Electricity: conductors and insulators – Conduits – cables or conductors – Conductive armor or sheath
Reexamination Certificate
1999-12-03
2001-07-03
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Conduits, cables or conductors
Conductive armor or sheath
C174S1020SP
Reexamination Certificate
active
06255591
ABSTRACT:
BACKGROUND OF THE INVENTION
Electric cables often are installed in hazardous or corrosive environments. Such cables employ a core of circular diameter which is covered by an external metallic sheath used as a protective member. These sheaths provide an impervious metallic envelope capable of preventing entry of humidity and resisting corrosion caused for example by moisture, acids, gases and the like. Conventionally, such sheaths are formed from aluminum or aluminum-manganese alloys. These sheaths form a protective envelope. The thickness of the sheath depends in part upon the size of the core diameter and increases with increasing size.
The installation of the sheath about the core utilizes strips of aluminum metals or alloys which are formed around outer surface of the core of the cable and then are longitudinally welded and corrugated.
However, cables utilizing metallic sheaths, as for example heavy power cables, are normally manufactured in long lengths and are wound on reels. For cores of larger diameter employing thicker sheaths, the weight of the upper layers of sheathed cables causes the upper layers to crush downward against the lower cable layers, often causing some deformation of the sheath and core in the lower cable layers. This deformation creates problems in subsequent manufacturing steps such as jacket extrusion, cable termination and also in final installation in cable ducts. In addition, the cost of the sheath material increases substantially as the sheath thickness is increased.
The present invention is directed toward a metallic sheath which retains sufficient crush resistance to overcome the deformation problem while at the same time exhibiting a reduction in the sheath thickness which provides substantial reduction in the amount and cost of sheath material.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a known metallic alloy never previously used as a protective sheath for the cores of electric cables which when used as a sheath has sufficient strength to prevent deformation during processing and sufficient reduction in sheath thickness to produce a substantial reduction in cost of the sheath.
These and other objects and advantages of the invention will either be explained or will become apparent hereinafter.
The mechanical strength of a cable sheath is determined by a so-called “crush test” in which an empty metallic sheath in the form of a hollow tube is mounted between two platens and subjected to compression until the sheath collapses. It has been determined experimentally that in order to avoid undesirable deformation of the sheath when a sheathed cable is wound on a reel, the maximum acceptable deformation of the sheath should be limited to about 5% of the outer diameter under a compression force of 1000 pounds applied to a sheath specimen of 150 millimeters.
The deformation characteristics of aluminum alloys commonly used as cable sheaths and identified in the art as type 3003 are marginally acceptable. However when these characteristics were compared with the deformation characteristics of an aluminum alloy identified in the art as type 3004 and never before used as a cable sheath, it was found surprisingly that alloy 3004 displayed much improved deformation characteristics using the crush test. Moreover, it was found that for any given diameter of cable core, the increased deformation characteristics of alloy 3004 enabled an acceptable sheath of alloy 3004 to be much thinner than a corresponding sheath of alloy 3003.
In particular the D/S which is the ratio of the outer diameter D of a sheath to its thickness S provides a means of comparison of alloy 3004 and alloy 3003.
For example, when the D/S ratio of alloy 3003 is compared to the D/S ratio of alloy 3004, over a range of diameters D between 10 and 100 millimeters, and the sheath thickness of these two alloys are computed using these ratios for the same diameter value, the sheath thickness of the newly used alloy will always be at least 20% smaller than that of the commonly used alloy.
Consequently, the sheath thickness can be reduced substantially as for example by at least 20% while maintaining the desired crush resistance when a type 3004 metallic alloy is substituted for a type 3003 metallic alloy. Both these alloys have the same unit weight and same unit cost, so that this reduction in sheath thickness results in substantial cost reduction. Alloy types 5052 and 5454 have even higher D/S ratios and permit further reduction in sheath thickness, but are more expensive.
REFERENCES:
patent: 1797851 (1931-03-01), Bossert et al.
patent: 3582536 (1971-06-01), Miller
patent: 3773965 (1973-11-01), Reynolds
patent: 3824330 (1974-07-01), Lang
patent: 3843830 (1974-10-01), Priaroggia et al.
patent: 3980807 (1976-09-01), Woytiuk
patent: 4426937 (1984-01-01), Miller
patent: 4749823 (1988-06-01), Ziemek et al.
patent: 5189719 (1993-02-01), Coleman et al.
patent: 5527995 (1996-06-01), Lasky
patent: 5760334 (1998-06-01), Ziemek
patent: 5919517 (1999-07-01), Levendusky et al.
Mayo III William H.
Reichard Dean A.
LandOfFree
Electric cables with metallic protective sheaths does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electric cables with metallic protective sheaths, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric cables with metallic protective sheaths will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2476244