Bonding equipment adhesive thickness

Before the application of the adhesive, the bonding surfaces have to be prepared. To clean the surfaces properly, the aluminum of the chassis is grit-blasted (corundum 20-30 pm grit) and the GRP of the cabin is ground with a very fine grinding pad. Then, any dirt and dust particles are removed with the Sika Cleaner-205 and brushed with a suitable Sika Primer. Then the cabin is set onto the chassis in the correct position using polyurethane distance holders to control the adhesive thickness, before Sikaflex -254 Booster is injected into the joint with the booster pump equipment, pressed, and skinned into the joint with a spatula. A small gap with a depth of 5 mm has to remain later, this gap is filled with Sikaflex -265 to achieve a durable seal. 

Films. Both structural and nonstructural adhesives are commonly available in film form. Adhesives applied in the form of dry films offer a clean, hazard-free operation with minimum waste and excellent control of film thickness. However, the method is generally limited to parts with flat surfaces or simple curves. Optimum bond strength requires curing under heat and pressure, which may involve considerable equipment and floor space, particularly for large parts. Film material cost is high in comparison to liquids, but waste or material loss is the lowest of any application method. 

Ease of fabrication is one of the many advantages of polyethylene foam. It can be skived to precise thickness, cut and shaped to form custom parts, and joined to itself or to other materials without major investment in complex equipment. It can also be vacuum formed. Expanded polyethylene will adhere to itself by the use of heat alone. Hot air, or a plate heated to approximately 350°F (177°C) can be used to simultaneously heat the surfaces of two sections of foam to be joined. Upon softening, the two pieces are quickly joined together under moderate pressure, and an excellent bond formed, with only a short cooling period required. Release of the melted foam is aided by a coating of fluorocarbon resin or silicone dispersion on the heating surface. The foam may also be bonded to itself and to other materials by the use of solvents or commercially available adhesives (6). 

Electrophoretic deposition is similar to electrochemical plating. But, instead of deposition from solution, particles are deposited from suspension. It is possible to produce thin and thick films of very consistent thickness, even on irregularly shaped substrates, with very short deposition times. Also, the equipment necessary to deposit the films has a relatively inexpensive power supply. However, the films are only physically bonded to the substrate and permanent chemical adhesion must be affected by firing, which can have deleterious results on the mechanical properties of metallic substrates. 

Most structural film adhesives require a primer. Adhesive primers are usually spray-applied by air or airless spray systems. Roller or brush apphca-tion is sometimes used in small areas, or where spray equipment is not available. The primer coat must be air-dried and sometimes over-baked to remove solvents. The thickness of the prime coat will usually affect the adhesive bond strength and must be controlled and verified. This is usually accomplished by periodically certifying the primer applicator, and by monitoring primer thickness after drying. ... 

Pressure equipment. Pressure devices should be designed to maintain constant pressme on the bond during the entire cure cycle. They must compensate for thickness reduction from adhesive flow-out or thermal expansion of assembly parts. Thus, screw-actuated devices like C clamps and bolted fixtures are not acceptable when constant pressure is important. Spring pressure can often be used to supplement clamps and compensate for thickness variations. Dead-weight loading may be applied in many instances however, this method is sometimes impractical, especially when heat cure is necessary. 

There are several processes that go by the name 3D printing. Some of these are compared in Table 3.2. Small desktop 3D printers are available, as well as large freestanding equipment. In one variation, the process starts by depositing a layer of powder object material at the top of a fabrication chamber. A roller then distributes and compresses the powder at the top of the fabrication chamber. A liquid adhesive is then deposited from a jet in a 2D pattern onto the layer of the powder, which becomes bonded in the areas where the adhesive is deposited, to form a layer of the object. Once a layer is completed, the fabrication piston moves down by the thickness of a layer, and the process is repeated until the entire object is formed... 

Tear speed = Cross head speed Speed of which samples are subjected to destruction in the testing equipment. Normally it is between 5 and 300 mm/min Thermosetting resins Closely cross-linked macromolecules that do not undergo plastic deformation even at high temperatures Thick-layer adhesive bonding Elastic bonding application where the thickness of the adhesive layer exceeds 3 mm... 

Low ambient temperature is quite detrimental to water-based emulsion adhesives. When the temperature is too low, the dispersed polymer particles will not coalesce or fuse together, and it will prevent the formation of a strong continuous film of adhesive. Instead, a powdery, cracked film will occur if the temperature is lower than a required minimum. There is a minimum film-forming temperature (MFFT) below which there will be no film formation and consequently no bonding. This temperature may be measured with several test methods ASTM D 2354 and ISO 2115, by using specific equipments such as the Sheen Instrument minimum film temperature bar (Fig. 19) a naicroprocessor controlled stainless steel plate is cooled at one end and heated at the other. The sample to be tested is laid down at 75 JLm film thickness and 25 mm width. After 45 -90 min, a clearly defined coalescence zone will be visually obvious, and the temperature at this point will be recorded as MFFT. 

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