Overhead monorails are primarily used to lift large or heavy items and move them horizontally. Monorails can be driven manually or powered. Power-operated overhead monorail systems are typically powered by air, hydraulics, or electricity. Overhead material handling systems can be supported on single or multiple girders and can be top-running or bottom-running. Bottom-running systems travel along the bottom flange of the supporting beam and are typically associated with monorails and bridge cranes. Multiple girders and top-running systems are typically not associated with monorails but rather with overhead or gantry bridge cranes. This course covers the basic design of a monorail with a bottom-running manually driven trolley hoist on a single girder or beam. The monorail crane design was first thought of with the thought and need to improve in these elements of business: Increase productivity and efficiency, reducing the risk of injury to individuals, producing greater cost savings, and to also improve quality.
Monorail System Designs and Operational Safety
The safe operation of a monorail crane design has some impact on the design of a monorail system. Engineers need to be concerned with the operational safety of the monorails they design. To that end, engineering drawings should include some or all of these factors: maximum lift design load, safety, impact, or load factors used, maximum angle or load due to side pull, method, and locations of labeling stating maximum capacity, warnings, etc. Additionally, the engineer needs to have a full understanding of how the final monorail system is anticipated to be operated. Without operations input, a monorail can be poorly designed for the intended use, ultimately resulting in the death or injury of the operator and/or bystanders.
A safety plan for the operation of the monorail should be developed with input from all parties involved: owner/specifier, engineer, inspector, and operator. The plan should incorporate, at a minimum, the following information: Responsibility of all parties, Design requirements (i.e., codes, safety or impact factors, labeling, etc.), General safety rules, Operational rules or instructions, Rigging requirements, Inspections, Maintenance, and Testing, Record keeping responsibilities.
Monorail Crane Design | Different Classifications
Monorails were designed with four different classifications. Each one specified based upon its level of service. The four types are as follows: Class A – Standby or Infrequent Service – Capacity load handled during installation and during infrequent maintenance. Class B – Light Service – Load varies from no load to the rated load and is lifted 2 to 5 times per hour and averaging 10 feet per lift. Class C – Moderate Service – Lifts 50% of a rated load 5 to 10 times per hour and averaging 15 feet per lift. Class D – Heavy Service – Lifts 50% of the rated load more than 10 times per hour.
In many cases, the classification can easily be determined; however, the code also provides a table that can be used to determine the classification based on more detailed information: load classes and load cycles. The four (4) load classes per the code are: L1 – hoist normally lifts with very light loads and very rarely the rated load. L2 – hoist normally lifts loads at 1/3 the rated load and rarely the rated load. L3 – hoist normally lifts loads 1/3 to 2/3 the rated load and lifts the rated load fairly frequently. L4 – hoist regularly lifts close to the rated load.