(5) after replacement of the working device, pouring, lifting, installation, piling and ramming operations can be carried out.

TWO.shopping elements
As the saying goes, "if you want to work well, you must first use your tools." Today, the problem before every construction unit or individual is how to choose the right engineering equipment. As one of the most important types of construction machinery in engineering construction, the correct selection of excavator becomes more important. How to choose hydraulic excavator correctly is decided by many factors, such as the nature of construction task, scale, technology, economy, matching equipment and construction time requirements in construction engineering.

In addition, the following factors are very important: good mechanical performance, reliability and durability, short payback period, improve comfort and safety is necessary. In addition, good after-sales service can reduce user downtime and improve economic efficiency. Of course, the supply and the price of accessories are important factors that must be considered when choosing equipment.

1. Engineering scale
The crawler hydraulic excavator can be selected in the case of large workload and poor working condition. In the case of strong bearing capacity, uneven, multi-pit or hard bulk ore, narrow crawler weighted hydraulic excavator should be selected; otherwise, in the case of weak ground bearing capacity and loose soil, wideband lengthened excavator should be selected.

Large-scale earthwork and medium and large-scale open pit engineering should be analyzed, compared and calculated scientifically by the design institute or relevant experts according to the total investment and supporting equipment and other factors to determine the specifications, models and quantities of hydraulic excavators. Generally periodic small and medium-sized projects, such as road maintenance, farmland water conservancy, just choose the ordinary model of excavator can be, such as the widely used 20-25T model of excavator can fully meet the requirements.

Tire-type hydraulic excavator should be used in the case of small workload, good working conditions and frequent changes in working face; backhoe and long-arm working devices can be used in cleaning and dredging river bed or waterway; and various working devices can be ordered to be replaced at any time according to construction requirements, such as shovel, backhoe, grab, hydraulic hammer, drill. Holes and other working devices are available.

2. Engineering matching equipment
When purchasing the excavator, we should consider the matching with our own existing equipment, including the matching of the excavator efficiency with the existing equipment efficiency. For example, the small excavator price is low, but it does not match the big dump truck, which is equivalent to the "small horse cart", and the "big horse cart" does not match. In construction practice, there is an empirical formula accepted by many construction managers, that is, the optimum combination of hydraulic excavator and dump truck should be 5-7 buckets of dump truck. The formula is:Q = Q / (5-7) r
Q: excavator bucket capacity (m3); Q: dump truck load (Ton); r: excavation material bulk density (t / m3)

3, existing capital situation
Now users are aware of the benefits of purchasing excavators, if you can receive the project, there will soon be cost recovery, Ko is instant effect. We can consider a variety of purchasing methods according to the capital situation: installment payment, bank mortgage, lease purchase, etc. If there is no problem with the funds, we can consider optimizing our own equipment structure and purchasing excavators of international famous brands, thus invisibly enhancing the competitiveness of our own large-scale project contracting.

4. Operation conditions and construction fluidity
The mobility of work engineering and construction directly affects the selection of excavator's walking structure and working device.

(1) matters needing attention when choosing walking parts.
The walking parts of excavators are generally divided into three main categories: crawler type, tyre type and floating boat type.

Tracked excavator is used relatively more, its characteristics are large traction, low ground pressure (generally 0.04-0.15 Mpa), good stability, good off-road performance and climbing performance. It is widely used in poor working conditions, according to the working conditions of the ground speed of the general selection of standard crawler excavator; if the working conditions of the ground bearing capacity is strong, and the uneven ground should choose narrow crawler plate excavator; if the working conditions of the ground station bearing capacity is poor, and the soil is loose, it should choose the track. Excavators with lengthened and widened caterpillar slabs should be selected for construction in marshes. But please note that the longer the track is, the better the track width is. If the track board is too long or too wide, the wear will be faster, and the supporting wheel, guide wheel and drive wheel will be damaged prematurely by frequent external impact; similarly, the machine with too short track, too short track and too narrow track board will also cause premature damage under unsuitable working conditions.

The use of tyres and floating boat excavators is relatively limited. Tyre excavator is characterized by high transmission efficiency, fast walking speed, good mobility and good mobility. Generally used for better working conditions, and the workplace needs frequent shifts. Floating dredgers are generally used for dredge of silt deposits such as riverbeds, rivers and lakes.

(2) matters needing attention in selection of working devices.
In general, the working device of excavator includes boom, bucket rod, bucket and related hydraulic cylinder and pipeline. Because the working device of the excavator can be replaced easily, the corresponding working device can be replaced according to different working conditions to meet the needs of various working conditions.

For example, the whole working device can be used to lengthen the arm (boom, bucket rod are lengthened, bucket capacity is reduced), so that the excavation scope of the excavator increased, especially suitable for general River dredging; dredging only from the river bank on both sides of the river can be. Rock excavation in mines with high working intensity needs to be equipped with strengthened Boom Bucket bars to deal with bad working conditions to ensure the smooth completion of the project.

In terms of buckets, according to different excavation conditions, the standard buckets for general working conditions, the rock buckets for enlarging buckets for soft soil and the silt removal buckets for dredging can be selected separately. In addition, the bucket part can also be replaced by a crusher, which is fully used in the crushing of large rocks. Small workload crushing is much safer than explosive blasting, and is easy to operate and highly efficient. Buckets can also be replaced by forks, grabs, fully used in the disposal of some waste items; replaced by hydraulic shears, fully used in the demolition of buildings and other buildings, is a good investment direction for the units or individuals engaged in municipal engineering. There are many other things that can be installed (e.g. loosers, crushers, cutting edges, piling machines, etc.), which are not explained in detail. Under special working conditions, the construction site should consider whether to install a cylinder protective cover to prevent falling objects from breaking or obstacles from crashing the cylinder.

Three, careful selection of models and brands.
According to the above four factors, the size, quantity, structure and working device of the selected excavator can be determined. The following three factors can determine the specific model and manufacturer of the selected excavator.

1. The performance, reliability and durability of the machine itself.
The main components such as engine, hydraulic pump, excavator valve and hydraulic motor are very important to ensure the reliability and durability of the machine. The performance of these components directly affects the life of the excavator. As the power source of the excavator, the engine requires high power, high torque and environmental protection. Therefore, as the power source of excavator, we must select the engine specially designed and manufactured by the world-famous engine manufacturer for construction machinery, and the hydraulic components such as hydraulic pumps, control valves and hydraulic motors should also be manufactured by the world-famous manufacturers of hydraulic components. Only in this way can the assembled excavator be durable.

2. Comfort and safety factors of driver's worktable.
The cab environment and operating system are directly related to the operating comfort and safety of driving, and affect the working efficiency. Attention should be paid to the installation of shock absorbers in the cab of excavators, the sealing effect, the adjusting angle of seats and their comfort, the equipments of air conditioners, radios, cigarette lighters and fire extinguishers, the emergency escape devices, and the selection of cab fences and FOPS for special working conditions to ensure the driver's safety. Safety.

3, the credibility of manufacturers and the perfection of after-sales service.
Good after-sales service can reduce user downtime and improve economic efficiency. Of course, the supply of accessories and the price are important factors that must be considered when choosing equipment.

(1) manufacturer's reputation survey
Because there are many factories producing excavators now, we can investigate each manufacturer before purchasing. For example, we can know the usage of excavators through the old users of each manufacturer, and we can also know some information about the quality assurance and performance of the products by visiting factories or exhibitions of each manufacturer. According to the collected information analysis and comparison, as far as possible to choose a good reputation, a sound sales system, quality assurance system of manufacturers to produce excavators.

(2) investigation on after-sales service of manufacturers
The manufacturer must have a perfect service system (including the situation of service agents, spare parts supply, service system within the guarantee period and the development of maintenance services beyond the guarantee period) to meet the maintenance, maintenance needs of construction units or individuals after purchasing equipment. If a manufacturer's service can not be guaranteed, even if the machine performance is no better do not buy this equipment, otherwise, it will bring a lot of trouble to users.

In short, after a comprehensive analysis of the above several issues, users will certainly be less blind in the selection of excavators, more rational, from a wide range of excavator brands to select a suitable one for their own.