claims

1. A plastic seat base for use in an office chair, the seat base including a metal connecting element for connecting a pedestal to the seat base, wherein the connecting element includes an internal socket shaped to receive an end of a pedestal and an external surface which is provided with a thread, and wherein the thread of the connecting element is embedded in the plastic of the seat base, and wherein the connecting element comprises means for connection to a tool for applying a torque force to the connecting element in order to remove the connecting element from the seat base.

2. A plastic seat base for use in an office chair according to Claim 1, wherein the internal socket of the connecting element has a tapered shape.

3. A plastic seat base for use in an office chair according to any preceding claim, wherein the external surface of the connecting element is provided with a continuous thread or a discontinuous thread.

4. A plastic seat base for use in an office chair according to any preceding claim wherein the means for connection to a tool to the connecting element comprises a plurality of castellations.

5. A metal connecting element for connecting a pedestal to a seat base forming part of an office chair, the connecting element including an internal socket shaped to receive an end of a pedestal, and an external surface which is provided with a thread, wherein the internal socket is shaped to receive an end of a pedestal and is adapted to form a static connection between the connecting element and a pedestal and wherein the connecting element comprises means for connection to a tool for applying a torque force to the connecting element.

6. A metal connecting element according to Claim 5, wherein the internal socked has a tapered shape.

7. A metal connecting element according to Claim 5 or 6, wherein the external surface is provided with a continuous thread or a discontinuous thread.

8. A connecting element according to any of claims 5 to 7, wherein the means for connection to a removal tool comprises means for connection to a tool comprises a plurality of castellations.

9. A method of making a seat base for an office chair comprising the steps of:(a) providing a metal connecting element, wherein the connecting element includes an internal socket shaped to receive an end of a pedestal and an external surface which is provided with a thread;(b) inserting said connecting element into a mould shaped to replicate the form of the seat base;(c) injecting plastic material into the mould so as to incorporate the external surface of the connecting element into the plastic material; and(d) removing the co-moulded seat base and connecting element from the mould.

10. A method of removing a connecting element from a plastic seat base according to claims 1 to 4, the method comprising the steps of:(a) providing a tool for exerting a torque force on a connecting element;(b) connecting the tool to the connecting element to form a static connectionbetween the tool and the connecting element;(c) applying a torque force to the connecting and tool in the direction of the thread on the connecting element and reacting the force on the plastic seat base; and(d) removing the connecting element from the plastic seat base.

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