Jökull - 31.12.2001, Page 31

Ice core drilling on Hofsjökull
Antitorque Motor Gear Coupling Hatches Core barrel Drill head
Figure 3a. The drill is 4m long and consists of the following components, shown here beside the outer cover
tubes: The top section is an antitorque system with three blade springs which exert a pressure on the hole wall
and thereby prevent rotation of the entire drill in the hole when the drill head is turning. A slipring unit built
into the antitorque prevents twisting of the cable in case of antitorque rotation. A motor section is connected to
the lower end of the antitorque. The electrical motor is of type Estan and has a power output of 0.55 kW. The
speed of rotation is 3000 rpm, which is reduced by a planetary gear. A mechanical coupling connects the core
barrel to the gear. The rotation rate of the drill head and barrel can be varied between 0 and 150 rpm. An outer
barrel encloses the core barrel, which is 2.5 m long. Drilling produces chip cuttings which are transported up
the outside of the inner barrel by polyethylene spirals and enter the barrel through hatches on the upper part.
During drilling above the water table (or in dry polar ice), the chips are collected above a disk which is posi-
tioned about 1.3 m above the lower end of the barrel. Below the water table, the chips float upward but transport
into the hatches is not efficient. The maximum obtainable corelength is normally 1.3 m, and the diameter of
the cores is 9.8 cm. The borehole diameter is normally 13.2 cm. The drill and winch are powered by a 6kW
generator and are controlled from a single control unit. Power is supplied to the drill by a cable with 4 inner
Cu-conductors and an outer shield made of steel. The cable is 250 m long and 6.35 mm in diameter. - Myndin
sýnir innri hluta borsins við hlið ytri hólkanna. Borkróna, þá kjarnarör með snigli, þá tenging, gír og mótor.
Efst er snúningsvörn og inni í því sigumagli. Kjarnalengd getur mest orðið 1,3 m og svarfið fellur inn um göt
ofariega á kjarnarörinu og safnast fyrir ofan við ískjarnann. Þvermál ískjarnans er 9,8 cm og borholunnar
um 13,2 cm. Bor og vindu er stýrt frá sama stjórnborði, sem knúið er 6 kW rafstöð. Rafstraumur er leiddur í
bormótorinn um 4 leiðara innan í stálkaplinum, sem er 250 m langur. Sérstakur mótor knýr vinduna.
Figure 3b. The drill head. The 3 cutters are round
shaped and a relatively small area is in direct contact
with the ice. The pitch (i.e. the vertical cutting distance
per rotation) can be adjusted by mounting shims of dif-
ferent thickness under the screws behind the cutters. As
the drill is pulled to surface, three core catchers grab
the ice core from the side and break it a few cm above
hole bottom. - Borkrónan. A henni eru 3 hnífar með
sporöskjulaga skurðflöt. Stilla rná skurðdýpt með því að
setja mismargar þynnur undir skrúfur, sem festar eru
á bak við hnífana. Þrír krókar spenntir með stálfjöðr-
um lœsast í kjarnann þegar borinn er hífður upp, brjóta
hann af holubotni og halda honum föstum í rörinu.
JÖKULLNo. 51 29