Wednesday 23 May 2012

Special torque applications: dental abrasive disks

Abrasive discs are used by dental technicians to sculpt and polish dentures. The discs are spun on the technician’s motorised hand piece at speeds of up to 20000 rpm. The abrasive surface applies sculpting and polishing friction, so high torque loads are normal. In order to reduce the possibility of the disc’s two parts – centre ring and abrasive disc – separating during use, the manufacturer wanted to test the torque performance of the join between them.

The specially made adaptor/jig fits directly over the rotating drive shaft of the Vortex-i torque tester to hold the sample securely and centrally, so that drive-shaft and centre ring are exactly aligned. Once the disc is placed in the recessed holding plate (reversible to accommodate the two sizes that the disc comes in), the clamp plate is screwed down over it. A probe, which is connected to the torque-sensing transducer, is lowered till its point penetrates the centre ring and can travel no further.

This video introduces the adaptor and shows the test being set up.

The test is designed to test to destruction the join between the centre ring and the abrasive disc. Pressure from the clamp plate ensures the abrasive disc does not spin inside the jig but rotates in unison with the jig.

The jig is rotated to 90 degrees clockwise and then 180 degrees anti-clockwise. If the centre ring and abrasive disk remain aligned (the radial marking will indicate this), the join between them is good and the disc passes the test. If the quality of join between centre ring and disk is insufficient, the centre ring will rotate independently of the disc and the sample will fail.

In this picture, the post-test misalignment of the markings on the disc indicate that the outer abrasive disk has slipped around the centre ring, so this sample has failed. The torque data is exported via the Vortex-i’s RS232 port to the PC for monitoring, analysis, and storage.

Packaging: bottle cap torque testing

Torque testing of PET bottle closures is performed to identify the torque required to open a closed cap. Systematic testing informs line managers that their capping machines are applying sufficient torque to produce the necessary degree of seal - but not excessive torque, which would make opening difficult.
"Spinners" are an unwanted occurrence in capping and can be caused by materials or excessive capping torque. Normal spinners are of two types:
  1. Following slip (initial break) torque, the cap's bridges do not break and the cap spins around the thread but is not separable from the bottle, resulting in a bottle whose cap is unscrewed but still attached.
  2. When closure torque is applied, the lid or cap does not bind to the thread and come to rest creating a tight seal, but continues to travel. The cap spins around the thread and returns to its state prior to tightening. Subsequent tightening results in the same.
Testing closure torque alerts managers to such problems, saving costs resulting from waste, downtime, and returns.

An Orbis torque tester is ideal for simple pass/fail closure torque tests. The following describes a typical test procedure:

  • An acceptable torque range is defined by registering minimum and maximum torque values (1 and 1.5 N, for example) on the Orbis. For enclosure opening tests, counter clockwise is specified (clockwise if measuring tightening torque).
  • The user places the bottle on the platen, then winds in the pegs to grip it securely. This prevents the bottle rather than the cap rotating when torque is applied.
  • The user zeros the display to cancel any torque detected during placement of the bottle, and then twists the cap in a counter-clockwise direction as if opening the bottle normally.
  • The Orbis detects the peak torque and reports this as the torque required to open the container. If this reading is between the minimum and maximum, the sample passes. If the torque required to open the container is outside the specified range (i.e. above the maximum or below the minimum), the sample fails. The torque reading will reveal if insufficient or excessive torque was applied by the capping machines. If several samples fail, a production line supervisor would call a technician to increase or decrease the torque exerted by the capping machines.
The Tornado torque tester is capable of all the functions of the Orbis, but has an additional, vital function: tamper evident testing.

Tamper-evident closures are a standard quality feature of beverage bottles and containers of other liquids that would degrade if adulterated or exposed. Tamper-evident closures consist of two parts - a cap and a band, which are connected by a “bridge” of regularly spaced, fine plastic tags. The content of a bottle that is capped with a tamper-evident closure can be accessed only if the cap is fully rotated counter clockwise (i.e. opened). This rotation will snap the bridge, resulting in separation of cap from band. A broken bridge provides visible evidence of prior opening or tampering.

To measure the torque required to breach a tamper-evident closure, the Tornado takes two peak torque readings: “slip torque”, which is the first and normally higher reading, and “bridge torque”, which is the second, normally lower reading. Slip torque identifies the torque required to initiate rotation of the cap around the thread of the bottle. Bridge torque identifies the torque required to initiate rupturing of the bridge. The Tornado can be easily configured to report these two torque readings.

A tamper-evident test can be quickly and easily configured with a simple push-button procedure:
  • %Tamper-evident is selected on the Tornado's menu screen, and a % selected (5% is the default - meaning the Tornado will identify a second peak when it detects a torque that is 5% below first peak)  
  • The bottle is placed on the platen and the user winds in the pegs to grip the bottle securely.
  • To cancel any torque reading resulting from bottle placement, the user zeros (resets) the Tornado.
  • The user then twists the cap and continues rotating it until the bridge is broken.
  • The first and second peak torques appear on the Tornado’s display and identify slip and bridge torque respectively.
The tamper-evident test reveals whether or not the cap can be removed and the bridge broken using pre-specified torque. Testing slip and bridge torque informs the bottlers that their product is leaving the production line properly sealed for integrity and consumer safety.

A Vortex-xt (pictured) motorized tester can provide much more sophisticated torque testing of container lids and caps. The Vortex-xt can output torque data in realtime to its touchscreen display/interface (Vortex-xt) or to a computer, where data can be displayed as a graph. Data and tests can be stored on the touchscreen or a computer for future retrieval. Test results can be overlaid for purposes of comparison. The grips and motorized rotation provide far greater sample stability and uniformity of torque, creating higher accuracy of results and reducing the influence of the variables that occur with manual, handheld testing.

Automotive: rotary selectors

A typical car dashboard features several rotary selectors. Temperature, vents, blowers, and headlights are operated by rotating dial-type switches. Automotive manufacturers test these components to determine whether the torque required to operate them is within acceptable limits.

A selector can be neither too stiff nor too slack. If too stiff, the driver will struggle to operate it efficiently and safely; if too slack, selection will be uncertain and slippage could result. Rotary selectors must also provide definite tactile feedback, to provide indication of the selector's position when visual contact is a problem, such as when the vehicle is in motion and the driver cannot be distracted. Working from carefully derived ergonomics parameters, manufacturers define torque ranges for their selectors. Samples of the finished component will undergo testing as part of the quality control process. The test will obtain measurement of the torque required to rotate the selector, so the test device must emulate the human motions involved and capture an accurate picture of the selector's torque performance.

In this photo, a rotary selector (temperature dial) is undergoing torque testing on a Vortex torque tester.
The long pegs grip the switch’s housing securely to the lower platen, so that unwanted movement does not influence the torque reading. Accurate torque measurement is possible only if the switch's axis, the tester's drive shaft, and the transducer are in direct alignment. While the alignment of transducer and drive shaft are engineered into the design of the Vortex and are unchangeable, the switch's axis is potentially variable, especially if the switch's surrounding housing is irregular in form. The housing must be held level and stable throughout the test. The holding mechanism could be component-specific or adjustable. An adjustable mechanism, such as that shown here, is a more economical solution for manufacturers who have a range of components and require short setup times and easy, simple reconfiguration of the test device. The Vortex's adjustable pegs and mounting table allow components of various shapes to be held level and central so that correct axial alignment can be achieved.

The switch's selector bar is gripped by the upper set of pegs. These upper pegs (also adjustable for neat, secure gripping of the selector bar) are fixed to a static platen and hold the selector immobile while the component housing is revolved by the lower platen. Together, these platens, via their fixtures, apply to the rotary selector the pinching and twisting motions performed by the human user.

The upper, static platen is connected to the torque-sensing transducer. The transducer reads the torque experienced by the switch during the test and sends this to a display or computer, where it is reported in graph form for analysis and stored.

(Axial alignment of stalk-mounted rotary selectors can be difficult, but the adjustable holding mechanism fitted to this Vortex-xt provides an effective solution.)

Tuesday 22 May 2012

Torque in medical: insulin pens

Insulin pens are used by diabetics to self-administer insulin shots. The user turns the cap section of the “pen” to select an insulin dosage. The pen manufacturer needs to know that the torque required to turn the cap does not exceed the ability of an ordinary user.

Dosage-identifying numbers are printed around the circumference of the cap, so selection is by rotation of the cap till the required number is aligned with the raised pointer on the body section of the pen. This rotation requires reasonable effort on the part of the user and distinct clicks provide resistance and response. The notches allow the user to select a dosage if they are experiencing vision problems or are administering in poorly lit environments.

Rotating the cap through the notches requires torque. The pen manufacturer specifies an acceptable range of torque and will conduct periodic torque testing to determine quality and uniformity of product. Insufficient torque would cause the selector to slip around too easily, complicating selection; excess torque would prevent less dexterous or weaker people selecting their insulin dosage with ease.

Testing insulin pen rotation torque requires a sophisticated torque tester. Mecmesin’s Vortex-xt (pictured) is such a device. The Vortex-xt holds the pen, gripping it between pegs at the pen’s base and cap. The Vortex-xt’s base rotates while the cap is held static under the torque transducer. This action simulates the user’s rotation of the cap and the resultant torque produces a stream of data that is reported in graph form on the touch screen display connected to the frame of the tester. The graph will identify the pen’s torque performance through one full rotation, revealing uniformity or discrepancy of torque between notches. Graphing occurs in real time, and data from multiple tests can be stored for later analysis.

Torque in pharmaceutical: childproof containers

Childproof closures are a standard safety feature of pharmaceutical containers. Their effectiveness is a critical quality concern for manufacturers of pharmaceutical packaging. These closures (caps) require accurate torque testing. They have to preserve the contents while protecting children from them, and provide accessibility to older but possibly frail persons.

Torque with Top-Load
The Vortex-xt torque tester features a weights tray that is connected by rods to the torque transducer. When loaded, the tray provides the pushdown (top-load) force necessary for simulating the manual compressive force that users apply when opening childproof caps. The platen rotates the container to simulate the user’s twisting of the cap (torque).

The Vortex-xt’s components are a torque-sensing transducer and a motor-driven platen that provides rotational motion at a specifiable speed (1-20 rpm) to a specifiable angle, time, or force (e.g. rotate to 180 degrees; rotate for N seconds or minutes; or stop at 5.5 Nm). Test results can be displayed on the touch screen (interface) attached to the stand (Vortex-xt) or exported via the RS232 port to Mecmesin’s Emperor software running on a computer. Graphing, analysis, and storage of test data are possible on either configuration.

Friday 18 May 2012

Torque testing adjustable lens dials

How is a Mecmesin torque tester helping an international optics company deliver vision to sight-challenged people in poor countries?

Adlens is a maker of adjustable lenses with an Innovation Centre in Oxford, UK. Their liquid- filled lenses allow the wearer to self-adjust the magnification of their spectacles manually. The lenses are adjusted by thumb-and-finger rotatable dials on the frame and are detachable once the correct magnification has been selected. This highly practical, low-cost optical technology provides profound benefits to vision-impaired people in less developed countries where optical services are inaccessible to many. Adlens, the innovative company behind the adjustable lens technology, use a Mecmesin Vortex-i torque tester to ascertain that the rotating components of the lenses are reliable and ergonomically acceptable.

You can find more details here.

Pot peel testing

Discover how a famous food manufacturer uses a Mecmesin peel testing device to reduce wastage resulting from seal adhesive defects and provide their customers with a safe, well sealed edible product at minimum cost. Efficient, economic peel testing of the seals of their microwavable pots reveal the force required for peeling and identify inconsistencies in the adhesive layering between seal and pot. Using their Mecmesin peel test solution, they are able to observe materials performance and adhesive layer performance in detail, store multiple tests, and overlay results for comparison purposes. The results are cost savings through elimination of excess adhesion, reduced wastage, and greater batch consistency, which translate to fewer returns, fewer customer complaints, and contribute to a successful, popular product. Full story here.

Torque testing at Água de Luso

Why does one of Portugal’s oldest and most famous mineral water companies use a Mecmesin digital torque tester? At the Água Luso bottling plant in Luso, Portugal, bottles are routinely tested for correct closure torque. Capping machines must cap bottles at a torque that provides a quality-assuring, leak-preventing seal but allows persons of ordinary strength access to the bottle’s contents. No bottler wants leakers: product is lost, transportation and storage become messy, and retailers will complain. Worse still, a degraded product could become a health hazard to the consumer, with ramifications for company image and sales. A quick, easily performable torque test provides an effective solution. Mecmesin's Tornado digital torque tester is a compact, portable, extremely usable device that offers packaging manufacturers line-side pass/fail and tamper-evident (slip and bridge torque) testing capability. Get the details here.

Whisky stopper testing

A famous Scottish whisky maker uses a specially designed, dual-function Mecmesin tester to measure the forces required to remove and reinsert a whisky bottle stopper. The Mecmesin device has been specifically configured to provide a combination of simultaneous pull/push and twist (compression/tensile and torque) forces to emulate the natural human movements involved in stopper removal and insertion. Testing stopper torque and force reassures the whisky maker that their product is unlikely to be compromised by inferior packaging. The test ensures that separation of the bar top and cork portion of the stopper does not occur, and that the cork portion will tolerate the torque and compressive/ tensile stresses it will experience during extraction and insertion. Data from the two tests, which occur concurrently, is exported to a PC, on which graphing and deep analysis can be performed.

Failure to test for stopper quality would likely result in broken stoppers that spill cork chips into the whisky, spoiling the product and damaging the company’s prestige. Since the company’s best selling lines include $1000 bottles of whisky, they rightfully take quality-assurance very seriously, and have chosen a custom-adapted MultiTest 2.5-i to assist them. Find the full story here.