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 We
are a well established metal polishing company, based in the heart of
Birmingham’s historic Jewellery Quarter. We specialise in Brass, Die Cast,
Aluminium, Stainless Steel, Linishing, Sateen, Bright Mirror Polishing and
Scotch Bright
Metal Polishing
Polishing is usually multistage process because the first stage starts with a
rough abrasive and each subsequent stage uses a finer abrasive until the desired
finish is achieved. The rough pass removes surface defects like pits, nicks,
lines and scratches. The finer abrasives leave very thin lines that are not
visible to the naked eye. Lubricants like wax and kerosene[ are used as
lubricating and cooling media during these operations. Buffing may be done by
hand with a stationary polisher or die grinder, or it may be automated using
specialized equipment.
When buffing there are two types of buffing motions: the cut motion and the
colour motion. The cut motion is designed to give a uniform, smooth, semi-bright
surface finish. This is achieved by moving the work piece against the rotation
of the buffing wheel, while using medium to hard pressure. The colour motion
gives a clean, bright, shiny surface finish. This is achieved by moving the work
piece with the rotation of the buffing wheel, while using medium to light
pressure.
When polishing brass, there are often minute marks in the metal caused by
impurities. To overcome this, the surface is polished with a very fine (600)
grit, copper plated, then buffed to a mirror finish with an airflow mop.
Polishing operations for items such as chisels, hammers, screwdrivers, wrenches,
etc., are given a fine finish but not plated. In order to achieve this finish
four operations are required: roughing, dry fining, greasing, and colouring.
Note that roughing is usually done on a solid grinding wheel and for an extra
fine polish the greasing operation may be broken up into two operations: rough
greasing and fine greasing. However, for inexpensive items money is saved by
only performing the first two operations
Polishing Equipment
Aluminium oxide abrasives are used on high tensile strength metals, such as
carbon and alloy steel, tough iron, and nonferrous alloys. Silicon carbide
abrasives are used on hard and brittle substances, such as grey iron and
cemented carbide, and low tensile strength metals, such as brass, aluminium, and
copper.
Polishing wheels come in a wide variety of types to fulfil a wide range of
needs. The most common materials used for polishing wheels are wood, leather,
canvas, cotton cloth, plastic, felt, paper, sheepskin, impregnated rubber,
canvas composition, and wool; leather and canvas are the most common. Wooden
wheels have emery or other abrasives glued onto them and are used to polish flat
surfaces and maintained good edges. There are many types of cloth wheels. Cloth
wheels that are cemented together are very hard and used for rough work, whereas
other cloth wheels that are sewn and glued together are not as aggressive. There
are cloth wheels that are not glued or cemented, instead these are sewed and
have metal side plates for support. Solid felt wheels are popular for fine
finishes. Hard roughing wheels can be made by cementing together strawboard
paper disks. Softer paper wheels are made from felt paper. Most wheels are run
at approximately 7500 surface feet per minute (SFM), however muslin, felt and
leather wheels are usually run at 4000 SFM.
Buffing wheels, also known as mops, are either made from cotton or wool cloth
and come bleached or unbleached. Specific types include: sisal, spiral sewn,
loose cotton, canton flannel, domet flannel, denim, treated spiral sewn,
cushion, treated vented, untreated vented, string buff, finger buff, finger
buff, sisal rope, mushroom, facer, tampered, scrubbing mushroom, hourglass buff,
rag, "B", climax, swansdown, airflow, cool air and bullet.
Powder Coating
Part Preparation Processes & Equipment
Removal of oil, soil, lubrication greases, metal oxides, welding scales etc. is
essential prior to the powder coating process. It can be done by a variety of
chemical and mechanical methods. The selection of the method depends on the size
and the material of the part to be powder coated, the type of soil to be removed
and the performance requirement of the finished product.
Chemical pre-treatments involve the use of phosphates or chromates in submersion
or spray application. These often occur in multiple stages and consist of
degreasing, etching, de-smutting, various rinses and the final phosphating or
chromating of the substrate. The pre-treatment process both cleans and improves
bonding of the powder to the metal. Recent additional processes have been
developed that avoid the use of chromates as these can be toxic to the
environment such as Titanium Zirconium and Silanes which offers similar
performance against corrosion and adhesion of the powder.
Another method of preparing the surface prior to coating is known as abrasive
blasting or Sandblasting and shot blasting. Blast media and blasting abrasives
are used to provide surface texturing and preparation, etching, finishing, and
degreasing for products made of wood, plastic, or glass. The most important
properties to consider are chemical composition and density; particle shape and
size; and impact resistance.
Silicon carbide grit blast media is brittle, sharp, and suitable for grinding
metals and low-tensile strength, non-metallic materials. Plastic media blast
equipment uses plastic abrasives that are sensitive to substrates such as
aluminium, but still suitable for de-coating and surface finishing. Sand blast
media uses high-purity crystals that have low-metal content. Glass bead blast
media contains glass beads of various sizes.
Cast steel shot or steel grit is used to clean and prepare the surface before
coating. Shot blasting recycles the media and is environmentally friendly. This
method of preparation is highly efficient on steel parts such as I-beams,
angles, pipes, tubes and large fabricated pieces.
Different powder coating applications can require alternative methods of
preparation such as abrasive blasting prior to coating. The online consumer
market typically offers media blasting services coupled with their coating
services at additional costs.
Powder Application Processes
The most common way of applying the powder coating to metal objects is to spray
the powder using an electrostatic gun, or Corona gun. The gun imparts a positive
electric charge on the powder, which is then sprayed towards the grounded object
by mechanical or compressed air spraying and then accelerated toward the work
piece by the powerful electrostatic charge. There are a wide variety of spay
nozzles available for use in electrostatic coating. the type of nozzle used will
depend on the shape of the workpiece’s to be painted and the consistency of the
paint. The object is then heated, and the powder melts into a uniform film, and
is then cooled to form a hard coating. It is also common to heat the metal first
and spray the powder onto the hot substrate. Preheating can help to achieve a
more uniform finish but can also create other problems, such as runs caused by
excess powder. See the article "Fusion Bonded Epoxy Coatings"
Another type of gun is called a Tribo gun, which charges the powder by
(triboelectric) friction. In this case, the powder picks up a positive charge
while rubbing along the wall of a Teflon tube inside the barrel of the gun.
These charged powder particles then adhere to the grounded substrate. Using a
Tribo gun requires a different formulation of powder than the more common Corona
guns. Tribo guns are not subject to some of the problems associated with Corona
guns, however, such as back ionization and the Faraday Cage Effect.
Powder can also be applied using specifically adapted electrostatic discs.
Electrostatic Fluidized Bed Coating: Electrostatic fluidized bed
application uses the same fluidizing technique and the conventional fluidized
bed dip process but with much less powder depth in the bed. An electrostatic
charging media is placed inside the bed so that the powder material becomes
charged as the fluidizing air lifts it up. Charged particles of powder move
upward and form a cloud of charged powder above the fluid bed. When a grounded
part is passed through the charged cloud the particles will be attracted to its
surface. The parts are not preheated as they are for the conventional fluidized
bed dip process.
Electrostatic magnetic Brush (EMB) Coating: an innovative coating method
for flat materials that applies powder coating with roller technique, enabling
relative high speeds and a very accurate layer thickness between 5 and 100
micrometre. The base for this process is conventional copier technology .
Currently in use in some high- tech coating applications and very promising for
commercial powder coating on flat substrates ( steel, Aluminium, MDF, paper,
board) as well in sheet to sheet and/or roll to roll processes. This process can
potentially be integrated in any existing coating line.
Curing: When a thermoset powder is exposed to elevated temperature, it
begins to melt, flows out, and then chemically reacts to form a higher molecular
weight polymer in a network-like structure. This cure process, called cross
linking, requires a certain degree of temperature for a certain length of time
in order to reach full cure and establish the full film properties for which the
material was designed. Normally the powders cure at 200°C (390°F) in 10 minutes.
The curing schedule could vary according to the manufacturer's specifications.
The application of energy to the product to be cured can be accomplished by
convection cure ovens or infrared cure ovens.
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