Field of the invention
The present invention relates to steel props for use as temporary support prop
for the roof mass load in underground mines, in particular, coal mines.
Background of the invention
It is customary to use props for use in underground mines for supporting the
roof mass load. Traditionally wooden props found use in underground mines
and later steel props came into use. Currently steel props are tubular steel
members (IS 1161 - 1979). Generally, the tubular steel member has a length
2.75 m and is fabricated by using mild steel sheets of 5.0 mm wall thickness
and having weight of 40 kgs. approximately. While such steel props are being
widely used in mining industry in particular, coal mining but such props suffer
from inherent shortcoming such as improper weight to load bearing capacity.
A further serious shortcoming of the conventional steel props is that the
height of the rigid pit props are not adjustable.
The industry has survived with the handicap and very little improvement has
been possible over the past several years.
Indian Patent No. 189955 teaches a rigid steel prop useful for supporting
underground mine/tunnel roofs which comprises a bottom tube having a plate
at its upper end, an upper tube being fixed on top of the said plate, the upper
portion of the said upper tube having a horizontal hole in which is fitted a cam-
integrated shaft by means of locking rings, the top end of the said upper tube
being provided with a guide ring, a tube having a top channel and a bottom
plate being fitted telescopically through the said guide ring so that the bottom
plate rests on the top of the said cam-integrated shaft, the said shaft being
provided with a handle having a locking lever fitted onto the outer surface of
the upper tube, means (hook, wire rope and pulley) being provided for remote
release of the said locking lever.
While the prop according to IP 189955 teaches a prop with a release
mechanism but such device does not fully address the shortcomings of the
existing props.
It is therefore an object of the present invention to provide a prop which is light
weight and in which the height is adjustable.
Summary of the invention
Thus the present invention relates to an improved prop having adjustable
height, comprising an upper part (main prop) and the lower part (base unit),
each of said upper and lower parts are tubular, said upper part having length
greater than the lower part, both the upper and lower parts being of circular or
polygonal cross section, the wall thickness of the lower part being greater
than that of the upper part; guide channel provided at the top of the main prop
for holding wooden wedge for jamming with the roof, the base unit having an
annular ring to prevent detachment of main prop and a plurality of support
members so as to efficiently transfer the load of roof mass to the ground, said
main prop having atleast two pieces of bars rigidly held thereto at its bottom
so as to provide bayonet mount to enable the upper part to move in and out of
the slots of base unit, and means for maneuvering the prop.
According to a preferred embodiment of the invention the base unit has
circumscribed circle diameter which is greater than the circumscribed circle
diameter of the upper part.
According to a further preferred embodiment of the invention the means for
maneuvering the prop comprises a plurality of slots and grooves provided in
the base unit.
According to another preferred embodiment of the invention two pieces of
bars are fixed at the bottom of the prop spaced 90° apart.
According to another preferred embodiment of the invention the diameter to
wall thickness and length to radius of gyration is maintained in the region of
50 and 60 respectively.
The invention will be described in further details with reference to figures 1
and 2 of the accompanying drawings in which figure 1 is a cross-sectional
longitudinal view of the prop according to the invention and figure 2 is a cross-
section along line II - II in figure 1.
The configuration of adjustable height type prop is an assembly of two units
i.e. the main unit of prop (upper part) (1) and a base unit (lower part) (2) of
larger tubular dimension as shown in attached drawing. The figure shows that
at the bottom of the main prop, two pieces of bars (3) fixed at 90° apart which
are welded together to serve the purpose of bayonet mount. The overall
height of prop can be adjusted by way of maneuvering the main unit of prop
through the slots (4) and grooves (5) cut in the base unit at three fixed
positions.
The preferred dimensional and constructional features of the upper and lower
parts are as under:
The main prop (Upper part)
• Length: 2.4 to 3.5 m
• Shape of cross section: Circular or polygonal (Octagonal)
• Circumscribed circle diameter: 100 mm to 180 mm
• Steel used: SAILCOR (Wheather Resistant Steel, SMYS > 350Mpa)
• Wall Thickness: 2.5 mm to 4.0 mm
Guide channels (10) are welded at the top of main prop for fixing wooden wedge
for tight fixing with the roof of the mine and imparting a small amount of setting
load in prop.
Base Unit (Lower part)
Length 0.5 m - 1.0 m
Section ; Circular or Polygonal (Octagonal)
Circumscribed circle diameter: 130 to 200 mm
Wall Thickness : 4.0 to 10.0 mm and above
Slots (4) and grooves (5) are cut in the base unit at three positions.The base unit
has been made more rigid and inseparable from the main prop by welding an
annular ring (made of 12 mm thick plate) (6) at the top of the base unit.
Further, the base unit is stiffened by welding four angles (ISA 25 x 25) (7) at an
equal interval all along its periphery. The bottom end is covered with 6 mm thick
flange plate (8).
The key factors so as to obtain best results are in the optimization of the props.
High strength (Minimum Specified Yield Strength 350 Mpa) weather resistant
steel was used for fabrication of light weight steel prop.
The efficiency of props in transferring the load of roof mass to the ground would
be greatest only when these are fixed in their vertical position.
Prior to fixing of these props, the roof height is measured and accordingly overall
height of the prop is adjusted. The height of these props could be adjusted in
three heights by placing the main prop in the appropriate groove cut in the base
unit of the prop. Handles (9) have been provided for easy haridling.
To fix the prop tightly in position, a wooden piece having lower width than that of
the channel fixed at the top of the prop (10) is inserted between the roof and
channel by hammering the wood.
The advantages of this type of roof support systems are (a) lighter in weight
compared to hydraulic or friction prop (b) easy and quick to adjust the prop height
with different roof heights.
Optimized configuration of newly designed props was found suitable for
sustaining minimum axial compressive load upto 300 kN when the diameter to
wall thickness and length to radius of gyration maintained closely to 50 and 60
respectively.
We Claim :
1. An improved steel prop having adjustable height as roof support system in
underground mines, comprising an upper part (main prop) (1) and the lower
part (base unit) (2), each of said upper and lower parts are tubular, said upper
part having length greater than the lower part, both the upper and lower parts
being of circular or polygonal cross section, the wall thickness of the lower
part being greater than that of the upper part; guide channel (10) provided at
the top of the main prop for holding wooden wedge for jamming with the roof,
the base unit having an annular ring to firmly hold the upper part and a
plurality of support members so as to efficiently transfer the load of roof mass
to the ground, said main prop having atleast two pieces of bars (3) rigidly held
thereto at the bottom of the upper part so as to provide bayonet mount to
enable the upper part to move in and out of the slots (4) of base unit, and
means for maneuvering the prop.
2. An improved prop as claimed in claim 1 wherein the base unit has
circumscribed circle diameter which is greater than the circumscribed circle
diameter of the upper part.
3. An improved prop as claimed in claim 1 or 2 wherein the means for
maneuvering the prop comprises a plurality of slots and grooves provided in
the base unit.
4. An improved prop as claimed in claim 1, 2 or 3 wherein two pieces of bars are
fixed at the bottom of the main prop spaced 90° apart.
5. An improved prop as claimed in any preceding claim wherein the diameter to
wall thickness and length to radius of gyration is maintained in the region of
50 and 60 respectively.

An improved prop having adjustable height comprising an upper part (main prop)
and the lower part (base unit), each of said upper and lower parts are tubular,
said upper part having length greater than the lower part. Both the upper and
lower parts being of circular or polygonal cross section, the wall thickness of the
lower part being greater than that of the upper part. A guide channel is provided
at the top of the main prop for holding wooden wedge for jamming with the roof,
the base unit having an annular ring to firmly hold the upper part and a plurality of
support members so as to efficiently transfer the load of roof mass to the ground.
The main prop has atleast two pieces of bars rigidly held thereto at the bottom of
the upper part so as to provide bayonet mount to enable the upper part to move
in and out of the slots of base unit, and means for maneuverinq the prop.