Caliper gauges

The extended jaws of a vernier caliper gauge are used to measure the bore or inside diameter of mbes in the same way. The bore of small diameter and capillary tubes can easily be measured with a taper gauge (Fig. 2.2). 

FIG. 2.1. (Left) (a) Vernier scale set at a reading 3.45 cm. (b) A typical Vernier caliper gauge, (c) Shows the coixect angle for accurate measurement of tube diameters, (d) An incoirect angle, which will result in enors of measurement. 

Figure 23 Recommended crimp dimensions for a 20-mm FEA standard glass bottle. H is crimp height, and d is the diameter beneath the neck as measured with a caliper gauge. 

Table 10.2 Aluminium foil caliper/gauge/area ...

Permeable intervals can be identified from a number of logging tool measurements, the most basic of which is the caliper tool. The caliper tool is used to measure the borehole diameter which, in a gauge hole, is a function of the bit size and the mudcake thickness. Mudcake will only build up across permeable sections of the borehole where mud filtrate has invaded the formation and mud solids (which are too big to enter the formation pore system) plate out on the borehole wall. Therefore the presence of mudcake implies permeability. 

Tools most commonly used for alignment procedures are dial indicators, adjustable parallels, taper gauges, feeler gauges, small-hole gauges, and outside micrometer calipers. 

Dimensions such as the width of a dumb-bell or the depth of a nick in a tear specimen will be less than 30 mm but could not be measured with a dial gauge. Because of the virtual impossibility of applying a known pressure, such measurements must be made in an essentially contactless manner. For low precision, calipers or a rule may suffice but for readings to 0.01 mm a travelling microscope or projection microscope is most suitable, and this is specified in ISO 23529 Method D and applies also to dimensions over 30mm. Projection microscopes also find use in examining profiles and for rapid swelling tests (see Chapter 16, Section 2.1). 

Computer-controlled automatic profile dies with electrical controlled sensors in closed-loop control systems have developed greater efficiency and accuracy to extrusion coating, cast film, and sheet lines. A scanner measures the web thickness and signals the computer, which then converts the readings to act on thermally actuated die bolts. The individual adjusting bolts expand or contract as ordered by the computer to control the profile. The more sophisticated systems measure adjusting bolt temperature and provide faster response time with less scrap and quicker startups. The scanner is typically an infrared, nuclear, or caliper-type gauge. 

It should be noted that combination materials are specified (from the outside inwards) by weight (g/m2), gauge or caliper. Most are made as a reel -fed operation and into sheets if required. 

Soft aluminium foil has a fairly low tensile and tear strength, so it is essential that very thin gauges are supported by paper or film. In general, foil of 0.025 mm and below has to be supported. For example, 0.025 mm foil laminated to 30 g/m2 LDPE is a widely used strip packaging laminate. In theory, 0.015 mm foil laminated to 30 g/m2 LDPE would be a more economical proposition. However, at this caliper any undue stretch would be likely to perforate and tear the foil. Hence it is possible to reduce the foil caliper only if support is increased, i.e. by the addition of a paper ply. Thus if cost savings are to be made the final laminate would probably be either... 

It is fairly obvious that the use of a different foot pressure would, with a soft and deformable material such as rubber, produce a different result. Hence, it is not permissible to use a dial gauge with a return spring, calipers, or a travelling microscope when this standard method is specified. The errors resultant on using different pressures have been reported by Clamroth and Dobrosehke [29]. 

The use of gauge blocks for measuring can be extended by the use of a range of accessories. These are covered by BS 4311-2 2009. A typical set of gauge-block accessories is shown in Fig. 5.5 and consists of (1) two pairs of jaws, type A and type B, which when combined with gauge blocks form an external or internal caliper, Figs 5.6(a) and (b) a centre point and a scriber, used in combination with gauge blocks to scribe arcs of precise radius. Fig. 5.6(c) ... 

These are also available as an easy-to-read dial depth gauge (Fig. 6.11) and an electronic model with an LCD digital readout (Fig. 6.12) operating in the same way as the caliper models. 

In the contacting measurement techniques, the micrometer caliper is a common instrument. The micrometer, however, can only be used for pot measurements and this is done manually. A spring-loaded dial gauge can be moved over the extrudate if the thickness variations are small. Thus, the dial gauge can be used to monitor the variation of thickness with time, i. e., in the extrusion direction. If an accurate traversing mechanism is constructed, the dial gauge can also measure the thickness variation perpendicular to the extrusion direction. At the point of measurement, the opposite side of the extrudate has to be firmly supported to avoid measurement errors. 

The vernier caliper does not comply with this principle (Fig. 6.2). To ensure greatest accuracy of measurement, the workpiece being measured should be moved as close to the main beam as possible. The vernier depth gauge, however, does comply with Abbe s principle. 

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