Same word, different worlds
Core
Core turns up in 5 fields: fiber optics, PCBs, concrete, asphalt, nonwovens. Here is what it means to the people in each one.
- 20FoFiber OpticsCore in Fiber Optics
The central glass region of an optical fiber where the light actually travels. The high-index center of the fiber that guides the light, surrounded by lower-index cladding so rays striking the boundary at shallow angles reflect back inward by total internal reflection. Core diameter defines the fiber family: about 9 µm for singlemode, 50 or 62.5 µm for multimode. Most connector and splice loss comes down to how well two cores line up and how closely their sizes match.
On the job: Splicer's showing the cores offset on the Y axis, clean the V-grooves and redo it before you heat the sleeve.
- 21PbPrinted Circuit BoardsCore in Printed Circuit Boards
Fully cured laminate with copper on both sides, etched into inner layers and bonded with prepreg into a multilayer. A core is a rigid sheet of cured laminate clad with copper foil on both faces, supplied in fixed thicknesses such as 0.1, 0.2 or 0.36 mm. In multilayer fabrication the inner-layer patterns are imaged and etched onto cores, which are then stacked with prepreg and outer foils and pressed together. Because a core's thickness is tightly controlled and does not flow during lamination, designers like to put their tightest impedance layers against core dielectrics.
On the job: Put the high-speed pairs on layer 3 against the core, the prepreg side moves too much in the press.
- 23CnConcrete & CementCore in Concrete & Cement
A cylinder of hardened concrete drilled out of a structure to test its strength or inspect its condition. Cut with a diamond core drill, usually about 4 in in diameter, cores are the standard follow-up when cylinder breaks come in low or the in-place concrete is in doubt. For acceptance, three cores must average at least 85 percent of f'c with no single core under 75 percent. Cores also reveal cover depth, voids, cracks, delamination and ASR in existing structures.
On the job: Engineer wants three cores out of the level 2 slab where the low breaks were, so scan for tendons before you drill.
- 24AsAsphalt PavingCore in Asphalt Paving
A cylinder of pavement drilled out of the finished mat and sent to the lab for density and thickness. A sample cut from the compacted pavement with a water-cooled diamond core bit, commonly 4 or 6 inches in diameter. The lab measures its thickness and bulk specific gravity and divides by Gmm to get in-place density, which on many contracts is the number that sets pay. Core locations are picked at random by the agency, and the holes are cleaned, tacked and filled with compacted mix.
On the job: State's pulling cores at stations 112 and 118 tomorrow, so get that last pull rolled out before anybody goes home.
- 27NwNonwovensCore in Nonwovens
Tube, usually paperboard, on which nonwoven fabric is wound to make a roll. Cores are ordered by inside diameter, commonly 76 mm (3 inch) or 152 mm (6 inch), plus wall thickness and a length that matches the slit width. A core must survive winding tension and the converter's unwind chucks without crushing. Crushed or out-of-round cores cause unwind vibration, web breaks and returned rolls.
On the job: Customer's chucks are 6 inch, so these rolls on 3 inch cores are coming straight back.