Ball screw is an ideal product for converting rotary motion into linear motion, or converting linear motion into rotary motion. The ball screw is the most commonly used transmission element in tool machinery and precision machinery. Its main function is to convert rotational motion into linear motion, or convert torque into axial repeated force. It also has high precision, reversibility and high efficiency characteristics. Due to its small frictional resistance, ball screws are widely used in various industrial equipment and precision instruments!

1. Nominal diameter of ball screw

That is the outer diameter of the screw. Common specifications are 12, 14, 16, 20, 25, 32, 40, 50, 63, 80 , 100, 120, but please note that among these specifications, each manufacturer generally only stocks 16~50, which means that most of its diameters are futures (see production order, delivery period is about 30~60 days) , Japanese products are about 2~2.5 months, European and American products are about 3~4 months). The nominal diameter is basically proportional to the load. The larger the diameter, the greater the load. For specific values, please refer to the manufacturer's product catalog. Only two concepts are explained here: dynamic rated load and static rated load. The former refers to the rated axial load in the moving state, and the latter refers to the rated axial load in the static state. Just refer to the former when designing. It should be noted that the rated load is not the maximum load. The smaller the ratio between the actual load and the rated load, the higher the theoretical life of the screw. Recommendation: Try to choose diameter 16~63.

2. Ball screw lead

It is also called pitch, which is the linear movement distance of the nut per revolution of the screw. Common leads are 1, 2, 4, 6, 8, 10, 16, 20, 25, 32, 40. The spot products with small and medium leads are generally only 5 and 10. The large leads are generally 1616, 2020, 2525, 3232, 4040 (the first two digits of the 4 digits refer to the diameter, and the last two digits refer to the diameter. Guidance process), its specifications are produced by most manufacturers upon ordering. 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 10 for the guide.

The choice of lead is related to the required movement speed, system, etc. It is usually selected among: 4, 5, 6, 8, 10, 12, 20. For larger specifications, the lead can generally be selected. Larger (mainly considering the thickness of the bearing teeth). When the speed is sufficient, a smaller lead is generally selected (which is beneficial to improving control accuracy); for occasions requiring high speed, the lead can exceed 20. For ground screws, the lead can generally be approximately equal to the nominal diameter. (Limited by the grinding helix angle), such as 32 (32*32), 40 (40*40), etc., of course it can also be larger (non-grinding, but rarely considered). The larger the lead, the larger the rotation component under the same conditions, the periodic error is amplified, and the faster the speed. Therefore, generally high-speed situations require flexibility, and giving up part of the demand for accuracy will make the clearance requirements less meaningful (lead accuracy deviation increases). Therefore, large-lead screws generally have single nuts.

3. Ball screw length

There are two concepts of length, one is the full length and the other is the thread length. Some manufacturers only calculate the total length, but some manufacturers need to provide the thread length. There are also two parts in the thread length, one is the full length of the thread, and the other is the effective stroke. The former refers to the total length of the threaded part, and the latter refers to the theoretical maximum length of the nut's linear movement. Thread length = effective stroke + nut length + design margin (if a protective cover needs to be installed, the compressed length of the protective cover must also be considered. Generally calculated as 1/8 of the maximum length of the protective cover).

When designing and drawing, the full length of the screw can be roughly accumulated according to the following parameters: full length of the screw = effective stroke + nut length + design allowance + support length at both ends (bearing width + locking nut width + margin) + power input connection length (roughly half the coupling length + margin if using a coupling). What needs special attention is that if the length is too long (more than 3 meters) or the aspect ratio is large (more than 70), it is best to consult the manufacturer's sales staff in advance whether it can be produced. The overall situation is that the maximum length of conventional products from domestic manufacturers is 3 meters. , 16 meters for special products, 6 meters for regular products from foreign manufacturers, and 22 meters for special products. Of course, it doesn’t mean that domestic manufacturers can’t produce longer ones, but the price of customized products is quite outrageous. Recommendation: Try to choose a length of less than 6 meters. If it is longer than 6 meters, it is more cost-effective to use a rack and pinion.

4. Ball screw nut form

Each manufacturer's product catalog will have many nut forms. The first few letters in the general model number indicate the nut form. According to the flange form, there are round flange, single trimmed flange, double trimmed flange and flangeless flange. According to the length of the nut, there are single nuts and double nuts (note that there is no difference in load and rigidity between single nuts and double nuts. Do not listen to the manufacturer's sales staff's speech on this point. The main difference between single nuts and double nuts is that the latter can adjust the preload. The former cannot, 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 a conventional form when selecting to avoid the delivery date problem of spare parts during maintenance. Recommendation: Choose double nuts for frequent movements and high-precision maintenance, and choose double and single-sided nuts for other situations. Recommendation: As far as possible, the nut form should be a single nut with an internal circulation double trimming flange.

5. Ball screw accuracy

Ball screws are classified into P type and T type according to GB, that is, transmission type and positioning type. The accuracy grades are 1, 2, 3, and 4. .....Several kinds, foreign products are generally expressed in C0~C10 or specific numerical values ??regardless of transmission or positioning. Generally speaking, for general machinery or ordinary CNC machinery, choose C7 (positioning error within any 300 strokes is ±0.05) or Below, choose C5 (±0.018) or above for high-precision CNC machinery and below C3 (±0.008), and choose C3 or above for optical or detection machinery. What needs special attention is that accuracy and price are closely related, and the concept of accuracy is combination and maintenance. In other words, the lead error of the screw cannot explain the error of the entire set of screws, and the qualified factory accuracy cannot explain the rated service life. This accuracy is maintained. This is a reliability issue, related to the manufacturer's production process. Recommendation: Choose C7 for accuracy.

When the ball screw pair is used for pure transmission, the "T" type (i.e., the transmission type mentioned in the mechanical manual) is usually selected, and its accuracy level is generally selected as "T5" level (the periodic deviation is within 1 wire or less), "T7" grade or "T10" grade, there is generally no requirement for deviation within the total length range (the influence of temperature difference during processing on the stroke accuracy can be ignored to facilitate processing). Therefore, the price is lower (it is recommended to choose "T7", and the price difference between the above three levels is not big); when used for precision positioning transmission (with positioning requirements on the stroke), you should choose the "P" category (ie mechanical Positioning category mentioned in the manual), the accuracy level should be at "P1", "P2", "P3", "P4", "P5" level (accuracy decreases in order), among which "P1" and "P2" levels are very expensive. Expensive, it is generally used for very precise work machines or very demanding situations. In most cases, it is used in open loop (not the mother machine). The "P3" and "P4" grades are the most commonly used and widely used in high-precision machine tools and require When very high precision is required, a grating is generally installed. When higher precision is required, it is also good to use open loop. "P5" uses most CNC machine tools and their modifications, such as CNC lathes, CNC milling, boring, CNC grinding and various CNC combinations. The transmission mechanism of the device can also be equipped with a grating when needed (because the "deviation of any 300mm stroke of "5" level is 0.023" and the curve is smooth, in many practical cases, the effect of matching the grating is very good).

The above mentioned are the main parameters. When selecting the model, the following parameters must also be used: number of bead rolls, bead diameter, manufacturing method code, preload level, etc. The respective explanations are as follows:

6. The number of ball screw rolls

This parameter is generally marked after the lead of the model, such as 4010-4, this "-4" is the ball roll Number, because the problem of circulation method is more complicated. Users can simply understand it as the number of cycles of rolling elements. "-4" means 4 cycles. The larger the value, the greater the load and the longer the length of the nut.

7. Ball screw diameter

This parameter refers to the diameter of the rolling element. It will not be reflected in the model, but will be marked in the technical parameter table of each manufacturer. Generally, it is the same as the diameter of the rolling element. The nominal diameter is related to the lead and the user does not need to pay attention to it. However, some users should pay attention to this parameter when the balls fall out of the nut due to improper use and need to reinstall the balls. The size is generally accurate to 0.001. Of course, users are not recommended to install it by themselves, otherwise the manufacturer will not provide free maintenance, even if the product is still in use. Within the warranty period. If the ball accidentally falls, the supplier should be notified to assist with installation.

8. Ball screw manufacturing method code

There are two main manufacturing methods of ball screw: rolling and grinding. The former is also called rolling manufacturing or transformation. Generally, Represented by F. The latter is also called grinding manufacturing. Generally represented by G. Due to different processes, the accuracy levels that the two can achieve are different. Currently, the highest accuracy that can be achieved by rolling is C5 level, while grinding can produce higher-precision products. However, please note that there is no inverse inevitability between the two manufacturing methods and accuracy and performance. That is to say, if the accuracy selected is C7, it has nothing to do with how it is manufactured. In fact, the professional sales staff I meet from many manufacturers may not know the detailed differences between the two, so I will say a few 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. However, the manufacturing equipment cost of the former is also much higher than that of the latter. In other words, the entry threshold for ground screws is lower, while the entry threshold for rolling production is higher. Manufacturers that can produce rolled screws can generally also produce ground screws, while manufacturers that can produce ground screws cannot. We must be able to produce rolled screws. Therefore, if you can buy rolled products with the same precision, don’t buy ground products. The reason is simple: they are cheap. In addition, rolling and grinding only refer to screws, and nuts are all made by grinding.

9. Ball screw preload

Also called preload. Regarding preloading, users do not need to know the specific preloading force and preloading method. They only need to select the preloading level according to the manufacturer's sample. The higher the grade, the tighter the nut and the screw fit, and the lower the grade, the looser the nut. The principles to be followed are: in the case of large diameter, double nuts, high precision, and large driving torque, the preload level can be selected higher, otherwise, the preload level can be selected lower.

② Determine the lead of the screw bearing through the motor and speed requirements;

④ Determine the average axial force and rotation speed through the load and speed distribution (acceleration and deceleration); < /p>

⑤The preload is determined by the average axial force;

⑥The expected life, axial load, and rotational speed are used to determine the dynamic rated load;

⑦The basic dynamic rated load, The lead, critical speed, and DmN value limits determine the outer diameter of the screw bearing and the nut form;

⑧The outer diameter, nut, preload, and load determine the rigidity (machine design);

⑨Ambient temperature, the total length of the nut determines the thermal change and cumulative lead;

⑩Screw bearing rigidity, thermal displacement determines the pretension force; The maximum speed of the machine tool, temperature rise time, and screw bearing specifications determine the motor drive Torque and specifications.

The ball screw is the most commonly used transmission element in tool machinery and precision machinery. Its main function is to convert rotational motion into linear motion, or to convert torque into axial repetitive force. It also has both Features of high precision, reversibility and high efficiency. Due to its small frictional resistance, ball screws are widely used in various industrial equipment and precision instruments. Ball screws are ideal products for converting rotary motion into linear motion, or converting linear motion into rotary motion.

Ball screw series products and applications:

Ultra-high DN value ball screw: high-speed tool machine, high-speed comprehensive machining center.

End cover ball screw: rapid handling system, general industrial machinery, automated machinery.

High-speed ball screw: CNC machinery, precision tools, industrial machinery, electronic machinery, high-speed machinery.

Fine grinding grade ball screws: CNC machinery, precision tools, industrial machinery, electronic machinery, conveying machinery, aerospace industry, actuators used in antennas, valve switch devices, etc.

Nut-rotating (R1) series ball screws: semiconductor machinery, industrial robots, carpentry machines, laser processing machines, transportation equipment, etc.

Rolling grade ball screw: low friction, smooth operation, fast delivery and low price.

Heavy-duty ball screws: all-electric injection molding machines, stamping machines, semiconductor system manufacturing devices, heavy-duty brakes, industrial machinery, and forging machinery.