Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Controls for resistance welding machines
The main controls required for a resistance welding machine are:i. Initiation and termination of the current.ii. Controlling the magnitude of the current.iii. Timing and controlling the mechanical operations of the welding machine.Three main categories of controls are:a. Welding contactorsb. Timing and sequence controllers andc. Other controls and regulators. Welding control is lifted in the primary circuit of the welding transformer. The contactors may be mechanical (foot pedal), magnetic (electromagnetic) or electronic of which electronic contacts are the most useful and reliable. The electronic contacts may be ignitrons, thyratrons or SCR's. We have to go in for ignitron tubes it the primary current exceeds 40 A.Time and sequence controls can be pneumatic, R - C controlled, motorised or digital. Synchronous and non synchronous controls are two main possibilities. Non - synchronous controls provide variations of timing and current input to the machine from closing and opening of the welding contractor at random points on the wave form. On the other hand, synchronous controls provide switching at the same electrical angle each time. Non - synchronous controls are accurate for weld times of 20 cycles or longer.Heat control: The major adjustment of the welding current is done by tap changing. For fine intermediate current control, electronic heat control is used. Ignitron tubes with SCR or thyratron firing is employed.Upslope control: Upslope permits the welding current to be increased over several cycles from a low value to that needed for welding, instead of having the full welding current applied instantly. This eliminates the expulsion of metal (splashing). This is used at high current values and for welding scally stock and for almost all plate metals.Downslope control: This permits the welding current to decay gradually to a low value, instead of ending suddenly, and it helps to produce good welds in some types of heat treatable metals by lengthening the cooling time of steels (less than 0.15 % carbon). Current and voltage regulators: Electronic current regulators are used to maintain a constant welding current under severe conditions by compensating for welding current variations or load changes resulting from insertion of magnetic materials into the throat of the welding machine.Preheat and postheat control: These controls are important for flash butt welding. The joint is first heated up in one or more stages by applying pressure to the joint and then separating it before the weld temperature is reached. This may be repeated several times, depending on the type of work and the capacity of the machine in relation to the size of the joint. By adopting this interrupted preheating process, it is possible to increase the maximum capacity of the machine, as the preheating operations reduce the final kVA needed to raise the joint to weld temperature. In sophisticated flash butt welding machines, the preheating is digitally controlled and ignitrons in the circuit, for each preheat cycle, the time for which the jobs are in contact, the time taken for retraction of one job, the time for which the jobs are allowed to cool and the time for bringing the jobs together can be independently set with the thumb wheel switches. The number of preheat cycles can also be selected.
A semi circular frame of flexural rigidity EI is built at A and caries a vertical load W at B. calculate the magnitude of the vertical and horizontal deflection at B and hence the
A multiple disc clutch, steel on bronze, is to transmit 4.5 kW at 750 r.p.m. The inner radius of contact is 40mm and outer radius of the contact is 70 mm. The clutch operates in oi
In mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the
A particle is acted upon by a force of constant magnitude which is always perpendicular to the velocity of the particle. The motion of the particle takes place in a plane, then wha
Lubrication System: This is an arrangement that consists of oil pump, oil sump, oil lines and lubricant. The lubricant is meant to lubricate the engine moving parts and it also cl
bending equation
Q. Define Non - consumable electrode? These types of electrodes are prepared from high melting point materials. Mainly carbon, pure tungsten and its alloy are used for electrod
Ask question #Minimum 100 words acceptedIf your requirement is for a sensor suitable for a heavy industrial application, with a linear characteristic, working in temperatures up to
COMPETENCY STATEMENT: In this programme, every learner shall be assessed on a continuous basis for his/her knowledge and skills during the programme duration. Learners' competenc
Determine the slopes at free end - cantilever beam: A cantilever beam of length l carries a point load W at a distance l /4 from free end. Determine the slopes at free end
Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd