DE1221767B - Precision molding process - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

B22d

German, 31c-5/01 _p ^ ^ '

Number 1221767 * ΚΪΖ.

File number: P 34143 VI a / 31 c

Filing date: April 28, 1964

Opening day: July 28, 1966

The invention relates generally to precision die casting and particularly relates to a better method and molds for precision casting of steels.

A common problem heretofore in the precision die casting industry has been the production of Steel die castings with an unmachined cast surface finish of high quality. In particular It is recognized that certain precision cast steels are subject to surface pitting, surface wear or cave formation on the surface, which is a main cause of being rejected as scrap Castings was subject to. This condition of surface pitting is often called chrome pitting referred to as all stainless or corrosion-resistant steels of the 400 type series at least to a certain extent are to be regarded as being prone to surface pitting. The said Condition is particularly bad in the case of stainless steels of types 410 and 416, and in the case of martensitic steels stainless steel of the type 410 it is specially called "410-erosion".

As will be known to those familiar with this problem, the state of seizure often takes shape of circular holes or depressions with diameters of up to 0.79 mm or more. Sometimes individual holes or depressions are through a smooth surface of 3.18 to 6.35 mm separated, while another time the holes or depressions are so close together that the entire surface of the casting appears rough. In general, however, the holes or depressions are then bigger and deeper when they are less numerous and they tend to be flatter and lower to be smaller when they are closer to each other. There can be both types of erosion at different Parts of the same casting are determined.

The process of the attack causing the attack is not entirely clear, although it can be assumed is that it is a reaction between the metal and the mold material which occurs after solidification occurs, acts. This reaction turned out to be very temperature dependent. So the condition at Alloys that have only a slight tendency to "410 pitting", such as types 420 and 440, generally controlled or controlled by avoiding excessive temperatures during casting to be influenced. With types 410 and 416, however, an additional action must be taken to avoid this the surface corrugation can be carried out.

Due to the fact that the causes of the surface pitting are not completely clear, were Precision molding process

Applicant:

Precision Metalsmiths, Inc.,

Cleveland, Ohio (V. St. A.)

Representative:

Dipl.-Chem. Dr. St. G. Beszedes, patent attorney,

Dachau near Munich, Am Heideweg 2

Named as inventor:
Robert Andrew Horton,
Chesterland, Ohio (V. St. A.)

in the past many different procedures and Theories developed in attempts to deal with this problem. One of the most common ways of working the prior art was the addition of halogenated hydrocarbons into the hot mold cavity immediately before watering. For this purpose, liquids such as trichlorethylene, Chloroethane and carbon tetrachloride, although solid materials such as polytetrafluoroethylene or Teflon turnings were used. It was believed that evaporation and partial combustion of these materials within the mold cavity creates a reducing atmosphere which prevented the seizure reaction between the metal and the mold.

This conventional method has had only partial success and is difficult to control. If one doesn't sufficient amount of the inhibitor is used or if too long a period between the time its addition to the mold cavity and the casting of the metal passes, so that the material if it burns or escapes, the desired effect will not be achieved. On the other hand, if there is too much Inhibitor is added, the risk that the material will not evaporate before casting and that in the casting is enclosed in gas. Further, when the shape of the mold is complicated, it is difficult to to obtain an even distribution of the inhibitor in the mold cavity.

The conventional method described above has other disadvantages inherent in it. It includes one additional work process for the foundryman at the moment when he is busy with other work is. If necessary, for relief

609 607/319

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the filling of narrow places or corridors is a par-

Applying a tial vacuum to the mold then tends to remove outgrowth as is known in the art

uses the vacuum to draw the inhibitor through the model material from the shell mold,

the pores of the mold before casting the metal. According to this procedure, the hollow shape in

Eventually, the combustion of the halogen 5 creates an elevated temperature furnace, for example

compounds vapors, -which annoying and in some 871.1 to 982.2 ° C, introduced. Under these conditions

Cases are poisonous. For example, there can be rapid heat transfer through the tetra- tion

chlorocarbon, trichlorethylene and the like. Phosgene molded shell, so that a surface skin of

form. , ---.- ·, wax melts before the mass of the wax so

It is an object of the invention to heat a precision casting sufficiently that it will expand and the

method and precision casting molds to obtain hollow form could blow or break. While

a high surface quality in the area of the steel - if the mass of the wax heats up, the melted

provide casting alloys. zene surface material either from the form,

Furthermore, the invention is directed to a precision or it seeps or penetrates through the hollow shape. this

sionsgießverfahren and precision molds, which 15 gives a space for adaptation or inclusion

the subsequent expansion of the mass of the previously in many precision-molded alloys

The condition of the surface freshening wax occurs in such a way that it does not damage the hollow shape

essentially switch off the solution. bursts or breaks. .

Another object of the invention is to provide removables made from synthetic resins

a precision casting process with the above-described models can be made from hollow molds through initial

benen advantages, which simply, cheaply and quickly soften the model material with a usable

can be carried out. Solvent for synthetic resins successfully developed

The invention is also directed to a method to be removed. The hollow mold is then heated in an oxidizing atmosphere in order to eliminate surface erosion, in order to drive off the last essential in precision molded steels, 25 remnants of the fashion material and which, with known ceramic hollow mold casting, the mold for receiving the molten metal or shell casting process for precision casting. to be completed.- · -..-.
according to the invention, the hollow mold is provided with a refractory material for hollow molds or shells coating with a deoxidizing agent. 30 after it has been used in the precision mold casting industry to accept the molten metal and has been sufficiently burned out and cooled to approximately room temperature. This is preferably done by mixing mold shells instead of the conventional coating of the hollow mold or casting shell by means of unwieldy or massive precision casting molds, immersion in a suitable slurry and the present invention is suitable for this 35 subsequent application of the coating from the modern shell casting process to precision casting slurry in the still damp condition with part especially. Since the shell molding process is accomplished by the skilled person of coarse deoxidizing agents, it is clear that only the following summary of this process is given for the purpose of hardening. temperature to form a coating to hold

Shell molds will generally be capable of deoxidizing agent infiltration and casting dipping a removable model that does not or does not disintegrate at a temperature of the metal Reproduction of the part to be cast is to be dismantled, including. The slurry used the necessary sprues or ■ inlet channels and, if necessary, the slurry of the fire-rising funnel into a slurry of refractory solid material which is used to build the hollow shape Material consisting essentially of a suspen- 45 was used in the manner described above, si'on a fine refractory powder in a suitable one.

Binder liquid. The binder is after the final coating has dried

one which is used for hardening during the drying process, the hollow mold is brought to the desired temperature

nens is capable under room conditions. After making the HobJform ready for pouring

the excess slurry is heated by the 50. The heating or firing of the mold is carried out in

coated model withdrawn or allowed to run off, an atmosphere which is sufficiently reduced

and the coating of the slurry is of a decorative nature to prevent sudden burning.

sanded, * d. H. with coarser refractory material to prevent the deoxidizing agent from burning away,

particles ⁷ pelted or coated; Performed these operations. When the mold is sufficiently heated

the dipping and pelting are repeated until is 55, then it is removed from the oven and it becomes

a hollow form of refractory material with a cast in the air in the usual way.

Thickness which ^: Sufficient to that in the following examples of those used according to the invention

Work processes occurring stresses to resist- Deoxidizing agents are graphite, also in the form of

stand around the model ■ is built. The usual flakes, crushed or ground coal elec-

Thickness of the shell-is 3.18 to 12.7 mm, ob- 60 troden, cork particles, charcoal and polystyrene grains,

probably for special cases also thinner or thicker ones whereby graphite and crushed or ground

Shells can be produced. The carbon electrodes are preferred. Is according to the invention

Removable model is then particularly advantageous from the graphite hollow form,

removed and the mold ready for casting- It is believed that the intense heat as soon as

provided or made available. ■■■ ■ · 65 the molten metal fills the mold, a rapid one

The removable models are usually obtained from combustion of the deoxidizer,

a combustible material such as wax or one that uses up the nearby or local oxygen

synthetic resin. In the case of wax and the hollow mold with a reducing atmosphere

5 6

covered. This reducing atmosphere prevents the plastic models and parts of the wax tree from reacting between the metal and the mold until the temperature has been reduced to a sufficiently low level in a trichlorethylene bath by soaking the mold with or soaking. After it falls that there is no further tendency to erosion, the essentially complete loosening of the art. There were castings made of stainless steel 5 fabric models, the hollow form or casting shell of the type 410 was removed by this process in large scale from the solvent bath and manufactured in an oxy-manufacturing or production scale, the atmosphere at 1093.3 ° C (2000 ° F) heated, which were completely free of "chromium pitting" in order to remove the rest of the wax and plastic from the same melt at the same time and away and to bring about a complete burnout or glow of the hollow form produced in conventional hollow molds.
Castings were so eroded that they were discarded. The mold was then cooled and had to be replaced with one because it did not meet the surface requirements for additional coating of the slurry of the feueran precision castings. solid material. The wet coating of

In almost all cases a single application of the slurry was made with coarse graphite, and

Deoxidizer sufficient. Possibly 15 with the one at The United States Graphite Com-

however, more than one coating of refractory No. 8 Mexican Graphite, available from the company, can be pelted at.

Material applied and with deoxidizer. The particle size distribution of the graphite was like

be thrown at. In addition to switching off the supply:

The level of surface pitting essentially retained the sieve opening in millimeters »/« have the additional deoxidizer coating 20

or the additional deoxidizer coatings ~> ^ ¹ ^ ¹¹ 25.0

the additional advantage of sealing or ab- ηί? ™ " ¹ 7

seal from any cracks or cracks that are ^ '^ ™ ¹ · ^

on the mold during the removal of the ent- ^ ™ ?> ⁹

removable model material could have formed. 25 u, U44mm 0.6

If according to the invention only an occasional% passed through

Hollow shape is made, the required diameter can be 0.044mm 1.3

reducing atmosphere in which the mold is heated

After the drying of the final, deoxidizing agent pelted hollow form on a graphite pelted coating, the hollow form plate made of refractory material and sprinkling of on a plate made of refractory material was placed, for example, about 0.227 kg of loose graphite sprinkled around the hollow form of coarse graphite to get the shape and a heat-resistant metal can. Then a usable lid can be placed over the top of the mold and the graphite. The hollow mold and the loose deoxidizer were placed in an ordinary one, and the entire structure was placed in an ordinary burn-out furnace, where it was placed in an oven for 1 hour. When large-scale production or held at 1093.3 ° C (2000 ° F). The hollow shape was production quantities to be cast from molds, removed and placed in a casting chamber, and then it is preferred, an oven, which for up were 9.185 kg of stainless steel of Type 410 at rather conservation of a useful reducing atmos- 4 ° 1635 ⁰ C poured into the mold. It was spherical at the desired temperatures able to provide during pouring to facilitate the filling. , a suction of 50.8 mm Hg on the mold

Specific examples of the invention applied. Sucking was stopped as soon as possible

are reproduced below: 'The casting was complete and the casting was left

It was a model build from forty-eight to 45 solidify and air cool,
While cooling, it was observed that the polystyrene models were made of a hollow cylindrical wax tree. Graphite burned on the model structure until the hollow form became red-hot by dipping it into a surface. After cooling, the hollow mold was removed slurry, which consisted of 3 parts of zirconium powder and and placed in a molten salt bath, and the 2 parts of molten silicon dioxide powder or 50 casting was cleaned with the sandblasting blower, hard-paste porcelain powder, which was in a binder - resulting in an excellent unprocessed Casting liquid, consisting essentially of a surface with no erosion, namely neither on colloidal silica sol, a small amount of an organic casting, nor on the tree. In a niche film former and small amounts of a similar hollow mold, but without graphite, the wetting agent and antifoam agent were suspended, and the same melt was poured at the same time, and the cast was made, six coatings of refractory pieces were so badly pitted that they would not be eroded applied to material. The first two coatings were acceptable.

Refractory material were made with granular zirconia There were numerous other hollow shapes that

pelted and the remaining coatings with a machined both with wax models and with plastic

Lenen coarse firebrick or fire clay. 60 models were formed, produced according to the invention.

The refractory material coatings were used. There was no zirconium acetate-1 in the wax models Hour of impregnation was required between dips and they were instantly dried. After drying, the first bars were removed by rapid burning at 1093.3 ° C If necessary, removes coatings with zirconium acetate. The atmosphere for preheating the hollow impregnated. Each layer of zirconia applied was made by adjusting the gas-air acetate was used to form a glass-like, in proportion to a normal burnout furnace, until the essential solvent-resistant barrier film hardening flame was sooty achieved. Left under these conditions the gas was burned incompletely, like

it was revealed by the fact that through the crevices around the door and through other parts of the stove escaping gases continued to burn during this state during normal (oxidizing) operation of the Furnace does not occur. In all cases, the castings were free from "410 pitting".

As explained above, graphite or another deoxidizer can be thrown at it Coating on the mold by simply dipping the mold in the usual slurry of refractory Material and application of graphite to the coating of the slurry in the wet state or another deoxidizer. So the invention is with known Hohlformguß- or shell casting process and with the usual refractory materials for hollow molds, such as Silicon dioxide, zirconium, aluminum oxide etc., well compatible. There is another very important benefit in that the process according to the invention does not have any special steps or measures at the time of Requires pouring the melt. Rather, the molds are used to cast in the usual way.

Furthermore, the method according to the invention is essentially "foolproof" and very easy to control. It also has the desired effect of creating a reducing atmosphere during the setting of the casting is preserved without prejudice to the complexity of the shape of the mold.

Many modifications of the invention are possible.

Claims (6)

Patent claims: 1. Precision die casting method using one suitable for precision casting of metals Mold made of refractory material with a model cavity and the metal in the air pouring into the mold, characterized in that the mold is coated with a coating layer of a flammable deoxidizer coating, the coating layer only provides outside the model cavity and the cavity and »the delimiting the cavity The surfaces of the mold are kept free of deoxidizing agent so that the mold can be finished the same heated for casting in a reducing atmosphere, the combustion of the deoxidizer to create a reducing atmosphere and the pouring on the fragrance under protection by the burning deoxidizer generated reducing atmosphere. 2. The method according to claim 1, characterized in that the precision casting of Metal mold made of refractory material around a combustible, removable model and removing the model from the mold to form a model cavity, the Mold heated in an oxidizing atmosphere to burn out the model cavity. 3. The method according to claim 1 or 2, characterized in that a hollow shape is used as the shape or casting tray used. 4. Process according to claims 1 to 3, characterized in that the mold with a slurry coated, the coating of the slurry in the wet state with the Deoxidizer, preferably a solid one, pelts, dries and dries the advertised coating pouring the metal in the mold at a temperature above the combustion temperature of the deoxidizer. 5. The method according to claims 1 to 4, characterized in that is used as the deoxidizer graphite and a temperature used to heat the mold in the reducing atmosphere of about 1093.3 ⁰ C. 6. Process according to claims 1 to 5, characterized in that the production of the mold in such a way that one creates a removable model, this with a slurry coated with refractory material, a grouting material on the coating of the slurry to form a hollow molded layer of refractory material and the aforementioned stages of dipping and pelting repeated to form a hollow shape, and that after removing the model from the Form as the other outer coating one of the aforesaid slurry of refractory Material applied to the mold, for throwing the same relatively coarse particles uses graphite as well as performs casting with stainless steel. 609 607/319 7.66 © Bundesdruckerei Berlin