DOUBLE ACTION LIFTING JACK

1.ESTABLISHING THE LOADS THAT STRESS THE ELEMENTS OF THE JACK

Figure 1.1

2. MAIN SCREW CALCULUS2.1 Choosing the material

It is choosen OL 50 STAS 500/2

2.2 Design calculus

· Load calculation , N for double action lifting jack

1

1

· Inner diameter of the thread , mm

=60….80

MPa for lifting wheights Q > 20000 N

· Choosing the standard thread It is choosen trapezoidal thread Tr 28x5 SR ISO 2904, with the main

dimmensions as shown in Fig 2.1 and Table 2.1

Figure 2.1

Table 2.1NominalDiameter

Pitch Medium Diameter

Exterior Diameter

Interior Diameter

30 6 27.00 31.00 23.00 24.00

2.3 Checking the self-locking condition

·The threads pitching angle

· Apparent friction angle

for steel

· Self-locking condition

2.4 Checking at composed stresses

2

2

· The torsion moment that acts on the screw

· Effective compression tension

· Effective torsion tension

· Equivalent tension

σac – see p. 2.2(design calculus) [3]

2.5 Buckling checking

· Slendering coefficient

Figure 2.2

3

3

· Buckling domain

λ < λ0 – plastic bucklingλ0 = 89 – for OL 50 · The safety coefficient for buckling

5.25

σf =335-0.62λ for OL 50

c = 8.2 > ca = 3….5

3. SECONDARY SCREW CALCULUS

3.1. Choosing the material

· It is choosen OL50 STAS 500/2-80

3.2. Calculus of the number of turns of the main screw nut  (located inside the secondary screw)

· Number of turns

Figure 3.1

4

4

It is chosen z = 7

d, D1, D4 (see pt. 2.2)

pa = 7…13 MPa admissible crushing pressure of the lubricant film between the turns

· Length of the nut

3.3.Choosing the exterior thread· Adopting the preliminary internal diameter of the thread

· Choosing the standardized threadIt is chosen trapezoidal standardized thread Tr 52x8 mm SR ISO 2904

with main dimmensions presented in Figure 3.2 and Table 3.1

Figure 3.2

5

5

Table 3.1 Nominal Diameter

Pitch Medium Diameter

Exterior Diameter

Interior Diameter

60 9 55.5 61 50 51

3.4.Checking the self-locking condition

· The threads pithcing angle ,degrees

· Apparent friction angle

· Self-locking condition

3.5. Checking at composed stresses

· The torsion moment that acts on the screw

· Effective compression tension

· Effective torsion tension

6

6

· Equivalent tension

σac= 60….80[MPa] (see pt. 2.2) [3]

4. FIXED NUT CALCULUS

4.1.Choosing the material

It is chosen OL50 STAS 500/2

4.2. Calculus of the number of turns

· Number of turns, z

Figure 4.1

pa = 7….13 MPa for steel/steel [3]6 ≤ z ≤ 10 integer

It is chosen z=9· Lenght of the nut

4.3.Checking the nut

7

7

4.3.1. Bending and shearing checking

· Steel nut (bending)

Figure 4.2

· Steel nut (shearing)

4.4.Choosing the nut dimensions

· Exterior diameter of the body

8

8

Figure 4.3

· Exterior diameter of the neck

· Height of the neck

4.5.Checking the nut at composed stresses

· Effective traction tension

· Effective torsion tension

· Equivalent tension

9

9

4.6.Checking the neck

· Crushing check

· Shearring check

4.7.Choosing and checking the stud nut that secures the nut in the jacks body

· Choosing the stud nut

Figure 4.4

It is chosen stud nut M6x25mm, with notch, cylindrical pin, represented in figure 4.6

10

10

Figure 4.5

· The friction moment on the surface of the neck Mg,[N*m]

µ= 0.15……0.2 for steel/steel

· The moment in the pin

So the checking of the pin is not necessary

5. CALCULUS OF THE BODY

·Choosing the dimensions of the body

Figure 5.1

11

11

· Checking the body at compression

· Checking the underlying surface at crushing

6. CUP CALCULUS

6.1. Double action lifting jack cup

· Choosing the pin which consolidates the cup to the main screw

d=32 – nominal diameter of the main screw

It is chosen cylindrical pin A 6 X 30 STAS 1599/OLC 45

Figure 6.1

12

12

· Verificarea stiftului la forfecare si la strivire ,in MPa

Figure 6.1

.Checking the reduced section of the screw head to composed stresses ,MPa

13

13

7. EFFICIENCY CALCULUS

7.1. Efficiency of the double acion lifting jack

d2I – see pt. 2.2(d2I=d2)β2I, φI’ – see pt. 2.3(β2I= β2 ; φI’= φI)d2II – see pt. 3.3(d2II= d2)β2II, φII’ - see pt. 3.4(β2II= β2 ; φII’= φ’)

14

14

8. THE METHODOLOGY OF DESINGNING A HORIZONTAL RATCHET MECHANISM

8.1.Mechanism sketch

Figure 8.1

15

15

8.2 The handle length calculus8.2.1 Total bending moment

8.2.2 The acting force ofone worker,

[3]

It is chosen Fm=300[N]

8.1.1. The calculus length of the handle,

n = 1 – no. of workersk = 1 – unsimultaneousness coef. of the workers action

8.2.3Length of the hanlde,

L0 = 50 mm for n=1- the additional length for hand-grabbing the handle

8.3Lengthener calculus8.3.1 Lengthener length

l = 50….80 mm – guidance length of the lengthener

8.3.2 Lengthener diameter

.Diametrul exterior al prelungitorului ,mm

Se alege ţeavă comercială 20x3/OLT 45 STAS 530/1

16

16

Verificarea prelungitorului la solicitarea de incovoiere ,MPa

8.4 Ratchet wheel calculus

8.4.1 Choosing the material

It is chosen OL50 STAS 500/28.4.2 Choosing the dimensions

· Wheel dimensions

Figure 8.2

8.4.3 Checking the ratchet wheel under stresses

· Checking the cog at bending

17

17

· Checking the cog at shearing

· Checking the contact surface of the cog at crushing

· Checking the assembly on polygonal contour at crushing

Figure 8.3

n = 6 – for assembly on polygonal contour

8.5 Ratchet calculus

18

18

Dimensiunile de amplasare aclichetului ,in mm

8.5.1 Choosing the dimensions

Figure 8.4

h=4.2 mm

___Verificarea clichetului la incovoiere

.Tensiunea de incovoiere

19

19

8.5.3. Checking the ratchet at excentric compression

· Total tension

8.6 Main handle calculus

8.6.1 Choosing the material

It is chosen OL 50 STAS 500/2

8.2.1. Alegerea dimensiunilor

A 12 X 40 STAS 5754/2/OL50

8.2.2. Verificarea bolţului la solicitări

· Verificarea bolţului la forfecare

Fig.8.5.

20

20

· Verificarea bolţului la strivire

· Verificarea bolţului la încovoiere

9 TECHNICAL SECURITY WORK RULES

21

21

The main work safety rules are:

- Jack repair if its failure will be made only by special people

- Jack is not inserted at random load, but only in places specially designed to load

- To prevent accidents, if the load is lifted after the intervention under high load, will always ensure load

- For a better functioning of the jack is recommended lubricationperiodic coupling of the jack screws

- Not running anointing of jack screws and couplings in use, ie while jack is required to a certain

- Will not lift a load greater than indicated in calculations

- To lift the load it will not use the ratchet drive mechanism provided in the calculations only lengtheners

- Use of any other type of extension can lead to forces that can lead to the breaking of the mechanism, and so to car accidents

10 SUPPORTING STATEMENT REGARDING THE CHOICE OF THE MATERIALS, THE BLANKS AND COSTRUCTIVE SOLUTIONS FOR THE MAIN PARTS OF THE JACK(NUTS, BOLTS)

22

22

For proper functioning of the jack the screws need to be not only resistant but also rigid. On that basis it will be chosen to manufacture screws from ordinary materials (OL), as follows: the main screw is recommended OL 37, for secondary nut and screw fixation is recommended OL 50. For the screw and nut need to be used trapezoidal thread fixed to increase the rigidity of the mechanism. Yet when to prevent wear to the cup assembly it can be chosen a heat treated or thermochemical steel. The manufacturing of the ratchet mechanism operated horizontally can also use ordinary materials, low alloy steels for general engineering STAS 500 / 2.  In the making it will be used commercilal tubes for extension. When running the drive spring mechanism will be used hot rolled and heat treated spring steel and for the blank springs is used carbon steel wire STAS 89

11 WRITTEN EVIDENCE ON THE CHOICE OF MATERIALS,

HALF-FINSHEDED AND CONSTRUCTIVE SOLUTIONS ON

THE MAIN PICES IN THE MECHANISMS CONSTRUCTION

The jack is a mechanism used for lifting different tasks, especially for auto repairs and interventions, which is composed from a screw-nut mechanism.

Considering that the lifting task is statically applied, for the

screw-nut mechanism, we choose trapezoidal thread, which although

has a lower rated capacity then the squared one, it has a better stiffness

and at the same time ensures a good alignment of the nut on the screw.

Also this type of thread allows the transmission of the task in both

directions, and has the advantage that can be executed by milling with

high productivity.

23

23

In choosing the materials we kept in mind that the operation is done manually, and the jack has a relatively small time of operating, but also in the fact that the screw-nut mechanism is the most requested component of the jack. For this reasons was chosen, for manufacturing the screw-nut mechanism, and the majority component parts, laminated steel OL50 STAS 500/2 – 80. OL50 steel allows a proper processing by cutting and it is not longer necessary to develop heat treatments to improve its mechanical properties. OL50 laminated plate, of which the levers were executed, has an increased resistance to buckling due to the grains orientation in the same direction – after the levers axis – after lamination. For the foot-plate of the jack, was chosen cast steel OT50 STAS 600 – 80, because it not longer requires further processing by cutting. For the arch of the acting mechanism, was chosen arch steel mark OLC55A, steel that gives the arch average properties.

In choosing the materials we had in mind, also the cost of the chosen materials, aiming to obtain high quality products, at a lower cost of production.

12 TEHNICAL SECURITY STANDARDS OF WORK

One nut lifting jack is included in the lifting mechanisms, of which

cause must be provided a series of instructions and measures to

prevent and avoid accidents at work.

Like any lifting mechanism, the lifting jack should ensure the self-braking condition, meaning that when the jack operating stops, it will not fall bellow the action of the lifting task. The self-braking condition is ensured by de screw-nut mechanism.

The users of this lifting mechanism will be trained on how to work correctly. It is recommended:

- The jack will be used only for manual acting;

- It will not be used for loads grater then 8200N. For this

reason we will mark, at a visible place, the maximum lifting

load;

24

24

- The lifting load should not allow horizontal movement, to

avoid the inverting of the jack. Also is forbidden to lift the

loads anchored on the ground, for not overloading the jack;

- The jack it will not be put directly on the ground, because it’s

resistance is unknown. In this way under the jack will be

inserted a plate, from a material sufficiently strong that will

not allow the sliding of the jack in horizontal plane;

- Checking the technical proper functioning of the jack before

using it;

- There will not be unattended loads left on the jack;

- The jack storage it will be made such that sub-assemblies

deformations will be avoided, in dry places such that the

crew-nut mechanism, oxidations will be not favored, which

will aggravate operating the jack for the appearance of

additional friction forces;

It will regularly be checked:- The bolts to be provided with elastic rings, for safety;- The levers are not deformed;

- The cup to be fixed well in the support;

- The screw-nut mechanism, not presenting advanced wear and it will be permanently greased to reduce friction forces and immature wear;- Check that no cracks exists on different parts of the jack;

25

25

13. REFRENCES1. ALEXANDRU, P. s.a. Mecanisme, vol. II. Universitatea din Brasov,

1984.

2. DRAGHICI, I. s.a. Indrumar de proiectare in constructia de masini, vol.

I. Bucuresti, Editura Tehnica, 1981.

3. DRAGHICI, I. s.a. Organe de masini. Culegere de probleme. Bucuresti,

Editura Didactica si Pedagogica, 1980.

4. GAFITANU, M. s.a. Organe de masini, vol. I. Bucuresti, Editura

Tehnica, 1981

5. JULA, A. s.a. Organe de masini, Indrumar pentru proiectul de an nr. 1,

Universitatea din Brasov, 1986.

6. JULA, A. s.a. Organe de masini, vol. I. Universitatea din Brasov, 1986

7. MOLDOVEAN, GH. s.a. Calculul si proiectarea formei arborilor

drepti. Brasov, Editura Lux Libris, 1998

8. Culegere de norme si extrase din standarde pentru proiectarea

elementelor componente ale masinilor, vol. I si II. Universitatea din

Brasov, 1984

26

26