DE2459797C3 - Process for the production of molded parts from cement - Google Patents

Description

The subject of the main patent 23 53 490 is a process for the production of molded parts Cement to which inorganic aggregates can be added, the cement with an aqueous or aqueous alcoholic solution of an acetylene-formaldehyde resin made into a paste, poured into the mold and is cured at a temperature between 30 and 100 ° C.

As disclosed in this patent specification, molded parts made of cement, which can also be mixed with inorganic aggregates, can be cured in a considerably shorter time if the cement is mixed with water and cured in the cold with an acetone-formaldehyde (AF) resin solution and hardens at elevated temperatures, namely in the range of 30-100 ° C., preferably 60-90 ° C. The hardening can be carried out at normal pressure or increased pressure of up to 150 kp / cm ² Faster hardening is accompanied by a considerable improvement in flexural strength. After about 2 hours of hardening, the molded parts have the same or even better flexural strength than cement molded parts of the same size that were mixed with water and hardened for 24 hours at 20 ° C. By extending the hardening time of the cement AF resin moldings for 24 hours, the flexural strength can be further improved.

10-10 parts by weight of AF resin solution, based on the solids content, are used per 100 parts by weight of cement. The AF resin is preferably an alkaline condensed at 20-100 ⁰ C resin of an AF MoI verhäitnisses of 1: 1.5 - 5 or is best 30-60gew.-aqueous or aqueous-alcoholic solution foige used as. Up to 25% of the acetone in the resin can be exchanged for other compounds which are reactive towards formaldehyde.

With the additional patent 23 53 474 the process according to the main patent is further developed, that molded parts based on cement can also be obtained which have a lower specific weight have and can be nailed, in that the cement wood in before pasting with the AF resin solution finely divided form is incorporated. 20-200 parts by weight of finely divided cement can be used for 100 parts by weight of cement Wood can be used.

In a further development of the method described above has now been found that the curing times can be shortened still substantially characterized in that the curing at temperatures between 100-200 ° C, preferably, is made of 140 to 170 ⁰ C. At these temperatures, a curing time of 3 hours is sufficient to obtain molded parts whose flexural strength is about as high as that of the same molded parts which, however, were allowed to cure ^{at about 80 ° C. for 24 hours.}

In addition, it was found, completely surprising, that curing in the temperature range of 100-200 ° C. has an advantageous effect on the hydrolysis resistance of the finished molded parts, as shown by the determination of the transverse tensile strength carried out in the following examples after storage in cold and in boiling water. The transverse tensile strength after storage, in particular in boiling water takes for cement AF resin molded parts which are cured at temperatures above 100 C, much less from, as for the same parts which have been cured under 100 ⁰ C.

Examples 1-3

In Examples 1-3 which now follow, a 60% strength by weight aqueous AF resin solution was used A to F molar ratio of 1: 2.5 sand with an average grain size of 0.28 mm and Portland cement 550 worked.

In a laboratory mixer, 750 g sand and 250 g cement were dry mixed for two minutes and from the mixture in a ram box (according to VDG leaflet P71, Jan. 1970) rods are made. At The flexural strength of the hardened rods was determined in accordance with DIN 52 404, Sheet 1. Also were Plates of usual size (450 X 420 X 60 mm) are made and the transverse tensile strength on them after hardening determined according to DIN 52 365. The curing conditions and the test values obtained are as follows Table 1 can be found.

Table I.

Hardening conditions

Flexural strength (Kp / cnv)

Ouer / iigigkeit (Kp.Vni ι according to sh
in water mn KHi ι m. dryer,
animal samples)

Example no.

2

h at 80 C lh at 80 C and 1 π at 80 C a.

2! I at 120 r 2 h at 1S0C

54 51

(I 1. <20

Table II

Curing conditions

Curing conditions

Press factor (press time in min./mm panel thickness)

Panel thickness (mm)
Specific weight (g / cm ² )
Flexural strength (kp / cm ² )

Transverse tensile strength (Kp / cm ² ) After 2 h in water at 20 ° C

After 2 h in water at 100 ° C after 8 hours in water of 100 ⁰ C swelling (%)

After 2 h in water at 20 ^° C. After 24 h in water at 20 ° C

Example No. 4 5

Min. 145 ^D C, 22 Kp / cm ²

b. 110 ⁰ C

Min. B. 110 "C 145 ^C C, 22 Kp / cm ²

1, C 1.3 1.6

16 16 16 1.32 1.32 1.30 155 236 248 243 8.2 9.7 13.3 9.3

4.1

2.1
6.5

4.5

2.6

3.2

4.5

1.9 5.8

Examples 4 and 5

In Examples 4 and 5, cement wood particle boards were produced according to the invention. There were 60 parts by weight of cement (it was the same cement used in Examples 1-3) and 40 parts by weight of wood chips (with a residual moisture content of 2%) with 24 parts by weight of a 56% by weight AF resin solution (acetone: formaldehyde molar ratio 1: 2.5) mixed and put on the platen press pressed under the conditions given in Table II. The finished panels were tested for flexural strength Tested according to DIN 52 362, transverse tensile strength according to DIN 52 365 and swelling according to DIN 52 364. the Curing conditions and the values obtained on the finished test panels are shown in Table II.

Claims (2)

Patent claims: 1. A process for the production of moldings of cement, the inorganic additives may be mixed, wherein dei cement with an aqueous or aqueous-alcoholic solution into a paste of an acetone-formaldehyde resin poured into the mold and cured at a temperature between 30-100 ⁰ C. is, according to main patent 23 53 490, and where the cement before pasting with the AF resin and wood in finely divided form can be incorporated according to additional patent 23 53 474, characterized in that the hardening is carried out at temperatures between 100 and 200 ° C . 2. The method according to claim 1, characterized in that the curing is carried out at temperatures between 140 and 17O ⁰ C.