Hydraulic cylinder body (cylinder barrel and honed tube)

01

Choose steel grade, size, tolerance and straightness

Datong Hydraulic lists honed tubes for hydraulic cylinders in E355, ST52, CK45, 4140, SCM440, 16Mn, 42CrMo, SAE1518, SAE4145, stainless 304/316 and duplex 2205, in delivery conditions BK, BK+S, GBK and NBK, with ID 20–1,500 mm and lengths up to 16 m. It gives inside tolerance H7, H8 or H9, outside tolerance to DIN 2391, EN 10305, GB/T 1619 or GOST standards, straightness of 0.5/1000 or better and roughness Ra 0.2–0.4 µm, with anti-rust oil inside and out and plastic end caps. It states that it makes honed tubes from seamless cold-drawn tube. [1]

Editorial calculation: at 0.5/1000 straightness a 3 m honed barrel may deviate up to 1.5 mm from straight; at the 0.2/1000 Datong gives for skived and roller-burnished tube, up to 0.6 mm. Check the allowed deviation against the cylinder's stroke, guide length and side load. [1]

Mannesmann Precision Tubes, a German seamless tube maker, describes its cylinder barrel (HP) tubes as seamless precision tubes machined inside to a specified ISO tolerance, with definable mechanical properties; the bore processes it names are skiving and roller burnishing, and honing. It lists outside diameters of 35–170 mm and walls of 5–28.5 mm, supplied in production lengths of 4–7 m (one order item varying by no more than 2 m), fixed lengths within ±500 mm, or cut to length with narrow tolerances by agreement; other finishing such as cutting, weld bevels, cross holes, grooves and threads is offered. [3]

Editorial calculation: a 6 m stroke cylinder needs a barrel of about 6.3 m or more with end allowances, which fits inside Mannesmann's 4–7 m production lengths only if the order specifies a fixed or cut length; Datong's lengths up to 16 m cover longer strokes. [3] [1]

Editorial note: give the supplier the working and test pressure and the wall thickness from your cylinder design, so the grade, delivery condition and wall can be checked; ask whether the grade is weldable if ports and mountings are to be welded.

Give the supplier the bore and outside diameter, wall thickness, length and quantity, steel grade and delivery condition, working and test pressure, bore tolerance class, roughness and straightness, finishing process (honed or skived and roller-burnished), welding of ports or mounts, end machining, mill certificates, inspection report, and packing and rust protection.

02

Choose honed or skived and roller-burnished bores

US patent 4,339,857 (Integrated cylinder finishing system) explains that hydraulic and pneumatic cylinders are formed by drawing steel over a mandrel, which can embed particles and copy mandrel imperfections into the bore, so the bore must be finished. Honing is the method the patent describes as usual practice but removes only small amounts of material; a combined skiving and roller-burnishing tool finishes the bore in one pass. [2]

The patent argues that a roller-burnished bore is too smooth for the applications it has in mind: the slight cross-hatch left by honing lets oil reach the cylinder walls, and without it the seals can wear prematurely; it adds that burnishing compresses the material and can cause laminations. Its system skives the bore and then hones it on one machine so the bore keeps a slight cross-hatch. [2]

Datong lists honed tubes at Ra 0.2–0.4 µm and skived and roller-burnished tubes under Ra 0.2 µm, both to DIN 2391 H8 in its stated tolerances. [1] Editorial note: ask the seal supplier for its recommended bore roughness range and specify the finishing process with it.

03

Match the tube to the right part of EN 10305

EN 10305 sets technical delivery conditions for cold drawn steel precision tubes, which it describes as having "precisely defined tolerances on dimensions and a specified maximum surface roughness". Part 1 covers seamless cold drawn tubes with outside diameter D ≤ 380 mm, Part 2 welded cold drawn tubes with D ≤ 150 mm, and Part 4 seamless cold drawn tubes "used in hydraulic and pneumatic power systems". All three NS-EN editions were published on 1 June 2016. [4]

Datong quotes outside tolerance to DIN 2391, EN 10305, GB/T 1619 or GOST standards [1], and Mannesmann supplies its cylinder barrel tubes as seamless precision tubes in 35–170 mm OD [3]. Ask which part of EN 10305 the tube is supplied to: Part 4 is written for hydraulic and pneumatic power systems, while Parts 1 and 2 are written for "precision applications", and Part 2 covers welded tube only up to 150 mm.

EN 10305-4 states that "the allowed pressure rates and upper temperatures are the responsibility of the customer", using the safety coefficients of the applicable regulations, codes or standards [4]. The tube standard does not give the cylinder its pressure rating; give the supplier the working and test pressure and check the wall against your cylinder design code. For low-temperature service, ask for impact test results, which Part 4 gives at 0 °C.

Editorial calculation: Mannesmann's largest listed OD, 170 mm, is within the Part 1 limit of 380 mm but above the Part 2 limit of 150 mm, so a 170 mm barrel would have to be seamless to fall under EN 10305. [3] [4]

Values are from the Standard Norge catalogue pages for NS-EN 10305-1, -2 and -4:2016; the tolerance tables were not reviewed.

04

Honed, SRB and plain cold-drawn tube on supplier lists

The suppliers reviewed list honed tubes, skived and roller-burnished tubes and cylinder barrels with chrome-plated rods; ask each for grade and mill certificates, bore tolerance and roughness reports, straightness, wall tolerance, and cut-to-length or machined supply.

05

Wall, bore, outside surface, straightness and protection on a barrel

06

Barrel size, wall, roughness and grade to put on the drawing

Bore roughness and straightness are the rows the seals and the stroke depend on; wall and grade can only be checked once the working pressure is stated.

07

Send the size, pressure and finish data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Size: [ID; OD; wall; length]
Pressure: [working; test]
Material: [grade; delivery condition]
Bore: [tolerance; Ra; process]
Straightness: [limit per metre]
Welding: [ports; mounts]
Documents: [mill certificate; inspection]
Packing: [oil; caps; bundles or cases]

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