According to the working principle of the multi-rope friction hoist, the friction insert installed on the cylinder shell of the friction wheel (main guide wheel) of the hoist is a very important part of the friction hoist used to drive the steel wire rope and lift the load. Its friction performance directly affects the working capacity, efficiency and safety of the hoist.

1-Liner material

There are two main uses of the liner: one is to increase the friction between the friction wheel and the steel wire rope to improve the working capacity and safety of the hoist;Second, it acts as an isolation friction inserts to isolate the cylinder shell and the steel wire rope, avoid direct contact and mutual friction, protect the cylinder shell and prolong the service life of the steel wire rope.

It can be seen from the purpose of the friction lining that the material for making the linings should have two main characteristics: one is good friction performance, that is, the friction coefficient dual to the steel wire rope should be high and stable;Second, the steel wire rope shall not be damaged, that is, the hardness of the friction inserts shall be lower than that of the steel wire rope.Around these two characteristics, most of the liner materials used in the early stage were natural materials, such as wood, leather, rubber and aluminum alloy.With the development of chemical industry, people gradually began to use synthetic materials, such as PVC, polyurethane rubber and resin materials.

According to the chemical characteristics of the material, the liner material can be divided into hot-melt type and non hot-melt type.Polyvinyl chloride and polyurethane are hot-melt materials.Polyurethane has many kinds due to its different types and components, and there are certain differences in properties. Polyester polyurethane is used to make gaskets, which is characterized by good toughness and wear resistance.However, polyurethane material has its insurmountable weaknesses, such as low melting point, which is generally only more than 100 degrees. In case of accidents, it is difficult to ensure the friction performance of the pad;In particular, the heat conduction capacity is very poor (it is proved by being used as refrigerator insulation material), which is easy to cause friction heat accumulation and local temperature rise to affect the friction coefficient;The transverse rigidity is poor, the deformation is large after stress, and fatigue fracture is easy to occur;Avoid ultraviolet radiation, short aging cycle and poor cutting performance.

Non hot melt materials refer to materials that will not melt until heated to combustion.Compared with hot-melt materials, non hot-melt materials have many advantages, such as non melting when heated, which can ensure the friction performance of the liner under unexpected circumstances;The friction coefficient is high and stable, and is less affected by temperature;High hardness, good transverse rigidity, small deformation after stress, not easy to fatigue fracture;Chemical corrosion resistance, anti-aging ability, long life and good cutting performance.The resin liner used more in China is non hot melt material, which has excellent friction performance.

According to the working characteristics of multi-rope friction hoist, it should be said that non hot melt material is more suitable for friction liners material.

2-Operating conditions of friction liners

The working conditions of the liner mainly include surface state, load pressure, wire rope creep speed and ambient temperature, which are also the four main factors affecting the friction coefficient of the liner.

2. 1 surface state

When the liner works, due to the influence of many factors on the use site, the rope groove surface will have different states, such as drying, watering or grease, but it is often not a simple one, but several states are mixed together, such as grease and watering, and it is also polluted by mineral powder, especially in the grease state. The mineral powder is adhered to the steel wire rope by grease and participates in the work of the friction surface.Groundwater is the direct cause of water drenching, while grease is the preservative of steel wire rope, which is adhered from the steel wire rope when the gasket contacts with the steel wire rope.In most cases in China, the liner works with wire rope anti-corrosion grease and drenched with water. This state is the worst of all surface states and has the greatest adverse impact on the liner friction coefficient.Of course, the grease mentioned here is not ordinary anti-corrosion grease, but special steel wire rope anti-corrosion grease for friction lifting, referred to as friction grease for short.

The test shows that the friction coefficient of the liner is different under different surface states, and the friction coefficient under the greased state is the lowest. Therefore, the friction performance of the liner is inseparable from the surface state.Generally speaking, the liner friction coefficient should refer to the friction coefficient in the greased state without special indication.

2. 2 Load pressure

When the pad works, it is under the pressure from the steel wire rope, which varies greatly due to the position of the pad.

2. 3 Creep speed of wire rope

During normal operation, relative sliding is not allowed between the pad and the steel wire rope. If sliding occurs, it is considered to be the failure of the friction pair, which is easy to bring potential accidents.However, because the steel wire rope is an elastomer, according to the elastomer transmission theory, the steel wire rope will produce elastic sliding or creep on the pad.Due to the influence of different elasticity, tension and running speed of steel wire rope, the creep speed of steel wire rope is different for different specifications of hoist.

The research shows that the creep speed of steel wire rope has a certain influence on the friction performance of the liner. From the perspective of speed influence, the increase of creep speed will appropriately improve the friction coefficient of the liner, but the wear will increase.

2. 4 ambient temperature

China has a vast territory. The outdoor temperature in winter and summer should be normal from - 30 ~ + 40 ℃, while the indoor temperature should be controlled within the range of 0 ~ 30 ℃.

The working environment of the pad is generally indoors, while the steel wire rope closely related to it is different.For tower hoist, the steel wire rope shall reach the shaft from the machine room through the well tower open around.For the floor type hoist, the steel wire rope must be completely exposed to the outside to reach the shaft, and the steel wire rope will be exposed to the sun and rain.In contrast, the working environment of the wire rope is much worse, but because the pad is always in contact with the wire rope, its friction performance will be affected by the wire rope temperature to a certain extent, especially when there is grease on the wire rope surface.

3-Performance requirements of friction pulley inserts

The use of the liner clearly shows that the friction coefficient is the most important performance parameter of the liner.From the perspective of use, the gasket shall have the following three main properties:

(1) the friction coefficient shall be high.According to the current level of domestic liner manufacturing industry, many friction coefficients should be more than 0.25.

(2) the friction coefficient shall be characterized by an upward trend with the increase of the creep speed of the steel wire rope, so as to ensure the convergence of the sliding speed in case of abnormal sliding caused by accidents.

⑶ good thermal stability.When abnormal sliding is caused by an accident, resulting in an increase in the surface temperature of the liner rope groove, it shall not melt, and the friction coefficient shall remain stable.

In addition, the liner shall have sufficient strength, uniform internal structure, no defects, oil and water resistance, stable performance in long-term contact with grease and water, no damage to steel wire rope, no substances polluting the environment and harmful to human health, and good cutting performance.

4-Conclusion

The liner is as important to the multi rope friction hoist as the tire is to the automobile. Without it, the hoist can not effectively drive the steel wire rope.The performance of the liner is related to the parameter level of the whole hoist. If the liner performance is poor, the hoist can not pull fast and run safely and reliably. Therefore, the liner is paid great attention at home and abroad and is constantly studied.