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Wednesday, June 8, 2011

Oil filter crusher

My friend has an oil burner installation business and brought up a problem he has. The burners have an oil filter that has to be changed regularly and these used filters are considered hazardous waste as such, so getting them processed correctly costs very much. But if the oil filter is crushed so that the remaining oil inside the filter gets out, this crushed filter can then be thrown in to a metal recycling bin. The oil from the filters is collected and either used in a waste oil burner or given to a hazardous waste plant as fuel for their burning processes.

At first I of course used Google to search for existing solutions to see how the crushing is done commercially. The search results indicated that most of the commercial crushers are using pressurised air and some work with hydraulic/electric power. The usual tonnage I saw was between 3 to 10 tons, most of the crushers being in the 6 to 10 tons category.

I first thought of using pressurised air as that is easily available at 10 bar pressure, but to get 10 tons of pressure needs a piston that is about 350 mm in diameter. The idea of turning the piston and cylinder myself in a lathe felt like a bad idea and I didn't even want to know how much a commercially made cylinder would have cost, so something else had to be considered.

I had thought of using hydraulics and investigated on the price to build a hydraulic pump unit and a some sort of press frame from steel, but the price would have been in the 500 EUR and up category just for the hydraulic parts. I talked about this idea at work and one guy suggested using a hydraulic log splitter.

Hydraulic log splitter. That idea had potential, as I knew those would cost very little and so I did a quick search. A local business called Motonet had on their website four different models, three ranging from 199 to 299 EUR for horizontal models and one vertical model for 399 EUR. Each had a 6 ton rated capacity, so they all had enough force. And for this price it would have been impossible to get this crusher parts let alone all the work neeeded. My friend wanted the vertical model as it had small foot print and seemed very sturdy.

The log splitter originally has a table that is stationary and the splitting wedge moves up and down by hydraulics. It has a 3 kW electric motor so it needs a 16 A wall outlet to run. In operation the motor runs constantly and circulates the hydraulic oil through the operating valve back to the tank. When you push down both hand levers the valve opens and the piston pulls the wedge down. When either the travel ends or the pressure is at its maximum, an overpressure relief valve opens and lets the oil flow past the cylinder. When the levers are let go, the valve moves to the other end by a spring load and the piston moves up until a small limit rod pulls the valve to its center position and the movement stops.

I measured that when the wedge is at its lowest position, there is a gap of 135 mm from the wedge to the table top. I also measured that the wedge is not parallel to the table but inclined about 5 mm from end to end. This meant that I had to use an angle grinder to get that inclination away and to make such an attachment that it has at least 135 mm height. The inclination was easy to get rid off, I just put a straight edge against the square tube and drew a line on the side of the wedge.

As the oil filters are about 75 mm in diameter I had to have at least about 100 mm square plates for crushing the filters. I found about 140 mm square plates from the scrap bin that were both about 25 - 30 mm thick, so I sawed off a section of U-beam to lift up the other plate enough from the table. I squared everything in a CNC mill and used it to make a 120 mm in diameter and 3 mm deep pocket on the lower plate. I also made the pocket to be a little bit concave on the bottom, so the center is at 6 mm deep to get the oil to flow to the center. In the center I drilled an almost through hole and from the side of the plate I drilled an 11.7 mm hole to the center and tapped this with G 1/4" pipe thread.

After removing paint from the parts, I used a MIG welder to put everything together. The welds were a not so good in some places as the welders copper tip was worn out, no new one was around and thus it gave me problems every 10 seconds or so.

Finally after cooling the parts I was able to assemble the not-so-log-splitter-anymore and to test it out. I screwed in a hose fitting on the side of the lower plate and ran a short length of hose to a collection bucket for the oil. The first test was to run down the piston to its lowest position to see how smmall gap there is between the crushing plates and this showed to be about 10-15 mm, so it might hurt your fingers a little if left between.

The second test was of course to put a used oil filter on the bottom plate and see if the machine has enough power to crush it. With safety glasses on I pulled the levers down and watched as the filter nicely folded down in to a pancake. In the almost end of the stroke I saw an ooze of oil squirt down the hose in to the bucket, so it worked just like it should. The end result was a very flat oil filter, about 25 % of its original size and about a 100 ml of oil. The total time to crush a filter was about 10 seconds.

Of course I called my friend to let him know that the machine was ready and that he would bring a box of used filters with him to test the machine. He showed up with about 50 oil filters in three carton boxes and together we crushed them in no time. End result was only a small bucket full of crushed filters and 5 litres of oil. No wonder they charge so much to dispose off as hazardous waste. Now he saves lots of money by recycling the empty oil filters as metal and by giving away the used oil as a fuel. And even if the regulations would say that the crushed oil filters are still hazardous waste, it would cost less to dispose off as they weigh a lot less and take up smaller space.

Now the only thing to do is an oil change to the crusher and adding an oil filter to the pipe that runs from the tank to the pump to keep the machine in operation for a lot longer than the original.

And as hydraulic log splitters can be had with a 1000 mm stroke and 6 tons of force and they contain everything needed between an electrical wall outlet and the hydraulic piston and the fact that they cost only 200-400 EUR, this will be my source for hydraulic power unit for a small hydraulic press. Nice to have electric motor running and just pressing a button to get all the movement without tedious hand cranking.