Power Jacks E Series Instruction Manual
MAINTENANCE MANUAL
E-Series
Machine Screw Jack
MM-SJ-EMS-EN-01b
Operation & Maintenance Instructions with Parts List
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Contents
E-SERIES
MACHINE SCREW JACKS
SPARES LIST & MANUAL
MM-SJEMS-EN-01b
1. Introduction .......................................................................................................................................................... 4
2. Product Code ........................................................................................................................................................ 8
3. Standard Performance......................................................................................................................................... 9
4. Installation.......................................................................................................................................................... 10
5. Operation ............................................................................................................................................................ 15
6. Maintenance ....................................................................................................................................................... 21
7. Recommended Lubricants................................................................................................................................. 26
8. Spare Parts......................................................................................................................................................... 27
9. Storage & Warehousing ..................................................................................................................................... 28
10. Disposal of Units ................................................................................................................................................ 29
11. Warranty ............................................................................................................................................................. 30
12. General Assembly & Parts List.......................................................................................................................... 31
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1
1.1 TranslatingCongurations
Introduction
Stop Nut
Secondary
Guide
Anti-Rotation
Key Adaptor*
Drive Shaft Gearbox
Motor Adaptor
Rod End
Clevis End
Top Plate
Bellows Boot
Rotary Limit
Switch Adaptor
Rotary Limit Switch
Brake
Hand Wheel
Protection Cap
Encoder
Fork End
Electric Motor with or without:
•Brake
•Encoder
•Forced Ventilation
Lead Screw Options:
1. Standard 1 x Pitch
2. 2 x Pitch
3. Anti-Rotation (Keyed)
4. Stainless Steel
5. Left Hand Thread
Coupling
Limit Switches
Trunnion Feet
Trunnion
1
2
3
4
5
* For use with Anti-Backlash and some safety nut models only.
Upright Inverted
Available as:
1. Standard
2. Anti-Backlah
3. Anti-Rotation (Keyed)
4. Safety Nut
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1
Introduction
1.2 RotatingCongurations
Drive Shaft
Gearbox
Motor Adaptor
Double Hub
Nut
Safety Nut
Safty Nut
Double Hub
Bellows Boot
Rotary Limit
Switch Adaptor
Rotary Limit Switch
Brake
Hand Wheel
Protection Cap
Encoder
Standard
Nut
Electric Motor with or without:
•Brake
•Encoder
•Forced Ventilation
Lead Screw Options:
1. Standard 1 x Pitch
2. 2 x Pitch
3. No Pilot End
4. Stainless Steel
5. Left Hand Thread
6. Larger Diameter Screw
Coupling
Trunnion Feet
Trunnion
1
2
3
4
5
6
Upright Inverted
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1Introduction
1.3 Introduction
E-Series screw jacks are exclusively designed for carrying out linear motion movements in accordance with the
specication detailed in Power Jacks product information and this maintenance manual.
Any other application other than specied or one going beyond the above mentioned capacity is unauthorised. The
manufacturer is not liable for damages resulting from such applications. The user alone has to bear the risk.
Since the screw jacks can be applied in various areas, the user is responsible for the specic application of use.
The E-Series machine screw jacks have been designed to comply with Machinery Directive 2006/42/EC and with
the relevant essential health and safety requirements as applies to the equipment itself. Where tted, Electric
Motors conform with Low Voltage Directive 2006/95/EC and EMC Directive 2004/108/EC.
1.4 Safety Instructions in The Operating Manual
This symbol indicates potential dangers to people.
Comply with the instructions in order to avoid injury.
This symbol indicates potential dangers to the unit.
Comply with the instructions in order to avoid damage to the unit.
This symbol indicates special information on:
• The best possible use of the unit
• How to facilitate operation of the unit
1.5 Residual Risk and Hazards
1.5.1 Should a risk of damage to material or injury to persons remain despite the structural safety of
the E-Series screw jack(s), the user must draw attention to such hazards by means of suitable
warning notices and written instructions indicating safety precautions.
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1.6 Operating Personnel
1.6.1 The E-Series screw jacks are designed according to state-of-the-art technology and are in line
with applicable safety regulations. However, the general risks of personal injury or damage to
property connected with the use of such machinery cannot be completely eliminated. Therefore
the units may only be assembled and operated by competent and qualied personnel and only
be used for the authorised application.
1.6.2 Therefore a careful study of this operating manual should be made before attempting to use or
service the unit and particular attention should be paid to the safety instructions.
1.6.3 Work to be performed on electrical parts, such as:
• Installation of limit switches
• Mounting of the drive
• Check of the direction of rotation
should only be carried out by qualied electricians.
1.6.4 The E-Series screw jacks and the installation should be inspected by the operating and
supervising personnel for externally visible damage and defects at least once every shift. Any
changes (including the operational conditions) which may affect the safety are to be reported
immediately.
Introduction 1
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Third Space Numerals (d)
The characters appearing in this space are to indicate
stroke in millimetres on all standard units, but not on
specials. This space on special
actuators helps to identify to our Engineering Depart-
ment the actual Screw Jack model produced. The
numerals do not indicate stroke or type of modication
performed on special orders.
Sufx (e)
B - Indicates bellows boot required to protect lift-
ing screw.
G - Secondary guide for the lifting screw.
L - Single-end worm shaft extension on left-hand
side only.
R - Single-end worm shaft extension on right-
hand side only.
1 - Gear ratio option-2 required.
X - Supplied without bottom pipe, but with guide
bushing.
Note 1. All sufxes (e) that do not conict with another
may be used in series against one Screw Jack.
Capacity and Series Designations (c)
Upright Translating Screw Jacks
E2625 E2501 E1802 E1805 E1810 E1820 E1830 E1850 E18100
5 10 25 50 100 200 300 500 1000
Inverted Translating Screw Jacks
Decrease the upright model number by 1, e.g. 1804, 50 kN inverted Screw Jack.
Rotating Screw Jacks
Increase the upright model number by 1, e.g. 1806, 50 kN rotating Screw Jack.
Anti-Backlash Screw Jacks
Replace the rst digit in the model number with a 4, e.g. 4805, 50 kN anti-backlash Screw Jack.
2.0 Example
KME1819-300-BR, 200 kN inverted keyed translating machine screw jack with top plate, 300 mm of stroke, bel-
lows boots tted to protect lifting screw and a single ended worm shaft extension on the right-hand side only.
K ME 1819 300 BR
↓↓↓↓↓
(a) (b) (c) (d) (e)
↓↓↓↓↓
Prex Basic Model Series No. Travel of Unit (mm) Sufx
Product Code
Prexes (a)
S - All Stainless Steel Screw Jack.
K - Keyed Lifting Screw
Basic Model (b)
TE - Threaded end on lifting screw (standard)
ME - Top Plate on end of lifting screw.
CE - Clevis End on lifting screw.
PE - Plain end, with no machining on end of lifting
screw.
DE - Inverted rotating screw jack.
UE - Upright rotating screw jack.
CCE - Screw Jack with double clevis mounting
arrangement.
Note
1. For E-Series Screw Jacks with plain ended lifting
screws consult Power Jacks.
2. For Stainless Steel Screw Jacks with varying mate-
rials and/or platings consult Power Jacks.
3. For external keyed guides consult Power Jacks.
2
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Model E2625 E2501 E1802 E1805 E1810 E1820 E1830 E1850 E18100
Capacity kN 5 10 25 50 100 200 300 500 1000
Lifting ScrewNOTE 1mm 16 x 3 20 x 5 30 x 6 40 x 9 55 x 12 65 x 12 95 x 16 120 x 16 160 x 20
Gear ratios
Option 1 5:1 5:1 6:1 6:1 8:1 8:1 102/3:1 102/3:1 12:1
Option 2 20:1 20:1 24:1 24:1 24:1 24:1 32:1 32:1 36:1
Turn of worm for travel
of lifting screw
Option 1 5 for 3mm 1 for 1mm 1 for 1mm 1 for
1.5mm 1 for 1.5mm 1 for 1.5mm 1 for 1.5mm 1 for 1.5mm 3 for 5mm
Option 2 20 for
3mm 4 for 1mm 4 for 1mm 4 for
1.5mm 2 for 1mm 2 for 1mm 2 for 1mm 2 for 1mm 9 for 5mm
Max. Input power (kW) Option 1 0.25 0.375 1.5 3 3.75 3.75 6 11.25 18.5
Option 2 0.12 0.19 0.375 0.55 1.125 1.125 1.9 4.5 8.25
Start up torque at full
load (Nm)NOTE 2
Option 1 2.5 6.8 19.8 56 115.9 263.8 480 904 2025
Option 2 1.1 3 8.7 25.5 60.5 137 284 504 1119
Weight (kg) - stroke = 150mm 1.03 2.27 8.17 15.88 24.72 45 86 195 553
Weight (kg) per extra 25mm 0.073 0.13 0.21 0.32 0.57 0.86 1.58 2.49 4.31
Option 1
Gear Ratio 5 5 6 6 8 8 10 2/3 10 2/3 12
Screw Jack Static
Efciency 0.189 0.233 0.201 0.213 0.206 0.181 0.149 0.132 0.131
Screw Jack
Dynamic Efciency 0.252 0.306 0.264 0.281 0.272 0.242 0.205 0.181 0.178
Option 2
Gear Ratio 20 20 24 24 24 24 32 32 36
Screw Jack Static
Efciency 0.107 0.130 0.115 0.117 0.132 0.116 0.084 0.079 0.079
Screw Jack
Dynamic Efciency 0.160 0.194 0.167 0.172 0.190 0.169 0.128 0.120 0.123
Notes:
1. All metric machine screws have a trapezoidal thread form.
2. For loads of 25% to 100% of screw jack capacity, torque requirements are approximately proportional to the load.
3. Efciency values for standard grease lubricated worm gear box and lifting screw.
4. All E-Series screw jacks have grease lubricated gearbox and lead screw as standard.
5. For performance data for Anti-Backlash, Anti-Rotation (keyed) and other variants please consult corresponding catalogue.
Standard Performance 3
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4.1 General Installation Notes
4.1.1 Before installing new parts, remove any rust preventative, protection grease etc.
4.1.2 Check before immediate installation for possible transit damage.
4.1.3 Components which have been stored for a long time (over 1 year) should be re-lubricated in
working conditions before they are put into operation.
4.1.4 Before putting the E-Series screw jack(s) into service, the User must ensure that the plant in
which it is installed complies with all applicable directives, especially those regarding health
and safety at work.
4.1.5 Handle the screw jack with care. The E-Series screw jacks should be handled with care to avoid
damaging the machined drive shafts and the threads of the lead screw.
4.1.6 Before putting the units into service, check the lubricant level. If necessary top up the lubricant
to the required level.
4.1.7 Do not mix greases of different nature or specications.
4.1.8 If the same type of grease already in use is not available, remove all of the existing lubricant
completely and ush its interior thoroughly with a light solvent before relling with a new
lubricant.
4.1.9 The structure on which the E-Series screw jack(s) are mounted must have ample strength to
carry the maximum load, and should be rigid enough to prevent undue deection or distortion of
the screw jack supporting members.
4.1.10 It is essential that the E-Series screw jack(s) be carefully aligned during installation so that
the lead screw is running true and the connecting shafts are exactly in line with the input drive
shafts.
4.1.11 When installing several screw jacks to move a common load/item/structure, the jacks should
rst be connected to the structure (refer 4.4). The load should be equally distributed between
the screw jacks. The screw jack input drive shafts should then be connected taking care not to
turn the input shaft and lose the screw jack position relative to the structure.
4.1.12 After the E-Series screw jack(s) is installed, shafting, gearboxes, motors, etc., are coupled
together it should be possible to turn the main drive by hand (no load on screw jacks). If there
are no signs of binding or misalignment, the screw jack system is then ready for normal
operation.
4.1.13 After the E-Series screw jack(s) are installed, they should be operated through their full travel
four or ve times under minimum load conditions. If the arrangement operates satisfactorily
and there are no signs of binding or misalignment the E-Series screw jack(s) are ready for
normal operation. Refer to section 5 for typical operating performance checks.
Installation4
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4
Installation
4.2 GeneralInstructionsforttingdetachableendsonleadscrews
In most circumstances the screw jack is delivered with the required end tting assembled to the unit.
4.2.1 It is important that the detachable ends are securely xed to the lead screws and the following
procedure should be adhered to.
4.2.2 Thread the detachable end on to the lead screw and tighten up as hard as possible without
damaging the components.
4.2.3 Select a twist drill which is a free t in the tapped holes of the detachable end. Using these holes
as a drill guide, drill dimple only into the lead screw. Clean out swarf and remove detachable
end. Select another drill which matches the set screw diameter and, using the drill dimples as
a guide, drill into the lead screw a full diameter depth of 1mm below the root diameter of the
threads. Ret detachable end.
4.2.4 Fit the knurled point set screws (supplied with detachable ends) rmly in place ensuring that
point of set screws make contact with bottom of drill dimples. Secure the set screws with
chemical thread locking compound (e.g. Loctite).
4.2.5 If screw jacks with keyed lead screws are involved, and it is required to
line up the clevis ats or top plate holes, etc., in a xed relationship
to the worm shaft centre line, it will be necessary to face the underside
of the detachable end to obtain the required relationship. This operation
should be done carefully as only a few hundredths of a mm (thousands
of an inch) removed from the attachment is equivalent to a fair amount
of rotational movement. After the correct relationship has been obtained
with the attachment rmly tightened up, proceed to install the screw jack
in accordance with this manual.
1mm deep
drill dimples
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Installation4
4.3 Unpacking and installation
4.3.1 Remove the E-Series screw jack(s) from their container. Dispose of the packaging material and
the desiccant in an environmentally friendly way.
4.3.2 If it is necessary and in order to avoid damages, please use soft straps to transport or mount the
screw jack.
4.3.3 For translating screw jacks in order to avoid damages, do not attach the straps to the lead screw
but to the lead screw end tting, cover pipe or to the screw jacks gearbox. Where possible lift
vertically.
4.3.4 For rotating screw jacks in order to avoid damages, do not attach the straps to the lead screw
but to the nut on the lead screw or to the screw jacks gearbox. Where possible lift vertically.
4.4 Mounting
4.4.1 Before starting assembly work, check the directions of rotation of all jacks, gearboxes and drive
motors with regard to the required direction of travel of each jack in the application.
4.4.2 All components must be carefully aligned, as alignment errors increase stress and power
consumption and lead to overheating and premature wear.
4.4.3 When installing screw jacks, ensure that the mounting face is at and square to the guides of
the load, to within 0.4/1000 millimetres.
4.4.4 Before attaching the drive unit, the screw jack should be turned through its entire stroke by
hand, without load. Variations in the amount of force required and/or marks on the screw or
guides indicate alignment errors. Loosen the relevant mounting bolts and adjust positioning
until the correct alignment is achieved.
4.4.5 All mounting bolts must be re-tightened after a short period of operation.
4.4.6 Mount the screw jack by xing the screw jack body to the structure by either its standard base
mounting points or via a mounting accessory like a trunnion. The screw end or nut should be
xed to the moving part of the structure (or vice versa).
4.4.7 Verify that the structural attachment that connects to the screw jack end tting or nut is aligned
throughout the screw jack stroke before connecting to the screw jack.
4.4.8 Take care when tting couplings. A blow on a shaft end could cause gear set damage.
4.4.9 Shaft alignment is critical, check on installation
4.4.10 Bellows Boots
4.4.10.1 Push the bellows over the lead screw and attach the collars with the jubilee clips provided. Be
careful not to rip or tear the bellows boot.
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4
Installation
4.4.11 Drive Motor
4.4.11.1 Power Jacks recommend that when you purchase a screw jack requiring a motor mounted
directly to the screw jack this is purchased as a complete item from Power Jacks. The motor is
then pre-assembled to the screw jack. If you have opted to t a motor yourself below is a typical
procedure for common motor types.
4.4.11.2 Before mounting the drive motor, check the direction of rotation of the screw jack drive shafts
relative to the linear motion of its lead screw. Also check the operation of any limit switches
tted to the unit.
4.4.11.3 Place the motor into the mounting position next to the screw jack.
4.4.11.4 Connect the motor to the power source and switch on the motor. Check the direction of rotation,
in association with the safety limit switches (if necessary, change the direction of the motor
shaft rotation).
4.4.11.5 Remove the worm shaft and ange ensuring that the worm shaft seal is not damaged as this
must be reused (alternatively order spares).
4.4.11.6 Attach the motor adapter ange to the shell / body of the screw jack, using 4 set screws.
4.4.11.7 Fit the worm shaft seal.
4.4.11.8 Typically a exible coupling with elastomeric element is used to connect the two drive shafts.
4.4.11.9 Attach one hub of the coupling half to the worm shaft of the screw jack.
4.4.11.10 Push the elastomeric element (spider insert) onto the coupling hub now on the screw jack.
4.4.11.11 Mount the second coupling hub onto the drive shaft of the motor.
4.4.11.12 Attach the motor to the motor adapter ange using 4 screws. Remember to radially orientate
the motor to the correct position for your application.
4.4.12 Limit Switches – Fitted To Cover Pipe
4.4.12.1 Power Jacks recommend that when you purchase a screw jack requiring limit switches mounted
directly to the screw jack this is purchased as a complete item from Power Jacks. The limit
switches are then pre-assembled to the screw jack provided suitable to transport. However
always reset and check limit switch operation when installing the screw jack. The following
procedure is for limit switches tted to the cover pipe of the screw jack with an adjustable clamp
ring.
4.4.12.2 Detach the corresponding clamping ring on the cover pipe by loosening the mounting bolt.
4.4.12.3 Move the limit switch into the desired position.
4.4.12.4 Clamp the ring by tightening the mounting bolt.
4.4.12.5 Check the position of the limit switch by turning the screw manually and checking that the
switches triggers at the desired screw jack stroke position.
4.4.12.6 If necessary, repeat the procedure.
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Installation4
4.4.13 Limit Switches – Rotary Cam Type (RLS)
4.4.13.1 Power Jacks recommend that when you purchase a screw jack requiring a Rotary cam type
Limit Switch (RLS) mounted directly to the screw jack this is purchased as a complete item from
Power Jacks. The RLS unit is then pre-assembled to the screw jack. If you have opted to t a
RLS unit yourself below is a typical procedure for common RLS unit types. However always reset
and check limit switch operation when installing the screw jack.
4.4.13.2 Before mounting the RLS unit, check the direction of rotation of the screw jack drive shafts
relative to the linear motion of its lead screw.
4.4.13.3 Place the RLS unit into the mounting position next to the screw jack.
4.4.13.4 Remove the worm shaft end ange ensuring that the worm shaft seal is not damaged as this
must be reused (alternatively order spares).
4.4.13.5 Attach the RLS adapter ange to the shell / body of the screw jack, using 4 set screws.
4.4.13.6 Fit the worm shaft seal.
4.4.13.7 Typically a exible beam coupling is used to connect the two drive shafts.
4.4.13.8 Attach the beam coupling to the worm shaft of the screw jack.
4.4.13.9 Attach the RLS unit to the adapter ange using 4 screws. Make sure that the drive shaft of the
RLS unit fully engages in the beam coupling. Tighten the clamp screw of the beam coupling.
Remember to radially orientate the RLS unit to the correct position for your application.
4.5 Regulations
The following regulations must be complied with:
• The relevant local regulations for the prevention of accidents.
• Generally recognized safety regulations.
• National regulations.
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5
Operation
5.1 Operational Recommendations
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
5.1.6
5.1.7
Select a screw jack which has a rated capacity greater than the maximum load that may be
imposed on it.
The screw jacks should have a greater stroke than is needed in the actual installation. Should
it be necessary to operate the screw jacks at the extreme limits of travel it should be done
cautiously.
It is important that the lead screws should not be closed below the specied closed height
dimension of the screw jacks, otherwise serious damage may result to the worm gear.
Lead screw end stops are to prevent over-travel or loss of screw. These are not load supporting
and should be treated as an emergency device only and must not be allowed to come into
contact with the worm gears during normal working cycles otherwise serious damage will
result to worm gears and bearings.
The maximum worm shaft speed for these screw jacks should not exceed 500 R.P.M. for heavy
loads. Refer to Power Jacks Limited for higher worm shaft speeds for lighter loads. In general
the maximum operating speed for the worm shaft is 1800 rpm providing the gear set power
rating is not exceeded.
The lead screws should not be permitted to accumulate dust and grit on the threads. If
possible, lead screws should be returned to the closed position (retracted) when not in use.
If equipped with bellows boot the boot must not be compressed bellow its minimum height
(consult Power Jacks product literature or engineers).
5.2 Operational Features
5.2.1 How a Rotating Screw Jack Works
The rotation of the worm shaft causes the worm gear to rotate. For rotating screw jacks the lead
screw is xed to the worm gear and they rotate at the same speed. As the worm gear turns, the
friction forces on the screw thread act to turn the nut also. The greater the load on the screw
jack unit, the greater the tendency of the nut to turn. If the nut turns with the screw, it will
not raise the load. Therefore the nut needs to be xed to a structure to prevent rotation. The
restraining torque required for the structure, also known as the "lead screw key torque" can be
found in product literature or requested from Power Jacks.
5.2.2 How a Translating Screw Jack Works
The rotation of the worm shaft causes the worm gear to rotate. For translating screw jacks
the worm gear is threaded to accommodate the lead screw thread. As the worm gear turns,
the friction forces on the screw thread act to turn the screw also. The greater the load on the
screw jack unit, the greater the tendency of the screw to turn. If the screw turns with the nut
(worm gear), it will not raise the load. In those cases where a single unit is used, and where the
load cannot be restrained from turning, it is necessary to use a screw jack with an anti-rotation
mechanism (keyed screw jack). Lead screw key torque (refer to product literature or requested
from Power Jacks) must be checked as excessively heavy unguided loads could break the Anti-
rotation mechanism (key).
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5Operation
5.2.3 Anti-Backlash Screw Jack – When To Use
For reduced axial backlash of the lead screw in the screw jack select a model with the "Anti-
Backlash" mechanism. This is typically used when the load direction changes from tension to
compression and minimal axial backlash is required. This design is only available for translating
screw jacks. It can be combined with Anti-Rotation mechanism as well.
5.2.4 Input Torque Required for a Screw Jack
The input torque for a single screw jack depends on the load, the worm gear ratio, type of screw
(machine screw, ball screw or roller screw) and the pitch of the lead screw. Torque values are
listed in the individual product specication charts based on capacity loads. For loads from 25%
to 100% of screw jack model capacity, torque requirements are approximately proportional to
the load.
Note: The input torque, as well as the efciency and side load ratings, is the same for both
translating screw and rotating screw jacks.
5.2.5 Maximum Input Power & Speed for a Screw Jack
The input power to the screw jacks should not exceed the power rating shown in the
specications table. Maximum input speed in rpm (revolutions per minute) to a screw jacks
worm shaft should not exceed 1800 rpm for E-Series screw jacks.
5.2.6 Efciency of a Screw Jack
Screw Jack model efciencies are listed in the individual product specication charts.
5.2.7 Expected Life of a Screw Jack
The life expectancy of a screw jacks lead screw, bearings, nut and worm gear set varies
considerably due to the extent of lubrication, abrasive or chemical action, overloading, excessive
heat, improper maintenance, etc. For detailed life calculations consult Power Jacks Ltd.
5.2.8 Screw Jack with Anti-Rotation (Keyed) Mechanism
This design is only available for translating screw jacks. If the structure/object connected to
the lead screw is not prevented from rotating or the lead screw is not always in contact with the
structure then a screw jack with an "Anti-Rotation" mechanism (keyed) should be used.
5.2.9 Standard Screw Jacks How To Prevent The Load from Rotating
For multiple screw jack systems, x the lead screw end ttings (e.g. top plate or clevis) to the
common member being lifted by all the units. For single screw jack applications, bolt the lead
screw end tting (e.g. top plate or clevis) to the load and ensure the load is guided to prevent
rotation.
A guided load is always recommended to ensure that the screw jack does not receive any side
load and so guidance can be scaled suitably for the load without altering the screw jack design
unnecessarily. Note that an external guidance system can provide a higher restraining "key"
torque than compared to an anti-rotation mechanism in a screw jack.
5.2.10 Self-Locking of Screw Jacks
Screw Jacks with 24:1 gear ratios are considered self-locking in most cases. Consult Power
Jacks for a recommendation specic to your application.
All screw jacks with double start lifting screws are considered not to be self-locking.
Screw Jacks considered not self-locking will require a brake or other holding device.
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5
Operation
5.2.11 Shock Loads on a Screw Jack
Shock loads should be eliminated or reduced to a minimum, if they cannot be avoided, the screw
jack model selected should be rated at twice the required static load.
For severe shock load applications, the load bearings can be replaced with heat-treated steel
thrust rings which is an option available from Power Jacks. Note this will increase the input
torque by approximately 100%.
5.2.12 Axial Backlash in a Screw Jack
5.2.12.1 Backlash in Standard Machine Screw Jacks
Machine screw jacks have backlash due not only to normal manufacturing tolerances, but to the
fact that there must be some clearances to prevent binding and galling when the screw jack unit
is under load. Usually, the axial backlash is not a problem unless the load on the screw jack unit
changes between compression and tension. If a problem does exist, then a unit with the anti-
backlash feature should be considered.
5.2.12.2 Screw Jacks with the Anti-Backlash Device
The anti-backlash device reduces the axial backlash between the lead screw and nut assembly
to a regulated minimum. As the backlash will increase as the lead screw thread on the gear
wears the anti-backlash device can be adjusted to remove this normal condition.
5.2.13 How the Anti-Backlash Device Works
When the screw (1) is under a compression load, the bottom of its
thread surfaces are supported by the top thread surfaces of the worm
gear (2) at point (A). The anti-backlash nut (3), being pinned to the
worm gear and oating on these pins and being adjusted downward
by the shell cap, forces its bottom thread surfaces against the upper
thread surfaces of the lifting screw at point (B). Thus, backlash
between worm gear threads is reduced to a regulated minimum.
When wear occurs in the worm gear threads and on the load carrying
surfaces of the lifting screw thread, the load carrying thickness of the
worm gear thread will be reduced. This wear will create a gap at point
(B) and provide backlash equal to the wear on the threads.
Under compression load, the lifting screw will no longer be in contact
with the lower thread surface of the anti-backlash nut. Under this
condition, backlash will be present when a tension load is applied.
The anti-backlash feature can be maintained simply by adjusting the shell cap until the desired
amount of backlash is achieved.
To avoid binding and excessive wear do not adjust lifting screw backlash to less than 0.025mm
(0.001”). This will reduce the calculated separation (C) between the anti-backlash nut and worm
gear and will reduce the backlash between the worm gear threads and the lifting screw to the
desired minimum value.
When separation (C) has been reduced to zero, wear has taken place. Replace the worm gear
(2) at this point. This feature acts as a built in safety device which can be used to provide wear
indication for critical applications.
5.2.14 Column Strength of the Screw Jack
Column strength of a screw is determined by the relationship between the screw length and its
diameter. For column strength charts consult product literature or Power Jacks.
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5.2.15
5.2.16
5.2.17
5.2.18
5.2.19
5.2.20
Side Loads on a Screw Jack
Screw jacks are designed primarily to move and position loads and any side loads (loads not
acting axially on lead screw) should be avoided. The units will withstand some side loads,
depending on the diameter of the lifting screw and the extended length of the lifting screw.
Where side loads are present, the loads should be guided and the guides, rather than the screw
jacks, should take the side loads - particularly when long raises are involved. Even a small side
load can exert great force on the housings and bearings and increase the operating torque and
reduce the life expectancy.
Allowable Duty Cycle of Screw Jack
Because of the efficiency of conventional worm gear screw jacks, the duty cycle is intermittent
at rated load. At reduced loading, the duty cycle may be increased. Higher performance screw
jacks with higher thermal efficiencies and higher duty cycles are available on request. For
detailed analysis consult Power Jacks Ltd.
Maximum Operating Temperatures For E-Series Screw Jack
Normal operation at ambient temperatures of up to 90ºC. Operations above 90ºC will require
special lubricants. For temperatures above 90ºC, the life of even special lubricants is limited.
Therefore consult Power Jacks on your application. For temperatures above 90ºC, advise Power
Jacks of full particulars of the duration of such temperatures. Power Jacks suggest that a
lubricant manufacturer be consulted for type of grease and lubrication schedule. As a general
rule, the screw jack unit should be shielded to keep ambient temperatures to 90ºC or less.
Minimum Temperature For E-Series Screw Jacks
With the standard lubricant and materials of construction, the screw jacks are suitable for use
at sustained temperatures of -20ºC. Below -20ºC, low temperature lubricant should be used
and no shock loads are present. Power Jacks application engineers must be consulted in these
instances for a recommendation. Screw Jacks with standard material of construction and
lubrication may be safely stored at temperatures as low as -55ºC.
Thermal / Heat Build-Up in a Screw Jack as it is operated
The duty cycle, the length of the screw, the magnitude of the load, and the efficiency of the
screw jack all have a direct influence on the amount of heat generated within the screw jack.
Long lifts can cause serious overheating. Higher performance screw jacks with higher thermal
efficiencies and higher duty cycles are available on request.
Screw Jacks to Pivot a Load
A screw jack can be built to pivot a load by two methods:
5.2.20.1 Double Clevis Screw Jack
The screw jack can be furnished with a clevis at both ends (commonly referred to as a double
clevis screw jack). The bottom clevis is welded to the bottom end of an extra strong cover pipe,
which is tted to the base of the screw jack. This cover pipe still performs its primary function of
encasing the lifting screw in its retracted portion.
5.2.20.2 Clevis - Trunnion Mounting
The screw jack is tted with the pivot end tting (e.g. Clevis) on the lead screw and a trunnion
mount adapter is bolted to the screw jacks base plate.
The design of the structure in which these types of screw jacks are to be used must be
constructed so that screw jack can pivot at both ends. Use only direct compression or tension
loads, thereby eliminating side load conditions
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Operation
5.2.21 Corrosion Resistant Properties
Screw Jacks can be supplied with alternative materials and/or paint specications for high
corrosive areas. These options include stainless steel, chrome plating, Electro-nickel plating,
epoxy paint, etc. Check the unit specication is suitable before installation.
5.2.22 Using Screw Jacks within a Rigid Structure or Press
Power Jacks recommend that the screw jack selected has a greater capacity than the rated
capacity of the press or of the load capacity of the structure. We also recommend that a torque
clutch or similar device be used to prevent overloading of the screw jack unit. Unless these
precautions are taken, it is possible to overload the screw jack without realising it.
5.2.23 Screw Jack Drift after Drive Motor is Switched Off
The screw jack will drift after the motor drive is switched off unless a brake of sufcient capacity
is used to prevent it. The amount of drift will depend upon the load on the screw jack and the
inertia of the rotor in the motor.
For machine screw jacks with no load, the amount of drift will depend upon the size and speed
of the motor. For example, a 1500 RPM input directly connected to a screw jack without a load
will give on average 35mm to 60mm of drift; a 1000 RPM input will give about 1/2 as much drift.
Note that the drift varies as the square of the velocity (RPM). The drift of the screw jacks screw
can be controlled by using a magnetic brake on the motor. Variations of drift will also be seen if
the motor drives the screw jack via a reduction gearbox.
5.2.24 Screw Jacks Operation where Vibration is Present
Screw Jacks will operate in areas with vibration, however the vibration may cause the lead
screw to “creep” or “inch” under load. For applications involving slight vibration, select the
higher of the worm gear ratios. If considerable vibration is present, use a motor equipped with a
magnetic brake, which will prevent the screw jack from creep and/or back-driving.
5.2.25 Use of Screw Jacks Fitted With Emergency Stop Disc
To prevent over travel of the lead screw a stop disc or nut can be tted to a screw jack that is
hand operated. It should not be used as a full power stop.
5.2.26 Use of Screw Jacks Fitted With Emergency Stop Nut
For motor driven units it is possible for the full capacity of the screw jack or even a greater force
(depending on the power of the motor) to be applied against the stop. These stops are called
"full power stop nuts". They must only be used as an emergency device and if such a condition
occurs an assessment made to discover why it happened in order to carry out preventative
action. If the full power stop nut is used at full load in an emergency it might be driven into the
unit jamming so tightly that it must be disassembled in order to free it.
It is recommended that external stops are tted where possible, however they must only be
used as a last resort (Note - limit switches are one possible solution to constrain screw jack
movement safely - consult Power Jacks for system advice). Under ideal conditions where a slip
clutch or torque limiting device is used, a stop pin or stop nut may be used - but Power Jacks
should be consulted.
5.2.27 Screw Jack System Arrangements
Perhaps the greatest single advantage of Power Jacks screw jacks is that they can be linked
together mechanically, to lift, lower, move or position in unison. Typical mechanical system
arrangements link 2, 4, 6 or 8 screw jacks together and are driven by one motor. As an
alternative screw jacks can be individually driven by electric motors and with suitable feedback
devices such as encoders be synchronised electronically by a control system.
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Operation5
5.2.28
5.2.29
5.2.30
Connecting Screw Jacks in Series
The number of screw jacks that can be connected in series is limited by input torque
requirements on the rst worm shaft in the line. For the E-Series the torque on the worm shaft
of the first screw jack should not exceed 300% of its rated full load torque (this does not
include the 200kN screw jacks which are rated at 150%).
Efciency of a Multiple Screw Jack System
In addition to individual device efciencies, the efciency of the screw jack arrangement must
be taken into consideration. The arrangement efciency allows for misalignment due to slight
deformation of the structure under load, for the losses in couplings, bearings, and for a normal
amount of misalignment in positioning the screw jacks and gearboxes. For efciency values
consult Power Jacks product literature or engineers.
Screw Jack Fitted with 3rd Party Accessories
If your screw jack is tted with a device not manufactured by Power Jacks then please consult
the provided manual for this device.
This manual suits for next models
10
Table of contents
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