Flexible Drive Shaft: Designed for Complex Applications-Jiangsu Sitong Cardan Shaft Co.,Ltd
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Flexible Drive Shaft: Designed for Complex Applications

Views:29     Author:Cardan Shaft Manufacturer     Publish Time: 2012-06-11      Origin:Sitong Cardan Shaft Co.,Ltd

You need to transmit a rotary motion where no straight line is possible. Or, you need to allow for some uncontrollable misalignment. How about transmission taking place between moving components? What if you need to control something in hazardous locations where you cannot directly handle the application, such as high-temperature environments, under hazardous conditions or in clean room applications? Functionally designed flexible drive shafts can meet all these challenges. 



Design concept of flexible drive shaft


A flexible drive shaft is a very effective and cost-efficient way to transmit rotary motion, power or torque. Flexible drive shafts are made with wire spiraled tightly around a central wire. With each layer you increase the diameter of the shaft and with that the torque it can transmit. Compared to a pull cable or a wire rope, where a bundle of wires is twisted together, the flexible drive shaft is designed and made to transmit rotary power. Layers of wire spirals are wound in opposite directions to each other and will not twist open if turned (as a wire rope would do).

 

Though it sounds like a very simple element, different applications require different designs, number of layers, number of wires, diameter and so on. In flexible drive shaft design, it is important to know how much torque has to be transmitted, how small the minimum radius for the shaft has to be, what RPM is required, the environment the flexible drive shaft will work in and the preferred turning direction. Length is not critically important for the torque but plays a role in torsional deflection and has to be considered accordingly.

 

In flexible drive shaft design, unfortunately not all parameters can be stretchedin all directions. For example, if more torque is required, the minimum radius goes down and with it the flexibility of the shaft. If the minimum radius can be reduced, the torsional deflection will go up, which for remote control cable is not a good thing.Related to this basic realityof flexible drive shafts, two main design groups emerge. First there are torque transmission shafts, mainly for higher speed, continuous speed, pure torque transmission applications like speedometer cable or shafts for drilling applications. Second are the torsionstable flexible drive shafts for mechanically remote applications, with low speed and focus on low torsional deflection.

 

Direct influences on flexible drive shaft specifications are: the number of layers; the number of wires-per-layer; the diameter of the wire; the wire material (with higher or lesser carbon; different tensile strengths; different plating);and the manufacturing process (settings on the winding machines). Considering influences related to shaft manufacturing processes, it has to be understood that winding is a high-speed process where gap settings will influence the flexibility of the shaft. The winding speed and the gaps must be uniform and controlled. Gap settings are a key parameter, but not the only one. There are others, like the tension of the wire, the quality of the spooled-wire package, the temperature of the operation and so on. Experienced producers effectively control their processes and assure highest quality flexible drive shafts, which in turn assures successful application.



The basic structure of the flexible drive shaft


A complete flexible drive will usually be made up of:




A flexible drive shaft. This is the part that does the work and transmits the rotary motion.

A flexible casing. This contains the flexible drive shaft and prevents excessive twisting under load.

End connections. These are usually required to connect to the driving (e.g. motor/hand wheel) and driven (e.g. gearbox, valve) elements of the system.

 

flexible drive shaft Typical combinations are:

The shaft only - with machined shaft ends attached or a squared formed onto the end of the shaft.

The shaft and casing only - as above but with the addition of a casing to restrict shaft twisting.

A complete flexible drive as described above.

 

Benefits of flexible drive shaft:


flexible drive shafts are a preferred rotary motion transmission device because they:

 

1). Eliminate alignment problems:

flexible drive shafts have no need for the tight tolerances that solid shafts require

 

2). Provide Greater design freedom :

Limitless possibilities in positioning motor and driven components

 

3). Have Higher Efficiency:

flexible drive shafts are 85%-95% efficient. Gears, U-Joints Belts and Pulleys give much lower performance due to greater frictional losses

 

4). Allow large offsets:

Flexible couplings allow only 5 degrees of offset and U-Joints 30 degrees, but with a 40-50% decline in efficiency. flexible drive shafts permit a full 180 degree off-set while maintaining their high efficiency

 

5). Are Light weight and powerful:

flexible drive shafts have a 3 to 1 weight advantage over other design solutions while transmitting greater power loads

 

6). Have Lower Installation Cost: flexible drive shafts install in minutes without special tools or skills. Solid Shafts, Gears, Pulleys, and Universal Joints require precise alignment and skilled mechanics for their installations.

 

7). Reduce parts cost:

Bearings and housings for Solid Shafts and Gears require precise machining operations. flexible drive shafts eliminate the need for such demanding tolerances and their excessive costs.

 

8). Are Easy To Install:

Need no special installation tools.

 

9). Can Be Designed At The Latter Stages Of A Project:

Unlike other rotary motion devices that need to be designed around because of their rigidness, defined configurations, and large mass.

 

10). Are not affected by vibrations:

Vibrations do not affect flexible drive shafts performance. Versatile flexible drive shafts 



Flexible drive shafts VS Cardan shafts



flexible drive shafts are preferred over universal joints because they:

are less expensive

have fewer components

are more efficient

do not require tight mounting tolerances unlike universal joints

have constant angular velocity

require minimal maintenance

make very little noise 


Flexible drive shafts Selection




Different factors will, for the most part, determine the design of the flexible drive shaft. First, consider the torque (or power) that needs to be transmitted; then the routing (defining minimum bending radius); the speed required; the torsional deflection (angle of deflection under load); and the environment.

 

The relationship of shaft diameter to what is roughly required to transmit a certain power (kW) under a given speed required is as follows: For a 15mm flexible drive shaft, you should consider 5 kW and 2,000 RPM. The routing of the power transmission will determine the smallest radius of the system and with that the friction or the loss of the system. A given flexible drive shaft has a minimum bending radius; below the minimum indicates permanent deformation of the flexible drive shaft.

 

If a system runs under minimum bending conditions, only 30 percent of the power will be transmitted; the rest is friction loss in the system radiated by heat. This needs to be considered when choosing the diameter of the flexible drive shaft. The degree of torsional deflection in a flexible drive shaft varies proportionally with the torque as well. To keep the deflection and the load as low as possible, the flexible drive shaft should be operated at the highest possible speed. If needed, gear systems can also be added.

 

Attention must also be paid to the environment in which the flexible drive shaft will be used. Examples include extremely high or low temperatures, moisture, corrosive influences, dust, magnetic fields, vibrations, etc. Environmental factors influence the choice of the material for the core and casing and their fabrication. The usage of brass-coated wires allows a nearly corrosion-free flexible drive shaft. Other effective materials are stainless steel or plastic-covered shafts (for convertible car top folding or headlamp mechanisms on some modern cars). By knowing torque and speed required requirements and minimum bending radius, you can roughly check if a flexible drive shaft will suit your needs.

 

As previously noted, there are many other parameters in flexible drive shaft design and manufacturing that influence the specification and performance of the shaft. It is possible to have a 3.2mm speedometer shaft designed in two different ways to achieve double flexibility and therefore a smoother running shaft. This can reduce the diameter, and with that the material consumption and weight. As a professional cardan shaft manufacturer can help you optimize flexible drive shafts for the price, performance, weight, and other criteria.


Application of Flexible drive shafts in Automoti



flexible drive shafts have a growing and compelling future in the automotive industry. Ongoing competitive challenges push suppliers to develop innovative and ever-more functional and efficient solutions. As important as changes in physical performance and outer design and style, automobiles also need equal or better interior improvements in function and comfort. Seat adjustments and other features controlled from the dashboard have made big contributions to the feel-good factor for new car owners. flexible drive shafts are small, durable, and extremely effective at transmitting rotary power from a small motor (where it needs to be) to where the motion is needed. Reliable and inexpensive flexible drive shafts avoid complicated (high-cost) gears, high tolerance alignments and can make difficult design situations possible.

 

flexible drive shafts, long known as speedometer cables, are not just doing the job in seat adjustments; today they are the solution in demanding head, ventilation, lighting adjustments, sunroof, or locking systems. In power seats, each movement requires a small electric motor. These motors, sometimes 8-per-seat, cant always be placed exactly where needed. Using flexible drive shaft technology, motors are placed in the most practical place for the designer and transparent to passengers.

 

Consider also door locking systems where car designs no longer permit solid shaft connection between the keyhole and the lock. A flexible drive shaft has given designers more freedom to create attractive designs for new models. Experience and the right machinery, processes, and knowledge assure you the best flexible drive shaft solution for the next innovation in cars. Self-opening doors, sliding doors, new convertible concepts, foot pedal adjustments, and moveable back-up cameras are all projects in the pipeline for flexible drive shafts.


Installation of flexible drive shafts




1. Never bend a flexible drive shaft, or a casing with a shaft inside it, in a radius smaller than the minimum operating radiusof the particular shaft.

 

2. Do not subject the shaft or casing to unnecessary end pull or compression. Excessive tension on shaft or casing may cause permanent damage.

 

3. When the installation is made, check for correct protrusion of shaft fittings to ensure proper engagement with mating parts.

 

4. After one end of a flexible drive shaft combination has been attached at the driving or driven end, be sure the shaft rotates freely before attaching the other end. Also, make certain that end fittings are properly engaged at both ends and that the shaft is not cramped in the casing.

 

5. Keep the flexible drive shaft and inside of casing free from dirt and grit.

 

6. Securing the casing with clamps at suitable intervals is desired in all fixed applications.

 

7. Frequent lubrication of flexible drive shafts is not always necessary except with large diameter shafts. Steel flexible drive shafts should always have a thin coating of grease to prevent corrosion. 


Lubrication of flexible drive shafts



flexible drive shafts generally require periodic lubrication. The frequency of lubrication depends on the nature of the service. Where the shaft operates for long periods or is subjected to considerable flexing during operation, the lubrication should be more closely supervised.

General lubrication - the following procedure is recommended:

1. Remove the shaft from the casing. Clean both the shaft and inside the casing thoroughly by washing in a degreasing agent.

2. Drain the casing and dry the shaft.

3. Coat the entire shaft lightly with a good grade of grease. Grease as the shaft is assembled into the casing. Do not force grease into the casing with grease guns or pressure lubricators.

 

We can also supply a range of stainless steel flexible drive shafts which require when used in our new flexible drive systems, no grease. 





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