1. Field of the Invention
The present invention relates to a double-walled liner and method and apparatus for the manufacture thereof. By way of example, the double-walled liner according to the present invention may be deployed as a borehole liner.
2. Description of the Prior Art
In the mining industry, blasting is considered to be one of the most cost-effective ways to fracture rock. Generally, blasting loosens the rock so it can be excavated. The rock is fractured enough to displace it and break it down to the size of the intended use. The blasting process requires drilling a borehole into the rock, placing an explosive into the borehole as a charge, and including a detonator or fuse to initiate the blast by setting off the charge.
Various explosives may be used as charges, such as dynamite or ammonium nitrate and fuel oil, known as “ANFO” to those in the mining arts. Oftentimes water collects in boreholes, either from rain or surface water or from underground sources, which has a deleterious affect on ammonium nitrate. Although wet ammonium nitrate will detonate, the detonation quality in fragmentizing rock is far from satisfactory. As a result boreholes are commonly lined with a borehole liner in the nature of a waterproof, plastic liner to keep the water away from the explosive. To maintain their waterproof integrity, it is necessary that borehole liners be resistant to cuts or abrasions caused by the often sharp inside surfaces of a borehole when a liner is lowered into the borehole.
Double-walled liners are desirable as they may provide greater durability, strength and resistance to moisture than single-walled liners. One of the ways of manufacturing double-walled liners is presented by U.S. Pat. No. 3,881,417. This patent reference discloses a borehole liner comprising a flattened, flexible, waterproof inner tube with a waterproof seal at its lower end, and an outer sheath which sheaths the inner tube and is substantially coextensive with the inner tube. A drawback of this process, however, is that the double-walled borehole liner is manufactured by manually inserting one tubing into another, a process that under most circumstances is time-consuming, labour intensive, and requires a large assembly area.
It is an object of this invention to attempt to mitigate or obviate at least one of the above-mentioned disadvantages.