ABRASIVE PROCESS

MARINESHELF publishes articles contributed by seafarers and other marine related sites solely for the benefit of seafarers .All copyright materials are owned by its respective authors or publishers.

ABRASIVE PROCESS

ABRASIVES
An abrasive is a substance that is used for grinding and polishing operations. It should be pure and have uniform physical properties of hardness, toughness, and resistance to fracture to be useful in manufacturing grinding wheels.

They are classified into two groups.
1. Natural 2. Artificial or manufactured

Natural: Sandstone, solid quartz, emery, corundum, diamond.

Sandstone: Natural abrasive stones.
Emery: Natural Aluminium oxide containing 55 to 65% Alumina, balance of iron oxide and other impurities.
Corundum : Natural Aluminium oxide containing 75 to 95 %. Alumina and the remaining are Impurities.
Both emery and corundum have a greater hardness and better abrasive action than quartz.
Diamonds of less than gem quality are crushed to provide abrasive grains for making grinding wheels to grind cemented carbide tools and to make lapping compound.
Only a very small percentage of grinding wheels are produced from natural abrasive due to the impurities and lack of uniformity of the natural abrasives.

Artifical : a) Silicon carbide b) Aluminium oxide

Silicon carbide (SiC) abrasive is manufactured from 56 parts of silicon sand, 34 parts of powdered coke , 2 parts of salt. 8 parts of saw dust in a long, rectangular electric furnace of resistance type that is built up of loose brick work. Sand furnishes silica, coke furnishes carbon, sawdust makes the, charge porous, salt helps to fuse it and gases escape through the open joints in the brickwork. The abrasive wheels are denoted by letter ‘S’.

Types of Silicon carbide abrasive- Green grit — contains at least 97% silicon carbides.
Black grit : contains at least 95% silicon carbide . This form is harder but weaker than the later.

Silicon Carbide follows diamond in order of hardness. But it is not as tough as oxide. It is used for grinding of metals of low strength such as cemented carbide, stow and ceramic materials, grey cast iron, brass, bronze, copper, aluminium, vulcanized rubber etc.,

Aluminium oxide(A1₂0₃) manufactured by heating mineral bauxite, hydrated Aluminium oxide clay containing silicon, iron oxide , titanium oxide mixed with ground coke and iron borings in an arc type electric furnance.

Aluminium oxides is tough and not easily fractured, so it is better adopted to grinding materials of high tensile strength such as most steels, carbon steels, high speed steels, annealed malleable iron, wrought iron, tough bronze. The wheels are denoted by’ A’.

ABRASIVE PROCESS TYPES:

1. Grinding

2. Honing

3. Lapping

1. Grinding:

     Grinding is performed by means of rotating abrasive wheel which act as a tool. This is used to finish work pieces which must show a high surface quality accuracy of shape and dimension. Mostly grinding is for finishing operations because it removes comparatively little material (i.e.,) 0.02 to 0.50 mm and even to the order of 0.000025 mm.

             Grinding is also done to machine materials which are too hard for other machining method that use cutting tools.

2.0 General Classification of grinding:

2.1 Rough or non precision grinding.

2.2 Precision grinding.

2.1 Rough Grinding: Other names are snagging or off hand grinding. The work is held in the operators hand. The accuracy & surface finish, are of secondary importance. Removal of excess metal, without regard to the accuracy of the finished surface eg. excess metal on weld called snagging.

2.2 Precision grinding: Produces good surface finish and high degree of accuracy.

3.0 Clasification of grinding according to type of surface to be ground

3.1 External cylindrical Grinding..

3.2 Internal cylindrical Grinding.

3.3 Surface Grinding.

3.4 Form Grinding.

3.1 External cylindrical Grinding: To produce a straight or tapered surface. The work pieces are rotated about its own axis between centers as it passes lengthwise across the face of a revolving grinding wheel

3.2 Internal Cylindrical grinding: To produce internal holes and tapers. The work pieces are chucked and rotated about their own axis. The grinding wheel rotates against the sense of rotation of work piece.

3.3 Surface grinding: To produce flat surface. The work may be ground by either the periphery or by the end face of a grinding wheels. The work piece is reciprocated at a speed below or on the end face of a grinding wheel.

3.4 Form grinding: is done with specially shaped grinding wheels that grind the formed surfaces as in grinding gear, threads, spline shafts, holes and spheres etc.,

4.0       GRINDING MACHINES  

4.1       Classification according to quality of surface            finish.

4.1.1    Rough grinders.

4.1.2    Precision grinders.

4.1.1 Rough Grinders : Main work is to remove metal without any reference to accuracy of results.

 The main types are

                 1. Floor stand and bench grinders

                 2. Portable & flexible grinders

                 3. Swing frame grinders

                 4. Abrasive belt grinders

Grinding machine is specified according to the size of the largest work piece that can be mounted on the machine.

                                         

4.1.2 Precision grinders

Precision grinders are those, that finish parts. to a very accurate dimensions.

They are classified according to the type of surface generated or work done as noted below.

1. Cylindrical grinders

      a. Centre type (Plain)

      b. Centre type (Universal)

      C. Centre less

2 Internal grinders

      a, Chucking -  i. Plain

                             ii. Universal

      b. Planetory

     C, Centerless

3. Surface grinders

           a. Reciprocating - i. Horizontal spindle

                                        ii. Vertical spindle.

           b. Rotating Table - i. Horizontal spindle

                                         ii. Vertical spindle

4. Tool and cutter grinders — i. Universal

                                             ii. Special

5. Special grinding machines —

                                             i. Tool and cutter grinder

                                            ii. Crank shaft grinder

                                            iii. Piston grinders

                                            iv. Roll grinders

                                            v. Cam grinders

                                           vi. Thread grinders

                                           vii. Way grinders

                                          viii. Tool post grinders

PLAIN CENTRE TYPE GRINDER:

                              

                                   

               The Plain grinding machine is essentially a lathe on which a grinding wheel has been substituted for the single point tool. It consist of the following parts:

Base is the main casting that rests on the floor and supports the parts mounted on it. Guide ways are provided for the table to slide. Also houses the table drive mechanism.

Tables: The lower table slides on ways on the bed provides traverse of the work past the grinding wheel. It can be moved by hand or power within desired limits.

             The upper table is pivoted at its centre and is mounted on top of the lower table.  It has  T-slots in which headstock and tailstock can be positioned  along the table to suit the length of the work. The upper table can be swiveled upto 10^o  for grinding tapers.

Headstock supports the work piece by means of a  centre or drive the workpiece in a chuck.

Tailstock can be adjusted and clamped in various positions to accommodate different lengths of workpieces.

Wheelhead carries a grinding wheel and its driving motor. The wheelhead may be moved perpendicularly to the table ways by hand or power, to feed the wheel to the work.

SURFACE FINISHING PROCESSES

INTRODUCTION

     In a manufacturing plant, a product may be shaped, turned, milled or drilled, and left in that condition as being satisfactory for use. However, if a better finish is desired, for looks, for accuracy, for wearing qualities, or for any other reasons, one of the microfinishes that include lapping, honing, superfinishing, polishing, buffing, may be employed. In some cases other operations are done only to get durable finishes.

LAPPING
Lapping is an abrading process that is used to produce geometrically true surfaces, correct minor surface imperfections, improve dimensional accuracy, or provide a very close fit between two contact surfaces. Very thin layers of metal (0.005 to 0.01mm) are removed in lapping and it is, therefore, evident that lapping is unable to correct substantial errors in the form and sizes of surfaces. It is, however, low efficiency process and is used only when specified accuracy and surface finish cannot be obtained by other methods.

Abrasive powders (flours) such as emery, corundum, iron oxide, chromium oxide, etc., mixed with oil or special pastes with some carrier are used in lapping. Most lapping is done by means of lapping shoes or quills, called laps, that are rubbed against the work. The face of a lap becomes “charged” with abrasive particles. Charging a lap means to embed the abrasive grains into its surface. Laps may be made of almost any material soft enough to receive and retain the abrasive grains. They are made of soft cast iron, brass, copper, lead or soft steel. The method of charging a lap depends upon the shape of lap. When the lap is once charged, it should be used without applying more abrasive until it ceases to cut. Laps may be operated by hand or machine, the motion being rotary or reciprocating. Cylindrical work be lapped by rotating the work in lathe or drill press and reciprocating the lap over the work in an ever- changing path. Small flat surfaces may be lapped by holding the work against a rotating disc, or the work may be moved by hand in an irregular path over a stationary faceplate lap.
In equalizing lapping the work and lap mutually improve each others surface as they slide on each other.

HONING
Honing is grinding or an abrading process mostly for finishing round holes by means of bonded abrasive stones, called hones. Honing is therefore a cutting operation and has been used to remove as much as 3 mm of stock but is normally confined to amounts less than 0.25 mm. So honing is primarily used to correct some out of roundness, taper, tool marks, and axial distortion. Honing stones are made from common abrasive and bonding materials, often impregnated with sulphur, resin, or wax to improve cutting action and lengthen tool life. Materials honed range from plastics, silver, aluminium, brass and cast iron to hard steel and cemented. carbides. This method is mostly used for finishing automobile crankshaft journals.
When honing is done manually the tool is rotated, and the workpiece is passed back and forth over the tool. For precision honing, the tool is given a slow reciprocating motion as it rotates. Honing stones may be loosely held in holders, cemented into metal shells which are clamped into holders, cemented directly in holders, or cast into plastic tabs which are held in holders. Some stones are spaced at regular intervals around the holder, while others are interlocking so that they present a continuous surface to the bore. A typical honing tool head is shown in fig. 16.1. The honing tool may be so made that a floating action between the work and tool prevails and any pressure exerted in the tool may be transmitted equally to all sides. Coolants are essential to the operation of this process to flush away small chips and to keep temperatures uniform.
Honing is done on general purpose machines, such as the lathe, drill press, and portable drills, as an expedient. But more economical results can be obtained by honing machines for production work. There are two general types of honing machines : Horizontal and vertical. A honing machine rotates and reciprocates the hone inside holes being finished. The two motions produce round and straight holes that have a very fine surface finish of random scratches. Vertical honing machines are probably more common. Horizontal honing machines are often used for guns and large bores.

                                           
               

VALVES

MARINESHELF publishes articles contributed by seafarers and other marine related sites solely for the benefit of seafarers .All copyright materials are owned by its respective authors or publishers.

                                                  VALVES

1. GLOBE VALVE

                  The globe valve has a bulbous body, housing valve seat and screw down

 spindle with disc arranged at right angle to the axis of pipe. Turning the hand wheel clockwise closes the valve while turning in anticlock direction opens the valve.

            The spindle or stem have a square thread, below or above the stuffing box

and it works on bridge (bonnet). Leakage along the valve spindle is prevented by a

Stuffing box, packed with suitable material and a gland.

            In one type of valve, the disc is attached to spindle. Hence the disc positively moves up and down with  the stem, allowing fluid flow in both directions. While the other type of valve having disc unattached to the spindle allows fluid flow only in one direction is known as Screw down non return (SDNR) valve. These valves are used in places such as bilge suction lines to prevent any back flow.

           Globe valves are primarily used for flow control and throttling purpose.

Generally not used in place which requires large flow quantity.  Globe valve can be normal (standard) type or angle type. Angle valves changes the flow directions by  90 degrees. The valves are made of materials such as Mild steel, Cast iron, cast steel, etc.,

2. GATE VALVE:

  

Gate valve (sluice valve) gives full bore flow without change of direction i.e they offer very little resistance to flow. They consist of chests divided at mid-length by a double membrane having central circular opening, furnished with seats, tapered or parallel on their inner, ie facing sides. A gate shaped appropriately can be move in a direction at right angles to flow by a screwed spindle working in a nut. ( valve moves Vertically up and down, on operating the spindle).

          Gate valve is not suitable for partially open operation or flow regulation,

since wire drawing of the seat will occur ie, they should be fully opened or fully closed. Gate valves are used for large quantity of flow.

3. BUTTERFLY VALVE:

                A Butterfly valve consists basically of a disc, pivoted across the bore of a ring body having the same radial dimensions as the pipe in which it is fitted. The full bore straight through flow arrangement of this type, especially if combined with a carefully streamlined disc profile, gives this type of valve excellent flow characteristics and low pressure drop ie it offers very little resistance to flow. The valve is quick acting, as it requires only a quarter turn of spindle to move from fully open to fully close position. Widely used in cargo, ballast and cooling water lines.    

4. RELIEF VALVE:

          Relief valve consists of a disc held closed by a spring – loaded stem. The

compression of the spring can be adjusted using the adjusting screw so

 that the valves opens at the set pressure. When the relief valve opens the excess pressure is discharged to the suction side or atmosphere. Relief helps in preventing excess pressure in the system. Relief valves are available at different ranges.

 

5. PRESSURE REDUCING VALVE:

       It is sometimes necessary to provide steam or air at a pressure less than that of the boiler or air reservoir. To maintain the downstream pressure within defined limits over the range of flow and despite any changes in supply pressure, a reducing valve is fitted.

       The working principle of a reducing valves is, the spring load causes the valve to open this is balanced by the reduced steam pressure P₂  acting on the area of the top of the valve, A₂. As this area is constant, any decrease in outlet pressure, will allow the valve to open and any increase will close it.

       The area on the underside of the valve, and that of the piston are equal A₁ , both these areas are exposed to the inlet steam pressure P₂ and so the loads on them will be equal and opposite, therefore they will balance. A regulating screw is provided for setting the tension on the spring.  

                                     PACKING AND JOINTS

            To create tightness or sealing between machine parts, a plastically deformable material, termed ‘ packing’ is often used. The various types of packing or sealing can be divided into two main groups:

1)      sealing between reciprocating / rotary parts ( dynamic)

2)      sealing between static parts.

The object of using packing material is :

1)      to prevent fluid, eg water, lub oil, fuel oil from escaping from system.

2)      to prevent gases and vapours from escaping from a system

3)      to prevent undesirable entry of gases, fluids and dirt into a system.

The three most important requirements that a packing or seal must fulfil are:

1)      it must be made of the correct material

2)      it must be suitably dimensioned

3)      it must be correctly mounted

Among the characteristics to be taken into consideration when selecting a packing material are:

1)      strength

2)      elasticity

3)      resistance to chemical influences

4)      resistance to high (or low) temperatures

5)      coefficient of expansion

6)      thermal conductivity

7)      density

8)      frictional properties

1. JOINTING BETWEEN ASSEMBLED PARTS:

              The jointing used between assembled parts is in the form of thin sheets. While metal joints are used in case of high temperatures and pressures eg. Cylinder head gasket used in a diesel engine. The metals used are aluminium, copper, steel, brass, etc.,

      1. Cold water     --  natural or synthetic rubber with or without linen lining

      2. Hot water       -- natural or synthetic rubber with or without linen lining                    

                                     for temperature upto 100deg C.

      3. Lub. & Fuel   -- bonded cork, oil paper and fibre

        

For all the above materials we can use General purpose (G.P) packing.

      4. Steam             -- Packing with metal lining

    

            In recent years, the synthetic materials such as Teflon, mipolan, nylon, perlon, trekollan and silicone rubber have found great application in the manufacture of sheet joints. Teflon and silicone rubber in particular have proved to be very suitable where other materials could not withstand the conditions. These two materials being resistant against many fluids and gases at temperatures as high as 250 degree C.

2. SEALING BETWEEN RECIPROCATING / ROTARY PARTS:

                The relative motion between the surfaces to be sealed can be:

a)      rotary

b)      translatory

c)      combined rotary and translatory

        eg. Pump rotating shafts, piston rods, valve stem, etc.,  For sealing between these parts either gland packing / stuffing box or mechanical seal will be used.

                                                   Stuffing box arrangement

                 The above stuffing box/gland packing is designed for use with fluids. The operational life and good function of a stuffing box depends on the ability fluid lubricating between the packing and shaft. This condition is obtained by tightening the packing bush so that leakage from the stuffing box is insignificant. In case of, presence of solid particles in the fluid, they get settled between the shaft and packing and cause wear and leak through the gland. In this case the gland packing has to be renewed.

               In certain cases the stuffing box is provided with a latern ring and sealing water or sealing oil with inlet and outlet connections. The pressure fed to the latern ring is slightly higher than the pressure to be tightened against, thereby preventing solid particles from forming deposits in the stuffing box eg. Boiler water circulating pump having sealing water connections.

KEYS

MARINESHELF publishes articles contributed by seafarers and other marine related sites solely for the benefit of seafarers .All copyright materials are owned by its respective authors or publishers.

                                                             KEYS

1. Introduction

                  A key is piece of mild steel inserted between the shaft and hub or boss of the pulley to connect these together in order to prevent relative motion between them. It is always inserted parallel to the axis of the shaft. Keys are used as temporary fastenings and are subjected to considerable crushing and shearing stresses. A keyway is a slot or recess in a shaft and hub of the pulley to accommodate a key.

2. Types of Keys

The following types of keys are important from the subject point of view:

1. Sunk Keys

2. Saddle Keys

3. Tangent Keys

4. Round Keys

5. Woodruff key

Sunk Keys

The sunk keys are provided half in the keyway of the shaft and half in the keyway of the hub or boss of the pulley. The sunk keys are of the following types.

a.  Rectangular sunk key:  A rectangular sunk key is shown in Fig. The usual proportions of this key are, Width of key, w = d / 4 and thickness of key, t = 2w /3 = d / 6      Where d = Diameter of the shaft or diameter of the hole in the hub.

The key has taper 1 in 100 on the topside only.

b. Square sunk key: The only difference between a rectangular sunk key and a square sunk key is that its width and thickness are equal i.e. w=t=d/4.

c. Parallel sunk key: The parallel sunk keys may be of rectangular or square section uniform in width and thickness throughout. It may be noted that a parallel key is a taperless and is used where the pulley, gear or other mating piece is required to slide along the shaft.

d. Gib-head key: It is a rectangular sunk key with a head at one end known as gib head. It is usually provided to facilitate the removal of key. A gib head key is shown in Fig.(a) and its use in shown in Fig (b).

The usual proportions of the gib head key are: Width, w=d/4;

And thickness at large end,    t = 2w /3 = d / 6

5. Feather key:  A key attached to one member of a pair and which permits relative axial movement is known as feather key. It is a special type of parallel key, which transmits a turning moment and also permits axial movement. It is fastened either to the shaft or hub, the key being a sliding fit in the key way of the moving piece.

The feather key may be screwed to the shaft as shown in Fig. (a) or it may have double gib heads as shown in Fig, (b). The various proportions of a feather key are same as that of rectangular sunk key and gib head key.

2. Saddle keys:

The saddle keys are of the following two types:

a. Flat saddle key, and b.Hollow saddle key.

a) Flat saddle key is a taper key which fits in a key way in the hub and is flat on the shaft as shown in Fig.  It is likely to slip round the shaft under load. Therefore it is used for comparatively light loads.

b) Hollow saddle key is a taper key which fits in a key way in the hub and the bottom of the key is shaped to fit the curved surface of the shaft. Since hollow saddle key hold on by friction, therefore these are suitable for light loads. It is usually used as ‘a temporary fastening in fixing and setting eccentrics, cams etc

3) Tangent Keys

The tangent keys are fitted in pair at right angles are shown in Fig.  Each key is to withstand torsion in one direction only. These are used in large heavy duty shafts.

4. Round Keys:

The round keys, as shown in Fig.(a), are circular in section and fit into holes drilled partly in the shaft and partly in the hub. They have the advantage that their keyways may be drilled and reamed after the mating parts have been assembled. Round keys are usually considered to be most appropriate for low power drives.

5. Woodruff key:  The woodruff key is an easily adjustable key. It is a piece from a cylindrical disc having segmental cross-section in front view as shown in Fig..  A woodruff key is capable of tilting in a recess milled out in the shaft by a cutter having the same curvature as the disc from which the key is made. This key is largely used in machine tool and automobile construction.

JIGS AND FIXTURES
14.1 INTRODUCTION
         The jigs and fixtures are the economical means to produce repetitive type of work by incorporating special work holding and tool guiding devices. The following are the advantages of employing jigs and fixtures in mass production work.

1.It eliminates the marking out, measuring, and other setting methods before machining.
2. It increases the machining accuracy, because the workpiece is automatically located and the tool is guided without making any manual adjustment.
3. It enables production of identical parts which are interchangeable. This facilitates the assembly operation.
4. It increases the production capacity by enabling a number of workpieces to be machined in the single set up, and in some cases a number of tools may be made to operate simultaneously. The handling time is also greatly reduced due to quick setting and locating of the work. The speed, feed and depth of cut for machining can be increased due to high clamping rigidity of jigs and fixtures.
5. It reduces the operator’s labour and consequent fatigue as the handling operations are minimized and simplified.
6. It reaches semi-skilled operator to perform the operations as the setting operations of the tool and the work are mechanized. This saves labour cost.
7. It reduces the expenditure on the quality control of the finished products
8. It reduces the overall cost of machining by fully, or partly automatising the processes.

The definition of jigs and fixtures are given below :

Jig : A jig may he defined as a device which holds and locates a workpiece and guides and controls one or more cutting tools. In construction, a jig comprises a plate, structure, or box made of metal or in some cases of non-metal having provisions for holding the components in identical positions one after the other, and then guiding the tool in correct position on the work in accordance with the drawing, specification, or operation layout.

Fixture : A fixture may be defined as a device which holds and locates workpiece during an inspection or for a manufacturing operation. The fixture does not guide the tool. The tools are set at the required position on the work by using gauges or by manual adjustment.

 The following are the fundamental differences between fixture and a jig:
1. A fixture holds and position the work but does not guide the tool, whereas a jig holds, locates and as well as guides the tool.
2. The fixtures are generally heavier in construction and are bolted rigidly on the machine table, whereas the jigs are made lighter for quicker handling, and clamping with the table is often unnecessary. -
3. The fixtures are employed for holding work in milling grinding, planning, or turning operations, whereas the jigs are used for holding the work and guiding the tool particularly in drilling, reaming or taping operations.

PROPERTIES OF PAINT

MARINESHELF publishes articles contributed by seafarers and other marine related sites solely for the benefit of seafarers .All copyright materials are owned by its respective authors or publishers.

Properties of Paint

The manner in which paint films are formed determines many of the key properties of a paint film. Therefore, paints are often classified according to their film-formation characteristics. In general terms, paints can be divided into two categories:
Physically drying paints and chemically curing paints.
In the physically drying paints, the binder molecules in the dry paint film are already present in the wet paint. There is no change in binder composition or molecule structure and size. The paint film is formed entirely by evaporation of solvents (a physical process), thus leaving the binder molecules as chains coiled up and intertwined in the coating.
In chemically curing paints, the final binder molecules in the dried/cured paint film are not present in the wet film. The smaller "wet" molecules react chemically during and after application thus creating new, larger binder molecules. Thus, the film is formed by crosslinking of the molecules (polymerisation), and often by the evaporation of its solvents as well.

Tar and Bitumen
Both are natural products. Tar comes from the distillation of coal (coal tar), bitumen is most often distilled residues from crude oil. The texture varies from liquid to solid matter.
Paints based on these binders have the following characteristics:
- good water resistance
- good penetration (that is, they adhere well even on poorly cleaned surfaces)
- poor resistance to sunlight exposure (causes cracking of the surface because of evaporation of low-molecular oils)
- black or brownish colour only (contain tiny, black carbon particles)
- low cost

Chlorinated Rubber
Chlorinated rubber is manufactured by adding approximately 65% chlorine to isoprene polymers, which come from the oil industry. A paint based solely on chlorinated rubber will form a hard and brittle film when it is dry. Consequently, a plasticizing agent is always added to the binder phase.
Paints based on chlorinated rubber have the following characteristics:
- good water resistance
- good chemical resistance
- yellowing (due to the chlorine content)
- chalking, i.e. a thin top layer of the surface disintegrates on exposure to sunlight, thereby reducing the gloss.

Acrylics
Acrylic paints consist of a copolymer made up of various acrylic monomers, which together define properties of the individual binder. Acrylics often contain a plasticizer.
Acrylic paints have the following characteristics:
- good water resistance
- good colour retention
- good gloss retention
- relatively poor wetting.

Vinyl
Vinyl binders for paint are often made from a copolymer of vinyl chloride and vinyl acetate, although other monomers may be present. All vinyl copolymers require a plasticizer in order to be used in paint.
Vinyl paints have the following characteristics:
- good chemical resistance, including resistance to weak solvents
- may yellow (because of the chlorine content)
- low solids content
- relatively poor wetting.
Solvent-borne vinyl-based paints are being used less and less, mainly because of the low content of solids and the high price.

Alkyds
When slowdrying oils (e.g. linseed oils) are combined with hydroxyl-compounds and acids, they are converted to faster-drying alkyds. Alkyds can be divided into three main groups: short-, medium-, and long-oil alkyds, depending on the content of oil. They cure by reacting with oxygen from the air.
Alkyd-based paints are known for:
- reasonably good colour and gloss retention
- good penetration
- relatively low cost
- non-resistance to alkali (and are therefore never specified for use on concrete or galvanised steel)
- non-resistance to long-term water exposure (and therefore never specified for use below the waterline).

Epoxy
Epoxy resin reacts with a curing agent (e.g. polyamine or polyamide or compounds) to form a dense three-dimensional network. The curing process can take place at temperatures down to -10ºC.
Epoxy-based paints have the following characteristics:
- chemical resistance
- good mechanical resistance
- chalking, i.e. a thin top layer of the surface degrades on exposure to sunlight, thereby reducing the gloss.
- are delivered as two-pack products with limitations on time after mixing of components (pot-life restrictions)

Polyurethane
Polyurethanes are polymers formed by reaction with isocyanates and polyalcohols. The main reaction occurs on-site when the two components are mixed just prior to use. The curing process can take place at temperatures down to -10ºC.
Polyurethane paints have the following characteristic properties:
- good gloss retention
- excellent colour retention
- good chemical and mechanical resistance
- moisture sensitive during production and application
- are delivered as two pack products with limitations on time after mixing of components (pot-life restrictions).

Zinc silicate
Zinc (ethyl) silicates are two-pack products in which metallic zinc dust is added to a solvent-borne silicate solution prior to use. They cure by absorption of water from the ambient air.
Zinc silicates have the following properties:
- excellent anti-corrosive properties
- excellent wearability and impact resistance
- excellent solvent resistance
- good chemical resistance within pH 6 - 9
- withstand temperatures up to 400°C.

Silicone
Silicone paints are silica-based resins which are liquid at room temperature but cure at elevated temperatures. At 200°C they react to form a dense network through crosslinking between the individual molecules.
Silicone paints have the following properties:
- temperature resistant up to 550 °C (pigmented with aluminium)
- relatively high cost.