Focusing in the joint fit up, is always convenient that no
gaps exists during the joint fit up because it can cause heat build-up and is
going to burn through on your edges. This normally happens in crappy fit ups
where spaces exists a lot of burning through can happen. Therefore, making sure
that the joint is smooth and complete fit up is necessary. Also, if a joint is
more than one-eighth inch thick and cold rod steel is probably better to
chamfer it first a little bit.
The purpose of jigging on seam welding is to provide
repeatability, accuracy and interchangeability in the manufacturing of
products. Is normally used to
give to the material a shape and bend metal, and also for the assembly of some
substantial thermal switches, the residual stresses lead to little deformations
and thermos-mechanical unbalanced concentration, at important changes of
temperature. This type of stresses can also be called as thermal stresses,
which disappears after a softening heat treatment being applied to it, because
of the shear effect on the lines of where the dislocations arises, disappearing
by a cancelation in the joints or by migrating these dislocations to the
material surface. The plastic deformation also occurs when the cooling rate of
motion is high. During the process, a great amount of heat is applied to the
welded area. The thermal expansion modifies the encircling area, which is
colder, providing a growth to thermo-mechanical and plastic stresses, because
of the enlargement and friction of lattice and phase changes. Therefore, a high
concentration of residual stress in distinct grains of the material is created.
Furthermore, reviewing the influence of parameters on joint
integrity, some of them can be time consuming and costly. Welded joint
strength, corrosion resistance and toughness, can be affected by one of its
mandatory operation used in many application codes and standards which is heat
treatment. In addition, when an item is machined or when it enters service in a
high residual stress locked into a welded joint, it can suffer deformation
outside acceptable dimensions. The risk of brittle facture in carbon and low
alloy steels can be increased by the high residual stresses and by providing a
driving force for crack. Residual stresses that are produced by weld shrinkage,
can be reduced by heat treatment, by allowing them to be redistributed by
parental metal and creep of the weld. From that, no harmful thermal gradients
can occur because cooling from the stress relief temperature is now controlled.
Voltage: Voltage, which is
measured in volts, is the force or pressure that causes the current to flow. As
an example, we could take a good analogy such as water entering through a pipe.
A greater water pressure is a result of larger voltage applied, which can cause
more water (current) to flow through the pipe. Constant voltage, could be used
in applications where pieces of work do not have flat surfaces, where the
resistance is variable and produce too short welds.
Stress relief: is considered
as the process that is most times specified after welding of most materials.
The reduction of residual stresses produced by welding is needed to improve the
dimensional stability of weldments.
Heat treatment: Is used to
alter the physical and chemical properties of a material.
Pressure: The pressure
is needed throughout the entire cycle of welding to assure a constant
electrical circuit flowing through the work that is being done. As resistance
seam welding operations are automatic, pressure is often applied by pneumatic,
hydraulic or mechanical systems.
Welding speed: Speed/velocity is a fundamental parameter,
and just like temperature, the material needs to be correctly selected. Increasing
or decreasing the weld speeds causes defects on the material. Therefore, it is
necessary that the speed is chosen correctly because if the wheel velocity goes
too fast it causes cold welds and the time to make each weld is reduced. If it
goes too slow, retrofits and engineering design changes may be required and it
causes hot welds.
Temperature: In order to maintain the control of temperature
and avoid any leaks, is crucial that temperature is chosen according to the
material. Because, if the temperature is too high it cause a leak and it can
still happen the same if the temperature is too slow. Once the material is
exposed to temperature it has to be exposed for a certain time because if it
exceeds the limit, the shape of the material can change and damage the whole
The welding current is one of the most important parameter to take into
account while taking about this specific type of resistance welding. The
welding current is measured to produce a number of different spots, yet might
become constant at a certain high speed applied where separations such as gaps
may occur between different spots. As the rate of motion of the wheel is
elevated, additionally to requesting higher current, each weld have to be
manufacture in a short amount of time. Due to less time provided to produce
each spot, it has to be produced and finished before a substantial portion of
the wheel rolls away from the place where it was being produced. Higher amount
of current impulses is often required to better control weld repeatability.
As well as voltage, thickness of the material.
The pressure that electrodes may transfer to the
work being done.
The amount of current that passes through the
Seam welding has some parameters/criterias such as:
Intermittent motion: The work pieces are moved
according to the size of the sheets and this method is suitable for sheets that
are too thick to be properly welded. It moves until the weld position stops and
Continuous motion: The work pieces move at a
programmed constant speed and current, to get an overlapping weld.
The current welding process is seam welding and is fairly
known as a sort of constant weld that arises between or upon coinciding metal
parts. It can be divided in two parts which are continuous motion seam
welding and intermittent motion seam welding.
Identify critical process parameters
for the current welding process and review the influence of parameters on joint
integrity. Include considerations of jigging and joint fit up.
Since the beginning of
the usage of plaster of Paris, it have been helpful on the areas that it can be
used. Some of the types of plasters are now not so popular, but still being
used in many areas such as medicine or any other. It can be made at home or
bought, it is cheap either way.
6.0 – Conclusion
It has some uses in
medicine as well, to make plaster casts to immobilise injured bones while they
recover, although some of the orthopaedic casts used for the same reason are
made of thermoplastics. It could be used while making types of art such as
sculptures, for example some sculptors prefer to work directly in plaster of Paris
due as the high rate at which the plaster physical bearings provides the work a
sense of reality and truth and allows the sculptor to reach the authentic idea
rapidly. In some orient times, the mix of plaster and glue resulted into gesso
which was applied to produce wood panels, plaster to provide the ground or
painting, taking tempera and oil painting as examples.
Plaster of Paris, has
so many forms of uses, one of the main uses of this is due to the fact that it
does not easily compress or crack when it gets dry, what makes it a lot good in
terms of casting moulds. It is also very used to precast and hold parts of
decorative work of plaster normally found on ceilings and cornices.
5.0 – Uses
Clay Plaster: is a made of a combination of
clay, sand and water plus plant fibers for bending strength over narrow strip
of straight-grained wood. Clay plaster has been in existence since the ancient
times. Some colonies used to clay plaster on the interiors of their houses,
used to use it for construction taking the building of house of frame as
examples and also inside of wattle filling in the first sort of frame house in
which some type of covers were not allowed. Clay plaster continued to be used
for so long after starting to adopt brick filling for the houses and buildings
frame. Due to the fact that clay plaster is one of type of plaster of Paris that
has a lot good workable consistency, if its combination becomes too plastic
while being made, it may compress, crack and deform when drying.
Gypsum Plaster: Is a typical type of plaster of
Paris, it is manufactured by melting gypsum to about 150 degrees Celsius. This
specific type of plaster of Paris can be used to impregnate compress bandages
to create a shaping material called plaster bandages. It may be also used to
clay, due to the fact that it can easily be shaped while wet. This has some
uses on medicine to make the plaster used for broken bone, to prevent them from
getting hurt, called orthopaedic casts.
Lime Plaster: Lime plaster is a mixture of
calcium hydroxide and inert fillers. Limestone is formed when the plaster sets
by transforming the calcium hydroxide into calcium carbonate and all of it is
caused by the carbon dioxide in the atmosphere.
Cement Plaster: Is a mixture of suitable
plaster, sand, Portland cement and water which is normally applied to masonry
interiors and exteriors to achieve a smooth surface. It is known for its
strength, durability, quick setting time and hardness. It can be used as
proprietary spray fireproofing product in every wall constructed with stock
Heat Resistant Plaster: Is used where gypsum
plasters cannot operate due to temperature. Gypsum plaster is unlikely to stay
on the wall when temperature is to high, therefore, heat resistant plaster
works as a replacement. It is used where in every case where the wall
temperature is bound to over 50 °C. It is also used for chimney breasts,
coating walls, hole in the wall fires and cassette stoves.
There are different types of plaster, such
as: Heat Resistant Plaster, Cement Plaster, Lime Plaster, Gypsum Plaster and
– Types of plaster
Plaster of Paris is made when plaster or gypsum
is heated in a temperature above 130 °C. Therefore, by doing this, hemihydrate
is going to be formed which will probably re-form as gypsum if mixed with
water. It is also known as Calcined Gypsum. Plaster of Paris are normally
confused as the same thing, but there is a difference between them. The
difference is that Gypsum is a soft mineral and plaster of Paris is made by
3.0 – How is it made?
Plaster of Paris was firstly found in
Montmartre, Paris district. At the time, materials like wax, starch and
cardboard were used to immobilize the fracture in a way that pain and deformity
can be avoided. Unfortunately, all these materials result in failure and
mobilisation was the perennial issue in orthopaedics. However, two surgeons,
Antonius Mathijsen and Nikolai Ivanovich Pirogov, started observing and
studying the Plaster of Paris and came with the idea of including it in
bandages. Later, patients with fractures in the bones were placed in wooden
boxes and the gaps filled with Plaster of Paris. By the time, results shown in
the first experience made it become essential for medicine and some other
things such as constructions and sculptors.
2.0 – History
Is a hemihydrate of calcium sulfate, made by
calcining gypsum, that hardens when moistened and allowed to dry, used to make
casts, moulds or sculptures. It is non-flammable and non-combustible.
1.0 – Definition