Thanks for your question. Impact testing was first carried out on metals and those tests were adapted to plastics. You are correct in saying that charpy is the test most often used when testing metals but it is not unheard of to do a metals izod or even a metals tensile impact test. Also, both charpy and izod are used for testing plastics. Izod historically has been the test of choice here in the US but the rest of the world tends to favor charpy testing according to ISO 179. In the past decade, more US users have started to use charpy testing, particularly those that supply the automotive industry. The auto industry is global in nature so 10-15 years ago they didn’t want data from 2 tests so they selected the ISO charpy test since it was in use globally. The point of the notch in the specimen is to try to get it to break in the same spot. For izod, the notch faces the striker so that you get a hinge type breaking action. For charpy you are getting a three point bend type action on the specimen. Hope this helps. Regards, Harry

I was researching the difference between the Charpy impact test and the Izod impact testing and I was wondering why the notches face different directions for the two test. Most literature say the Izod testing is for plastics and the Charpy testing is for metals. Is there a significant reason for why the notch for the Izod test faces away from the striker compared to the Charpy test?

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ASTM D638 does reference a Poisson's Ratio test which is similar to the N-value test. ASTM D20.10 ran a round robin a year or so ago and I know the results were pretty scattered among the participating labs. I believe the next revision of D638 will remove reference to the Poisson's Ratio test in the main body of the standard, but it will reference it in the appendix section of the standard incase anybody wants to use it. Hope this helps!

Harry, Is there an equivalent test for Plastic products that would be similar to N-Vlaue in the testing of metals?

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ASTM requires the operator to fill the bore, insert the piston and start the test within a minute. As soon as it is finished, the test is started on the machine and the preheat countdown begins. Generally, ASTM D1238 requires 420 seconds +/- 30 seconds for the pre-heat period but that can be overruled in the materials specification if there is one.

Harry, how much time do I have to fill the Melt Indexer Barrel and start the test in a Method A Test. I have heard 60 Seconds to fill and then wait 300 Seconds or 420 Seconds. What is the proper procedure?

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Hi Thanks for your question. Unfortunately I don't have any experience in the analytical testing side. My experience is mainly based on physical and mechanical testing.

Harry how can i detect the percentage of PVC content in PET grinded? we are a recycling company look for improve our quality control lab?

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You should be able to see them now. There was a technical issue with our server.

why I can't see the answers when I click on the questions?

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Thanks for your question. I spoke with a collegue at ASTM D20 who works with polyethlene. He told me that it is a common test in the industry (and PP as well) but there are a number of different molds and procedures. There is no standardized procedure in ASTM for the test. I'm not sure about ISO. I'll check on that and if I find something, I'll let you know. Thanks again. HEY

Dear Harry is there any standard for measuring the spiral flow of polyethylene

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What you read is correct. Over-tightening grips is a common mistake many users make when trying top prevent specimen slippage when using mechanical wedge grips. Unfortunately, over-tightening wedge grips is not really an effective way to prevent test specimen slippage. In fact it can damage the grip and exert unwanted load on the specimen Mechanical wedge grips are designed to be self-tightening – the higher the tensile load, the harder the jaw faces squeeze in on the specimen. When a tension force is applied to the specimen, the tension force causes the specimen to pull downward on the jaw faces (provided there is good bite between the jaw faces and the specimen). The faces slide down through the grip body along the wedge path causing them to squeeze the specimen. Users can further minimize slippage by improving the bite through the use of proper jaw faces, ensuring the specimen contacts at least 2/3rds of the grip faces and that the faces are clean and in good condition. Grip faces are consumable items and should be replaced when damaged.

I have TO HW12 wedge grips and read somewhere that specimen slippage is not necessarily eliminated by heavily tightening the grips?

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Instruction manuals are available from Tinius Olsen. Please contact your salesman or call TO's Production Department at 215-675-7100. Thanks.

How can I get a operator manual for Extruder Plastometer MP600?

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Hi. Thanks for your question. There are many different potential causes of variation in melt flow results. I would need to know more details. In the meantime, if you consult the Appendix of ASTM D1238, you will find a troubleshooting guide which you may find helpful. Thanks again.

Hi harry. I am doing my university project now. I was facing a problem in my MFI testing Method A. I keep on getting results which are greatly differ from each others, since every parameter in the test is remain the same. The results are very unstable. Why will this happen?

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Thanks for the question and sorry for the delay in answering. Generally speaking, measuring the flexural strength gives an indication of a materials resistance to bending under a load. The test methods most often used for plastics are ASTM D790 and ISO 178. Tensile strength is an indication of a materials resistance to being pulled apart. A tensile test generates a stress/strain curve which is used to determine tensile modulus which can provide an indication of how much a material will stretch before it breaks. The test methods most often used for tensile testing of plastics are ASTM D638 and ISO 527. I recognize that these are rather simple explanations but rather that go into a lot of detail here, I suggest that you obtain a good reference book. You will find a book called The Basics of Testing Plastics, edited by Stephen Driscoll, to be an excellent reference guide. It is available from www.astm.org. ASTM Stock #MNL35. Hope this help.

Hi harry. I would like to know what the differences between flexural and tensile strength and modulus? Is it the similar of them?

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Thanks for your question, Mark. In HDT and Vicat machine, temperature accuracy can refer to both the temperature measurement and ramp rate control. For HDT testing, the ramp rate for ASTM D648 is 2oC +/- 0.2oC/minute and is considered to be met if the temperature of the heat transfer medium (usually silicon oil) is made rise 10o C +/- 1o C every 5 minutes until the maximum temperature is reached. ISO 75 has essentially the same requirement but it is stated as 120o C +/- 10oC/hour and is considered met if the temperature of the heat transfer medium is made to rise 12oC +/- 1oC /6 min For vicat testing, there are 2 ramp rates for ASTM D1525. Rate A is 50oC +/- 5oC /hour, which considered to be met if the heat transfer medium is made to rise 10oC +/- 1oC every 12 minutes. Rate B is 120oC +/- 10oC/hour which considered to be met if the heat transfer medium is made to rise 12oC +/- 1oC /6 min. ISO 306, also has 2 rates, 50oC +/- 5oC /hour (5oC +/- 0.5oC /6 min) and 120oC +/- 10oC/hour (12oC +/- 1oC /6 min) For the temperature measurement system (probe & readout), ASTM D648 requires and accuracy of at least +/- 0.5oC. The Tinius Olsen 603 HDTM and 303HDTM meet this requirement with the use of individual RTD’s located by the specimen in each test frame. You may hear someone refer to temperature gradient, which is the difference in temperature displayed for a test frame vs. the temperature displayed on a test frame at the opposite side of the bath. There is no requirement for this in either the ASTM or the ISO standards for temperature gradient. It is usually a function of heat transfer medium viscosity, bath circulation and temperature. Bath temperature gradients generally do not affect test results. Typically, when the test is first started and the heat transfer medium is at room temperature, you may see some variability from test station to test station. However, any temperature gradient between stations usually goes away quickly after the heat transfer media warms and circulation starts. Also, all TO equipment produced since 1994 has an RTD at each individual station to monitor and record the temperature of penetration or deflection of each individual specimen under test. Hope this helps.

Hi Harry Can you please tell me the temperature accuracy of the Tinius Olsen HDT, I know the resolution is 0.1degree C but I need the accuarcy

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Thanks for the question. I assume that you are trying to determine the uncertainty of your melt flow test, and I will base my answer on that assumption. Melt index is not a fundamental physical property. The test result obtained is dependent on the metrological specifications and the method of testing contained in the test method followed. Tinius Olsen's Quality System is based on ISO Guide 17025. Note 2 under paragraph 5.4.6.2 of ISO 17025 states, “In those cases where a well-recognized test method specifies limits to the values of the major sources of uncertainty of measurement and specifies the form of presentation of calculated results, the laboratory is considered to have satisfied this clause by following the test method and reporting instructions (see 5.10).“ ASTM and ISO Test methods are written so that the variability in test results within and between laboratories is controlled. By having your machine calibrated to ensure that it meets metrological requirements of ASTM D1238 and testing and reporting in accordance with ASTM D1238, we believe you fulfill and meet the intent of ISO 17025 paragraph 5.4.6.2 and Note 2. As stated earlier, Tinius Olsen operates in accordance with ISO 17025. Because we provide a calibration service, we are required to determine the uncertainty of our indivisual measurements (see ISO 17025 paragraph 5.4.6.1). We include them on our certificates because some of our customers have asked for them. However, there is no recognized way to translate the uncertainties given on our calibration certificate to the uncertainty of a melt index test. While you probably cannot determine the uncertainty of your melt index tests, we believe it can be beneficial to do control tests on a material to determine your repeatability over time and with your various operators. Proficiency testing with other laboratories can also be useful to access your reproducibility. You can refer to the back of ASTM D1238 for a troubleshooting guide which may give you an idea where to look for a source of variation in your test results. Hope this helps!

Hi Harry, I did the statistical study (Within the lab repeatability and reprocibality) in our lab for MFR usin MP600 extrusion plastometer. But the results found are veriating from 5 to 10%. It is known that the variation is contributed from sample, operator, equipment, Method of testing, etc. What is the equipment contribution in this variation.

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Hi guys - Thanks for the question. I'm very sorry for the delay in getting back to you. A melt indexer is one of the more economical ways of determining flow rates of plastics.

Harry, We are a small recycling company and have need of a device to test plastics for different grades. i.e. injection grade HDPE, HMW, ect. Is a melt flow index tester what we need, or is there a more economical product we can use? Thanks

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