FAQ's

 

Welcome to the FAQ's section of the website. Here you will find a range of frequently asked questions, if you have a question, please get in touch.

 

Q:  Why are my spot welds failing?

A:  95% of the time it will be down to the diameter of electrode tip in contact with the material being welded. A new standard tip has a spot diameter of 5mm, which gives 19mm2 of contact area . If the tip is not dressed and the contact diameter is allowed to increase to 7mm, visually not a big change, the contact area has doubled to 38mm2, so you’ll have only half the heating effect.

 

 

Q:  The cooling pipe inside my electrode tips has been lost. Does this matter?

A:   The pipe ensures that a jet of cooling water is applied to the inside face of the tip. If there’s no pipe, there may be no flow anywhere near the “business” end of the electrode. When a weld takes place, the static water inside the face will be vaporised  and steam is not a good coolant! Always check the pipe when replacing tips.

 

 

Q:   Does the force at the tips matter? Surely the current is the most important thing?

A:   Certainly if the force is not right for the material, it’s normally possible still to get a good weld. But for example,  if it’s too low, you will have to reduce the current and increase the weld times to get this result,  so you’re losing production efficiency. The force has to match the material thickness for the ideal results. See the PW website for guide settings.

 

 

Q:  Can I spot weld aluminium?

A:  Yes, it’s always been possible, but with new technology it’s even easier. Aluminium has a low electrical resistance, so you need a lot of current to heat it up. This used to mean a huge transformer and a sub-station outside the back door. Now, with Medium Frequency transformers, driven by an Inverter, a small transformer can deliver a very high current. It’s still a good idea to pre-treat the material to remove the oxide layer, as this will make the welds much more consistent.

 

 

Q: I’ve been told I need 30kVA and you’re recommending a welder with a 54kVA transformer. Why the difference?

A: All spot welders are rated using a thermal rating. In other words how hot will the transformer get if it delivers a given current at a given duty cycle. The “nominal 50%” kVA is the standard – how much will the transformer give at a 50% duty cycle?    Let’s look at the terminology:-

 

Term	What does it really mean?
Duty cycle	Length of weld ‘ON’ time compared with total time	Example:- 10 spots a minute, weld timen each 15cycles long.  Total weld time 150 cycles. Total time in 1 minute = 3600 cycles so duty cycle is 150 ÷ 3600 = 4,2%
Nominal kVA @ 50% duty cycle	What current (I2N ) will the transformer give at this duty cycle and what’s the voltage across the tips?	Example :- 54kVA transformer with 7,3V at the tips will deliver 54000 ÷ 7,3 = 7400 Amps when the weld time is 50% of the total.
Max. welding current	The most the welder will deliver with standard steel in the tips.	Example:- 15kA (15,000 Amps)
Working kVA example		Taking the above duty cycle the 54kVA transformer which will give 7400A at 50%, will give 28,000 Amps at 4,2%

 

 

Do you have a question for PW? Post it here and we’ll give you the answer.