A tramming stick is a useful tool for checking roller-to-roller parallelism. Strangely not readily available from any supplier, most tramming sticks are custom-made. Also called a wiki-stick, named for its quickness, a tramming stick is comprised of:
An extending shaft (often a tripod leg)
A reference roller end, usually an angle iron modified to hold the tripod leg perpendicular to the reference roller
A dial indicator, measuring down to 25 micron increments over a 25mm range (or 1 mil over 1 inch)
The Nedo measuring stick is a compact and convenient tool similar to a tramming stick, measuring long lengths to small increments. One model measures down to 1 mm over a 0.5 to 2m range ( 40mil over a 20-80 inch range),
Durometer Rubber Hardness Tester
The Durometer is the international standard for the hardness measurement of rubber, plastic, and other non-metallic materials. Durometers are described in the American Society for Testing and Material specification ASTM D2240. The measurement is neither metric or American units, instead reads in units proportional to the penetration of a conic, spring-loaded probe where less penetration is considered ‘harder’ and scores a higher Shore value.
Shore A Durometer is used for most rubber covered rollers in web handling applications. Shore A Durometer measurements use a lower spring value and truncated cone probe. Typical Shore A values range from 20 (elastic band), 40 (pencil eraser), 70 (automobile tire), to 90+ (shopping cart wheel).
Pusey and Jones Plastometer
The Pusey & Jones (P&J) hardness tester rates hardness based on the depth of indentation (in hundredths of a millimetre) of a 3.175 mm (0.1250 in.) diameter steel ball under a vertical force of 9.8 N (2.2 lbf). This value, read after 60 seconds of load, is opposite of Durometer with higher values indicating more indentation and softer rubber. A P&J of zero is the hardest rating, indicating zero indentation. P&J rating may be used to compare the indentation resistance of rubber and rubber-like materials, including paper rollers with a minimum thickness of 13 mm (0.5 in). P&J is based on ISO 7267 and ASTM D531-15.
Above, P&J Plastometer from 1915.
Handheld Force Gauge
A handheld force gauges are a tool any web handler should have. Forces are important in web processes (e.g., tension, nip forces), but many are not measured or directly controlled. A force gauge is vital to calibrate these mysteries. There are many levels of sophistication to force gauges, going from simple fish-weighing scales (see below), to mechanical push-pull gauges, to electronic load cells with digital output and recording. Look for a force gauge with a 25-50 kgf (50-100 lbs) range if you intend to use it by hand. Larger force gauges are useful for higher load measurement inline with a rope or cable (i.e., when not held by hand).
Nipping Rollers Footprint and Pressure Measurement
Footprint measurements quantify differential indentation of rubber rollers, showing changes in contact at a single crossweb (CD) position or the profile from several CD measurements.
Simple devices similar to carbon paper can ‘record’ the contact length of nipping rollers.
Pressure sensing papers or films create a full-width, continuous, analog map of footprint length vs CD position.
Digital footprint measurement uses thin electronic sensors in a segmented array to measure local footprint length and changes in with load.
Footprint by Tape or Post-It® Notes
These are two quick, easy, and incredibly inexpensive methods to measure nip footprint length and CD variations. Like most nip footprint measurement, these are static, single condition measurements (i.e., the nip opens and closes, but does NOT rotate).
Using tape, lightly place strips of tape down on the open nip roller, intentionally leaving bubbles in the tape-roller contact area. This works best with tape on a chrome roller. After applying the tape, close the nip to the desired setting, then open it and measure the MD distance that the bubbles are ironed out in the contact zone.
Using sticky notes (such as 3M Post-It® notes), first, close the nip at the desired settings, then insert the sticky notes in from either side of the nip footprint as far as they will go, one note from either side (upstream and downstream) and tack them down to the roller. Next, open the nip and measure the MD length of the gap between opposing the sticky note pairs.
Footprint Pressure-Sensing Webs
Listed below are three sources for nip impression kits/paper. These systems are similar to carbon paper. One roll contains a paper coated with the ‘donor’ material and the other roll of paper is an engineered ‘receiver’ paper. The donor material is similar to blue waxy coating. The two layers are inserted in a pressure point, such as between two nipping rollers, and squeezed. The blue waxy coating transfers to the donor paper where there is sufficient pressure and shows some gradient of pressure with darker blue transfer indicating higher pressure contact. Where tape and sticky notes are strictly used in open-close stationary nips, nip impression paper can also be fed through a rotating nip (usually at slow speeds) to measure pressure variations vs nip MD position.
Three suppliers are listed below. The Valmet product has been previously sold as Beloit and Metso paper. You can sometimes find old stock of this product on eBay and similar sites.
Passaic Rubber Co.
Nip Impression Paper
Valmet Nip Impression Kit
KD II GmbH & Co. KG
Nip Impression Paper
Fuji Pre-Scale Film
Similar to the footprint pressure-sensing webs, Fuji Prescale Film is an engineered donor-receiver pressure-sensitive two-sheet system. One roll is the donor paper with a unique coating of dye encapsulated inside microscopic glass beads. The other roll of paper is an engineered ‘receiver’ paper. Based on the glass bead size, Prescale film is available from “ultra extreme low” to “super high” each designed to measure over pressure over a specific range of pressures. Prescale film can be used for simple open-close footprint length measurement or for rotating MD pressure contour mapping. Each pressure range of PreScale film includes a color chart of light to dark pink color density vs pressure. Software and scanners are also available to translate the pink density variations into pressure units.
Tekscan and Sensor Products are the two major US-based distributors of Fuji Prescale film (SPI renames it PressureX).
Color Density vs Pressure
Mapping Laminator Pressure
Footprint vs MD Pressure Mapping
Digi-Nip2 from Tablet Measure offers dual sensors systems to measure nip footprint lengths and is specifically marketed to the central impression press application. Footprint measurement is based on the number of discrete MD spaced circuits of pressure-conductive ink closed in the contact zone in a non-rotating closed nip. The Digi-Nip2 connects the battery-operated sensors to a smartphone app via Bluetooth.
Nip Control Footprint or Pressure Measurement
Nip Check Footprint Sensor and Calibration Block
Nip Control, from Sweden, offers two handheld nip sensors systems to measure footprint or maximum pressure. Footprint measurement is based on the number of discrete MD spaced circuits of pressure-conductive ink closed in the contact zone in a non-rotating closed nip. The footprint system includes a footprint calibration clamp. Pressure measurement is based on a calibration of the pressure-conductive ink and includes a spring-loaded calibration clamp of 400 N/cm2 (580 psi). The pressure sensor range is listed as 15-999 N/cm2 (20-1400 psi). The pressure sensor can measure a static closed nip or the maximum pressure found by slowly rolling the sensor through the nip zone.
Nip Check Pressure Sensor and Calibration Clamp
Note: TJWA Inc. has worked with Nip Control on a few US sales.
Tekscan I-Scan Sensor and Display
Tekscan systems measure the pressure between two surfaces, utilizing a thin and flexible sensor and have repeatedly proven useful in measuring nipping roller variations. The laminated sensors estimate pressure from the calibrated resistance changes of a thin conductive ink. There are many pre-designed sensor shapes, some especially useful for nip pressure measurement. Most measurements are non-rotating, closed nip measurements of footprint pressure contour vs MD and CD. Some proof-of-concept trials used the Tekscan Versatek to collect internal roll pressures during the winding and unwinding process. Beyond many standard sensors, custom sensors can be created for different geometries and pressure ranges.
Tekscan I-Scan Sensor, Handle, and Software
Tekscan Nip Pressure Alignment Tool
Note: TJWA Inc. and Tekscan have co-presented two conference papers.
Roll Hardness Measurement
Web bagginess is difficult to measure. Roll hardness profile often strongly correlates to bagginess. Hardness profile, alone or combined with thickness or basis weight profile, is the best predictor of web bagginess for roll suppliers and customers. Ranging from manual ‘billy club’ rebound vs width to highly sophisticated mechatronic units, some form of roll profiling will help understand your web quality and correlate it to runnability.
A manual roll hardness measurement that is very similar to a policeman’s billy club or a night man’s self defense stick. The club is swung and struck against the bilge of the wound roll. The operator listens for the pitch of the impact as an assessment of web profile and wound roll tightness. It works well with many stiff materials except foils, but may not work as well for soft materials such as tissue. The method is still in everyday use on almost every paper machine for detecting web profile problems and is still quite useful in web and wound roll diagnostics for other materials. In film, this may be done much more crudely and somewhen less commonly by swinging a tool at hand, such as a screwdriver or utility knife. (David Roisum – AIMCAL Knowledge Base)
Kershaw Roll Density Tester
The Kershaw Roll Density Tester is a fully automatic tester measures force vs displacement of a probe pushing into a roll of paper, tissue, or nonwoven product. Described as roll density, the units suggest a radial spring constant. Both material properties and winding conditions will change this value. For a given product, a higher number implies a more tightly wound roll which may correlate to product performance such as thickness, porosity, and softness.
Kershaw Graph Force vs Displacement
Proceq Paper Schmidt
The PaperSchmidt is the first integrated rebound hammer designed specifically for the testing of roll profiles. It features high accuracy and repeatability and delivers instantly all key parameters required for assessing the roll quality. The PaperSchmidt has an extended lifetime to cope with the heavy demands of the paper industry.
Original Schmidt Hammer Concrete Tester
Proceq Equotip 550
The Equotip 550 Leeb U is the successor of the Parotester and perfectly suited for large rolls, thin foils, and films. The Equotip 550 now includes enhanced software, user touchscreen display, custom reporting. This device measure hardness by the Leeb methods, measuring the difference in velocity downward and rebounding impacting mass. The ease of use and immediate histogram displays have made the Parotester and now Equotip 550 a favorite hardness device to measure paper and film rolls in the converting industry. It enables the user to quickly and precisely diagnose roll imperfections, hardness inconsistencies, and uneven winding, thereby preventing problems for printing and converting operations.
Mill Assist Rho Meter
The Rho-Meter measures the peak force generated by contact of a striker moving at a known velocity against a surface of unknown hardness. During a collision between two objects, both experience a common and opposite force. This reactive force, or “impulse force”, rises from zero to a maximum value then returns to zero. The area under a plotted force-time curve is called “impulse” and is measured in units of pound-seconds.
The original Rho-meter is shown above. The newer product, the Bel-Rho 2000 acoustic hammer is shown below. Both are used for roll hardness average and profile, though their units are not equal.
Bel-Rho 2000 Acoustic Hammer
Tapio Technologies’ RQP v2.0 measures roll hardness based on a position measurement (instead of the acceleration measurement used in the original RQP). Hitting velocity and the shape of the hammer’s tip can be selected to suit each customer’s preferences. The goal is to mimimize the possible damage inflicted to the tested material (paper, plastic rolls or aluminum foil rolls) and to provide accurate measurements. The RPQ2 data can be stored to an on-unit SD card or shared to a PC wirelessly using Bluetooth or wired with the USB cable.
The ACA RoQ (Roll Quality) hardness tester combines many desirable features in a single unit, including touchscreen display, position sensing wheels, too fast/slow scanning rate feedback, high frequency and gentle impact, bar code scanner, on-device graphical display and averaging, compact and light weight. For high volume hardness profile testing, this is an excellent choice.
TJWalker + Associates, Inc.
Timothy J. Walker
President / Web Handling Specialist