The fixed block and pressing block are two important parts on the multi rope friction hoist, which are installed on the friction wheel to fix the friction pad. Since our company produced the multi rope friction hoist, the two parts are cast and processed with aluminum alloy materials. The material cost is high and the processing process is complicated. The process only installed on the friction wheel needs to be carried out twice. Therefore, in order to reduce the cost, reduce the processing hours, reduce the labor intensity of workers and reduce the moment of inertia of hoist, it is necessary to carry out research. A non-metallic material with low cost and low specific gravity, which can meet the use requirements, is selected to replace the cast aluminum alloy material.

1) Current situation at home and abroad

At present, there are two ways to fix friction pad on multi rope friction hoist at home and abroad: one is turning inverted trapezoid on the opposite surface of circular steel plate on friction wheel as fixed friction pad. The structure has large processing capacity, heavy friction wheel, large rotating inertia of hoist and less application; The other is the commonly used fixed block and pressing block method. Its material is often made of metal, but it can also be non-metallic. For example, Sweden once used specially treated wood, and the former Soviet Union used wood chips pressed products treated with special processes.

2) Experimental study

2.1 material screening

Thermoplastic products and phenolic sandwich cloth are mainly considered. After further research and demonstration, and referring to relevant materials at home and abroad and the actual use experience of the hoist, the scheme of using thermoplastic products is excluded. Because the thermoplastic products have large elasticity and are easy to deform under bending conditions, which will affect the clamping force and easy aging of the products, which will affect the use, the scheme dominated by phenolic materials is selected.

2.2 characteristics of phenolic sandwich material

Phenolic sandwich is a thermosetting plastic and a polymer with linear structure. Its molecular structure contains free hydroxyl groups that can be further reacted

Methyl (- CH2OH) is unstable. After heating and pressurization, the molecular structure is transformed from linear to body structure by the reaction between its own functional groups, and the shape is fixed. However, if you continue to press and heat, the molecular chain will break and the surface will be broken. Therefore, the pressure and temperature of this kind of plastic products must be controlled when they are finished. The manufacturing method of this kind of materials is to impregnate various reinforcing materials such as cloth into phenolic glue solution and dry and crush them. The cloth reinforcing filler can effectively improve the strength of phenolic materials.

2.3 structural design of test piece

Referring to the structural dimensions of the fixed block and pressing block of the original cast aluminum alloy material, after detailed stress analysis and calculation, equal strength treatment is adopted, and the drawings of the fixed block and pressing block made of phenolic sandwich material are designed on the premise that the assembly and relevant dimensions remain unchanged.

Product physical test

1) Strength test

Fixed block: according to the stress condition of the fixed block, we simplify it into the stress form of simply supported beam according to the most dangerous working condition, as shown in the figure

L = 310mm, when p rises to 49kN, cracks appear in the product, so we can get the bending stress = 35.4mpa

Briquette: according to the working conditions, we also test according to the form of Figure 2, l = 116mm. When p rises to 90kN, the product cracks, and its bending stress = 37mpa

2) Immersion test

We selected the fixed block for water immersion test, soaked the fixed block in water for 24h, repeated the above strength test, and obtained the bending stress = 36.3mpa, which is very close to that before water immersion. In this way, it can be considered that water immersion has no effect on the strength. At the same time, before the strength test, we tested its overall dimensions, and there was little change.

Assembly test

We choose a large-scale and representative jkm-2.8 * 6 multi rope friction hoist as the object of assembly test. After assembly, the fixed block and pressure block fit well with the friction pad, the gap between each fixed block and pressure block meets the technical requirements, the width is the same, and the bolt holes on the fixed block and pressure block fully correspond to the workpiece. At the same time, we conduct pressure test on the fixed block and pressure block on the workpiece.

Fixing block: install the fixing block on the cylinder shell of the hoist according to the assembly requirements, tighten the connecting bolt with a wrench, and continue to apply force until the nut fails, but the fixing block is not damaged.

Pressing block: according to the tightening torque of the connecting bolt given in the design, tighten it with a constant torque wrench until it meets the requirements, and check that the pressing block is intact.

Benefit

The research results have been applied to the series of multi rope friction hoists of our company since the early 1990s, and remarkable economic benefits have been obtained. Although the sizes of fixed blocks and pressing blocks of multi rope friction hoists of various specifications are not exactly the same, after we have done a lot of effective work in the popularization of fixed blocks and pressing blocks, we have minimized the die cost and shared it among multiple hoists, Thus, the manufacturing cost is greatly reduced.

4.1) process route comparison

Original process route: Casting - Drilling connecting holes - car inner circle - installing on the friction wheel - car forming - removing (marking before removal) - installing on the friction wheel.

New process route: the hot press adopts mold forming - installed on the friction wheel.

4.2) cost saving

For the hoist of the same specification, under the condition of the same size of fixed block and pressing block, the production cost can be saved by about 40% by using phenolic sandwich material than aluminum alloy material.

4.3) as the weight of the fixed block and the pressing block is reduced, the displacement weight of the hoist can be reduced by 5%, the current can be saved by 2% when the hoist is started, and the power consumption of one hoist can be saved by 50000 kW / h every year.

Conclusion

1) The fixed block and pressing block made of non-metallic phenolic sandwich cloth instead of metal material can fully meet the application requirements of multi rope friction hoist, and the benefit is remarkable.

2) Although the material is brittle, it falls freely from a height of 1.3m on the cement ground without hanging angle or local damage. And its strength and size are not affected by water immersion, which is suitable for the mine environment.

3) Reduce production costs, positive benefits.

4) Press molding, beautiful appearance, good interchangeability, improved the assembly efficiency in the factory, and was highly praised by the production units, especially the assembly workers.

5) Light weight, can reduce the moment of inertia of the hoist, save energy and reduce consumption.