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Automate your production with automatic slag and part removal tables

Cleaning interval

During processing on a downdraft table, the slag bins slowly fill up during production with molten slag from cutting. After a while, which can be 4 weeks up to 12 weeks depending on what you are processing, the table will be full and fume extraction / air flow through the table will be below acceptable levels. Delaying table maintenance even longer can lead to plasma dust not being properly extracted and creating an unsafe environment for employees.

Some prefer to increase the interval between the cleaning of bins while some prefer to reduce the number of hours per cleaning cycle which is why some use intervals longer than others. The longer you wait however, the harder it can become to clean the bin because everything becomes clogged. When the table is full, the operator is often responsible for carrying out this arduous task of cleaning these downdraft tables.

Labor intensive work

This task can take between 4-8 hours per cleaning cycle for a 6 m / 20 ft table and often requires two people. Based on an average 6 week changing interval, approximately 1 to 2 work weeks on an annual basis per shift are used for cleaning the downdraft tables. The cutting slats and deck have to be removed from the table, bins or slag trays have to be extracted from the table and brought to a container and tilted for removing the slag.

Return on investment with labor costs

There are, however, options to automate this maintenance process with self-cleaning tables. From a return on investment perspective, while only looking at the labor costs of the cleaning cycles, the payback rate will be too large for most, taking close to a decade instead of a few years when only running the machine on one shift. With double shifts, and shorter cleaning intervals, the payback rate becomes interesting for most at around 5 years or so.

Return on investment when extra downtime for cleaning is included

Of course, in the above, only the labor costs are included with the assumption in mind that this extra downtime for cleaning the table does not lead to the loss of turnover or machine production hours. If manufactures are able to run the machine with full shifts, machine depreciation rates per hour and even lost profit margins should be included as well because these lost hours for cleaning the table cannot be used for processing parts. Idle or down time during cleaning is an important consideration. If one has a machine with multiple tables, one table can be manually cleaned while the machine is processing parts somewhere else which eliminates this downtime. If the assumption that this is not the case and you only have one cutting table, cleaning leads to extra downtime and payback rates are more than halved on average leading to interesting payback rates even at one shift.

Hidden costs

However, even for manufacturers and fabricators that run one shift and where production capacity is not filled up to the maximum yet or otherwise where cleaning does not lead to extra idle time, an automatic cleaning table could be a cost effective option. This is due to a lot of hidden costs that are not directly associated with an automatic cleaning table. In production where smaller parts are being processed, quite often these parts still drop into the slag bins. The skeleton rests on top of the downdraft table not leaving room for the operator to grab the part or which severely complicates part removal. While the machine continues cutting, the spatter from adjacent cuts can damage the part dropped into the slag bin if they are not retrieved fast enough.

Parts that dropped into the slag bin are sometimes discarded or require significant post-processing for clean-up which could also lead to the cheaper option of just cutting a new part. Especially if a lot of smaller parts are cut, these costs could reduce the payback rate of an automatic cleaning table to 1 to 3 years, even for shops that don’t use the machine at full capacity.