ARRANGEMENT IN A HOISTING DEVICE, ESPECIALLY FOR A DERRICK

ARRANGEMENT IN A HOISTING DEVICE, ESPECIALLY FOR A DERRICK.

The present invention relates to an arrangment in a hoist¬ ing device, especially for a derrick comprising two parallel vertical derrick components, each of which carries a rack rail along which the hoisting device can move vertically by means of a respective driving means provided for each derrick component and via toothed wheels engaging the rack rails, the hoisting means comprising a transverse supporting member extending between said two driving means.

In such hoisting devices, the transverse supporting member will be loaded with heavy weights suspended therefrom, for example the weight represented by a drilling string.

If one of the gear transmissions should jam during the lowering of the hoisting device including such large loads, the overall hoisting device including rack rails and the main structure would have a- breakdown.

The object of the present invention is therefore to provide a device of the type mentioned in the preamble, which reduces the risk of breakdown upon unbalanced load¬ ing, there also being aimed for a system which supervise the various variations of loadings during a drilling ope¬ ration.

According to the invention the object is achieved in that the transverse supporting member in the area of each driv¬ ing means comprises a rotatable bearing which at abnormal unbalanced loadings on the two driving means allows a re¬ latively largely slanted position of the supporting member, and that the supporting member in the area of one of the driving means also comprises a bracing means which during normal parallel operation of the driving means stiffens the supporting member, but which during abnormal operati¬ on is made to collapse to allow a slanted position of the transverse supporting member. Preferably the bracing means will have a connection to a load measuring device which supervises the loadings on the bracing means, and which when a given load is exceed¬ ed actuates the mechanical brakes for the driving means.

If the driving means should still be moving after the engagement of the mechanical brakes, the bracing means would be loaded so heavily that it will break , a fact which involves that the transverse supporting member no longer represents a rigid structure, but an articulated connection allowing for a certain difference in level be¬ tween the driving means without involving any breakdown of hoisting machinery including rack rails and main structure.

Further features and advantages of the present invention will appear from the patent claims, and will in the fol¬ lowing be further discussed in connection with the attached drawings illustrating an embodiment of the present arrangement.

Figure 1 illustrates perspectively a derrick stucture in¬ cluding associated equipment, installed on a platform.

Figure 2 is a view at a larger scale of an embodiment of the device according to the invention.

In Figure 1 there is illustrated a derrick structure which is generally designated by reference numeral 1, and which comprises an upper traverse 2 and two parallel derrick components 3 and 4, respectively, which together with the traverse 2 define a space 5 for accomodating a ver¬ tically movable hoisting device 6, which is further illu- stated in Figure 2.

The hydraulic hoisting device 6 comprises for example four hydraulic motors 7, each of which via a transmis¬ sion gear 8 drives its own gear wheel 9, which in turn is in engagement with rack rails 10 mounted along the derrick components 3 and 4, respectively.

The braking of the hydraulic hoisting device 6 takes place by means of for example mechanical brakes, which are adap¬ ted to be activated automatically if the hydraulic pres¬ sure should disappear. The shafts of the gear wheels 8 and 9 can be supported in ball bearings and work prefer¬ ably in a closed oil bath.

10

In Figure 2 there are also illustrated guiding wheels 11 cooperating with the rack rails 10 for horizontal guid¬ ance of the hoisting device 6.

Figure 1 also illustrates a control desk 14 provided in

15 a control room 22, as well as a drilling string 15 which at its upper end is connected to a drilling machine 18, and which at the other end extands down into a drilling center 19. The drilling machine 18 is mounted on a

20 transverse supporting member 23 extanding between the two driving means 6a and 6b included in the hoisting de¬ vice 6. Further, the derrick comprises a pipe handling apparatus 20 for handling pipe lengths 21. Reference numeral 25 refers to guiding and connection means between «c the drilling and hoisting machinery.

The transverse supporting member 18 is in the area of each driving means 6a and 6b, respectively, pivotably supported, i.e. in the area of the driving means 6a by

3_Q means of a first pivoting means 30 rendering a single pivoting point, whereas in the area of the second driv¬ ing means 6b it is pivotably supported by means of a second pivoting means 31 comprising two pivoting points 31a and 31b connected by means of a link 33. Without any brac- 5 ing, the transverse supporting member 18 will thus take a slanted position relative to the horizontal if the two driving means 6a and 6b should be displaced unevenly relative to each other. However, in the area of the driving means 6a, there is provided a bracing means 34 which during normal parallel operation 'of the driving means 6a, 6b will stiffen the supporting member 18, but which during irregular operation is brougth to collapse for there- by allowing a slanted position of the supporting member 18.

The bracing means 34 is appropriately connected to a mea¬ suring means 35 which for example can be provided in the area of the bracing means 34, and which when a certain loading is exceeded, activates the mechanical brakes of the driving means 6a and 6b.

Preferably, the bracing means 34 may comprise a shear pin extanding from the housing of the first driving means, here driving means 6a, and to the supporting member 18, said shear pin at its one end being connected to a shear tap 34a.

When the hoisting device 6 is running up and down between the derrick components 3 and 4, the supporting member 18 will have large weigths suspending therefrom, for example weigths corresponding to a drilling string. During normal operation the hoisting means 6a and 6b will travel along the two pairs of rack rails 10 which are mounted 5 meters apart, and it is especially important that the driving means 6a and 6b follow each other and are given approxima¬ tely equal loading during lowering and raising operations. Such a rack rail hoisting device can especially during lowering of the hoisting device including large loads, be subjected to wedging of one of the gear transmissions, which involves a risk for breakdown of the overall hoist¬ ing device including rack rails and main structure.

Since the transverse supporting member 18 has been pro- vided with articulated connections 30 and 31 as well a bracing means 34 cooperating with a measuring means, the risk of breakdown will be reduced to a remarkable degree. During normal operation the measuring means will register any skew loadings and actuate all the mechanical brakes of the hydraulic motors if the loadings should exceed a certain limit. In case the brakes operate unevenly, such that the driving means 6a and 6b are displaced relative to each other as regards a horizontal level, the shear tap 34a will be torn offand thereby allow that the trans¬ verse supporting member 18 can take an inclined position for thereby avoiding unnecessary loading on the gear transmissions and rack rails. It is possible for the supporting member to take this inclined position be- cause the pivotable bearing arrangement 31 including two pivoting points allows a displacement of the first end point of the supporting member away from the area of a normal vertical line 36 through the two said pivo¬ ting points.

The use of the shear tap 34a involves that breakdown can be avoided during irregular operation, and the shear tap also contributes to a stiff structure during normal ope¬ ration, such that the driving means including their hydraulic motors always will run in parallel along the two rack rail paths•