Low Cost Automation Tutorial

#068 Air Cylinder Selection Basics

Category : Pneumatic Drives

January28, 2011

Selection key points on air cylinders for LCA designs are organized and shown below.

(1) Checkpoints on Air Cylinder Selections

Checkpoints		Evaluation Parameters
1	Actuation direction	Single action type, Dual action type
2	Linear motion or oscillating motion	Selection of support type (Clevis, Flange, etc.)
3	Required actuation force	Cylinder bore diameter , Applied air pressure
4	Load travel distance	Cylinder stroke (Cylinder buckling limit stroke)
5	Load travel velocity	Valve size, Plumbing size
6	Shock force at stroke ends	Cushion (Evaluation of cushion effects)
7	Operation environment temperature range (5~60°C or less?)	Gasket material
8	Surrounding environment (dusts, cutting chips & fluids)	Protective cover
9	Possibilities for corrosions	Corrosion resistant cylinders (surface coated cylinders, corrosion resistant materials

Cylinder force is determined by piston diameter and air pressure used. (See [Fig.1])

(2) Air Cylinder Force Calculation

(a) Checkpoints on Air Cylinder Selection - Dual Action Cylinders

Cylinder force is determined by piston diameter and air pressure used. (See [Fig.1])

[Fig.1] Dual Action Cylinder Construction

Effective Force of an Air Cylinder　　FA＝F・μ＝（A・P）×μ
　　　FA：Effective Force [N]
　　　F ：Theoretical Force [N]
　　　P：Applied Pressure [MPa]
　　　A：Piston Pressure Area [mm²]
　　　μ：Cylinder Force Efficiency [％]

(b)Single Action Cylinders

The value is a sum of dual action cylinder force and the internal spring force (for positive or negative pressure).

Force of Single Action Push Cylinder (See [Fig.2])
　　Force FPUSH＝π／4×（D2・P・μ）−（Spring Return Force）
　　D：Cylinder Diameter [mm]

Force of Single Action Pull Cylinder
　　Force FPULL＝π／4×（（D2--d2）・P・μ）−（Spring Return Force）
　　d: Piston Rod Diameter

(3) Efficiency of Cylinder

The force generated with compressed air would be less than the theoretical force due to internal friction force, etc. Select cylinders based on cylinder force efficiency μ=approx. 50% for applied air pressure of 0.3MPa or more.

(4) Allowable Lateral Load

If lateral loads are applied on the piston rod, gouging can occur due to increased contact pressure on cylinder head bushing and cylinder tube inner wall. For max. lateral load limit, use 1/20 of cylinder max. force (μ=100%) for calculations.

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