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外文資料
Hardened gear reducer prices and Analysis
The purpose of the pump ,to give pressure to the oil ; in other words, to give power to the machine .The purpose of the valves is to control the flow of oil and to apply the power when and where it may be needed .To illustrate as simply as possible how this is accomplished in a “circuit”, that is , in the run of oil from the reservoir ,through the pump , the valves , the driven unit , and back to the reservoir, references are made to the diagrams shown in Figs,11.1 and 11.2.
Every fluid-power system used one or more pumps to pressurize the hydraulic fluid the fluid under pressure, in turn, performs work in the output section of the fluid-power system. Thus, the pressurized fluid may be used to move a piston in a in a cylinder or to turn the shaft of a hydraulic motor.
So we find that find that every modern fluid –power system used at least one pump to pressurize the fluid.
TYPES OF PUMPS
Three types pumps find use in fluid-power systems: rotary , reciprocating, and centrifugal pumps .
Simples hydraulic systems may use but one type of pump, The trend is to use pumps with the most satisfactory characteristics for the specific tasks involved . In matching the characteristics of the pump to the requirements of the hydraulic system, it is not unusual to find two types of pumps in series . For example , a centrifugal pump may be may be used to supercharge a reciprocating pump , or a rotary pump may be used to supply pressurized oil for the controls associated with a reversing variable-displacement reciprocating pump .
ROTARY PUMPS
These are built in many different designs and are extremely popular in modern fluid-power system. The most common rotary-pump designs used today are spur gear , internal-gear , generated rotor , sliding-vane , and screw pump . Each type has advantages that make it most suitable for a given application.
Spur-Gear Pumps. These pumps (Fig.11.3) have two mating gears are turned in a closely fitted casing. Rotation of one gear, the driver, causes the second , or follower gear , to turn . The driving shaft is usually connected to the upper gear of the pump .
When the pump is first started , rotation of gears forces air out the casing and into the dis-charge pipe . This removal of air from the pump casing produces a partial vacuum on the suction side of the pump . Fluid from an external reservoir is forced by atmospheric pressure into the pump inlet . Here the fluid is trapped between the teeth of the upper and lower gears and the pump casing. Continued rotation of the gears forces the fluid out of the pump discharge.
Pressure rise in a spur-gear pump is produced by the squeezing action on the fluid as it is expelled from between the meshing gear teeth and casing . A vacuum is formed in the cavity between the teeth as they unmeshed , causing more fluid to be drawn into the pump . A spur-gear pump is a constant-displacement unit ;its discharge is constant at a given shaft speed . The only way the quantity of fluid discharged by a spur-gear pump of the type in Fig,11.3 can be regulated is by varying the shat speed . Modem gear pumps used in fluid-power systems develop pressure up to about 3000psi.
SLIDING-VANE PUMPS SLIDING
These pumps have a number of vanes which are free to slide into or out of slots in the pump rotor . When the rotor is turned by the pump driver , centrifugal force , springs , or pressurized fluid causes the vanes to move outwad in their slots and bear against the inner bore of the pump casing or against a cam ring . As the rotor revolves, fluid flows in between the vanes when they pass the suction port . This fluid is carried around the pump casin until the discharge port is reached . Here the fluid is forced out of the casing and into the discharge pipe.
CONTROL VALVES
Pressure control valves are used in hydraulic circuits to maintain desired pressure levels in various parts o the circuits . A pressure-control valve maintains the desired pr4essure level by diverting higher-pressure fluid to a lower-pressure area , or restricting flow into another area . Valve that divert fluid can be safety , relief , counter-balance , sequence , and unloading types , Valves that restrict flow into another area can be of the reducing type .
A pressure-control valve may also be defined as either a normally closed or normally open two-way valve . Relief , sequence , unloading and counterbalance valves are normally closed , two-way valves that are partially or fully open while performing their design function . A reducing valve is a normally open valve that restricts and finally blocks fluid flow into a secondary area . With either type of operation , the valve can be said to create automatically an orifice to provide the desired pressure control . An orifice is not always created when the valve is piloted from an external source .One valve of this type is the unloading valve –it is not self-operating ; it depends on a singal from an external source . Relief , reducing counterbalance , and sequence valves can be fully automatic in operation , with the operating signal taken from within the envelop .
TYPE OF PRESSURE-CONTROL VALVES
Some popular devices for pressure-control service are ;
Safety valve . Usually a poppet-type two-way valve intended to release find to a secondary area when the fluid pressure approaches the set opening pressure of the valve. This type of valve protects piping and equipment from excessive pressure .
Relief valve . Valve which limits the maximum pressure that can be applied in that protion of the circuit to which it is connected .
Counterbalance valve . Valve which maintains resistance against flow in one direction but permits free flow in the other direction .
Sequence valve .Valve which directs flow to more than one portion of a fluid circuit , in sequence .
Unloading valve . Valve which allows pressure to build up to an adjustable setting , then by-passes the flows as long as remote source maintains the preset pressure on the pilot port .
Ppressure-reducing valve . Valve which maintains a reduced pressure at its outlet regardless of the higher inlet pressure .
CONTROLS
Volume or flow control valves are used to regulate speed , As was developed in earlier chapters ,the speed of an actuator depends on how much oil is pumped into it per unit of time . It is possible to regulate flow with a variable displacement pump , but in many circuits it is more practical to use a fixed displacement pump and regulate flow with a volume control valve .
FLOW CONTROL METHODS
There are three basic methods of applying volume . control valves to control actuator speeds . They are meter-out and bleed-off .
Meter-In Circuit In meter-in operation . the flow control valve is place between the pump and actuator . In the way , it control the amount of fluid going into the actuator . Pump delivery in excess of the metered amount is diverted to tank over the relief valve .
With the flow control valve installed in the cylinder line as shown , flow is controlled in one direction . A check valve must he included in the flow control or placed in parallel with it for return flow . If it is desired to control speed in both directions . the flow control can be installed in the pump outlet line prior to the directional valve .
The meter-in method is highly accurate. It is used in application s where the load continually resists movement o the actuator , such as raising a vertical cylinder under load or pushing a load at a controlled speed .
Meter-Out Circuit . Meter-out control is used where the load might tend to “run away“ The flow control is located where it will restrict exhaust flow from the actuator .To regulate speed in both directions , the valve is installed in the tank line from the directional valve .More often control is needed in only one direction and it is placed in the line between the actuator and directional valve. Here too a bypass check valve would be required for a rapid return stroke.
Bleed-Off Circuit. IN a bleed –off arrangement ,the flow control is bleed off the supply line from the pump and determines the actuator speed by metering a portion of the pump delivery to tank .The advantage is that the pump operates at the pressure required by the work , since excess fluid returns to tank through the flow control instead of through the relief valve.
Its disadvantage s some less of accuracy because the measured flow is to tank rather than into the cylinder , making the latter subject to variations in the pump delivery due to changing work loads .
Bleed-off circuits should not be used in applications where there is a possibility of the load running away.
TYPES OF FLOW CONTROLS
Flow control valves fall into two basic categories ;pressure compensated and non-pressure compensated , the latter being used where load pressures remain relatively constant and feed rates are not too critical .They may be as simple as a fixed orifice or an adjustable needle valve,although more sophisticated units may even include a check valve for free flow in the reverse direction.Use of non-pressure compensated valves is somewhat limited,since flow through an orifice is essentially proportional to the square rot of the pressure drop ( p) across it .This means that any appreciable change in the work load would load would affect the feed rate.
THE APPLICATION OF HYDRAULIC POWER TO MACHINE TOOLS
The application of hydraulic power to the operation of machine tools is by no means new, though its adoption on such a wide scale as existe at present, is comparatively recent. It was infact the development of the modern self-contained pump unit that stimulated the growth of this form of machine tool operation.
Hydraulic machine tool drive offers a great many advantages.one of them is that it can give infinitely-variable speed control over wide ranges.In addition they can change the direction of drive as easily as they can vary the speed.Asin many other types of machine,many complex mechanical linkages can be simplified or even wholly eliminated by the use of hydraulics.
The flexibility and resilience of hydraulic of hydraulic power is another great virtue of this form of dirve.Apart from the smoothness of oreration thus obtained, a great improvement is usually found in the surface finish on the word and the tool can make heavier cuts without detriment and will will last considerably longer without regrinding.
By far the greater proportion of machine tool hydraulic drives are confined to the linear motions ,a rotary pump being used to actuate one or more kinear hydraulic motors in the form of double-acting hydraulic rams, usually of the piston type. In some cases, as in certain hydraulic lathes both the linear motions of the cutting tool and the rotary motion of the work may be hydraulic.ally driven and /or controlled. Such rotary motions are produced by the use of a rotary hydraulic motor.
外文翻譯
硬吃面齒輪減速取得價格狀況及分析
齒輪類減速器包括了各類展開式圓柱齒輪減速器、同軸齒輪減速器、行星齒輪減速器各類專用齒輪裝置以及各類組派生產品，齒輪采用滲碳、淬火、磨齒工藝、精度4~7級，廣泛應用于冶金、起重、礦山、石化、建筑、建材、輕工及能源等行業(yè)?，F(xiàn)對硬齒面齒輪減速器的價格現(xiàn)狀進行簡要的分析。
1．齒輪減速器產品的價格目前波動在2.5~6萬/噸之間，視單機重量、精度高低、材質種類、配套件水平等而有所不同。一般平臺重量輕者、要求采用進口配套件或材質及精度要求較高者，價格偏上限，通用產品價格偏下限應當說明的是，由于國內目前市場秩序的不規(guī)范和個別生產企業(yè)生產工藝的不嚴肅性，市場上充斥著一定比例的未嚴格按硬齒面生產工藝要求進行生產的產品，其突出特征是壽命短，由于齒面未進行磨削，噪聲也較大，該類產品以低價格沖擊市場，部分用戶由于對減速器產品的生產工藝情況并不熟悉，或由于其它原因，采購中一味地只以價格作為主要采購依據(jù)，常導致正規(guī)廠家產品難以進入采購視野，給用戶也造成了不應有的損失，也給不法生產廠家以可乘之機，嚴重影響了一個成熟的減速器產品市場的發(fā)展和成長。
2．行星齒輪減速器又包括了許多產品種類，如一般低速重載行星齒輪箱，各類專用回轉行星齒輪箱和行星傳動裝置等，一般外齒輪滲碳淬火磨齒，內齒輪調質或氮化，價格方面對通用產品一般在3~6萬/噸左右，對于單臺重量輕的回轉類行星減速器，多以臺計價，價格略高于前者，總體而言，對行星齒輪減速器，由于制造裝配工藝均較為復雜，因此價格較硬齒面圓柱齒輪減速器要高些。如要求配套件為進口軸承，并采購優(yōu)質齒輪鋼，則價格會更高些。
3．價格分析，根據(jù)國內生產減速器企業(yè)的數(shù)量，現(xiàn)狀及水平，行業(yè)價格競爭在一定范圍和時間內仍會十分激烈。特別是隨著入世的迫近，國外產品也必將大舉進入國內市場，有的國外廠商也已開始了他們的本土化戰(zhàn)略，因而導致產品競爭，包括價格競爭也會更趨激烈。
然而不容回避的是，由于受生產手段、管理水平、企業(yè)規(guī)模及自主開發(fā)能力的制約，國內企業(yè)目前的價格競爭還多集中在一般層面的產品上，隨著用戶質量意識的進一步增強。行業(yè)競爭的進一步分化及國內知名品牌的崛起，市場競爭包括價格競爭將會農步趨于理性和規(guī)范?？v觀該行業(yè)的發(fā)展現(xiàn)狀及對比，有兩點應引起國內業(yè)界的關注:
（1）規(guī)?；a優(yōu)勢應不容忽視，只有達到一定規(guī)模才有可能形成經(jīng)濟規(guī)模，才能降低成本和提升競爭力，因此有條件的企業(yè)可通過規(guī)模擴張，資本運作等手段盡快提升企業(yè)生產規(guī)模，進而增強市場競爭能力。
（2）產品開發(fā)能力的加強，要特別注意研究市場的變化，及時調整產品的研發(fā)戰(zhàn)略，及時更新老一代產品，不斷地用適應于規(guī)?；a的新產品取代老產品，用較高技術含量的產品占領市場，目前國內齒輪減速器行業(yè)還沒有出現(xiàn)能有適應規(guī)模及水平與國外同行競爭的企業(yè)，在產品開發(fā)及更新?lián)Q代方面也步履蹣跚，產品規(guī)格、種類和總體水平較之國外同行們有一定差距，這一狀況如不盡快改變，將對入世后我國傳動基礎件行業(yè)的生存發(fā)展產生嚴重影響，因此應予高度重視，希望行業(yè)同仁團結一致，共同努力，盡快改變上述狀況，使我國的減速器行業(yè)在公平、有序的競爭中健康地向前發(fā)展。減速器以固定的傳動比實現(xiàn)減速的齒輪傳動裝置。常安裝在箱體內成為獨立部件。減速器由于結構緊湊、效率較高、傳遞運動準確可靠、潤滑良好、使用壽命長、維護簡單且可成批生產，所以在現(xiàn)代機器中廣泛應用。
減速器種類很多，按傳動類型分，有齒輪減速器、蝸桿減速器、齒輪蝸桿減速器、行星齒輪減速器等；按傳動級數(shù)分，有1級減速器、2級減速器、 3級減速器和多級減速器；按軸的位置分，有立式和臥式減速器；按功率傳遞路線分，有展開式、同軸式和分流式減速器。減速器的箱體應具有足夠的剛度，以免受載后變形過大而影響傳動質量，一般用灰鑄鐵鑄成，少量生產時可用焊接結構，大量生產小型減速器可采用板材沖壓而成。減速器中傳動的潤滑一般采用油池潤滑，對于重載或高速傳動宜采用噴油潤滑；軸承的潤滑一般采用飛濺潤滑(圓周速度在2～3米／秒以上)或刮油潤滑（圓周速度在2～3米／秒以下）等。另外，與減速器類似，在少數(shù)場合下也使用增速器，它是封閉在箱體內具有固定傳動比的齒輪增速傳動裝置。