Magnetic Contactor

Our machine is run with control switches with MAGNETIC CONTACTORS or magnetic starters (CHINT brand). These are necessary to run the electric motors of our block machine. A current goes through the contactor, and its electromagnet pulls back its moving contacts and brings it together with the fixed contacts to rapidly send a large amount of current to the electric motors.

These contactors are designed to be robust especially with our machine where some of the motors run at least 100 cycles each day. So, imagine a light switch that you flick a hundred times a day, but in this case it doesn't just switch the light on, but the switch itself is involved in a complex mechanism. 

The Sassin Contactor replacement that also burned up

One of our contactors seemed to be replaced much earlier than the others. It seemed odd that the electrical guy who first installed this used a "smaller capacity" contactor, when in fact the motor it operates is one of the larger ones. The damaged contactor was immediately replaced at first with a similar capacity contactor from a different brand - Sassin (though both Sassin and Chint are made in China), but after a week, the same thing happened. We decided to get a larger capacity of the same Sassin brand, and so far its been months since any problems arose.We are however tempted to try our some German brands, but costs of these are prohibitive.

The larger capacity contactor

But obviously, the best advice we can give is to consult your electrical engineers to determine the correct ratings of your electrical components. This would avoid further damage, and potential harm to the workers.

Pinion Shaft

After discovering that the helical gear in our gearbox was damaged, we also found the PINION SHAFT to be severely damaged as well. This had to match with the helical gear's teeth so the machine shop had to fabricate a new 2" diameter pinion shaft for us. 

The damaged pinion gear

 Total downtime to have both gears fabricated was about three weeks because of the steel hardening process that was involved. This affected production schedules and cost us a lot of money, not including the cost of fabrication. We decided to increase frequency of periodic maintenance shutdowns to avoid major problems like these in the future.

Helical Gear

A few weeks ago, we did something to our Hollow block mould to improve the shape and size of our resulting blocks. This resulted to a heavier mould - my guess would be about 40kgs added from the existing 150 kgs. Unfortunately, the machine's mechanical gear box seemed to experience difficulty in lifting the the entire mould box together with concrete materials (approx 100kgs) inside. It was able to function for about a week, but afterwards, it seemed frequently to stop about half way through lifting. 

Gearbox minus the gears and shafting

We were too lazy to take the machine apart and expose the gearbox. So we first thought about the 3hp induction motor that was driving the gearbox to be the culprit. Hence, we checked its A.C. Contactor and replaced it with a new one. Nope, that didn't work. We finally decided it was the gearbox. 

 

The damaged gear with its shafting (plus someone not wearing safety shoes)

 We took it apart and voila, the 10 inch helical gear was missing a number of its teeth on two different areas of the circumference. We foolishly thought there would be a replacement gear readily available in your leading hardware stores. Surprise surprise, it had to be machined. In the end, we had to have the entire gear fabricated using hardened steel. The old one was made out of casted steel.

Damaged gear with missing teeth. If it doesn't have teeth, then it sure won't bite!

The machine shop told us to always check for the acceptable loads to avoid future problems with the gearbox. Also check alignments, not to over-tighten the belts, ensure proper lubrication of both gears and bearings. Well, we failed miserably on step number one alone. Lesson learned. But that single gear wasn't the only problem. 

To be continued..