A SEALING AND TENSION-RELIEVING SCREW FITTING FOR CABLES

Abstract: A sealing and tension-relieving screw fitting for leading electric cables through the casing or housing of electrical apparatus, the screw fitting comprising a sleeve (1) which is connected at one end to the casing and the other end of which presents a lead-through opening which can be adjusted through the agency of a chuck-like arrangement, in a manner to accommodate the cable. Arranged within the sleeve (1) is a sealing sleeve (8) which is constructed so as to seal against both the sleeve (1) and against cables having a diameter which lies with a given diameter range for which the screw fitting is intended, irrespective of the extent to which the chuck arrangement is tightened.

Description: A sealing and tension-relieving screw fitting for cables TECHNICAL FIELD The present invention relates to a sealing and tension- -relieving -screw fitting intended for leading electric " cables through the casings of divers electrical appara¬ tus. The screw fitting, which is of the so-called chuck kind, incorporates a sleeve having provided on one end part thereof a first external screw thread by means of which the screw fitting is attached to the apparatus casing or like component The screw fitting further in¬ corporates a barrel or gland nut which partially embra¬ ces the sleeve and which is screwed onto a second screw thread provided externally on the sleeve. The barrel or gland nut has provided internally thereof a funnel shaped part which lies in abutment with finger-like elements arranged on the other end of the sleeve, these finger- -like elements being pressed against and into gripping contact with a cable drawn through the screw fitting, when the gland nut is screwed onto the sleeve. BACKGROUND PRIOR ART The requirements placed on bushings and like lead-throughs intended for leading electric cables through the casings or housings of electrical apparatus vary in dependence on, inter alia, the construction and function of the appa- ratus in question and the environment in which it is used. In some cases it suffices to protect the cable against direct contact with the apparatus casing or housing, whereas in other cases it is necessary to ensure that the bushing is waterproof. It is also necessary in some cases to relieve the cable of tensile loads acting there¬ on. A conventional and much used bushing is one which comprises a sleeve having provided on one end thereof an external screw thread by means of which the bushing can be attached to a casing or housing, and in which the other end of the sleeve accommodates internally a sleeve-like nut which is operative in pressing a rubber seal against a seating, this rubber seal being intended to be pressed against a cable drawn through the bushing, when the nut is screwed into the sleeve. Provided that the size of the cable coincides generally with the size of the hole pro¬ vided in the rubber seal, the seal will abut tightly against the cable in a sealing fashion, while at the same time relieving the tensile load on the cable to some extent. When a higher tension-relieving facility is required, the nut is usually provided with an extension which co-acts with a locking means to this end, the cable being clamped firmly to the nut extension upon co-action of the nut with the locking means. One drawback with bushing of this kind is that the seals used must be of the correct size, and that the nut must be screwed tight with the aid of a suitable tool, in order to obtain a satisfactory seal. In tightening the nut fully, it is possible that the position taken by the nut is such as to make it virtually impossible to mani¬ pulate the locking means . In addition in those cases where an apparatus casing or housing is fitted with a plurality of cable bushings, the bushings are normally located very close together, making it difficult and time- -consuming to fit a nut with the aid of a tool. This often results in inefficient sealing of the bushings. Bushings of the so-called chuck-type have also been developed. These bushings comprise an outer barrel or gland nut which embraces the bushing sleeve and which is provided with an internal funnel-shaped part which abuts finger- -like elements extending axially from one end of the sleeve and surrounding a tubular rubber seal, this seal being pressed against a cable drawn through the bushing, when the barrel or gland nut is screwed onto the sleeve. Such bushings can only be used effectively with cables over a small range of diameters and, furthermore, the barrel or gland nut must be screwed very tight. in order to afford a satisfactory seal and to satisfactorily re¬ lieve the cable of tensile load. DISCLOSURE OF THE INVENTION The object of the present invention is to provide a bush¬ ing which is not encumbered with the aforesaid drawbacks, i.e. a bushing with which the size of the seal need not be adapted to individual cables, but which will provide an effective seal in respect of cables lying within a wide range of diameters, irrespective of the extent to which the nut is tightened. A further object is to pro¬ vide a readily fitted screw fitting which can be tighte¬ ned by hand to the extent required, without needing to use a tool herefor. These objects are achieved in accor¬ dance with the present invention by means of a resilient sealing sleeve, or constricted nipple, which is arranged in the bushing sleeve in sealing engagement with the inner surface thereof, and which is so formed as to pro- vide a fully adequate seal against cables extending through the screw fitting and having a diameter which lies within the diameter range for which the fitting is intended, irrespective of the extent to which the barrel or gland nut has been tightened. BRIEF DESCRIPTION OF THE DRAWINGS An exemplifying embodiment of the invention will now be described in more detail with reference to the accompany¬ ing drawing, in which Figure 1 is an axial sectional view of a bushing and Figure 2 is an exploded, perspective view of a bushing. DESCRIPTION OF A PREFERRED EMBODIMENT In Figure 1, which is an axial sectional view of the bushing, the reference 1 identifies a sleeve having pro¬ vided on one end thereof an external screw-thread 2 , by means of which the bushing is screwed onto an apparatus casing or housing, not shown. The sleeve 1 is partially embraced by a barrel or gland nut 3 having an internal screw-thread 4 which engages a further screw-thread 5 provided externally on the sleeve 1. The barrel nut 3, the outer surface of which is serrated, includes an in¬ ternal, funnel-shaped part 6 which abuts against finger- -like elements 7 arranged in the other end part of the sleeve 1. When the barrel nut is screwed onto the sleeve, the free ends of the finger-like elements 7 are intended to be pressed against and in gripping engagement with a cabel (not shown) drawn through the bushing. Located within the sleeve 1 is a sealing sleeve 8, or constric¬ ted nipple, which incorporates a funnel-shaped part 11 surrounded by a substantially cylindrical tubular part 9 which sealingly abuts against the inner surface of the sleeve and against a shoulder 10 provided on the sleeve wall. When the barrel nut 3 is screwed onto the sleeve, the finger-like elements 7 bend over the edge of the sealing sleeve 8, and press the sealing sleeve against the shoul¬ der 10, the sleeve thus lying against the shoulder under pressure. The references used in Figure 2, which is an exploded view of the bushing, are the same as those used in Figu- re 1 to identify similar components. It will be seen from Figure 2 that the bushing comprises a substantially hexagonal part 12, which facilitates the attachment of the bushing to the casing or housing of a piece of appa¬ ratus. Because the sealing function of the bushing has been se¬ parated from its tension-relieving function, and as a re¬ sult of the construction of the sealing sleeve and its locked positioning in the sleeve, a good seal will always be obtained between the cable and the bushing, irrespec¬ tive of whether the nut is tight or not. This is an im¬ portant step forward in the art, since experience has shown that a significant number of conventional bushings do not provide the desired sealing effect when fitted, due to both forgetfullness on the part of the workman and to the difficulty in reaching the barrel or gland nut with a spanner to tighten the same. Since when scre¬ wing the barrel nut onto the sleeve of the illustrated bushing no seal or like element is deformed, the cable can be locked by simply screwing on the barrel nut by hand, without the aid of a tool. Additionally, because of its particular construction, the bushing can be used in conjuction with electric canles lying within a dia¬ meter range in which the ratio between the smallest and the largest diameter encompassed thereby is 1 to 3. This means that one and the same bushing can be used in con¬ nection with cables ranging, for example, from 5-15mm in diameter. This greatly reduces the number of diffe¬ rent sized bushings which need be held in store, while at the same time completely eliminating the need to pro¬ vide rubber seals adapted to the individual diameters of the cables in question.

Claims: AMENDED CLAIMS [received by the International Bureau on 18 February 1986 (18.02. 86) ; original claims 1 * replaced by new claims 1 -4 (2 pages)] 1. A sealing and tension-relieving screw fitting through which electrical cables can be lead to the casing of electrical apparatus of various kinds, the screw fitting comprising a sleeve (1) having provided on one end part thereof an external screw-thread (2) for connection of the sleeve to the casing or like part of a piece of appa¬ ratus, and further comprising a barrel or gland nut (3) which partially embraces the sleeve (1) and is in screw- -thread engagement with a further screw-thread (5) pro- vided externally on the sleeve, and which barrel or gland nut (3) presents an internal funnel-shaped part (6) which abuts finger-like elements (7) arranged on the other end part of the sleeve, these finger-like elements, upon screwing the barrel or gland nut (3) to the sleeve (1) , being pressed against and into gripping engagement with a cable drawn through the screw fitting, c h a r a c ¬ t e r i z e d by an elastic sealing sleeve (8) located in the sleeve (1) and in sealing contact with the inner surface of said sleeve, said sealing sleeve being so constructed as to provide a satisfactory seal against cables passed through the screw fitting and having a dia¬ meter lying within a range of cabel sizes for which the screw fitting is intended, irrespective of the extent to which the barrel or gland nut tightened on the sleeve (1) . 2. A screw fitting according to Claim 1, c h a r a c¬ t e r i z e d in that the sealing sleeve (8) includes a funnel-shaped part (11) which is surrounded by a sub¬ stantially cylindrical tubular part (9) . 3. A screw fitting according to Claim 1 and 2, c h a- r a c t e r i z e d in that the sealing sleeve (8) abuts a shoulder (10) provided internally in the sleeve, via a first edge surface of the tubular part (9) . 4. A screw fitting according to Claim 3, c h a r a c -> • t e r i z e d in that when screwing the barrel or gland nut (3) onto the sleeve, the finger-like elements bend over a second edge surface (12) presented by the tubular > part (9) of the sealing sleeve (8), and therewith cause the first edge surface of the tubular part to abut the shoulder (10) under pressure.

Inventors: KARDEFELDT BJOERN, MELIN LARS MAGNUS, KARDEFELDT, BJOERN, MELIN, LARS, MAGNUS
Applicants: THORSMAN & CO AB
Application year: 1985
Main classification: H02G15
IPC codes: H01B17, H02G3, H05K7