Short Cycles The time it takes for the cutter to go through this cycle can be reduced only within limits since it takes a certain amount of time to power down the vacuum turbine. As the break mechanism engages, excess kinetic energy is absorbed by a break resistor and transformed into heat. There is a limit to acceptable heat build-up. If temperature levels become too elevated, the turbine will automatically shut down. The shorter the time between stoppages, the more the resistor heats up. By adding a second resistor, it is possible to reduce the total cycle time by approx. 50%. The values in the table for minimum cycle times are valid for G3 cutters equipped with vacuum turbine. If cycle times need to be minimized, testing must be done with relevant materials, using the required timings and making sure the ambient temperature is taken into account.
Cycle time t5 with 1 break resistor (standard) Material off-load and reload
Vacuum buildup
Material Processing
Vacuum stoppage
t1
t2
t3
t4
t5
Material off-load and reload
Vacuum buildup
Material Processing
Vacuum stoppage
t1
t2
t3
t4
t5 There are 4 steps in the production cycle of a cutter with vacuum generator/turbine: material off-load/reload + vacuum buildup + cutting process + vacuum stoppage Min. cycle time t5 Testparameter: t1 = 0s (without material handling), t3 = 0 (without processing)
The times needed for vacuum buildup (t2) and stoppage (t4) are not affected by adding a second resistor; the turbine will not power down faster, nor will the vacuum be reduced any quicker. For loading and unloading materials (t1), a distinction must be made between static machines and those equipped with material transport. Typically, the time it takes to automatically load material with a material transport ranges between 10 to 16 seconds, depending on cutter length as well as material transport acceleration and speed.
Vacuum turbine 1-15kW
1 break resistor (standard)
30 Seconds
60 Seconds
2 break resistors optional)
15 Seconds
30 Seconds
Specifications
Benefits
Above values represent a worst-case scenario, i.e. with the vacuum turbine running at max. performance level 10 and an ambient temperature of 40째 C/104째F.
With the addition of a 2nd break resistor, minimal cycle times can be reduced to 15-30 seconds. Since this lies within the typical time span required for automatically loading/off-loading material, the delay becomes irrelevant, which makes the vacuum turbine with 2nd resistor suitable for nearly all applications.
The lower the ambient temperature, the greater the margin for remaining below temperature levels that will trigger an automatic shut-off.
ZST-02-2010-pho/tna
Vacuum turbine 1-9kW
Savings
Cycle time t5 with 2 break resistors (optional)
If shorter cycle times (t5) are needed, the best option is to replace the turbine with a standard vacuum pump. Because of the switch-valve supplied with vacuum pumps, turning the vacuum on/off is nearly instantaneous and, therefore, no issues exist with heat generation and minimum cycle times.
The lower the level of vacuum the turbine is required to produce, the lesser the amount of heat generated by the break resistor, and thus the greater the margin for avoiding an automatic shut-off. The more porous the material being processed, the greater the resulting airflow; this helps slow down the turbine, which in turn reduces cycle times. After a cold-start, the minimum cycle time may be temporarily prolonged for the first few minutes until the turbine reaches optimum operating temperature.
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