CS217877B1 - Hardener for foundry molds and cores - Google Patents

Abstract

The invention provides a hardener for foundry mixtures for the production of molds and cores with water glass as a binder. The hardener consists of quartz, fireclay, shale or chrome-magnesite grinding media in an amount of 100 parts by weight, water glass in an amount of 1 to 8 parts by weight as a binder. The essence of the invention lies in the addition of monoacetate, or glycerin-chlorohydrin diacetate, or their combination in an amount of 0.1 to 2 parts by weight, as a hardener. This hardener has similar properties to known glycerol acetates, but due to the substitution of one -OH group by a less reactive chlorine atom, the incubation time is significantly extended, so that the workability time of the mixtures according to the invention is in the range of 60 to 180 minutes. After the workability time has elapsed, the strength increases within a short time to the values required for casting.

Description

SUMMARY OF THE INVENTION The present invention provides a hardener for the manufacture of a mold and core foundry composition with waterglass as a binder.

At present, in foundries, a process for producing molds and cores is introduced into self-setting mixtures bonded with water glass, in which the necessary consolidation is achieved by chemical reaction of water glass with added hardener. The essence of the process is the existence of an incubation period during which it is necessary to homogenize the mixture, fill it in the core box or molding frame, insert reinforcements, adjust the vents and pack up. Only after the incubation period, which indicates the so-called pot life, has been exceeded, do the bonding bridges begin to form and the strength increases. The unprocessed mixture, which has exceeded the incubation period, quickly becomes obsessive and loses its binding properties.

A number of possible hardeners have been described, in particular esters of acetic acid and glycerol or ethylene glycol are used in practice. Workability time of mixtures with these hardeners can be controlled by adjusting the composition of the mixture in the range of 1 to 45 minutes and can therefore be successfully used for a range of cores and molds that can be completed in these Czech, especially for cores and molds small to medium weight, event. with less labor.

However, there is an extensive assortment of cores and molds that require substantially further - even several hours - pot life in production. These are in particular cores and molds of heavy castings, such as reactor vessels, turbine nozzles, some metallurgical castings, or castings of high articulation, such as pump impellers, cylinder heads. To date, these castings have to be manufactured into conventional drying compositions that have low productivity, high energy consumption and impose considerable demands on the skills and craftsmanship of the workers.

These disadvantages are overcome by the hardener for the production of the foundry molds and cores according to the invention. The mixture consists of quartz, chamotte, flake or chromium-magnesite grit in an amount of 00 parts by weight, of water glass in an amount of from 8 to 8 parts by weight as binder. The invention is based on the addition of glycerol-chlorohydrin monoacetate or diacetate or a combination thereof in an amount of 0.1 to 2.0 parts by weight. This hardener has similar properties to known glycerol acetates, but due to the substitution of one -OH group with a less reactive chlorine atom, the incubation time is greatly extended so that the pot life of the compositions of the invention is in the range of 60 to 80 minutes. After the pot life has elapsed, the strength increases within a short time to the casting values.

The spice and water glass used may be of normal foundry quality, no special treatment is required. Monoacetate or diacetate of glycerin-chlorohydrin, optionally. a mixture thereof can be readily prepared by direct esterification of epi-chlorohydrin with acetic acid or acetic anhydride. The advantage is the easy availability of epi-chlorohydrin, which is produced in large volumes as a basic raw material for the production of epoxy resins. By changing the ratio of mono and diacetate in the hardener, reactivity can be easily controlled, thereby adapting the process of the core and mold production process to external conditions.

A further advantage of the hardener according to the invention is the possibility of using the existing equipment for ST mixture technology for an extended range of castings. Due to the extended processing time, large-volume cores or molds can also be produced using low-capacity and inexpensive mixers. By slow curing, a less stretched and more perfectly organized structure of the bonding bridges is formed, so that the resulting strengths per unit binder content are higher compared to prior art hardeners. The binder content of the mixture may therefore be lower, which will significantly improve the disintegration after casting.

Example,

A foundry mixture of the following composition was prepared:

quartz sand water glass h. 1.51 mixture of 90% mono and 10% glycerin-chlorohydrin diacetate

100 parts by weight 3 parts by weight

0.15 parts by weight.

50/50 standard measuring bodies were prepared from the mixtures in a standardized manner, on which the following time dependence of the increase in strength was measured:

pot life: 150 min compressive strength - MPa over time

1 h 2 h 4 h 24 h 48 h - - 0.5 3.3 4.0

Example 2

A foundry mixture of the following composition was prepared:

quartz sand 100 parts by weight water glass, h 1.5 '3 parts by weight mixture of 30% by whom and 70% glycerine-chlorohydrin diacetate 2.0 parts by weight

Under the same conditions, the following curing process was observed:

pot life: 90 min

compressive strength - MPa over time 1 h 2 h 4 h 24 h 48 h - 0,8 3,2 4.7 4.9

Claims (1)

Hardener for the production of foundry molds and cores consisting of quartz, chamotte, flake or chromium-magnesite grit in an amount of 100 parts by weight, of water glass in an amount of 1 to 8 parts by weight, characterized in that it contains glycerin-chlorohydrin monoacetate or diacetate, in an amount of 0.1 to 2.0 parts by weight.