Joint area

The bearing surface of each joint is cushioned by cartilage. This tissue minimizes friction. The cartilage also reduces force on the bone by absorbing shock. The joint area is a narrow space known as an articular cavity which allows freedom of movement. 

Surface prqiaiation of the joint area may be required to remove oxides, grease, moisture, etc. (prior to adhesive application) by mechanical, solvent, etching or degreasing processes to facilitate wetting. 

Proper chain-drive lubrication increases drive life by dissipating frictional heat generated in the joint area. Heat varies according to the chain speed, horsepower transmitted, center distance, sprocket ratio, drive size, amount of lubricant, and viscosity. It generally ranges from surrounding temperature to 60 to 70°F above the ambient temperature. Normal chain drive temperatures should not exceed 180°F. 

An interesting example of judicious choice of braze filler is to be found in the selection of silver alloys for the brazing of stainless steels to be subsequently used in a tap-water environment . Although the brazed joint may appear to be quite satisfactory, after a relatively short exposure period failure of the joint occurs by a mechanism which appears to be due to the break-down of the bond between the filler and the base metal. Dezincifica-tion is a prominent feature of the phenomenon and zinc-free braze alloys based on the Ag-Cu system with the addition of nickel and tin have been found to inhibit this form of attack. A similar result is obtained by electroplating 0-007 mm of nickel over the joint area prior to brazing with a more conventional Ag-Cu-Zn-Cd alloy. 

The wire beads used are produced from a combination of multi-strand copper, zinc or brass coated high-tensile steel wires. The required number of wires are formed into the required shape and then passed through a cross-head extruder to be coated with rubber compound. The coated wire layers are then formed into a coiled ring and the free wire ends secured together. For certain heavy duty applications use is made of either a light weight rubberised fabric or a small fibre filled rubber sheet to cover the joint area. In some cases the bead construction is also partially vulcanised. 

At least three joint areas simultaneously have soft tissue swelling or fluid (not bony overgrowtir alone) observed by a physician. The 14 possible joint areas are (right or left) PIP, MCP, wrist elbow, knee, ankle, and MTP joints. 

At least one joint area swollen as above in wrist MCP, or PIP joint... 

Simultaneous involvement of the same joint areas (as in 2) on both sides of the body (bilateral involvement of PIP, MCP, or MTP joints is acceptable wilhout absolute symmetry). 

To check for construction joint leakage, scan all joint areas from a distance of 6 in. at a speed of approximately 10 in./min. 

The physical properties of the filler metal are based on its metallurgical properties. The composition will determine whether the filler metal is compatible with the metals being joined—capable of wetting them and flowing completely through the joint area. There arc also special... 

Arthritis of 3 or more joint areas At least 3 joint areas simultaneously have had soft tissue swelling or fluid (not... 

The type and amount of fillers are chosen so that a practical bond line thickness will result after application of the necessary pressure (usually only contact pressure, approximately 5 psi) during cure. Ordinarily, the objective is a bond line thickness of 2 to 10 mils. Consideration, of course, must be given to the curing temperature. Viscosity of the formulation could drastically be reduced at elevated temperatures, and unless there is a furrow designed into the joint to contain the adhesive, much of the adhesive could flow out of the joint area before the adhesive is completely cured. 

Another option is to design mechanical shims into the joint itself. The parts to be assembled are designed with bps or stops so that the adhesive cannot flow out of the joint area or so that a certain predetermined adhesive thickness is always maintained. 

Structural adhesives that are commonly used for composites are supplied in two basic forms semisolid B-stage film and thixotropic pastes. The film adhesives are cast or extruded onto carrier fabrics or films and partially cured to a semisolid. They can easily be handled, cut, and applied to the joint area. There is no need for mixing, metering, or dispensing of liquid components. In use, these adhesive systems are activated by heat and pressure. The semisolid B-stage film liquefies briefly on application of heat and then cures to an insoluble state. Epoxy, polyimides, epoxy-nylons, epoxy-phenolic, and nitrile-phenolic adhesives are available as B-stage film. 

Bond Inspection. After the adhesive or sealant is cured, the joint area can be inspected to detect gross flaws or defects. This inspection procedure can be either destructive or nondestructive. The nondestructive type of tests can be visual or use advanced analytical tests. These types of bond inspections are described below. 

The joint area and mode of failure should be examined closely, for this generally leads to clues that are indicative of problems. The causes and remedies for faults revealed by such mechanical tests and visual inspection after testing are described in Table 19.1. 

As time passes, national standards for area classification have been superseded by international standards (IEC, International Electrotechnical Commission, Geneva/Switzerland, and EN, European Standard or European Norm, established by CENELEC, Comite Europeen de Normalisation Electrotechnique, Brussels/Belgium), which have been adopted as subsequent national standards. In the member countries of the European Community (EC), a joint area classification is defined by a directive (Directive 1999/92/EC of the European Parliament and of the Council, dated 1999-12-16). 

Flash - In welding thermoplastics, molten plastic that seeps out of the joint area during the welding process. In molding, surplus plastic attached to the molding along the parting line. Flash must usually be removed before parts are considered to be finished. 

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