- Detail

It has been more than 30 years since the reform and opening up. It has brought earth shaking changes to our society, but also brought an unprecedented impact on the ideology of our people, and some inherent understanding has been gradually changed. Among them, the biggest "drop" should be the traditional cognition of "vast territory and abundant resources", which has been proved to be a misunderstanding of China's resource situation in the course of social development. The poverty of water resources per capita is even more shocking. According to statistics, among the more than 600 cities in China, there are more than 300 water deficient cities, of which more than 100 are seriously water deficient. The direct economic losses caused by water shortage amount to 200billion yuan every year, and the country produces 70 ~ 80billion kg of grain every year due to water shortage

In the 21st century, the contradiction between supply and demand of water resources in China is further aggravated. According to the prediction 10 years ago, the total water supply in China will be 620 ~ 650billion m3 in 2010, the corresponding total water demand will reach 730billion m3, and the gap between supply and demand will be nearly 100billion m3. The total water demand in China will reach 100billion m3 in 30, the water shortage in China will be 400 ~ 450billion m3, and the water shortage in China will be 600 ~ 700billion m3 by 2050. At the same time, the increasingly frequent extreme climate has brought unprecedented challenges to China's water resources. The extreme drought in Yunnan, Guizhou and Sichuan, which began in the second half of 2009 to the first half of 2010, is a typical example. The severe fact of the extreme drought at the source of China's important water resources reminds us what kind of crisis the water resources as an important resource are facingsince there are many inaccessible places at the source, how to make full use of the limited water resources and make them fully recycled is a problem that needs human beings to actively use their own wisdom to solve. Sewage treatment and reuse capacity will be an effective method to ensure the normal operation and development of society on the basis of poor natural resources

by the end of 2008, there were 1018 urban sewage treatment plants in China, with a drainage pipeline length of more than 315000 km, a sewage treatment capacity of 80.16 million m3/day, a total annual sewage treatment capacity of 25.6 billion m3, and a sewage treatment rate of 70.2%. Compared with 1949, the length of drainage pipeline has increased by 51 times, and the sewage treatment capacity has increased by more than 2025 times. According to the current construction speed of sewage plants, it is expected that by the end of the 11th Five Year Plan period, the scale of sewage plants will reach about 3000, and the length of pipeline and auxiliary facilities will also maintain an increase of about 15%. The growth of drainage pipeline laying length in China is shown in the figure below

in such a huge and rapidly growing market, traditional cement concrete pipes, glass fiber reinforced plastic pipes with sand and various cast iron pipes still occupy a certain number and still have a certain increase. However, due to the unique advantages of plastic pipes (structural wall pipes) such as light weight, corrosion resistance, good flexibility and convenient construction, all kinds of plastic structural wall pipes are more and more used in municipal drainage and drainage systems

among the plastic structural wall pipes used in urban drainage system in China, U-PVC double wall corrugated pipe and annular ribbed pipe are developed first. In the mid-1990s, the U-PVC ring ribbed pipe production line of corma in Canada was introduced, and then the U-PVC double wall corrugated pipe production line of unick in Germany was introduced. In the following years, the production technology of Polyethylene double wall bellows was gradually introduced into China, among which the equipment of Germany drussbach was typical. Because the forming condition of polyethylene resin is better than that of PVC, it has greatly improved the pipe diameter and waveform change compared with PVC pipes. Pipes with a pipe diameter of 1600mm can be produced in China. In the late 1990s, after the foreign production technology of double wall corrugated pipe was gradually digested and absorbed by China, cattle production equipment began to be localized, and the production cost of products decreased significantly. According to statistics, by 2005, there were 100 domestic manufacturers of all kinds of plastic buried drainage pipes in China, with more than 200 production lines and an annual production capacity of 300000 tons

2 analysis of influencing factors on the stiffness of plastic structural wall pipe ring

the rapid development of plastic structural wall pipe industry also brings many problems. A typical example is that in the face of fierce market competition, there is a deviation in the direction of technological innovation of production enterprises. Due to the lack of understanding of the stress state in the process of pipe construction and application, "high ring stiffness" has gradually become the ultimate goal pursued by production enterprises and construction units. How to improve the ring stiffness can be divided into three categories according to the methods adopted by enterprises at present:

(1) resin modification: adding additives that change the strength characteristics of the resin to increase the rigidity of the material

(2) change the structural characteristics of pipes

(3) composite high-strength materials such as profile steel to improve the overall rigidity

the effect of these methods, such as the drop weight test method of non plastic transition temperature of gbt6803 (1) 986 ferritic steel, needs further analysis and research. Around 2006, our center undertook the research work of the analysis and test method of the Ministry of science and technology of the people's Republic of China, "analysis of the rotating moment of inertia of structural wall tubes". Some of the research results have certain reference significance for how to improve the stiffness of structural wall tube rings

2.1 analysis process of rotating moment of inertia of structural wall pipe

this analysis work takes common PVC-U double wall corrugated pipe and high density polyethylene (HDPE) double wall corrugated pipe as the object

gb/t "determination of ring stiffness of thermoplastic pipes" gives the ring stiffness calculation formula as

where f - force value at 3% deformation relative to the pipe (KN)

i - length of sample (m)

y - deformation (m)

d - inner diameter (m)

from the formula, it is difficult to see the direct relationship between ring stiffness and pipe structure size. At the same time, there is no clear definition of the coefficient. For the purpose of simplifying the calculation of pipeline bearing external load pressure, the basic definition of ring stiffness is given in the appendix of is09969 determination of ring stiffness of thermoplastic pipes:

e modulus of elasticity of materials

i moment of inertia

d average diameter of pipe ring

s unit is kn/m2

it can be seen here that there is no obvious technical difference between the two precision experimental machines, namely, the ring stiffness of the pipe and the moment of inertia of the stressed section of the pipe. For the moment of inertia I, the purpose of optimization can be achieved through design. The main ideas of this analysis are as follows:

(1) theoretical ring stiffness value obtained based on the definition formula and through physical scanning, physical measurement, pro/e modeling, autocad'moment of inertia analysis and calculation

(2) based on the empirical formula, and passing the stiffness test of the physical ring

(3) verify the scientificity of modeling through data correlation analysis

(4) according to the analysis results, find out the internal factors and relationships that affect the rotational moment of inertia of the stressed interface of the structural wall pipe and even the ring stiffness

take the analysis process of Polyethylene double wall corrugated pipe as an example:

acquisition of samples and models: considering the representativeness of sampling, two types of pipes made of resin, polyethylene (PE) and unplasticized polyvinyl chloride (PVC-U), are obtained this time, and the ring stiffness is limited to S1 (> 4) and S2 (> 8)

sample slices are obtained by cutting in the direction parallel to the axis. Try to remove the edge burrs and other processing traces of the sample to prevent unnecessary interference factors during scanning. The scanning diagram is shown in figure 2:

the actual measurement of this section is carried out with vernier caliper and goniometer, and the measurement results are shown in table 1:

considering various expansion and contraction during polyethylene processing, as well as structural arc transition for processing convenience, which may cause interference to the analysis, during the analysis, a single wave crest is regarded as a trapezoidal section according to the measured data. Through pro/e modeling, the physical object can be basically restored according to the measured data for further analysis by AutoCAD. The restoration steps are as follows:

(1) use the solid "rotation" command to create a pipe solid model, including the ripple shape, as shown in Figure 3:

Figure 3 solid wall model

(2) use the "shell pulling" command to retain the shell with the outer wall thickness, including the ripple shape, As shown in Figure 4:

Figure 4 ripple model

(3) the entity "rotation" command is used to establish the inner wall model of the pipeline. The final physical drawing and the model tree of the entity modeling are as follows:

Figure 5 recovery drawing

from the physical drawing obtained from the above modeling, it can be seen that for the "moment of inertia m4/m per linear meter of pipe wall of the longitudinal section of the pipeline" to be calculated, Firstly, the pipe section moment of inertia of one ripple length of the pipe longitudinal section can be obtained by CAD analysis, and then the value obtained by analysis can be divided by the ripple length, so as to convert it into "the pipe longitudinal section moment of inertia per linear meter of pipe wall m4/m"

at present, the domestic enterprises used for the production of PE double wall corrugated pipes mainly use low-pressure high-density polyethylene with Yanshan Petrochemical brand of 6360m and Qilu Petrochemical brand of qhe16a/b as the main resin raw materials, and their elastic modulus is about 960mpa. Therefore, the elastic modulus E value in the following analysis is calculated as 960mpa

sample 1: according to the measured data obtained above, draw the section figure 6 in AutoCAD as follows:

Figure 6 AutoCAD drawing

use the region command in CAD to create two regions as shown in the following figure respectively for the section figure:

Figure 7 region analysis figure

and then subtract the redundant regions with the subtract command, The area of the longitudinal section of the bellows within a wavelength is obtained as shown in the following figure:

figure 8 area analysis figure

finally, the moment of inertia of the section is analyzed by using the masspop command, and the analysis results are shown in the following figure:

Figure 9 AutoCAD moment of inertia analysis

according to the above analysis results and the physical drawing obtained from pro/e modeling, the bellows is stressed on the Y axis relative to the above analysis coordinate axis, Therefore, the inertia moment value of the area of the section graph at the longitudinal section of the bellows is:

ix=40766.3327mm4

at the crest s=ei/d3

where: ix=40766.3327mm4

because I in the formula ei/d3 is strictly defined as the inertia moment per linear meter of the pipe wall of the longitudinal section of the pipe (mm4/mm), the resulting value of IX should be divided by the length of the ripple and converted into the inertia moment within a unit length, The calculation is as follows (all the following analyses are the same):

i=ix/51.10=40766.3327mm4/51.10mm=797.78mm4/mm

then: i=797.78mm4/mm=o.79778x10.6m4/m

the value e=960mpa

d=500mm+30.37mm=0.530m. Since the ring stiffness at the wave crest is considered, the d here should take the outer diameter of the pipe. Considering the influence of processing error, the nominal diameter is substituted here.Outside diameter value

the calculation shows that: s=ei/d3=5.13kn/m2

through the above methods, we analyzed the impact strength and flexural strength of nearly 20pvc/wood flour composites, which tend to rise first and then fall. Through the comparison between the calculation and the two groups of data measured by empirical formula, considering the simplification of some elements and the influence of measurement uncertainty in the modeling process, the two groups of data have basic correlation. Similar conclusions were drawn from the analysis of PVC-U

2.2 summary

the results show that:

(1) direct influencing factors of moment of inertia I:

according to the principle of material mechanics, we know that the method to obtain a large moment of inertia is to use structural walls while reducing materials. Through the theoretical analysis and practical measurement of the samples, we can get the following factors affecting the moment of inertia:

① inner wall thickness; ② Inner wall thickness; ⑧ Laminated wall thickness; ④ Outer wall width; ⑤ Internal angle size

through the collocation and integration of the above five elements, try to make the materials distributed far away from the centroid

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