|Title of Invention||
"A METHOD OF MAKING A MOLDED ARTICLE FOR USE IN A CASTING PROCESS"
|Abstract||In a method of making a molded article for use in a casting process, sand particles are mixed with protein and water to effect a coating of protein on the sand particles. Then, the protein coated sand particles are dried and blown into a pattern mold to form a molded article without active cooling of the coated sand particles. Steam is then passed through the molded article to hydrate and melt the protein, thereby forming bonds between contiguous sand particles. Finally, hot, dry air is passed through the molded article to harden the protein bonds between the contiguous sand particles. This forms a protein coated sand core for use in casting molten metals.|
|Full Text||Background of the Invention
1 Field of the Invention
The present invention relates to a molded article and a method of making the same
2 Descnption of the Pnor Art
Molds for casting molten metals comprise several mold members working together to define the internal and external shape of the casting Such mold members include core members for forming and shaping the interior cavities of the casting The core members are typically made by mixing sand with a binder, introducing the binder-sand mix into a mold containing a pattern for shaping the sand-binder mix to the desired shape for making the metal casting, and curing/hardening the binder in the pattern mold to harden the binder and to fix the shape of the mold-forming material
Gelatin has been used as a binder for the sand Gelatin is desirable because it is water soluble, environmentally benign, and less costly than synthetic resins used in many sand-binder systems In addition, less heat is required to break the bonds of the gelatin's protein structure to thermally degrade the binder than is required for the synthetic resin binders As a result, in the case of mold members which are cores, the gelatin binders break down readily from the heat of the molten metal, and thereby permit ready removal of the core sand from the casting with a minimum of additional processing such as shaking or hammering
Moreover, because the gelatin is water soluble, any sand that is not removed from the casting mechanically can be readily washed therefrom with water Solubility of gelatin also permits ready washing of the binder from the sand for recycling and reuse of the sand to make other mold members and thereby eliminate the cost of using new sand for each mold
Gelatin is a protein material obtained by the partial hydrolysis of collagen, the chief protein component of skin, bone, hides and white connective tissue of animals and is essentially a heterogeneous mixture of polypeptides comprising amino acids including primarily glycine, proline, hydroxyprohne, alanine, and glutamic acid Gelatin is sold commercially as a by-product of the meat producing industry "Dry" commercial gelatin actually has about 9% to about 12% by weight water entrained therein, and is an essentially tasteless, odorless, brittle solid having a specific gravity between about 1 3 and 1 4 Gelatins have a wide range of molecular weights varying from about 15,000 to above 250,000, but can be separated one from another by suitable fractionation techniques known to those skilled in the art Gelatins-are classified by categories known as "Bloom" ratings or numbers The Bloom rating or number is determined by the Bloom test which is a system for rating the strength of gels formed from different gelatins Gelatins having high Bloom ratings/numbers comprise primarily polypeptides with higher average molecular weights than gelatins having lower Bloom ratings/numbers The Bloom rating/number is determined by evaluating the strength of a gel formed from the gelatin Typically, the viscosity of the gelatin is measured at the same time as the Bloom rating/number by using the same gelatin sample as is used for the Bloom test The viscosity of the gelatin is generally correlated to the Bloom rating/number In other words, as the Bloom rating/number increase so does the viscosity
US Patent 5,320,157 to Siaketal teaches an improved gelatin binder for sand core members wherein a ferric compound is incorporated into the binder The ferric compound enhances the thermal breakdown of the binder during the casting process thereby simplifying removal of the spent sand from the cast article A typical method for forming a core mold is disclosed
U S Patent 5,582,231 to Siak et al requires chilling the gelatm coated sand with or without rehydiation to ambient temperatures or below before blowing the gelatin coated sand into the mold This chilling step is performed so
that the gelatin coating will gel when it is hydrated and the sand will be less sticky The, chilling step can require expensive cooling systems in metal foundries wjheie the environment is typically warm due to the piesence of molten metals When the hydrated, coated sand temperature is above ambient temperatures, the gelatin gel coating melts and the sand is sticky, which hinders the flow of the sand However, even if the hydrated, coated sand is chilled, it still does not flo,w as well as dry sand or even sand coated with phenolic urethane (cold box) resin
In another patent to Siak et al, U S Patent 5,749,409, a method for providing a topcoat of refracting particles to a foundry core formed from gelatin coated sandj is disclosed An organic waterproof layer is applied to the surface of the core and the refractory particles are then applied as an aqueous suspension The waterproof layer protects the core from deterioration resulting from water in the aqueous suspension The core is formed according to the description m U S Patent 5,320,157
U S Patent 2,145,317 to Salzberg teaches the use of a mixture of a soluble proteinaceous material such as gelatin and a crystalhzable carbohydrate as a binding material for making baked foundry cores The method of forming core molds is discussed in general terms
A method for removal of a sand core from a molded product with water is taught m US Patent 5,262,100 to Moore etal This patent discloses binder materials including carbohydrates and proteins such as gelatin A general process for forming a core mold is described
U S Patent 5,580,400 to Anderson et al discloses packaging materials formed from fiber reinforced aggregates held together by organic binders including gelatin Various methods of forming molded articles are disclosed
Summary of the Invention
In a preferred embodiment method of making a molded aifticle for use m a
casting process, sand particles are mixed with protein and watei to effect a coating
of protein on the sand particles The protein coated sand particles are then dried
and blown into a mold without active cooling Steam is then pass ed through the
protem coated sand particles to hydrate and melt the protein, thereby forming
bonds between contiguous sand particles to form a molded article Hot, dry air is
then passed through the molded article to harden the protein bones between
contiguous sand particles
In a preferred embodiment method of making a sand core, sand particles
are mixed with gelatin and water while supplying heat, wherein the heat melts the
gelatin to effect a coating of gelatin on the sand particles and dries the gelatin
coated sand particles The dry, gelatin coated sand particles are blown into a
mold without active cooling, and then steam is passed through the gelatin coated
sand particles to hydrate and melt the gelatin, thereby forming bonds between
contiguous sand particles to form a molded article Hot, dry air is then passed
through the molded article to harden the gelatin bonds between contiguous sand
In another preferred embodiment method of making a sand core, sand
particles are mixed with gelatin and water to create a mixture Heat is supplied to
the mixture to effect a coating of gelatin on the sand particles and! to dry the water
thereby drying the mixture The dried mixture is then ground thereby making the
mixture free flowing, and the dry, gelatin coated sand particles are blown into a
mold Steam is passed through the gelatin coated sand particles to hydrate and
melt the gelatin, thereby forming bonds between contiguous sand particles to form
a molded article Hot, dry air is passed through the molded article to harden the
gelatin bonds between contiguous sand particles
In another preferred embodiment method of making a sand core, sand particles are heated to above 40° C and then mixed with gelatin ahd water,
wherein the heated sand particles melt the gelatin thereby coating the sand
particles with gelatin The gelatin coated sand particles are then dried and blown
into a mold Steam is passed through the gelatin coated sand particles to hydrate
and melt the gelatin, thereby forming bonds between contiguous sand particles to
form a molded article Hot, dry air is passed through the molded article to harden
the gelatin bonds between contiguous sand particles
In another preferred embodiment method of making a sand core, sand
particles are mixed with protein and water to effect a coating of piotein on the
sand particles The protein coated sand particles are then dried and blown into a
mold The protein coatmg the sand particles is then rehydrated within the mold
thereby forming bonds between contiguous sand particles to form a molded
article Hot, dry air is then passed through the molded article to harden the
protein bonds between contiguous sand particles
Brief Description of the Drawings
Figure 1 shows a prior art process for making a sand core, Figure 2 shows the piocess of the present invention for making sand core,
Figjure 3 shows the equipment setup used to evaluate the use of steam to
hydrate gelatin coated sand in a core mold
Detailed Description of the Preferred Embodiment Figure 1 shows a prior art process for making a sand core Prior art generally teaches coating sand particles with an aqueous solution of gelatin at
about 80 to 100° C, cooling the coated particles to about ambient temperature
(e g 21 ± 2° C) to promote gelling of the gelatin prior to core blowing, and then conditioning the gel coated sand to provide a watei content m the coating of 70 wt% to 85 wt% In tins process, cooling the sand prior to blowing the sand into the coie box is important because if the sand is warm, the gelatin will become
sticky and the sand will not flow easily into the core box The coated, conditioned sand is blown into a pattern mold which is at or is heated to 80° C to 120° C to promote melting of the gelatin gel and formation of gelatin bonds between sand particles The gelatin is hardened by passing hot dry air through the porous molded coie to reduce the water content to less than 15 wt% Control of temperature dunng the blowing step appears to be critical to prevent premature drying of the gelatin Premature drying can cause the coated sand to become "sticky" and clog the equipment
Figure 2 shows the preferred embodiment method of making a molded article for use in a casting process Generally, the present invention is a process of using dry, gelatin coated sand particles that are blown into a core box, hydrating and melting the gelatin with steam through the core box., and then drying the gelatin with a dry air purge to harden the gelatin between contiguous sand particles A preferred embodiment of the present invention utilizes a gelatin of the type disclosed in U S Patent 5,582,231 to Siak et al, which JS incorporated by reference herein It is also understood that other gelatin or proiein binders known in the art may be used in this process However, the present invention does not require active cooling of the coated sand, and the coated sand possesses excellent flow characteristics similar to dry sand The flow properties of gelatin coated sand are important in the correct functioning of the sand in' automatic core machines used in commercial foundries The sand must readily flow from hoppers above the core machine into the sand magazine in preparation for blowing a core Then the sand must also flow uniformly into the pore box dunng the blowing of the core using high pressure air
In the preferred embodiment, fiist sand particles, water, and gelatin are mixed in a muller with a heat source until the sand particles are coated with gelatin and then the gelatin is dned The gelatin is used at about 0 5 to 2 0% of the sand weight The gelatin to water latio should be sufficient so that when heated above the gelatin melting point, which is approximately 4C° C, a gelatin
solution is formed with low enough viscosity that it will flow around the sand particles to coat them The gelatin to water ratio should be about 1 1 to 1 5, with the optimum gelatin to water ratio being 1 2 to 1 3 Excess water at this point just requnes more energy to remove it during the drying process The water can be dried from the gelatin coated sand while mixing by supplying excess heat to the mixture beyond what is requned to melt the gelatin In practice this means using temperatures of approximately 60 to 120° C, the optimum temperature of the mixture being approximately 80 to 90° C The heat source may either be a heated mullei or sand that is heated prior to mixing it with water and gelatin in the muller Although the present invention utilizes a muller, it is recognized that any type of mixer that will uniformly mix the gelatin, sand, and watei in a reasonable amount of time may be used Using heat during the mixing step melts the gelatin to coat the sand particles, and the excess heat dries the moisture from the gelatin coated sand particles The gelatin should be dned so that the gelatin contains less than 15% mbisture by gelatin weight Drying the mixture in the mixer is convenient because the mixe'r can break up the coated sand into a free flowing material thar is easy to transfer and blow into molds The dry, gelatin coated sand particles are approximately 65 to 95° C when removed from the muller However, the gelatin coated sand particles could be removed from the mixer before the gelatin is dned and either air-dned or dned in an oven at the above tempeiatures Then the dry, coated sand would likely need to be ground to make it free flowing for blowing into the mold Again, the gelatin should be dned so that it contains less than 15% moisture by gelatin weight
After the sand is coated in a heated muller and the gelatin is dried, no active cooling of the coated sand particles is required pnor to blowing the coated sand particles into the mold as required in the pnor art Depending on the size of the system, some cooling of the coated sand particles may occur dunng the transfer of the coated sand from the muller to the mold, but active cooling of the coated sand particles is not a required step in this piocess The present invention
eliminates the active cooling and conditioning steps prior to molding by blowing the dry, coated sand particles recovered from the coating step directly into a pattern mold The temperature at which the coated sand particles are blown into the mold does not matter as long as the temperature is below the boiling point of water The dry, free flowing coated sand particles do not clump together or stick to the sides of the pattern mold when being blown into the pattern mold, and this helps create a uniform mold because gaps in the sand particles are not formed in the pattern mold
In the preferred embodiment using a "dog bone" test core nold having a standard shape with a center cross section area of one square inch, approximately 100 grams of dry, coated silica sand particles are blown into the mold at a preferred temperature range of 21 to 66° C The "dog bone" test tore mold used in the present invention has the dimensions shown and described under Procedure AFS 3301-00-S in Mold & Core Test Handbook, 3rd Edition by American Foundry Society, Des Plaines, Illinois, Copyright 2001, which is incorporated by reference herein Low pressure steam at 3 to 4 psi is then passed hrough the core mold at approximately 105° C for about 20 seconds to hydrate the gelatin thereby promoting bonding of the gelatin between adjacent sand particles The amount of steam required is enough to provide adequate moisture so that the gelatin coating the sand will be hydrated, melt and flow between the sand particles to form connections between the sand particles Although the amount of steam used is difficult to quantify, the weight of the steam is probably about one to two times the weight of the gelatm used The temperature of the mold and coated sand should be such that water will condense on the sand to melt the gelatin, which generally means that the temperatures should be less than 100° C
Finally, hot, dry air is passed through the core mold for approximately 150 seconds to harden the gelatin The temperature range of the drying air can be quite wide, from approximately ambient temperature to 300° C, with the preferred range being approximately 100 to 150° C The drying air removes the moisture
from the sand m the mold The heat of the mold and sand will supply enough energy to eventually evaporate the moisture so that the gelatin contains less than about 15% jmoisture by gelatin weight and is rigid so the sand core will retain its shape after removal from the mold Using heated air will merely acceleiate the drying process and is preferred since it 1 educes the time it takes to make a core It is understood that the time for passing steam and dry air through the mold may vary depending upon the dimensions of the mold, how much sand is in the mold, temperature of the mold and drying air, and amount of steam used
The gelatin coated sand core is then ejected and ready for use The present invention results in saving energy by eliminating the cooling step and in improving the efficiency of the process by eliminating the conditioning step prior to blowing the sand into the mold It also eliminates the need for active coolmg of the sand molding magazine and blow plate in commercial core blowing equipment In addition, the present invention eliminates drying and hardening of the gelatin coated sand m the blow tubes caused by tube contact with the heated core box |
As discussed above, the standard method used to make sand cores from gelatin coa~ed sand is to cool the sand to room temperature or below and then add 2 to 3% co.d water (based on sand weight assuming 1% gelatin coating) to hydrate the gelatin This mixture is blown into the heated core mold and after a short dwell time, hot air is blown through the core to dry the gelatin and harden the sand core It is important to have the hydrated sand temperatuie below the melting po.nt of the gelatin coatmg If the gelatin starts to melt before blowing the core, the sand will become sticky and will not blow uniformly into the mold This requirement for keeping the hydrated sand cool makes cooling of the sand necessary in actual practice in a foundry where machinery and environmental temperatures can often be over the melting point of the gelatin, which has a melting pojit of about 25 to 30° C To avoid the requirement for cooling the
hydiated sand in a foundry environment, tests weie set up to blow dry, coated sand into the mold, flush steam through the mold, and then dry w.th hot air In the initial testing, 4086 grams of standard 55 gfn (grain fineness number, which measures the average particle size of the sand) lake sand, which is a type of silica sand, was used Sand coated with 1% GMBOND™ gelatin at Techmsand in late February 1999 was used as the room temperature coated sand To create the heated, coated sand, the sand was heated to approximately 105° C and was placed in an electrically heated muller with approximately 41 grams of 1 % GMBOND™ gelatin Then 82 grams of water was added to tie muller and the sand was mixed until it was dry and free flowing The dry sand was taken directly out of the muller for making a dog bone core at approximately 55° C Figure 3 shows the equipment setup used to evaluate the use of steam to hydrate gelatin coated sand in a core mold rather than hydrating the gelatin coated sand prior to blowing into the core mold
In the initial tests, "dog bone" cores having the dimensions described above of good strength, greater than 200 psi break force, containing approximately 100 grams of silica sand having a standard shape with a center cross section area of one square inch were made with the following process First, dry, coated sand either at an ambient temperature or at about 55° C immediately after coating was blown into the dog bone core mold at approximately 100° C Steam was flushed through the mold for 20 seconds using the dry ng air inlets Using steam at 3 to 4 psi would be approximately 104 to 106° C Then, hot, dry air at 50psi and approximately 200° C was flushed tlirough the mold using the air inlets for 150 seconds, which is the time used in the normal dog bone core procedure, but a shorter time period could be used Although the break strength was good, the surface finish was not quite as good as the standarc dog bone core This may be due to using the air inlets for the steam and/or having a small amount of condensate m the steam line
From these tests, the optimum settings were determined The best core mold temperature is approximately 100° C, and the blowing air is room temperature at 100 ps1 The steam is 3 psi and the core box contains a purge to drain open to pi event condensate from accumulating inside the core box It is important that the steam flow through the core box continuously so that no water accumula es inside the core box The sand inlet is blocked with a card ovei the opening and is held down by a pressurized sand magazine while the drying air is flowing through the mold The best drying air pressure is 50 psi, the temperature is 200° C, the dwell time is 15 seconds, and the drying time is 150 seconds The results aie shown in Table 1 below These settings aie the optimum found for making a dog bone core with good break strength and reasonable surface hardness
Less satisfactory lesults were obtained in various settings of the tests If the mold was at the 149° C used in the standard hydrated sand dog bone core process, ths bieak strength was okay but the surface was very crumbly This is
probably due to the sand being too hot at the surface of the mold to0 let the steam hydrate the gelatin and bind it If the mold was at 70° C, it seemec that the break strength was not okay until the dog bone cores were dried m an oven If the sand inlet was not covered but used in a foil plate that was held down by the pressurized sand magazine, when the drying air was introduced some of the sand would blow out the top before solidification had taken place With the sand mlet blocked, the air can still escape from the vents on the top corners of the dog bone core mold Lowering the drying air pressure from 100 to 50 psi he.ped reduce the tendency to blow the sand out or make holes at the two air inlet ports at the bottom of the dog bone core At the standard air temperature of 149° C, the dog bone cores did not seem quite dry in 150 seconds, but raising the temperature to 200° C seemed to get the dog bone core dry Increasing the steam pressure caused holes to be formed at the air mlet ports Steam time above 20 seconds just seemed to add excess moisture Steam was visible coming out of the dog bone core mold vents at about 10 seconds, a 20 second steam purge seemed to give more consistent results than shorter times Having inlet ports on both sides of the mold could probably improve the surface hardness of the dog bone core using the optimum settings, particularly on the side wheie the steam drying air inlet ports are located
The above specification, examples and data provide a comp ete description of the manufacture and use of the composition of the invention Since many embodiments of the invention can be made without departing from the spmt and scope of the invention, the invention resides in the claims hereinafter appended.
We Claims :-
1. A method of making a molded article for use in a casting process,
a. mixing sand particles with protein and water to effect a coating of protein
on the sand particles;
b. drying the protein coated sand particles;
c. blowing the dry, protein coated sand particles without active cooling into
d. rehydrating the protein coating the sand particles by passing steam
through the protein coated sand particles, thereby forming protein bonds between
contiguous sand particles to form a molded article; and
e. passing hot, dry air through the molded article to harden the protein bonds
between contiguous sand particles.
2. The method as claimed in claim 1, wherein the molded article is a sand core.
3. The method as claimed in claim 1, wherein the protein is gelatin.
4. The method as claimed in claim 3, wherein gelatin is used at approximately 0.5 to 2.0% of the sand weight.
5. The method as claimed in claim 3, wherein a ratio of gelatin to water is approximately 1: 1 to 1: 5.
6. The method as claimed in claim 3, wherein a ratio of gelatin to water is approximately 1: 2 to 1: 3.
7. The method as claimed in claim 1, wherein the drying step is performed using heat.
8. The method as claimed in claim 7, wherein the heat is at a temperature of approximately 60 to 120° C.
9. The method as claimed in claim 1, wherein the mixing and the drying steps are performed simultaneously.
10. The method as claimed in claim 1, wherein the steam is passed through the molded article for approximately 20 seconds at approximately 3 to 4 psi.
11. The method as claimed in claim 1, wherein the hot, dry air is passed through the molded article for approximately 150 seconds.
12. The method as claimed in claim 11, wherein the hot, dry air is approximately ambient temperature to 300° C.
13. The method as claimed in claim 11, wherein the hot, dry air is approximately 100 to 150° C.
14. A method of making a sand core, comprising:
a. mixing sand particles with gelatin and water while supplying heat,
wherein the heat melts the gelatin to effect a coating of gelatin on the sand particles and
dries the gelatin coated sand particles;
b. blowing the dry, gelatin coated sand particles without active cooling
into a mold;
c. rehydrating the gelatin coating the sand particles by passing steam
through the gelatin coated sand particles , thereby forming gelatin bonds between
contiguous sand particles to form a molded article; and
d. passing hot, dry air through the molded article to harden the gelatin
bonds between contiguous sand particles.
15. The method as claimed in claim 14, wherein the heat is at a temperature of
16. A method of making a sand core as claimed in claim 14 optionally, comprising grinding the mixture of sand particles, protein and water, thereby making the mixture free flowing.
17. The method as claimed in claim 16, wherein the mixture is heated and dried in an oven.
18. A method of making a sand core as claimed in claim 14, optionally, comprising heating of sand particles to above 40° C prior to mixing with water and protein.
19. The method as claimed in claim 18, wherein the mixing and drying steps are performed simultaneously.
|Indian Patent Application Number||2160/DELNP/2004|
|PG Journal Number||12/2010|
|Date of Filing||26-Jul-2004|
|Name of Patentee||HORMEL FOODS CORPORATION|
|Applicant Address||ONE HORMEL PLACE, AUSTIN, MN 55912, U.S.A|
|PCT International Classification Number||B22C 9/12|
|PCT International Application Number||PCT/US2002/07842|
|PCT International Filing date||2002-03-13|