The ball screw is a high-precision transmission element. The rolling screw is used instead of the sliding screw, and the sliding friction is converted into rolling friction. Therefore, it has the advantages of low wear, high transmission efficiency, stable transmission, long life, high precision, and high temperature rise. The ball screw has low friction, which is convenient for eliminating transmission gaps and other outstanding advantages. It brings great benefits to the performance improvement of the motor integration system. However, the ball screw cannot be self-locking, and a locking device is required when used for lifting transmission. Pre-tightening is to prevent the ball from slipping. The self-locking property of the ball screw is poor, or even non-existent, and it is easy to fall off without pre-tightening. However, not all ball screws are pre-tightened. It mainly depends on the accuracy requirements. Generally, the pre-tightening has high accuracy and large load capacity. There are four commonly used pre-tightening methods for ball screws. Let's take a look! 1. Double nut gasket pre-tightening, add a gasket between the double nuts, and the manufacturer can adjust the pre-tightening force in advance according to the user's request. It is very convenient to use and load and unload. 2. Double nut threaded pretightening uses the external thread on one nut to adjust the relative axial position of the two nuts through the round nut to achieve pretightening. 3. Double nut tooth difference pretightening, gears with a tooth number difference of 1 are cut out on the flanges of the two nuts respectively, and the two gears are meshed with the corresponding inner gear rings at both ends, and the inner gear rings are fastened to the nut seat with screws. By rotating and changing one of the nuts, the relative position of the two nuts is changed to adjust the gap and apply pretightening force. 4. Single nut variable lead self-pretightening, the internal thread raceway of the nut produces a lead mutation on the middle circle, so that the balls on the left and right ends are axially dislocated after installation to achieve pretightening. In general, the nut gasket pretightening method is simple and reliable, has good rigidity, is the most widely used, and is also more popular.

In the non-standard automation and logistics conveying industry, engineers frequently use the term "C7." As a "perennial" in precision transmission, C7-grade ball screws almost dominate the general conveying and positioning market. But have you ever wondered: Is the precision of C7 sufficient? When is it necessary to upgrade to C5? Today, we'll dissect the "truth about the cost-effectiveness" of C7 screws. I. A "Visualized" Definition of Precision: What exactly is the concept of C7? First, we need to clarify the precision standard of C7. According to ISO and JIS standards, the precision level is mainly determined by the "cumulative lead error within a 300mm stroke": C7 grade: 0.05mm (50 micrometers) C5 grade: 0.018mm (18 micrometers) Visual comparison: 50 micrometers is approximately the diameter of a human hair. For most ordinary packaging machines, palletizers, or conveyor line translation mechanisms, this error is almost negligible compared to the tolerances of mechanical assembly. Therefore, C7 can be considered the "gold standard" for ordinary conveying equipment. II. Why is C7 the "optimal solution" in terms of cost-effectiveness? In engineering design, "good enough" is the highest level of wisdom. The popularity of C7 lead screws stems from their manufacturing process—cold rolling. Cost Advantage: Cold rolling, achieved through die extrusion, boasts extremely high production efficiency, and its price is typically only 1/3 or even lower than that of ground grade (C5 and above). Mechanical Performance: The rolling process is equivalent to cold work hardening of the material; the fibrous structure on the lead screw surface is not severed, resulting in very robust wear resistance in certain heavy-duty conveying scenarios. Delivery Cycle: C7 lead screws typically have a large inventory, supporting rapid cutting and processing, making them ideal for non-standard automated equipment with tight project cycles. III. Caution: C7 May Not Be Sufficient in These Scenarios While C7 offers balanced performance, please choose carefully if your conveying equipment involves the following three characteristics: 1. The "snowball effect" of ultra-long strokes Although the error is only 0.05mm per 300mm, if your conveying stroke is as long as 2 meters or even 3 meters, and there is no secondary positioning at the end, the cumulative error may reach more than 0.3mm. 2. Extreme requirements for "quietness" and "smoothness" Because the surface roughness of cold rolling is not as good as that of ground grade, the vibration and noise of C7 lead screws will be slightly greater during high-speed operation. If used in a laboratory environment or on high-precision testing equipment, it is recommended to upgrade to C5 ground grade. 3. Extremely high-frequency reciprocating motion C7 lead screws are usually paired with clearance nuts or slightly preloaded nuts. If you require extremely high reversing accuracy (backlash approaching zero), the raceway consistency of C7 may not be able to support long-term "zero-backlash" operation, easily leading to localized overheating. Instead of pursuing excessive precision, it is better to focus on dust prevention and lubrication solutions for the lead screw, as well as the parallel installation of the support base. These details have a far greater impact on the lifespan of the equipment than a precision difference of 0.03mm.