Precision Ground BallScrew Characteristics
Product Image
首頁 > Shopping Cart > Precision Ground BallScrew Characteristics
-
Information
-
SOAR-BallScrews SOAR BallScrews -
Precision Ground Miniature BallScrews Miniature Series -
Precision Ground Internal BallScrews Internal Series -
Precision Ground External BallScrews External Series -
Precision Ground Heavy Load BallScrews Heavy Load Series -
Precision Ground Heavy Lead BallScrews High Lead Series -
Precision Ground End Cap BallScrews End Cap Series -
Precision Ground End Deflector BallScrews End Deflector Series -
Rolled BallScrews-FSIN -
Rolled BallScrews-FSIW -
Rolled BallScrews-FSKW -
Rolled BallScrews-FSBW -
Rolled BallScrews-SSVW
Feature description
High reliability
PMI has accumulated many years experience in production managing. It covers the whole production sequence, from receiving the order, designing, material preparation, machining, heat treating, grinding, assembling, inspection, packaging and delivery. The systemized managing ensures high reliability of PMI Ballscrews.High accuracy
PMI Ballscrews are machined, ground, assembled and Q.C. inspected under the constant temperature control (20°C) to ensure high precision of Ballscrews. Fig.1 accuracy inspection certi cate. The ground ball screw which accuracy grade is C5 or above, will attach an accuracy certi cate of inspection.Long durability
PMI Ballscrews are Alloy steels, which are well quenching and tempering treated for good rigidity, along with suitable surface hardening to ensure long durability.High working e ciency
Balls are rotating inside the Ballscrew nut to o er high working e ciency. Comparing with the traditional ACME screws, which work by friction sliding between the nut and screw, the Ballscrews needs only 1/3 of driving torque. It is easy to transmit linear motion into rotation motion.No backlash and with high rigidity
The Gothic pro le is applied by PMI Ballscrews. It o ers best contact between balls and the grooves. If suitable preload is exerted on Ballscrew hence to eliminate clearance between the ball nut and screw and to reduce elastic deformation, the ballscrew shall get much better rigidity and accuracy.
Design concept
The ball screw scraping mechanism is specially designed and developed. The ball screw uses a multi-layer contact dust-proof unit to exert the product's superior chip removal and scraping capabilities.High matchability
The ball screw high dust-proof wiper is currently available with various internal and external circulation nut types such as E-type and D-type.Improved dustproof effect
The spring bearing surface of the scraper itself is reduced to increase the single-point tooth-shaped fit effect and enhance the scraping ability.Excellent squeegee life
The outer ring of the wiper is tightened by a spring. When the wiper wears, the wiper preload will be automatically adjusted.High durability
The use of a scraper that fits the screw tooth profile and a seal close to the shaft cross-sectional shape prevents sawdust-level dust from entering the inside of the nut.High sealing gasket
The special groove design of the screw allows the high dust-proof sealing washer inside the scraper to completely fit the thread surface, thus achieving the dual effects of chip removal and dust prevention at the same time.Scraper design
The extension design of the scraper to fit the tooth shape greatly improves the scraping effect. The total length of the nut is different from the general specifications. For questions about the total length of the nut, please contact us.Screw shaft end design
It is recommended that the shaft end on either side of the screw be smaller than the screw root diameter dr. If you have problems with the screw shoulder size, please contact us.High dustproof ball screw application
Woodworking processing machinery, laser processing machines, high-precision conveying equipment, robotic arms or general machine tools and other processing environments that require dust protection.Accuracy standard level
High precision guaranteed
The screws and nuts of PMI's ball screws are precision processed, ground, assembled and quality controlled in a constant temperature room to ensure high-precision quality.:
Excellent durability and high efficiency
PMI has accumulated more than ten years of ball screw production technology, using German-made steel and applying the company's unique processing and grinding technology to provide ball screws with excellent durability. The operation of the ball screw relies on the rolling motion of the steel balls in the nut. It is more efficient than the traditional sliding screw. The required torque is only less than 1/3 of the traditional sliding screw, so it can easily convert linear motion into rotary motion.No backlash and high rigidity
PMI's ball screw adopts Gothic arch groove shape (as shown on the right), which allows the steel ball to have optimal contact with the groove for easy operation. If appropriate preload is added to eliminate the axial clearance, the ball screw can have Better rigidity reduces elastic deformation between balls and nut screws to achieve higher accuracy.
Lead accuracy
Preloading Torque
The preloading torque of the Ballscrew is controlled in accordance with JIS B 1192.
- Preload：The purpose of preload is to eliminate axial play and increase rigidity of Ballscrew.
- Preload torque：Torque needed to continuously turn a Ballscrew with preload with no other load applied to it.
- Reference torque：Preload torque set as a goal.
- Torque fluctuation：Fluctuation from a goal value of the preload torque. De ned as positive or negative in respect to the reference torque.
- Rating of torque fluctuation：Rating on reference torque and torque fluctuation.
- Actual torque：Preloaded dynamic torque measured by using an actual value of Ballscrew.
- Mean actual torque：In the effective thread length, the net reciprocate to measure the maximum actual torque and minimum actual torque are doing count mean.
- Actual torque fluctuation：In the e ective thread length, the net reciprocate to measure the maximum fl uctuant value.
- Rating of Actual torque fluctuation：Rating on mean actual torque and actual torque fluctuation.
Allowable range of preload torque
Reference torque
Tolerances on Various Areas of Ballscrew
Those on above are samples of accuracy of tolerance on various areas of Ballscrew:
Accuracy on various areas of Ballscrew has to measure items:
- Radial run-out of the circumference of the screw shaft supported portion in respect to the B-B' line.
- Perpendicularity of the screw shaft supported portion end face to the B-B' line.
- Radial run-out of the nut circumference in respect to the A-A' line.
- Perpendicularity of the ange mounting surface to the A-A' line.
- Parallelism between the nut circumference to the A-A' line.
- Overall radial run-out to the A-A' line.
Preload and rigidity
Nomenclature of PMI Ballscrew◎ Nomenclature of External Circulation Ballscrew
◎ Nomenclature of Internal Circulation Ballscrew
◎ Special code
- CE type reflow method (suitable for high lead)
- WE type reflow method (suitable for high lead)
- EE type reflow method (suitable for high lead)
- QSelf-lubricating
- >BWith retainer
- TNut self-transforming
- DE type reflow method + self-lubricating type
- FE type reflow method + retainer included
- GE type return flow + self-lubricating + retainer included
- HHigh load ball screw
Mounting Method
Production Limit Length of Screw ShaftProduction limit length of precision ground Ballscrew:
When screw shaft O.D. is 4 mm, Limit length of Ballscrew is 150 mm.
When screw shaft O.D. is 120 mm, Limit length of Ballscrew is 10000 mm.
Note: Please contact with our sales people in case a special type is required.
Production limit length of rolled Ballscrew:
When screw shaft O.D. is 8 mm, Limit length of Ballscrew is 1000 mm.
When screw shaft O.D. is 80 mm, Limit length of Ballscrew is 6000 mm.
Note: Please contact with our sales people in case a special type is required.
Mounting Method
The permissible axial load and permissible rotational speed vary with the screw-shaft mounting method used, so the mounting method should be determined in accordance with the operating conditions.
Permissible Axial Load
(1)Buckling load
The Ballscrew to be used should not buckle under the maximum compressive load applied in its axial direction. The buckling load can be calculated by using equation.
- α ： Safety factor (α=0.5)
- E ： Young's modulus (E = 2.1 X 104kgf / mm2)
- I ： Minimum geometrical moment of inertia of the screw shaft cross section (I = πdr4 / 64 mm4)
- dr： Screw shaft thread minor diameter (mm)
- L ： Distance between mounting positions (mm)
-
m．N：Coe cient depending on the mounting method
supported-supported m = 5.1 (N=1)
fixed-supported m = 10.2 (N=2)
fixed- xed m = 20.3 (N=4)
fixed-free m = 1.3 (N=1/4)
(2)Permissible tensile-compressive load of the screw shaft
Where the axial load is exerted on the Ballscrew, the screw shaft to be used should be determined in consideration of the permissible tensile-compressive load that can exert yielding stress on the screw shaft：
- Permissible tensile-compressive load of yield stress of screw shaft ：
P = e． A = e．π．dr2 / 4
Here:
- e： Permissible tensile-compressive stress (147MPa)
- A： Cross section area of root diameter of scrrew shaft (mm2)
- dr：Screw-shaft thread minor diameter (mm)
- Permissible Load of contact point of ball groove
The maximal axial load must be less then the basic static rate load of the ball screw shaft.
Permissible Rotational Speed
(1)Critical rotation speed
When the rotation speed of driving motor coincides with the natural frequency of feed system (mainly the ballscrew), the resonance of vibration shall be triggered. This rotation speed is then called critical rotation speed. It shall make bad quality machining, since there is wave shape surface on the workpiece. It may also cause damage of machine. Hence it is very important to prevent the resonance of vibration from happening. We choose 80% of critical rotation speed as allowable speed. It is shown as formula :
It may be required to have additional supports in between the ends bearing supports to make the natural frequency of Ballscrew to be higher and hence to raise the allowable rotation speed.
(2)dm,n Value of Ballscrew
dm is the BCD (ball circle diameter) of screw shaft, and n is the maximum rotation speed. The dm.n value relates and a ects the noise, temperature raise, working life, balls circulation of the ballscrew.
In general cases, the dm.n value is limited as follows：
Precision Ground : dm,n ≧ 70000
Transformation level : dm,n ≦ 50000
However, with the improvement of manufacturing technology, the dm,n value is no longer subject to this restriction. There are even ball screws worth more than 100,000 yuan.
If you need a large dm,n value, please contact our company's sales personnel.
These dm.n values are for reference only.
In fact, the dm.n value shall be decided by the ways of end supporting and the distance between them.
Notes on Screw Shaft
1、Through end thread
For the Ballscrews with internal ball circulation Ballnut, it is required to have at least one end with complete thread to the end of Ballscrew for Ballnut assembly to screw shaft. If it is impossible for through end thread, it is required to have at least one end with complete thread and the journal area is with diameter to be 0.2mm smaller than the diameter of thread root area.
2、Machine design for the area of Ballnt and ends area Ballscrew
It is very important to check if there is enough space for assembly of Ballscrew onto the machine during machine design. In some cases, there is not enough space for assembly and the Ballnut has to be disassembled from the screw shaft for easier work. It may cause problems, such as the balls falling out from Ballnut, worse accuracy of squareness and roundout of Ballnut, change of preload and damage to external ball circulating tubes. In some more serious cases, the ballscrew may be damaged and not to be used. Please contact with our people if said above disassembling is required.
3、Not effective hardended area
The threads on screw shaft are hardened by induction hardening. It shall cause about 15mm at both ends of thread area are not hard enough. It is required to pay attention during machine design for the e ective thread length of travel.
4、Extra support unit for long ballscrew
For a long ballscrew, the bending due to self weight might happen. It may cause radial direction load to ballscrew. The radial direction vibration during rotation might also be more serious. To prevent these problems from happening, it may be required to have extra supports for ballscrew in between the existing supports at both ends. There are two types of supports; one is movable to move along the Ballnut. The other one is xed type; it is located in a xed position. The Table must be designed not to hit with this support during moving.
-
-
Q&A
