Structural principle characteristics of the ball screw
Ball will be transformed into each other in the production life of linear motion and rotary motion . Widely used in CNC machine tools , electronic equipment, automation equipment, laser equipment, medical equipment and so on. Industries, including : IT industry , automobiles, household appliances, machinery , railway , steel, construction machinery plants power plants, petrochemical machinery.
Ball principle:
1 , Ball ( now largely replaced by trapezoidal screw , lead screw has been commonly known ) is used to rotary motion into linear motion ; or linear motion into rotary motion of the actuator
2 , as the active substance when the ball screw , the nut will be in accordance with the rotation angle of the screw corresponding to the specifications of the lead into a linear movement of the workpiece may be connected by passive nut bracket and a nut , in order to achieve a corresponding linear movement.
Ball features:
1, the drive torque is compared with the sliding screw deputy do have a lot of balls rolling motion between 1/3 of the screw shaft and ball screw nut , they are able to get higher efficiency of movement . Compared with the previous slide screw vice drive torque of 1/ 3 or less, that the power needed to achieve the same results as using the rolling motion screw pair is 1/3 . Helpful in saving .
2 , high-precision ball screw is used in Japan to ensure the world's highest level of manufacturing machinery and equipment produced consistent , especially in the grinding , assembly, inspection of the process plant environment, temperature • humidity were strictly controlled , due to improve the quality management system so that accuracy can be fully guaranteed.
3 , ball screw micro-feed because it is likely to take advantage of ball movement, so a very small starting torque , does not appear as a creeping phenomenon sliding motion , to ensure accurate micro-feed .
4 , no backlash , high rigidity ball screw can be added to the pressure , due to the negative pressure axial clearance can achieve , and then get the higher rigidity ( Ball ball through to add to the pressure , the actually used mechanical devices, due to the repulsion ball nut can enhance the rigidity department ) .
5 , high-speed ball screw feed may be due to the high efficiency of movement , little heat , so I can feed high-speed ( sport ) .
Ball screw machining attention to the problem : When the ball screw machining , screw pretension is required in the assembly of the longitudinal direction of the screw to adjust the tension applied to certain positive and negative reverse screw nut screw tightness at both ends of the lock nut , the reason is that when the operation temperature of the screw , the screw elongation thermal stress effect , that the length of the screw becomes unstable. The purpose is to effectively eliminate the flexibility of the component variables in order to obtain a smooth motion accuracy . Otherwise, when the micro-feed when the saddle or the table is greater than the elastic damping force torque screw and nut bench displacement does not occur , with the feed screw and nut torque exceeds the cumulative elastic damping torque table at this time bench impulsive displacement . Although the total amount of feed may be affected, but the output of the actual number of steps , each step of the feed and the controller generates an error , the consequences are serious impact on the processing accuracy.
Ball 's structure:
The structure of the traditional ball screw into the loop structure ( circular and elliptical inverter inverter as a representative ) and the outer loop structure ( as represented in intubation ) two. These two structures is the most commonly used structures. This performance is no essential difference between the two structures , but the inner loop structure installation and connection of small size ; outer loop structure installation to connect large size. At present , the structure of ball screw has more than 10 kinds , but more commonly used are: inner loop structure ; outer loop structure ; cap structure ; cover structure.
Introduces an important component of ball screw
Ball screw is between the screw and nut with ball screw drive components for the rolling elements . There are many types of ball screw structure .
Press the ball circulation and the outer loop is divided into two major categories of circulation .
Used tube outer loop back style beads more Used inner loop back waist beads embedded -block -shaped grooves more. Ring is divided into the outer loop and inner loop into two categories. Used tube outer loop back style beads more Used inner loop back waist beads embedded -block -shaped grooves more. Press -sectional shape of the track is divided into single- threaded dual circular arcs and two cross-sectional shape. Due to the axial stiffness of double arc truncate truncate larger than a single arc , by cross-sectional shape of the track is divided into single- threaded dual circular arcs and two cross-sectional shape. Due to the axial stiffness of double arc truncate truncate larger than a single arc , so now generally circular cross-sectional shape of the double screw . Commonly used double arc before truncate screw .
According to pre- load in the form of points, can be divided into single nut without pretension , the lead single nut preload displacement , radial ball to increase preload single nut , double nut gasket forms by pre- loading can be divided into single nut without pretension , the lead single nut preload displacement , radial ball to increase preload single nut , washer preloaded double nut , preloaded double nut poor teeth , double nut threaded preload . CNC machine tools commonly used double nut preload shim type , preload , poor teeth preloaded double nut , double nut threaded preload . CNC machine tools commonly used double nut preload shim style , its preload is generally axial load of 1/ 3.
Ball screw and sliding screw nut comparison has many advantages : high transmission efficiency , high sensitivity , stable transmission : Small abrasion , long life ; eliminate axial clearance , improved axial stiffness . Eliminate axial clearance , improved axial stiffness .
Ball screw nut drive CNC machine tools are widely used in small and medium feed drive system . In the short-stroke heavy-duty CNC machine tools (6m or less ) feed line drive ball screw nut is widely used in small and medium sized CNC machine tool feed drive systems. In the short-stroke heavy-duty CNC machine tools (6m or less ) system is also frequently used. The system is also frequently used.
Installation of ball screw CNC machine tool feed system to get higher transmission stiffness , in addition to strengthening the rigidity of the ball screw nut itself outside CNC machine feeding system to obtain higher transmission stiffness , in addition to strengthening the ball screw stiffness itself outside nut bars , ball properly installed and supported structural stiffness factor can not be ignored . Nut and bearing seat should have sufficient rigidity and precision. Structural rigidity and support equipment is also not be ignored . Nut and bearing seat should have sufficient rigidity and precision. Usually appropriate to add and the support base should have sufficient contact area stiffness and precision large and machine coupling member to increase the contact area and the nut bracket local stiffness and the contact strength, and machine coupling member in order to improve the local stiffness nut seat and contact strength , the new design of the machine in the process conditions often allow the nut seat or bearing seat formed integrally with the machine body to increase stiffness. Often the nut seat or bearing seat formed integrally with the machine body to increase stiffness.
In order to improve the axial stiffness of the support , and select the appropriate rolling bearing is also very important. China is currently mainly in two combinations. In order to improve the axial stiffness of the support , and select the appropriate rolling bearing is also very important. China is currently mainly in two combinations. One is the use of radial bearings and tapered bearing assembly , although its structure is simple, but the lack of axial stiffness . Is the radial bearings and tapered bearings used in combination , although its structure is simple, but the lack of axial stiffness . Another is the thrust bearing or radial thrust bearings and use a combination of radial bearings , axial stiffness has been improved , bearing and use a combination of radial bearings , axial stiffness has been improved , but increases the bearing friction and increased heat resistance and structural dimensions of the bearing bracket .
Note that the selection parameters when the ball screw
Different parameters will result in the selection of the final product produced qualitatively different , ball in the production of life is a small but significant presence , but probably because it 's causing some minor differences in technological accidents , and therefore in production should be strictly following are the main parameters of the selection should focus on a few :
1 --- nut form . On the manufacturers of the product samples will have a variety of nuts in the form of general type the first few letters that said nut form . By flange form of a circle around the flange , single flange trimming , trimming double flange and flangeless types . According to the length of a single nut nut and double nut ( Note that there is no difference between the load and the rigid single nut and double nut , which is not subject to manufacturers speech salespeople , single nut and the main difference is that the latter double nut preload can be adjusted and the former can not , another price and length of the latter are roughly 2 times the former ) . In the case of installation size and performance promised , designers should try to choose a selection of conventional form , in order to avoid delivery problems maintaining spare parts . Recommended : frequent movement , maintaining high precision double nut occasions election , and on other occasions election double edge single nut . Recommended : nut inside the loop as much as possible in the form of double- trimming flange single nut .
2 --- nominal diameter . That is the outer diameter of the screw , common specifications are 8,12,14,16,20,25,32,40,50,63,80 , 100,120 , but please note that these specifications , the manufacturers generally only 12 to 50 goods, that is to say , other diameters are mostly futures ( see single production, delivery of between about 30 to 60 days , the Japanese product is about 2 to 2.5 months, European and American products is about 3 to 4 months ) . Nominal diameter and load basic proportional to the load the greater the larger the diameter , the value can access detailed product manufacturers samples. Here only two concepts : dynamic load and static load rating , axial movement of the former state of the rated load , which refers to the nominal axial load static state . Design reference to the former . It should be noted that the ratio of the rated load is not the maximum load , the actual load and the rated load , the higher the theoretical life of the screw . Recommended : try to choose a diameter of 16 to 63.
3 --- lead . Also known as pitch , namely the linear motion of the screw nut per week rotation distance , there is a common lead 1,2,4,6,8 , 10,16,20,25,32,40 , small lead spot products are generally only 5 , 10 large lead generally 1616,2020 , 2525,3232,4040 ( 4 digit refers to the diameter of the first two , the two guide -way ) , other specifications most manufacturers see a single production . And the line speed of the lead , in a case where the input rotational speed , the greater the faster the lead . Recommended : Lead try to choose 5 and 10.
4 --- accuracy. Ball screw according to GB Class P and T classification categories, namely, transmission category and class positioning accuracy levels are 1, 2, 4 ..... several foreign products in general , regardless of the drive or location, all with C0 ~ C10 or specific numerical representation , in general, general machinery , or general election CNC machinery C7 ( 300 arbitrary stroke positioning error ± 0.05) or less , high-precision CNC machinery election C5 (± 0.018) than C3 (± 0.008) or less, optical or mechanical detection of selected C3 above. Of particular note is that the accuracy and relevance of great price , and the concept is a combination of precision and maintenance , that is, the lead screw error error can not explain the whole screw , factory precision passing can not explain the rated life have to maintain this accuracy.
5 --- length. Length of two concepts, one full length and the other is the length of the thread . Some manufacturers count only full-length , but some manufacturers need to provide thread length . Thread length also has two parts, one is the thread length of a stroke is valid . The former refers to the total length of the threaded portion , which is the theoretical maximum linear movement of the nut length, thread length = effective stroke length + + nut design margin ( if you need to install the protective cover , but also consider the length of the hood after compression , general 1/ 8 guard calculated maximum length ) . When designing graphics , full-length screw roughly what parameters can follow accumulate : full length screw nut length = effective stroke + + + design margins at both ends of support length ( bearing lock nut width + width + margin ) + Power lose
Into the connection length ( if using couplings are roughly general + margin coupling length ) . Of particular note is that if the length of your long ( greater than 3 m ) or aspect ratio is large ( greater than 70 ) , the best salespeople prior consultation with the possibility of producing factory , the overall situation is the largest domestic manufacturer of conventional product length 3 meters , 16 meters extraordinary items , foreign manufacturers of conventional products 6 m , 22 m special items. Of course, not to say that domestic manufacturers can not produce much longer , but the price of a given product comparison outrageous. Recommended : try to choose the length of six meters below the rack and pinion with more than a bargain .
Ball Screws and Lead Screws discriminant analysis
" Ball and Lead Screws are not interchangeable in many cases , is always required between accuracy, rigidity and load capacity to weigh and I also heard that does not necessarily correspond exactly between the specifications and performance , and I hope from comparison mature perspective to understand their real difference . "
Ball screw and trapezoidal screw applications there are some differences . Original equipment manufacturer applications often need to " just right " products , and trapezoidal screw is often the right choice. Trapezoidal screw products are easily combined with specific application to be adjusted to achieve the desired performance, while the cost to a minimum . In some cases , the need for life testing at the design stage , but for original equipment manufacturers, such additional work in the early and help reduce product cost. Ball can run continuously withstand much higher loads and achieve faster , therefore increasing the cost is worth it. For end users, the ball screw has good predictability , thus ensuring that the best choice for rapid integration and reliability . For example , factory automation systems is largely dependent on the ball screw technology. Of course , there are many original equipment manufacturers also need ball screw applications , such as the machine tool industry . For original equipment manufacturers, technology decisions are performance and cost , rather than predictability.
The main difference between the ball screw and trapezoidal screw is the way the load bearing surface between the mobile . The ball recirculating ball bearing to minimize friction and increase efficiency , the lead screw will have to use a low coefficient of friction between the sliding surfaces . Therefore , trapezoidal screw generally reach the ball screw efficiency ( about 90% ) . Tribology simple analysis mechanism ( Wear and friction ) can be found: sliding friction predictability necessarily lower than the transmission technology using recirculating ball . Fatigue life equation ( such as L10 life ) within its scope is very reliable. In summary, the ball screw and trapezoidal screw because of differences in the ability to predict performance and life , so its applications are fundamentally different .
Although the screw has many advantages ( load , stiffness , efficiency, load cycle , predictability ) , but its high cost . Although compared with other linear motion translation program , their high cost, but the ball screw design is more complex and requires hardened precision ball bearing surface and a circulation device . The trapezoidal screw size is small, it is very flexible design , in the case of the proper use of a small noise, corrosion resistance , and can be applied in order to meet the needs of the vertical configuration of the self-locking feature. They play an important role in many applications, of course, itself also has some limitations.
Protection and lubrication of ball screw
Ball screw nut protection and lubrication
( 1 ) Ball screw ball screw deputy vice- protection and other rolling friction transmission devices , like hard to avoid dust or dirt into the chip , and therefore must be equipped with protective devices . If the ball screw exposed on the machine , you should adopt a closed protective cover, such as spring steel spiral tube , telescopic tube and folding casing. When installing the shield is connected to one end side of the ball nut , ball screw and the other end fixed to the support base. If the ball screw in a secluded location , you can adopt protective seals , seals installed at both ends of the nut. Contact resilient seal with oil made from rubber or nylon , which made the hole with a screw thread to match the shape of the raceway ; good contact seals dust effect, but because of the contact pressure , the friction torque increased slightly . Non-contact labyrinth seals , also known as seals, which uses a hard plastic, the opposite shape of the hole with the screw thread raceway , and a slight gap , so to avoid friction torque, but the dust and poor results. Work should be avoided crashing guards , guards a damaged should be replaced.
( 2 ) ball screw lubrication lubricant can improve the wear resistance and transmission efficiency . Lubricant oils and greases can be divided into two categories . Lubricating oil is generally total loss systems : Grease can be lithium grease , high speed , we recommend using a lubricant is 40 ℃ viscosity index range 32 ~ 68 cSt (ISO VG 32 ~ 68) (DIN 51519) . At low speeds, the recommended oil viscosity is 40 ℃ index range 90 cSt (ISO VG 90) above. Grease the general increase in the raceway and mounting nut threaded housing space, and lubricants through the hole on the inner nut shell space injection. Every six months to replace the grease on the ball screw and clean of old grease on the screw , apply new grease . With oil lubricated ball screw , machine work can refuel before each refueling once or timing according to job requirements.
Fifth, the ball screw precautions when using the ball screw assembly for precision mechanical parts , so when you use need to note the following:
( 1 ) Because of the low friction ball screw , the screw will not be imposed if the vertical preload ( Micro preload same ) placement , nuts due to its own weight fell off from the screw axis , so the vertical use , please do Be careful . If you screw the nut off , the ball will fall off. In addition , the Ministry of ball circulation loop catheter there is a danger of damage. If the nut off from the screw , please contact sales technical staff.
( 2 ) due to ball screw nut circulation department ( circulation duct , end caps , etc. ) to highlight the external nut , please be careful not to knock and collision .
( 3 ) Please do not put radial load , torque load applied directly to the ball screw . If the role of a radial load , torque load , will make life extremely reduced screw or lead screw may not run smoothly .
( 4 ) When the screw is installed in combination with other mechanical parts , do not remove the nut from the screw . If the event must be separated , use a screw groove diameter of less than 1mm in a small tube system as an auxiliary tool , remove the nut and ball together , taking care not to let the ball fall off.
( 5 ) ball screw thread grooves are hardened and polished , and if forced into the external parts of the screw shaft or nut edge will produce indentation on the rolling grooves, so when installing components , be careful not applying excessive force on the screw or nut.
( 6 ) If the center support at both ends of the center axis of the ball screw and nut different heart , then to produce excessive friction ball screw , resulting in increased torque , heat and so on. Early wear ball screw appeared greatly shorten its life. Therefore , the installation must be corrected screw "3.1 ." In addition , after installation , please be sure to turn the screw , the nut moves on effective stroke of the screw, to confirm whether there is interference and other anomalies.
