Study of polymer adhesion to steel

. Tests on the dependence of glues shear strength on: gluing temperature, keeping time before testing, cooling environment, surface roughness, surface conditions, temperature and time of drying on air and in drying oven were carried out to select proper thermoplastics to use as glues for connection of steel elements together. The highest shear strength was showed by the following materials: desmopan 150, antifriction polyamide PA 610-L-DM, impact-resistant glass-filled polyamide. Given results allow significantly expanding scope of application of polymers as gluing compositions.


Introduction
Polymers and elastomers are increasingly used in general mechanical engineering, transport and metallurgical equipment. One of directions of polymers widespread introduction is reduction of non-technological loads in metallurgical equipment [1][2][3][4][5]. Polymers and elastomers are low-modulus but rather durable materials. Their energy efficiency is comparable to energy efficiency of spring grades of steel. Elastomer-based shock absorbers are simple in design and operation, they are superior to springs in many basic parameters [6][7][8][9][10][11][12].
On the basis of modern structural polyurethanes effective elastic couplings and shafts can be created [13]. The main difficulty is the method of connecting elastic polyurethane element with steel coupling halves, i.e. compound elastomer with steel [14][15][16][17][18]. Such connection should be durable and technological.
Existing glue compositions do not provide either required strength or technological ability of process of gluing. Shear strength of glue line must be not less than strength of base material (polyurethane or some other elastomer). At the same time, ultimate shear strength should be  sh = 20…30 МPа.
Works [19][20][21] on study of glued connections are known for the above mentioned purposes. However, in these works required results were not achieved. In this paper polymer melts were tested as glues. Gluing technique was initially technological and required strength was achieved in stages by varying gluing conditions.

Research Material
To select the most promising thermoplastics as glues (refer to fig. 1) rapid tests with following polymers were carried out (given grades are used in CIS countries): • desmopan 150; • glass-reinforced polyethylene terephthalate PETF(В)-KС-40; • composition based on polyamide PA 610-L-T20; • glass-reinforced polypropylene PP-KC 30; • glass-filled antifriction polyamide PA66-KС(М); • antifriction composition based on polyamide (PA6-МоS2); • composition of polypropylene with mineral filler PP-Т20; • glue-melt polyamide; • antifriction polyamide PA 610-L-DM; • impact-resistant glass-filled polyamide.   Samples are made from steel grade 45 (grade is used in CIS countries, refer to fig. 3), they were heated in a special furnace; polymer granules were placed on one of heated halves of the sample and after they were melted (formation of transparent drop), this half was combined with the other one that was also heated. Then the sample was cooled on air or in water.  In addition, effect of keeping time of the glued samples before testing the strength of the glued connection was investigated. Results of these tests are shown in table 2. Desmopan requires at least five hours to achieve maximum (calculated) strength; there was no particular difference in strength (at different keeping time) for polyamides. Table 3 shows results of testing samples that were cooled in two ways: on air and in water. All samples showed significantly greater strength under condition of air cooling.
In the next series of experiments effect of gluing surfaces state of steel samples on strength of glued connection was investigated. Samples with grinded and rough surfaces were tested. Results of these tests are given in  Another series of samples was tested with various surface conditions: non-oxidized and oxidized. Adhesion to oxidized surfaces was slightly higher (refer to table 5).   fig. 4 and fig. 5) and diagrams (refer to fig. 6-9).