GB2370872A - Reinforcements to windshafts - Google Patents

Abstract

A reinforcing tube 1 is inserted into the hollow core of a windshaft 2 and anchored 7,8 and 9 at each end. The tube is preferably tensioned to provide a degree of precompression in the windshaft. Alternative forms of anchors may be used. The ends of the tube may be fitted with closing and bearing devices 10, 11 and 12 to support the striking rod 5 which passes through the windshaft and provide weathertight seals and means of lubricating the striking rod. The device may be applied to existing hollow windshafts of whatever construction, or to new constructions. An extension tube (15, fig 4) may be used to locate the stocks for the windmill sails when a poll end canister is used. The tube may be replaced by a solid bar if a striking rod is not required.

Description

SAFETY IMPROVEMENTS TO THE WINDSHAFTS OF TRADITIONAL WINDMILLS This invention relates to an economic method for reinforcing the windshafts of traditional windmills to improve their safety against breaking, and to contain any damage should they fail.

Such windshafts are normally made in cast iron, or occasionally in wood with cast iron poll ends. They are the primary rotating drive shaft of traditional windmills and also the supports for the sails, but suffer a number of disadvantages: They are single line components in critical situations and in the event of breakage the sails of the mill may collapse and fall to the ground; Many windshafts in use are over 100 years old; It is very difficult to check the condition and quality of the cast iron from which they are made, and breakages have occurred with severe consequential damage; It is usually impossible to demonstrate that old windshafts can support loads from severe winds as required by modem codes of practice relating to the design of buildings and structures. However it is not desirable to replace them with new or modem materials as apart from the high cost, doing so would upset the historic context and be unacceptable to statutory conservation bodies.

An object of the invention is to strengthen the windshaft as far as practicably possible, and thereafter to limit any damage caused in the event of a fracture occurring. A further objective is to avoid altering the visual appearance of the original structure, in order to be acceptable on heritage grounds.

The reinforcement could also be used with advantage in new windshafts for added security. Other features may prevent water ingress, facilitate lubrication, reduce maintenance costs and lengthen the life of the windshaft.

Accordingly the invention makes use of the hole that exists through the centre of most windshafts which is normally provided to carry a striking rod, part of the mechanism for operating the sails of the mill. This hole in an existing windshaft may require to be cleared of products of corrosion or even partly bored to enlarge it sufficiently it to pass the reinforcing tube. The reinforcing tube or bar is passed through the central hole and tensioned from one or both ends in order to provide a small compressive prestress in the windshaft. The tension may be applied by turning the screwed end nuts, or be applied by hydraulic or other jack. The end anchorages may be screwed, swaged or wedged.

The small prestress will make the windshaft more resilient and reduce the amount of stress reversal in the shaft, thus reducing the risk of failure. However for practical reasons the size of the tube or bar that can be provided within existing windshafts is limited and is unlikely to be sufficient to entirely eliminate the possibility of failure in the most adverse conditions. In such a catastrophic case, should the shaft fail, the reinforcing tube or bar will yield a little and hold the sections together, thus minimising secondary damage to other parts of the mill and to persons or property on adjacent ground.

The striking rod (where required) will now pass through the centre of the reinforcing tube. Because of the better support from the tube to the striking rod the size of the rod can be effectively reduced. Where a striking rod is not required, the reinforcement may be a solid bar.

The details vary depending on the system existing for connecting the sails, most commonly comprising a'cross'or a'poll end'. The number of sails is immaterial.

Provision can be made for excluding water from the bore of the windshaft, a significant problem in traditional mills, and for lubricating the bore to ease movement of the striking rod and prevent corrosion. The striking rod could with advantage be made of stainless steel to prevent corrosion, particularly at the exposed outer end.

The size of the reinforcing tube or bar and its metallurgical properties are carefully selected for each individual installation, after engineering calculations have been undertaken. The tube or bar will be pretensioned by a carefully calculated amount.

Preferred embodiments will now be described with reference to the attached drawings comprising 8 figures on 4 sheets, which because of the wide variety of windshafts existing in practice are typical only to illustrate the principles, and in which: FIGURE 1 shows the location of the windshaft in relation to a typical traditional windmill.

FIGURE 2 shows in long section the arrangement of the reinforcement to the simplest form of windshaft wherein the sails (of whatever material) are fastened to a cross at the head end of the shaft.

FIGURE 3 shows a typical section through the reinforced windshaft FIGURE 4 shows the arrangement of reinforcement in a windshaft having a poll end or canister FIGURE 5 shows an example of the application of the tube to a hybrid windshaft where the poll end has been modified by the insertion of a steel cross.

FIGURES 6, 7 and 8 show details, partly in elevation and partly in section, of the main reinforcing tube As shown in Figure 1, the windshaft (2) is a key component of the windmill supporting the sails (16). Where remotely controlled, the shutters in the sails are operated by the striking rod (5) which passes through the centre of the windshaft.

The reinforcing tube (1) is inserted in the annular space between the windshaft and the striking rod, as shown in cross section in Figure 3.

Figures 2, 4 and 5 show the different arrangements of the reinforcing tube (1). For windshafts with a cross (3) it is as shown in Figure 2 or with a poll end canister (4) as shown in Figure 4. The hybrid arrangement shown in figure 5 is an example where the poll end has been converted to a cross.

Figure 2 shows that in the simplest arrangement the reinforcing tube is anchored at each end by an arrangement of bearing plate (7), screwed nut (8) and locknut (9).

The nuts may be square, hexagonal, or a serrated round ring form fastened with a'C' type spanner. Alternatively, a swaged or wedged anchorage could be used.

Tension may be applied by screwing or by use of a hydraulic jacking device. At the outer head end the tube is sealed with an end cap (10), which encloses a sealing support ring (11) and also has a greasing point (12). Grease holes and grooves are provided through the tube to spread the lubricant. A similar end cap arrangement may also be used at the tail end.

Figure 4 shows the arrangement when a poll end canister (4) is used. In this case the head end anchorage of the reinforcing tube has to be recessed to enable the stock of the sails (16) to be inserted into the canister. In this case a wedge anchorage is used, comprising an outer shell (17) and an inner shell (18) which is split to permit assembly and tightening. The tube is grooved and the inner shell ridged to match to provide a positive grip between them. The tail end anchorage may be screwed, swaged or wedged as previously described.

With the poll end canister shown in figure 4 an extension tube (15) may be used to extend the reinforcing tube (1) to the outer face of the canister (4). The extension tube is screwed into the end of the reinforcing tube after the installation of the sail stocks, and also acts as a locating pin for the stocks. At the outer end a thin nut (13) is screwed on and lightly tightened against a compressible washer (14). The end is sealed with an end cap, sealing support ring and lubrication point (10, 11 and 12) as before.

Figure 5 shows an example where the cross (3) has been inserted into the poll end (4) to support the sails (16). The reinforcing tube (1) is extended beyond the head anchorage and through to the outside face of the poll end (4). It is fitted with a thin nut (13) and with an end cap, seal and lubrication point (10, 11 and 12). Enlarged key details are shown in figures 6, 7 and 8. Figure 5 also shows that the windshaft (2), which is shown in solid section in this figure, may be jointed along its length, as at position (19).

Claims (12)

1. CLAIMS 1 A tube inserted into a hollow windshaft of a windmill and anchored at each end, which may be tensioned so as to precompress the windshaft, the amount of tension being predetermined to suit the application.
2. 2 As claim 1 but with a solid bar in place of a tube.
3. 3 As claims 1 and 2 with anchors which may be screwed, wedged or swaged, or any combination of these.
4. 4 As claims 1 to 3 wherein one or both anchors is or are wholly or partially inserted into the end or ends of the windshaft.
5. 5 As claim 1, 3 or 4 wherein an extension tube is jointed to the end of the tube or to its anchor.
6. 6 As claim 5 wherein the extension tube forms a locating and securing device for the sails stocks of the mill where a poll end canister is used.
7. 7 As claim 1 and 3 to 6 wherein closing pieces are fitted to the end of the tube to seal against water ingress and to facilitate lubrication of a striking rod.
8. 8 A tube to provide effective support to a striking rod to permit a reduction in size of the striking rod.
9. 9 A tube or bar which may be made of steel, high tensile plastics or composites.
10. 10 A tube which may be used with a windshaft of any material or combination of materials.
11. 11 A tube which will provide support and/or strengthen any joints in the windshaft.
12. 12 A tube substantially as herein described and illustrated in the accompanying drawings.