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The angle is exposed to the basic shaft system that the ball bearing is used to be traditional


4th September 2013 Bearing Technology 0 Comments

Cut the basic shaft system of the lathe with numerical control gold, as its name suggests have high rotation speed, but this does not have rigorous demarcation line. For that regarded as machining center and numerical control milling machine which cut the representatives of lathes, it is greater than or equal to the main shaft system of 10,000r/min to refer to the highest rotational speed the same, and have high angles to add reduce correspondingly The speed, in order to realize the instant of the basic shaft hoists or lower the speed and start-stop. In order to meet the manufacturing industry to more and more high requirement of the machining accuracy of the lathe, there is higher gyration precision to cut the basic shaft, usually require the diameter run-out of the basic shaft to be smaller than 1 or 2μ m, axial looseness is smaller than 1μ m. In addition, basic shaft will have sufficient and quiet, dynamic stiffness, by bearing sure cutting load and keeping the high gyration precision.

The traditional basic shaft system includes transmitting links the middle belt, gear,etc., not merely the moment of inertia is large, difficult to realize the high angle to add minus Speed,and when transmit by vibration and noise that link appear the middle settlement. So present basic shaft system to ” two combine into one ” electric motor and basic shaft mostly , shorten for zero electric the intersection of main shaft and unit drive chain, put around basic shaft between the bearing main motor basically at the structure. Such an electric basic shaft, the axial size is relatively short, compact, the rigidity of basic shaft is high, it is relatively great to exert oneself. The electric basic shaft used for machining center and numerical control milling machine of Germany GMN Company is this kind of structure, its bearing is that an accurate angle that is suitable for operating is exposed to the ball bearing generally equivalent to international standard P2 and P4 grade ,All key parts must carry on precision finishing and accurate to assemble, will use the thermostatical cooling water GMN will be 23± 0.7 ℃ even 0.3 ℃ of ± at the same time Cool stator and front and back bearing of the main electrical machinery. GMN electric main shaft used for machining center and numerical control milling machine has 20 odd kinds of types in all, the highest rotational speed is from 8000r/min to 60000r/min, the power is from 5.5kW to 76kW, the torsion torque is from 0.9Nm to 306Nm.

Now, have a few light to cut milling machine too, use electric basic shaft that locate after rear bearing of basic shaft main electrical machinery. Such structural electric basic shaft axial size is long, but can improve the heat-dissipating condition. In addition, some basic shaft highest rotational speed in machining center and milling machine of 10000r/min to 15000r/min, not because adopt the electric basic shaft but pass shaft couplings such as the film type,etc., connect the main motor with directness of basic shaft, thus save the cooling system of basic shaft. However, this way has increased the moment of inertia, has influenced corner to add make a reduction of Speed, and the two nonlinearity after the directly connect can cause, shake ,So unsuitable to be used in the main shaft speed more high lathe.

Present electric basic shaft, it is nearly all a built-in asynchronous AC induction motor. The advantage of the asynchronous type electric basic shaft is that the structure is relatively simple, the manufacture process is relatively ripe and installs and convenient, especially can weaken the magnetic field to maximum degree, it is apt to realize melting. This kind of mainshaft dynamo is further improving too, for example Mitsubishi Electric Co. can reduce the electricity and loss and shorten stator length, high-efficiency built-in reaction spindle motor to develop recently.

Recently, are discussing the built-in problem of exchanging the permanent magnet synchronous motor in the electric basic shaft abroad. Compared with asynchronous induction motor, the permanent magnet synchronous motor has the following advantages: The trochanter made of permanent-magnet material does not generate heat in the working course, has solved the problem that the Built-in: asynchronous induction motor trochanter generate heat and difficult to be fully cooled at present; Power density is great, operating efficiency is high, can receive greater power and torsion torque with the minor size; Of good performance at a low speed, it is apt to realize fine control,etc.. However, the permanent magnet synchronous motor has its weaknesses, that is that power is limited in capacity, the weak magnetism is difficult, unfavorable to realizing melting. So up until now, only the specific lathe company has electric basic shafts of the built-in permanent magnet synchronous motor that appears at the exhibition, there is no this kind of product to sell yet in the specialized electric basic shaft works. Have few people think, to in that weak magnetic field operate high the intersection of rotational speed and electric basic shaft, seem to drive more suitably with the asynchronous induction motor.

Realize the melting of the electric basic shaft by technology of PWM speed regulation by frequency variation mainly at present, carry out the turning ordinarily into the speed controller of this task, there is a vector control driver. The former drives for the constant-torque, the output power is proportional to rotational speed; The latter carries in low speed under rated revolution Drive for the constant-torque, drive for constant power on the middle, end. The electric basic shafts of machining center and numerical control milling machine, basically all adopt the latter namely vector control driver . Vector control driver have, turn on circular type closing circular type differencing, close circular type to equip with high-performance Coder as detector at basic shaft, in order to realize position and rate feedback, thus there are better dynamic characteristics, can also realize the orientation of the basic shaft stops accurately and C axle function.

Bearing that the main shaft uses

Cut the characteristic of the basic shaft of the lathe, depend on the main shaft bearing and lubricate to a great extent with numerical control gold. Antifriction bearing can make great, bearing capacity strong and structure relatively simple because of the intersection of rigidity and fine, precision, not only generally cut the choosing first of the basic shaft of the lathe also cut the favoring of the lathe. From the viewpoint of sex, preferably contact the ball bearing in the cornu medium of the antifriction bearing, the cylindrical roller bearing takes second place, the taper roller has the worst bearing.

The angle contacts the ball namely the ball of the ball bearing Revolve round the sun as well as rotation, will produce centrifugal Fc and top force moment Mg. With the increase of the main shaft speed, centrifugal Fc and top force moment Mg will be strengthened sharply, make bearing produce very great contact stress, thus cause the intersection of bearing friction and aggravate, Wen Sheng increasing, precision dropping and loss of life. So, improve the characteristic of this kind of bearing, should try every means to inhibit the increase of its Fc and Mg. The formula exposed to the ball bearing Fc and Mg from the angle learns, it helps to reduce Fc and Mg to reduce the density, spherical diameters and spherical contact angles of the ball material, so the basic shaft use more contact angles as 15 degrees or 20 degrees of small bearings of spheroid diameter now. However, the spheroid diameter can’t be reduced too many, it basically can only be 70% of the spheroid diameter of the standard series, so as not to weaken the rigidity of the bearing, the more keyly one will be sought to improve on the spherical material.

Compared with GCr15 bearing steel, silicon nitride Si3N4 41% that the ceramic density is only it, the ball made of silicon nitride is much lighter, centrifugal force and top force moment produced are much smaller during gyration naturally. Meanwhile, silicon nitride ceramic elastic modulus and hardness are 1.5 times and 2.3 times of the bearing steel, and thermal expansion coefficient is only 25% of the bearing steel, this can already improve rigidity and life-span of the bearing, make the cooperation interval of the bearing change under different temperature rise conditions small again, it is reliable to work, in addition the high temperature resistant pottery and not glue and grip with the metal, obviously make the spheroid of pottery of silicon nitride and suitable for turning round. Practice show, ceramic the intersection of ball and corner exposed to ball bearing the speed can be raised by 25%~35% compared with corresponding steel ball bearing, but the price should be a little higher.

Referred to as, mix bearing for steel, rolling element Internal and external cycle for ceramic bearing abroad. Mixing the bearing at present has a new development: First, ceramic to use for, produce cylindrical the intersection of roller and roller of bearing already, appear ceramic column mix the bearing at the market; Second, with the stainless steel for example FAG Company uses nitrogenization stainless steel Crodinur30 Produce the Internal and external cycle especially inner circle of the bearing instead of the bearing steel, because stainless steel thermal expansion coefficient is smaller by 20% than the bearing steel, during gyration naturally, the contact stress caused because of thermal expansion of inner circle will be inhibited while increasing the trend.

As everyone knows, dmh value express the intersection of antifriction bearing and speed factor of characteristic ‘ dm in the antifriction bearing, mean diameter of outer lane, unit mm; H is the rotational speed of the bearing, unit r/min . The characteristic that the angle is exposed to the ball bearing not merely correlates with spherical contact angle, diameter and material, and in close relation with bearing lubricating method. The antifriction bearing has lipoprotein lubricating, oil fog lubrication and oil gas that lubricate three ways at present, the oil fog lubrication among them though the result is good, polluting the environment and worker’s health of danger, have already seldom adopted abroad.

It is the simplest and environmental protection preferably a lubricating method that the lipoprotein is lubricated. Because lipoprotein exceed, turn round, down apt and rotten, so dmh lower in value, for only up to 80* 104 at the steel ball bearing, reachable 110* at the time of a ceramic game 104 its dmh value of low-temperature bearing of new generation which FAG Company develops can also increase by about 10% on this basis . What the main shaft bearing was used most is oil gas lubricating method now, it was the timing, supplied with the bearing with the oil – angry admixture quantitatively, make every placement of the bearing obtain the optimal trace and lubricate and reduce pollution to very small. The steel ball or ceramic ball angle adopting the oil gas and lubricating contacts the ball bearing, its dmh value can generally be up to to 140* 104 and 210* 104 respectively, if adopt, compare special the intersection of oil gas and lubricating method, ceramic the intersection of ball and corner exposed to ball the intersection of dmh and the intersection of value and reachable even higher 250* 104 of axle special the intersection of oil gas and first kind of lubricating method a bit, already been up to 280* in its dmh value of experimental indoor 104.

Electric the intersection of basic shaft and disposition of antifriction bearing take many forms, but typical before being and rear bearing took the form of ” O ” Type overall arrangement two opposite angle contact ball bearing. Because the rear bearing is that the angle contacts the ball bearing, generally set up the ball set in order to let the rear bearing move axially along the shell, very free after making the basic shaft heated to swell to the rear. Generally speaking, the angle is exposed to the ball bearing to need to have ability normal operation of initial load axially, the bigger the initial load is, the higher the rigidity of the bearing is, but Wen Sheng is the bigger. Simpler method is, according to the speed range of the electric basic shaft and load born, select an optimal fixed initial load value; Better method is that the initial load can change and adjust with the main shaft speed, reduce the initial load in the high rotational speed, increase the initial load in the slow speed.










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