Access the full text.
Sign up today, get DeepDyve free for 14 days.
Production and Maintenance Section AIRCRAFT ENGINEERING December, 1945 handwhee l elevates th e platen to put the specimen A New Brinell Machine Rapid Dynamic Balancing Machines in contact with th e ball penetrator. Major adjust Th e Avery 64/1416 Brinell hardness testing Th e Avery 3,001/A00 (Fig. 2) is a balancing men t is mad e b y thi s elevating screw handwheel, and machin e has been designed to meet the dual de machin e designed for determining the out-of- final adjustment is by a star handle on the ball- mand s of modern process control and scientific in balance weights occurring in small cylindrical holder spindle. For repetition tests, once th e major vestigation. Other tests requiring a high degree of articles (such as rotors and armatures) of from adjustmen t is made , a fraction of a turn of th e star precision or repetition tests for control purposes can 3½ oz. to 10 lb . in weight during rotation. wheel is all that is required to set the test for be carried out on the same standard machine. I t is Th e correction of dynamic unbalance demands individual specimens. claimed to be a great advance on the usual type of testin g in two vertical planes—these being deter Th e electric motor and hydraulic pump are built hardnes s testing machine. Consistent conditions can mined by the position at which material has to be int o the machine, th e motor casing being exposed be maintained in any series of tests; as th e machine adde d or removed. In this machine, the entire for cooling. The push-button starter on the left of is power operated, th e load is applied at a controlled balancing process is confined to operating a knurled th e machine and the control handle on the right, rate , and the rate of loading is adjustable. kno b with the right hand and a knurled wheel with with speed control knob in front near th e indicator th e left. The attainment of dynamic balance is A clear picture of th e speed of load application is panel, are all easily accessible t o the operator sitting indicated automatically on a chart which shows provided by a specially devised indicator, protected facing the indicator panel. th e magnitude of the out-of-balance forces in oz. by a glass panel . Ther e is special accommodation for Furthe r particulars can be had on application to and in. oz. The angular disposition of the force is large specimens, which are easily positioned, the W . and T. Avery Ltd., Soho Foundry, Birming indicated by an angular disc. The machine is so final adjustment being speedily performed. Ball- ham , 40. simple to operate that it can be left in the hands holders are quickly inserted and removed and are retained in position by a snap-action catch. of unskilled labour. A D.C. Impulse Magnetizer Th e diameter of the impression is measured by Th e principles of the machine, which are simple, I t is a well-known fact that alternating current mean s of a microscope, which is specially designed are shown diagramatically in Fig. 3. tend s to travel in the outer surfaces of the con t o read th e diameters of impressions up t o th e 7 mm. Larger and more complicated machines than the ductors carrying it. This is known as the "skin" limit for Brinell test. foregoing are those of th e 72/3,002 series (Fig. 4), of effect. As a result the corresponding magnetizing Th e machine is of rigid cast-iron construction. All which there are the following: 3,0002/AO, 5 lb. to effect is also confined to the surfaces of the parts th e working parts are encased, but are easily 100 lb.; 3,002/A1, 10 lb. to 220 lb.; 3,002/AIR, being tested, with the result that Direct Current accessible. 25 lb. to 350 lb.; 3,002/A2, 50 lb. to 1,100 lb. As magnetization is to be preferred where sub-surface A single lever, mounted on knife-edges, applies with the smaller and simpler machine, errors due defects are sought or where the depths of cracks to the human element have been reduced to a th e load. Th e lever carries a hange r for loose weights, require to be known by the build-up of th e magnetic minimum : the balancing process is controlled by which enables loads to be applied from 250 kgs, to particles in the detecting ink. This feature has two handwheels after setting the work by a chart 3,000 kgs. alread y been recognized by many users of Magnetic system . Again the dynamic balance is indicated Raising and lowering of the lever is hydraulic, Crack detection, and Inspection Authorities have in automaticall y on a chart which gives the out-of- control being by a small hand-lever. The speed is some cases stipulated that D.C. impulses should be balance error in oz. in., while its angular position is se t by a knob beside th e indicator panel a t th e front employed in the testing of certain parts. shown by an indicator disc. of the machine. Excessive speed is prevented by a To meet this requirement much research work safety device in th e hydraulic system. The range of Full particulars of the foregoing machines can ha s been involved. The production of low-voltage speeds allows a slow speed for special precision tests, b e obtained from the manufacturers, W. and T. Direct Currents of high value is not an easy matter. and relatively high speeds for repetition tests. Shock Avery, Ltd., Soho Foundry, Birmingham 40. I n some cases accumulators of th e car starter type and impact loadings are eliminated because a feature hav e been used, bu t here th e complication due to re of the machine is th e slowing down of the speed of charging and maintenance ha s been a serious matter. application of th e load as it builds up. Th e indicator Another difficulty which is associated with the panel signals "set" position and speed of load ap A.C. Impulse Magnetizer is tha t of inductive effects. plication; moreover,, it shows "no test" should the These are almost impossible to avoid and form a specimen be wrongly placed, or should there be any serious impedance to the high amperage currents, over-deflexion or no specimen on th e table. In none especially where large loops in th e connecting cables of these cases can damage to the machine result. are unavoidable. For instance, where impulse tests Th e specimen approach is open and free. A depth hav e to b e applied t o long metal bars it is generally of 15 in . is provide d and a distance of 7½ in . from th e necessary to increase th e output voltage of th e A.C. centr e of the ball-holder to the machine column generating unit to overcome the inductance in gives ample side space. Th e specimen is placed on a volved. Again, when testing parts by passing a hardene d steel platen or other fixture attached to a magnetizing A.C. cable round them, it is quite substantia l elevating screw, The machine is placed easy to produce such a choking effect which induces a t the "set " position by th e hand-control lever. The th e impulse current to a very small value. These difficulties do not arise with direct current impulses an d thus the tests produced are more certain and reliable. Th e development of the high capacity selenium meta l rectifier has facilitated the production of a suitabl e magnetizing unit for th e generation of high value low voltage D.C. impulse currents, which has been put on the market by the Equipment and Engineering Co. Ltd., of 2/3 Norfolk Street, Strand, London, W.C.2, and is known as the W.A. type. I t is of a portable nature, being contained in a steel cabine t mounted upon swivel-type rubber-tyred cas tors for easy transportation about a works. The uni t is operate d from a three-phase supply and gives a D.C. impulse outpu t up to 1,000 amperes a t a low pressure. I t is fitted with a main three-phase transformer operate d from a regulating Auto transformer which gives four values of current adjustment through a four-way step switch. The unit is arranged to operat e upon three-phase supply of 50 cycle period icity between 346 to 440 volts. The impulse is con trolled by a pneumatic timing relay which confines th e period to approximatel y one second duratio n and th e duty cycle is rated at one impulse every thirty seconds. Two pilot lights are incorporated on the plant . One (a red one) which becomes illuminated directly the main three-pole switch is turned to the "on " position. The other (a green one) lights up durin g the passage of the impulse current and proves sound contact of th e connexions to th e parts unde r test. A three-pole contactor is incorporated to close th e main circuit to the transformers, which is controlled by an operating push on the front panel. Three main fuses are also fitted. The rectifier units ar e arranged in multiple banks and are easily accessible and well ventilated. Th e D.C. outpu t terminals are conveniently fitted unde r th e control panel and can be connected t o an y of the standard Cirflux accessories such as bench blocks, insulated current bars, prod contacts, etc.
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Dec 1, 1945
Access the full text.
Sign up today, get DeepDyve free for 14 days.