1- nominal diameter. 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- leading. 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.
Three times the 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 your length is too long (more than 3m) 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 the special products are 16m, while the conventional products of foreign manufacturers are 6m and the special products are 22m. Of course, it's not that domestic manufacturers can't produce longer ones, but the price of customized products is ridiculously high. Choose custom-made processing screws to find titanium Hao, professional quality assurance! Because of professionalism, it is excellent! 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 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- 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.
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:
Bead number: 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 the user can simply understand it as the number of cycles of the rolling body. "-4" is four cycles, and the greater this value means that the greater the load, the longer the nut length.
Bead diameter: 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 do not need to pay attention. 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.
Manufacturing mode code: There are two main manufacturing modes 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 expressed by G, because of different processes, they can achieve different levels of accuracy. At present, the highest precision that can be achieved by rolling method is C5 grade. And 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 accuracy you choose is C7, it has nothing to do with how it is manufactured. In fact, the professional salesmen of many manufacturers I met may not know the detailed differences between them, so I will 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.
Preload: Also called preload. 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.
There are usually three fixing forms of lead screw, namely, two ends are fixed, one end is fixed with a bracket, and the other end is fixed and the other end is free. In these three cases, the screw with fixed end has the best rigidity. The bearings at the fixed end are generally a pair of opposite angular contact bearings, and the bearings at the support end are generally deep groove ball bearings. For us, it is best to have one end fixed and one end supported, and the Z axis can also have one end fixed and the other end free.