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Industrial gases and associated equipment
News Release from: Manufacturing Service Solutions | Subject: Nitrogen gas generator systems
Edited by the Manufacturingtalk Editorial
Team on 14 June 2006
Lasers' nitrogen supply costs reviewed
Faster cutting of SS, aluminium and thinner carbon steels with nitrogen as the assist gas demands that users pay closer attention to nitrogen supply system costs says Neil Jackson.
Laser Industry trends indicate that sheet and plate working fabricators are increasingly selecting higher power lasers for not only cutting thicker materials, but also faster cutting of stainless steels, aluminium and thinner carbon steels with nitrogen as the assist gas Some five to 10 years ago, the most common laser power levels ranged between 1500 and 3000W, however, surveys show in recent years a huge swing towards installations of 4000, 5000 and even 6000W lasers
This article was originally published on Manufacturingtalk on 30 Nov 2006 at 8.00am (UK)
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Today, the more experienced laser fabricators are purchasing high power lasers to expand their nitrogen laser cutting capabilities and consequently differentiating themselves from their competitors.
However, like all lasers users regardless of laser power available, great consideration needs to be taken in the method and source of nitrogen supply.
* Gas Consumption - when processing stainless steel with nitrogen, large volumes of assist gas are used, with more than 65% of the hourly laser running and maintenance costs being associated with nitrogen gas usage.
Further reading
Nitrogen generator cuts laser consumption costs
Subcontractor purchased a nitrogen generator to replace an expensive manifold cylinder pack supply and has had no customer complaints due to edge quality, no breakdowns, or 'gas-outs'.
Sheet metal parts deburred and rounded off
One of two machines for oxide removal and deburring of sheet metal parts can deburr and edge round both sides of sheet metal components in a single pass, including all the internal contours.
Sheet metal parts deburred in one pass
Sheet metal deburring machine is capable of deburring and edge rounding both sides of sheet metal components in a single pass, including all the internal contours.
In such cases the cost of the gas makes a significant contribution to the overall economics of the laser process.
For instance if we take the following example of a 6mm stainless steel component produced on a 3000W laser with nitrogen supplied via MCP (Bottled Manifold Cylinder Pack).
Bearing in mind that gas costs and overall laser running costs vary greatly dependant on type of laser cutting machine used and also gas volume usage, discounts, etc, the above simply serves as a representation for estimating purposes.
It is important to point out that for thicker stainless steel, that nitrogen gas costs could be as high as 90% of the hourly running costs.
Part size - 126mm x 100mm.
Material - 6.0mm thick stainless steel.
Cutting time - 46s.
Cutting speed - 1.5m/min.
Laser machine running cost per 100 parts - including electricity, consumables, maintenance, labour, laser gas - GBP 18.10.
Bottled nitrogen cost - GBP 35.75, Total cost - GBP 53.85 Nitrogen is 66% of the hourly laser running cost.
* How can nitrogen gas costs be reduced? - Although some improvements can be made through negotiating gas, delivery and rental charges with gas suppliers and even replacing conventional MCPs with bulk liquid storage, etc, not all options are available to everyone; in particular, space and access restrictions can make bulk storage impractical.
An alternative, which is becoming more common place within the laser cutting industry, is the use of nitrogen generation equipment, which for the example illustrated above, would see nitrogen gas costs reduced from GBP 35.75 to just GBP 3.50, a saving of 90%.
* Nitrogen generation principle - a typical system layout uses the pressure swing adsorption principle, a continuous flow of nitrogen is produced from compressed air.
In the case of an R2 GAS Generator, extruded aluminium towers, filled with a carbon molecular sieve (CMS) are used to adsorb the oxygen from the compressed air.
With nitrogen being 78% of the composition of air at the outset, the adsorption of unwanted oxygen is relatively quick and simple.
* Nitrogen purity and flow rates - the single biggest misconception of nitrogen generation relates to the purities, flow rate and pressure of nitrogen as well as the options for future expansion.
We should address all these points individually.
* Purity - although it is the case that some generators can only produce nitrogen at a purity of 99.95% (500 ppm oxygen) this is not the case with all systems.
For instance R2 GAS Nitrogen Generators have variable nitrogen purities to 99.995% (50 ppm).
Another misconception is that higher purities similar to that obtained in bottles or liquid bulk storage are required when laser cutting.
For the majority of material thickness' this simply is not the case, it can be demonstrated for instance that 3mm stainless steel cut with nitrogen at a low purity of 99.95% gives an edge quality with an identical appearance to that achieved with bottle gas.
Likewise by setting the generator to a higher purity of say 99.99% an identical scenario is achieved in 6mm+ thickness stainless steel.
* Flow rates - flow rates generally are never a problem.
A single generator is able to supply gas to up to three laser cutting machines cutting 10mm stainless steel simultaneously.
Ultimately the flow rate achievable is related to the purity of gas required.
For example, a typical mid size generator can supply gas with a purity of 99.95% at a flow rate of 61Nm3/h, but if a higher purity of 99.99% is required the flow rate is reduced to 38Nm3/h.
* Stored gas pressure - typically gas is stored high pressure at around 42 bar, which is more than adequate for all major CO2 laser system manufacturers.
* Future Expansion - it would be fair to say that not all nitrogen generators, offer a simple means of expansion if usage increases significantly, i e, change in work pattern or addition of a new machine.
* Aluminium towers - in the case of an R2 GAS Nitrogen Generator this is not the case, the initial system is specified with room for cost effective expansion, with the simple addition of one or more pairs of aluminium towers.
* Laser cutting advantages - low cost nitrogen, typically GBP 0.04/m3 gas.
* Suitable for all thicknesses of stainless steel and aluminium.
* Continuous 24h operation, * No machine downtime for changing gas.
* No unexpected running out of gas, especially weekends.
* No disruptive gas deliveries to accommodate.
* No gas waste with MCP's returned partially full.
* No gas rental, delivery charges or restrictive gas supply contracts.
* Enables high power lasers to cut mild steel faster and cheaper than oxygen cutting, with an 'oxide free' edge.
* The laser user takes complete control of the Nitrogen supply process.
* Summary In the past, laser users were restricted to either bottled or cryogenic nitrogen supply.
However, with an increasing number of laser users taking advantage of the benefits listed above and realising considerable savings on nitrogen costs, 'in house' Nitrogen production is proving to be a viable and cost effective alternative.
* About the author - Neil Jackson is with manufacturing Service Solutions (MSS) and produced 'In House' Nitrogen Generation ( an extract from Association Of Industrial Laser Users 10th Anniversary Magazine - Oct 2005).
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