Welcome

DonNTU Masters' portal

Introduction

Construction is the one of the most important processes in the development of industry, business, housing of the country. It is implemented in all sectors of the economy, providing a basis for increased production.

Currently, construction works, whether the construction of industrial buildings, residential complexes, roads, railways, bridges, made possible by mechanized and automated manner at all stages of construction.

The use of scrapers in the preparatory phases of construction works on the digging, transport and the creation of mounds of soil, significantly increases the efficiency compared to the work by hand.

In the work process scraper interacts with the ground through the working body, which is a bucket with a blade system. Different constructions of scraper's buckets and knife systems depending on the physical and mechanical properties of the soil provide one or another performance of the machine and the wear of its working bodies. [1, 2]

Topicality

Digging machines, earthwork machines used in the construction of industrial and civil buildings, construction and repair of railway and cartage roads, underground pipelines. Digging machines works with soils of all categories, including frozen, rocky, marshy, and mineral deposits.

Later, perhaps, the results can be adapted and applied not only for the scrapers, but also for various earth-moving machinery.

Currently, the increase of productivity and efficiency scrapers do Dnepropetrovsk Civil Engineering Institute, Kirovohrad State Technical University and other technical institutions of the country. The process of cutting and digging the soil study such Ukrainian scientists, as Khmara, Boginya, Karpushin, Ankudinov, Starunsky, Sokolov, Litvinov, Urih and others [3, 4].

The main problems associated with increase productivity of scrapers are: cutting resistance of the soil, uneven filling of the bucket in relation to the resistance movement of soil, adhesion processes [2, 3, 5]. Increased productivity of scrapers directly linked to increasing the efficiency of earthmoving for any construction.

Purpose and objectives

The purpose of the research work is to identify and propose ways to increase scrapers productivity. To achieve this mission will be fulfilled the following objectives:

• study the interaction of working bodies of the scraper with the ground;
• examination and review of existing structures working bodies, patents review;
• assess the effects of physical and mechanical properties of the soil on the process of cutting, digging, loading, unloading and transportation;
• identify the main parameters affecting the adhesion properties of soil;
• offer ways to improve the design of the bucket for increased productivity basis of the analyzed material and the conclusions reached.

Review of patents showed that the problem of unloading soil from a scraper is proposed to solve mechanical means at the moment of unloading. This is proposed to use screws, double flaps, flexible bottom and other solutions to the impact on the soil [4]. This complicated structure. The idea of this work is to influence the soil already in the transportation process. To propose the principle of impact on the soil need to understand the nature of its adhesive properties.

Adhesion properties of soil

Adhesion properties of soil are manifested in the interaction of its parts among themselves, as well as with the working surface of the machines.

Adhesion - adhesion of the surfaces of two different solid or liquid bodies [6]. Adhesion is caused by the same causes as adsorption. Quantitatively, the adhesion is characterized by the specific work expended on the separation of bodies. This work is calculated per unit area of contacting surfaces.

In practical application to manufacturing processes adhesive properties of the soil is sticking together and sticking it to the working surfaces of equipment, freezing.

A distinctive feature of transportation cohesive soils — dependence of efficiency on the season and climatic conditions. To a great extent this is characteristic just for the transportation of cohesive moist soil. This is explained by the tendency of this species to intensive adhesion processes.(The ability to stick and freeze to the surfaces of vehicles).

In difficult conditions, especially in fall and spring and winter periods, the efficiency of transportation is reduced to 50% because of intensive trapping and freezing the soil to the surfaces of vehicles. Because of this unloading scraper is not complete. The volume of not unloaded soil sometimes reaches 30% of useful capacity of the bucket (if you do not use coercive methods of unloading), which leads to the underutilization of its useful capacity [6].

In case of contact working surface of the vehicle with the soil begins the process of wetting the surface with the pore fluid. This process occurs almost instantaneously. Simultaneously, there is a process of condensation of fluid in the gaps between the mineral soil particles and the surface [7].

In any case, contacting a real soil with the work surface leads to the formation of liquid cuff between the surface and mineral particles. As a result, the interaction of particles of soil connected with the work surface of a vehicle going through a layer of liquid cuffs in wetting areas. In this case, the following options wetting:

• individual mineral particles interact with the surface through a layer of segregated liquid cuffs (low soil moisture);
• some mineral particles interact with the solid surface through a layer of joint fluid cuff (high soil moisture).

Other options of contacting the mineral particles with a solid surface can not be [6].

Heating of the bucket's contact surface with disperse cohesive soils

Calculations show that heating of the contact surface is an effective way of evaporation of liquid cuff that prevents the build-up of soil on the walls and bottom of the bucket. The calculations are based on [7, 8] for particles of radius from 5x10 ^-6 m to 500x10 ^-6 m at different temperatures. The results were summarized in Table 1 and presented in a graph in Figure 1

Table 1. The results of the calculation of adhesion force at different temperature, F _ad x10 ⁶ , N

Particle radius, Rx106m	Temperature, °К (°С)
	293 (20)	313 (40)	333 (60)	353 (80)	373 (100)	393 (120)	413 (140)
5	153,92	88,63	47,96	27,88	17,35	12,58	8,92
10	255,83	136	72,47	43,51	28,27	17,35	11,15
20	367,58	208,34	112,79	65,85	38,69	24,3	16,36
40	537,41	272,67	156,27	87,09	51,6	31,25	25,28
50	594,12	310,23	176,76	97,7	54,58	32,55	24,16
100	840,15	443,45	241,98	145,18	84,36	47,74	33,36
250	1340	733,78	403,41	237,36	161,29	97,66	74,36
500	1862	1024	527,64	363,06	223,35	108,522	92,95

Fig. 1. The adhesion force dependence from temperature for different radii of the particles disperse cohesive soil

The graph shows that with increasing temperature, the adhesive force of a single is reduced. For example, the temperature increases from 20 to 120 degrees Celsius adhesive force of the particle radius 5x10^-6m decreased 12 times.

It is also noticeable that when the temperature reaches a certain value ceases to vary the adhesive force and continues to remain virtually unchanged. This temperature - 120-140 degrees Celsius for a flat metal surface contact - in good agreement with experimental results [9].

Implementation of heating the contact surface

Perform heating surfaces of the scraper's working body is proposed by the exhaust gases of the tractor's engine. It needs a little modification of the construction bucket, namely: necessary to construct a system of canals on the outer or inner surface of the bucket's walls for passing into them hot gases and to link this system with the exhaust system of the tractor scraper.

Thus:

• eliminates the need for additional energy consumption;
• provided the relative simplicity of bucket construction compared to the known methods of forced cleaning [4];
• passive bucket cleaning achieved.

From the above advantages, it follows that the development method of cleaning the bucket with warm contact surface with the exhaust gases of the tractor engine is a promising avenue to increase productivity, efficiency and effectiveness of the scraper.

To implement and develop the design of scraper with a heating system it is necesary determine how the contact surface temperature depends from exhaust gasses temperature. Also, the final result depends on the physical properties of the gasses, geometrical parameters of the bucket and the canal system, ambient temperature and other parameters [7, 10].

To answer this question invented the mathematical model in the MathCAD, allowing to calculate the final temperature of the contact surface, taking into account the influence of all parameters and empirical coefficients.

The calculation of the temperature of the tube wall, heated by exhaust gases of the scraper's engine [2, 10, 11]

To make the calculations it's necessary to determine the nature of fluid flow inside the tube, this Reynolds number is calculated: where: – average flow velocity, m/s;
d – diameter (for circular tube) or equivalent diameter (for a tube of arbitrary cross section), m;
- kinematic viscosity of fluid, m²/с. where: V – second volume of fluid, m³/с;
F – sectional area of tube, m².

Grashof number: where: β – coefficient of thermal expansion of the medium, for gas β=1/T;
l – tube length, m;
Δt - temperature difference between fluid and wall, deg.
g – acceleration of free fall.

The nature of fluid flow may be laminar, turbulent and transitional. Identify it by using the Reynolds number. If Re<2x10³, a laminar mode of flow is, at Re>10⁴ turbulent regime of flow is. If the Reynolds number is between these values, the flow of the fluid is transition. Depending on the nature of flow is calculated Nusselt number for various empirical formulas.

Calculation of the Nusselt number for laminar fluid flow: Where: Pr_f,Pr_w – Prandtl number at temperature of fluid and wall temperature, respectively.

Calculation of the Nusselt number for turbulent fluid flow:

Calculation of the Nusselt number for the transition regime of fluid flow:

Then calculate the average heat transfer coefficient : where: λ – thermal conductivity of fluid, ^W/_(m•deg.).

Calculated wall temperature after heating: where: h_ст – wall thickness, m;
λ_w – the thermal conductivity of the wall, ^W/_(m•deg.);
t_w – initial wall temperature (ambient temperature), K.

Currently under development is construction of scraper with a heating system. The results of the work on the process of heating and temperature influence on the stickiness of cohesive fine-grained soils take into account. It is assumed that the proposed construction would reduce the amount of soil adhering to the walls and a bottom scraper in a few times, which in turn will increase the efficiency of the unloading process and increase machine productivity.

The results were presented at a student conference "Science Day" in the Donetsk National Technical University in 2009 and 2010. In 2010, the work involved in the final of the All-Ukrainian contest of student research papers in the field of science "Transport" in "Machines for ground road and forestry work", following which received a diploma "For the original method of research."

When writing this author's abstract work was far from over, therefore, the results and conclusions of the work may differ materially from the information in this synopsis. The final completion of the work - December 2010

Sources

1. Артемьев К.А. Основы теории копания грунта скреперами/ К.А. Артемьев. – М.: Машгиз, 1963. – 128 с.
2. Зеленин А.Н. Машины для земляных работ/ А.Н. Зеленин, В.И. Баловнев, И.П. Керов. – М.: Машиностроение, 1975. – 422 с.
3. Баловнев В.И. Повышение продуктивности машин для землеройных работ/ В.И. Баловнев, Л.А. Хмара. – К.: Будівельник, 1998. – 21 с.
4. Описания изобретений (полезных моделей) патентов Украины №5303 C1, №59669 А, №4920 U, №31977 A, №53997 A.
5. Общие сведения о грунтах: [Electronic resource]. - Access mode: http://ru.wikipedia.org/wiki/Грунт
6. Гончаров С.А. Перемещение и складирование горной массы/ С.А. Гончаров. – М.: Издательство Московского горного университета, 1996. – 285 с.
7. Гончаров С.А. Влияние температуры на липкость связных пород/ С.А. Гончаров, С.А. Потапов. – Изв. ВУЗов «Горный журнал». – 1976. – с. 74–77.
8. Калачев В.Я. Новая методика изучения липкости глинистых грунтов/ В.Я. Калачевю. - М.: МГУ, 1975. – 89 с.
9. Потапов С.А. Экспериментальное определение адгезионных свойств пород. В кн.: Комплексные исследования физических свойств горных пород/ С.А. Потапов. – М.: 1977. – с. 4, 11–12.
10. Нащокин В.В. Техническая термодинамика и теплопередача. Учебн. Пособие для неэнергетических специальностей вузов/ В.В. Нащекин. – М.: «Высшая школа», 1975. – 496 с.
11. Кукателадзе С.С. Справочник по теплопередаче/ С.С. Кукателадзе, В.М. Боришанский. – М.: «Госэнергоиздат», 1958. – 417 с.

On top