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（二）Hardened gear reducer prices and AnalysisThe 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 PUMPSThree 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 PUMPSThese 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 SLIDINGThese 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 VALVESPressure 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 VALVESSome 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 .CONTROLSVolume 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 METHODSThere 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 CONTROLSFlow 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 TOOLSThe 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.硬齿面齿轮减速器的价格现状及分析齿轮类减速器包括了各类展开式圆柱齿轮减速器、同轴齿轮减速器、行星齿轮减速器各类专用齿轮装置以及各类组派生产品，齿轮采用渗碳、淬火、磨齿工艺、精度47级，广泛应用于冶金、起重、矿山、石化、建筑、建材、轻工及能源等行业。现对硬齿面齿轮减速器的价格现状进行简要的分析。1齿轮减速器产品的价格目前波动在2.56万/吨之间，视单机重量、精度高低、材质种类、配套件水平等而有所不同。一般平台重量轻者、要求采用进口配套件或材质及精度要求较高者，价格偏上限，通用产品价格偏下限应当说明的是，由于国内目前市场秩序的不规范和个别生产企业生产工艺的不严肃性，市场上充斥着一定比例的未严格按硬齿面生产工艺要求进行生产的产品，其突出特征是寿命短，由于齿面未进行磨削，噪声也较大，该类产品以低价格冲击市场，部分用户由于对减速器产品的生产工艺情况并不熟悉，或由于其它原因，采购中一味地只以价格作为主要采购依据，常导致正规厂家产品难以进入采购视野，给用户也造成了不应有的损失，也给不法生产厂家以可乘之机，严重影响了一个成熟的减速器产品市场的发展和成长。2行星齿轮减速器又包括了许多产品种类，如一般低速重载行星齿轮箱，各类专用回转行星齿轮箱和行星传动装置等，一般外齿轮渗碳淬火磨齿，内齿轮调质或氮化，价格方面对通用产品一般在36万/吨左右，对于单台重量轻的回转类行星减速器，多以台计价，价格略高于前者，总体而言，对行星齿轮减速器，由于制造装配工艺均较为复杂，因此价格较硬齿面圆柱齿轮减速器要高些。如要求配套件为进口轴承，并采购优质齿轮钢，则价格会更高些。3价格分析，根据国内生产减速器企业的数量，现状及水平，行业价格竞争在一定范围和时间内仍会十分激烈。特别是随着入世的迫近，国外产品也必将大举进入国内市场，有的国外厂商也已开始了他们的本土化战略，因而导致产品竞争，包括价格竞争也会更趋激烈。然而不容回避的是，由于受生产手段、管理水平、企业规模及自主开发能力的制约，国内企业目前的价格竞争还多集中在一般层面的产品上，随着用户质量意识的进一步增强。行业竞争的进一步分化及国内知名品牌的崛起，市场竞争包括价格竞争将会农步趋于理性和规范。纵观该行业的发展现状及对比，有两点应引起国内业界的关注:（1）规模化生产优势应不容忽视，只有达到一定规模才有可能形成经济规模，才能降低成本和提升竞争力，因此有条件的企业可通过规模扩张，资本运作等手段尽快提升企业生产规模，进而增强市场竞争能力。（2）产品开发能力的加强，要特别注意研究市场的变化，及时调整产品的研发战略，及时更新老一代产品，不断地用适应于规模化生产的新产品取代老产品，用较高技术含量的产品占领市场，目前国内齿轮减速器行业还没有出现能有适应规模及水平与国外同行竞争的企业，在产品开发及更新换代方面也步履蹒跚，产品规格、种类和总体水平较之国外同行们有一定差距，这一状况如不尽快改变，将对入世后我国传动基础件行业的生存发展产生严重影响，因此应予高度重视，希望行业同仁团结一致，共同努力，尽快改变上述状况，使我国的减速器行业在公平、有序的竞争中健康地向前发展。减速器以固定的传动比实现减速的齿轮传动装置。常安装在箱体内成为独立部件。减速器由于结构紧凑、效率较高、传递运动准确可靠、润滑良好、使用寿命长、维护简单且可成批生产，所以在现代机器中广泛应用。减速器种类很多，按传动类型分，有齿轮减速器、蜗杆减速器、齿轮蜗杆减速器、行星齿轮减速器等；按传动级数分，有1级减速器、2级减速器、3级减速器和多级减速器；按轴的位置分，有立式和卧式减速器；按功率传递路线分，有展开式、同轴式和分流式减速器。减速器的箱体应具有足够的刚度，以免受载后变形过大而影响传动质量，一般用灰铸铁铸成，少量生产时可用焊接结构，大量生产小型减速器可采用板材冲压而成。减速器中传动的润滑一般采用油池润滑，对于重载或高速传动宜采用喷油润滑；轴承的润滑一般采用飞溅润滑(圆周速度在23米秒以上)或刮油润滑（圆周速度在23米秒以下）等。另外，与减速器类似，在少数场合下也使用增速器，它是封闭在箱体内具有固定传动比的齿轮增速传动装置。
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