BALL SCREW TECHNOLOGY

PPT on BALL SCREW TECHNOLOGY

A ball screw uses ball bearings to eliminate the friction between the nut and screw and lead screws do not. The screw and nut on a ball screw have matching helical grooves that allow ball bearings to re-circulate in those races and are typically semi-circular in shape to accept the spherical ball bearing. Lead screws use deeper helical threads and a mating nut, which is usually made of a polymer composite or bronze.
The rolling nature of ball screws eliminates the sliding friction associated with lead
screws.


Topics Covered:

THE ADVANTAGES/DISADVANTAGES OF BALL SCREWS.
BASIC DIFFERENCE BETWEEN LEAD SCREWS VS BALL SCREWS.
PRINCIPLE OF BALL SCREW.
PARTS OF BALL SCREW.
PRECAUTIONS WHEN USING BALL SCREW.
CHARACTERISTICS OF BALL SCREWS AND APPLICATION EXAMPLES.

1. BALL SCREW TECHNOLOGY 5/25/2019 PRESENTED BY AMIT SINGH RAWAT 8 TH SEM, MECHANICAL 1ST11ME015 SaIT

2. SCREW : By the 1st century BC, wooden screws were commonly used throughout the Mediterranean world in screw presses for pressing olive oil from olives and pressing juice from grapes in winemaking. Metal screws used as fasteners were rare in Europe before the 15th century, if known at all. A screw, or bolt, is a type of fastener characterized by a helical ridge, known as a male thread (external thread), wrapped around a cylinder. The most common uses of screws are to hold objects together and to position objects.

3. the screw is a mechanical element that converts a rotational motion into a linear motion. These screws that move things or transmit forces are the means to convert small rotational force into large thrust (a force to push). MECHANICAL LINEAR ACTUATOR

4. VARIETY OF SCREWS Sliding contact screws Triangular thread screws Acme thread lead screws 2 . Rolling contact screws Ball screws Roller screws

5. THE ADVANTAGES/DISADVANTAGES OF BALL SCREWS: Ball screws have lower friction and run at cooler temperatures. Ball screws are more efficient, requiring less torque . Ball screws can have problems with vertical applications. Ball screws require braking systems. Ball screws require grease or oil lubrication to achieve design life. Ball screws need to be replaced less frequently. Ball screws are noisy. Ball screws require braking mechanisms to eliminate back driving. Ball screws are more expensive than lead screws.

6. BASIC DIFFERENCE BETWEEN LEAD SCREWS VS BALL SCREWS: A ball screw uses ball bearings to eliminate the friction between the nut and screw and lead screws do not. The screw and nut on a ball screw have matching helical grooves that allow ball bearings to re-circulate in those races, and are typically semi- circular in shape to accept the spherical ball bearing. Lead screws use deeper helical threads and a mating nut, which is usually made of a polymer composite or bronze. The rolling nature of ball screws eliminates the sliding friction associated with lead screws.  

7. What is friction force? (Sliding and rolling friction) When you want to slide a box sitting on a floor, it does not move while your pushing force is yet too small (static frictional force). But, it starts moving when the pushing force has reached a certain level. In order to keep the box moving on, you need to maintain your pushing force at its dynamic frictional force, which is far less than the static friction force. OR the force which opposes the motion of one body over the another body. As described above, the friction force is the force that two objects exert upon each other t hrough their contact surface and hinder each other's relative movement when they are in contact. t he intensity of frictional force varies with the state of contact.

8. BALL SCREW : A ball screw is a mechanical linear actuator that translates rotational motion to linear motion with little friction. A threaded shaft provides a helical raceway for ball bearings which act as a precision screw. As well as being able to apply or withstand high thrust loads, they can do so with minimum internal friction. They are made to close tolerances and are therefore suitable for use in situations in which high precision is necessary. The ball assembly acts as the nut while the threaded shaft is the screw .

9. THE HISTORY OF THE BALL SCREW According to a literature in the 19th century, there was an attempt to replace sliding friction with rolling friction by means of balls inserted between a male screw and a nut, namely this is an concept of the ball screw. A Division of General Motors in the United States used ball screws practically for the first time in automobile steering gears in the 1940’s. In Japan, as mechanical industries advanced, the call for ball screws grew louder. Responding to these voices, NSK took the initiative to develop ball screws using its expertise in ball-bearing design and manufacturing, and the company eventually succeeded in launching the first ball screw type automobile steering gears in Japan in 1958. Although the main application target for the precision ball screws was NC machine tools, the first job for which it was used was to convert acme thread lead screws of the X, Y and Z axes of a milling machine called K5, manufactured by Makino Milling Machine Co. Ltd., into ball screws. This K5 model was the best-selling brand in the industry back then, and over fifty machines were produced monthly. The NSK precision ball screws were used for the first time in them. Thereafter, due to ever-progressing improvement in design techniques and manufacturing technologies, as well as needs for streamlining production in general, the high performance characteristics of ball screws soon made them one of the vital elements of NC machines, laborsaving machinery, and so on.

10. PRINCIPLE OF BALL SCREW When you rotate a ball nut around its axis, the ball nut moves in its axial direction since screw grooves are continuously provided in a helical form. Namely, the screw is a mechanical element that converts a rotational motion into a linear motion. These screws that move things or transmit forces are the means to convert small rotational force into large thrust (a force to push). Ball screws, also called a ball bearing screws, recirculating ballscrews , etc. it consists of a screw and a nut integrated with balls and the balls return mechanism, return tubes or return caps. Ball screws are the most common type of screws used in industrial machinery and precision machines. The primary function of a ball screw is to convert rotary motion to linear motion or torque to thrust, and vice versa, with the features of high

11. BALL SCREW AS AN ACTUATOR

12. A: Steel ball B: Screw shaft C: Ball nut D: Seal (both sides of ball nut) E: Reciculation parts (return tube, etc.)

13. STEEL BALLS : The diameter of steel balls is determined, after giving due consideration to the balance between the screw shaft diameter and lead , rigidity, load capacity, smooth operation, etc.

14. SCREW SHAFT A screw, or bolt, is a type of fastener characterized by a helical ridge, known as a male thread (external thread), wrapped around a cylinder.

15. SEALS : When debris or foreign matter enter the inside of the nut, it could affect smoothness in operation or cause premature wearing, either of which could adversely affect the ball screw ’ s functions. To prevent such things from occurring, seals are provided to keep contaminants out.

16. PRECAUTIONS WHEN USING BALL SCREW : When ball screws are used in an environment that is not clean, appropriate measures are required to prevent foreign matters from attaching to the screw shaft or entering the inside of the nuts. Individual ball screws have a limitation with respect to allowable rotational speeds , Therefore ball screws shall be used within their specified allowable rotational speeds. (Otherwise, it results in breakage of ball-recirculation parts, vibrations of screw shafts which trigger chain reaction in vibrations of entire machine body, damage on rolling surfaces and other failures.) The service temperature of the ball screw is limited to 80°C. if we exceed this limit, special measures will be necessary for the ball screws.

17. CHARACTERISTICS OF BALL SCREWS AND APPLICATION EXAMPLES High mechanical efficiency Most (90% or more) of the force used to rotate the screw shaft can be converted to the force to move the ball nut. (Since friction loss is extremely low, the amount of force used to rotate the screw shaft is as low as one third of that needed for the acme thread lead screw.) Ball screws are used where motion direction must be changed (converted). From rotations to linear motion From linear motion to rotations Low in wear Because of rolling contact, wear is far less than that of sliding contact. Thus, deterioration of accuracy is extremely low. This is used for application that calls for precise positioning. Low in wear Ball screws move smoothly enough under very slow speed. They run smoothly even under a load. Used when a light, smooth motion is needed Used when precise positioning is required. Used when heavy items must be moved lightly. Estimation of life is possible. Estimation of fatigue life of ball screw under given conditions is possible because the basics of life estimation are the same as those of rolling element bearings. It is possible to design a machine based on required life. Decision of ball screw specifications is easy. Ball screw lead The specifications of ball screws are standardized in ISO, JIS, etc.

18. APPLICATIONS CNC MACHINERY: CNC machine center, CNC lathe, CNC milling , CNC EDM, CNC grinder, Boring machine, Wire cutting machine etc.

19. CONCLUSIONS TECHNOLOGY WILL LEAD TO REDUCTION IN TIME AND BETTER OUTPUT. THE TECHNOLOGY CAN PROVE TO BE SUPERIOR TO LEAD SCREW IN THE LONG RUN.

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