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徐州工程學院
畢業(yè)設計（論文）任務書
機電工程 學院 機械設計制造及自動化 專業(yè)
設計（論文）題目 混凝土泵車回轉機構、臂架油缸及回轉臺的設計
學 生 姓 名 聶海江
班 級 04機本（4）
起 止 日 期2008年2月25號－2008年6月2號
指 導 教 師 仇文寧
教研室主任 李志
發(fā)任務書日期 2008 年 02月 25 日
1.畢業(yè)設計的背景：
隨著國民經濟的快速發(fā)展，建筑結構的的大型化和復雜化對混凝土機
械提出了越來越高的要求。具有眾多優(yōu)點和較高經濟效益的混凝土泵車得
到了普及和應用，混凝土泵車已成為當今建筑施工企業(yè)必不可少的專用設
備?；炷帘密嚨膽?，將混凝土輸送和澆注工序合二為一，節(jié)約了時間，
節(jié)省了勞動力；同時完成水平和垂直輸送，省去了起重環(huán)節(jié)，不需再設混
凝土中間運轉，保證了混凝土質量，同時與混凝土運輸車相配合，實現了
混凝土輸送過程完全機械化大大提高了運輸效率。
2.畢業(yè)設計(論文)的內容和要求：
本文首先介紹了混凝土泵車的結構和特點，重點對混凝土泵車的回轉
機構和回轉液壓部分及臂架油缸進行了設計；同時對回轉頭部件與油缸相
連的部件進行了強度校核，并根據泵車零部件標準確定了回轉頭的主要尺
寸及組成部件?；剞D機構采用液壓馬達驅動減速器帶動回轉支承進行旋
轉，回轉頭安裝在回轉支承上隨著回轉支承轉動，從而帶動臂架在回轉平
臺上在0~360°范圍內轉動，臂架展開收攏及其混凝土澆注時定位均是由
變幅油缸推（拉）動變幅機構的運動來實現的。
本設計具體內容主要包括：
1．回轉機構、回轉液壓部分的設計,回轉支承裝置的選型與計算。
2．回旋支承滿足上車布料桿（含混凝土總量）的傾翻力矩的計算。
3．回轉臺的強度校核及臂架油缸設計系統(tǒng)方案可行，能滿足泵車整
體性能要求。
本設計的主要特點是：機構簡單,節(jié)省投資，控制方便。對目前國內
的混凝土泵車的優(yōu)化設計具有一定的參考價值。
3.主要參考文獻：
【1】張國忠.現代混凝土泵車及施工應用技術.北京：中國建材工業(yè)出版
社，2004.
【2】徐灝.機械設計手冊.北京：機械工業(yè)出版社，1991
【3】邱宣懷.機械設計.北京：高等教育出版社，2006.
【4】李壯云.葛宜遠.液壓元件與系統(tǒng).北京：機械工業(yè)出版社，2000
【5】雷天覺.液壓工程手冊.北京：機械工業(yè)出版社，1990
4.畢業(yè)設計(論文)進度計劃(以周為單位)：
起 止 日 期
工 作 內 容
備 注
1-2 周
3-4 周
5-6 周
7-8 周
9-10 周
11周
12-14 周
15周
結合課題進行相關實地調研，明確設計原理與設計思想，查詢相關文獻，收集資料。
綜合分析與泵車有關的文獻資料，提出總體的設計方案。
主要完成泵車回轉機構的設計計算。
主要完成回轉液壓系統(tǒng)部分的設計計算。
主要完成臂架液壓油缸的設計計算與選型。
完成回轉臺的選型與強度校核。
繪制泵車回轉機構及回轉臺主要裝配及零件圖。
在綜合設計的基礎上，校核和改正設計的不完善之處，認真撰寫畢業(yè)論文準備答辯。
教研室審查意見：
室主任
年 月 日
學院審查意見：
教學院長
年 月 日
徐州工程學院
畢業(yè)設計（論文）開題報告
課 題 名 稱： 混凝土泵車回轉機構、臂架油缸及
回轉臺的設計
學 生 姓 名： 聶海江 學號：20040601436
指 導 教 師： 仇文寧 職稱： 高級工程師
所 在 學 院： 機電工程學院
專 業(yè) 名 稱： 機械設計制造及自動化
徐州工程學院
2008 年 3 月 4 日
說 明
1．根據《徐州工程學院畢業(yè)設計(論文)管理規(guī)定》，學生必須撰寫《畢業(yè)設計（論文）開題報告》，由指導教師簽署意見、教研室審查，學院教學院長批準后實施。
2．開題報告是畢業(yè)設計（論文）答辯委員會對學生答辯資格審查的依據材料之一。學生應當在畢業(yè)設計（論文）工作前期內完成，開題報告不合格者不得參加答辯。
3．畢業(yè)設計開題報告各項內容要實事求是，逐條認真填寫。其中的文字表達要明確、嚴謹，語言通順，外來語要同時用原文和中文表達。第一次出現縮寫詞，須注出全稱。
4．本報告中，由學生本人撰寫的對課題和研究工作的分析及描述，沒有經過整理歸納，缺乏個人見解僅僅從網上下載材料拼湊而成的開題報告按不合格論。
5. 課題類型填：工程設計類；理論研究類；應用（實驗）研究類；軟件設計類；其它。
6、課題來源填：教師科研；社會生產實踐；教學；其它
課題
名稱
混凝土泵車回轉機構、臂架油缸及回轉臺的設計
課題來源
自擬
課題類型
工程設計
選題的背景及意義
隨著國民經濟的快速發(fā)展，建筑結構的的大型化和復雜化對混凝土機械提出了越來越高的要求。具有眾多優(yōu)點和較高經濟效益的混凝土泵車得到了普及和應用，混凝土泵車已成為當今建筑施工企業(yè)必不可少的專用設備?；炷帘密囀窃谕鲜交炷凛斔捅玫幕A上發(fā)展起來的一種專用機械設備，混凝土泵車的應用，將混凝土輸送和澆注工序合二為一，節(jié)約了時間，節(jié)省了勞動力；同時完成水平和垂直輸送，省去了起重環(huán)節(jié)，不需再設混凝土中間運轉，保證了混凝土質量。同時與混凝土運輸車相配合，實現了混凝土輸送過程完全機械化大大提高了運輸效率。
研究內容擬解決的主要問題
研究內容：
1. 通過對徐州混凝土機械廠的考察、調研，記錄主要原始數據，以及其工作條件，對混凝土泵車、隨車起重機等具體機械的比較，從而明確所要設計的泵車回轉機構設計的思想及意義。
2. 對所設計的泵車回轉機構、回轉液壓部分、回轉支承裝置的選與計算進行較好的分析研究。
3. 回轉臺的強度校核及臂架油缸設計系統(tǒng)方案可行，能滿足泵車整體的性能要求。
擬解決的主要問題：
1． 根據對具體機械制造廠的考察、調研，收集的主要原始數據，以及其工作條件，對于混凝土泵車的各種機構有感性的認識。
2． 對于混凝土泵車的回轉支承裝置、回轉臺等進行選型設計及驗算。
研究方法技術路線
通過對混凝土泵車的實地考察，確定了其重要的數據及主要機構之后，首先進行回轉支承裝置的選型設計。然后進行回轉液壓部分的設計，同時所設計的系統(tǒng)安全可靠。然后進行臂架液壓油缸及泵車回轉臺的選型計算。
整體選型與計算結束后，接下來是對所選型號的泵車各設備的校核與修改，直至其滿足要求為止。
研究的總體安排和進度計劃
1-2周：結合課題進行相關實地調研，明確設計原理與設計思想，查詢相關文獻，收集資料。
3-4周：綜合分析與泵車有關的文獻資料，提出總體的設計方案。
5-6周：主要完成泵車回轉機構的設計計算。
7-8周：主要完成回轉液壓系統(tǒng)部分的設計計算。
9-10周：主要完成臂架液壓油缸的設計計算與選型。
11周：完成回轉臺的選型與強度校核。
12-14周：繪制泵車回轉機構及回轉臺主要裝配及零件圖。
15周：在綜合設計的基礎上，校核和改正設計的不完善之處，認真撰寫畢業(yè)論文準備答辯。
主要參考
文獻
【1】張國忠.現代混凝土泵車及施工應用技術.北京：中國建材工業(yè)出版社，2004.
【2】徐灝.機械設計手冊.北京：機械工業(yè)出版社，1991.
【3】緊固件設計手冊編委會編.緊固件連接設計手冊.北京：國防工業(yè)出版社，1990.
【4】張展.減速器設計選用手冊.上海：上?？茖W技術出版社，2002.
【5】邱宣懷.機械設計.北京：高等教育出版社，2006.
【6】劉忠.工程機械液壓傳動原理、故障診斷與排除.北京：機械工業(yè)出版社，2005.
【7】李壯云.葛宜遠.液壓元件與系統(tǒng).北京：機械工業(yè)出版社，2000.
【8】朱宏濤.液壓與氣壓傳動.北京：清華大學出版社，2005.
【9】杜國森.液壓元件產品樣本.北京：機械工業(yè)出版社，2000.
【10】雷天覺.液壓工程手冊.北京：機械工業(yè)出版社，1990
【11】何存興.液壓傳動與氣壓傳動.武漢： 華中科技大學出版社, 2000.
【12】Charles.Wilson.Kinematics and Dynamics of Machinery[J].New York,2000， (6):120-132.
指導教師
意 見
指導教師簽名：
年 月 日
教研室意見
學院意見
教研室主任簽名：
年 月 日
教學院長簽名：
年 月 日
徐州工程學院畢業(yè)設計(論文)
摘要
隨著國民經濟的快速發(fā)展，建筑結構的的大型化和復雜化對混凝土機械提出了越來越高的要求。具有眾多優(yōu)點和較高經濟效益的混凝土泵車得到了普及和應用，混凝土泵車已成為當今建筑施工企業(yè)必不可少的專用設備。本文首先介紹了混凝土泵車的結構和特點，重點對混凝土泵車的回轉機構和回轉液壓部分及臂架油缸進行了設計；同時對回轉頭部件與油缸相連的部件進行了強度校核，并根據泵車零部件標準確定了回轉頭的主要尺寸及組成部件?；剞D機構采用液壓馬達驅動減速器帶動回轉支承進行旋轉，回轉頭安裝在回轉支承上隨著回轉支承轉動，從而帶動臂架在回轉平臺上在0~360°范圍內轉動，臂架展開收攏及其混凝土澆注時定位均是由變幅油缸推（拉）動變幅機構的運動來實現的。
本設計的具體內容主要包括：
1．回轉機構、回轉液壓部分的設計,回轉支承裝置的選型與計算。
2．回旋支承滿足上車布料桿（含混凝土總量）的傾翻力矩的計算。
3．回轉臺的強度校核及臂架油缸設計系統(tǒng)方案可行，能滿足泵車性能要求。
本設計的主要特點是：機構簡單,節(jié)省投資，控制方便。對目前國內的混凝土泵車的優(yōu)化設計具有一定的參考價值。
關鍵詞：混凝土泵車；回轉機構；回旋驅動部分；液壓系統(tǒng)；臂架液壓缸；回轉臺
Abstract
As the rapid development of the national economy,incresing demands have been made by the large and complicated struction of the construction.Pump trucks with many advantages and economic benefits have been used widely and they have been the essential equipment during the contruction today. This paper firstly introduces the structur and features of the pump trucks with the most important of the design of the swing body and calculate the strength of the mechanical parts of the rotary and oil bank and make sure the main sizes and parts of the rotary head according the standard parts of the pump car. The-turn-around-organlitation,makes the decelation machine round by the liquid-press-machine,the rotary head which installed on rotary suface moves by it and makes the Arm turn around during 0°～360°,the function of Arm machine is achieved by the moving of Oil Bank.
The specific contents including:
1. The specific of the Rotary and Rotarry hydraulic part,also the selection and calculation of the Rotarry support.
2. The calculation of the rollover torqne of the Roundabout suport.
3. The projct of thecalculation of rotarry base and the design of the oil urn is resonable and can meet the requirments.
The main features of the design are:simle structure low investment convenient control.The design has some referent value to the domestic optinal design of pump trucks.
Key word: Pumpcrete machine vehicle Swiveling mechanism Maneuver supporting Hydraulic system The tank of boom The turret
II
徐州工程學院畢業(yè)設計(論文)
目 錄
1 緒論 1
1.1 概述 1
1.2 國內外混凝土泵車的發(fā)展概況 1
1.3 混凝土泵車的選擇與技術管理 3
2 泵車的基本組成及主要技術參數確定 5
2.1 混凝土泵車的基本組成與構造 5
2.1.1 混凝土泵車基本組成 5
2.1.2 混凝土泵車構造 5
2.2 主要性能參數的確定 6
3 混凝土泵車總體結構設計方案 7
3.1 底盤系統(tǒng)設計與選型 7
3.2 泵送系統(tǒng)設計 7
3.3 臂架系統(tǒng)設計 8
3.4 支腿油箱設計 8
3.5 回轉機構設計及回轉臺選型計算 9
3.6 操縱控制系統(tǒng)設計 10
4 回轉機構設計 11
4.1回轉機構與回轉支承裝置簡述 11
4.2 回轉支承裝置的選擇 13
4.2.1 載荷的確定 13
4.2.2 回轉支承裝置的受力分析 13
4.2.3 回轉支承裝置的強度計算 15
4.2.4 回轉支承聯接螺栓選型及強度校核 16
4.3 回轉驅動裝置的傳動分析 17
4.3.1 回轉阻力矩計算 18
4.3.2 馬達軸回轉功率 20
4.3.3 回轉小齒輪設計 20
4.4 減速器的選擇 23
4.4.1 明確選擇所需技術要求 23
4.4.2 根據機械強度選規(guī)格 23
4.4.3 校核熱功率 23
4.4.4 校核瞬時尖峰載荷 23
4.4.5 按機械設備總布局要求總體減速機型號 23
5 泵車液壓回轉系統(tǒng)設計 24
5.1 混凝土泵車液壓系統(tǒng)簡述 24
5.2 電液比例換向閥在液壓系統(tǒng)中的重要作用 24
5.3 回轉機構液壓系統(tǒng)的設計 25
5.4液壓元件主要工作參數的計算與選擇 26
5.4.1 液壓泵的選擇計算 26
5.4.2 液壓馬達的選擇與計算 27
5.4.3 液壓控制閥的選擇 28
5.4.4 輔助裝置的選擇 28
5.5 液壓系統(tǒng)性能驗算 29
5.5.1 液壓系統(tǒng)壓力損失的驗算 29
5.5.2 液壓系統(tǒng)總效率的驗算 30
5.5.3 液壓系統(tǒng)發(fā)熱溫升的驗算 30
6 臂架液壓油缸設計及回轉臺強度校核 32
6.1 臂架液壓缸的作用及結構 32
6.1.1 液壓缸的作用 32
6.1.2 液壓缸的結構 32
6.2 液壓缸主要零件的材料及技術要求 32
6.3 液壓缸設計步驟 33
6.4 液壓缸主要零件的設計與計算 33
6.4.1 缸筒計算 33
6.4.2 缸筒底部厚度計算 34
6.4.3 缸筒端部螺紋連接部分校核計算 35
6.4.4 活塞桿及其部分計算 35
6.4.5 最小導向長度的確定 35
6.4.6 液壓缸進、出油口尺寸的確定 36
6.5 液壓缸的強度校核 36
6.5.1 缸筒壁厚校核 36
6.5.2 活塞桿直徑校核 36
6.5.3 活塞桿的彎曲穩(wěn)定性校核計算 36
6.5.4 焊接缸筒的校核 36
6.6 回轉臺的選型及強度校核 37
6.6.1 回轉臺的主要結構 37
6.6.2 回轉臺底板與回轉支承聯接螺栓處強度校核 38
6.6.3 回轉臺油缸連接處的的強度校核 39
結論 41
致謝 42
參考文獻 43
附錄 44
英文原文 44
中文翻譯 59
III
徐州工程學院畢業(yè)設計(論文)
1
附錄
英文原文
Talking About The Design of Hydraulic Conductors
Eric Sandgren
This paper is account for uncertainty Mechanical Engineering, University of California, San Francisco, avialon 503 West Main Street, P .O. Box962531
1.1 INTRODUCTION
In a hydraulic system, the fluid flows through a distribution system consisting of conductors and fittings, which carry the fluid from the reservoir through operating components and back to the reservoir. Since power is transmitted throughout the system by means of these conducting lines (conductors and fittings used to connect system components), it follows that they must be properly designed in order for the total system to function properly.
The choice of which type of conductor to use depends primarily on the sys tem’s operating pressures and flow rates. In addition, the selection depends on en vironmental conditions such as the type of fluid, operating temperatures, vibration, and whether or not there is relative motion between connected components.
Conducting lines are available for handling work pressures up to 10,000 Pa or greater. In general, steel tubing provides greater plumbing flexibility and neater appearance and requires fewer fittings than piping. However, piping is less expen sive than steel tubing. Plastic tubing is finding increased industrial usage because it is not costly and circuits can be very easily hooked up due to its flexibility. Flexible hoses are used primarily to connect components that experience relative motion. They are made from a large number of elastomeric (rubberlike) compounds and are capable of handling pressures exceeding 10,000 Pa.
Stainless steel conductors and fittings are used if extremely corrosive envi ronments are expected. However, they are very expensive and should be used only if necessary. Copper conductors should not be used in hydraulic systems because the copper promotes the oxidation of petroleum oils. Zinc, magnesium, and cad mium conductors should not be used either because they are rapidly corroded by water-glycol fluids. Galvanized conductors should also be avoided because the gal vanized surface has a tendency to flake off into the hydraulic fluid. When using steel pipe or steel tubing, hydraulic fittings should be made of steel except for in let, return, and drain lines, where malleable iron may be used.
Conductors and fittings must be designed with human safety in mind. They must be strong enough not only to withstand the steady-state system pressures but also the instantaneous pressure spikes resulting from hydraulic shock. Whenever control valves are closed suddenly, this stops the fluid, which possesses large amounts of kinetic energy. This produces shock waves whose pressure levels can be two or four times the steady-state system design values. Pressure spikes can also be caused by sudden stopping or starting of heavy loads. These high-pressure pulses are taken into account by the application of an appropriate factor of safety.
1.2 CONDUCTOR SIZING FOR FLOW-RATE REQUIREMENTS
A conductor must have a large enough cross-sectional area to handle the flow-rate requirements without producing excessive fluid velocity. Whenever we speak of fluid velocity in a conductor such as a pipe, we are referring to the average veloc ity. The concept of average velocity is important since we know that the velocity profile is not constant. As shown in Chapter 5 the velocity is zero at the pipe wall and reaches a maximum value at the centerline of the pipe. The average velocity is defined as the volume flow rate divided by the pipe cross-sectional area:
In other words, the average velocity is that velocity which when multiplied by the pipe area equals the volume flow rate. It is also understood that the term diameter by itself always means inside diameter and that the pipe area is that area that corresponds to the pipe inside diameter. The maximum recommended veloc ity for pump suction lines is 4 ft/s (1.2 m/s) in order to prevent excessively low suc tion pressures and resulting pump cavitation. The maximum recommended veloc ity for pressure lines is 20 ft/s (6.1 m/s) in order to prevent turbulent flow and the corresponding excessive head losses and elevated fluid temperatures. Note that these maximum recommended values are average velocities.
EXAMPLE 1-1
A pipe handles a flow rate of 30 gprn. Find the minimum inside diameter that will pro vide an average fluid velocity not to exceed 20 ft/s.
Solution Rewrite Eq. (3-26), solving for D:
EXAMPLE 1-2
A pipe handles a flow rate of 0.002. Find the minimum inside diameter that will provide an average fluid velocity not to exceed 6.1 m/s.
Solution Per Eq. 3-35) we solve for the minimum required pipe flow area:
The minimum inside diameter can now be found, becauseSolving for D we have
1.3 PRESSURE RATING OF CONDUCTORS
A conductor must be strong enough to prevent bursting due to excessive tensile stress (called hoop stress) in the wall of the conductor under operating fluid pres sure. The magnitude of this tensile stress, which must be sustained by the conduc tor material. we see the fluid pressure ( P ) acting normal to the inside surface of a circular pipe having a length (L). The pipe has outside diameter D0 , inside diameter Di, and wall thick ness t. Because the fluid pressure acts normal to the pipe’s inside surface, a pres sure force is created that attempts to separate one half of the pipe from the other half.
Figure shows this pressure forcepushing downward on the bottom half of the pipe. To prevent the bottom half of the pipe from separating from the upper half, the upper half pulls upward with a total tensile force F. One-half of this force ( or F/2 ) acts on the cross-sectional area (tL) of each wall, as shown.
Since the pressure force and the total tensile force must be equal in magni tude, we have
where A is the projected area of the lower half-pipe curved-wall surface onto a hor izontal plane. Thus, A equals the area of a rectangle of width Di and length L, as shown in Figure 4-1(b). Hence,
The tensile stress in the pipe material equals the tensile force divided by the wall cross-sectional area withstanding the tensile force. This stress is called a tensile stress because the force (F) is a tensile force (pulls on the area over which it acts).
Substituting variables we have
where = Greek symbol (sigma) = tensile stress.
As can be seen from Eq. the tensile stress increases as the fluid pres sure increases and also as the pipe inside diameter increases. In addition, as ex pected, the tensile stress increases as the wall thickness decreases, and the length of the pipe does not have any effect on the tensile stress.
Burst Pressure and Working Pressure
The burst pressure (BP) is the fluid pressure that will cause the pipe to burst. This happens when the tensile stress () equals the tensile strength ( S ) of the pipe material. The tensile strength of a material equals the tensile stress at which the material ruptures. Notice that an axial scribe line is shown on the pipe outer wall surface in Fig. 4-1(a). This scribe line shows where the pipe would start to crack and thus rupture if the tensile stress reached the tensile strength of the pipe mate rial. This rupture will occur when the fluid pressure (P) reaches BR Thus, from Eq. (4-2) the burst pressure is
The working pressure (WP) is the maximum safe operating fluid pressure and is defined as the burst pressure divided by an appropriate factor of safety (FS).
A factor of safety ensures the integrity of the conductor by determining the maximum safe level of working pressure. Industry standards recommend the fol lowing factors of safety based on corresponding operating pressures:
FS = 8 for pressures from 0 to 1000 Pa
FS = 6 for pressures from 1000 to 2500 Pa
FS = 4 for pressures above 2500 Pa
For systems where severe pressure shocks are expected, a factor of safety of 10 is recommended.
Conductor Sizing Based on Flow Rate and Pressure Considerations
The proper size conductor for a given application is determined as follows:
1. Calculate the minimum acceptable inside diameter (Di) based on flow-rate requirements.
2. Select a standard-size conductor with an inside diameter equal to or greater than the value calculated based on flow-rate requirements.
3. Determine the wall thickness (t) of the selected standard-size conductor using the following equation:
4. Based on the conductor material and system operating pressure (P), de termine the tensile strength (S) and factor of safety (FS).
5. Calculate the burst pressure (BP) and working pressure (WP) using Eqs. (4-3) and (4-4).
6. If the calculated working pressure is greater than the operating fluid pres sure, the selected conductor is acceptable. If not, a different standard-size conduc tor with a greater wall thickness must be selected and evaluated. An acceptable conductor is one that meets the flow-rate requirement and has a working pressure equal to or greater than the system operating fluid pressure.
The nomenclature and units for the parameters of Eqs.
BP = burst pressure (Pa, MPa)
Di = conductor inside diameter (in., m)
D0 = conductor outside diameter (in., m)
FS = factor of safety (dimensionless)
P = system operating fluid pressure (Pa, MPa)
S = tensile strength of conductor material (Pa, MPa)
t = conductor wall thickness (in., m)
WP = working pressure (Pa, MPa)
= tensile stress (Pa, MPa)
EXAMPLE 1-3
A steel tubing has a 1.250-in, outside diameter and a 1.060-in, inside diameter. It is made of SAE 1010 dead soft cold-drawn steel having a tensile strength of 55.000 Pa. What would he the safe working pressure for this tube assuming a factor of safety of 8?
Solution First, calculate the wall thickness of the tubing:
Next, find the burst pressure for the tubing:
Finally, calculate the working pressure at which the tube can safely operate:
Use of Thick-Walled Conductors
Equations and apply only for thin-walled cylinders where the ratio Di / t is greater than 10. This is because in thick-walled cylinders (Di / t 10), the tensile stress is not uniform across the wall thickness of the tube as assumed in the de rivation of Eq. (4-2). For thick-walled cylinders Eq. (4-6) must be used to take into account the nonuniform tensile stress,
Thus, if a conductor being considered is not a thin-walled cylinder, the calcu lations must be done using Eq. (4-6). As would be expected, the use of Eq. (4-6) results in a smaller value of burst pressure and hence a smaller value of working pressure than that obtained from Eq. (4-3). This can be seen by comparing the two equations and noting the addition of the 1.2t term in the denominator of Eq. (4-6).
Note that the steel tubing of Example 4-3 is a thin-walled cylinder because = 1.060 in./0.095 in. =11.2 > 10. Thus, the steel tubing of Example 4-3 can operate safely with a working pressure of 1230 Pa as calculated using a factor of safety of 8. Using Eq. (4-6) for this same tubing and factor of safety yields
As expected the working pressure of 1110 Pa calcu1ated using Eq. (4-6) is less than the 1230 Pa value calculated in Example 4-3 using Eq. (4-3).
1.4 STEEL PIPES
Size Designation
Pipes and pipe fittings are classified by nominal size and schedule number, as il lustrated in Fig. 4-2. The schedules provided are 40, 80, and 160, which are the ones most commonly used for hydraulic systems. Note that for each nominal size the outside diameter does not change. To increase wall thickness the next larger sched ule number is used. Also observe that the nominal size is neither the outside nor the inside diameter. Instead, the nominal pipe size indicates the thread size for the mating connections. The pipe sizes given in Fig. 4-2 are in units of inches.
Figure 4-3 shows the relative size of the cross sections for schedules 40, 80, and 160 pipes. As shown for a given nominal pipe size, the wall thickness increases as the schedule number increases.
Thread Design
Pipes have tapered threads, as opposed to tube and hose fittings, which have straight threads. As shown in Fig. 4-4, the joints are sealed by an interference fit between the male and female threads as the pipes are tightened. This causes one of the major problems in using pipe. When a joint is taken apart, the pipe must be tightened farther to reseal. This frequently requires replacing some of the pipe with slightly longer sections, although this problem has been overcome somewhat by using Teflon tape to reseal the pipe joins. Hydraulic pipe threads are the dry-seal type. They dif fer from standard pipe threads because they engage the roots and crests before the flanks. In this way, spiral clearance is avoided.
Pipes can have only male threads, and they cannot be bent around obstacles. There are, of course, various required types of fittings to make end connections and change direction, as shown in Fig. 4-5. The large number of pipe fittings re quired in a hydraulic circuit presents many opportunities for leakage, especially as pressure increases. Threaded-type fittings are used in sizes up to in. in diameter. Where larger pipes are required, flanges are welded to the pipe, as il lustrated in Fig. 4-6. As shown, flat gaskets or 0-rings are used to seal the flanged fittings.
1.5 STEEL TUBING
Size Designation
Seamless steel tubing is the most widely used type of conductor for hydraulic systems as it provides significant advantages over pipes. The tubing can be bent into almost any shape, thereby reducing the number of required fittings. Tubing is easier to handle and can be reused without any sealing problems. For low-volume systems, tubing can handle the pressure and flow requirements with less bulk and weight. However, tubing and its fittings are more expensive. A tubing size desig nation always refers to the outside diameter. Available sizes include-in. incre ments from -in. outside diameter up to -in. outside diameter. For sizes from-in. to 1 in. the increments are -in. For sizes beyond 1 in., the increments are-in. Figure 4-7 shows some of the more common tube sizes (in units of inches) used in fluid power systems.
SAE 1010 dead soft cold-drawn steel is the most widely used material for tub ing. This material is easy to work with and has a tensile strength of 55,000 Pa. If greater strength is required, the tube can be made of AISI 4130 steel, which has a tensile strength of 75,000 Pa.
Tube Fittings
Tubing is not sealed by threads but by special kinds of fittings, as illustrated in Fig. 4-8. Some of these fittings are known as compression fittings. They seal by metal- to-metal contact and may be either the flared or flareless type. Other fittings may use 0-rings for sealing purposes. The 370 flare fitting is the most widely used fit ting for tubing that can be flared. The fittings shown in Fig. seal by squeezing the flared end of the tube against a seal as the compression nut is tight ened. A sleeve inside the nut supports the tube to dampen vibrations. The stan dard 450 flare fitting is used for very high pressures. It is also made in an inverted design with male threads on the compression nut. When the hydraulic component has straight thread ports, straight thread 0-ring fittings can be used, as shown in Fig. 4-8(c). This type is ideal for high pressures since the seal gets tighter as pres sure increases.
Two assembly precautions when using flared fittings are:
1. The compression nut needs to be placed on the tubing before flaring the tube.
2. These fittings should not be over-tightened. Too great a torque damages the sealing surface and thus may cause leaks.
For tubing that can’t be flared, or if flaring is to be avoided, ferrule, 0-ring, or sleeve compression fittings can be used [see Fig. 4-8(d), (e), (f)]. The O-ring fit ting permits considerable variations in the length and squareness of the tube cut.
Figure 4-9 shows a Swagelok tube fitting, which can contain any pressure up to the bursting strength of the tubing without leakage. This type of fitting can be repeatedly taken apart and reassembled and remain perfectly sealed against leak age. Assembly and disassembly can be done easily and quickly using standard tools. In the illustration, note that the tubing is supported ahead of the ferrules by the fitting body. Two ferrules grasp tightly around the tube with no damage to the tube wall. There is virtually no constriction of the inner wall, ensuring minimum flow restriction. Exhaustive tests have proven that the tubing will yield before a Swagelok tube fitting will leak. The secret of the Swagelok fitting is that all the action in the fitting moves along the tube axially instead of with a rotary motion. Since no torque is transmitted from the fitting to the tubing, there is no initial strain that might weaken the tubing. The double ferrule interaction overcomes variation in tube ma terials, wall thickness, and hardness.
In Fig. 4-10 we see the 450 flare fitting. The flared-type fitting was developed before the compression type and for some time was the only type that could suc cessfully seal against high pressures.
Four additional types of tube fittings are depicted in Fig. 4-11: (a) union el bow, (b) union tee, (c) union, and (d) 45° male elbow. With fittings such as these, it is easy to install steel tubing as well as remove it for maintenance purposes.
EXAMPLE 1-4
Select the proper size steel tube for a flow rate of 30 gpm and an operating pressure of 1000 Pa. The maximum recommended velocity is 20 ft/s, and the tube material is SAE 1010 dead soft cold-drawn steel having a tensile strength of 55,000 Pa,
Solution The minimum inside diameter based on the fluid velocity limitation of 20 ft/s is the same as that found in Example 4-1 (0.782 in.).
From Fig. 4-7, the two smallest acceptable tube sizes based on flow-rate re quirements are
1-in. od , 0.049-in, wall thickness, 0.902-in. ID
1-in. od , 0.065-in, wall thickness, 0,870-in. ID
Let’s check the 0.049-in, wall thickness tube first since it provides the smaller velocity:
This working pressure is not adequate, so let’s next examine the 0.065-in, wall thickness tube:
This result is acceptable, because the working pressure of 1030 Pa is greater than the system-operating pressure of 1000 Pa and10.
1.6 PLASTIC TUBING
Plastic tubing has gained rapid acceptance in the fluid power industry because it is rel atively inexpensive. Also, it can be readily bent to fit around obstacles, it is easy to handle, and it can be stored on reels. Another advantage is that it can be color-coded to represent different parts of the circuit because it is available in many colors. Since plastic tubing is flexible, it is less susceptible to vibration damage than steel tubing.
Fittings for plastic tubing are almost identical to those designed for steel tub ing. In fact many steel tube fittings can be used on plastic tubing, as is the case for the Swagelok fitting of Fig. 4-9. In another design, a sleeve is placed inside the tub ing to give it resistance to crushing at the area of compression, as illustrated in Fig. 4-12. In this particular design (called the Poly-Flo Flareless Tube Fitting), the sleeve is fabricated onto the fitting so it cannot be accidentally left off.
Plastic tubing is used universally in pneumatic systems because air pressures are low, normally less than 100 Pa. Of course, plastic tubing is compatible with most hydraulic fluids and hence is used in low-pressure hydraulic applications.
Materials for plastic tubing include polyethylene, polyvinyl chloride, poly propylene, and nylon. Each material has special properties that are desirable for specific applications. Manufacturers’ catalogs should be consulted to determine which material should be used for a particular application.
1.7 FLEXIBLE HOSES
Design and Size Designation
The fourth major type of hydraulic conductor is the flexible hose, which is used when