Critical to quality physical dimensions of pharma glass vials - Part 2. Flange and body OD

Hello everyone – I briefly covered the concept of Critical to Quality (CTQ) dimensions of pharmaceutical glass vials in Part 1 of this new series.? We will now go on to consider each of these CTQ dimensions, including how they can be measured for the purpose of quality control (see Footnote 1). ?

I’ll actually be covering two dimensions in this post, flange outer diameter (OD) and body OD, given that the measurement approach is essentially identical.? In both cases, we are measuring a feature that is ideally a perfect circle.? The circularity of the vial body is largely dictated by the incoming glass tubing, while the flange geometry is directly controlled by the converting process.? The OD of the vial body is a CTQ because it strongly impacts handling behavior during fill-finish manufacturing.? For example, format parts (a.k.a. change parts) such as star wheels, screw feeds, etc. responsible for conveying vials through various steps of the process assume a particular vial outer diameter to properly function (see Footnote 2).? The outer diameter of the flange is a CTQ because of its potential impact on the performance of the stopper and seal components that are used to create a sterile container-closure system (see Footnote 3).?

The OD of the vial body and flange can be readily measured with a caliper. ?Let’s do a quick overview if you’ve never used a caliper.? Figure 1 is a photo of my personal digital caliper (Footnote 4).? It works great but seems to gets me stopped at airport security when I choose to pack it for training classes (see Footnote 5).? The portion of the caliper with a digital display is capable of sliding along the linear scale marked with distances in millimeters and inches.? Doing so simultaneously adjusts the positions of all three measurement elements: 1) the external jaws, 2) the internal jaws, and 3) the depth rod (see Footnote 6).? The external jaws (the element with flat surfaces pointing inwards) will be used to measure the flange and body OD.? The internal jaws (the element with knife edge surfaces pointing outwards) can be used to measure the flange inner diameter – more on this in a future post.? The depth rod can hypothetically be used for measuring bottom concavity, although that’s not technically a CTQ that falls within our topical series.? Perhaps that will be a bonus post.? The “Zero” button can be useful for cases in which we want to create a reference point at a distance other than the fully closed position. ?We can assume that will not be necessary in our case.

Let’s begin by measuring the flange OD. ?We loosen the locking screw and open up the external jaws with the aid of the thumb wheel to a distance that exceeds what we intend to measure.? Figure 2 shows a 2R vial that has been inverted to rest on a table; the caliper is also resting on the table.? This method helps ensure the external jaws are parallel to the datum feature of interest.? It’s also possible to keep the vial upright by using a block to elevate the caliper to an appropriate height for measuring the flange.? However, I’m partial to inverting the vial for the sake of simplicity.? Also note that the vial is positioned well within the depth of the external jaws so that it is engaging with the flat jaw surfaces (as opposed to the thinner, wedge-shaped tips of the external jaws).? The external jaws of the caliper are gently closed until firm contact is made with the flange and the result is recorded.? It’s typical practice to then open the jaws, rotate the vial, and repeat the measurement some number of times.? What’s the right number of repetitions?? There’s no single correct answer here.? I’ll reiterate what’s been said in other posts – it’s always important to align with your supplier on quality standards.?

Measuring the body OD can look very similar to Figure 2, in principle.? We flip the vial back onto its bottom, place the caliper on the flat surface, and once again gently close the external jaws to make firm contact with the vial body as shown in Figure 3.? One potential watchout is the location of the external jaws relative to the vertical axis of the vial.? The most recent post of my “Pharma Glass Defects” covered the “Flared Bottom” and “Flared Shoulder” defects.? You’ll notice in Figure 3 that the external jaws are at a point that might capture flaring at the heel region.? If you want to be more thorough, it might be wise to use additional blocks that elevate the calipers to heights that are mid-way along the body and at body/shoulder transition to catch shoulder flaring (see Footnote 8).

Questions or comments?? Please leave them below of feel free to directly contact me.

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Footnotes

1.?????? I’m specifically calling out quality control here because the systems used to measure dimensional conformance of vials in real time during manufacturing will be quite different from what we are covering here.

2.?????? There are five different nominal body outer diameters that appear in the dimensional specifications for converted tubular vials as defined in ISO 8362-1: 16 mm (2R, 3R, and 4R formats), 22 mm (6R and 8R formats), 24 mm, 30 mm (20R, 25R, and 30R formats), 40 mm (50R), and 47 mm (100R).? The ability of one tubing size to cover multiple vial formats provides a manufacturing advantage for converted tubular vials relative to molded vials that require a unique set of tooling for each format.

3.?????? ISO format converted tubular vials rely on just two nominal flange outer diameters – 13 mm (2R, 3R, and 4R) and 20 mm (6R and up).

4.?????? There is more than one type of caliper out there – Vernier, dial, digital, etc.? The digital caliper is by far the easiest to use, but any readers out there who know how to properly read a Vernier caliper get bonus points.

5.?????? This caliper can record distances in millimeters to a resolution of 0.01 mm.? There is a “Rule of 10” stating that a measuring device should have a resolution that is at least ten times smaller than the tolerance of interest.? In this case, the tolerance range for body and flange OD can extend to the hundredth decimal place.? I technically shouldn’t be using this caliper to make ?measurements for evaluating whether a part is in spec, but it’s fine for purposes of demonstration.? Anyone with a spare caliper of higher precision is more than welcome to send it my way. ??

6.?????? I’m actually ignoring a fourth measuring element.? The leading fixed edge of the caliper can be used with the sliding portion of the interior jaws to perform a step measurement, but it’s not relevant to our current discussion.

7.?????? You’ll find related terms used to describe the same features labeled in Figure 1.? For example: - External jaws = exterior jaws, outside jaws, lower jaws, etc. – the word “jaws” might also be replaced with “beak” or “claw” - Internal jaws = interior jaws, inside jaws, upper jaws, etc. - Locking screw = set screw, clamp screw, limit screw, lock nut, etc. - Beam = blade – you’ll also find reference to a scale, although I would say that more appropriately refers to the graduations (millimeters and/or inches) marked on the beam - Thumb wheel = thumb screw, thumb grip, pushing roller, etc. - Depth rod = depth blade, depth gauge, depth bar

8. As an alternative to resting the caliper on flat blocks, you could also revert to holding the caliper manually with the understanding that this can introduce more variability.? Another alternative is to use a ring gauge instead of a caliper to check body OD.? I’ll likely discuss go/no go gauges (of which ring gauges are one variety) in a future post.