1, nominal diameter of ball screw
That is, the outer diameter of the lead screw, the common specifications are 12, 14, 16, 20, 25, 32, 40, 50, 63, 80, 100, 120, but Please refer to the manufacturer's product samples for specific values. Only two concepts are explained here: dynamic rated load and static rated load. The former refers to the rated axial load in motion, while the latter refers to the rated axial load at rest. Just refer to the former when designing. It should be noted that the rated load is not the maximum load, and the smaller the ratio of the actual load to the rated load, the higher the theoretical life of the lead screw. Suggestion: Try to choose the diameter 16~63.
2, ball screw lead
Also known as the pitch, that is, the distance that the nut moves in a straight line every time the screw rotates, the common leads are 1, 2, 4, 6, 8, 10, 16, 20, 25, 32, 40, while the small and medium lead spot products are generally only 5,/kloc-0. Lead is related to linear speed. When the input speed is constant, the greater the lead, the faster the speed. Suggestion: Try to choose 5 and 10 as clues.
The selection of lead is related to the required movement speed and system, and generally it is selected from: 4, 5, 6, 8, 10, 12, 20, and the specifications are large, so the lead can be selected generally (mainly considering the bearing tooth thickness). In the case of meeting the speed, generally choose a smaller lead (to improve the control accuracy); For occasions requiring high speed, the lead can be greater than 20. For grinding screw, the lead can generally be equal to the nominal diameter (limited by the angle of grinding screw), such as 32(32*32), 40(40*40) and so on. Of course, it can be bigger (not grinding, it is rarely considered). The larger the lead, the greater the rotational component, the greater the periodic error and the faster the speed under the same conditions. Therefore, flexibility is generally required in high-speed situations, and if some accuracy requirements are abandoned, the significance of clearance requirements will not be great (the lead accuracy deviation will increase). Therefore, large lead screws are generally single nuts.
3, the ball screw length
There are two concepts of length, one is full length and the other is line length. Some manufacturers only calculate the full length, but some manufacturers need to provide the thread length. Thread length also has two parts, one is the total thread length and the other is the effective stroke. The former refers to the total length of the threaded part, while the latter refers to the theoretical maximum length of the nut's linear motion, and the threaded length = effective stroke+nut length+design margin (if it is necessary to install the protective cover, the compressed length of the protective cover should also be considered, generally calculated as 65438+ 0/8 of the maximum length of the protective cover).
When designing and drawing, the total length of the lead screw can be roughly accumulated according to the following parameters: total length of the lead screw = effective stroke+nut length+design allowance+supporting length at both ends (bearing width+lock nut width+allowance)+power input connection length (if coupling is used, it is roughly half of coupling length+allowance). It is particularly important to note that if the length is too long (more than 3 meters) or the aspect ratio is too large (more than 70), it is best to consult the sales staff of the manufacturer in advance whether it can be produced. Generally speaking, the maximum length of conventional products of domestic manufacturers is 3m, and that of special products is16m; that of conventional products of foreign manufacturers is 6m, and that of special products is 22m. Of course, it's not that domestic manufacturers can't produce longer ones, but the price of customized products is ridiculously high. Suggestion: Try to choose the length within 6 meters, and it is more cost-effective to use rack and pinion if it exceeds the length.
4, ball screw nut form
There are many kinds of nut forms in the product samples of various manufacturers, and the first few letters of the general model indicate the nut form. According to the flange form, there are approximately circular flanges, single-sided flanges, bilateral flanges and flanges. According to the length of nuts, there are single nuts and double nuts (note that there is no difference in load and stiffness between single nuts and double nuts, and don't listen to the comments of factory sales staff. The main difference between single nut and double nut is that the latter can adjust the pre-tightening force while the former can't, and the latter's price and length are roughly twice that of the former. When the installation size and performance permit, the designer should try to choose the conventional form to avoid the delivery date of spare parts during maintenance. Suggestion: Choose double nuts for frequent actions and high maintenance accuracy, and choose double nuts and single nuts for other occasions. Suggestion: Try to choose single nut internal circulation double trimming flange as the nut form.
5, ball screw accuracy
Ball screws are divided into P type and T type according to GB, that is, transmission type and positioning type, and the accuracy grade is 1, 2, 3, 4 ... Foreign products are generally expressed as C0~C 10 or specific values regardless of transmission or positioning. Generally speaking, C7 (positioning error within any 300 stroke) is selected for general machinery or general CNC machinery. It is particularly important to note that the accuracy is closely related to the price, and the concept of accuracy is combination and maintenance, that is to say, the lead error of the lead screw cannot explain the error of the whole set of lead screws, and the factory accuracy cannot explain that this accuracy can be maintained within the rated service life. This is a question of reliability, which is related to the production process of the manufacturer. Suggestion: For accuracy, try to choose C7.
When the ball screw pair is used for pure transmission, it is generally selected as the "T" type (that is, the transmission type mentioned in the mechanical manual), and its accuracy level can generally be selected as "T5" level (the cycle deviation is below 1 wire), "T7" level or "T 10" level, and the deviation within the total length range is generally not required (the temperature difference during processing affects the stroke accuracy) When the price difference of the above three grades is used for precision positioning transmission (positioning is required on the travel), it is necessary to select "P" grade (namely positioning grade mentioned in the mechanical manual), and the accuracy grades should be "P 1", "P2", "P3", "P4" and "P5" (decreasing precision in turn), where "P/kloc-" Grating is generally installed when high precision is needed, and it is also good to use it in open loop when high precision is needed. "P5" uses most CNC machine tools and their modifications, such as CNC lathes, CNC milling machines, boring machines, CNC grinders and various transmission mechanisms with CNC devices. Grating can also be installed if necessary.
The above are the main parameters, and the following parameters must be used when selecting the model: bead number, bead diameter, manufacturing mode code, preloading grade, etc. The explanation is as follows:
6. Ball number of ball screw
This parameter is generally marked after the lead of the model, such as 40 10-4. This "-4" is the number of beads, because the problem of circulation mode is complicated, and users can simply understand it as the number of cycles of the drum. "-4" is four cycles, and the greater the value, the longer the nut length.
7. Ball diameter of ball screw
This parameter refers to the diameter of the rolling body, which will not be reflected in the model, but will be marked in the technical parameter table of each manufacturer, which is generally related to the nominal diameter and lead, so users don't have to pay attention to it. However, some users should pay attention to this parameter when the ball falls out of the nut due to improper use, and the size is generally accurate to 0.00 1. Of course, users are not advised to install it themselves, otherwise the manufacturer will not provide free maintenance, even if the product is still under warranty. If the ball accidentally falls, the supplier should be informed to assist in installation.
8, ball screw manufacturing mode code
There are two main manufacturing methods of ball screw: rolling and grinding. The former is also called rolling manufacturing or remanufacturing, which is generally represented by F, and the latter is also called grinding manufacturing. Generally represented by G, because of different processes, they can reach different accuracy levels. At present, the highest precision that can be achieved by rolling method is C5 grade, while grinding can produce products with higher precision. However, please note that there is no reverse inevitability between the two manufacturing methods and accuracy and performance, that is, if the selected accuracy is C7, it has nothing to do with the manufacturing method. In fact, the professional sales staff of many manufacturers may not know the detailed differences between them, so let's say a few more words: rolling belongs to batch manufacturing and grinding belongs to precision manufacturing. The production efficiency of the former is much higher than that of the latter, but the manufacturing equipment cost of the former is also much higher than that of the latter. In other words, the entry threshold of grinding screw is low, and the entry threshold of rolling production is high. Manufacturers who can produce rolled wire can generally produce ground wire, but manufacturers who can produce ground wire may not be able to produce rolled wire. Therefore, if you can buy rolled products with the same precision, don't buy ground products. The reason is simple: cheap. In addition, tumbling only refers to screws and nuts that are all ground.
9, ball screw preloading
Also called pre-tightening. As for preloading, users don't need to know the specific preloading pressure and method, but only need to choose the preloading grade according to the samples of the manufacturer. The higher the contour, the tighter the fit between nut and screw, and the lower the grade, the looser it is. The principles to be followed are: under the conditions of large diameter, double nuts, high precision and large driving torque, the pre-tightening grade can be higher, otherwise it can be lower.
② Determine the lead and speed requirements of the lead screw bearing through the motor;
④ Determine the average axial force and rotational speed through load and speed distribution (acceleration and deceleration);
⑤ Determine the pre-pressure with the average axial force;
⑥ The expected life, axial load and rotating speed determine the dynamic rated load;
⑦ Limit the basic dynamic rated load, lead, critical speed and DmN value, and determine the outer diameter and nut form of the lead screw bearing;
⑧ Determine the rigidity by outer diameter, nut, pre-tightening force and load (mechanical design);
Pet-name ruby ambient temperature, the total length of the nut to determine the thermal change and lead accumulation;
Attending screw bearing stiffness, thermal displacement to determine the pretension;
The maximum speed of the machine tool, the temperature rise time and the specifications of the screw bearing determine the driving torque and specifications of the motor.