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Troubleshooting Crusher/shredding machine

Troubleshooting Crusher/shredding machine

Troubleshooting Crusher/shredding machine

(OP)
Hi everyone!

We have a fairly new (1 month old) crusher that's part of a PET recycling line. The crusher is supposed to crush 35mm pieces of PET bottles into 9mm flakes.

The crusher motor size is 90kw and it is supposed to be able to process up to 1000kg an hour of post consumer plastic bottles. The crusher was installed with a 12mm mesh initially and was comfortably processing 400 - 500kg per hour.

However, we got an order for 9mm flakes. Immediately we changed to a 9mm mesh, we saw capacity drastically reduce. The crusher can barely manage 200kg per hour. It gets full very quickly,and has begun to over heat every 45 minutes sometimes with a small stream of smoke coming out of the opening.

In addition, when it powers up, it is using up so much power that it regularly trips off the breakers in the panel, and sometimes our 500kW generator. We are also starting to hear some squeaks in the bearings which may be the issue.

I would really love any help with trying to manage this, as it is a major bottleneck for our production.

I've attached images and videos.

https://files.engineering.com/getfile.aspx?folder=...

https://files.engineering.com/getfile.aspx?folder=...

https://files.engineering.com/getfile.aspx?folder=...
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RE: Troubleshooting Crusher/shredding machine

There must be a manufacturer to contact.

Other than that, if it has blades, ensure they are sharp. There should be power interrupters to ensure the machine cannot run during the inspection process. If they are dull the power required will be vastly increased.

It does not look like a new machine even if a new purchase; if not the previous owners may have improperly sharpened the blades.

RE: Troubleshooting Crusher/shredding machine

(OP)
Hi @3DDave,

Thanks a lot for your comments. In response:

1. We also suspected that the blades might be the issue, but sharpened them before this production run started.

2. It's a new machine. We received all brand new parts and it was installed on site by the manufacturer. Me and my team inspected each item.

3.We have contacted the manufacturers who are in a different country from us. They will be sending someone over. However, that will take at least a week and we need to be able to produce before then.

We will have another look at the blades

RE: Troubleshooting Crusher/shredding machine

How was the fan size determined? Can you increase speed on the fan? It seems as though there may not be enough air flow to transport the smaller particles.

RE: Troubleshooting Crusher/shredding machine

The pictures show almost nothing relevant to troubleshooting the problem. PET is a tough plastic. The grinder you have may not be capable of grinding PET to the size you want at the rate that you want. I would expect that a grinder for soda bottles chops the bottles between rotating blades and stationary blades that have adjustable clearances. The clearance should be about half the thickness of the bottle walls. If that is a hammer mill, about all you can do is to chill the material cool enough to make it brittle. Smoke coming out of the mill is a very bad sign that you are generating too much heat and thus melting the plastic, which requires an extensive clean-up of the mill.

You need to measure the temperature of the air leaving the mill and control feed rate to keep below a certain temperature. If you feed faster than the grinding rate, the material will accumulate in the mill and heat until it melts. As the temperature rises the plastic gets softer and grinding rate goes down rapidly. You must start with a low feed rate and increase slowly while monitoring temperature. Spraying water into the mill with the bottles can help keep it cool, but that will interfere with pneumatic transport. High air flow is important for cooling.

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