High Tech/Low Tech,
(Published August 2003 in Die Casting Management magazine)
I often encounter the attitude that goes something like this, "I can't afford those high tech instruments for my operation".
Making needed repairs and adjustments result in the following:
Instrument #2: Hydraulic pressure gage.
Benefits of correcting include:
Instrument #3: Tie bar strain gage. OK, this one will cost more and you won't find one in every maintenance person's tool box, but read on. It is recommended that you purchase one for each tie bar so you can observe all four tie bars at once.
i. Reasons for loss of lock up include:
1. Blow-by in the locking cylinder
2. Regenerative valve or circuit malfunctioning
3. Inadequate hydraulic pressure
4. Machine so grossly imbalanced that it binds
5. Linkage defective
6. Tie bars adjusted improperly
7. Broken tie bar
8. Machine locks past center
9. Machine doesn't reach full forward stroke (Lost mechanical advantage)
· Reduced flash
· Improved yield
· Reduced melt loss
See free offer at the end of this article.
Instrument #4: Shot monitor
Most shops have one of these around. Not everyone uses them to the fullest advantage.
1. Measure the maximum fast shot capability
a. This is the basic information for developing PQ^2 capability
b. Test should be performed with a properly charged accumulator
c. Results should be fairly consistent from year after year
d. Acceleration to maximum velocity should begin immediately when actuated and reach full velocity within .5 to 1.5 inches depending on the maximum speed.
i. Slow acceleration can be the result of faulty directional or Pilot operated check valves.
e. Maximum velocity should be adequate for the product line of castings you produce. The machine tonnage is no indication of a required fast shot velocity. I have observed 2,500 ton machines making castings at over 200 IPS (5.08 meters/second). I have also observed 400 ton machines that could only reach 80 IPS (2.03 meters/second).
2. Measure the maximum slow shot capability
a. Maximum capability should be in excess of 30 IPS (.76 meters/second). 50 IPS (1.27 meters/second) would be a target.
b. This will also identify faulty valve performance
3. Intensifier attributes
a. Maximum pressure
b. Rise time from the end of stroke until 95% of the intensifier pressure is reached. This is measured in milliseconds and should begin immediately. A delay of 60 milliseconds before starting can result in micro porosity.
c. Hold time for the intensified pressure. Pressure should maintain for at least 10 to 15 seconds. Pressure that drops off quickly indicates blow-by and wear in the shot system.
4. Other hydraulic performance checks you can perform using a shot monitor system:
a. Connect the transducer(s) to other points in the hydraulic circuit to troubleshoot valve performance and timing. Symptoms would include pressure drops or lack of pressure at test points.
b. Examples include:
i. Pilot Operated check valves (accumulator check)
ii. Directional valves
iii. Pressure relief valves
iv. Pressure reducing valves
v. Accumulator performance
vi. Pump response
5. Capability and repeatability studies:
a. By connecting a shot monitor to trigger automatically, you can perform capability studies. This has been proven to identify sporadic problems that created seemingly random scrap. We have observed anomalies that only occurred once or twice in 3 shifts. These could only be documented by 24 hour monitoring.
While this list is by no means exhaustive, it does list many of the critical items often missed when we are asked to improve quality and productivity.
For a free customized tie bar strain gage spreadsheet contact: Bob McClintic at RMcClintic@DrDieCast.com
E-mail Bob at: RMcClintic@DrDieCast.com
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Revised: August 2017
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