When selecting a suitable air plasma arc power supply, it is important to consider several key criteria.
To achieve the maximum financial and performance benefit from an air plasma arc power supply, analyse the following prior to making a purchase.
As in the case of many tools and devices, making the right choice is important, taking time to compare purchase cost, performance, job site suitability and running costs prior to purchase can save having regrets when its too late, with Thermacuts® guidance, making the right choice is less of a minefield.
Decide on what the intended use of the plasma power supply will be, manual cutting, gouging, machine or combined cutting applications.
TYPE OF MATERIAL TO BE CUT
The most common material types that are cut using the air plasma arc process are: Carbon steels, Stainless Steels, Nickel alloys, Aluminium etc. The air plasma arc process can be used to separate any conductive material.
DURATION OF THE CUT
An important factor to consider is the duration of the cut especially when using an automated or CNC process. The maximum duration of the cut is determined by the duty cycle of the power supply, when the duty cycle is exceeded, the power supply shuts down to protect itself from overheating, after a cooling down period work can resume. An 80% duty cycle is considerd to be an excellent performance, then there is the 100% duty cycle EX-TRAFIRE® 75SD. Non-stop cutting, No down time, No frustration.
Information on the duty cycle is stated in the EX-TRAFIRE® catalogue for every power supply type, or see the specifications in the manuals.
THICKNESS CUTTING RANGE
For manual cutting, the recommendation is to select the power supply with the closest performance specification for the range of material to be cut. (This is identified as "material thickness" in the cut charts.)
When chosing a power supply for machine cutting, consider the material thickness to be cut and compare it to the mid-range value on the cut chart. Below is an example taken from the FHT-EX®105RTX torch operator manual.
The customer frequently cuts 10 mm thick Mild Steel and occasionally 20 mm thick Mild Steel.
The 75 A cut chart in the operator manual for the FHT-EX®105RTX torch indicates that the 10 mm thickness is a mid-range value, whereas the 20 mm thickness is close to the bottom of the cut chart.
Review of the 100 A cut chart in the FHT-EX®105RTX torch operator manual shows the 20 mm thick Mild Steel in the mid-range of the cut chart. Based on this information, the EX-TRAFIRE® 100SD power supply is the most "Fit for purpose" option as it covers the customers need to cut 10 mm and 20 mm Mild Steel. By using the cut chart amperage and thickness values, cut quality and system performance will be opitimised.
What else to remember?
BREAKER TYPE AND VALUE
A "C" type breaker is recommended. Check the Specification table in the operator manual for the I1 RMS current value and choose the next highest nominal breaker value.
Ensure that the electrical connection (input voltage, circuit breaker) comply with the specification of the intended plasma power supply (see the operator manual – Chapter: Specification). Where the electrical input is not suitable, the options are to modify the electrical input or to use an alternative plasma power supply.
COMPRESSED AIR FEED TO THE POWER SUPPLY
The minimum internal diameter of the air hose or tubing that can be used for the feed to the power supply is 8 mm (I/D = D8). The recommended air pressure from the compressor/distribution network is 7-8 bar, however 6 bar is the minimum.
USE OF EXTENSION CABLE
In the event that a mains input power cable extension is required for the EXTRAFIRE®45SD, 55SD, 75SD and 100SD three-phase power supplies, it is advisable that the extension cable is the "armoured" type with a minimum wire cross section of 6 mm2 for lengths up to 15 m, and a wire cross section of 10 mm2 for lengths over 15 m.
Single-phase power supplies, EX-TRAFIRE®30H, 40SD and 45SD require an extension cable with a wire cross section of at least 2.5 mm2.
SETTING THE VOLTAGE DIVIDER RATIO OF THE PORTAL FOR MACHINE CUTTING
There is a DC voltage present between the electrode (hafnium insert) and the material to be cut. The voltage value depends on the distance between the hafnium insert and the material to be cut. The greater the gap, the higher the voltage. For example: When a distorted or uneven sheet of metal is to be cut and the operator sets the value of 140 V on the portal in accordance with the cut chart (which can for example equate to a 2.8 mm torch to work distance). When performing the cutting, the torch moves up and down following the contours of the material in order to maintain the set distance between the torch and the material. The portal cannot read the voltage value of 140 V, therefore the divider must divide the voltage in a given ratio (50:1, 40:1: 20:1 etc.) so that the portal can read the voltage. (the voltage value can have a critical influence on cut quality and consumable life - see the cutting charts)EX-TRAFIRE® power supplies are pre-set at the ratio of 50:1 (this value is also used for the EX-TRACK® mobile cutting system).
Where an alternative divider ratio is required, this can be easily set using the DIP switches as shown in the operator manual.
Some portals need a real arc voltage value (for example, the above mentioned 140 V). It is not technically possible to set such a ratio directly on the voltage divider from the power supply nor to take it from the CNC connector on the rear side of the power supply. What is possible, is to take this voltage directly from the power supply - namely from the work cable and the power line on TCS connector.
CONNECTING A CNC CABLE BETWEEN THE POWER SUPPLY AND THE PORTAL
The connecting CNC cable is not included with the power supply package. In most cases it is supplied with the portal. In the event that a CNC connection cable is required, it can be ordered as an accessory under the part number EX-0-803-004 with a cable length of 6 m.
We also recommend other related articles called "Package content of EX-TRAFIRE® sets" and "Competitive advantages of EX-TRAFIRE® plasma power supplies".
Text: Thermacut, k. s.
Photo: archive of Thermacut, k. s.