1) causes of failure for the scissor jacks. Also,

1)   Introduction

 

A jack is a great option in a vehicle for many
reasons. It could be used for as simple as a tire change on the roadside, or
carrying out maintenance on the vehicle from home. The jack is used to ensure
the vehicle is lifted to a suitable height, so work can be carried out. The
purpose of the jack is to lift a heavy object or a vehicle in this scenario. As
safety is a key aspect, when a heavy object is being lifted there are a few
things that are needed to be taken under consideration. The surface of floor;
flat surface, smooth and not weak so the jack sinks in. When the jack is in use
the condition of the jack and the vehicle should be checked in terms of no
damage to the jack and any corrosion or weak spots on the vehicle. After,
suitable research acquired the scissor jack is prone to failure due to certain aspects.
The aim of the project is to improve or develop a way to reduce the number of
scissor jacks failing. This report will include some background research to
understand what scissor jacks are used for and how they are operated. The key
topic is the causes of failure for the scissor jacks. Also, some aspects
include lack of use and corrosion. Some jacks have been used incorrectly, for
example many scissor jacks have markings and stickers to represent the weight,
some of these don’t which mean that when an incorrect jack is used for the
wrong vehicle it cannot withstand the weight which results in failure.

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Many manufactures provide breakdown tools with their
vehicles such as jacks, wheel braces and spare wheels. This report will be
discussing some aspects of research that has been carried out with regards to
safety.

The report will also cover some advantages and
disadvantages of certain jacks to understand various jacks are needed in
different sections around a vehicle. Furthermore, alternative designs have been
provided to understand that there are innovative designs evolving which are
reducing the cost in the production, ease of use and mainly to be safer. The
materials for each jack will be provided to initialise the sequences of
development in the material. Finally, the testing procedure will be carried out
along with the methodology of how each step will be taken with regards to the
jack testing.

 

 

 

Fig 2.0

 

 

 

 

2) Background of jacks

 

The first diamond shape jack was built by Mr Joseph LaFrance (1920). A
scissor jack is used to lift heavy objects, or a more specific object will be a
vehicle. The most generic form of jacks is; floor jacks or garage jacks, which
are used so that maintenance can be performed on vehicle or just lifting a
heavy object around the workshop. The average small jacks such as scissor jacks
are usually fixed for a maximum lifting capacity around 1.5-3 ton. Industrial
jacks use greater loads, so they will have a lot more lifting capacity. Scissor
car jacks use manual force for lifting whereas some use electrical powered
motor to do the lifting. The scissor jacks have a slot where it fits onto the
sill of the vehicle to enable it to lift. Some scissor jacks are designed to be
only lifted from the sills and some can be lifted from other places. A scissor
car jack is designed by bolting pieces of metal elements into a kite shape with
hinges and a screw connecting the opposite sides of the diamond. When the screw
is turning with the spanner/hook it will raise the diamond or lower it depending
on the direction of the turn. The scissor jack comes as standard feature for
majority of vehicle as a kit with the spare will and various other accessories.
However, large vehicles such as trucks and high clearance vehicles with
integrated jacks or heavy-duty jacks due to the size and weight. This jack
operates by transferring rotational motion into linear, so this means the
turning of the screw causes expansion or contracting of the kite shape, which
then translates to an upward force or downward, when the jack is placed between
solid grounds and jacked to the vehicle chassis or sill.

Operation

When the screw section is turned, two ends of the
diamond move closer together. This occurs due to the gears/ threads of the
screw are pushing the arms, the size of force is being applied is multiplied.
Not much force is required when the crank/hook is turning the gears yet the
action that is being caused results in the brace arms to slide across and
together. That procedure helps the arms extend upward to life the
object/vehicle.

 

Usage

The uses of the scissor jack can be simple as changing
a wheel on a car due to a puncture. Also, it can be used on a flat surface to
work on a vehicle at home, for example changing some brake pads, oil change and
various other components on a vehicle that need changing can be done. It is
highly recommended with any vehicle jack that an axle stand will need to put
underneath for safety reasons. Scissor jacks are a standard feature in some
cars and can be bought for around £10/15. Scissor jacks are the ones that
typically come in a vehicle’s boot kit in case of an emergency. These jacks
benefit because they don’t take up much space can be stored in the trunk of a
vehicle also they don’t require any additional maintenance.

 

3)   Causes of failure

 

Sliding

One of the common reason of this jack is prone to
failure is because of the head of the jack. The head is shaped as a sphere, so
when the jack is lifted elsewhere apart from the sills, due to not being stable
the vehicle begins to slide. To overcome this problem the jack head will have
to be re-designed or a polymer can be used above the head prevent the jack from
sliding. A rubber pad can be used to prevent the car from sliding; this will
firmly grip the structure of the vehicle. Some vehicles have soft sills which
mean users will prevent jacking up from these sorts of areas.

Below is an incident where a scissor jack was used and
slid of the vehicle.  

‘He
said he had jacked the passenger’s side tire off the ground with a scissor
jack, and was looking to “find a good jack stand point.” The car shifted a
bit’, David Tracy 2016 This article
suggests that a scissor jack was used incorrectly and caused major injury to
the user.                Fig3.0

Non-slip material

The
jack needs a material that prevents the vehicle sliding of it, to achieve this;
a rubber pad must be fitted to the scissor jack. Friction is defined as the
force opposing motion. One type of friction is static friction. The lower the
static friction, the easier it is to make an object start moving.

 

                                              Fig3.5

 

 

Safety of the operation

Chocks- wheel
chocks can be used to prevent the vehicle from rolling. The chock fits in front
and behind the wheel, this is made from a thick polymer. As, the vehicle is
being lifted from one side using the scissor jack the load is increasing on the
opposing side which can surge the vehicle to roll. The vehicle must be put into
gear as well as handbrake must be applied.

Surface- As
the scissor jack is lifted the diamond shape turns into a tall rectangle. This
becomes a down fall because it has higher chances of toppling over. The surface
of the ground must be flat because the jack will start to slide depending on
the slope of the surface.

Stands- With
any type of lifting operation whether it’s a vehicle or a heavy object axle
stands are a must. They are placed on the chassis of the vehicle during lift or
the load of the jack can be released onto the stands for safety
precautions. 

4)   Testing/Methodology

 

The testing consists of three sections. The first
section is Ansys; the scissor jack will be simulated on the software. A 3D
model will need to be made on computer aided design or even on ansys.

 Once this is
done the file will be converted onto ansys to enable it to run. The jack will
go through the testing procedure which will involve a load being set, which
will represent the weight of a car. On the jack, certain points must be fixed
during the test to demonstrate that the jack is not moving as it’s under load.
The test will begin and create a set of results which depend on the jack
material and various other aspects. The results gained such as stress, strain,
fatigue and fracture can then be noted so they can be used later for
validation.

Some drawings will be made to interpret modern designs
keeping in consideration the scissor jacks.

Each part of the jack will then be analysed to
determine each component weak point. Calculations will be carried out for each
component individually. The weakest component will then be modified to overcome
its weakness to enable a strong structure.

As the main goal is to analyse a scissor jack, the
material and shape will be taken under consideration.

The next test will involve an actual jack being
tested. A hydraulic press will apply a load to the scissor jack. This is like
the ansys test where the load will represent the wright of a vehicle and pushed
against the car. The procedure will be carried out with various loads to
represent various vehicles.  At a point,
the jack will have fractured or have some signs of fatigue in the material. The
results gained from the jack will be then calculated to support the ansys.

The final test is hand calculations; these will
validate both tests by getting comparable results. If the results are different
this means, there is a problem between the three tests.

So far, the 3D model of the scissor jack has been
made. It will now need to go through the ansys procedure for the finite element
analysis. The first material that will be used for the test will be structural
steel and understand what effects it has on the design and any damage caused.
The second will be the improved version with aluminium and see the correlation
between both the materials when a load is applied.

The tests the four materials will determine if the
final project design will be from aluminium or steel. The rough of idea of the
3d model will be then improved.

 

 

5)   Materials

 

Structural steel

Any jack that is made acquires components made from
steel, they may have been assembled with an aluminum structure, but steel is
required for the fixings, pins and many other components. ‘While aluminum tends to win out on weight, steel jacks tend to
acquire out on cost. Steel jacks are normally always a tiny bit more expensive
on ordinary for a graded capacity than aluminum jacks. This is because the
weight economies, aluminum jacks are normally promoted as superior solutions’. Matt Seals 2017. The development of scissor
jack from steel is improving to gain tick certain boxes such as price,
durability, ease of use and various other aspects. The strength of steel can be
increased by the addition of alloys such as manganese, niobium and vanadium.
However, these alloy additions can also adversely affect other properties, such
as ductility, toughness and weldability.  The properties of steel also include the
strength and reliabilities of the material.

Aluminium Alloy (Alternative)

The key features of aluminium are that, it is very
light in weight and it is one of the materials that don’t rust. The focus of
having a floor jack made from aluminium is to decrease its weight. As previous
jacks, were made from steel and they are very heavy to carry and move around a
workshop. Steel is a much denser material than aluminium which implies that if
two identical sized blocks of these materials measured in weight, steel would
weigh more.

Many people misunderstand the strength of aluminium.
This is due to the misconception of aluminium being soft and weak in various
products. ‘The truth is that depending
on the grade of aluminum and the process by which a part is manufactured
aluminum parts can be every bit as strong as steel’. Matt Seals 2017 This material is used in a lot of
products floor jacks, jack stands, or airplanes made all from aluminum’.  The
specific weight of aluminium is roughly around 2.7 g/cm3.  Various treatments can be applied to
aluminium such as paint lacquer to improve its properties and make it stand out
from other jacks.

This material is also recyclable which means that any
scrap aluminium can be reused to make a scissor jack. This process of recycling
requires less energy and roughly 5 percent of the energy is used to produce the
primary metal.

Furthermore, this material has a tensile strength between
70 and 700 MPa. Aluminium doesn’t get brittle at low temperatures however it
increases its strength.

Aluminium alloy can be attached to other aluminium
products or to various materials by the following methods: welding, brazing,
soldering, bolting, riveting, clinching, crimping, clipping, adhesive bonding
and slide-on, snap together or interlocking joints.

 

Mild steel,
and cast steel will go through material testing

 

6)   Current Progression

 

Research-
a scissor jack has been chosen to analyse and improve the material properties,
the design and strength to reduce the number of failures. The scissor jack is a
mechanical device that is failing a lot more than other jacks. The research
includes recent incidents relating to scissor jacks failing. The research has
created the foundation of the project, by providing some information on the scissor
jack. The background information helps the reader understand what the report is
about.

Ongoing

 

CAD- A
3D model has been designed to represent the scissor jack. The jack is consists
of 6 parts. The design of the scissor jack is to get a rough idea of the
scissor jack also it will be used on Ansys to gain some results.

Completed

 

Jack- The
physical testing involves a jack being tested on a press. A scissor jack has
been brought for the testing.

 

Design
options – A few design options have been developed regarding
the scissor jack head, the shape and the material.  The standard 3d design will go through Ansys
first to see the results and then the improved design will be tested.

Further Plan/Objectives

 

Ansys-
As the 3D model is made, the testing will need to be done to see the maximum
stress and strain.  Deadline: 18th
January

Jack
testing- The next step after Ansys will be the testing of the
jack; a load will be applied to the scissor jack and will increase till the
jack cannot withstand the load. This procedure will result fracture will then
will be calculated. Deadline: 23rd January

Calculations-
The following will need to be calculated:

Maximum Stress, Strain, fracture, crippling Deadline: 29th
January

Material
testing- The materials mentioned will be tested on the press to
determine which one will be used in the final design. Deadline: 23rd
January

 

7)   Alternative Designs

Type
of
Jack

Features

Pros

Cons

Price
(Average)

 
 
 
 
 
Bottle Jack
Steel
 

The max capacity of this jack is 10-ton
 
150mm stroke and an 80mm adjustment screw
 
230mm to 460mm lifting range
 
Strong a durable
 
Automatic safety overload valve

The bottle jack is small and compatible
 
 It has a very
high lifting capacity.
 
It can lift heavy objects and vehicles with ease due
to its high lifting capacity.
 
The bottle jack is small and can be stored anywhere
and doesn’t take much space

 
The small base design of the bottle jack causes
instability.
 
The bottle jacks can lift heavy item buts only to a
certain height.
 
This escalates a problem when standard vehicles need
lifting and there isn’t enough clearance.

£21.99

 
 
Exhaust Air
Jack
PVC/Polyester

Capacity:  4
tons, size: 58 x 75 cm
 
 Weight:  4 tons:6.5kg
 
2 x Protective mat sizes: 640mm x 670mm
 
5.6 meters one-way air hose

Uses the exhaust gases to full up the bag which
lifts the vehicle.
 
Can lift around 30 inches from the ground.
 
Cost less to manufacture

stay inflated for as long as 45 minutes
 
car must be started up during the procedure,
consumption of fuel
 
Depending on surfaces can pop the bag
 
 

£23.00

 
 
 
 
Floor Jack
Aluminium
 
 

Racing style 1.5 tonne trolley jack
 
Low profile with dual pumps for a quicker lift
 
Fast access with front roller wheel
 
Lifting range is 90-358 mm

This enables it to lift lowered vehicles.
 
The floor jack is very simple to use due to the long
pumping handle.
 
The floor jack remains stable throughout the
procedure of work being carried out

The floor jack has a low rate of lifting capacity.
 
Cannot be carried around like the other jacks
 
Takes a lot of space due to its size.

£122.04

8)   Scissor Jack Head                                              

The scissor jack head varies from different shapes and
designs, the scissor jack is mainly used for jacking up from the sill of the
vehicle. However, as said above that some users avoid jacking up from weak
structures due to rusty sills or a weak structure. To avoid jacking up from the
sills or to prevent the vehicle from sliding some research has been done to
overcome these issues.

One of the ways
is to re-design the head of the scissor jack into a claw or an adjustable head
which can be adjusted to the users need. This will be universal, so it can be
jacked up from the sills and other strong structures. 

The floor of the scissor jack will need to be improved
so it can prevent the vehicle from sliding. This can be done by having a rubber
floor pad for the jack or the structure of the floor can be re-designed.        Fig4.5

Another improvement could be, having the scissor jack
heads screw into the jack so they can be used for more than one option. By
having the head of the scissor jack screwed into the jack, it will improve the
structure of the jack.

 The rubber pad
can also be fitted over the jack head to prevent the vehicle from sliding. The
higher the jack is lifted there is a greater chances of the jack the jack
sliding or falling.

Some design ideas have been shown above, the next step
is to create some drawings to get a visual idea of the design.

Progression of scissor jacks

Scissor
jack (Mechanical)

 The scissor
jack today is well-known jack used daily when needed. They are the cheapest out
of all the jacks. Vehicle manufactures use this jack into their vehicles as a
standard feature along with wheel braces and various other items. These jacks
are small, so they can be carried around unlike trolley/floor jacks. They are
very easy and simple to use. These jacks don’t need maintaining as much as the
hydraulic jack due to it being a mechanical device. These jacks restrict
lifting certain vehicles up due to the weight. Furthermore, as people got lazy
a new jack was invented which was an electric scissor jack powered by a motor.

Scissor
jack (Electrical)

This
jack is an improved version of the scissor jack. This jack is manufactured from
heavy duty steel; a motor has been added to the scissor jack which means less
motion is required. The electric powered jack has equivalent properties to the
normal scissor jack however this is quicker to operate and has a remote to
control the lift. This jack operates by a wire from the jack connected into
the vehicle’s cigarette lighter socket. The electric scissor jack is powered by
12-volt electricity provided directly from the car’s cigarette lighter port
which means that no extra power pack is needed.