1. The nominal diameter of the ball screw
is the outer diameter of the screw. The common specifications are 12, 14, 16, 2, 25, 32, 4, 5, 63, 8, 1 and 12, but please note that in these specifications, manufacturers generally only prepare 16~5 goods, that is to say. The nominal diameter is basically proportional to the load, and the larger the diameter, the greater the load. 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 and the latter refers to the rated axial load in static state. 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. Recommendation: Try to choose a diameter of 16~63.
2. Lead of ball screw
is also called 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, 1, 16, 2, 25, 32 and 4, while the small and medium lead products are generally only 5 and 1, and the large lead is generally 1616 and 22. The lead is related to the linear speed. When the input speed is constant, the larger the lead, the faster the speed. Recommendation: Try to choose 5 and 1 for the lead.
the lead selection is related to the required movement speed and system, and it is usually selected from: 4, 5, 6, 8, 1, 12 and 2, with larger specifications, and the lead can also be selected generally (mainly considering the bearing tooth thickness). When the speed is satisfied, generally choose a smaller lead (to improve the control accuracy); For occasions requiring high speed, the lead can be more than 2, and for grinding lead screws, the lead can generally be equal to the nominal diameter (limited by the angle of the grinding screw), such as 32(32*32), 4(4*4), etc. Of course, it can be larger (not grinding, but rarely considered). The larger the lead, the greater the rotational component under the same conditions, the greater the periodic error and the faster the speed. Therefore, flexibility is generally required in high-speed occasions, and giving up some precision demands makes the clearance requirements less meaningful (lead precision deviation increases). Therefore, large lead screws are generally single nuts.
3. Ball screw length
There are two concepts of length, one is full length, and the other is thread length. Some manufacturers only calculate the full length, but some manufacturers need to provide the thread length. There are also two parts in the thread length, 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 moving in a straight line, and the thread length = effective stroke+nut length+design margin (if a protective cover needs to be installed, the compressed length of the protective cover should also be considered, which is generally calculated as 1/8 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: the total length of the lead screw = effective stroke+nut length+design margin+supporting length at both ends (bearing width+lock nut width+margin)+power input connection length (if a coupling is used, it is roughly half of the coupling length+margin). 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 7), it is best to consult the sales staff of the manufacturer in advance whether it can be produced. In general, the maximum length of the regular products of domestic manufacturers is 3 meters, the special products are 16 meters, the regular products of foreign manufacturers are 6 meters and the special products are 22 meters. Of course, it doesn't mean that domestic manufacturers can't produce longer ones, but the price of customized products is outrageous. Recommendation: Try to choose a length of less than 6 meters, and it is more cost-effective to use a rack and pinion if it exceeds the length.
4. Nut form of ball screw
There are many nut forms in the product samples of various manufacturers, and the first few letters in the general model indicate the nut form. According to the flange form, there are about circular flange, single trimming flange, double trimming flange and flange. According to the length of nuts, there are single nuts and double nuts (note that there is no difference in load and rigidity between single nuts and double nuts, so don't listen to the speech of the sales staff of the factory. The main difference between single nuts and double nuts is that the latter can adjust the preloading while the former can't, and the price and length of the latter 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 problem of the delivery date of spare parts during maintenance. Recommendation: Choose double nuts for frequent actions and high-precision maintenance, and choose double and single nuts for other occasions. Recommendation: Try to choose single nut with internal circulation and double trimming flange as the nut form.
5. Ball screw accuracy
Ball screws are classified into P and T categories according to GB, that is, transmission category and positioning category, with accuracy levels of 1, 2, 3, 4 ................................................................................................................ 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 screw can not explain the error of the whole set of lead screws, and the factory accuracy can not 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. Recommendation: Choose C7 as far as possible for accuracy.
when the ball screw pair is used for pure transmission, it usually chooses "t" type (that is, the transmission type mentioned in the mechanical manual), and its accuracy level can generally choose "T5" level (the cycle deviation is less than one thread), "T7" level or "T1" level, and the deviation within its total length range is generally not required (the influence of temperature difference during processing on stroke accuracy can be ignored, which is convenient for processing). Therefore, the price is lower (it is recommended to choose "T7", and the price difference of the above three levels is not big); When it is used for precise positioning transmission (with positioning requirements on the travel), it is necessary to choose the "P" class (that is, the positioning class mentioned in the mechanical manual), and the accuracy levels should be at "P1", "P2", "P3", "P4" and "P5" (the accuracy decreases in turn), among which "P1" and "P2" are very expensive and generally. While "P3" and "P4" are most widely used in high-precision machine tools. Gratings are generally installed when high precision is needed, and open-loop use is also good when high precision is needed. "P5" uses most CNC machine tools and their modifications, such as CNC lathes, CNC milling, boring, CNC grinding and various transmission mechanisms with CNC devices. Gratings can also be installed when necessary (because of the "5" level "arbitrary"
All the above are the main parameters, and the following parameters should be used when selecting the model: number of beads, bead diameter, manufacturing mode code, preloading grade, etc. The explanations are as follows:
6. The number of balls of ball screw
This parameter is generally marked after the lead of the model, such as 41-4. This "-4" is the number of balls, because the problem of circulation mode is complicated, and users can simply understand it as the number of cycles of the roller. "-4" is four cycles, and the larger this value means that the greater the load, 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 do not 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 .1. Of course, users are not recommended to install it themselves, otherwise the manufacturer will not provide free maintenance, even if the product is still under warranty. In case of accidental dropping of the ball, the supplier shall be informed to assist in installation.
8. Code of manufacturing method of ball screw
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. The latter is also called grinding manufacturing. Generally represented by g. Because of the different processes, the two can achieve different precision grades. 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 to say, if the accuracy chosen is C7, it has nothing to do with how it is manufactured. In fact, the professional sales staff of many manufacturers may not know the detailed difference 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 rolling screw can generally produce grinding screw, but manufacturers who can produce grinding screw may not be able to produce rolling screw. Therefore, if the products with the same precision can buy rolled products, don't buy ground products. The reason is simple: it is cheap. In addition, rolling and grinding only refer to screws, and nuts are all made by grinding.
9, ball screw preloading
is also called preloading. With regard to preloading, users do not need to know the specific preloading force and method, but only need to select the preloading grade according to the manufacturer's samples. The higher the equal height, the tighter the fit between the nut and the screw, and the lower the grade, the looser it is. The principle to be followed is: the preloading grade can be higher under the condition of large diameter, double nuts, high precision and large driving torque, and lower on the contrary.
② determine the lead of the lead screw bearing according to the motor and the speed requirement;
④ determine the average axial force and rotational speed by load and velocity distribution (acceleration and deceleration);
⑤ determine the pre-pressure by the average axial force;
⑥ life expectancy, axial load and rotating speed determine the dynamic rated load;
⑦ Limit the basic dynamic rated load, lead, critical speed and DmN value to determine the outer diameter of the lead screw bearing and the nut form;
⑧ outer diameter, nut, preloading and load determination rigidity (machine design);
pet-name ruby ambient temperature and total length of nut determine thermal change and cumulative lead;
attending screw bearing rigidity, thermal displacement to determine the pre-tension; 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.
Non-standard parts are mainly other parts that are freely controlled by enterprises without strict standard specifications and relevant parameters. There are many varieties of non-standard parts, and there is no very standardized classification at present. Roughly classified as follows:
Metal non-standard parts:
Customers provide drawings, and manufacturers use equipment to produce corresponding products according to the drawings. Usually, there are many molds, and the tolerance requirements and finish are stipulated by customers, so there is no certain paradigm. Products from casting to finishing completely need corresponding quality control, the process is complex and variable, and the general cost is higher than that of standard parts.
Non-metallic non-standard parts:
It is the processing of some non-metallic materials. Such as plastics, wood, stone, etc., in recent years, the injection molding industry, the development of plastic molds has become increasingly sophisticated, and the introduction of curved surface design and programming numerical control has greatly improved the cost and tolerance level of non-standard processing. Non-standard products refer to products or equipment that are not manufactured according to the unified industry standards and specifications promulgated by the state, but are designed and manufactured according to their own needs. And the appearance or performance is not in the national equipment product catalogue.
in order to meet the needs of large-scale industrial production, the mechanical equipment that has been produced and proved to have good performance after use is shaped and serialized, which is called standard product. According to the requirements of users, on the basis of standard products, products produced, modified or customized are called non-standard products.
Standardized and serialized products are mainly suitable for general mechanical equipment. In fact, when designing a new industrial device, some equipment is special, which cannot be found in the existing serialized list, and needs to be designed and manufactured separately, and its versatility will not be high in the future. This kind of equipment is called non-standard products.
At present, there are many fields where non-standard products are mentioned, mainly chemical and petrochemical industries. Because there are many products and different processes in this industry, there are also many non-standard products.