INSTRUCTION MANUAL
PRIMA MULTI 190
PRIMA MULTI 190
VERSION 01-01
1 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
TABLE OF CONTENTS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
IMPORTANT SAFETY RECOMMENDATIONS ...................................................................................... page 3
TECHNICAL FEATURES ........................................................................................................................ page 5
CONTROL OF CURRENT PEAKS ......................................................................................................... page 6
GAS CONNECTION ............................................................................................................................... page 6
LOADING OF WIRE COILS .................................................................................................................... page 6
REVERSE POLARITY………………………………………………………………………………………….page 6
OPERATION DESCRIPTION.................................................................................................................. page 7
ARC LENGTH ADJUSTMENT ................................................................................................................ page 7
INDUCTANCE ADJUSTMENT ................................................................................................................ page 7
ADJUSTMENT AND DISPLAY................................................................................................................ page 8
PROGRAMS MULTIFUNCTION WELDING PRIMAMULTI 190 ............................................................. page 9
PACKING……………………………………………………………………………………………………….page 10
UNPACKING……………………………………………………………………………………………… ....... page 10
STORAGE………………………………………………………………………………………………… ....... page 10
LIFTING AND HANDLING………………………………………………………………………………… .... page 10
CONNECTION-INSTALLATION-WARNINGS-CHECKS……………………………………………… ..... page 11
START UP…………………………………………………………………………………… ......................... page 11
LIMIT OF USE………………………………………………………………………………. ......................... page 12
ENVIRONMENT…………………………………………………………………………….. ........................ page 12
STARTING THE MACHINE………………………………………………………………… ........................ page 12
MAINTENANCE……………………………………………………………………………… ....................... page 12
SCHEDULED MAINTENANCE…………………………………………………………….. ....................... page 12
EXTRAORDINARY MAINTENANCE……………………………………………………… ........................ page 13
FIRE…………………………………………………………………………………………… ....................... page 13
DISASSEMBLY – DISPOSAL………………………………………………………………. ....................... page 13
ALARMS AND SIGNALS……………………………………………………………………. ....................... page 14
ELECTRIC DIAGRAM………………………………………………………………………. ........................ page 15
VERSION 01-01
2 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
IMPORTANT SAFETY RECOMMENDATIONS
BEFORE USING THIS GENERATOR, CAREFULLY READ THE CONTENTS OF THIS MANUAL. THIS
MANUAL MUST BE KEPT IN A SAFE PLACE, WHICH MUST BE KNOWN AND ACCESSIBLE TO ALL USERS
FOR THE ENTIRE LIFE AND OPERATION OF THE MACHINE.
THIS GENERATOR MUST ONLY BE USED FOR WELDING OPERATIONS.
1. DECLARATION OF CONFORMITY
The machine described in this manual must be used professionally in an industrial environment. This machine is
built in compliance with the EN 50199 standard (electromagnetic compatibility) and EN 60974-1 standard.
In case of malfunction, contact a qualified technician.
1.1 WEEE DIRECTIVE
The symbol on the packaging of the product indicates that it cannot be disposed of as normal domestic waste.
The machine must be sent to special collection facilities and/or operators specialised in the disposal of
electric/electronic waste. The correct disposal of the machine’s parts and components will help prevent potential
negative consequences to the environment and human health.
For more detailed information please contact your local waste disposal authorities.
2. SAFETY PRECAUTIONS
The electric arc generated in welding or cutting may be harmful to you and others. Therefore, the operator must
be well informed and instructed on the risks and dangers deriving from the welding operations and described in
this manual.
ELECTRIC SHOCK – CAN KILL
Connect the machine to the mains power supply according to the applicable safety standards,
making sure the mains installation itself complies with these standards and is fitted with an
appropriate earth connection.
Do not touch with bare hands the conductive elements or potentially conductive elements of the
machine, its cables and electrodes, and do not use wet gloves and clothing. Insulate yourself from
the workpiece and the ground. Make sure to work in a safe environment and position.
FUMES AND GASES – CAN BE HAZARDOUS TO YOUR HEALTH
Keep your face away from welding fumes and try not to breathe the emissions. Work in a well
ventilated environment and, if necessary, wear approved masks and/or personal protection devices
and aspirators.
ULTRAVIOLET AND INFRARED RAYS – CAN BURN EYES AND SKIN
Protect your face and eyes with an approved welding helmet fitted with proper filtering lenses, and
protect your hands and body with approved safety clothing. Use protective screens or barriers to
protect others from flash, glare and sparks.
WELDING – CAN CAUSE FIRE AND BURNS
Welding spatter can cause fire and skin burns. Make sure the working environment does not have
any flammable substances or materials and always wear protective clothing.
VERSION 01-01
3 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
NOISE
This machine does not produce noise levels exceeding 80 dB. However, it is recommended to wear
approved ear protection if noise level is high.
PACEMAKERS
The magnetic field generated during the arc welding process could affect the functioning of
pacemakers. Wearers of life support devices (e.g. pacemakers) should consult their doctor before
performing any type of welding operation.
EXPLOSIONS
Do not weld near pressurised containers, explosive or potentially explosive powder, fumes or gas.
Gas cylinders and pressure reducers must be in perfect working order and must be handled with
care.
GENERAL INFORMATION
THIS MACHINE IS A DIRECT CURRENT GENERATOR BUILT AND DESIGNED TO WELD CONDUCTIVE
MATERIALS (METALS AND ALLOYS) BY MEANS OF AN ELECTRIC ARC PROCESS. THIS IS THE ONLY
USE PERMITTED.
For the definition of the terms used in this manual, refer to the standard UNI EN 292.
This machine has been manufactured in compliance with the following regulations:

Machine Safety Directive 89/392/CEE, 91/368CEE, 93/44/CEE, 93/68/CEE

89/336/CEE Directive, electromagnetic compatibility.

73/23/CEE Directive, low voltage electric material.

EN 50063 Standard, building and installation of resistance welders.

UNI EN 292/1 and 292/2 Standard, machinery safety.
VERSION 01-01
4 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
TECHNICAL FEATURES
MIG/MAG
TIG
MMA
1~ 230 V 50/60 Hz
16-25 A
4,8 KVA
4,8 KVA
4,8 KVA
8 ÷ 190 A
5 ÷ 190 A
10 ÷ 190 A
190 A 40%
160 A 60%
140 A 100%
190 A 40%
160 A 60%
140 A 100%
0,6-0,8-1,0 SG2
0,8-1,0 SST
0,9 FLUX
0,8-1,0 Al
0,8-1,0 CuSi
---
---
ø 100 - 1 Kg
ø 200 - 5 Kg
---
---
---
---
ø 1.5 ÷ 4
Electronic
IP 21 S
●
10 Kg
118 x 360 x 300
VERSION 01-01
5 of 16
180 A 40%
160 A 60%
130 A 100%
INSTRUCTION MANUAL
PRIMA MULTI 190
MOTOR GENERATOR – CONTROL OF CURRENT PEAKS
The standard machine is also set up to operate with motor generators and/or long power supply cords, within
the voltage limits of +/- 10% of the V 230.
When the voltage exceeds these limits, the machine stops functioning and the front display will indicate the
current peak, as shown in the figure.
GAS CONNECTION
The generator is fitted with one gas connection tubes, connect the pressure reducer on the cylinder, then
connect the gas tubes, open the cylinders and adjust the gas output at around 12 litres/minutes for each outlet.
ATTENTION:
Make sure the cylinders are well secured to the cylinder support before proceeding with the welding process.
LOADING OF WIRE COILS
The machine is set up to use wire coils with a diameter of 100 mm (with the kit of the assembly also wire coils
with a diameter of 200 mm). The welding machine can weld any type of material.
a) Make sure the wire feed rollers are positioned according to the diameter of the wire used;
b) Position the coil, insert the wire between the rollers and in the Euro connection, and then secure the rollers
properly;
c) Connect the MIG/MAG torch;
d) Press the torch button, the wire will exit slowly, press the button (+) on check panel together the button on the
torch, in this phase the wire will exit quickly and there is not exit of the gas to avoid unnecessary waste
REVERSE POLARITY :
ATTENTION:
In the processes of welding TIG and FLUX (flux cored wire without gas) is necessary to reverse the polarity
welding by changing the position of the lugs into the terminal.
VERSION 01-01
6 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
OPERATION DESCRIPTION
ATTENTION:
The thickness of the base materials is calculated according to a normal horizontal welding procedure. In case of
joints or different positions, increase or reduce the current/thickness values.
ADJUSTMENT OF THE ARC LENGTH
The arc length has thermal effects on the welding to be executed, and therefore, depends on the thickness of
the piece to be welded.
Effects of the arc length on the welding process.
LONG ARC (+):
The welding becomes flatter and the bead becomes wider, consequently the welding
temperature increases.
SHORT ARC (-):
The welding becomes more concentrated and the bead becomes smaller, consequently the
welding temperature decreases.
ADJUSTMENT OF THE INDUCTANCE
Effect of the adjustment of the inductance on the weld bead.
HIGH INDUCTANCE (+)
With a high inductance, the welding gets wider and the penetration decreases.
LOW INDUCTANCE (-)
With a low inductance, the welding gets smaller and the penetration increases.
VERSION 01-01
7 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
ADJUSTMENT AND DISPLAY
Connector Euro for::
1. Mig/Mag/Flux Torch
2. Tig Torch
3. Mma Gun(electrode)
Display:
Visualize programs, values and
alarms.
P= synergic and manual programs.
T= thickness material (mm).
A= welding current (A)
V= welding voltage (V)
M= wire speed (m/min)
Arc= arc length (from -15 to +15)
Key Set:
1) Press for 3 seconds to start
to welding programs Menù
with the keys (+) and (-)
select the wished welding
program.
2) Press more times to
visualize the current in
Amper, voltage in Volts, the
speed of the wire m/min.
Key + (
Key Timer:
1) Press to activate or not activate
the welding points..
2) Press for 3 seconds for select
with the keys (+) and (-) the time
in seconds about the welding
point.
L e d:
Blinking with welding points
active
̶
Key
:
1) Press to shorten the doing
operation in standby and in
welding.
2) Press to the search of programs
(P..) with activated menù.
3) Press to shorten the welding time
with activated timer.
Le
e d:
1) Blinking during the turning
the knob.
2) Short flashes with the
welding machine is standby.
saldatrice è in standby.
Knob:
1) With synergic programs P1÷P11,
turn the knob to select the
thickness t in mm of the sheet to
weld.
2) With manual programs
P12 Man, P13 Mma and P14
Tig, turn the knob to select the
welding current
Led:
1) Led on, indicate the welding
synergic funcion activated
with the programs P1÷P11.
2) Led off, indicate the welding
function P12 Man, P13 Mma
and P14 Tig.
Switch on-off
VERSION 01-01
):
1) Press to lengthen the arc, doing
operation in standby and in welding.
2) Press to the search of programs (P..)
with activated menù
3) Press to increase the time of the
welding point with active timer.
4) Press the key and together the
button on the torch to activate the
fast forward function of the wire
without gas leakage
Connector earth
cable
8 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
PROGRAMS MULTIFUNCTION WELDING PRIMAMULTI 190
PROG
N°
MATERIALE
BAS
MATERIAL
WIRE
WIRE
Ø mm
GAS
NOTES
P1
Syn
Steel or Iron
SG2
0.6
Mix
Program SYNERGIC with gas Ar-CO2 (Mix).For
thicknesses greater than 3 mm using wire with a larger
diameter.
Steel or Iron
SG2
0.8
Mix
Program SYNERGICO with gas Ar-CO2 (Mix).
Steel or Iron
SG2
1.0
Mix
Program SYNERGIC with gas Ar-CO2 (Mix).
Steel or Iron
SG2
0.6
CO2
Program SYNERGIC with gas CO2.
Steel or Iron
SG2
0.8
CO2
Program SYNERGIC with gas CO2.
Steel or Iron
SG2
1.0
CO2
Program SYNERGIC with gas CO2.
Steel or Iron
Cored wire
Flux
0.9
No
Gas
Program SYNERGIC with cored wire, without gas. Use
roll with 0,8 mm throat.
Inox steel
Inox
0.8
Mix
Program SYNERGIC with gas mixture Ar-CO2 (Mix).
Steel or Iron
Cu-Si3
0.8
Ar
Steel or Iron
Cu-Si3
0.8
Mix
Aluminum
Al-Mg5
1.0
Ar
Program SYNERGIC with gas Argon.
Aluminum
Al-Si12
1.0
Ar
Program SYNERGIC with gas Argon.
Steel or Iron
Tungstene
2.4
Ar
Program SYNERGIC for welding TIG DC Lift with gas
Argon.
Steel or Iron
Tungstene
2.4
Mix
Program SYNERGIC special for welding TIG DC Lift
with gas mixture Ar-CO2 (Mix).
Steel or Iron
Electrodes
1.5÷4.0
---
P16
---
---
---
---
No Prog
P17
---
---
---
---
No Prog
P18
Man
All
All
0.6÷1.2
All
P2
Syn
P3
Syn
P4
Syn
P5
Syn
P6
Syn
P7*
Syn
P8
Syn
P9
Syn
P10
Syn
P11
Syn
P12
Syn
P13*
Tig
P14*
Tig
P15
Mma
Program SYNERGIC with gas Argon.
Program SYNERGIC special with gas mixture Ar-CO2
(Mix).
Program MANUAL for electrode welding (MMA).
The manual
parameters..
program
requires adjustment of all
* ATTENTION: Reverse the polarity with the programs P7 Flux, P13 Tig and P14 Tig.
The size of the throat of the roll feeder must be appropriate to the diameter of the wire being used.
Tighten the wire feeder to approximately 2/3 for programs P1÷P10 and P18, for programs P11 and P12 to about 1/3.
For best results use welding wires and gases listed.
VERSION 01-01
9 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
EXAMPLE: Welding of steel sheet thickness of 1 mm with a synergic program P2.
 Install a coil of wire type SG2 wire 0,8 mm
 Install a gas cylinder Mix (Ar-CO2).
 Check that the roll feeder is positioned on the side for wire 0.8.
 Insert the wire and tighten the wire feeder to 2/3, to move the wire by pressing the torch button, to move the
wire quickly without leakage of the gas, hold the button on the torch and key
.
 Check that the wire remains well placed in the throat of a roll.
 Check that the torch is mounted on the tip of the wire guide 0.8 mm.
 To select the welding program, press the
for 3 seconds.
 Press the keys
or
to look for and to visualize the wished program P2.
 Press the key
for 3 seconds to exit from menù, or waiting for some seconds for the automatic exit.
 Turning the knob to select the values, t 1.0 indicates the thickness of the sheet metal to be welded, with this
setting you have the optimal parameters for the welding of steel sheet with thickness of 1 mm.
Note: turning the knob, you can also change the values during the welding.
UT ILIT Y:
 With keys
welding.
or
to increase or decrease the length of the arc, the adjustment can also be done during
 During the welding the display shows the following values:
for Ampere,
for Volt,
for speed of the wire (m/min), to select the wished value press the
key .
PACKING
The welding machine comes packed in a box on the pallet, fastened with steel strips and wrapped in a plastic
film.
UNPACKING




Remove the panels of the wooden case (if provided).
Remove the steel strips
Remove the protective plastic material and the cartboard.
Lift the spot welder with suitable means and remove the pallet.
CAUTION: The packing materials – wood, nails, plastics etc. – must not be left within the reach of children, as
they could be a source of danger.
The packing materials must be subdivided and disposed of in compliance with the applicable Codes.
STORAGE
The spot welder must be stored at a temperature between 0 and 40 °C in a dry place, protected from weather
and far from heat sources.
LIFTING AND HANDLING
The welding machine must be lifted and handled with care, avoiding bumps and falls which could compromise
its integrity.
VERSION 01-01
10 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
CONNECTION – INSTALLATION – WARNINGS – CHECKS
The connection must be made by qualified personnel in compliance with the applicable regulations connecting
to an electrical panel to an efficient grounding system with a differential circuit breaker of adequate capacity to
power the welder.(tab. 1 page 5, technical features).
CAUTION: The welding machine is monophase and is equipped with a power cable with two conductors, plus a
third conductor used exclusively for connection to the grounding and thus must be connected to single-phase
distribution lines, make the sizing of the power line, section of the conductors and the capacity of the fuses.
CAUTION: During all installation and connection operations, the machine must be absolutely isolated from the
power supply line.
CAUTION: Installation must be made by qualified personnel in compliance with the applicable regulations and in
accordance with the instructions of the manufacturer.
CAUTION: Before connecting the machine to the mains supply, make sure that the data on the nameplate of
the spot welder correspond to the voltage and frequency of the mains supply available on site. Check that the
installed power on the electric supply meter as well as the cables of the electrical plant are adequate for the
rated power of the welding machine.
Electrical safety of the spot welder is obtained only when connected to an efficient grounding system made in
compliance with the applicable Regulations.
Have qualified personnel check the system for functional efficiency.
CAUTION: The Manufacturer cannot be held liable for possible damage caused by absence or inefficiency of
the grounding system.
CAUTION: In case the user makes modifications, alterations or changes of the spot welder or integrates it in a
plant, any liability of the Manufacturer decays and the user is obliged to remove the CE label.
The non-observance of the above instructions will render the safety system provided by the Manufacturer
ineffective, causing serious risks of personal injuries and material damage.
START UP
CAUTION: Remember some safety precautions to be taken in order to avoid hazardous situations.
The operator must have adequate knowledge and training in resistance welding procedures with this type of
spot welder.

Do not allow unauthorized persons to access the working area.

Avoid that more then one person works simultaneously on the same spot welder.

The spot welder is equipped with moving elements, therefore all precautions must be taken to prevent these
elements from striking against persons or things
CAUTION: Do not wear magnetic metal objects as rings, bracelets, watches etc. during welding operations,
because these objects can be violently attracted by the magnetic field generated by the spot welder or
considerably overheated due to the Joule effect and cause burns.
The operator must wear safety glasses, gloves and an apron to protect himself against ultraviolet rays made by
the arc and against sparkling incandescent particles, burns and cuts in the hands.
Notes: The individual protective systems must be in compliance with the applicable Regulations.
VERSION 01-01
11 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
LIMIT OF USE
This welding machine has been designed, dimensioned and manufactured for resistance welding on thin steel
sheet. Any use with different welding procedures, non-iron metals, different sheet thickness as indicated may
affect proper operation and cause damage to the welding machine.
Therefore the machine must be destined only for the use foreseen and described in this manual, any other use
is to be considered improper and may cause hazards to the operator's safety and material damage.
The manufacturer cannot be held liable for possible personal injuries or material damage arising from improper
or unreasonable use.
ENVIRONMENT
Working ambient temperature: 5°C to 35°C.
Working air humidity: lower than 90%.
STARTING THE MACHINE
WARNING: The first start-up of the spot welder must be made by qualified personnel. Before performing any
welding operation, a series of checks and adjustments must be made.







Make sure the electrical connection has been made properly and in compliance with the applicable
Regulations.
Check that the gas is suitable for welding to be performed, open the gas cylinder and adjust the flow.
Check that the wire feed roller and the liner of the torch match the diameter of the wire used.
Set on the control of welding parameters depending on the type and quality of the sheet to be welded.
Operate the switch, turning on the display confirms the proper feeding of the welding machine.
Place the ground clamp close to the welding area.
Move to the welding area, press the button and run the welding torch.
CAUTION: The spot welder must be used by trained personnel.
MAINTENANCE
CAUTION: Never remove the panels of the welding machine and access the interior without having previously
removed the power cord from the power supply box.
CAUTION: Possible checks inside the spot welding machine, performed when energized, can cause heavy
electrical shocks generated by direct contact with current carrying parts. CAUTION: Maintenance must be
performed by qualified personnel.
SCHEDULED MAINTENANCE
Maintenance of components and wear materials must be performed on a regular basis once a week or more
often according to the use and the environmental conditions as listed below.





Check and replace the wire guide and nozzle, eliminate the waste caused by the welding arc.
Check the integrity of the torch, cable and earth clip.
Check the status of the power cable.
Check the tightness of the gas tubes.
Inspect the welding machine and remove dust and particles that were deposited on the various
components.
VERSION 01-01
12 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
EXTRAORDINARY MAINTENANCE
Repair and replacement of components of the welding machine, if required, must be performed by qualified
personnel using only original spare parts.
CAUTION: Replacement of components with not original spare parts and/or alterations of the machine causes
the decay of any liability of the manufacturer for personal injuries or material damage that may arise.
FIRE
In case of fire, use only powder extinguishers complying with the applicable Regulations.
CAUTION: NEVER USE LIQUID FIRE EXTINGUISHERS, BECAUSE THE MACHINE COULD BE
ENERGIZED.
CAUTION: WHEN BURNING, SOME PARTS OF THE MACHINE MAY PRODUCE TOXIC COMBUSTION
GASES OR SMOKE.
DISASSEMBLY - DISPOSAL
CAUTION:
If the machine is to be put out of service, provide for disassembly and disposal according to the applicable
Regulations.
Subdivide the different materials:

Metal

Electric material

Electronic material

Plastic and rubber material
ATTENTION: Waste materials must be subdivided and disposed of in compliance with the applicable Laws.
VERSION 01-01
13 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
ALARMS AND SIGNALS
MESSAGE ON
DISPLAY
DESCRIPTION OF THE MESSAGE
= °C
followed by the value in
degrees of
The temperature of the machine has exceeded
this limit, thermal protection with indication of
temperature.
temperature.
SOLUTION OF THE PROBLEMS
Leave the machine turned on with the fan running, wait for it to
continue to work.
The temperature of the control board of the
machine has exceeded this limit, thermal
protection with indication of temperature.
Leave the machine turned on with the fan running, wait for it to
continue to work.
Torch in contact with the workpiece or ground.
Make sure that the torch has not been in contact with the
workpiece or ground.
Torch in contact with the workpiece or ground.
This message also appears when the display shows one of 3
messages described above.
= POL.
You have selected a program that requires
welding polarity reversal.
Reverse the negative and positive poles, acting on the
terminals.
= vr.P.
High friction in the sliding of the wire, limitation,
wire pressure exceeded.
Replace the sheath, hold the torch at most stretched.
Progress of the blocked wire.
Check the coil, torch, wire feeder and every possible obstacle to
the advancement of the wire ..
Torch button pressed when the power of the
welder.
Check the button on the torch.
Torch button pressed.
The signal will terminate upon release of the torch button.
= t°C
= tr.c.
All leds flashing
= vir
= E01
= E02
Make sure the wire is flowing properly, check the settings of
welding.
Display flashes during
welding.
Values of welding different than the synergic
program selected.
Point flashes at the
right of the display.
Welding values unreliable.
The signal will expire on the next welding.
Point flashes at the
right of the display.
The synergic welding is not stable.
The signal will expire on the next welding.
Problem with the engine of the wire feeder.
Check the motor connections.
Electrical power problem.
Check that the mains voltage is within the normal range.
Stability of the electricity grid, when you turn off
the welding machine.
Check the connection to the electricity grid, switch, sockets,
voltage and frequency.
Electrical power problem.
Check the voltage drop across the net.
= Mot
= V.in
=r
= vc
= noP
Central led flashing
VERSION 01-01
Welding program not exist
Automatic standby function, after seven minutes Any intervention, the torch button, knob or button to revert to its
normal operating state.
of inactivity.
14 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
ELECTRIC DIAGRAM
VERSION 01-01
15 of 16
INSTRUCTION MANUAL
PRIMA MULTI 190
PRIMA
PRIMA SRL
I - 35020 ALBIGNASEGO / PD Via Garibaldi, 28
Tel. +39 049 8625963 r.a. - Fax. +39 049 8625968
P. IVA 00069400281
Reg. Impr. PD 43705 – R.E.A. PD 247779
Capitale Sociale Int. Vers. € 100.000,00
http: www.primasald.com
VERSION 01-01
16 of 16
Download PDF