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Designing Reliable Conveyor Belt Systems and Methods of Measuring Winder Rope Degradation

Nowadays, modern mining approaches are putting much greater emphasis than ever before on the reliability of the belt conveyor system that removes mined material, say coal, from the face. More specifically, with modern long-wall methods’ application, it is quite possible that up to 90% of the mine production comes from one face, and it, in turn, must be handled effectively by only a single-gate conveyor. Thus, modern mines are looking for a conveyor reliability of around 100%, and the conveyor industrial sector is under increasing pressure for achieving this target.

This target or objective can be achieved by the industrial sector by the following five design-associated guidelines [9]:

  • Guideline I: Design and plan for future requirements.
  • Guideline II: Design for simplicity.
  • Guideline III: Design for effective maintenance.
  • Guideline IV: Design for unplanned events.
  • Guideline V: Design for monitoring of equipment.

Winders that use steel wire ropes are generally used for moving materials in underground mines. During usage, the steel wire ropes are always subjected to continuous deterioration or degradation. Therefore, the ropes’ reliability is very important for the performance of shaft-equipped mines as well as for the miners’ safety. Past experiences, over the years, clearly indicate that the type of damage that occurs in winder ropes during their usage period includes, but not limited to, corrosion, abrasion formation of loops and kinks, and wire fatigue and resulting breaks [10-12]. Due to safety-related concerns, many mining regulatory authorities around the globe mandate periodic inspections to be conducted for determining the conditions of winder ropes. Thus, generally two types of inspections (i.e., magnetic non-destructive testing and visual inspection) are conducted as it is impossible to discover internal damage and corrosion through visual inspection alone.

Both magnetic non-destructive testing and visual inspection methods are described below, separately.

Magnetic Nondestructive Testing Method

Electromagnetic or permanent magnet-based methods are considered quite effective for detecting damage anywhere within a rope in both exterior and interior wires [11,13,14]. Magnetic rope testing is conducted by passing the rope through a permanent magnet-based device/instrument. In this case, rope’s length is fully magnetized as it passes through the test device. Magnetic rope testing devices are utilized for monitoring two distinct types (i.e., types I and II) of magnetic field changes caused by the existence of anomalies.

Type I is called loss of metallic area (LMA) and it may simply be described as a relative measure of the amount of material mass missing from a cross-section in a wire rope. LMA is measured by comparing a section’s magnetic field intensity with that of a reference section on the rope that represents the maximum, unworn metallic cross-section area. Type II changes involve a magnetic dipole produced by a discontinuity in a magnetized section of the rope such as a wire break, a groove worn into a wire, or a corrosion pit. It is to be noted that quite often these are known as leakage flux (LF) flaws.

Visual Inspection Method

This method is considered quite useful for highlighting changes in rope lay length and diameter, visible corrosion, crown wires’ wear, external wire breaks or loose wires, and any other external damage. In fact, visual inspection is the only effective approach to highlighting the severity of rope external abrasive wear as the magnetic approach/method tends to underestimate the crown wire wear.

Seven steps of the visual inspection method are as follows [l 1,15]:

  • Step 1: Measure the rope diameter and the lay length at a number of points/ sections.
  • Step 2: Examine for broken wires as well as excessive crown wear.
  • Step 3: Examine the entire rope end to end for damage or abuse.
  • Step 4: Examine the rope termination for broken wires, condition of fastening, and corrosion.
  • Step 5: Examine the sheaves for misfit, wear, etc.
  • Step 6: Examine the drum’s condition in the case of drum winders.
  • Step 7: Check for appropriate lubrication.

Typical Mining Equipment Maintenance Errors and Factors Contributing to Maintenance Errors

There are many mining equipment-related maintenance errors that may, directly or indirectly, compromise safety. Some of the typical/common ones are as follows [3,16]:

  • • Failure to follow properly prescribed procedures and instructions
  • • Installation of wrong part
  • • Parts/components installed backward
  • • Failure to detect while inspecting
  • • Failure to check, calibrate, or align
  • • Use of wrong lubricants, greases, or fluids
  • • Omitting a part/component
  • • Failure to act on indicators of problems due to factors such as time constraints, priorities, or workload
  • • Error resulting from failure to complete task due to shift change
  • • Failure to lubricate
  • • Reassemble error
  • • Failure to close or seal properly

There are many factors that directly or indirectly contribute to mining equipment maintenance errors. Some of the important ones are as follows [3,15]: [1]

  • • Poor manuals
  • • Poor provision for cable and hose management
  • • Poor layout of components/parts in a compartment
  • • Inadequate task inspection and checkout time
  • • Confined workspaces

  • [1] Lack of appropriate tools and troubleshooting guides • Inaccessible parts/components • Inability for making visual inspections • Inappropriate placement of parts/components on equipment • Excessive weight of parts being manually handled
 
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