Butt-joints

In some applications the butt joint may be the only possible method of assembling the component parts and, if aesthetics are important, the small fillet of excess adhesive outside the joint (which adds to the strength of the joint) may also be undesirable. One example of this in the plastics industry is the assembly of shelving where acrylic or polycarbonate sheets are bonded together to form points of sale display equipment. 

In these applications a variety of adhesives are used including UV cure, cyanoacrylates and two-part adhesives (epoxies or acrylics) and the adhesive is selected for its clarity, cost, speed of cure and ease of use. 

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Ultrasonic Welding. Ultrasonic welding has been appHed to Tefzel with weld strength up to 80% of the strength of the base resin. Typical conditions include a contact pressure of 172 kPa (25 psi) and 1—2 s cycle time. The two basic designs, the shear and butt joints, employ a small initial contact area to concentrate and direct the high frequency vibrational energy. 

Glass-reinforced polyester is the most widely used reinforced-resin system. A wide choice of polyester resins is available. The bisphenol resins resist strong acids as well as alkahne solutions. The size range is 2 through 12 in the temperature range is shown in Table 10-17. Diameters are not standardized. Adhesive-cemented socket joints and hand-lay-up reinforced butt joints are used. For the latter, reinforcement consists of layers of glass cloth saturated with adhesive cement. 

Unfired steam boilers with design pressures exceeding 345 kPa (50 Ibftin") have restrictive rules on weided-joint design, and all butt joints require full radiography. 

Two wooden beams are butt-jointed using an epoxy adhesive (Fig. A1.3). The adhesive was stirred before application, entraining air bubbles which, under pressure in forming the joint, deform to flat, penny-shaped discs of diameter 2fl = 2 mm. If the beam has the dimensions shown, and epoxy has a fracture toughness of 0.5 MN mT , calculate the maximum load F that the beam can support. Assume K = cT Tra for the disc-shaped bubbles. 

Single-welded butt joint without use of backing strip... 

Welded butt joints should be used instead of bolted or riveted ones. 

Butt Joint a connection between the ends or edges of two parts making an angle to one another of 135° to 180° inclusive in the region of the joint. 

Countersunk rivets or screws give a surface profile which is compatible with painting protuding bolts and rivets are very much more difficult to coat adequately. Welded joints can aid optimum shaping for painting. Butt joints are preferable to lap joints. 

The only difference between this type of joint and a normal butt joint is in the preparation of the capillary tube first the end of this is sealed off and a small fairly thin-wall bulb btown equal in diameter to the hole in the wide tube. The end of this bulb is then blown out and the joint made by the normal method. The flame must be directed so that the capillary is not collapsed. If the capillary has a very fine bore some difficuhy will be found in blowing through it. This may be overcome by connecting it to a compressed air line while the smaU bulb is btown the end of the bulb can then be pulled out with a rod and cut off to give the prepared end. 

The life of equipment subjected to corrosive environments can be increased by proper attention to design details. Equipment should be designed to drain freely and completely. The internal surfaces should be smooth and free from crevasses where corrosion products and other solids can accumulate. Butt joints should be used in preference to lap joints. The use of dissimilar metals in contact should be avoided, or care taken to ensure that they are effectively insulated to avoid galvanic corrosion. Fluid velocities and turbulence should be high enough to avoid the deposition of solids, but not so high as to cause erosion-corrosion. 

Where butt joints are made between plates of different thickness, the thicker plate is reduced in thickness with a slope of not greater than 1 in 4 (14°) (Figure 13.42). 

ISO 6922 1987 Adhesives - Determination of tensile strength of butt joints... 

S) is the allowable stress and for Stainless Steel, TP 316 is taken to be 18750 lbs/sq.in. over the temperature range of 0-l00°C,(3) (E) is the longitudinal weld point factor and is taken for double welded butt joints as 0.85(3)... 

Only welded and seamless construction should be adopted. Butt welds in both butt joints and T joints should be made with more than one run of electrode or blowpipe. The weld should be ground smooth and flush. Welding should be done from the side to be rubber lined wherever possible, as shown in fig 6.4 A. Where... 

Allowable tensile stresses are one-fourth the ultimate tensile strength of the material of construction. Values at different temperatures are given in Table 18.4 for some steels of which shells and heads are made. Welded joint efficiencies vary from 100% for double-welded butt joints that are fully radiographed to 60% for... 

The basic design needs to be confirmed by the customer. Does the proposed part actually look like what is required, and will it fit into the rest of the equipment if it is part of a larger assembly If not previously discussed with the supplier, any potential trouble points like sharp corners or butt joints should be brought to the attention of the customer and the potential problems resolved. If the part is a noncritical item or if there is knowledge available from previous similar items, the part can be evaluated by the customer. Flexibility, deformation under load, and correct functioning in an assembly can be verified using the part. 

Sheet or panel (metal, plastic, etc.) wall siding. Seal tight all lap or butt joints. Make certain that caps, covers and flashings don t have hidden voids due to siding configurations (flutes, corrugations, etc.)... 

Reverse-side treatment may be caused if the dielectric film is not wrapping the treater roll smoothly and becomes wrinkled also at poor butt joints of the dielectric. In turn, unwanted treatment can cause the ink from the printed surface to adhere to the under-side when film is re-wound or collected in batches of bags, spoiling the work and rendering the printed material unsuitable for use. Such troubles are noticeable in particular with film of high surface gloss. 

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