During the installation and use of mine hoist, the brake disc deflection is out of tolerance, which is a frequent problem. The requirements of coal mine safety specifications: the end face runout of the newly installed lifting mechanism's moving disk shall not exceed 0.5mm; The end face runout of the moving disc of the lifting mechanism that has been used for more than 1 year shall not exceed 1mm. After the installation of the mine hoist, if the deflection detection fails to meet the standard, it indicates that the hoist has a major potential safety hazard (the auxiliary shaft hoist is inspected once a year after use, and the main shaft hoist is inspected once a year), which will have a serious impact on the safe production of the mine.

1 Cause analysis

1.1 Analysis of problems and causes in the manufacturing process The manufacturing of mine hoists is relatively strict, and the process is relatively complex. The quality of assembly personnel is required for processing equipment and processing. Take a single brake disc (two half split structure) as an example. The brake disc belongs to the thin plate half ring structure. If it is placed improperly after processing (such as leaning and leaning, or the bottom is not evenly padded when it is laid flat), the brake disc may be deformed. Elastic deformation will occur in a short period of time, which can be eliminated during assembly in the factory. After assembly, the table inspection can also meet the requirements of specifications and drawings. After assembly in the factory, for the large hoist, the brake disc is disassembled for packing in order to facilitate transportation. If it is improperly placed for a long time before packing, the brake disc will have plastic deformation. Since the manufacturing process in the factory has been completed, the problem will not be exposed again before shipment, which is one of the reasons for the brake disc deformation. In addition, if the packing design is unreasonable, the brake disc will also be deformed.

1.2 Problems in installation and cause analysis

The installation period of one hoist is closely related to the professional level of the installation unit, the placement of tools and the site environment. Generally, it should not exceed one month. In the field installation process, if the brake disc is taken out of the box in advance and placed improperly, the brake disc will be deformed after several days of use. In particular, the hoist installed in the adit or underground chamber cannot be transported in the tunnel due to the large volume of the brake disc packing box. The brake disc must be taken out and transported to the installation site. The mining flatbed truck is used for transportation. If the bottom is not leveled when placed, it is very easy to cause deformation due to bumps during processing. In addition, because the working site is narrow, most brake discs lean against the wall rather than lay flat. Even if they are laid flat, due to the limited environment, the staff will inevitably step on the brake disc frequently, and may pile debris on the brake disc. In addition, the bottom of the brake disc cannot be leveled, causing the brake disc deformation. When installing the hoist, it is required that after the winding drum is closed, the base surface of the winding drum and the brake disc shall be checked first, and the end face runout shall be less than 0.5mm.

If the end face runout of the drum base surface should not exceed the tolerance (the machining accuracy of the machine tool can be guaranteed) when the drum is not bumped during loading, unloading and transportation, the causes of the brake disc runout after installation are: the brake disc itself has been deformed; When the installer tightened the connecting studs between the brake disc and the drum, the operation mode was wrong, and the brake disc was not tightened symmetrically, evenly and repeatedly, resulting in deformation of the brake disc.

1.3 Analysis of problems and causes in use

After the hoist is installed and tested as qualified, it will enter the use preparation stage, including the winding of the single rope winding hoist drum and the change gear of the multi rope friction hoist.

(1) The greater the lifting height (total lifting length of inclined shaft) of single rope winding hoist, the greater the rope winding amount. When the rope is wound, the drum must run at a very low speed, so the disc brake is used to brake the brake disc for operation. After a long time, the brake disc heats up, and in severe cases, the brake disc turns blue. After the rope is wound and the brake disc cools down, serious deformation will occur, which is common.

(2) The safety regulations require that the contact area between the brake shoe and the brake disc should be ≥ 6O%. Many of the contact areas between the newly installed hoist brake shoe and the brake disc cannot meet the specification requirements, so the brake shoe needs to be treated. Most mines do not use mechanical processing to repair the brake shoe (more complex, difficult to control), but use the method of grinding the brake shoe against the brake disc. That is, the drum runs at full speed before winding (hanging rope), and the brake shoe gradually rubs against the brake disc until i>60% contact is reached. Although this method is simple and feasible, it will take several days to actually grind the brake disc. During this period, the surface temperature of the brake disc shall not exceed 80 ℃. When the temperature reaches 80 ℃, the brake disc shall be stopped, the powder on the brake shoe surface shall be removed, the brake disc surface shall be wiped, and the grinding shall be carried out after the temperature is reduced to room temperature, and the grinding shall be repeated until the requirements are met. In order to catch up with the construction period, some units make the brake disc stick grinding under high temperature for a long time, and the brake disc deforms after cooling. This is often the case for the deformation of the moving disc of a multi rope friction hoist.

(3) The set deceleration distance of the winding hoist is longer, so the braking time of the disc brake is longer. Especially when the inclined shaft is lifted, the brake disc is very easy to heat up more than 80 ℃, and the brake disc will be out of tolerance deformation after a short time of operation.

2 Treatment method for disc brake deflection

3 Practice Results and Test Data

According to the experience accumulated in many years of after-sales service, more than 90% of the brake discs installed on site can meet the coal safety requirements after baking and turning.