Plastic working in China and related environmental issues

,I~araal~

ELSEVIER

Journal of Materials Processing Technology 59 (1996) 205- 212

Materials Processing Technology

Plastic working in China and related environmental issues Ruan Xueyu a,*, Zhou Decheng b, He Yongbiao

Chen Weimin

Shanghai Research histitute of Tool and Die Technology, Shanghai Jiao Tong University, 1954 Hua Shah Road, Shanghai 200030, People's Republic of Ch#ta b Department of Forg#lg and Stamp#tg, Harbin Institute of Technology, Harbin, People's Republic of China Department of 2nd Mechanical Engineering, Huazhong University of Science and Technology, Huazhong, People's Republic of Ch#1a Received 25 January 1994

Industrial summary

The People's Republic of China consistently pays great attention to environmental protection. The PRC Environmental Protection Law and the PRC Environmental Sound Pollution Prevention Regulation were formulated in 1989. Moreover, the Environmental Protection Committee of the State Council, China, has worked out the Catalogue of the Development of Present Environmental Protection Industry and the national standards concerned. Some environmental protection problems related to metal forming in China are introduced. Keywords: Environment; Plastic working; China

1. Vibration and noise in metal forming and its control

1.2. Noise standard and noise research #1 the metal-pktstic working hutustr.v of Chhla

1.1. Noise caused lo' .,;"~.... ..,...~,"'. . .,.,.,~;",,~/iarobfuhwss .

1.2.1. Noise standard [2-5] Table I shows the standards of allowable noise level in industrial areas [2].

The noises caused by ham:',e~ir.,8 during metal forging, vibration of the hammer ,base, clutch on-off and stamping of the press, exhaust of the gas circuit, operation of the blower and the air compressor, the operation of the furnace burner and air supply, gear engagement of the steel mill and press, and transportation of raw materials, are usually the main sources of noise in industry. Of them, the noise of hammering is the strongest, accounting for 60% of total industrial noise pollution. Generally, the noise in China's forging and stamping workshops reaches 120 dB (A); sometimes the impulsive noise during hammering will reach as high as 120-155 dB (A) or even 300 dB [1]. Noise can injure workers' hearing, affect their daily work, and lead to different kinds of diseases.

* Corresponding author. Elsevier Science S.A. SSDI 0924-0136(95)02132-6

1.2.2. Study of noise control #I metal-plastic work#ig 01 China In China, many fruitful researches and practical applications have been, for the first time, conducted on damping and noise reduction in forging and stamping by Gao Naiguang and Chen Weimin of the Teaching and Research Section of Metal-Plastic Working, Harbin Institute of Technology (HIT), and He Yongbiao of the Teaching and Research Section of Forging and Stamping, the Huazhong University of Science and Technology (HUST). Subsequently, much research work has also been done in the Ji'nan Research Institute of Forging and Casting Machinery, Xi'an Jiaotong University and in the Jiangxi Institute of Technology. Their main achievements are introduced briefly as follows: 1.2.2.1. Study on the noise reduction of air hammers [Z8]. The noise source of the air hammer and the mechanism of noise formation was studied and analyzed

R. Xueyu et al./Journal of Materials Processing Technology 59 (1996) 205-212

206

Table 1 Standards of allowable noise levels in industrial areas [2] Time subjected to noise per working day (h)

Allowable noise level in newly-built, extended, and remodeled enterprises [ d B (A)]~

Allowable noise levels for those existing enterprises temporarily under the standards [dB (A)]

8 4 2 I 0.5

85 88 91 91 97

90 93 96 99 102

aNo higher than 115,

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Hg Fig. 1, Signal amplitude spectrum of the noise at the gas nozzle of a ! 50 kg air hammer: (a) 512 times attenuation; and (b) 256 times attenuation.

in depth with the conclusion that the basic approach to reducing exhaust noise is to install an exhaust muffler. In the forging and stamping laboratory of HIT, a C41-150 150kg air hammer was tested and analyzed by spectroanalysis and selective covering methods, four types of mufflers with different structures being proposed. With the help of an ND2 precision soundlevel motor, a cassette tape-recorder and a signal protossing machine, the noise was detected as 109 dB (A) at a location 0.5 m away from the upper gas nozzle of the compression engine and at an angle of 45 degrees to the shaft line of the gas nozzle. The signal amplitude spectrum of the noise was also obtained at the gas nozzle of the hammer, as shown in Fig. l(a), in which the vortical ordinate is the amplitude spectrum:

Fig. 1 shows that the exhaust noise is characterized by medium and low frequencies with a wide frequer~cy band, and has distinct peak values within the range from 39 to 577.76 Hz. Since the exhaust noise of the air hammer has a wide frequency band, neither a resisting muffler nor a resistant muffler alone will work ideally. Nevertheless,

although the resisting muffler can reduce high-frequency noises successfully, it cannot reduce low-frequency noises. Therefore, four types of mufflers were experimented on in HIT: (a) multi-aperture expansion muffler; (b) monolayer micropunch resonance vibration muffler; (c) double-layer micropunch muffler; and (d) small multi-aperture impedance complex muffler (SMICM). The SMICM, shown in Fig. 2, is the most effective of the four. The acoustical mechanism of the SMICM is exactly contrary to that of the diffusion muffler. The SMICM takes advantage of the fiequency-rising effect of high-speed airstreams passing through small holes. AL, the noise increment in dB (A), is related to the cube of the nozzle diameter, i.e., AL=-

10 l o g ( 4 X 3)

where X~ = 0.165 D (when the holes are blocked). In the above muffler, the diameter of the spouting body D = 100 mm, the body's height H = 420 mm, the ratio of the height to the diameter H:d= 4.2, the diameter of the small holes d=0.8mm, the distance between the centers of the holes is 5.01(5d), and the ratio between the area of an aperture to that of an exhaust hole is 1.55. After the 150 kg air hammer had

207

R. Xueyu et al./Journal of Materials Processing Technology 59 (1996) 205.-212

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19j Fig. 2. A small multi-aperture impedance complex muffler (SMICM): (l) lower bulkhead; (2) cavity; (3) spouting body; (4) cavity; (5) acoustical foam; (6) middle bulkhead; (7) acoustical foam; (8) cartridge container; (9) surface protecting wire net; (10) shell; and (l l) cavity.

been matched with this kind of muffler, the exhaust noise was determined as 80 dB (A) by the above means. In addition, finite-element analysis and experiments were conducted on the resistant muffler of the internal intubate in HIT. Such mufflers may solve more complicated problems and, therefore, are more practical. 1.2.2.2. Research on the reth~ction of the noise hammer#Ig dur#1gforgfllg. Research has shown that hammering noise is concerned with the mass of the hammer head and the anvil, the hammering speed, the hammering action time, the behavior of the material, and the dynamics and geometrical characteristics of the hammer. If the he,mmering time is short, the hammering

Fig. 4. Steel-wire and butterfly-spring combined damper: (1) anvil; (2) butterfly-spring; (3) steel-wire damper; (4) flexible steel-wire counterpressure device; (5) foundation: (6) pin roller; (7) stand; and (8) fence plate.

speed is fast, the anvil's mass is small, and the amplitude of vibration is wide, then the noise will increase. When the hammering time is doubled, the noise will be reduced by about 6 dD (A). Increasing the damping and the height-to-diameter ratio of the hammer head may reduce the noise. When the ratio increases from 1 to 3, the sound pressure level decreases by 5 dB (A). To decrease the vibration and noise of the forging hammer, much research work has been done on the damper of such hammers in China. Rubber dampers, viscous-damping and spiral-spring combined dampers, steel-cable dampers and sheet-spring dampers were studied in HIT and HUST (see Figs. 3 and 4). 1.2.2.3. Research on radiation noise #1 stamp#~g [7,12,171. During the stamping process, the most harmful sources of noise are as follows: clutch-on-noise, stamping noise and clutch-off noise. Usually, the loo

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Fig. 5. Variation of the instantaneous fluctuating power with the crank rotary angle when co = l0 rad s- m.

R. Xueyu et al,/Journal of Materials Processing Technology 59 (1996) 205-212

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Fig. 6. Variation of the instantaneous fluctuating power with the crank rotary angle when ~o = 50 tad s -

stamping noise is the highest, and mainly comes from the fluctuating energy of the executive mechanism, i.e. excitation potential. On the basis of this, Ref. [19] presents a mathematical model for predicating the stamping noise and describing the stamping noise by an instantaneous fluctuating power. With the receipt of the two fluctuating powers, the difference between the two noises can be obtained. Figs. 5 and 6 show how the instantaneous fluctuating power of the punch press varies with the crank rotary angle when w increases from 10rads -I to 50 rad s - i When o~ increases, the peak value of the fluctuating power increases by about 864 W, which leads to an increase in the peak value of the stamping noise by about 10 dB (A). The effects of the punch press structure and the technical load on the stamping noise were also studied. Table 2 shows the simulation results by a computer. Stamping noise can be reduced by adopting a light slide and a light and bevelled-edge die, and arranging the gap between the dies to be as small as possible, matching an appropriate working table, performing good lubrication, etc.

1.3, Noise control practice during plastic working in China 1.3.1. Reducing noise from sound sources (1) In China, it is common to reduce the noise from the forging hammer by damping, and usually the noiselevel can be reduced by about 5-8 dB (A). The analysis of damping of the forging hammer has been mentioned previously. In China, damping and noise-reduction of the forging hammer have been performed in tens of factories nationwide. Some of the results are shown in Table 3. After the damping technique for forging hammers was adopted, the maximum vertical acceleration of the

hammer-base reduced to about 0.07 m s -2, and the vibration amplitude was controlled to about 0.024 mm, reaching the level of the advanced world. (2) Replacement of hammers with an anvil base for forging equipment with a small impact vibration. Many factories in China have been using the rotary forging press recently, to produce forgings in replacement of various hammers. For instance, a 4000 kN rotary forging press has been applied in the Harbin Automotive Gear Plant in China to replace a 250 kJ die hammer to manufacture large gear blanks; a 1000 kN horizontal rotary forging press has been used in the Wuhan Automotive Gear Plant to produce automotive half-axles; a 1000 kN rotary forging press has been used in the Harbin Railway Spare-parts Plant to make pins for railway vehicles; and a 27 kN rotary riveting press has been used in the China No. 2 Automobile Works to make vehicle parts. Because the rotary forging press has no vibration, and no noise, it can be installed in the production line. CJ 83 serial hydraulic die hammers have been massproduced in the Forging Equipment Plant in Jilin province, China, the maximum blow energy of which can reach 25-75 kJ. They can replace the traditional 25-75kJ anvil-fixed die forging hammer, so that power will be saved greatly, and the harm caused by impact vibration avoided. In the China No. 2 Automobile Works, all the pressing processes have been mechanized by using presses instead of forging hammers. Today, many have imported helical presses and KHZ serial pneumatic hydraulic hammers from abroad, such as the Dalian Forging Plant and the Chendu Forging Plant, to replace traditional forging hammers. (3) Mufflers or sound damping wells have been set up in the vapor or exhaust pipelines of the forging hammer.

1.3.2. Control of noise propagation In order to reduce noise, an isolated chamber has been specially put up in many factories to install the blower of the air compressor. The Changshu Nozzle Plant in China has manufactured 2 JWL double-stage worm gears, noise-free. In some large-scale stamping plants, dies are separated by blimp during blanking to limit the noise radiation.

1.3.3. Self-protection of workers An SFES soft polyvinyl-chloride earplug has been developed successfully in the Shanghai Textile Equipment Research Institute in China. Normally, the sound-reduction factor of high-frequency can reach 30-38 dB (A). An NH-78RTV silastic earplug has been developed jointly by the Shanghai No. 2 Military Medical College and Nanjing University, of which the sound reduction factor can reach 32-38 dB (A).

R. Xueyu et al./Journal oJ" Materials Processing Technology 59 (1996) 205-212

209

Table 2 Effect of different factors on the stamping noise Serial No. 1 2 3 4 5

Affecting factors

Variation-range of parameters

Noise increment AL(dB A)

Crank rotation rate to (rad s)-i Gap between the pair (sl = s2 mm) Friction conditions (#, friction coefficient) Pair stiffness (N m -I)

10-50

+(0-10)

0.04-0.2

+(0-8)

I~ =//2 -----/t3= 0-ltl =/22 = lt3 = 0.06,

+(0-3.8)

Damping ratio

It, = 0.05 k l = 1.15 x 10t°-l.15 k2 = 1.0 x 101°-l.0 x 0.1-0.3

x 10 9

+(0-6)

10 9

-(0-5.5)

(~'t = 72) 6 7 8 9 10

Gap between plunges and matrix AD (mm) Height-to-diameter ratio of bevelled edge (H:D) Buffer stiffness (N m)- i Buffer position (mm) Blanking position (mm)

0.12-0.96

+(0-6)

1:15-4:15

-(4-13.5)

2.61 x 106-2.96 x 10 7 Away from the bottom head center 2.5-4.5 Away from the bottom dead center 3-7

-(2.8-6) -(4-6) +(0-2.8)

Table 3 Examples of forging hammer damping in China Equipment name

User

Year of operation

!

27 kJ air hammer

1984

2 3 4 5

19 kJ air hammer 19 kJ air hammer 25 kJ die hammer 180 kJ bridge-type free-forging hammer 19 kJ air hammer 13.7 kJ air hammer 250 kg air hammer 75 kJ die hammer 70 kJ free-forging hammer 9.5 kJ air hammer 19 kJ air hammer 19 kJ air hammer 13.7 kJ air hammer 152 kJ free-forging hammer 152 kJ free-forging hammer 76 kJ die hammer 70 ka free-forging hammer

11 lth plant of the Ministry of Space Industry Harbin steel rolling mill Kaifeng machinery plant, Henan Harbin automotive gear plant Harbin vehicle plant

1985 1986 1986 1986

Harbin forging plant Heilongjiang textile machinery plant Heilongjiang textile machinery plant Jiangxi forging plant Jiangxi forging plant

1986 1987 1987 1986 1986

Wuxi machine tool plant Shenyang railway signal plant Jilin light vehicle brake plant Jilin light vehicle brake plant Shenyang vehicle plant

1987 1988 1988 1988 1990

Wuhan metallurgical equipment manufacturing plant Harbin Jiancheng machinery plant Northeast light alloy manufacturing plant

1991

Serial No.

6 7 8 9 lO !l 12 13 14

15 16 17 18

2. Air pollution and its prevention during metal-plastic working processes T o d a y , the f l a m e - h e a t i n g m e t h o d is used widely for billet heating in f o r g i n g a n d rolling in C h i n a . H o w e v e r , because o f s h o r t a g e o f electricity, except for a few

1989 1992

factories such as the B a o s h a n Forging Plant using the process o f electric heating, a n d the C h a n g c h u n N o . 1 A u t o m o b i l e Plant a n d the Qiqihar Peace M a c h i n e Building Plant using the process o f gas or h e a v y oil heating, coal-fired furnaces are still used in m o s t Chinese forging factories. In the mechanical industry,

R. Xueyu es el./Journal of Materials Processing Technology 59 (1996) 205-212

210

Table 4 Standard of smoke and dust discharged from industrial furnaces and kilns (GB 9078-88) Allowable concentration

Regions applicable to

Classification of division

Existing enterprises

Sight-seeing spots and relics-protected areas and other special protected areas Planned residential areas Industrial districts, suburbs, and towns Other areas

1

2 3 4

Allowable Lingerman grade

Newly-built or extended enterprises

200

300 300

200

600

400

Note: According to GB 4911-85, the maximum concentration limits of pollutants discharged by roll heating furnaces is: 200 mg m- 3 in existing plants, and 150 mg m -3 in newly-built plants.

Table 5 Application range of the coal-fired furnace and its environmental-protection effects No.

Name of the machine

Content of dust (mg m - 3)

Lingerman grade

Application range

!

Plane-reciprocating coal-fired furnace Step-reciprocatinggrate coal-fired furnace Sprial-type coalfired furnace

60-150

1

< 150

I

< 170

!

Jack-up-type coalfired furnace Creep-type mechanical coal-fired furnace

< 165

I

50- ! 50

1

Large- and medium-sized furnaces Medium-and small-sized furnaces Medium-and small-sized furnaces Small-sized furnaces Medium-and small-sized furnaces

2

3

4 5

l

I l

m

~.

.4 o

..

Fig. 7. Combustion chamber with a plane-reciprocating grate: (1) coal bucket; (2) fixed grate; (3) unfixed grate; (4) unfixed grate flame; (5) speed rtduccr; (6) ash bin.

R. Xueyu et al./Journal of Materials Process#lg Technology 59 (1996) 205-212

China has over 10 000 furnaces, 80% of which are coal furnaces scattered over 4000 forging factories. They consume 1 000 000 tons of coal and discharge quantities of smoke and dust into the atmosphere every year. The dust density from the coal furnaces is estimated to be over 450 mg m -3, and the smoke darkness Lingerman 5. Usually, they are offenders given penalties by the environmental protection department (EPD).

2.1. Pollutants and the harnfulness of burning fuel [20,211 The pollutants produced from burning fuel are primary pollutants, including mainly nitrogen oxide (NO.,.), sulfur oxide (SO,), carbon monoxide (CO), dust and organisms (mostly hydrocarbons that are left). When these pollutants exceed particular limits, they will cause lung and heart diseases, cancer, and suffocation in human beings.

2.2. Standard of smoke and dust discharged by industrial furnances and kilns [20] To prevent smoke and dust pollution, China has formulated a standard for smoke and dust discharged by industrial furnaces and kilns, including its blackness Lingerman grade, as shown in Table 4.

2.3. Air pollution during metal-plastic workfllg process [22,23] 2.3.1. The mechanical coal-fired furnace adopted to improve combustion and min#nize pollution Now, mechanical coal-fired furnaces are being used widely in China to minimize smoke pollution and improve the working conditions for workers. The main environmental indices are shown in Table 5. Zhou Decheng of HIT designed a WJM type forging furnace characterized by energy conservation, no smoke and high efficiency. It adopts the structure of a combustion chamber with a plane grate (Fig. 7) and a passing-type heating chamber. A jet heat exchanger (for air pre-heating) and a tubular heat exchanger (for hot-water recovery) are fixed in the smoke pipe. The dust concentration of the smoke was estimated at 59 mg m-3, and the blackness at lower than Lingerman 1 by the EPD. Moreover, the new design saves coal by 70% on average. In many machinery factories, a hot-gas generator has been installed behind the forging furnace to send hot gas directly into the furnace, such as the No. 2 Valve Plant, Suzhou. After burning, the dust concentration of the fumes is reduced to 171 mg m -3, and its blackness to below Lingerman 1. In other words, the thermal efficiency is raised and the requirements of environmental protection are satisfied. Nevertheless, the simple gas

211

furnace usually requires coal of high quality, i.e., its thermal value should not be below 220 934 kJ kg -~, and its ash melting point should be over 1300 °C. Only the high-quality coal of Datong, Fushun, etc., in China, can guarantee the quafity of the gas.

2.2.3. Excellent pre-heatfl~g facilities used to preheat the combustion supporting aft', to improve the burning effects and to lessen environmental pollution During the 1940s, many furnaces adopted heat-exchangers. However, because the integral heat-exchanger and the acicular heat-exchanger were often blocked, they were gradually withdrawn from use, which caused the furnaces, especially the oil furnaces, to send out black mist due to bad combustion. In recent years, many new types of heat-exchangers have been used to conserve energy and ameliorate burning, such as radiation heat-exchangers. Thus, a better environmental-protection effect has been achieved. For example, the former well-type furnaces used in the Qiqiha'er Peace Machinery Plant, China adopted 12 spray nozzles. In winter, the ignition was difficult, and a large amount of black mist was discharged also, due to the un-preheated air and the badly-atomized heavy fuel oil. Later, an etflux heat-exchanger was used to pro-heat the air to 300 °C, the combustion condition was improved to a great extent, and the black mist was eventually eliminated. 2.2.4. New-type burners adopted to #nprove the combustion condition of the furnace and el#n#~ate environmental pollution In recent years, many new types of burners have been developed and manufactured in factories in China, including the flat-flame burner, the self-heating burner, the high-velocity burner, the F-type burner, Yon combustion facilities, coal liquid combustion facilities, etc., and good effects of energy conservation and environmental protection have been obtained. For example, the Harbin Bearing Plant not only saved a large amount of energy, but also solved the black smoking problem of the farmer Soviet C-type burners by using the self-heating burners developed by the Design and Research Institute of the Ministry of Aeronautic Industry.

References [1] Huang Xiaolin, Research on noise problems in forging and stamping workshop, J. Forging Stamping Math., 5 (1989) 8-14. [2] A Practical Handbook oll the Environmental Protection Work, Environmental Protection Bureau of Heilongjiang Province, 1991, pp. 596-606. [3] Collected Works on the PRC New Laws and Regulm'ions, Vol. 4, Law Press, Law and Regulation Bureau of the State Council, 1990, pv~. 187-198. [4] Zhu Naifan, Noise and its control during the forging and stamping process, J. Forging Stamping Mach., 1 (1981) 40-46.

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[5] Zheng Changju et al., Practical Technology of btdustrial Noise Control, Shanghai Scientific Press, 1982, pp. 19-47. [6] Cao Xinbin, Research on the Noise Reduction Mechanism of Forging Hammer, 1988, pp. 39-120. [7] Chen Weimin, Gao Naiguang, Cao v~i~in ,~r~dYuan Shuxin, The method of controlling tile noise of air lift gravity hammer and the effective path to reduce the exhaust noise, J. Forging Stamping Mach. 1 (1989). [8] Du X u ~ o n g , Finite-element analysis of the loss of resistant mumer used in forging hammer, Thesis for Master's Degree, Harbin Institute of Technology, 1989, pp. 1 - 12, 83-97. [ 9 ] Chen Weimin and Gao Haiguang, Development isolation of the forging hammer foundation for vibration, J. Forging Technol., 5 ( 1 9 8 6 ) (in Chinese). [10] He Yongbiao, Damping devices for vibration isolation foundation in West Germany, J. Ind. Constr., 3 (1989). [! 1] He Yongbiao and Tang Jia xiang, The vibration isolation foundation for free forging hammer, China invention patents instructions, Application No. 91, 164123. [12] He Shanhang, A study of the vibrating, J. Heavy Machinery, 6 (1992). [13] Ding Xianglin, The solution with damping and its application of the double degree freedom theory used in the forging hammer vibration isolation foundation, Thesisfor Master's degree, HIT, pp. 72-89. [14] Wu Jianguo, Theory and analysis of forging hammer vibration isolation and the study of vibration isolation machines used in hammering, Thesis for Master's degree, HIT, 1989, pp. !-15.

[15] Ma Xinyong, Development of the forging ht~mmer damping test stand, and the study on the performance of different dampers (1990) 50-79. [16] Chen Weimin, Gao Naiguang et al., Vibration analysis of forging hammer and study on direct vibration absorption under forging hammer, J. Mech. Eng., I (1992) 2. [17] Chen Weimin, Cao Xibin and Gao Naiguang, Optimum design for stiffness and damping ratios of forging hammers, J. Mech. Eng., 2 (1993). [18] Li Pumin, Study on impact noise of the punching machine and noise control, Thesis of Master's Degree, Harbin Institute of Technology, 1991, pp. 61--96. [19] Cao Jiabin, Analysis of dynamics in the stamping process of the crank press and study of stamping noise, Ph.D. Dissertation, Harbin Institute of Technology, 1991, pp. 91-109. [20] Zhou Decheng (ed.), Industrial Furnaces--Basic Principals, Structure and Energy Conservation, Harbin Institute of Technology Press, 1991, pp. 46-51, 116-120. [21] Wu Banqiu, Control of Air Pollution, Heilongjiang Educational Press, 1989, pp. 116-120. [22] The Environmental Protection Office of the Mechanic Industry Department Edited Proc. Comprehensive Prevention Technology of Industrial Furnace Pollutants in Mechanic Industry, 1985, pp. 55--114. [23] Zhou Decheng, WJM model forging furnace characterized by energy conservation, no smoke and high efficiency, J. Forging Stamping Mach. (! 990) 34- 37.