The design of experiments in the rubber industry: a European viewpoint.

The design of experiments in the rubber industry: A European viewpoint

The following is a portion of a review that encompasses design of experiments in the rubber industry.

Industrial applications: 1947 to 1965

In the UK Davies and Goldsmith[1] at ICI produced the first industrially based manual on the use of statistics in manufacturing. We should of course recall, that Shewhart[2] published his book on quality control back in 1931. This work included extensive use of statistics, but is not directly applicable to the subject. This was followed by Brownlee[3] and Davies and Hay[4]. Box and Wilson[5] wrote on attaining optimum production conditions and Box[6], Davies and co-workers[7] produced the most important single work on industrial experimentation in the West in the 1950s.

From 1949 until the mid 1960s Youden[8-32] regularly published short notes on all aspects of experimental design in the chemical processing industry. These provide a singular documentation on all approaches available during this period. Most of his papers are simple, directed at technologists and engineers (in that sense Japanese) and have lost nothing over the intervening years. I can recommend these to all concerned.

Lindner[33] uses, as practical illustrations in his book, optimization studies from pharmaceutical and food stuffs production, which were carried out in Switzerland in the 1940s. Read[34] wrote on the design of chemical experiments, Vaurio and Daniel[35] on process variation. In 1955 Hamaker[36] wrote on the use of experimental designs in industry and McArthur[37] discussed practical designs in chemical research, Bicking[38] reports on a number of industrial experiments. Daniel[39,40] discussed the importance of fractional replication in industrial experiments in 1951 and again in 1957.

The first paper on statistics and polymerization was that of Pasteelnick and Leder[41]. Bradley[42] wrote on process optimization. An important collection of papers was that edited by Chew[43] which appears to have been the first conference on DOE in Nov. 1956 at North Carolina State College and which included examples from industry. This was the first in a series of over 30 conferences which were sponsored by military research establishments. Papers were presented among others by Box and Tukey.

Mitchell[44] gave an example of DOE in designing a complex robust component. Smith and Jones[45] and Dean and Jones[46] wrote on the use of DOE to optimize a ceramic process. Bicking[46a] reported on a number of industrial experiments.

One of the most important events of this period was the publication of Technometrics in 1958, which has done for industrial application of DOE at least as much as Biometrika in the UK and Biometrics in the USA for biology and agriculture. No technologist concerned with research or quality problems, should be without a subscription to this magazine.

The Japanese contribution

Where were the Japanese? Well we all know by now that modern Japanese industry was "born" about 1950. So was DOE in Japan. From the outset DOE was considered to be a quality assurance tool. Using the bibliography from Federer and Balaam[47] on DOE up to 1967, I found the earliest Japanese refrences to be Masuyama in 1946 with papers on pharmaceutical applications[48-50]. It would appear that nothing had been published in Japan before then. However, this may be a matter of inaccessibility. None-the-less even Taguchi[51] mentions nothing before 1953 when Kitagawa and Mitsutome[52] published lists of an array of sources for DOE. The first paper on an industrial application is a further paper from M. Masuyama[53], which explains DOE for plant technicians. G. Masuyama[54] also takes the credit for the first Japanese textbook on the subject. According to Taguchi[51], Masuyama's[56] work on orthogonal arrays was revolutionary and, with Okumo, he also discussed optimal designs[57]. Fumiro and co-workers wrote on optimization of a process in wool spinning[58] while Kakehashi wrote on paper manufacturing[59]. Kayano explained DOE for technicians[60]. These examples already illustrate a major difference between Japan and the West: within the ten years after the appearance of DOE in Japan, emphasis, in published papers, was on industrial applications. I will return to this later in the discussion.

Taguchi's first paper appeared in Hinsitu Kanri in 1953, a short note on experimental design[25]. A more important text, the precursor of his now famous book was published in 1956[61] while his papers on orthogonal arrays came in 1959[62,63].

DOE and rubber manufacturing

Derringer[64] gave a comprehensive review of the use of statistical methods in the rubber industry. Indeed he has been the major single contributor to the literature on the use of statistics, particularly for compound development[64-78].

In 1954 Youden[15] reported on the use of DOE to optimize the testing of the abrasion loss of rubbers. Also in 1954, Box and other co-workers at ICI in the UK in Davies[7] illustrated the different methods of design and analysis of experiments with practical industrial problems, including the study of abrasion of rubber, road tests on tires and wear resistance. This was followed in 1955 by a paper on statistics in rubber technology by Box[6].

In the same year Gore[79] published a paper on statistical design in compounding elastomers in Rubber Age. I am not aware of Taguchi having included rubber experiments in his original book but he certainly does in his (1978/1987) book[80,51], where he includes experiments on oil seals and carbon black.

Further papers in the 1950s are fairly scarce, but include the following: Tyron, Horowitz and Mandel on the spectroscopy of natural rubber[81]; Zimmerman, Hart and Horowitz[82] on the sulfur content of vulcanizates. Youden[19] on the estimation of error in physical testing.

In 1961 Bertsch[83] reported on response surfaces in compounding experiments and Frankel[84] on optimizing the yield of MBT, the latter has, of course, more to do with chemistry than with rubber.

In the 1960s the first technical brochures with information based on mixture experiments and what appear to have been full factorials appeared. Examples include: Schoenbeck, Roche, Bedwell and Souffle[85] apparently used response surface methods to prepare a brochure on EPDM. Weissert and Cundiff[86] used response surfaces in a compounding experiment for BR/NR blends for truck tires. Roche[87] and Shaw[88] used response surfaces for EPDM compounding. Behnken[89] used optimum two level designs and non-linear regression to estimate polymer reactivity ratios. Hirutani[90] wrote on the use of optimum constrained designs for compound development.

1965-1980

Buckler and Kristensen[91] used response surfaces for the appraisal of elastomers. Williams[92] wrote on DOE in rubber compound development. Buzulica and Moscovici[93, 94] published three papers on compound optimization in Romania. Derringer[65,66] published two papers using response surfaces in compound development, the first using a central composite design in an accelerator study, the second using a five level design to optimize silica filled SBR compounds.

The first experiments in product development appeared. Johnston[95] studied pneumatic springs. Klosner and Segal[96] examined the mechanical properties of natural rubber and Kolsky[97] looked at elastic responses. Liebscher and Klitzsch[98] used EVOP to improve textile adhesion in Germany. Ploi[99] used DOE to study NR/BR and BR/SBR blends.

In the 1970s the flow of papers using DOE for the study or optimization of rubber products slowly continued to increase. In my files there are 43 references to the use of DOE in rubber studies in this period. This isn't much, but it probably does not reflect its growing use. Some of the more important papers were Sarbach et al[100] on filler levels in SBR, Lane[101] on EPDM using response surfaces. Cox[102] used DOE to study the effects of sulfur levels on rubber properties.

Derringer[78] published a manual on DOE methods in compound development, this was followed in Germany by Ploi[103] and Kryzek. Rohde and Fendel[104] used large constricted designs to optimize the flame resistance of polychloroprene. In the Soviet Union, Gurevich[105] and others used Scheffe mixture designs to study vulcanizate properties. Good[106] adapted decision theory to the design of experiments for compound development.

Important papers on the use of computers in compound optimization were published. These were Hartmann and Beaumont[107] on optimization of compounding by computer, Claxton and co-workers[108] on the role of computers in elastomer research, Schleuter[109] on using computers as a compounding tool, Derringer[68] and Silvey and Haller[110] on computer prediction of the properties of EPDM in a compound development study, followed by Gatza and Macmillan[111] on the use of experimental design and computerized data analysis in elastomer development studies.

However it was not until the 1980s that this type of experimentation became widely known within the rubber industry. However the number of papers published worldwide, in which the use of DOE in rubber studies is apparently only 93. Many papers contain mathematical information, which may have been obtained through the use of DOE but where this is unclear. In many papers there is no reference to the statistical or mathematical methods used to collate data.

However in view of the fact that the benchwork methods and instruments used, as well as, for example, the mixing method for preparing the compound, there may be a case for the ACS, Rubber Division to think about including the statistical methodology in future papers.

Among the more interesting papers published after 1980 are: Derringer[71] on the role of DOE in testing and problem solving, Derringer and Suich[77] and Derringer[73] on the use of Harrington's Desirability Function and response surfaces for compound optimization, and on the use of SPC and DOE to optimize an elastomer widget[75], Derringer and Watkins[112] on testing and optimizing elastomers in multicomponents aggressive environments. Basir and Freakley[113] used a central composite design in a mixing study on PVC/nitrile blends. Carlson[114] recommended DOE to reduce the costs of compound development. Wardig[115] improved the flame resistance of EVA cable jackets using response surfaces. Rulon[116,117] tried to optimize the production of sponge weatherstrips using Taguchi methods. Church[118] discussed different strategies for product improvement in rubber manufacturing, including DOE. Dunn and co-workers[119] used Taguchi methods to improve the high temperature aging properties of EPDM. Tobing[120] used resolution V fractional factorials to improve the properties of NR/EPDM blends. Karg[121] discussed the injection molding of EPDM using L8 and L16 Taguchi arrays. Ruiz[122] on DOE in the rubber industry and Ruiz and Benefeld[123] on DOE to study the effect of polymerization conditions of EPDM on the properties of polyolefinic TPEs.

In our area a considerable contribution has been made through the symposia of the American Suppliers Institutes with over 20 papers on rubber studies[117,124-141). These are, however, very one sided, because only Taguchi Methods are used. Often the details have been fudged or blurred to maintain propriety secrecy, which of course is understandable. This may be useful for the presenter, but is extremely limiting for the reader, especially when the data have been so manipulated as to make the predictions ludicrous.

None-the-less the rubber contributions are worthy of attention. Papers were presented by Gaston[124] on injection molding; Lear and Stanton[125] on reducing contact staining of sponge weatherstrips. Terasek[126] on injection molding, Finley[127] looked at the problem of shrinkage in the extrusion of EPDM in continuous curing, Lear[128] reduced compression set of sponge weatherstrips. Smith[129] improved compound quality of extrudates. Stanton[130] used Taguchi L18 arrays in experiment on sponge weatherstrips. A molded part was improved by Enriquez[131]. Harrell[132] looked at the extrusion of weatherstrips. Miller[133] studied the molding process for a filler plug. Flock adhesion optimization of EPDM weatherstrips was carried out by Rickel and Griffith[134]. Seagrave[135] developed a better adhesion system for automotive windshields. Sparks[136] improved the splicing of EPDM weatherstrips using hot adhesive bonding. The closing forces on the Ford Tempo and Topaz car models were improved through the optimization of the sponge weatherstrip by Stanton[137].

Caudill[138] created a better design of a rubber connector and at the same time improved the molding process. DeMates and co-workers[139] improved the insulated cable extrusion process. A tire treadwear experiment was carried out by Fluegge and co-workers[140].

References

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