Sprut-4 adhesive

The Sprut-5M adhesive consists of unsaturated polyester resin 100 parts hy weight, ATG-M 80 parts (a mixture of 50 parts of macrodiisocyanate md 30 parts of ATG), polymerization initiator (MEKP(O)) 2 parts. Usually lwt% of CN is integrated additionally into the adhesive base. Sprut-5M can be produced using various polyester resins, but the most applicable one is the adhesive based on PM-I resin owing to its availability and low cost. For this reason we will consider the properties of the adhesive based mainly on this resin although it has adhesion strength 20—40% lower than that of adhesives based on PN-11, NPS 609-21M, and other resins, especially when cementing in water. 

Figure 3.1 presents the maximum stress surfaces when St3 steel is cemented with the Sprut-5M adhesive and the polyester and poly-... 

Figure 3.1 Surfaces of maximum stress of steel specimens cemented with Sprut-5M (I), polyester (II), and polsnirethane (III) adhesives.

Figure 3.2 Long-term strength <73 of St3 adhesive-bonded joints at various loadings (1, 3, 5), Sprut-5M (4) polyester adhesive.

We investigated the effect on the adhesion strength of shear stresses applied to the adhesive interlayer MDI as a component of Sprut-5M adhesive. An equimolar quantity of butylene glycol was added to MDI to cure it. The shear stresses were created by the torsion of one dolly of standard size relative to another in a special device the adhesive was placed between the dollies. On reaching the prescribed shear stress (due to the increase of the adhesive viscosity) the torsion of the dolly... 

Properties of Sprut-5M adhesive-based reinforced coatings... 

Thus, Sprut-5M adhesive-based reinforced coatings allow an increase in the strength of the metal, mainly under the conditions in which the load on the specimen exceeds the elastic limit of the steel. 

These are frequently the condtions under which structures operate that are weakened by intensive metal corrosion—pipelines, oil tanks, ships. Sprut-5M adhesive is successfully used for strengthening... 

Let us consider some mechanical properties of biplates. These are steel plates onto which glass-reinforced plastics are molded, with Sprut-5M adhesive used as a binder. The types of mechanical load selected were those that were encountered in the course of the coating operation. 

When adhesives are applied for the repair of ships, blowholes in pipelines, and other objects, the adhesive interlayers are frequently subjected to impact loads under tension this occurs, for example, in hydraulic impacts on pipelines, in ships during mooring, and so on. In this context it is interesting to investigate the effect of the modifying additives in Sprut-5M upon the strength of adhesive-bonded joints under tensile impact loads. 

In Sprut-4, the quantity of ATG is increased to 30%. Increase of the number of intermolecular crosslinks and of polar groups enhances the resistance of this adhesive to oil products. The fluorinated alcohol introduced into the adhesive works as reactive surfactant because it can react with the isocyanate groups of ATG. The amount of fluorinated alcohol is selected to bond not more than 30% of the isocyanate groups in the adhesive. The fragment of the macromolecule of the polymer formed in this case has the structure... 

The additional introduction of the fluorinated alcohol into the adhesive enhances its water resistance. Thus, the adhesion strength of adhesive-bonded joints of steel using Sprut-4 adhesive does not change significantly over time even with many years in water. 

Because of high adhesion strength and deformability of the VAK and Sprut-4 adhesives, low internal stresses in the adhesive-bonded joints ensured their serviceability when used as binders for the formation of reinforced coatings on metal and other surfaces. The thickness of such coatings can reach some centimeters and their strength is comparable with that of metals. Such coatings are suitable to... 

Taking Sprut-5M adhesive as an example, consider the modulus of elasticity of the polymer in the adhesive layer in terms of the distance... 

Determining thermal internal stresses. Experimentally, the stress with a particular temperature change is determined by the deflection of the free end of the cemented three-layer plate fixed as a cantilever. The deflection of the plate end was determined by means of a projection optical system. Figure 4.3 displays the distribution of the thermal internal stresses in a Sprut-5M adhesive-bonded joint for temperature change from 20 to 42°C. Plates made of IKhlSNlOT steel 0.07 mm thick and aluminum foil 0.02 mm thick were used as substrates. It is evident that the internal stresses are characterized by maximum values on the interfaces. 

Let us consider how to determine experimentally the shrinkage internal stresses. An optical system similar to that descrihed in Section 4.2.1 was used to determine the displacement of the free end of the cantilever-fixed adhesive-honded plate. Plates made of aluminum foil 5 X 10 m thick E = 0.7 x 10 MPa) and of steel 10 x 10 m thick (E = 2 X 10 MPa), hoth with areas of 1 x 10 cm, served as substrates. Sprut-5M adhesive was used to cement the plates. The shrinkage internal stresses were determined at 293 K 2 days after the specimens were prepared. 

It is evident that with temperature elevation from 293 to 314 K the modulus of elasticity of the Sprut-5M adhesive changes insignificantly, demonstrating the apphcahiUty of the method of temperature stresses. 

The variation of specimen strength with the time of adhesion using the Sprut-5M composition is represented in Fig. 7.1a by the curves 1— 3. As shown, strength of adhesion with Sprut-5M (28 and 24 MPa under normal fracture and shear) is considerably higher than that achieved by PN-1 and PU (18, 12, and 8.5 MPa, respectively). The strength of the specimens tested increases in the course of time, but... 

The kinetics of strength variation for adhesive joints, imder water or oil, had not previously been investigated. When formed in liquids, PN-1, PU, and AK compositions do not display adhesion properties. The adhesion strength for underwater fixing with Sprut-5M is 14 and 12 MPa under imiform fracture and shear for VAK adhesive the values are 13 and 12 MPa. 

A gradual decrease in strength is noted for specimens cemented with Sprut-5M. The strength decreases under water over 24 x 10 h, by cohesion fracture pattern. The strength decrease practically stops then, but fracture occurs predominantly by mixed or adhesion pattern. This is probably connected with diffusion of water at the pol5rmer— metal phase bomidaries and with low water resistance, typical of polyester resin-based adhesives. 

Thus, the experimental dependences show that the strength of these adhesive joints imder normal fracture and shear depend substantially on the time from the moment of cementing to the beginning of the test. Variations in intensity and dimation of the strength depend on the formulation of the adhesive composition and on polymerization conditions, which in principle allows for active control of these processes. The results enable the recommendation of Sprut-5M mainly for adhesive joints operating in oil media and the VAK composition for use in imderwater conditions. 

Results under normal compression for steel specimens glued with Sprut-5M and VAK compositions in air, under water, and in oil are given in Fig 7.1. As is obvious, the strength of adhesive joints under normal fracture is practically the same up to a certain critical value of precompression stress. Evidently, the applied normal compression stresses do not result in essential fractures in the adhesive joint the fracture occurs in the elastic zone. Using Sprut-5M composition (Fig. 7.1a), these compression stresses remain within 0-43.0 MPa in air, within 0-50.0MPa under water, and within 0-52.0 in oil the corresponding values for VAK are 0-104.0 MPa, 0-90.0 MPa, and 0— 84.0MPa (Fig. 7.1b). 

The brittleness of specimens under normal compression depends also on the ambient medium and on exposme. Specimens fixed with Sprut-5M under water and in oil are less brittle than specimens fixed in air. Reduction of brittleness mder water and in oil is somewhat characteristic of the specimens glued with VAK also. This may be explained by the plasticizing influence of the hquid medium on the adhesive joint borders, leading to partial elimination of the stress concentration factor [360] that occurs with adhesive shrinkage in the process of polymerization. 

Figure 7.2 presents diagrams of the limiting state of specimens made of stainless steel and aluminum alloy fixed with Sprut-5M composition and VAK in air. Evidently, the values of adhesion strength for specimens made from different materials differ only slightly, and their limiting state diagrams are practically equidistant. 

Figure 7.2 Diagrams of the limiting stressed state of adhesive specimens under the combined action of normal fracture and shear (bonded in air) (a, c) bonding of specimens made of stainless steel (1), steel (2), and aluminum alloy (3) using Sprut-5M and VAK (b) bonding of steel specimens with PN-1 (1) and PU (2) (d) the same as (b) for AK adhesive.

Surfaces of the limiting stressed states for steel specimens fixed in air using Sprut-5M, PN-1, as well as VAK and AK, are presented in Fig. 7.3. As is obvious, specimen strength increases with time. The kinetics of short-term adhesion strength change with time under the combined action and under the separate actions of normal fracture and shear breaking stresses shows similar patterns. Thus, the increase in the strength with Sprut-5M and PU stops in 24 x 10 h, with PN-1 in 6 X 10 h, and with VAK and AK in 8-12 x 10 h. In all the cases failure of specimens occurs by cohesion pattern. 

Specially developed methods were used for investigation of the strength of adhesive specimens imder normal compression and shear. Specimens fixed with Sprut-5M and VAK in air, under water, and in oil remained in these media until tests began. The specimens were exposed to compression in the stresses range iTc = 0—28.0MPa and failed under the action of shear stresses t. 

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