At present, lifting machinery is widely used in industrial and civil construction. Among them, crawler cranes are favored by the construction industry due to their strong adaptability and large lifting capacity. Crawler crane lifting and luffing are completed by the winch action, winch failure is light to trigger safety risks, and heavy car damage. So how to ensure the safety of winch operation is the top priority of crawler crane operation.

The winch pawl locking mechanism is to prevent the brake system of the winch because of internal leakage and brake failure caused by the lifting arm and lifting objects falling safety devices.

1. Introduction of winch pawl locking device

· Crawler crane mainly has the main hook, vice hook, main boom luffing, vice boom luffing four pawl locking mechanism, and the structure is consistent. The outer edge of the side wall of each reel is processed into a ratchet, and its locking pawl is combined or separated by the pull line and spring control. One end of the pawl cable is connected to the control handle in the cab, and the other end is connected to the locking pawl.

When the control handle is pressed, the pawl snaps into the ratchet on the side wall of the reel under spring pressure, so that the reel cannot turn counterclockwise to avoid accidents caused by the winch braking system or hydraulic motor internal leakage of the lifting weight and the falling of the boom, that is, in the pawl-locked state of the mechanism; and when the control handle in the cab is pulled up, the wire rope in the pull wire pulls the pawl and compresses the spring, so that the pawl turns downward around the pin and is separated from the ratchet. In the pawl release state of the mechanism.

Traditional winch pawl locking device structure is simple, mainly by the pawl, spring, fixed bracket, pawl pull line, control handle, low maintenance costs.

But this pawl locking device also has multiple problems, such as pulling wire jamming, spring elasticity is not enough, handle operation inconvenience, etc., seriously affect the use of pawl locking device, is the main reason for the high maintenance rate of the pawl device, the use rate of less than 100%.

·In order to ensure the safety of crawler lifting operation, to ensure that the crawler crane winch safety locking device maintenance rate is low, the utilization rate of 100%, the crawler crane winch pawl locking device optimization, to ensure that the pawl locking device sensitive and reliable and easy to operate.

Using the latest hydraulic technology, the pawl cable and spring are replaced by a hydraulic cylinder. When the piston rod of the hydraulic cylinder is extended, the pawl is stuck into the ratchet on the side wall of the reel and the reel cannot rotate in the direction of the rope winding out; when the piston rod is retracted, the pawl is detached from the ratchet and the reel is not controlled by the pawl.

The hydraulic control circuit is connected to the hydraulic servo system of the whole machine, and the accumulator is directly connected, while the commutation of the solenoid valve is controlled by the switch in the cab. And the circuit controlling the hydraulic cylinder is connected to the central control circuit of the crawler crane, so that the flameout switch cannot be activated without locking the pawl to ensure the usage rate of the pawl locking mechanism reaches 100%.

2.Two kinds of winch pawl locking device comparison

2.1 Operability comparison

· Traditional pull-wire winch pawl locking device uses the handle to compress the spring to open the pawl, and then operate the handle to use the spring force to lock the pawl. When operating the handle, it is easy to be affected by the pull wire jam, spring elasticity fatigue, and the operation is more laborious.

· hydraulic winch pawl locking device using the hydraulic principle, the use of electronic buttons for control, simple and convenient operation.

2.2 Safety comparison

·Pull wire type winch pawl locking device in the long-term use process, pull wire and spring by the weather and climate corrosion, affecting the normal operation of the device, a certain project in Shenzhen two 250t crawler crane and a 50t crawler crane pawl locking mechanism failure times for statistics, the average number of failures for 6 times / unit ˙year.

Crawler crane winch pawl locking mechanism failure times are more, pawl locking mechanism in the maintenance process, the winch is not in the pawl safety protection, there is a security risk. Moreover, during the operation of the pull-wire pawl locking device, the driver is influenced by the mental state, safety awareness and external environment, and forgets to lock the pawl, which brings great safety risks to the normal operation of the crawler crane.

The hydraulic crawler crane pawl locking device has a complicated structure, using hydraulic system instead of pulling wire and spring, and the hydraulic system is divided into five parts: power element, control element, execution element, auxiliary element and working medium.

The power element is hydraulic pump, the control element is directional control valve to change the direction of liquid flow, flow control valve to adjust the speed of movement and pressure control valve to adjust the pressure, the execution element is hydraulic cylinder, auxiliary components tank, pipe fittings, accumulator, filter, etc., and the working medium is hydraulic oil, in which the power element, some auxiliary components and working medium can use the hydraulic system of the crawler crane itself to save production cost and maintenance cost.

Maintenance cost. The hydraulic system has high precision and is a mechanical operation system with low failure rate, which can ensure the long-term stable operation of the pawl locking device. The circuit of the hydraulic system can be connected with the central control circuit system of the crawler crane, so that the flameout switch cannot be activated without locking the pawl, which ensures the safety of crawler crane parking.

2.3. Comparison of maintenance

In addition to regular maintenance, the pull-wire pawl locking device also requires regular replacement of the pull-wire, for example, a project in Shenzhen 250t crawler crane, due to the coastal location, iron products corrosive, 250t crawler crane average 2 months to pawl pull-wire maintenance, to disassemble the pull-wire, soak with diesel, requiring 1 man days; every 12 months to replace the pull-wire, requiring 0.5 man working days.

The cost of labor is: 300 yuan/working day; material cost: 600 yuan/wire; gasoline 7.4 yuan/L, each soaking needs diesel 10 L. Machinery costs: each time the crane for the removal of the wire shall not be lifting operations, 250t crawler crane shift cost of 8630 yuan/shift (project internal transaction standards).

The cost of annual maintenance is: labor cost + material cost + machinery lost labor cost

Labor cost=(6×1+0.5)×300RMB/working day=1950RMB

Material cost=6×10L×7.4RMB/L+600=1044RMB

Machinery lost time = (6 × 1 + 0.5) × 8630 yuan / shift = 56095 yuan

The cost of annual maintenance = 1950 yuan + 1044 yuan + 56095 yuan = 59089 yuan

·The maintenance of hydraulic pawl locking device mainly includes replacing hydraulic oil filter, hydraulic oil and aging oil pipe. As the hydraulic oil used is the hydraulic oil of the main hydraulic system of the crawler crane, this hydraulic oil, hydraulic oil filter will be replaced every year, all the pawl locking device only need to replace the aging hydraulic oil pipe in the system can be, the current market hydraulic oil pipe are made of multi-layer rubber and steel wire pressed, durable, and the hydraulic system is not a stressed hydraulic system, the hydraulic oil pressure in the pipe is small, the hydraulic oil pipe can be used for a long time The hydraulic system is not a force hydraulic system, the hydraulic oil pressure in the pipe is small, the hydraulic oil pipe can be used for a long time.

After two kinds of crawler crane pawl locking device comparison, we found that the hydraulic crawler crane winch pawl locking device is simple and convenient to operate, reliable, and effective maintenance times less, greatly reducing maintenance costs, improve the integrity of lifting machinery, so that the crawler crane can better serve the construction units.