Hydraulic and earth engineering – Earth treatment or control – Rock or earth bolt or anchor
Patent
1994-12-21
1998-09-08
Bagnell, David J
Hydraulic and earth engineering
Earth treatment or control
Rock or earth bolt or anchor
411385, 411395, 29463, E21D 2100
Patent
active
058036717
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to hollow bars, particularly hollow bars that are suitable for use as rock bolts and drill rods, and to a method of manufacturing hollow bars.
A known method, commonly referred to as the "pierced-billet method", of manufacturing hollow drill rods comprises drilling a billet of steel, typically up to 150 mm in diameter and 1.2 m in length from both ends to form a hole that is approximately 20-30 mm in diameter and inserting a manganese steel mandrel into the hole. The method further comprises heating the billet with the mandrel inside to about 1150.degree. C. and then passing the billet/mandrel through a series of rolls to form the required transverse section (i.e. round, square, hexagonal etc.) and to reduce the external diameter to the required dimensions. The method further comprises allowing the rolled billet/mandrel to cool and removing the mandrel to form the final product of a rolled steel bar having a central hole and the required external profile and dimensions. In order to remove the from the rolled billet/, the is gripped and pulled in tension to reduce its diameter slightly and the mandrel is cut while in tension so that it flies out of the billet.
The method involves several steps and also necessitates the use of a special manganese steel for the mandrel which has to be scrapped after being removed from the rolled steel bar. Consequently, the method is relatively expensive and is not suited to large scale production as would be required for rock bolts.
A known method of manufacturing tubes comprises rolling a long, flat strip of steel into a round shape and then continuously welding the two sides of the strip together to form a tube. In practice, the method is carried out on a continuous basis and the welding is completed very quickly.
The method can produce tubes of different sizes within limits, although it is very difficult to produce a relatively thick walled tube as would be required for rock bolts without the further step of "sinking" the tube through a die to reduce the outside diameter and at the same time to increase the wall thickness. In addition, it is very difficult to roll a profile on the outside of the tube as would be required for rock bolts of the type having an external threaded profile.
It is an object of the present invention to provide a method of manufacturing hollow bars which alleviates the disadvantages of the known methods described in the preceding paragraphs.
According to the present invention, there is provided a method of manufacturing a hollow bar, comprising: the hollow bar; and members to form the hollow bar.
The term "hollow bar" as used herein is understood to cover any elongate element, such as hollow rock bolts, drill rods, pipes or tubes.
The terms "rock bolt" and "drill rod" as used herein are understood to cover hollow members which have an axial bore or bores and a relatively large wall thickness compared with the bore diameter. Specifically, the terms are understood to cover rock bolts and drill rods which have a maximum bore diameter which is less than or equal to four times the maximum wall thickness.
It is preferred that the method comprises forming two members to form the hollow bar.
It is preferred particularly that the two members be identical.
It is preferred that the step of forming the members comprises rolling or die drawing the members.
In one embodiment, it is preferred particularly that the step of rolling the members forms sections of a threaded profile on each of the members so that the hollow bar formed by connecting the members together comprises a threaded profile and is suitable for use as a threaded rock bolt.
In another embodiment, it is preferred particularly that the step of rolling the members forms a half hexagonal shape on each of the members so that the hollow bar formed by connecting the members together comprises a complete hexagonal profile and is suitable for use as a hexagonal drill rod.
It is preferred that the method comprises connecting the members together by welding or gluing.
It is pre
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Bagnell David J
Clarke Dennis P.
Lagman Frederick I.
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