It is a medium size raise drill ranging from 18 to 31

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: rers. Most popular and widely used model Robbins 73RM. Considered as a reliable workhorse for virtually any raise boring application. It is a medium size raise drill, ranging from 1.8 to 3.1 m (6–10 ft) in diameter. (Courtesy: Atals Copco – Robins).3 © 2005 by Taylor & Francis Group, LLC 348 SURFACE AND UNDERGROUND EXCAVATIONS pilot hole can be abandoned. The reverse procedure can be also adopted i.e. first driving the pilot hole upward from the lower level towards the upper level and then reaming it from the upper level towards the lower one. This technique is less popular. However, machines are available to drive either way. The space and facility available at each end of a raise mainly govern the choice of method. Raise borers are available for driving in soft as well as hard ground. This unit can disassemble into its various components that can be transported to the raise site and can be assembled again. The unit is available with crawler, wheel and skid mountings. Usually an operator with a helper can operate this machine. Trained personnel are required to operate and maintain it. While drilling stabilizers are used. A stabilizer follows the pilot bit; and then drill rods are inter spaced with stabilizers, the spacing of which varies with type of rock. On completion of the drilling up to the targeted end, the reamer replaces the bit. This operation is then carried in the reverse direction to withdraw the drill rods. Removal of cuttings from a down drilled pilot hole is done by air or sometimes by water – which deposits them around the hole collar where from they can be removed by hand shoveling. During up reaming the cuttings fall by gravity. Where the raise borer is located at the lower level of the raise, the cuttings from both operations (drilling and reaming) drop by gravity into a hopper and then via a chute or pipeline to the ore conveyance (i.e. any transportation unit). In general, it is cheaper to drill down and ream up. However, decision on drilling manner requires consideration of several factors. Important amongst them are: the availability of access to the raise site, ease in the transportation and installation of the raise borer, speed, energy required and over all economy of the operation. The rotational speed during pilot hole drilling varies from 35–72 r.p.m and the pressure on the pilot bit from 30,000 (for 9.8 in. bit) to 125,000 lb. for a 15 in. bit11 [Paul et al.]. The r.p.m. during reaming is in the range of 10–20 and the pressure on the reaming head in the range of 20,000 lb. (for 48 in.) to 36,000 lb. for 60 inches. Since the early 1960s, the name Robbins has been synonymous with raise drilling. This has been recently taken over by Atlas Copco Rock Drilling Division. Since the development of the first production raise borer, the Robbins 41R, more than 35 Table 13.1 Robbins raise borers’ usual range of some of the parameters.7 Robbins raise borers – important parameters Models designation (with max. raise dia. and length capabilities in meters) H. P. Range Drive speed Full load torque Machine weight Type of drive Recommended raise dia. Length range Accessories: Tri...
View Full Document

This document was uploaded on 02/12/2014.

Ask a homework question - tutors are online