Magnetic particle testing – 2

Hi my identify is Ron Jabari so in these days we’re going to proceed on this magnetic particle trying out which now we have began in the final lecture as part of this lecture sequence on entity so before we proceed in these days allow us to have a speedy relook what we did within the last class so we realized about the common precept at the back of this system and we saw it is principally the leakage discipline which comes because of the presence of a discontinuity on a magnetized floor as a result of that leakage flux or due to that leakage subject it creates a small magnet alongside the discontinuity and then in the event you observe magnetic particles they will be interested in this small magnet being created on the discontinuity and that is how it will be made obvious through this magnetic particle trying out okay so the foremost element here or the most important the the foundation for that is the magnetic flux leakage at a discontinuity then we mentioned one of a kind methods of magnetization the first step on this case is to magnetize the surface and there are special approaches that are to be had for magnetizing the phase and relying on how you cross the current you can see the magnetic discipline how it’s created and the direction of the magnetic field as I mentioned earlier than can also be determined by means of this proper hand thumb rule as you would see right here k so if on your right hand if the thumb be the direction of the present then the fingers will factor closer to the path of the magnetic field ok so these are jointly perpendicular to each other as you would see on this case for illustration in the first one here so for those who move a current like this via this part it is being examined so the magnetic area will probably be created on this course so these are referred to as circular magnetic area the path of which is perpendicular to the course of the present ok so that is what we saw and we additionally saw that the fine feasibility you’ve gotten when the discipline and the discontinuity are perpendicular to one another ok this doesn’t mean that different orientations may not be noticeable they will nonetheless be obvious however the strongest signs shall be got when the discontinuity is perpendicular to the subject ok so this is what we noticed and then the went forward and saw exceptional ways few methods by which which you could magnetize the phase and this was the primary one utilising two electrodes and clamping the part in between these two electrodes so for clamping the phase probably the most electrodes is movable and the other one is constant k after which we saw the present requirement also for this type of magnetization the magnetizing current is in there in this range depending on the size of the phase after which we noticed one more system we uses this type of electrodes which might be often called prods so that you could either use a single prod or a double prod and on this case once more while you cross the current via this phase alongside this prod this type of you understand circular magnetic area will likely be once more generated like how you see over here and the defects around this magnetic discipline will probably be made visible so in this case one thing I will have to point out right here the requirement of the magnetizing current when you find yourself utilizing prods it is going to rely upon the thickness of the section for illustration if the phase thickness is not up to 19 mm okay the current requirement for this case can be 35 to forty five amps per centimeter of brought spacing so it will depend on the gap between the 2 lakes of the prod so it’ll rely on this distance so that suggests when you have a ten centimeter distance for instance then you can need for part of thickness less than 19 mm you want the present in the range of 350 to 450 amps when the spacing between the prod legs is 10 centimeter k and for a part thickness of better than 19 mm the current requirement would also develop so if that’s the case it might be forty to 50 amps per centimeter of rod spacing okay so that is the requirement of the magnetizing current for this distinctive procedure then we pointed out this additionally if in case you have a component which is hole then in these cases that you would be able to take a conductor and move it via the principal gap so with the aid of this relevant conductor when you go the current by way of it that you may magnetize the phase by induction k in a similar fashion you need to use a coil and insert the part through it so if so also it will nine attach the part and on this case when you find yourself sending the current by way of this coil allow us to say this is the direction of the current as you could see so here the magnetic field isn’t round correctly in this case it’s longitudinal so the cracks which are transverse that is perpendicular to the axis will be having the satisfactory visibility and cracks like this which lie along 45 measure they’re going to also have excellent visibility ok so when you’ve got a central conductor depending on the scale of the section you have got to position it so if it is a small cylinder like this then which you can situation it at the center ok so that is the a cylindrical phase that is being examined and this is the primary conductor which is carrying the magnetizing current so if the phase is small you could situation the conductor along the center as a way to have a uniform magnetization on the surface of the cylinder ok but when you’ve got a larger phase let us say like this k so if so should you location the conductor along the middle then the magnetizing may not be uniform throughout the periphery or throughout the circumference of this section so if so the relevant conductor is placed in contact with the wall of the trail in on one portion like this so this is the crucial conductor so that you ought to magnetize a special element of the part it is being examined so if the diameter of this vital conductor let us say whether it is d then in this case you may be ready to duvet a distance alongside this so that it will be equal to 4 d four times the diameter of the primary section so in order to be the amazing distance of magnetization when you use a important conductor like this at a part which is bigger and the conductor is placed in contact with the wall of the phase at a exact area ok so that is how it’s going to be if you happen to see along the circumference the gap that you could magnetize in this case will probably be 4 instances the diameter of the critical conductor similarly if you find yourself using this type of coil depending on whether the diameter of this coil is tightly stuffed via the phase or the part diameter it’s so much smaller in comparison with the diameter of the coil then due to the fact that that is enormously stuffed k that is known as a excessive fill and on this case you could see the filling of the coil isn’t that much so because of this that is referred to as low fill in case of high fill the amazing distance of magnetization from the center of the coil is 22 centimeters on both aspect from the middle and on this case the amazing distance is our we’re in r is the radius of the coil ok so in case of – it’s 22 centimeter the robust distance of magnetization so in case of Highfield it’s 22 centimeters and in case of low fill it is equal to the radius of the coil okay so this is how it’s in case of a coil or a high-quality after which we talk about this additionally a u-formed electromagnet which is referred to as a yoke that can also be used to magnetize the section and on this case the path of the magnetic lines the magnetic lines of drive are throughout this when you join these two legs so along this line is the course of the magnetic subject so that implies cracks that are lying like this perpendicular to this area can have the high-quality visibility k and on this case as I instructed you would have a hinge additionally like this so one can enable you to maneuver this legs and you could be capable to adjust the distance between the legs so that you would be capable to vary the effective distance of magnetization in this case so these are the distinctive approaches of magnetizing the phase ok so allow us to proceed on that in this lecture so first thing that you simply do you clean the surface of all dot oil grease and many others and then you magnetize the phase k with the aid of using any such methods relying on your requirement and the suitability so while you magnetize we all know what are the exceptional approaches that is all satisfactory however when you’re magnetizing the phase how have you learnt what’s the stage of magnetic subject which is most useful or which is good for magnetizing a certain a part of given measurement okay so if you want to be aware of that first you have to recognize a little bit concerning the concept of magnetization that suggests we ought to return and speak about just a little bit about the fundamentals of magnetism and then you definitely need to see the magnetic homes of the material which is being verified okay so when you refresh your memory on the theory of magnetism let’s say you follow a area H on this path so in the phase which is being magnetized it’s going to create a magnetic flux or it will magnetize it so if you plot the magnetic flux or the magnetization on this y-axis magnetic flux often is denoted by means of B or you could additionally use magnetization M alongside this axis so as you proceed to broaden the magnetic subject the magnetic flux within the fabric would increase like this and eventually it is going to saturate okay so that is the saturation magnetization so what clearly happens right here you may also understand that in a ferromagnetic fabric you will have what is called as magnetic domains or magnetic dipole moments so this within the commencing when you don’t practice any discipline when the discipline is zero these magnetic dipole moments are randomly oriented like this k and as you continue to develop the magnetic subject in a particular course then probably the most dipole moments which might be favorably oriented with admire to the course of the field will grow in measurement it’s this one on the rate of the other one so the opposite ones will lessen so as you continue to expand this path will continue to develop the favorable course and it is going to also are likely to align alongside the direction of the utilized field k so at this point when you reach this saturation factor the entire dipole moments which are favorably oriented along this magnetic field will probably be now aligned they usually additionally develop in size on the expense of the others and they will be almost aligned to the course of the magnetic subject and that is while you reach magnetic saturation ok now if you reverse the subject k if you happen to change the path of the field for those who do field reversal then it’s going to now not even as coming back it will now not comply with this same automobile rather it’s going to comply with a curve like this so now at this point although your field is zero okay however it’s nonetheless having some magnetic flux it’s nonetheless having some magnetization okay so that suggests it is protecting one of the vital magnetization which used to be offered in the opening and this is the reason this factor is referred to as remanent so if we denote that as our okay and then in the event you proceed to reverse the discipline then it’s going to ultimately saturate on the reverse direction also and now at this point it is the magnetization is fitting zero to be able to take it again to the zero magnetization you have to practice a area in the reverse direction and this exact point the discipline H similar to the factor when the magnetic flux is fitting zero is known as the coercivity so again this is a property of the material and now in the event you develop again on the equal course then this hysteresis loop develops so this is the magnetic hysteresis that everyone knows ok so now coming back to this as to what must be the extent of the magnetic area that we apply to magnetized the phase k in order you might see in the end the applied area must be better than the question subject so it ought to be higher than the where it is a subject which is this one so that it is the magnetization is not zero it is it’s some positive price it’s greater than zero quite often a field practically saturation is applied in order that whilst you do away with the subject you have got ample magnetic flux last k so theoretically this tells you what will have to be the level of the magnetic field that you just follow to magnetize the part however whilst you honestly do it this theory is first-class given that this offers you the inspiration as to how much you must have lie but when you’re almost do it and as you observe the area you have no idea what is the specific magnitude of the subject which is being utilized ok so that suggests for the period of doing it nearly you need a reference ok or anything which might at least point out if now not tells you the distinct price of the magnetic subject which you’re going to as a minimum indicate that the subject which is being utilized is excellent enough to magnetize that precise phase okay so that is the place these area indicators come into snapshot because the name suggests this will indicate the extent of the magnetic area of path in a qualitative method whether or not it is most excellent or whether or not it is adequate to magnetize the part or now not okay so there are distinct types of field indications depending on what variety of section you might have which can be used to indicate the level of the magnetic area being utilized and one among them is referred to as keto string so that is clearly a ring like this with a gap at the center okay and then along the periphery you will have some smaller holes at distinct distances from the brink like this so as you go on this distance from the threshold increases okay so you have one of a kind holes like this at distinct distances from the brink and this holes are given numbers like this 1 2 three 4 and so forth as the distance from the edge raises this number additionally increases k and should you see the normal dimensions of this specific indicator that is like this so the diameter is a hundred twenty five mm okay and its thickness is 22 mm and this sequence of holes that you have the dimensions of the hole the diameter of the holes is around 1.75 millimeter so this is what you’ve now what you are able to do that you could by means of this central gap okay you can put a relevant conductor and go the magnetizing current and as you pass the current this can be magnetized now depending on how many holes are obvious or how many holes are being indicated by way of the magnetic particles so you first magnetize this ring and then you definitely practice the magnetic particles after which see what number of holes are being indicated by using the magnetic particles clearly okay so it is going to depend on what’s the degree of present you’re utilising and what kind of magnetic particles are being used so in case you see this desk for illustration which is the magnetizing current which is being utilized to magnetize magnetized the section and the minimum quantity of holes indicated by way of the magnetic particles so this magnetic particles can both be used in a suspension in a low viscosity liquid that we will talk about later in little extra detail or they are able to even be applied as dry particles okay so allow us to say you might be using a block suspension and if that’s the case the number of minimal holes that will have to be indicated that may depend on what is the magnetizing current which is used so let’s consider for these black suspension these are the phases of present then for this for each of these currents the minimal number of gap that should be indicated for 1400 amps it should be three then for two thousand 5 hundred amps it must be 5 and then for 3 thousand four hundred amps it will have to be six k so that is how this key toasting would point out that the magnitude of the magnetizing current which is being utilized whether it’s excellent adequate or not k so if you’re applying for illustration one thousand four hundred amperes and then should you see three holes are clearly indicated when you observe the magnetic particles then for that designated current for that special state of affairs this a lot current is adequate k so this is how it’ll be for black suspension and if you happen to use dry powder for the equal stage of current this quantity must be 4 six and 7 little high k so that is how depending on what sort of magnetic particles are getting used and what number of holes are being indicated with the aid of them the ultimate level of the magnetizing current may also be determined k so this is how these Kito’s rings is going to denote whether the magnetic area or the magnetic or the magnetizing current which is being applied whether or not it is greatest or not so this is without doubt one of the ways some of the indications wherein you are able to do it there are two or three more ways which we’re going to speak about little later however I think we can take that in the subsequent lecture for the reason that in these days this is all i have so i’ll discontinue right here at present thanks for your awareness and i’ll see you subsequent time

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