Designing Power Screw

 

Designing Power Screw

A power screw is a tool that is mainly intended to convert turning locomotion into linear motion. They are used in distinct machines, big jacks, vises, and presses. Its operation involves usage of the powertrain in connection with a nut, depending on the position of the ball (mobile or static. This fundamental construction principle that entails two parts possesses various advantages like smoothness, a self-locking ability, capability to carry a heavy load, reduced components, no specialization machine needed for its manufacture and cut expenses in maintenance. The tool produces increased friction between the contacts with screw mate, a phenomenon that is special when compared to bearings or rolling surfaces. This attests to power screws reduced the degree of efficiency (ranging between 25-75%). This minimized degree inhibits them from being applied in power transmission systems. The article analyzes the report of modeling a power screw and its significance.

Higher friction in power screws results in wearing out of threads easily triggering nut replacement. The corrosion can be minimized by switching the geometry profile if the thread. This confirms the reason behind the classification of power screws by using threads. The primary threads are buttress, V, and the acme profiles. They are entirely obtained from the profile threads of the screws, with a square-shaped threadlike. It is the essential profile since it possesses the lowest friction. However, they are complicated machines because they are applied with screws transmitting high power. The profile angle of acme standing at 30 degrees Celsius enhances its manufacturing but adjusts its friction an effect emerging from the edge of the profile. Contrastingly, buttress angle stands at 3% enabling their efficiency as square threads and simple to produce. However, it can only be applied where the force of the load points to a specific direction.

Thirdly, due to increased friction of V-threads, they are not convenient for power screws. They have threads modeled to trigger friction to prevent the loosening of a fastener in cases where the screws observe a particular design that aims at reducing resistance, thus improving efficiency.

Power screw

σB =151.33 MPa

σy = -33.2 MPa

The stress of von Mises on threads

σ’=172.6 MPa

AISI 1050

Stress yield= 350 Mpa

n= 2.03

 

 

 

Design Bushing

These are sleeve bearings that glide over level rods and offer reduced frictional motion which lowers power consumption, minimizes wear and noise. Bushings take the shape of flat metals. However, they are merely sophisticated components.

Manufacture of bushing involves the application of bronze powder. The material is combined to enable the microscopic pores are created in the metal. The contents are then smeared with oil volume of about twenty percent. Consequently, as the shaft slides past the bushing, the oil is generated to the bushing surface through an action of the capillary to enhance the fixed deposit of a thin lubricating oil upon the shaft. This means that the bushings of bronze materials are self-lubricating.

The keyless bushing is the most efficient bushing method since it does not depend on torque transmission, but applies the whole shaft circumference for its operation with slight recoiling. It distributes the hydraulic pressure evenly upon the full-length link and minimizes micro-motion that can result in fretting. Since they can alleviate milled keyways that exist in shafts, reduced shafts can be applied in relaying the similar torque amount, thus saving material and space. Figures 1 and two below shows bushing procedures.

 

Over other ball bearing methods, self-lubrication is one of the merits of using a bushing. It also has reduced expenses. The bushings cost ranges between 6-10 lesser in charge as compared to ball bearings of linear characteristics. Thirdly, they have minimized noise, unlike other ball bearings. The bushings are flexible since they can be used both in non and hardened shafts, while linear bearings can be applied solely to the hardened shafts at higher costs. Lastly, bushings also draw low maintenance costs as compared to the upper elongated bearings.

Nonetheless, bushings also have shortcomings. Firstly, they possess a problem called “stick and slip’. Bronze bushing must overcome constant friction before their move. Particularly in instances where linear progression is not appropriately aligned, thus the jerky kind of motion. Relatively cheaper bushings can influence significantly on broad tolerances making it a worse fit on level rods.

2.0 FEA

When undertaking FEA, the procedure of time becomes a function of material size.A thread element size is defined by the distance between the distinct threads. However, geometry may necessitate the use of several elements so express a thread. Subsequently, the functionality of time must be slightly reduced to adjust the smaller items for precise modeling of stress waves and vibration features. Nonetheless, minimized times comes with some demerits like necessitating more iterations during the analysis period. For instance, decrease in an element five times its value will result in time reduction too for the operation. Thus, meaning it will require a similar degree of time to undertake analysis because each time signifies a single strain computation. The figures below illustrate different types of FEA thread analysis.

2.1. FEA for a single thread (Figure 1)

2.1 The bushing threads FEA (Figure 2a&b)

The von Mises variations after the first and the second load had a maximum value of 1.717e+002 and a yield of 3.500e+002. However, it decreased from 7.266e+001 to 1.498e+001.Whereas the friction coefficient varied at 0.002 to 0.001. After the tightening of the power screw, there was an adjustment upon the stresses at the transition zones of the upper edges of the screw. The stresses demonstrated a level distribution at the screw circumference bore and minimized with an adjustment of the coefficient of friction averagely from at 7.266MPa (μ =0.002) to 1.498 (μ =0.001). The stresses were quantitatively shown at the upper regions too, 1.717 (μ =0.002) to 1.575 (μ =0.002).

 

In figure 2 b

The von Mises variations after the first and the second load had a maximum value of 1.757e+002 and a yield of 3.250e+002. However, it decreased from 8.232e+001 to 1.539e+001, whereas the friction coefficient varied at 0.002 to 0.001. After the tightening of the power screw, there were variations at transition points in the upper zones of the screw. The stresses highlighted a smooth distribution at the screw circumference bore and minimized the adjustments of the coefficient of friction averaging between 8.232MPa (μ =0.001) to 1.539 (μ =0.001). The stresses were quantitatively shown at the upper regions too, 1.465 (μ =0.002) to 1.319 (μ =0.002).

 

 

 

3. Determining handle length of Power screw

The length of the screw handle is given by:

TR=77765.5 N*mm

F=667 N Max

Where L=116.5

 

4. Frame with varied sections (Figures 3 & 4 Flange calculations)

 

 

 

 

 

 

 

 

 

 

 

 

 

Section C

The frame applied excel values to determine the stress and the equation given by n=2.

 

FEA Frame (Figure 5)

 

 

Result evaluation

For an examination to be undertaken regarding the behavior of the power screw during the loading and the tightening procedure, the extent of shaft force generated was examined from the first and second procedure of loading. Comparison of the model analysis with different coefficients required the examination of von Mises at the abutment selected regions. Areas demonstrating high stresses after external loading (abutment areas) and tightening (at the screw interface) were selected for further examination. The strains were determined at regions along its inner edge after load procedure, and it measured 1.130e+004 at maximum with a yield strength of 2.611e+004. The area is crucial for tight linkage between the screw and its abutment.

The von Mises after the first and the second load-reduced from9.418 to 7.979 while the friction coefficient decreasing from 0.005 to 0.002. After the tightening of the power screw, increased stresses were determined at the transition zones of the upper edges of the screw. The weights portrayed a level distribution at the screw circumference bore and minimized with an adjustment of the coefficient of friction averagely from at 9.418 MPa (μ =0.002) to 7.979 (μ =0.005). The stresses were quantitatively shown at the upper regions too, 1.130 (μ =0.004) to 1.036 (μ =0.004).

 

In conclusion, the design of power is evaluated, the design process is highlighted, the power screw components like nut, bar, and screw are designed to reaffirm strength. Calculations are undertaken to provide the mathematical procedures of the friction coefficient and the load capacity. Subsequently, the lengths of the handle, FEA of the single and bushing thread are critically analyzed and their operations established. The jackscrew is then described using figures and their components on the design model.