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Technical Tips

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Concrete Compression Testing Machines


Maximum piston travel should be kept to a minimum, allowing more of the cylinder to support the piston.  If you over-extend the piston, first try to let it retract on its own. If this is not successful, you should contact us or the manufacturer for further assistance.  Most manufacturers have a maximum travel of 2 1/2", please refer to your operators manual or Contact us for your particular application.

Compression Platens or steel bearing blocks
--ASTM & AASHTO specifications (C-39 & T 22) state the machine shall be equipped with two steel bearing blocks with hardened faces (not less than 55HRC), one of which is spherically seated that will bear on the upper surface of the specimen and the other on which the specimen shall rest.  There faces shall have a minimum dimension at least 3 percent greater than the diameter of the specimen to be tested.  Except for the concentric circles, the faces shall be plane within 0.001" in any 6 inches.  If  there are any nicks or dents in the plate or if you can take a 6" straight edge and fit a 0.001" thick feeler gauge under it, the platen is out of tolerance.  Most platens can be re-surfaced, providing the imperfection are not so large that you grind out the hardened face or targets. Contact  your Ad-Tek Service Technician to replace or have your platens re-surfaced.

Any testing machine that has threaded tie rods should be checked periodically for loose nuts.
  If excessively loose they can cause inaccurate test results and permanent damage to your machine.  Our AD-TEK technicians routinely check them when they perform an annual calibration.

Rate of Loading
-- ASTM & AASHTO specifications (C-39 & T 22) state the rate of loading shall be applied continuously and without shock at a rate of 20 to 50 psi per second.  During the application of the first half of the anticipated loading phase a higher rate of loading shall be permitted.  Make it easy on yourself; load the first half of the test in fast advance then set up a number that you can easily see on your machine. 20 to 50 psi / sec. on a 6" dia. cylinder is 565 to 1414 lbf / sec.  Most machines have 1,000 lbf increments, use this as your loading rate, it's easy to see and falls within the specification.  20 to 50 psi / sec on a 4" dia. cylinder is 251 to 628 lbf / sec., 500 lbf / sec or 1000 lbf / for 2 seconds meets the criteria.  Using these calculations for all of your samples makes it easier and more consistent for your technicians.

Often the question comes up, "When should I have my testing machine calibrated?"  According to the ASTM & AASHTO specifications (E-4 & T 67):  It is recommended that testing machines be verified annually or more frequently if required.  In no case shall the time interval between verifications exceed 18 months.  Testing machines shall be verified immediately after repairs that may in any way affect the operation of the weighing system or the values displayed.  Verification is required immediately after a testing machine is relocated and whenever there is a reason to doubt the accuracy of the force indicating system, regardless of the time interval since the last verification.  Please read the specifications that are pertaining to your specific tests; ASTM E-4 and AASHTO T 67 meet the majority.

Preventative maintenance is the preferred medicine for your equipment. For example:

--Most testing machines, on the average, should have their hydraulic fluid changed & filter serviced after 600 hours of use. Contact your Ad-Tek Service Technician for the recommended maintenance schedule & proper fluid type for your machine.

--the upper spherical should be disassembled, cleaned, and re-lubricated on a regular basis to avoid damage or unnecessary replacement.

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--FURNACE WON'T SHUT DOWN.  If your furnace is still running (in burn mode) after two hours or an abnormally long burn time, you should push the stop/start button and investigate.  The furnace is not receiving a stable weight from the scale.  This is caused by one of the following:  1) The baskets are rubbing a wall or the door.  2) The ceramic insulators are rubbing the edges of the holes.  3) The furnace itself is not stable or is not level.  4) A scale or logic board has failed.  Please keep in mind NEVER OPEN THE DOOR IF YOU SUSPECT THE SAMPLE IS STILL BURNING!!  This can cause a serious injury or even death.  Please use caution, if you have questions please call us.

--PRINTER ERRORS.  There are several reasons for a printer not to print.  Make sure the paper is loaded properly.  On the early models, there is a black rocker switch located on the front lower panel, this switch commonly goes out and was eliminated on the newer models.  Disconnect the two wires leading to the back of the switch and connect them together.  If you have a newer furnace, the ribbon cable and its connections should be check.  If this fails Contact  us here at Ad-Tek where we have trained technicians on staff to diagnose and repair your furnace.  You most likely need a new printer or logic board.

--"ERROR CODE 8" (one of the more common error codes).  This error occurs when the furnace receives an inaccurate signal from the scale.  The first things to check are:  1) Cable connections both on the scale and on the logic board. 2) Damaged cables. 3) Hearth plate and ceramic insulators located in the center and not rubbing anything.  After checking these items out try performing a "hidden key 2", reset to factory defaults.  A "hidden key 2" is performed by turning off the furnace, holding down the 2 key while turning the furnace on.  Please note:  This will reset the furnace back to all factory defaults i.e. chamber temperature, filter temperature, sample weight, and calibration factor, just to name a few.  If this fails Contact  us here at Ad-Tek where we have trained technicians on staff to diagnose and repair your furnace.  You more than likely need a new scale or logic board.

--One of the most important things to remember on a Barnstead Thermolyne ignition furnace is to exhaust it properly.  The factory recommends using the appropriate exhaust tubing, connect the tubing from the exhaust port at the top of the furnace case to an appropriate negative pressure exhaust system.  Failure to connect the exhaust port to an adequate exhaust system will result in smoke and gases to enter the work area.  We have seen exhaust systems that appeared to be proper in the lab or trailer, until :  A exhaust fan or a hood was turned on.  This causes the gases, smoke and extreme heat to flow the wrong direction in the furnace.  It will damage the furnace and possibly cause a heath hazard.  If you are going to use a exhaust fan please make sure there is plenty of free air for it to draft from, a window or door open should be enough.

--The Barnstead Thermolyne ignition furnace has many built in safeties.  Most of these safeties, if triggered, will display an error code to help diagnose the problem.  Sometimes these error codes are displayed due to a software glitch.  By performing a "hidden key 2", reset to factory defaults, the software is reloaded from the e-proms and the glitch is gone.  A "hidden key 2" is performed by turning off the furnace, holding down the 2 key while turning the furnace on.  Please note:  This will reset the furnace back to all factory defaults i.e. chamber temperature, filter temperature, sample weight, and calibration factor, just to name a few.

--Is your Barnstead Thermolyne ignition furnace taking longer than normal to warm up?  The average furnace chamber warms up to 538° C within 2 hours and the filter temp up to 750° C within 3 hours.  If your furnace is taking a bit longer or is not reaching it's set point at all, it could be suffering from a bad heating element.   Contact  us here at Ad-Tek where we have trained technicians on staff to diagnose & repair your furnace.

--If your Barnstead/Thermolyne NCAT ignition furnace will not start up in cold weather, here is the solution: When the indicating temperature is 0° C, the furnace will not start. Light a match or lighter, warm up the thermocouple located inside the ignition chamber until it indicates above 0° C, close the door and your furnace should start right up.

Watch for other helpful tech-tips from AD-TEK technicians on this page.

 
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