For the proper operation of rolling stock, traffic management, and for commercial calculations, accounting of goods transported by rail is of great importance. It is also important in metallurgy, where the weight of raw materials delivered directly to blast furnaces and open-hearth furnaces in railway trolleys plays a significant role in the technological process, and for in-plant transport. To ensure such an account, we also need a railway balance.
Classification of Railway Scales
With the help of railway scales, empty and loaded wagons are weighed, and therefore, the mass of the transported cargo is also determined as the difference of these values.
The first scales for weighing cars were mechanical, including lever ones, based on a balancing mechanism. Then came the electromechanical devices that convert the mechanical effect of gravity into an electrical signal. This variety of scales include tensometric scales.
Today, with the help of railway scales, we can weigh wagons that are separately standing in statics and in motion without disengaging the train, that is, in dynamics. Automation of modern weighing devices recognizes locomotives, identifies the type of car, determines the unevenness of its load and the direction of movement.
Railway carriage scales are foundational and foundationless, for weighing in statics and dynamics.
Static weighing
With static weighing, the railway scales began . Weighing the train in statics is very slow. The train disengages, and the wagons, one after the other, are fed to the scales, weighed with a stop on the platform, their mass is fixed, then the train is formed and sent. The road and cargo owners suffer enormous losses due to downtime.
This problem became especially acute with the development of the railway network and the increase in cargo flows. They tried to solve it using the same static scales, on which the train moved very slowly, at a speed of 3 km / h. A special signaling system was even developed that helped the driver maintain this speed. Downtime was slightly reduced, but the weighing process was rather complicated, and the error was high, more than 1%.
Dynamic weighting
Automatic train scales are used to weigh the rolling stock. Weighing in dynamics, I must say, the direction of weight measurement is promising, and not only on the railway.
The process consists of determining the mass of a car passing through a lifting platform in a fraction of a second, registering it and transferring it to a control computer or automated transportation control system.
In the process of weighing, the types of cars are determined, since with axial weighing, the weight of the axles of each car is important, and the loading is correct, locomotives are recognized, because they are not weighed.
The recognition of rolling stock is based on the determination of their interaxal and interbase distances.
The most vulnerable unit in the weighing system are track alarms that issue a signal when the flanges of the wheel or the axis of the car pass over them. The reliability of these devices is subject to very high requirements, and they work in harsh conditions, both operational and climatic.
Load platform
Railway scales for weighing cars differ in a variety of design solutions, but the common thing for them is the presence of one or more load platforms. A car passes through them during weighing, and the vertical forces that act on them are transmitted to the transducers.
When rolling a car, not only vertical forces act on the platform, but also longitudinal forces, which create certain errors during weighing. To reduce their impact, various mechanical and electronic devices are included in the loading platform. It can be restrictive emphasis, stretching strings, transitional bridges; force transducers that convert force into a specific electrical signal; track control devices.
Electronic devices that control the weighing process, process the signal from the converter and give the result to the computer and for visual reading on the scoreboard. Using special software, the computer processes the weighing results and generates a report.
Types of load receptors
Railway railroad scales also contain mechanical weighing devices. They are of two types:
- good old lever devices, in which through summing levers the load is perceived by one load meter;
- Leverless devices with four or more load meters, on which the load-receiving platform is located.
Lever - reliable, stable, easy to adjust according to the method for all types of lever scales. But bulky levers, firstly, are made by special technology only at enterprises with a high level of production. And secondly, their work requires an expensive special foundation.
The linkless devices are simple in design. They can be made in small workshops, and the foundation can be much smaller.
Railway weight meters
Today, railroad railroad scales are manufactured dynamically with strain gauge or vibration-frequency converters as force meters.
Vibration-frequency converters with the simplicity of communication lines and processing of output signals, noise immunity, and the absence of information loss, which eliminates additional errors, are preferred in scales with a lever device. The volume of secondary equipment is the same as when using strain gages. It increases significantly if these transducers are used in scales with a leverless load receptor, since they need to be installed four or more and their signals pass independently through different channels, and the separately obtained characteristics are summed.
With strain gages, force transducers are connected in parallel or in series, and one common signal is processed.
All devices are mounted in the pit of the foundation on which the railroad scales are located. The rails of the supply paths are also stacked on the concrete base in order to reduce vertical fluctuations of the composition in the weighing zone. In a special room next to the loading platform, secondary electronic equipment and a computer are installed.
Weighing accuracy
Railway scales for weighing freight wagons must ensure weighing accuracy that meets the established standards, of which there are four today: 0.1; 0.2; 0.5 and 1% of the mass of the cargo.
With static weighing on a lever scale, only the last two standards of accuracy are met. When weighing in dynamics, the influence of the automatic coupler, acceleration, and weighing method is superimposed on the error of the device.
Practice has shown that an accuracy rate of 1% is ensured for the mass of cargo in each train of a train, 0.5% - for inertia-moving disengaged cars and the total mass of the train, 0.1% - if no more than 20 cars are engaged in the train.
Weighing Methods on a Rail Scale
Railroad railway scales dynamic differ in the way of weighing. It is selected based on several conditions:
- the necessary accuracy of weighing and the associated maximum speed of the composition;
- capital costs for the installation of a weighing system.
Car weighing is carried out on a long platform on which the entire car is placed. This method is convenient in cases where the entire rolling stock consists of the same cars.
During body-weighting, each carriage of a car is separately weighed, their masses are stored and summed by a measuring device, and the result is entered into a computer.
With axial weighing, the masses of all axes are weighed and summed up, displaying the total on the display and transferring it to the computer.
Advantages and disadvantages of the methods
All weighing methods have their advantages and disadvantages. The wagon method is the most accurate, but the platform should be long, and only a train coupled from wagons of the same type, or rather the same length, can be weighed. The load with this method is measured in the range from 80 to 160 tons.
Weighting on the same scale is possible for most types of cars, but this method also requires a fairly long platform. The load on the railway scales in this case varies in the range from 40 tons, if a four-axle car is weighed, to 80 tons, if the car is eight-axle.
The axial weighing method requires a small platform. Since the distance between the axles of cars of various types is the same, then the whole fleet can be weighed on the same scales. The maximum load in this case is 20 tons.
The disadvantage of axial weighing is the high probability of the redistribution of load on the axis. It is possible to reduce the influence of this factor on the reliability and accuracy of measurements by choosing more rigid paths and stacking them more carefully. In this case, axial weighing is the most profitable both in terms of installation costs and maintenance of different types of wagons.
Rail Scale Installation
The installation method of the carriage scales depends on their type. For example, there are portable railway scales (see photo below), which are installed on the inside between the rails and weigh each axis in series.
Scales can be installed on the foundation and without it. In different types of scales, strain gauges can be built into rails, into sleepers, or between them.
Having chosen the type of scales, you need to determine the place of their installation. Firstly, using the device should be convenient. Secondly, the slope can be no more than 1: 2000, and the straight section - at least three car lengths (experts advise 15 meters on both sides of the weighed car).
Before installation, you need to find out how close the groundwater is to the surface and whether there are underground utilities in this zone, whether rain and melt water are collected in it.
The manufacturerโs manual contains quite detailed installation instructions, including a drawing of the concrete base and the necessary embedded elements for the foundation installation of the scale.
During installation, the gaps between the rails of the cargo receiver and the main should be maintained.
According to GOST R 53228-2008, calibration of railway scales to determine the measurement error should be performed annually.
Repair of railway scales
During prolonged or improper operation of the carriage scales, mechanical breakdowns of structural elements, malfunctions in the electrical circuit or malfunctions of the software may occur.
Different specialists are needed to eliminate these problems, therefore it is better to purchase measuring equipment in specialized companies licensed to repair the scales, which can subsequently carry out repair work, replace failed parts and assemblies, and check.
Summing up, we can say that we need to choose a railway scale, firstly, at the required accuracy; secondly, according to operating conditions; thirdly, on financial opportunities. And just as meticulously should choose the company in which this equipment will be purchased. Low starting cost can lead to serious problems in the operation and maintenance of the balance, which ultimately entail additional costs.
Operating conditions - this is not only the number of goods transported per day. This is the presence of electricity, because it is not available in all regions, and strain gauges cannot work without it. In low temperatures of the Far North regions, mechanical force measuring sensors work better and more accurately.