Ripper

Ripper

A ripper is a machine which cuts, as it travels, 0.6 to 1 m deep furrows in the ground and it can be_ well compared with the farmer's plough. The ripper is essentially a crawler mounted heavy duty diesel tractor with a ripper attachment as shown in Fig. 5.4. Like a farmer's plough, the ripper with the ripping tool thrust into the ground by hydraulic pressure, travels along close parallels paths, 1.2 to 1.5 m apart and during the travel rips open the ground. The broken ground or rock can be dozed to form a stockpile for convenience of loading or, can be loaded by a scraper. If the overburden or mineral is suitable for ripping its breaking is possible with the help of a ripper and the process of drilling and blasting can be dispensed with. Soft rocks and medium hard rocks, below hardness 5 on Moh's scale, which are laminated and stratified, provide suitable material for ripping. The alluvial surface deposits, weathered sandstones and shales underlying them in the coalfields can be easily ripped and the relative rippability of the rocks can be known with the help of an instrument known as Refraction Seismograph

The Refraction Seismograph operates on the principle that "Sound waves travel through subsurface material at different velocities, depending upon the degree of consolidation of the material". It is believed that the same factors that affect consolidation also affect rippability. Thus poorly consolidated material with low seismic wave velocities could be ripped easily, while highly consolidated material with high velocities would be difficult to rip.

Equipment needed for seismic analysis includes a source of a sound or shock wave, a receiver, an electric counter, and a set of cables. The main items are:

1. Refraction Seismograph: An electronic counter that determines the time interval between the strike of the hammer and the arrival of the seismic wave at the geophone.

2. Geophone: Receiver of sound waves. A geophone is a velocity gauge suitable for defecting frequencies in the range of 1-100Hz. The geophone converts the mechanical vibrations into its electrical analogue. This electrical signal is then amplified and transmitted to the monitoring station.

3. Sledge Hammer and Impact Plate: Source of sound wave transmits sound through earth and also through an impact switch having direct connection with seismograph, through a connecting wire.

4. A 30 m Tape: For measuring distances between the geophone and various impact points (wave sources).

The seismic wave is produced by a-sledge hammer striking a steel plate at various distances from a geophone receiver. Immediately upon impact, a wave "front" composed of innumerable seismic waves travels in all directions away from the point of impact, or source. Some of the waves are refracted into the layers of sub surface materials and the angle of refraction is determined by Shell's law which gives the following relationships.

Sine of angle of incidence = Sine of angle of refraction

Wave velocity in upper layer    Wave velocity in lower layer

The geophone receiver is sensitive only to the first seismic wave that reaches it. Thus, either the wave which travels the shortest distance, or one which travels a longer path but which includes a high velocity segment, arrives first at the geophone.

In addition to determining the degree of consolidation or rippability of each layer, it is also possible to determine the depth of each layer.

In iron ore areas of Goa the practical results obtained with seismograph were as follows: Seismic velocity in overburden (practically laterite) was 600 to 1,200 m per second. In iron ore it was 1,050 to 1,500 m per second, but in some cases velocities as high as 1,800 to 2,100 m per second were also recorded.

When selecting a tractor for ripping purposes, it is necessary to consider (1) the down pressure on the tooth to determine whether penetration can be accomplished, (2) the tractor H.P. which should be capable of advancing the tooth through the rock and break it, (3) tractor weight which provides traction for full use of the H.P. in advancing the tooth.

The tractor speed is 0.8 to 2.5 km/hr during ripping. If the rock is soft it is advisable not to increase the speed but to add one or more ripping teeth. The distance between adjacent furrows during ripping may be 1 to 2 m and the harder the rock, the c-loser are the furrows.

In some rock formations ripping is possible after sparse blasting of widely spaced charges