Steel wire rope for hoisting and basic knowledge

Steel wire rope has the characteristics of the same section, high strength, large elasticity, good toughness, wear resistance, stable high-speed operation and can bear impact load. It is the main rope in hoisting and can be used for hoisting, traction, binding, etc.

1. Structural characteristics and types of steel wire rope

According to the twisting method, the steel wire rope is divided into single winding, double winding and three winding steel wire rope. The double winding steel wire rope is first twisted into strands around the central steel wire with a diameter of 0.4-3mm and a strength of 1400-2000n / mm2, and then several strands around the rope core to form a whole steel wire rope. Double wound steel wire rope has a large number of steel wires, large flexibility and is easy to wind on pulley and drum. Therefore, double wound steel wire rope is generally used in hoisting operation. Steel wire rope for hoisting and basic knowledge

(1) According to the direction of twisting, the steel wire rope is divided into three types: same direction twisting, interactive twisting and mixed twisting.

(2) The steel wire rope can be divided into 6 strands and 19 wires according to the number of rope strands and the number of steel wire ropes in one strand; 6 strands of 37 silk;; 6 strands, 61 wires, etc. 6 in daily work × 19+1，6 × 37+1，6 × 61 + 1. When the diameter of the steel wire rope is the same, the more the number of steel wires in the rope strand, the thinner the diameter of the steel wire, the softer the steel wire, and the better the flexibility.

(3) According to different rope cores, steel wire ropes can be divided into hemp core (cotton core), asbestos core and metal core. The steel wire rope with oil soaked hemp or cotton yarn as the rope core is relatively soft and easy to bend. At the same time, the oil soaked rope core can lubricate the steel wire, prevent the steel wire from rusting, and reduce the friction between the steel wires, but it can not work under heavy pressure and high temperature. Steel wire rope for hoisting and basic knowledge

2. Safe load of steel wire rope

(1) Breaking force of steel wire rope the so-called breaking force of steel wire rope is the tensile force required to break the whole steel wire rope, also known as the breaking force of the whole steel wire rope, expressed in PP, unit: n. To calculate the breaking force PP of the whole steel wire rope, the total breaking force of the steel wire rope shall be found out from the specification and performance table of the steel wire rope in the metal material manual according to the specification and model of the steel wire rope Σ P value, multiplied by the conversion factor φ Value, i.e. PP integer= Σ P· φ In fact, due to the uneven twisting of the steel wire rope in use, there is mutual extrusion and friction between the steel wires, and the stress of each steel wire is different. To break the whole steel wire rope, its breaking force should be less than the total breaking force of the steel wire, so it should be multiplied by a coefficient less than 1, that is, the conversion coefficient φ Value.

The conversion coefficient of breaking force is as follows:

When the wire rope is 6 × At 19 + 1, φ= 0.85；

When the wire rope is 6 × At 37 + 1, φ= 0.82；

When the wire rope is 6 × At 61 + 1, φ= 0.80。

(2) Allowable tensile force and safety factor of steel wire rope in order to ensure the safety of hoisting, the allowable tensile force of steel wire rope is specified according to the stress condition during use, which is called the allowable tensile force of steel wire rope. The calculation formula is: S = PP / K, where s - allowable tension of steel wire rope, N; K - safety factor; PP ---- breaking force of steel wire rope, n. The allowable tension of the steel wire rope is lower than several times of the breaking tension of the steel wire rope, and this multiple is the safety factor. See the following table for the safety factor of steel wire rope. Safety factor K value table of steel wire rope

Safety factor of steel wire rope use safety factor of steel wire rope use as cable wind rope 3.5 as sling when there is no bending 6 -- 7 load-bearing rope of cable crane 3.75 as binding sling 8 -- 10 manual lifting equipment 4.5 elevator for carrying people 14 motor lifting equipment 5 -- 6

3. Approximate formula for the weight of steel wire rope. The weight of steel wire rope needs to be known during use, transportation, loading and unloading. Generally, the reference weight per 100m can be found from the steel wire rope table, but it is inconvenient to use temporarily on site, so it can be calculated by simplified approximate formula.

The theoretical weight of steel wire in steel wire rope is g = a net L ρ (kg) where a -- net cross-sectional area of steel wire rope; L - length of steel wire rope, m; ρ---- Density of steel wire, ρ= seven point eight five × 10-6kg/mm3

The relationship between net cross-sectional area and gross cross-sectional area of wire rope is a net = 0.47a gross = 0.47 × (π D2 / 4), where D - nominal diameter of steel wire rope, mm. Then the weight per meter of the steel wire part of the steel wire rope is g = a net L ρ= 0.47a gross L ρ= zero point four seven × （πd2/4） × L × one thousand × seven point eight five × 10-6=0.0029Ld2

In addition to the weight of steel wire, the weight of steel wire rope also includes the weight of fiber core and oil. Its weight increases by about 20%, so g = 0.0029ld2 × 1.2≈0.0035Ld2

4. Scrapping of steel wire rope after long-term use, the surface layer of the standard steel wire rope will be gradually damaged due to atmospheric conditions and chemical corrosion. When the corroded pitted surface on the outer surface of the whole steel wire rope is obvious, the fiber core in the middle will be extruded, weakening its structural performance, and the steel wire rope can no longer be used. When the diameter of the steel wire rope decreases and the wear exceeds 30%, it shall be scrapped. Scrapping standard of steel wire rope after wire breaking

Initial safety factor of wire rope wire rope structure 6 × 19+16 × 37+16 × 61 + 1 the number of broken steel wires in the full length of one thread pitch is interactive twisting in the same direction, interactive twisting in the same direction, interactive twisting in the same direction, less than 6, 12622136186-7147261338197, more than 16830154020

5. Safe use and management of steel wire rope

(1) The selection of steel wire rope shall be reasonable and overload use is not allowed.

(2) Always keep the steel wire rope clean and regularly apply anhydrous antirust oil or grease. After the steel wire rope is used, the rust and dirt on it shall be brushed off with a steel wire brush. The unused steel wire rope shall be maintained and stored in a clean place according to the specifications. The steel wire rope stored in the open air shall be padded up below and covered with rainproof cloth cover.

(3) When the steel wire rope is wound on the drum, it shall be closely arranged in order one by one, and shall not be staggered or separated from the seam.