In this paper is described a possibility for estimation of the bench life of the furan moulding sands by using of two criteria - their shearing strength and friability. On a facilitation of the work, a computer program introduced here concisely is made.
Introduction
The goal of this report is the presentation for the first time the opening version of a simple computer program, giving information about the strength characteristics of group of moulding mixtures with furan resin as well as for the time in that these characteristics keep themselves and the manufacturing of moulds and cores is without problem. The program is made based on standard technology explorations, held in the Foundry lab at the Technical University of Sofia. The opening version is intended for using in the education of the students in Foundry Engineering.
Bench life of furan sand
The bench life of furan moulding sands the most frequently is determinated by the described by J.Loix in 1972 procedure [1]. At that procedure the specimens on strength tests are made consecutive, as the gradual worsening of the quality of the mixture is expected intentionally, due to interaction between the furan resin and and the hardener. The time for which the strength decreases by 15 percent with respect to the strength of the specimen, made immediately after preparing the mixture, is calculated so.
If the bench life (i.e. time), min, of the mixture with some ingredients content is determined according to the change of different strength characteristics, the picture shown in Fig.1 [2] will be got. It is noted that in accordance with chosen strength, the time,
 |
when the mixture is still serviceable for exploitation, is various - in the frameworks
of 5-9 min. For that difference to be avoided it is possible for it to enter in two manners. The coefficients can be entered with
first, which give an account the relations between separate strength properties. The second means is as an additional criterion for the bench life to be find some critical value of the friability (surface strength) of the mixtures, over that value they become inoperable. The experiments here in that second direction are made. Introducing the friability as one more criterion for the bench life, it is the best in comparison to use shearing strength instead of other strength characteristics. This is predetermined by the identity in the form and the manner of making of the cylindrical specimens 50/50, as from holding the test as well in lower workloads than in compressive strength, done with the same type of specimens. The very important circumstance, became clear in the tests, is as well that the 15% lessening of the shearing strength is practically |
Fig.2. Bench life determined by the shearing strength and the friability
By means of the regression equations (1) and (2), the bench life of the mixtures with the content of furan resin and hardener, extra-exposed in Fig.2, can be determined as well:
by the shearing strength: Ts = 17.42 - 3.99232*Resin - 0.169749*Hardener (1)
by the friability: Tf = 17.16 - 3.21194*Resin - 0.226754*Hardener (2)
With the received experimental data the initial version of a calculation program of specifying the bench life of the furan moulding mixtures is developed. The screen is shown in Fig.3 and it consists of the following sections:
- Input data section, with windows for the type of ingredients furan resin and hardener (for now only one type of them), and their content - furan resin to the sand and hardener to the furan resin;
- Results section, in left. It shows: 1) strength characteristics, defined 24 hours after the specimens making, which are made immediately after preparing the mixture; 2) the example color of the mixture;
- Results section, in right. It shows: 1) the bench life by the 15% lessening of the shearing strength and the bench life found by the 0.3% increasing of the friability, i.e. the moment at which the friability overshoots 0.3 percent; 2) the visualization of the calculations.
Fig.3. The screen of the program for the computing of bench life
Conclusion
It is thought that the developed program will be useful in the education process.
It is envisioned the experimental results will be entered in the next version of the program for: 1) materials from the product list of world-renowned manufacturers of furan resins; 2) such properties as the gas evolution capacity, adherence to patterns, time for stripping of the patterns, demoulding force, etc. At one widening of database, it is possible to create interest by the manufacturers of castings in furan moulding sands as well. Then, the user (manufacturer) will choose what in this two values of the bench life Ts or Tf, or the interval between them, will be helpful at his production work.
The program is usable at the following address (url): Bench Life of Furan Sands.
References
- Loix, J., Quelques problemes poses par l'utilisation en fonderie des sables autodurcissants lies aux resines
furanniques,
La Fondene Belge, 1972, No 1, p. 9-14. - Alipiev, D., About some properties of the furan moulding sands, Research Work Reports of University of Rousse, Bulgaria, 1994, 35, p. 224-229.
* Paper of the Annual Scientific Conference 2007, November 8-10, 2007, The University of Rousse "Angel Kanchev", Rousse, Bulgaria.
