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工程学是一种对技术的执行及合规监控：这是一项难以实现的结果。一个经过认证的 ISO9001 模型会被分成几个阶段：从认证、对每项单一组件所用材料的控制开始，到分析表面处理（涂料），乃至制造子组件的逆转工程，以达到产品和子组件的质量标准，并创建出一个整合数据库。
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工程学
液压缸（也被称为：线性 液压马达) 是一种通过单向性冲程，用于提供一种单向力的机械促动器件。它应用广泛，尤其是用在建筑设备及工程车辆、生产机械和土木工程方面。
Buckling without side loading
Special problems to do with stability occur when cylinders with long stroke lengths are used. For the purpose of calculation these cases are divided into areas:
- Non elastic buckling loads (Tetmajer’s calculation) and n
- Elastic or Hook’s buckling loads (its critical limiting load is determined
by Euler’s equation) n
In hydraulic cylinder Euler’s calculation is basically the calculation used, as the piston rod may
usually be considered to be a slender strut (negligible diameter).
Buckling load and operation load are then calculated as follows:
- Buckling load K= ………In N (1) i.e. the rod buckles under this load
- Max. operating load F = K/S In N (2)
- Sk = free buckling length in mm
- E = modulus of elasticity (2.1 x 10 * for steel ) in N/mm
- J = moment of inertia for circular cross-section in mm* …..
- S = safety factor (3.5)
The length to be used as the free buckling length may be determined from the Euler loading cases (see table 4). In order to simplify the calculation the stiffening due to the
cylinder tube is ignored. This provides the required safety margin in standard cylinders, the installation position of which is usually not known, in order to cater for any superimposed bending loads.
Table 4: Euler’s loading cases
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Euler’s loading case |
Case 1 One end free, one end rigidly connected. |
Case 2 (Basis case) Two ends pivoted. |
Case 3 One end pivoted, one end rigidly connected. |
Case 4 Two ends rigidly connected. |
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Illustration |
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Free buckling length |
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Installation position
for cylinder |
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Hydraulic force - area formulas and calculator
The force produced by a double acting hydraulic piston on the rod side can be expressed as
F1 = (π (d22 - d12) / 4) P1 (1)
where
F1 = rod pull force (lb, N)
d1 = rod diameter (in, m)
d2 = piston diameter (in, m)
P1 = pressure in the cylinder (rod side) (lff/in2 (psi), N/m2 (Pa))
The force produced opposite the rod can be expressed as
F2 = (π d22 / 4) P2 (2)
where
F2 = rod push force (lb, N)
P2 = pressure in the cylinder (opposite rod) (lff/in2 (psi), N/m2 (Pa))
Push Diagram
Rod pushing force for hydraulic cylinders are indicated below:
- 1 psi (lb/in2) = 144 psf (lbf/ft2) = 6,894.8 Pa (N/m2) = 6.895x10-3 N/mm2 = 6.895x10-2 bar
- 1 N/m2 = 1 Pa = 1.4504x10-4 lb/in2 = 1x10-5 bar = 4.03x10-3 in water = 0.336x10-3 ft water = 0.1024 mm water = 0.295x10-3 in mercury = 7.55x10-3 mm mercury = 0.1024 kg/m2 = 0.993x10-5 atm
- 1 lbf (Pound force) = 4.44822 N = 0.4536 kp
- 1 N (Newton) = 0.1020 kp = 7.233 pdl = 7.233/32.174 lbf = 0.2248 lbf = 1 (kg m)/s2 = 105 dyne = 1/9.80665 kgf
- 1 in (inch) = 25.4 mm
- 1 m (meter) = 39.37 in = 100 cm = 1000 mm
Pull Diagram
Rod pulling force for hydraulic cylinders are indicated below:
Piston Rod Size Selection
The selection of a piston rod for thrust (push) conditions requires the following steps to be carried out:
1. Determine the type of cylinder mounting style and rod end connection to be used. Consult the Stroke Factor table and determine which factor corresponds to the application.
2. Using this stroke factor, determine basic length from the equation:
Basic Length = Net Stroke x Stroke Factor
( The Piston Rod Selection Chart, below, is prepared for standard rod extensions beyond the face of the gland retainer. For rod extensions greater than standard’ add the increase to the stroke to arrive at the basic length’)
3. Find the load imposed for the thrust application by multiplying the full bore area fo the cylinder by the system pressure, or by referring to the Push and Pull Force charts.
4. Using the Piston Rod Selection Chart below, look along the values of ‘ basic length ’ and ‘ thrust ‘ as found in 2. and 3. above, and note the point of intersection.
The correct piston rod size is read from the diagonally curved line labeled ‘Rod Diameter‘ above the point of intersection.
Long Stroke and Stop Tubes
When considering the use of long stroke cylinders, the piston rod should be of sufficient diameter to provide the necessary column strength.
For tensile(pull)loads, the rod size is selected by specifying standard cylinders with standard rod diameters and using them at or below the rated pressure.
For long stroke cylinders under compressive loads, the use of stop tubes should be considered, to reduce bearing stress. Selection of a stop tube is described.
CALCULATION OF CYLINDER DIAMETER
Given that the load and operating pressure of the system are known, and that a piston rod size has been estimated taking account of whether the rod is in tension(pull) or compression (push), then the cylinder bore can be selected.
If the piston rod is in compression, use the ‘Push Force’ table below.
- Identify the operating pressure closest to that required;
- In the same column, identify the force required to move the load (always rounding up);
- In the same row, lock along to the cylinder bore required.
If the cylinder envelope dimensions are too large for your application increase the operating pressure, if possible, and repeat the exercise.
If the piston rod is in tension, use the ‘Deduction for Pull Force’ table. The procedure is the same but, due to the reduced piston surface area resulting from the piston rod, the force available on the ‘pull’ stroke will be smaller, To determine the pull force.
If this force is not large enough, go through the process again but increase the system operating pressure or cylinder diameter if possible. If in doubt, Our design engineers will be pleased to assist.
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