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1.3.7 Technical requirements for guide sleeves
The previous articles in this series discussed the Technical requirements for design and manufacturing of hydraulic cylinders-Barrel tube, Technical requirements for hydraulic cylinders-Piston and Piston rod. Technical requirements for Cylinder head and cylinder bottom. Today this article will explain Technical requirements for guide sleeves.
The guide sleeve is a sleeve-shaped cylinder part that guides the piston rod.
1.3.7.1 Structural Types
Guide sleeves can be manufactured as an integral unit with the cylinder head, or as separate units, i.e., cylinder head type and bushing type.
Generally, sealing grooves are designed and machined on both the inner and outer cylindrical surfaces of the guide sleeve, for (equivalent to) static sealing of the piston, dynamic sealing of the piston rod, and dust prevention (sealing) of the piston rod.
For steel guide sleeves, the inner bore must also be machined with a support ring mounting groove for guiding and supporting the piston rod.
Guide sleeves must be positioned (with locking mechanisms) and should be easy to disassemble and assemble.
See the drawings in future Chapter of this newsletter for various guide sleeve structural types.
Guide sleeves of the same model and type manufactured by the same manufacturer must be interchangeable.
1.3.7.2 Materials
Common materials for guide sleeves are as follows:
① Gray cast iron grades, such as HT150, HT200, HT250, HT300, etc.
② Malleable cast iron grades, such as KTZ650-02, KTZ700-02, etc.
③ Vermicular graphite cast iron grades, such as RuT300, RuT340, RuT380, RuT420, etc.
④ Ductile iron grades, such as QT400-15, QT400-18, QT450-10, QT500-7, etc.
⑤ Carbon steel, cast carbon steel, etc.
⑥ Others, such as bimetallic, (die)cast aluminum, cast copper, plastics (non-metallic materials), and wear-resistant cast iron (HT-1, HT-2, HT3, QT-1, QT-2, KT-1, KT-2), etc.
Note: The wear-resistant cast iron grades are referenced from pages 8-14 of Volume 2 of 《Modern Mechanical Design Handbook》, published by Chemical Industry Press.
During the hydraulic cylinder pressure test, it must be ensured that the guide sleeve does not undergo permanent deformation, including crushing. Under rated static pressure, no failure mode of the pressure chamber specified in international standard 《Test Methods for Rated Fatigue Pressure and Rated Static Pressure of Pressure Cavities of Hydraulic Components》 must occur.
Steel cannot be used for guide sleeves with a guide sleeve inner diameter fit to the piston rod outer diameter of H8/f7, H8/h7, H8/f8, or H9/f9.
1.3.7.3 Heat Treatment
Internal stress should be eliminated by heat treatment or other stress-reducing methods.
Steel guide sleeves should generally be quenched and tempered (QT); cast iron can be surface quenching hardened.
1.3.7.4 Geometric Dimensions and Tolerances
During design, the guide sleeve inner diameter is generally determined as the datum element.
(1) Basic Dimensions
The basic dimensions of the guide sleeve include the (nominal) inner diameter, the matching inner diameter, the outer diameter, the (guide or support) length, and the sealing, guiding, and positioning (locking) dimensions.
(2) Guide Sleeve Inner Diameter
① The recommended values shown in Table 1-33 should be preferentially selected for the (nominal) inner diameter of the guide sleeve.
Table 1-33 Recommended Inner Diameter of Guide Sleeve (Nominal) mm
For non-steel guide sleeves, the inner diameter can be selected according to Table 1-33.
② The tolerance of the guide sleeve inner diameter should not be lower than H9 specified in international standard; generally, H8 is selected.
③ The inner diameter of the guide sleeve. For guide sleeves with guide rings (bands) or support rings installed in the inner hole, generally only the guide ring (band) or support ring contacts the outer diameter d surface of the piston rod, while the inner diameter surface of the guide sleeve does not contact the outer diameter d surface of the piston rod.
Assembly clearance g [defined in international standard as the (single-sided radial) clearance between mating parts in a sealing device] can generally be selected according to Table 1-34; during design, it can also be selected according to the technical requirements in the product catalog of the selected sealing components.
During design, the inner diameter of the guide sleeve is calculated using the following formula: Inner diameter of guide sleeve = d + 2g, and a tolerance value is given between H7 and H10.
(3) Outer diameter of guide sleeve
① Generally, the outer diameter of the guide sleeve is machined with sealing grooves on the cylindrical surface and matches the inner diameter of the cylinder body (barrel). Therefore, the outer diameter of the guide sleeve is selected according to the inner diameter of the cylinder (tube).
Table 1-34 Reference values for the assembly clearance between the guide sleeve and the piston rod mm
② The outer diameter tolerance of the guide sleeve shall be selected from f7; however, for some special-purpose hydraulic cylinders or hydraulic cylinders with special requirements, the fit between the guide sleeve and the cylinder body (barrel) can be selected between H7/k6 or H8/k7～H8/g7.
(4) Guide Sleeve (Guide or Support) Length
The guide sleeve length generally refers to the guiding length or support length of the guide sleeve. The following factors should be considered when determining the guide sleeve length:
① Operating conditions of the hydraulic cylinder.
② Hydraulic cylinder installation method.
③ Basic parameters of the hydraulic cylinder.
④ Design margins for the strength, stiffness, and lifespan of the hydraulic cylinder.
⑤ Longitudinal bending strength and stability of the piston rod under pressure.
Generally, the guiding length or support length B of the guide sleeve should be ＞ 0.7d.
(5) Geometric Tolerances
① The roundness tolerance of the guide sleeve inner bore shall be no less than grade 7 as specified in international standard.
② The cylindricity tolerance of the cylinder head inner bore shall be no less than grade 8 as specified in international standard.
③ The cylindricity of the mating part between the guide sleeve and the cylinder block (tube) shall be no less than grade 8 as specified in international standard.
④ The coaxiality tolerance of the outer surface of the guide sleeve [the mating part with the cylinder block (tube)] to the axis of the guide sleeve inner bore (equivalent to the guide sleeve part) shall be no less than grade 7 as specified in international standard.
⑤ The perpendicularity tolerance of the end face of the guide sleeve (inside the rod cavity) to the axis of the inner bore shall be no less than grade 7 as specified in international standard.
1.3.7.5 Surface Quality
(1) Inner Hole Surface
① The surface roughness value of the inner hole should not be greater than Ra1.6μm, and Ra0.8μm is generally selected. Alternatively, it can be selected from Table 1-35 according to the design requirements.
② The inner surface of the hole should be smooth and free from visible defects such as shrinkage cavities, inclusions (slag), white spots, ripples, scratches, dents, cracks, scars, peeling, and rust.
Table 1-35 Surface roughness of internal holes (μm)
(2) End Face
The surface roughness of the end face of the guide sleeve installed in the rod cavity should not exceed Ra 1.6 μm; however, the surface roughness of the end face selected as the inspection datum should generally not exceed Ra 0.8 μm.
(3) Outer Surface
The outer surface should be free from visually visible defects such as shrinkage cavities, inclusions (slag), folds, ripples, cracks, scratches, dents, and draw marks caused by built-up edges from the outer mold during cold drawing.
Sharp edges on the guide sleeve, except for the sealing groove edges, should be removed if not shown in the working drawing; especially the chamfers at all locations with lubrication grooves.
The outer surface of the cylinder head should be rust-proofed, or a plating or passivation layer may be used.
★★★Review of previous selected articles
- Classification and Structure of Hydraulic Cylinders
- Hydraulic Cylinder Parameters and Parameter Calculation
- Hydraulic Cylinder Parameter Calculation Example
- Technical requirements for design and manufacturing of hydraulic cylinders-Barrel tube
- Technical requirements for Piston and Piston rod
- Technical requirements for Cylinder head and cylinder bottom
- Several Design Methods for Flow Regeneration Using Differential Circuits
- Design, calculation and processing points of hydraulic cylinders: recommended collection
- Piston rod that is too smooth or too rough will affect the sealing life of the hydraulic cylinder
- Master the core technical requirements of hydraulic cylinders parts