If it's worth building, it's worth testing !!!: August 2007

Saturday, August 25, 2007

What is Melt flow testing?

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Among the first instruments plastics molders, extruders, and compounders are likely to consider when outfitting a new lab is a melt-flow indexer or “melt indexer.” Known as an extrusion plastometer in more technical jargon, this apparatus has long been used to determine the melt-flow rate or mass-flow rate (MFR) of virgin and compounded thermoplastic resins.

With the increased pressure on plastics processors to

comply with ISO 9000 standards for quality management, more of them than ever are using these instruments to evaluate incoming material and test finished products.

The melt-flow test detailed in the ASTM D1238 and ISO 1133 standards quickly measures one point on the viscosity curve under standard conditions.

While the relative simplicity of this test has remained the same, melt indexers have evolved considerably since they appeared in the 1950s. Computerization and automation have reduced operator-to-operator variables, yielding results with greater accuracy and repeatability.

Why measure melt index?

The melt indexer consists of a heated barrel and piston assembly to contain a sample of resin.

A specified load (weight) is applied to the piston, and the melted polymer is extruded through a capillary die of specific dimensions. The mass of resin, in grams, that is extruded in 10 minutes equals the MFR, expressed in units of g/10 min. (This value is also commonly called the melt index, MI, or melt-flow index, MFI.) Some instruments can also calculate the shear rate, shear stress, and viscosity in centipoise.

The basic property measured by the melt flow test is the melt viscosity or flow resistance of the polymer at a particular shear stress (related to the applied load) and temperature. Polymer chains of short length and simple geometry “slide” past one another relatively easily and offer little flow resistance. In contrast, long chains of high molecular weight and more complex structure yield greater flow resistance or viscosity.

Which method to use?

Both ASTM 1238 and ISO 1133 offer two variations of the standard melt-flow test: Method A

and Method B. Method A describes a basic manual melt indexer. It involves making “cuts” of the extrudate at timed intervals as it exits the extrusion die. The “cuts” are weighed on an analytical balance to determine the average mass and this value is extrapolated to the mass that would be extruded in 10 minutes—the MFR.

Weights range from 1.2 to 21.6 kg to permit measuring materials ranging from very low to very high viscosity (more viscous melts require more weight to force them through the die). The load and temperature to be used are determined by the material and the ASTM test method.

Whether you use method A, method B, or a combination of method A & B, the Tinius Olsen MP600 melt indexer is the model of choice for companies like Dow Chemicals, and other manufacturers worldwide.

The newly released MP200 is a lower cost alternative for compunders and companies who recycle resins.

For information please contact -
Amit Mitbawkar
Sigma Enterprises LLC - Instrumentation Division
Tel : +9714 8803100
Fax: +9714 8803101
Mobile : +97150 4450907
Email - amit_mitbawkar@sep.ae

Friday, August 24, 2007

Materials testing for the water-proofing industry.

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Customers – and sometimes even competitors – are constantly surprised at the diversity of testing programmes that can be performed with standard Tinius Olsen equipment. One of the more interesting programmes involves the waterproofing membranes applied on the roof of buildings around the world and the UAE.

With the advent of the boom in the civil industry in the UAE and number of buildings zooming up in the UAE skyline, you can imagine the amount of waterproofing that would be needed as a whole.

But making and applying these membranes on the top of these buildings is no child’s play.

These membranes have to withstand the forces of nature i.e. the extreme temperatures, humidity and of course rain. Their very function prevents the rain-water from getting into the structure of the building and ultimately into our homes.

Just how can Tinius Olsen equipment be used to test the membranes for these parameters?, read on to find out. Some of the tests performed by standard Tinius Olsen test equipment are as follows:

Tensile Strength, Elongation and Modulus of Elasticity to BS 6319 Part 7, ASTM D 412, ASTM D 638, BS 2782 – Method 320E & F, and UEATC test method.
Initial tear resistance of plastics sheets to ASTM D1004 test method.
Crack bridging strength of membranes to ASTM C836.
Puncture resistance of membranes to ASTM E154.

The high temperatures on rooftops in the UAE cause expansion in the concrete slabs on which the waterproofing membranes are applied. Therefore tensile strength and elongation are measured in both rubber and bitumen waterproofing membranes to know how much tensile forces the material can withstand and how much they are able to elongate without breaking or the appearance of defects.

Resistance to tearing is also an important parameter that needs to be measured for the plastic sheets applied on top of bitumen membranes. Bitumen is sticky in nature and therefore bitumen waterproofing membranes are covered with plastic sheets on the exposed side, hence tear resistance of this covering is a crucial parameter.

Cracks are a common defect that appear in buildings due to the stresses on load bearing faces and also as they age. These cracks aid the water leakage problems and affect the integrity of the structure as well. Waterproofing membranes are therefore required to have crack bridging capabilities which prevent water from going into the cracks. These membranes also have to be strong enough to withstand the expansion and contraction cycles that are typical to cracked structures.

Resistance to puncture is also an important parameter, as this is one of the major stresses that construction materials like waterproofing membranes are subjected to. All these factors highlight the importance to testing when manufacturing these kind of membranes. The experts at Tinius Olsen have known this for years and this reflects on the abilities of their testing machines in the ease-of-use and high testing rate of samples.

Ask the quality control department of Al Gurg Fosroc LLC, who are one of the leading manufacturers of waterproofing membranes in the UAE about the 25KN Tinius Olsen testing machine they use, to test their products. They will tell you how the QMAT PRO software allows them to accurately and quickly conduct their specialised tests thereby assuring the quality of their products.

For information please contact -

Amit Mitbawkar
Team Leader - Industrial Materials Testing
SIGMA ENTERPRISES LLC
Engineering Products Division
PO Box - 96241,
Dubai, UAE
Tel - +971 4 8851828
Fax - +971 4 8851628
Mobile - +971 50 4450907
Email – amit_mitbawkar@sep.ae
Website - www.sigma-epd.com

Tensile Testing in the paper industry

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We at Sigma are always approached by customers who want innovative solutions to their problems.

One such customer, a paper coupon manufacturer, wanted to test the

force required by children to tear apart one ticket from another before redeeming it for food or games at various playing areas in malls worldwide.

The solution offered was a fully automatic 1 KN single column Tinius Olsen Tensile testing machine with side-loading, rubber-faced vice grips to pull apart the tickets at a uniform rate and determine the maximum force required for the tickets to separate.

This particular model H1KT can test the samples independently without the use of computers and software, display the test results and online graph on the built-in display and provide detailed printouts of test reports.

The detailed test results can provide the production engineers with the data required to change production parameters easily to suit the customer's requirements.

For information please contact -

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