Comp 2

Applications for pneumatics

2.

Applications for pneumatics

2.1

The advantages of compressed air

Pneumatics faces increasing competition from mechanical, hydraulic and electrical appliances on all fronts. But pneumatic devices have fundamental advantages over the other technologies:

Easily transported Air is available everywhere, and there is plenty of it. Since outlet air escapes into the open, there is no need for return lines. Electrical and hydraulic systems need a return line to the source. Compressed air can be transported over great distances in pipelines. This allows the installation of central generation stations that can supply points of consumption via ring mains with a constant working pressure. The energy stored in compressed air can be widely distributed in this way.

Easily stored It is easy to store compressed air in purpose-built tanks. If there is a storage tank integrated in a pneumatic network, the compressor only needs to work when the pressure drops below a critical level. And because there is always a cushion of pressure, a work cycle can completed even if the power network fails. Transportable compressed air bottles can also be used at locations where there is no pipe system (e.g., under water).

Clean and dry Compressed air does not cause soiling or leave drops of oil if the lines are defective. Cleanliness in fitting and operation are extremely important factors in many sectors of industry, e.g., food, leather, textiles, and packing.

Lightweight Pneumatic devices are usually much lighter than comparable equipment and machinery with electrical power units. This makes a big difference with manual and percussion tools ( pneumatic screwdrivers and hammers).

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Applications for pneumatics

Safe to use Compressed air works perfectly even when there are great temperature fluctuations and the temperatures are extreme. It can also be used where there are very high temperatures, e.g., for operating forge presses and blast furnace doors. Pneumatic devices and lines that are untight are no risk to the safety and serviceability of the system. Pneumatic systems and components in general wear very little. They therefore have a long working life and a low failure rate.

Accident-proof Pneumatic elements are very safe with regard to fire, explosion and electrical hazards. Even in areas where there is a risk of fire, explosion and extreme weather conditions, pneumatic elements can be used without large and expensive safety apparatus. In damp-rooms or outdoors too, there is no danger with pneumatic equipment.

Rational and economical Pneumatics is 40 - 50 times more economical than muscle power. This is a major point, particularly in mechanisation and automation. Pneumatic components are cheaper than the equivalent hydraulic components. There is no need for regular medium changes, as with hydraulic equipment, for instance. This reduces costs and the servicing requirement, and increases operating times.

Simple The design and operation of pneumatic equipment is very simple. For this reason it is very robust and not susceptible to malfunctioning. Pneumatic components are easy to install and can be re-used later without difficulty. Installation times are short because of the simple design. The fitters require no expensive special training. Straight-line movements can be executed without extra mechanical parts such as levers, cams, eccentric disks, screw spindles and the like..

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Applications for pneumatics

Overload-proof Compressed air equipment and pneumatic working parts can be loaded until they stop without being damaged. This is why they are considered to be overload-proof. In contrast to electrical systems, the output of a pneumatic network can be overloaded without risk of danger. If the pressure drops too much, the work can not be done, but there will be no damage to the network or its working elements.

Fast work medium The very high flow speeds allow rapid completion of work cycles. This provides short cut-in times and fast conversion of energy into work. Compressed air can achieve flow speeds of over 20 m/s. Hydraulic applications only manage 5 m/s. The pneumatic cylinders reach linear piston speeds of 15 m/s. Maximum control speeds in signal processing lie between 30 and 70 m/s at operating pressures of between 6 and 8 bar. With pressures of less than 1 bar it is even possible to obtain signal speeds of 200 to 300 m/s.

Fully adjustable Travel speeds and exerted force are fully and easily adjustable. Both with linear and rotary movement, force, torque and speeds can be fully adjusted without difficulty by using throttles.

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Applications for pneumatics

2.2

Pressure ranges Low pressure range to 10 bar Most pneumatic applications in industry and the crafts lie in the low pressure range of 10 bar and below. Compressors used : – one and two-stage piston compressors – one-stage screw compressors with oil-injection cooling – two-stage compressors

Compaction pressure in bar

– rotary compressors

High pressure range

Medium pressure range to 15 bar HGV and other heavy vehicle tyres are filled with compressed air from 15 bar compressors. There are also other special machines that operate with such pressures.

High pressure range

Compressors used : – two-stage piston compressors

Medium pressure range Low pressure range

– one-stage screw compressors ( up to 14 bar ) with oil-injection cooling

High pressure range to 40 bar The compressors in this pressure range are generally used for starting large diesel engines, testing pipelines and flushing plastic tanks. Compressors used :

Fig 2.1 : Pressure ranges

– two and three-stage piston compressors – multi-stage screw compressors

High pressure range to 400 bar One example of the use of compressed air in the high pressure range is the storage of breathing air in diving bottles. High pressure compressors are used in power stations, rolling mills and steel works and for leak testing. Compressors of this type are also used for compressing utility gases, such as oxygen. Compressors used: – three and four-stage piston compressors

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Applications for pneumatics

2.3

Possible applications for compressed air

Compressed air is used intensively in all sectors of industry, the crafts, and everyday life. The range of possible applications is diverse and all-embracing. Some of the technical uses are mentioned and explained briefly below. In view of the versatility of this medium it is only possible to outline a few of the possible applications. The arrangement of the chapter can not be unambiguous since the criteria for assessment and differentiation are too varied.

2.3.1

Tensioning and clamping with compressed air

Tensioning and clamping with compressed air is mainly used in applications involving mechanisation and automation. Pneumatic cylinders or motors fix and position the tools needed for work processes. This can be done by linear and rotary movement, and also by swivel movement. The energy in the compressed air is converted directly into force and movement through the exertion of pressure. The amount of tensioning force required must be dispensed with precision.

Fig. 2.2: Pneumatic-mechanical clamp

2.3.2

Conveyance by compressed air

Conveyance by compressed air is found in mechanisation and automation. In these applications, motors and cylinders are used for timed or untimed conveyance, or according to work processes. Automated storage and receipt also belongs in this category, as does the turn-around of tools and other items on longer conveyor belts. Another variation of pneumatic transport is the conveyance of bulk material and liquids through pipes. With this method, granulates, corn, powder and small parts can be quickly and comfortably conveyed over relatively long distances. The pneumatic post concept also belongs in this category.

Fig. 2.3: Bridging the heights with a pneumatically powered elevator

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Applications for pneumatics

2.3.3

Pneumatic drive systems

Fig. 2.4: Valveless pneumatic hammer

2.3.4

Spraying with compressed air

Pneumatic drive systems are found in all areas of industry and the crafts. These can perform rotary and linear movements. Linear movement with the aid of cylinders in particular is seen as a highly economical and rational application. The utility work is performed by dropping the pressure and changing the volume of the compressed air. Pneumatic percussion machinery and tools (e.g., pneumatic hammers) are of great importance in this category. The energy in the compressed air is converted into kinetic energy for a moving piston. Vibrators and jolting devices belong to this category. Pneumatic power is also used by a multitude of valves and slides, tools, adjustment devices, feed systems and vehicles.

With Spraying applications, the energy of the expanding compressed air is used to force materials or liquids through a spray nozzle. This procedure is used to apply or atomise various substances. Surface treatment processes, such as sand and gravel blasting, shot peening and painting with spray-guns belong to this category. Concrete and mortar are also applied using this method.

Fig. 2.5: Arc-type metal spraying system

If high temperatures are also used, compressed air can be utilised for applying liquid metals. Arc-type spraying is an example worthy of mention here.. Another application is the atomisation of liquids through spray nozzles, e.g., for spraying weedkillers and insecticides.

2.3.5

Blowing and flushing with compressed air

When blowing and flushing the compressed air itself is the work medium and tool. The flow speed generated by dropping pressure and/or the expanding volume performs the utility work. Examples of this type of work are blowing out glass bottles, blowing out and cleaning tools and moulds, fixing light tools for processing or conveyance and flushing out metal chips and residue. Compressed air in this form can also be used to let off heat.

Fig. 2.6: Air gun with spiral hose

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Applications for pneumatics

2.3.6

Testing and inspection with compressed air

In pneumatic testing and inspection procedures, the changes in pressure at the measuring point are used to determine spacings, weights and changes in shape. This allows passing articles to be counted, correct positioning to be checked and the presence of workpieces to be ascertained. This process is an integral part of many sorting, positioning and processing systems.

Fig. 2.7: Reflex nozzle with impulse emitter

2.3.7

Using compressed air for process control

All pneumatic applications must be controlled by some means. They must receive instructions. In general this is done by press-switches, direction valves and so forth. These control mechanisms are in turn actuated in many different ways, e.g., by mechanical switches, cams, or by hand. Electrical and magnetic switches are also in widespread use. The results determined by pneumatic process control systems can be used directly by direction valves or press-switches. Pneumatics is of great importance for checking flow processes with liquids and gases. It is used for the remote control of valves, slides, and flaps in large industrial installations.

Fig. 2.8: Flow diagram of a BOGE screw compressor, aircooled version with fully-adjustable output control

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Pneumatics (fluidics) is also used for information processing and logical switching. These logic plans are comparable with integrated electronic circuits. They require much more space, but are characterised by high operating precision in certain applications. If the demands on the logic elements are not too high, fluidics can offer an alternative.

Applications for pneumatics

2.4

Examples of specialised applications

The following list will give the reader an idea of the many applications of compressed air in industry, the crafts and everyday life. Obviously, it is not possible to list all the possibilities for pneumatics since new areas appear and old ones become disused in the course of development and progress. This can therefore only be an incomplete summary of typical applications to be found in the various sectors of the economy. A list of the typical applications in general mechanical engineering has not been included, since pneumatics touches practically every area, and mentioning all would be beyond the scope of this manual.

Construction trade – Drill and demolition hammers ( hand rams ) – Concrete compactors – Conveyor systems for brickworks and artificial stone factories – Conveyor systems for concrete and mortar Mining – Rock drilling hammers and carriage systems – Loading machinery, shuttle and demolition cars – Pneumatic hammers and chisels – Ventilation systems Chemicals industry – Raw material for oxidation processes – Process control – Remote-controlled valves, and slides in process circuits Energy industry – Inserting and withdrawing reactor rods – Remote-controlled valves and slides in steam and coolant circuits – Ventilation systems for boiler houses

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Applications for pneumatics

Health system – Power packs for dentists’ drills – Air for respiration systems – Extraction of anaesthetic gases The crafts – Staplers and nail guns – Paint spray-guns – Drills and screwdrivers – Angle grinders Wood processing industry – Roller adjustment for frame saws – Drill feed systems – Frame, glue and veneer presses – Contact and transport control of wooden boards – Removal of chips and sawdust from work areas – Automatic pallet nailing Steel mills and foundries – Carbon reduction in steel production – Jolt squeeze turnover machines – Bundling machinery for semi-finished products – Coolants for hot tools and systems Plastics industry – Transport of granulate in pipes – Cutting and welding equipment – Blowing workpieces from production moulds – Locking mechanisms for casting moulds – Shaping and adhesive stations Agriculture and forestry – Plant protection and weed control – Transport of feed and grain to and from silos – Dispensing equipment – Ventilation systems in glasshouses

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Applications for pneumatics

Food and semi-luxury food industry – Filling equipment for drinks – Closing and checking devices – Bulk packing and palleting machinery – Labelling machines – Weighing equipment Paper-processing industry – Roller adjustment and feed machinery – Cutting, embossing and pressing machinery – Monitoring of paper reels Textiles industry – Thread detectors – Clamping and positioning equipment in sewing machines – Sewing needle and system cooling – Stacking devices – Blowing out residual material and dust from sewing Environmental technology – Forming oil barriers in the water – Enriching water with oxygen – Keeping lock gates free of ice – Slide actuation in sewage plants – Increasing pressure in the drinking water supply – Mammoth pump for submarine applications Traffic and communications – Air brakes in HGVs and rail vehicles – Setting signals, points and barriers – Road-marking equipment – Starting aids for large diesel engines – Blowing out ballast tanks in submarines

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