DESIGN PHILOSOPHY

INTRODUCTION

The Hoist mechanism shall include a driving motor, a gear reduction unit, two rope drums, ropes, shafts, gears, couplings, brakes, emergency manual arrangements, limit switches, gate position indicator (both analogue and digital), covers etc., all mounted on a fabricated steel frame. Electrical controls and all necessary electrical and mechanical accessories shall be provided for the satisfactory operation of the hoist. The hoist shall be capable of fully opening/closing the gate. Sufficient space shall be provided around the hoist components for repair/maintenance.

HOIST DESIGN CONSIDERATION

Manual and power operated hoist are of two types. One has drive unit centrally located and other has drive unit located at one of the hoist which allows a narrower concrete deck to use. Hoisting speeds for power operated hoist vary from 0.3 to 0.6 m/min. The rope pull on each drum is assumed to be 60 % of the rated hoist capacity, since inequality may exist due to greater friction or sticking of gate seals on one side of gate which produce a greater load on drum than other.

The hoist drum gearing and related parts are accordingly designed on the above basis. The rope is steel hoisting rope of 6X37 constructions with a factor of safety of not less than 5 for smaller hoists and 6 for large hoists. In case of highly corrosive water, stainless steel ropes may be used all parts of the equipment have sufficient strength to hoist the forces produced by 25% break down torque of motor without exceeding 80% of the yield point of the materials. Ball or roller self aligning bearing or ball – bearing aligning pillow block are used for all hoist except those operated manually. Flexible coupling are of the all metallic and dust proof and fully enclosed gear type.

Design criteria

The design requirements for the rope drum hoist are broadly mentioned as under as per IS: 6938:

1.) Capacity of hoist.2.) Lift of Gate3.) Operating speed 4.) Number of Drums : 2 (Two) with single/double layer of rope (for each hoist) with

L.H. and R.H. groove on drum for two points lifting of gate 5.) Rope : IS:2266 , 6x37 Construction

MATERIAL TECHNICAL SPECIFICATION a) Hoist bridge, Hoist supporting

Structures, treastles etc., Structural Steel IS 2062

b) Rope drum and Gear wheels Cast Steel IS1030

c) Pinions Forged Steel IS2004

BS 970

d) Shafts Rolled Steel IS 2062 .

Forged Steel 45C8 IS 2004

e) Bush bearings Al Bronze IS 305

Hoist Capacity:-

The hoist capacity shall be determined by taking into consideration the following forces which might be required to overcome:

a) Weight of the gate along with all its components including the weight of wire rope and its attachments and ballast, if any;

b) All frictional forces comprising of

1) Wheel friction,

2) Guide friction, and

3) Seal friction including friction due to initial interference;

c) Any hydrodynamic load, like downpull/uplift force, etc;

d) Silt and ice load wherever encountered;

e) Weight of lifting beam, if used; and

o) Any other consideration specific to a particular site.

The worst combination of the above forces, during either lowering cycle or raising cycle, shall be considered. The hoist capacity thus arrived at shall increased by 20 percent to cater for the reserve hoist capacity.

The usual operating speed for such hoist shall be 300 to 700 mm/min. However, higher values may be adopted depending upon the requirements.

Wire Rope:-

Wire rope diameter shall be decided by maximum rope tension which is calculated by using pulley efficiency. The wire rope shall bemade from improved plough steel, galvanized ( if required ), Lang’s lay and fibre core or normally of 6 x 36 or 6 x 37 construction and shall conform to 1S-2266. The breaking strength of wire rope, shall be calculated on the basis of IS- 2266. The minimum factor of safety based on minimum breaking strength and safe working load of the wire rope shall be as given in Table1.

S1 No. Operating Condition Minimum Factor of Safety

1 Normal operation condition 62 Breakdown torque condition 33 For counterweight suspension 5

Drum:-

The grooved drum shall be of such a size that normally there will not be more than one layer of rope on the drum when the rope is in its filly wound position unless specified. The length of the drum shall be such that each lead off rope has minimum two full turns on the drum when the gate is at its lowest position, and one spare groove for each lead off the drum when the gate is at its highest position. The drum may be flanged at ends. The flanges shall project to a height of not less than two rope diameters above the rope. A spur gear secured to the drum may be regarded as forming one of the flanges.

The lead angle.( fleet angle ) of the rope shall not exceed 5° or”1 in 12 on either side of helix

angle of groove in the drum.

The drums shall be made from one of the following materials:

a) Cast iron conforming to IS21 0,

b) Cast steel conforming to IS 1030, and

c) Mild steel plates conforming to [S 2062.

NOTE — Use of cast iron shall be limited to small capacity hoists only.

Strength of drum

The drum shall be strong enough to –withstand the crushing as well as the bending. The crushing strength of drum shall be calculated by the following formula:

Ct= K* T/p*t

where

Ct = compressive stress, in N/mm2;

K= coefficient which depends upon the number of layers of rope over the drumand may be taken from Table 2;

T= tension on one wire rope in N;

P= pitch of scoring or centre to centre distance between adjoining grooves, in mm; and

t = thickness of drum.

NOTE — The minimum thickness of drum shall not be less than 16 mm in case of cast steel and 20 mm in case of cast iron.

Grooves on Drum

The rope drum shall be machine-grooved and contour at the bottom of grooves shall be circular over an angle of at least 120°. The radius of groove shall be 0.53 times the diameter of rope rounded off to next full millimeter. The depth of groove shall not be less than 0.35 times the diameter of the rope.

The grooves of the drum shall be so pitched that there is a clearance of not less than the following values between adjacent turns of rope:

a) 1.5 mm for ropes up to and including 12mm

diameter,

b) 2.5 mm for ropes over 12mm and including

30 mm diameter, and

c) 3.0 mm for ropes over 30 mm diameter.

Diameter of Drum

The minimum pitch diameter of the drum shall be 20 times the diameter of rope of 6/36 or 6/37 construct ion.

Motor is designed as per IS-325.

Column and platform shall be designed as per IS-800.