Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles – Stratified or layered articles
Patent
1992-01-17
1995-02-21
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
Stratified or layered articles
264 63, 264220, 264225, 264305, 164518, B29C 6700
Patent
active
053913418
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for the manufacture of ceramic shells for use as molds in which which contains a colloidal, aqueous silica sol and polymers to form a wet coating the pattern, desired thickness.
The invention also relates to a binder in the above process.
BACKGROUND OF THE INVENTION
In such a process, pattern clusters of wax or a similar material are provided with a solid ceramic layer with a thickness of a few millimeters by applying several dip coats. The individual layers, after having been applied, are dried or hardened separately. On each individual wet dip coat a coarse, refractory powder or sand is scattered as a binding agent for the following dip coat. Following dewaxing the shells are fired and can then be used for casting whilst still hot or after cooling down.
Processes of the type described above which use aqueous binders are limited in their use in that, contrary to alcoholic binders, aqueous binders require a very extended drying process and, ultimately, had to be subjected to suitable vacuum drying to obtain complete dryness. It has been tried to overcome these problems by mixing alcohol, e.g. isopropanol, into the aqueous binder. The alcohol replaced part of the water and had the characteristic feature to evaporate quicker than water. However, the water alcohol mixture was unable to prevent, during the subsequent dipping operations, the water/alcohol mixture from penetrating again into the previously applied and already dried coat, so that with progressive dipping ever increasing drying times were required. Other methods were also tried to solve the pertinent problems.
From the U.S. Pat. No. 3,005,244 it is known to add to a 30% aqueous silica sol binder with a quantity of resinous polymers so that the solid content of the resulting binder consists of 60 to 80% by weight of SiO.sub.2 and 8 to 35% by weight of resinous polymer. Ceramic shells which are produced with this binder have, among other things due to the addition of the polymers, an increased green strength of the shell which is said to permit fusion of the wax from the shell without the intermediate use of an autoclave.
The U.S. Pat. No. 3,126,597 describes a ceramic shell with an aqueous binder based on silicic acid (30% by weight), to which water is added for dilution and to which sodium fluoride is added for accelerating the sol/gel reaction. The sodium fluoride leads merely to a quicker hardening of the individual ceramic layers applied but does not prevent penetration of the aqueous binder into the previously applied ceramic layers during the subsequent dipping operations. This binder combination requires long drying times and, in the case of shells with a higher number of layers, ultimately vacuum drying.
The U.S. Pat. No. 3,165,799 describes a triple dipping process for the manufacture of a ceramic shell for multiple-core investment castings in which the first ceramic dip layer is applied with an aqueous binder with subsequent sanding. Following this, a second ceramic dip layer with aqueous binder, to which 0.5 to 2% by weight of polyvinylalcohol has been added, is applied without sanding or stuccoing. Thereafter, a third ceramic dip layer with aqueous SiO.sub.2 binder with 0.5 to 2% by weight of polyvinyl alcohol is applied under vacuum with finish sanding or stuccoing. The aforementioned dipping sequence has the advantage of permitting the manufacture of investment castings with core parts which can otherwise only be manufactured with ceramic cores.
From the U.S. Pat. No. 3,752,689 the manufacture of a ceramic shell by a rapid process with an aqueous binder with 26.4% by weight of SiO.sub.2 and 4.2% by weight of Al.sub.2 0.sub.3 is known, with the aforementioned binder being converted from the sol state into the gel state by respectively organic and inorganic bases. This process permits applying the individual ceramic layers relatively quickly but has the disadvantage that each ceramic layer is infiltrated by the aqueous binder subsequently applied layer, and that lengthy final
REFERENCES:
patent: 3005244 (1961-10-01), Erdle et al.
patent: 3126597 (1964-03-01), Operhall
patent: 3165799 (1965-01-01), Watts
patent: 3196506 (1965-07-01), Operhall et al.
patent: 3745139 (1973-07-01), Kachur
patent: 3752689 (1973-08-01), Moore
patent: 3859153 (1975-01-01), Beyer
patent: 3894572 (1975-07-01), Moore, Jr.
patent: 3898313 (1975-08-01), Taylor
patent: 3933190 (1976-01-01), Fassler
patent: 5159970 (1992-11-01), Burkarth
Derwent, Preparation Cast Model Shape Relief Coating . . . p. 2 Oct. 22, 1991.
Ballewski Heinrich
Graf Herbert
Grossmann Wolfgang
Ballewski Heinrich
Graf Herbert
Grossmann Wolfgang
Theisen Mary Lynn
LandOfFree
Process and binder for the manufacture of ceramic shells for use does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process and binder for the manufacture of ceramic shells for use, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process and binder for the manufacture of ceramic shells for use will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1928330