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8/12/2019 Pages From Festo_hydraulics

1/19

1 Festo Didactic GmbH & Co. KG TP

13. Hydraulic cylinders

The hydraulic cylinder converts hydraulic energy into mechanical energy. t generates linear movements. For this reason! it is also re"erred to as a #linear motor$.

There are t%o basic ty es o" hydraulic cylinder single'acting and double'acting cylinders.

(ectional vie%s o" these t%o basic ty es are sho%n in the diagrams belo%.

) * + , - /

1 0ounting scre%2 1entscre%

3 Piston rod4 Cylinder

barrel

5 Piston rodbearing Pistonrod seal/ 2i er

(ingle acting cylinder

) *

- , +

1 Piston2 Piston rod3 Piston rod bearing4 3nnular iston sur"ace- Piston sur"ace

Double acting cylinder


2/19

)+. Hydraulic cylinders

)+.)(ingle'actingcylinder

n single'acting cylinders! only the iston side is su lied %ith hydraulic "luid.

Conse4uently! the cylinder is only able to carry out %or5 in one direction. These cylinders o erate according to the "ollo%ing rinci le6

The hydraulic "luid "lo%s into the &iston area. 7%ing to the counter "orce 8%eight9load:! &ressure builds u& at the &iston. 7nce this counter "orce hasbeen overcome! the &iston travels into the "or%ard end &osition.

During the return stro5e! the &iston area is connected to the reservoir via theline and the directional control valve %hilst the &ressure line is closed o"" by the

directional control valve. The return stro5e is e""ected either by intrinsic load! bya s&ring or by the %eight load. n the &rocess! these "orces 8load "orces:overcome the "rictional "orces in the cylinder and in the lines and valves anddis&lace the hydraulic "luid into the return line.

m

3 3

P T P T

P T P T

Ts Ts

0 0

(ingle acting cylinder ; hydraulic ram


3/19

Possible a lications

hori?ontal mounting6 "or single'acting cylinders %ith s&ring'return.

n large hydraulic resses! the return stro5e is brought about by ullbac5 cylinders.

(cissor li"ting table


4/19

)+.*Double'actingcylinder

n the case o" double'acting cylinders! both iston sur"aces can be ressuri?ed. There"ore! it is ossible to er"orm a %or5ing movement in both directions. Thesecylinders o erate according to the "ollo%ing rinci le6

The hydraulic "luid "lo%s into the iston area and ressurises the iston sur"ace. nternal and e=ternal resistances cause the ressure to rise. 3s laid do%n in the

la% F @ 3! a "orce F is roduced "rom the ressure and the iston sur"acearea 3. Conse4uently! the resistances can be overcome and the iston rode=tends. This is ossible o%ing to the conversion o" hydraulic energy intomechanical energy %hich is made available to a consuming device.

Double acting cylinder

t should be borne in mind that %hen the iston e=tends the oil on the iston rod side must be dis laced via the lines into the reservoir. During the return stro5e! thehydraulic "luid "lo%s into the 8annular: iston rod area. The iston retracts and the oil 4uantity is dis laced "rom the iston area by the iston.


5/19

3 A 3 A

P T P T

P T P T

Ts Ts

0 0

Double'acting cylinder

n double acting cylinders %ith a single'sided iston rod! di""erent "orces 8F@ 3:and s eeds are roduced "or the same "lo% rate on e=tension and retractiono%ing to the di""ering sur"aces 8 iston sur"ace and annular iston sur"ace:.

The return s&eed is higher since! although the "lo% rate is identical! thee""ective sur"ace is smaller than "or the advance stro5e. The "ollo%ing e4uationo" continuity a&&lies6

v =B

3


6/19

The "ollo%ing designs o" double'acting cylinders e=ist "ul"illing varying re4uirements6

Designation Description Symbol

Differential cylinder

3rea ratio *6)8 iston sur"ace6annular iston sur"ace:

iston return stro5e t%iceas "ast as advance stro5e.

* : )

Synchronous cylinder

Pressurised areao" e4ual si?e.

3dvance andreturn s eedsidentical.

3 ) @ 3*

Cylinder withend-positioncushioning

To moderate thes eed in the case o"large masses and

revent a hard im act.

Telescopic cylinder

onger stro5es

Pressure intensifier

ncreases ressure

Tandem cylinder

2hen large "orces are re4uired and only smallcylinder dimensionsare ossible.

Cylinder ty es


7/19

The movements generated by hydraulic cylinders are used "or6 0achine tools

; Feed movements "or tools and %or5 ieces ; Clam ing devices ; Cutting movements on laning machines> shoc5'testing machines

and broaching machines

; 0ovements on resses ; 0ovements on rinting and in ection moulding machines! etc.

Handling devices and hoists ; Tilting! li"ting and s%ivel movements on ti ers! "or5'li"t truc5s! etc.

0obile e4ui ment ; * m9min! s ecial cushioning or bra5ing rocedures are re4uired.

2hen the &iston returns to the retracted end &osition! the normal discharge o"the hydraulic "luid "rom the &iston area is interru&ted by the cushioning &istonand "lo% is reduced "rom a certain &oint until it is "inally closed. The hydraulic"luid in the &iston area must then "lo% a%ay via a restrictor 8see diagram:.

n this %ay! the iston s eed is reduced and there is no danger o" mal"unctions resulting "rom high s eeds. 2hen the cylinder e=tends! the oil "lo%s unhindered viathe non'return valve! the throttle oint being by' assed. To achieve end ositioncushioning! the ressure relie" valve 8"lo% division: must be used.


8/19

Festo Didactic GmbH & Co. KG TP*

Flo% control scre%on'return

valve

Cushioning

3 A 3 A

P T P T

P T P T

Ts Ts

M

Double'acting cylinder %ith end osition cushioning

n addition to this sim le ty e o" end osition cushioning! there is also double

cushioning "or "or%ard and retracted end ositions. 2ith this ty e o" cushioning! ahard im act is avoided both on advancing and on retracting.

)+.,(eals

The "unction o" seals is to revent lea5age losses in hydraulic com onents.(ince ressure losses also occur as a result o" lea5age losses! seals are o" considerable im ortance "or the e""iciency o" a hydraulic system.

n general! static seals are inserted bet%een stationary arts and dynamicseals bet%een movable arts.

(tatic seals6 ; 7'rings "or the cylinder housing ; Flat seals "or the oil reservoir cover

Dynamicseals6

; Piston and iston rod seals ; Eotary sha"t seals on turning devices


9/19

The recommended ma=imum iston s eed is a ro=. .* m9s. and is de endenton the o erating conditions as %ell as the sealing material and ty e o" seal. 2heree=tremely lo% s eeds and9or a minimal brea5'a%ay "orce are re4uired! s ecial

sealing materials! systems and modi"ied cylinder sur"aces must be used.The seals ictured o osite are used on cylinders according to re4uirements 8 ressure! tem erature! velocity! diameter! oil! %ater:6

Cylinder seals


10/19

Festo Didactic GmbH & Co. KG TP10

)+.-Ty&es o"mounting

Cylinders are mounted in various %ays according to usage. (ome ty es o"mounting are sho%n in the diagram.

Ty es o" mounting

Foot mounting

Flange mounting

(%ivel design

(%ivel mounting %ith trunnion

)+.1enting

3 hydraulic cylinder must be vented to achieve olt'"ree travel o" a cylinder iston!i.e. the air carried along in the lines must be removed. 3s tra&&ed air al%aysgathers at the highest &oint o" a system o" lines! a vent scre% or automatic

venting valve must be &ositioned at this &oint.

Hydraulic cylinders are su lied %ith vent scre%s at both end ositions. These ortscan also be used "or connecting ressure gauges.


11/19

)+./Characteristics

The cylinder is selected to suit the load F. The re4uired ressure is selectedin accordance %ith the a lication.

F @ 3

This can be used "or calculating the iston diameter. The hydraulic! mechanical e""iciency Thm must be considered here. This e""iciency is de endent on the roughness o" the cylinder barrel! the iston rod and the ty e o" sealing system. The e""iciency im roves %ith increases in ressure. t lies bet%een . - and .I-. Thus!the iston diameter is derived "rom6

F = & 3 hm

3 =d

= F

,

d =,F

hm

hm

The volumetric e""iciency Tv ta5es into consideration the lea5age losses at theiston seal. 2here the seal is intact! Tv @ ). and is not! there"ore! ta5en into

consideration.

Cylinder diameter! iston rod diameter and nominal ressures are standardised in D *,++, and D (7 ++* 9++**. n addition! a re"erred ratio @ iston area

3 TPto annular iston area 3 TPE is laid do%n.

Internal diameter of the cylinder

)* ) * *- +* , - +

) )*- ) * ** *- * +* + ,

Piston rod diameter

) )* ), ) ) * ** *- * +* + , ,- - + / I

) )) ))*

), ) ) * ** *- * +* +

ominal pressures

J*- J , J +J ) J) J * J*- J +)- J, J - J + J

The values %hich are underlined are recommended values. The recommendedrange o" iston stro5es is laid do%n in D (7 ,+I+ and "or iston rod threads inD (7 ,+I-.

*

T


12/19

n the table belo%! the area 3T

P a ro riate to the cylinder diameterd T and theT

annular iston area 3 TPE 8not the iston rod area 3 TPT

: "or the &iston rod diameter d TT

are assigned to the area ratio.

(T T (T T

3 K @ 3 KE

KE

@P 3 (T

Table for the area ratio

ominal

!alue

d TPT *- +* , - + ) )*-

* T"

TPcm TT ,.I) . , )*. )I. * .+ +).* - .+ / .- )*+

#$%& d )* ), ) ** *- * + ,- -

* T"

TPE cm TT +./ .- ) . )-. *+., *-. , .) *.* I .)

"ctual !alue ).+ ).*, ).*- ).*, ).*) ).*- ).*- ).* ).*-

#$' d ), ) ** * +* + ,- - /

* T"

TPE cm TT +.+/ -.- .// )+.- * .* *) +,., -, ,.*

"ctual !alue )., )., ).,, ).,- ).+I ).,I )., ).,- ).,

#$( d ) * *- +* + , - +

* T"

TPE cm TT *.I ,.I /. )). ) .* ) . + . ,/./ /*.,

"ctual !alue ). I ). , ). , ). I ).-- ). ). , ). ). I

% d(T

) ** * + , ,- - / I

* T"

TPE cm TT *.+ ,.*, .,) I., )-./ )-.+ *-. , . -I.)

"ctual !alue *. ).I ).I *. ). *. , ).I ).I *.

%$& d * *- +* , ,- - + )

*T

"TPE cm TT ).// +.)+ ,.-* /. / )*.+ )).- )I.) * ., ,,.*

"ctual !alue *./ *.-/ *./ *./ *.+ *./ *. , *./ *./

& d ; ; ; ,- -- - / I ))

* T"

TPE cm TT ; ; ; +./+ ,.-, .-, )). ),.I */./

"ctual !alue ; ; ; -.* .* ,.// ,.*/ -.* ,.,+

This table gives the area ratios u to a iston diameter o" )*- mm. The com lete

table is included in D ++* .

3

3


13/19

)+.Auc5ling resistance

Auc5ling resistance as de"ined by


14/19

Cylinders are designed "or tensile and ressure "orces only. (hearing "orces mustbe absorbed by guides.

ote6The ty&e o" mounting and installation determines the


15/19

)+.I(electing a cylinder


16/19

Auc5ling resistance diagram


17/19

The sa"ety "actor is already included in the buc5ling resistance diagram.

Calculate the re4uired iston diameter d TP.

3vailable system ressure6 ) bar minus line loss6 - bar

ressure loss in the directional control valve6 + bar bar

ressure "rom the return movement6 %hen @ *6) @*

+ bar

Thus! the "ollo%ing ressure "orce remains at the cylinder

* T) ')) @ ),I bar @ ),I G9cm T

F = & 3 P hm F , cm

*

3 P =

=

=

hm

*

),I .I- = * .+ cm

3dP

P

,

dP = , 3 P

=

, * .+ cm *=

+ cm* = . cm = mm

Chosen iston diameter d TP @ + mm.

The iston rod diameter d T(T @ ,- mm is read "rom the table "or the area ratio @*6). 3 ma=imum stro5e length o" ),, mm is read "rom the buc5ling resistancediagram "or , 5 and a iston rod diameter d T(T @ ,- mm. " an area ratio o" *6) isnot re4uired "or the ob! a smaller d T(T can be selected.

Calculating the advance stro5e s eed

v6 t @ - sec(tro5e @ - mm

@s

@.- m

@ .) m9s @ m9mint - s

T

v

+


18/19

Festo Didactic GmbH & Co. KG TP*)

Ee4uired um delivery B TP6

3 TK* T

@ +).* cm T* T

@ .+)* dm T

1 @ m9min @ dm9min

= =.+)*

dm*B 3 v

dm= =)H./ dm

+ 9min )H./ l9min

Kmin

Calculating the return s eed v TE6

= B 3 PE v

v =B

3 PE

T


19/19

3 T is read "rom the table "or the area ratio @ *6)%here d

T @ ,- mm6

3 PE

= =)-.+ cm * .)-+ dm *

v = ) ./ dm= =

)** dm9min )*.* m9min.)-+ dm * min

2hen selecting a cylinder! it should be borne in mind that end osition cushioning isnecessary "or a iston s eed o" m9min u %ards.

Conditional on the area ratio @ *6)! the return s eed o" the iston is t%ice that o" the advance stro5e. This also means that the outlet "lo% o" the cylinder is t%icethat o" the advance stro5e. For this reason! you are advised to calculate the s eedo" the return "lo% be"ore a system is si?ed and! %here necessary! to select a larger cross' section "or the return line. The control valve should also be suitable "or the increased return "lo%! i" not! then an additional valve must be installed "or the e=haust.

+

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