畢業(yè)設(shè)計（論文）
相關(guān)資料
題目： VF-0.8/50空氣壓縮機的設(shè)計
整體、曲軸箱部件、曲軸部件設(shè)計
信機 系 機械工程及自動化專業(yè)
學(xué) 號：
學(xué)生姓名：
指導(dǎo)教師：
5月25日
目 錄
一、畢業(yè)設(shè)計（論文）開題報告
二、畢業(yè)設(shè)計（論文）外文資料翻譯及原文
三、學(xué)生“畢業(yè)論文（論文）計劃、進度、檢查及落實表”
四、實習(xí)鑒定表
畢業(yè)設(shè)計（論文）
開題報告
題目： VF-0.8/50空氣壓縮機的設(shè)計
整體、曲軸箱部件、曲軸部件設(shè)計
信機 系 機械工程及自動化 專業(yè)
學(xué) 號：
學(xué)生姓名：
指導(dǎo)教師：
年11月12日
課題來源
“VF-0.8/50空氣壓縮機的設(shè)計”的課題來源于企業(yè)；
結(jié)合所學(xué)知識，老師擬定題目；
綜合大學(xué)里所學(xué)知識，將理論與實踐相互結(jié)合。
科學(xué)依據(jù)（包括課題的科學(xué)意義；國內(nèi)外研究概況、水平和發(fā)展趨勢；應(yīng)用前景等）
1、 化工、冶金、化肥、食品、醫(yī)療等眾多企業(yè)的生產(chǎn)過程需要用到氣體
壓縮機，而活塞式空氣壓縮機由于有較高的壓縮比，在高壓氣體生產(chǎn)
與輸送中尚不能被其它設(shè)備所替代，是許多工程項目中的關(guān)鍵設(shè)備。
2、 活塞式壓縮機上所用的密封活塞環(huán)通常用自潤滑材料聚四氟乙烯制
成，由于活塞環(huán)長期運行在劇烈的摩擦環(huán)境下，活塞環(huán)極易磨損，導(dǎo)
致壓縮機不能正常工作。為了減少高分子材料的摩擦磨損，傳統(tǒng)氣體
壓縮機活塞環(huán)需要用油潤滑，以減少活塞環(huán)與氣缸壁的摩擦磨損，提
高活塞環(huán)的使用壽命。
3、 無油潤滑壓縮機采用自潤滑聚合物復(fù)合材料制造活塞環(huán)，活塞部位不
用油潤滑，所生產(chǎn)的壓縮氣體潔凈無污染，既節(jié)省了大量的潤滑油，
又可簡化生產(chǎn)工藝流程，降低能耗，減少環(huán)境污染，是當(dāng)前活塞式壓
縮機的發(fā)展方向。
4、目前壓縮機制造業(yè)已經(jīng)發(fā)展成為機械制造工業(yè)的一個重要組成部分。
研究內(nèi)容
1、 活塞式空氣壓縮機的工作原理以及工作形成；
2、 活塞式壓縮機參數(shù)與結(jié)構(gòu)的設(shè)計；
3、 活塞式滑壓縮機設(shè)計圖紙的繪制。
擬采取的研究方法、技術(shù)路線、實驗方案及可行性分析
研究方法：通過閱讀有關(guān)資料，文獻，收集篩選，整理課題研究所需的
有關(guān)數(shù)據(jù)，理論依據(jù)，綜合運用所學(xué)理論知識研究論文課題。
技術(shù)路線：分析活塞式空氣壓縮機的各個參數(shù)的取值情況，包括結(jié)
構(gòu)參數(shù)、工藝參數(shù)、熱力學(xué)參數(shù)和動力學(xué)參數(shù)。確定各參數(shù)
的具體數(shù)值或取值區(qū)間。
可行性分析：通過對論文課題的學(xué)習(xí)研究，達到鞏固，擴大，深化已學(xué)
理論知識，提高思考分析解決實際問題等綜合素質(zhì)的目的。
研究計劃及預(yù)期成果
1、 首先對活塞式空氣壓縮機整體結(jié)構(gòu)進行分析，對傳動結(jié)構(gòu)進行篩選，初步選擇達到設(shè)計要求的結(jié)構(gòu)方案；
2、 對活塞式壓縮機的熱力部分及動力部分進行計算，通過壓縮機機構(gòu)的分析計算可提高其自身的精度；
3、 對活塞式壓縮機的主要零件進行強度校核，提高機構(gòu)穩(wěn)定性，穩(wěn)定性。
特色或創(chuàng)新之處
通過對活塞式空氣壓縮機的設(shè)計及計算，形成一整套現(xiàn)代的設(shè)計方法，對理論和實踐的結(jié)合，起到整體的規(guī)劃的作用，達到降低損耗提高效率，優(yōu)化結(jié)構(gòu)設(shè)計方便使用。
已具備的條件和尚需解決的問題
已具備的條件：擁有機械設(shè)計手冊等參考資料及文獻；到企業(yè)進行參觀，
對空氣壓縮機進行直觀的了解與認(rèn)識，對所學(xué)的機械基礎(chǔ)
知識有較好的掌握；能熟練運用CAD制圖軟件，提高作
圖效率。
尚需解決的問題：對于活塞式空氣壓縮機的工作原理不是非常清楚和熟悉，缺乏自主設(shè)計的經(jīng)驗。
指導(dǎo)教師意見
指導(dǎo)老師簽名：
年 月 日
教研室（學(xué)科組、研究所）意見
教研室主任簽名：
年 月 日
系意見
主管領(lǐng)導(dǎo)簽名：
年 月 日
Compressors
The main difference between pumps and compressors is that the fluid delivered by compressors -- air -- is compressed and under pressure at the time it is delivered, even if there is no load on the system. Most devices used to compress air are very similar in concept and -- perhaps even in hardware -- to hydraulic pumps, and selection considerations are similar.
The only other substantive difference is that most hydraulic systems are powered by a single pump that is actually a part of the system, whereas a host of pneumatic systems are often powered by a single compressor, which is almost a "utility" in the plant like water or electric service. Nevertheless, many small compressors are available for specific, discrete jobs; typically they are positive-displacement compressors. Dynamic, or nonpositive-displacement compressors are typically larger, facility-type units.
Compressors are fairly simple devices, capable of long periods of maintenance-free operation if properly integrated into pneumatic systems. Yet time and again they suffer from early failures because obvious precautions were ignored during system design. Four basic rules can provide substantial improvement in compressor life with only moderate design effort:
? Pumps and compressors should be sized to provide at least the required pressure and flow, and preferably 10 to 25% more.
? Filters should be selected to protect the pumping unit, and sometimes to protect downstream components or products as well.
? Relief valves should be selected to keep pressure or vacuum at appropriate levels.
? Pumping units should be placed in a clean, cool, dry environment.
Bellows compressors consist of a welded metal bellows connected to inlet and outlet ports with check valves. These compressors typically cover the pressure range up to 10 psig, and are used in pollution detecting and measuring devices, gas-sampling instruments, and medical applications. Lubrication is not needed, allowing high purities to be maintained.
Vane compressors are simple machines with few moving parts. Like their hydraulic counterparts, vane pumps, the compressors are inexpensive, with low operating cost, and low starting-torque requirement. They are compact and relatively vibration free, with little pulsation in the compressor output. The sliding vanes are closely fitted in the rotor slots and wear very little during operation. These compressors are available in power ranges from 10 to 500 hp, at pressures to 150 psi.
Reciprocating compressors consist of a piston moving within the cylinder to trap and compress the gas. In principle, such a unit is like an automobile engine, with the pistons compressing the gas and valves controlling its inlet and outflows. Sizes range from less than 1 to over 5,000 hp. Reciprocating compressors have good part load efficiencies and are useful for wide variations in operating conditions.
Diaphragm compressors are a modification of the reciprocating compressor. Compression is performed by the flexing of a metal or fabricated diaphragm which is caused by the motion of a reciprocating piston in a cylinder under the diaphragm. The space between the diaphragm and the piston is usually filled with liquid.
Lobed-rotor compressors have two rotating elements that revolve in opposite directions in a chamber. In most compressors, the rotors do not actually touch and do not drive each other, being driven instead by timing gears. Because the rotors do not actually touch, air leaks between them at a small but constant rate. This leakage, called "slip," is constant for a given compressor at a given pressure. For highest efficiency, these compressors should be operated at maximum speed. They are available in power ranges from 7 to 3,000 hp, delivering pressures to 250 psi. Because the internal lobes do not contact, they need no lubrication.
Liquid piston compressors have no moving parts in wearing contact. A rotor with multiple forward-curved blades rotates in an elliptical casing. Fluid, trapped within the casing, is carried around the inner periphery by the blades. Space between the blades changes volume due to the elliptical fluid path, and the inner surface of the liquid ring trapped between the blades serves as the face of a liquid piston. These compressors accept liquid slugs and fine particles without serious damage. Lubrication is required only in bearings located outside the pump housing. These compressors deliver up to 150 psi throughout the range of 10 to 500 hp.
Centrifugal compressors are best suited to moving large volumes of air at relatively low pressures. Basically, they consist of a high-speed rotating impeller, a diffuser section where velocity is reduced and pressure increased, and a collector section that further reduces velocity and increases pressure. Centrifugal compressors can handle high flow demands well, but when demand decreases much below rated flow and output pressure rises, the compressors can surge. In surge, the pressure field at the compressor outlet varies randomly. If allowed to continue, this condition can damage bearings, blades, and even the housing itself. Centrifugal compressors typically use from two to six stages, supplying from 400 to 3,000 cfm at speeds to 20,000 rpm.
Regenerative blowers (also known as peripheral blowers) use a disclike impeller with blades mounted around its outside edge. As the impeller revolves, air is drawn into the space between the blades. Centrifugal force moves the air in a spiral path outward to the housing, where it slips by the initial blade and returns to the base of the succeeding blade, where the process is repeated. In some models, a flow splitter creates two flow paths, so that the air must make two circuits around the impeller. In other models, the splitter is omitted, and the air makes only one circuit before exiting. Regenerative blowers provide air flows up to 1,000 cfm and pressures to 8 psi.
Helical compressors look like two giant screws meshing together; they work much like hydraulic screw pumps. Maximum pressure from these machines is approximately 125 psi in single-stage configurations. Helical compressors may be either oil flooded or dry.
Dry helical compressors, like lobed units, require timing gears to maintain proper clearance between the rotating elements. These units are most efficiently operated at high continuous speeds.
Flooded compressors do not require any timing gears, because the oil-laden screw surfaces can drive each other. However, oil separators are needed to remove the oil from the air as it leaves the compressor. They are available over a power range of about 7 to 300 hp.
Single-screw compressors are based on the same principle as helical compressors. As the central screw rotates, air trapped between the screw teeth is compressed against the star-shaped rotors. These compressors tend to have low vibration and noise levels, and low discharge pressures. Lubrication is required.
Pumps
vacuum pumps In principle, industrial vacuum pumps are merely compressors run with the inlet attached to the vacuum system and the outlet open to exhaust. In smaller sizes, compressors and vacuum pumps are often identical machines. However, in the large sizes that might power a plant-wide vacuum system, the machines differ in minor ways that are intended to enhance efficiency for one application or the other. Manufacturers strongly advise that the same machine not be used for both vacuum and compression at the same time. The heavy loads will damage it.
Three criteria control pump selection: degree of vacuum produced, rate of air removal, and power requirement. However, applications such as filtration may subject the unit to the ingestion of foreign material.
The first pump performance criterion is the vacuum it produces. Manufacturers provide a maximum vacuum rating expressed as absolute pressure in mm Hg, or vacuum in in. Hg. Larger units are usually rated only for continuous duty, but smaller units may have a higher vacuum rating for intermittent duty. In smaller units, temperature-rise considerations limit the vacuum that can be produced.
Continuous and intermittent vacuum ratings are determined for standard atmospheric pressure: 29.92-in. Hg. Lower ambient pressures reduce the vacuum that can be produced. The rating is determined from:
where Va = adjusted vacuum rating, in. Hg; Vo = original vacuum rating at standard conditions, in. Hg; and Pa = anticipated atmospheric pressure at the application site, in.Hg.
Rate of air removal is the second criterion. Vacuum pumps are flow rated according to the volume of air exhausted with no pressure differential across the pump. Manufacturers provide curves showing free air delivery at rated speed for vacuum levels ranging from 0-in. Hg (so-called "open capacity") to maximum vacuum rating. Some manufacturers also provide curves of capacity at different speeds for a given vacuum.
The last pump criterion is power requirement. Compared with air compressors, vacuum pumps require relatively little power. At low flows, vacuum (or pressure differential) is high; at high flows, vacuum is low. Therefore, power, which is proportional to flow and pressure differential, is generally low.
Power output of the pump can be found from pressure-flow curves provided by manufacturers. Input power and speed requirements are also shown in the data. Overall pump efficiency (including both volumetric and mechanical efficiency) can be evaluated by combining this data. This is done by dividing the free-air capacity of the pump at the required vacuum level by drive power required at that condition. The result is proportional to the product of gage vacuum and air-flow rate and is representative of efficiency.
All three performance criteria -- vacuum, flow and power -- can be affected by pump temperature. At higher vacuum levels, little air flows through the pump, so little heat is transferred to the air. Much of the heat generated by friction must be dissipated by the pump. This heat gradually raises pump temperature and can drastically reduce service life. Temperature excursions are especially important to intermittent-duty pump, which can overheat if on time greatly exceeds off time.
Vacuum pumps are classified as either positive or nonpositive displacement. A positive-displacement pump creates vacuum by isolating and compressing a distinct, constant volume of air. The compressed air is vented out one port, and a vacuum is created at the other port where the air is drawn in. This generates relatively high vacuum, but little flow.
A nonpositive-displacement pump, on the other hand, uses rotating impeller blades to accelerate air and create a vacuum at the inlet port. While nonpositive-displacement pumps cannot produce high levels of vacuum, they provide high flow rates.
Principal types of positive-displacement vacuum pumps include piston, diaphragm, rocking-piston, rotary-vane, lobed-rotor, rotary-screw, and liquid-ring designs.
Reciprocating-piston pumps generate relatively high vacuums -- from 27 to more than 29 in. Hg -- under a variety of operating conditions. Typical pumps of this type have one or more pistons linked to a rotating crankshaft. The alternating piston action moves air past check valves in the cylinder head to create a vacuum at the inlet port. Lubricated piston pumps are quieter, produce less vibration, have a higher capacity, and feature a much longer life than oilless designs, but they are also heavier and more expensive.
Diaphragm pumps offer the advantage of the fluid chamber being totally sealed from the pumping mechanisms. An eccentric connecting rod mechanically flexes a diaphragm inside the closed chamber to create a vacuum. This results in somewhat lower vacuum compared to that produced by a reciprocating piston. However, the diaphragm's lower compression ratio -- low flow, large diameter, and short stroke -- makes for quiet, economical, and reliable operation. The design is available in both one and two-stage versions. Single-stage pumps provide vacuum up to 25.5 in. Hg, while two-stage units are rated to 29 in. Hg.
Rocking-piston pumps combine the compact size and quiet, oilless operation of the diaphragm pump with the high-vacuum capabilities of the reciprocating-piston pump. Here, a piston is rigidly mounted (no wrist pin) on top of the diaphragm unit's eccentric connecting rod. An elastomeric cup skirts the piston and functions both as a seal -- equivalent to the rings on a piston compressor -- and as a guide member for the rod. The cup expands as the piston travels upward, thus maintaining contact with the cylinder walls and compensating for the rocking motion. The absence of a wrist pin is the key to the pump's light weight and compact size.
Single-stage rocking-piston pumps produce vacuum to 27.5 in. Hg; two-stage designs can generate 29 in. Hg or more of vacuum. Rocking-piston pumps are also relatively quiet, operating at sound levels as low as 50 dBA. A drawback to rocking-piston pumps is that they cannot generate a lot of airflow. Even the largest twin-cylinder models have flow rates of less than 10 cfm.
Rotary-vane pumps use a series of sliding, flat vanes rotating in a cylindrical case to generate vacuum. As an eccentrically mounted rotor turns, the vanes slide in and out, trapping a quantity of air and moving it from the inlet side of the pump to the outlet.
Rotary-vane pumps usually have lower vacuum ratings than piston pumps, in the 20 to 28 in. Hg range. However, there are a few exceptions. Some two-stage, oil-lubricated designs have vacuum capabilities up to 29.5 in. Hg. Pumps with recirculating oil systems reach still higher vacuums, in the less than 1-torr range. The pumps offer a number of advantages, including high flow capacities, low starting and running torque requirements, vibration-free operation, and continuous airflow. No valves restrict flow or require maintenance in the rotary design. The compact units are also quiet, generating as little as 45 dBA or sound.
Depending on the application and vacuum level required, an economical alternative to using a high-vacuum pump is two standard, staged rotary-vane pumps. Or, a high-volume, low-duty pump rated for continuous duty of 20 in. Hg sometimes can be operated at restricted airflow or "blanked-off" conditions for short periods of time to provide higher vacuums. As with other types of pumps available in both lubricated and oilless configurations, lubricated rotary-vane pumps are capable of slightly higher vacuum compared to oilless designs.
Liquid-ring pumps feature a multiblade impeller, mounted eccentrically in a cylindrical case that is partly filled with water. As the impeller rotates, liquid is thrown outward by centrifugal force to form a liquid ring concentric with the periphery of the casing. Due to the eccentric position of the impeller, the air space in the impeller cell expands during the first 180° of rotation, creating a vacuum. During the next 180° of rotation, the air space is reduced, discharging compressed air and water. In addition to being the compression medium, the liquid ring absorbs the heat of compression as well as any powder or liquid slugs entrained in the air.
Rotary-screw and lobed-rotor vacuum pumps are two other types of positive displacement pumps. Neither lubricated design is as widely used as rotary-vane and piston pumps, especially in smaller sizes. Due to the size of the gears and rotors, both designs lend themselves to larger installations.
A rotary-screw pump's vacuum capabilities are similar to those of piston pumps, with the added advantage of being nearly pulse-free. Two meshing rotors with helical contours trap air as the screws turn in opposite directions. This action creates chambers of decreasing volume behind and increasing volume in front of the rotor chambers.
Lobed-rotor pumps bridge the gap between positive and nonpositive-displacement units. The pumps have a pair of mating lobed impellers that rotate in opposite directions, trapping air and withdrawing it from the system.
High-speed, multistaged centrifugal blowers and regenerative blowers are the major types of nonpositive-displacement pumps, generally operating at high speeds and attaining moderate vacuum levels.
Centrifugal blowers, for example, are an excellent choice where only intermittent use is required. To keep costs down, a short-life brush-type ac or dc motor powers these blowers, which are widely used in vacuum cleaners.
Regenerative blowers have many advantages because individual air molecules pass through many compression cycles with each revolution compared to the single compression per stage for multistaged centrifugal types. At first glance, regenerative blowers are similar to rotary-vane pumps, but have a special blade and housing configuration.
As the impeller rotates, centrifugal force moves the air molecules from the blade root to its tip. Leaving the blade tip, the air flows around the housing contour and back down to the root of a succeeding blade, where the flow pattern is repeated. This action provides a quasi-staging effect to increase pressure differential capability. The speed of the rotating impeller determines the degree of pressure change.
The end result is not a particularly high vacuum -- approximately 100-in. H2O in single-stage models. But flow capacity is very high, up to several hundred cfm. Multistage versions produce higher vacuum levels, but at lower flow rates.