Parent Roll Handling Crane, Dry End Crane, and Winder Crane: Essential Mechanical and Electrical Configurations for Paper Mills

The parent roll handling crane is one of the essential pieces of equipment in a paper mill. It can be used for both the dry end and the wet end of the paper machine, so it can also be referred to as a dry end crane or a winder crane. Considering the specific environmental characteristics of the paper mill and the operational requirements of the parent roll-handling crane, this paper provides specific recommendations for the mechanical and electrical configurations of the parent roll-handling crane to meet practical production and usage needs.

With the continuous development of the paper industry in China, the demand for parent roll handling cranes in paper mills has also increased. The dry end crane is generally equipped with dual trolleys or triple trolleys, with special lifting tools attached below the hook for handling paper rolls, changing rollers, and other tasks. Sometimes, it is also necessary to operate in the wet section of the paper machine to assist with the replacement, repair, and maintenance of the machine’s components. As one of the crucial pieces of equipment in a paper mill, the operation of the winder crane is directly related to the normal functioning and production efficiency of the paper production line, highlighting its importance. This paper offers detailed recommendations for the design and configuration of the dry end crane, providing a reference for practical design and manufacturing.

1. Operating environment

Paper mills are primarily characterized by convection heat and humid heat conditions, with equipment surface temperatures ranging from 30°C to 100°C and room temperatures reaching up to 40°C to 45°C. The relative humidity in the air is typically above 90%, sometimes even reaching 100%. The mill contains large equipment, such as continuously operating paper machines, which generate significant electromagnetic interference. The handling of paper rolls requires both high efficiency and precise alignment at stable, low speeds. Therefore, compared to general cranes, the parent roll handling crane requires targeted design and configuration.

2. Mechanical configuration

Winder cranes are typically divided into two forms: dual-trolley cranes and triple-trolley cranes. Dual-trolley cranes are generally used for daily paper roll handling, while triple-trolley cranes are typically used for paper machine maintenance and auxiliary paper roll handling. The rated lifting capacity of a dry end crane is usually determined based on the type of paper, the width and speed of the paper machine, and other parameters. It is also necessary to consider the weight of the paper roll lifting tools, paper rollers, and paper rolls, with an additional margin of about 15% to 20%. In triple-trolley cranes, the rated lifting capacity of the middle trolley needs to account for the maximum lifting load required during the installation, maintenance, and component replacement of paper machine equipment. For parent roll handling cranes with larger rated lifting capacities, it may be advisable to install a 5t or 10t electric hoist beneath the main beam or walkway to improve the efficiency of handling smaller items.

By calculating the cycle of paper roll formation based on the speed of the paper machine and combining it with the weight of the paper roll, the required duty cycle of the parent roll handling crane can be determined. Considering the need for smooth operation, the lifting and traveling speeds should not be too fast. Winder cranes are generally installed on the second floor, and when determining their lifting height, it is necessary to consider the installation of the hook on the first floor. Additionally, to meet the process requirements for hook distance and hook limit positions, specialized designs are required to reduce the trolley wheelbase and overall width. For the triple-trolley crane configured at the wet end, to adapt to the work at the dry end, the dry end crane may impose requirements on the hook distance of the two side trolleys to enable the lifting of paper roll lifting tools.

The lifting and traveling mechanisms typically use frequency conversion speed control, with dual-speed or multi-speed configurations. In terms of control methods, to avoid interference with the paper machine equipment below, it is advisable not to use a cab for operation but to use remote control instead, with an independently movable ground control pendant as a backup. In practical applications, multi-speed joystick remote controls are increasingly being used.

The parent roll handling crane generally uses a winch-type lifting mechanism, though some cranes use foreign-brand electric hoists as the lifting mechanism. Winch-type lifting mechanisms typically have two sets of service brakes to ensure braking safety. To safeguard the lifting mechanism and avoid hook overtravel, it is recommended to add a weight switch in addition to the upper limit switch. Furthermore, installing a lower limit switch for the lifting mechanism can effectively prevent the lifting tools from continuing to descend after touching the ground, which could cause the wire rope to come off the drum.

To adapt to the humid and hot environment of the mill, it is recommended to use H-class, IP55 motors. If using frequency conversion motors, an independent cooling fan should be installed. Additionally, to better protect the motor, thermistors can be installed in the stator. The frequency converter should have an appropriate margin, and some brands offer “three-proof” products, where protective coatings are added to the chips and circuit boards of the frequency converter for better corrosion resistance. The resistors should be made of stainless steel, and galvanized wire ropes are recommended to extend the lifespan of the wire ropes.

Given that the paper mill environment typically contains corrosive gases, high temperatures, and high humidity, to ensure the longevity of the winder crane’s surface paint, the structure of the dry end crane should pay attention to the quality of pretreatment during manufacturing, use appropriate matching paints, and increase the thickness of the paint film as needed. Additionally, ordinary polyurethane buffers can become hard and brittle after some time, leading to failure.

If components like reducers on the parent roll handling crane leak or seep oil, it could contaminate the paper machine equipment and paper rolls below. A good solution is to install an oil collection pan beneath the reducer. Furthermore, excessive application of lubricant on the wire rope should be avoided. For the winder crane’s air conditioning, condensation water should not drip directly onto the mill floor; it can be collected in a bucket or drained to the sides of the mill through pipes.

3. Electrical configuration

The harsh environment of the paper mill poses a significant challenge to the electrical control system of the parent roll handling crane. To ensure the stable operation of the dry end crane’s electrical system, attention should be paid to the following issues:

1. Measures should be taken to reduce harmonic distortion and electromagnetic interference from the mill’s equipment on the winder crane’s power supply and electrical system. This includes installing input reactors in the frequency converter circuits and using shielded cables as control lines for critical components like PLCs, frequency converters, and remote control receivers.

2. Proper grounding treatment should be ensured for electrical components such as motors, rotary encoders, frequency converters, PLCs, and transformers.

3. Attention should be given to cooling and moisture-proofing measures for electrical control cabinets. Specific methods include setting up dedicated air-conditioned electrical rooms, equipping electrical control cabinets with cooling fans or air conditioners, and ensuring that the air conditioner’s cooling capacity is matched. The air conditioning temperature should not be set too low, generally not below 26°C, to prevent condensation inside the cabinet due to the temperature difference.

4. The protection level and sealing of electrical control cabinets and terminal junction boxes should be emphasized to prevent external moisture from entering and corroding internal electrical components.

5. In a humid and hot environment, relying on the contact between the trolley wheels and tracks for trolley grounding is unreliable. It is generally necessary to add dedicated grounding wires in the trolley’s traveling cable.

6. High-quality electrical components should be selected, including rotary encoders, limit switches, and electrical wires and cables.

In some cases, special electrical designs may be needed to meet the higher hook synchronization requirements of dual trolleys. Additionally, it is important to note that different types of paper production environments may vary significantly. For instance, tissue paper production workshops have a lot of scattered paper dust, which can easily cause blockages and fires. Packaging paper production workshops may have higher temperatures and relative humidity. These factors require different design approaches to address and resolve.

4. Conclusion

The winder crane, during its actual operation, will face the challenges of high temperature and humidity in the paper mill, as well as the demand for reliable and stable operation. To extend its service life and reduce equipment failures, appropriate mechanical and electrical configurations should be made for the parent roll handling crane to ensure its adaptation to the mill environment and safe operation.

This post is translated from Design and Configuration of Paper Roll Cranes.

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