Annex I
(informative)
Design example of ordinary tension gas spring

I.1 Example

Design requirements of ordinary tension gas spring: using horizontally, the fully extended length is 334 mm, the working stroke is 55 mm, the force ratio α is 1.52, the minimum tension force is 147 N, and the piston rod diameter is 8 mm. See Figure I.1 for the design example of tension (stretching) gas spring.

Figure I.1 Design example of tension gas spring

I.2 Solution

I.2.1 Design of ordinary tension gas spring stroke, cylinder length and gas chamber length

I.2.1.1 Design of stroke

According to 7.3.2, the general tension gas spring safe stroke S₂ ≥ 5 mm, the gas spring safe stroke is set to 5 mm, and the design stroke S = S₁ + S₂ = 55 + 5 = 60 mm.

I.2.1.2 Design of cylinder length L

Calculate the cylinder length according to formula (15):

B = L- S – L₁ – L₂ = 334 – 20 – 60 – 20 = 234 mm

NOTE  The rod end length of the gas spring L₁ = 20 mm, and the cylinder end length of the gas spring L₂ = 20 mm.

I.2.1.3 Design of gas chamber length

Derived from formula (I3):

mm

I.2.2 Design of cylinder inner diameter D₁

According to 7.5.1 and Annex C, when the piston rod diameter d = 8 mm, the cylinder inner diameter D₁ is 16 mm.

I.2.3 Design calculation of gas spring force

L.2.3.1 Design of minimum tension force F₅

According to I.1, the minimum tension force F₅ = 147 N.

I.2.3.2 Calculation of internal pressure in gas spring

Derived from formula (7):

MPa

According to Table B.1 of Annex B, the dynamic friction force of the gas spring F_r = 20 N.

I.2.3.3 Calculation of maximum tension force F₆

Calculated by formula (8):

N

I.2.3.4 Calculation of minimum resilience force F₇

Calculated by formula (9):

N

I.2.3.5 Calculation of maximum resilience force F₈

Calculated by formula (10):

N

I.2.3.6 Calculation of nominal force a and nominal force b

Calculate according to Table 1:

N

N

I.2.4 Design of cylinder thickness and verification of cylinder strength

I.2.4.1 Calculation of cylinder thickness

The cylinder material is 20# steel tube. Calculate according to formula (21):

mm

According to 7.5.2, a cylinder thickness of δ₁ = 1 mm is selected for this gas spring.

I.2.4.2 Verification of cylinder strength

Calculate the radius ratio according to formula (F.1):

Calculated by formula (F.2):

MPa

This is less than the allowable stress 130 MPa for 20# steel tube, in line with the requirements.

I.2.5 Diagram of tension gas spring

L.2.5.1 Working diagram of tension gas spring

See Figure I.2 for the working diagram of tension (stretching) gas spring.

Unit: mm

Technical Requirements:

1. Materials: the cylinder is made of 20# steel piping, and the piston rod is 45# steel;

2. Extended length L = 334 mm ± 1.8 mm;

3.Design stroke S ≥ 60 mm;

4. Minimum tension force F₅ ≥ 147 N;

5. Manufacturing accuracy corresponds to the standard tolerance value of level IT16 in GB/T 1800.1.

Figure I.2 Working diagram of stretching gas spring

I.2.5.2 Design calculation data

The design calculation data are shown in Table I.1.

Table I.1

No.	Parameter name	Code	Numerical value	Unit	No.	Parameter name	Code	Numerical value	Unit
1	nominal force a	Fa	127	N	11	safe stroke	S2	5	mm
2	nominal force b	Fb	192.5		12	extended length	L	334
3	minimum tension force	F5	147		13	rod end length	L1	20
4	maximum tension force	F6	212		14	cylinder end length	L2	20
5	minimum resilience force	F7	107		15	gas chamber length	L3	161
6	maximum resilience force	F8	173		16	cylinder length	B	234
7	force ratio	α	1.52		17	piston rod diameter	d	8	mm
8	pressure within the gas spring	P	0.84	MPa	18	cylinder inner diameter	D1	16
9	design stroke	S	60	mm	19	cylinder outer diameter	D2	18
10	working stroke	S1	55		20	thickness of cylinder	δ1	1

Bibliography

[1] Cen JunJian. (2008). Non-standard Design Manual (Volume 1). National Defence Industry Press. 

[2] Authors panel of Gas Spring Design Calculation. (1987). Mechanical Design Manual (2nd Edition). Chemical Industry Press.

Gas spring design calculation (English version of national strandard, initiated by LeiYan Gas Springs), proposed and prepared by SAC/TC 235 (National Technical Committee 235 on Spring of Standardization Administration of China).