1. Koja je glavna funkcija cijevi jezgra?
ü To store the core sample during diamond core drilling.
2. Koje su glavne komponente u bačvi s konvencionalnom jezgrom s dvostrukom cijevi?
ü Diamond drill bit
ü Reaming shell
ü Landing Ring
ü Core lifter case
ü Core Lifter
ü Stop Ring
ü (Inner Tube Extension tube)
ü Inner tube
ü Outer tube
ü Core barrel head ( Head Assembly)
ü Inner Tube Stabilizer
3. Kako razbiti jezgro? Opišite proces.
ü When the inner tube is filled with the core sample the core barrel shall be taken up to the surface and the core sample shall be placed in a core box. The core sample is however a part of the rock and it has to be separated from the rock before the core barrel can be taken up to the surface. This operation is called to break the core. The core lifter case and the core spring are used to break the core.
ü These components are mounted on the inner tube. The core lifter case is tapered on the inside and the core spring, which is slotted, is tapered on the outside. When the core barrel is pulled out of the hole the core spring will grip the core and the harder the core barrel is pulled the firmer the core lifter will grip the core sample. When the pulling force is larger than the tensile strength of the rock the core will break. In a hard competent rock it might be necessary to use a pulling force of 10 – 20KN or more to break the core.
4. Why can't the inner tube or the core barrel head take the loads that occur when breaking the core? How is this prevented?
ü Neither the inner tube nor the bearing assembly in the core barrel head are designed for the pulling forces necessary to break a hard rock core.
ü Therefore the core lifter case, the core spring and the inner tube can slide down and rest on a tapered shoulder inside the drill bit and thus the pulling force is transferred to the outer tube which is designed to take such forces.
ü The thin inner tube as well as the bearing assembly is thus completely without tension and/or loads during the core breaking operation.
5. Zašto se unutrašnja cijev ne smije okretati i kako se to sprječava?
ü The function of the inner tube is to store the core sample during the drilling and the hoisting operations. It is important that the inner tube does not rotate since a rotating inner tube will destroy the quality of the core. The upper end of the inner tube is attached to a bearing assembly in the core barrel head. The bearing assembly includes radial as well as axial bearings which stabilize the inner tube and stops it from rotation with the outer tube.
6. Zašto bi se razmak između kućišta podizača jezgra i konusnog ramena unutar svrdla s vremena na vrijeme trebao prilagođavati? Kako se ovo prilagođavanje vrši?
ü The flushing water passes first through channels in the stabilizer of the core barrel and then via the annular space between the core barrel head/inner tube and the outer tube and finally down to the gap between the core lifter case and the shoulder inside the drill bit. This gap can be adjusted by means of a nut on the core barrel head. When drilling in hard consolidated formation the gap can be fully opened enabling the flushing water to pass with as small pressure drop as possible. The part of the core sample located between the rock and the core lifter case will be flushed with water but as long as we are drilling in a hard and competent rock this does not matter.
ü On the other hand when drilling in soft and friable formation it is important to keep the gap as small as possible in order to guide the loose core into the core lifter case and in order to prevent that the loose core is flushed with water and possibly eroded.
7. Gdje se u buretu jezgra nalazi ventil za vodu? Koja je svrha ovog ventila?
ü Normally there is water shut off valve incorporated in the core barrel head. When the inner tube is filled with the core sample or in case of a core blockage, the inner tube is pushed against the core barrel head and the water shut off valve is closed.
ü This will block the waterways and the water pressure will increase. The driller will notice this, by looking at the water pressure gauge normally placed on the control panel of the drill rig, and he can then take the appropriate measures.
8. Šta je jezgro sa trostrukom cijevi?
ü A double core barrel can be equipped with a liner that is placed inside the standard inner tube. Thus the core barrel will consists of three tubes and is then called a triple tube core barrel. The liner tube is usually split axially and does thus consist of two halves. The reason for this is that it shall be easier to recover the soft core sample.
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