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The method of improve the strength of gypsum cornice molds

Author锛歮icheal Date锛11/1/2010 8:25:36 PM

A, grouting molding with model of three elements grouting molding with the main functions of the model from the mud from moisture, make the mud by the fluid shape thixotropic status to have plasticity

A, grouting molding with model of three elements

 gypsum cornice mouldings
gypsum crown
gypsum line
gypsum medallion
gypsum mold
gypsum mould making
gypsum mouldings
gypsum plaster
gypsum product
gypsum skirting
mould gypsum powder
plaster column
plaster cornice
plaster mouliding

Grouting molding with the main functions of the model from the mud from moisture, make the mud by the fluid shape thixotropic status to have plasticity of mud solid billet. By the start of the water cut nearly 30% of mud and water cut 17% of the clay into a billet. Although in absorb water at the same time, also have a variety of complex such as ion exchange reaction, but mainly is to absorb moisture, make about 13% water and mud formed mud billet. Of course, formation of billet should have certain mud shape, this is also one of the function of the model. Therefore, no matter what material of model has three elements can shape with grouting. The three elements is: one can inhale and can hold a certain amount of water. If you can't water absorption, and can't accommodate a certain amount of water, to have the mud become porcelain body. At the same time also have will accommodate water release out of the ability. 2 have the appropriate bibulous rate. The bibulous rate available diffusion coefficient Dg said (Dg behind in detail), Dg too big or too small against the porcelain body form. The strength of the three has ideal. Should have adapted to different requirements of the strength, can withstand the handling, installation and use of corrosion and abrasion and impact. Therefore shall have the flexural, compressive, surface hardness water resistance, alkali resistance requirements, etc.


In addition to the three elements, also should consider to model the manufacturing cycle, manufacturing technology and manufacturing cost should comply with the "short, Jane, low" requirements. Such as gypsum model should consider to initial setting and final set time, gypsum price, and so on.


No matter what material, as long as have three elements can be making model, so we can adjust accordingly the performance of gypsum model, also can use gesso outside of the material to make the model.


Second, improve the strength of gypsum model approach

In order to adapt to the needs of the new process, must the plaster models after the dry flexural strength of about 2.6 MPa by usually increased to 5 MPa above, many new material and additive, the emergence of forming the realization of high strength for the mechanization of gypsum model manufacture and application to lay the foundation. So may adopt the many kinds of ways improve strength: 1, use high purity plaster powder; 2, use high strength plaster powder; Three, use the vacuum takes off the gas stirring; 4, appropriate use of additives; 5, use process after the water mixing into gypsum slurry; 6, use reinforcement or strengthen fiber; 7, the use of some kind of material compound layer model; 8, reduce gypsum slurry water added in, the model density; 9, the model of making reasonable drying; 10, use model of temperature and humidity should be properly; 11, stir the gypsum slurry after injection molding sieve before; 12, gypsum plaster powder fineness of the fine shall be the better.


Three, by improving the plaster model to improve the strength of density model is feasible


Usually think grouting of porosity by model should be 45 ~ 55% between, modeling of water than when cream for 1-0. 8-0. 9. But as people know development, test and production prove anointed water is more than 1: < 0.8. Porosity < 40%, if the model with the appropriate additive, model of suction slurry performance is better than the cream instead of water than 1-0. 85 model. The same environment, the same slurry form the same thickness of the porcelain body, the former just 45 minutes, the latter should be 60 minutes model the flexural strength: before when: = 2:1, wet when front: = 3:1. This shows, choose appropriate gypsum plaster powder with appropriate additive. The model of the dense more conducive to good porcelain body form. Due to the density model, strength increases. Our experimental proof: anointed ratio of water 1-0. 6 made also applies when model.


Four, improve send density to plaster model USES suction stabilize the speed of the late slurry


The experiment and production are proved that the model of the dozens of times after use, as water, electrolyte, clay materials and surface erosion wear, thin, also become loose. Loose density decreases in capillary model means for getting too big diameter. Porosity increases, equivalent to anoint water than smaller, at the same time strength drops, or casting speed slowing, and that is a model is one of the reasons for the late easily damaged.


In a certain range, casting speed and cream into water than is as shown in figure (a) relationships: such as the new model began to cream ratio of water B, then later move to C, casting speed Wp into drop; As the new model for A water than start paste, and later moving to B, Wp steadily trend.

The model can be found in proper density is favorable.


Five, the plaster model and the relationship between the Dg Wp


Diffusion coefficient said in unit of time of liquid in the area of the diffusion in porous materials. The plaster models of diffusion coefficient is expressed as:


Dg = X2 / t. Among them: t for time (in seconds), X for the water rose height (cm). WP for a certain time form porcelain body thickness (cm).

Dg relationship with reference as shown in figure (b) as shown.


In a certain range Dg, WP instead of small, in certain scope changes in Dg, WP unchanged; In a certain range increased Dg, WP also increased.

Dg big, the water absorption ability, Dg too big, mud surface model in the early formation too close, thus influence further bibulous, hinder porcelain body continue to hinder formation; Dg is too small, suction small, also go against porcelain body formation; Dg proper, can make the porcelain body cambium early keep porous, do not affect the inner water through making porcelain body form quickly and even, make body outer density difference billet is too large, also reduce porcelain body contraction of the defects, so how to make Dg moderate? See below.


Six, the influence factors of Dg gypsum model and its control


Influence factors of Dg plaster models are: 1, gypsum plaster powder type and purity; 2, anointed water ratio; 3, stirring time; 4, whether the vacuum takes off the gas stirring; 6, additive type and quantity; 7, the fine degree of gypsum plaster powder.


If the θ gesso, high purity, anointed water, stirring time and speed than moderate, use the vacuum takes off the angry all can make Dg improve, and use appropriate additive can make be Dg improve, also can make Dg decline. According to current understanding: organic, water-soluble strong, the viscosity of can make Dg down; And viscosity small, inorganic, water-soluble poor can make Dg unchanged or make Dg improve. Because Dg too much too small are bad, but the Dg again by various factors common effect, which must be based on the different condition and need to adjust, can also be difficult to provisions of Dg exact numerical value, such as mud composition is different need different Dg value.


Seven, vacuum mixing and mould sieve strength, finish before good hardness and improvement


Vacuum mixing is helpful to improve the strength of the model has become a consensus. But the effect not only that, it still has to finish and the improvement of hardness. Because the vacuum mixing, reduce the many bubbles, make model more dense, thus increasing the surface hardness and finish of the model. Because of the mass production of gypsum plaster powder is coarse, mass-produced model is not uniform when mixture, stirring barrels and pipeline may have remaining! These impurities into model, will surely influence strength, finish and surface hardness. As in gypsum slurry after a 30 before into model on screen around, can be effective in keeping out impurities, so as to improve the strength of the model, finish and surface hardness. Sifting the greater hinggan mountains have a role: as a cast of the sieve buffer slurry into the mold speed, which destroyed the impact of possible bubble, the model more density.


Eight, ought to be in increase strength while the thinning thickness plaster models


Common plaster models are the thickness of a thick: general in 65 ~ 90 mm or so, investigate its reason, largely due to the strong strength of gypsum too poor, thin no, easily damaged. Results some to 100 mm. Is neither the plaster, increased the cost, and handling difficult, increase the Labour strength of the workers, and also not easy to dry, but also increase the occupancy space, is not conducive to improve the productivity of unit operating area. Maybe someone think thin will influence model for the amount of water that is not really so? Reduced to just how much thickness qualified? This paper aside for strength, and only from the smallest thickness of how much it analysis:


Usually in the mud weight for grouting 1.8, dry weight 71.2%, plastic state of wet billet weight for 2.07, dry weight is 83%; A form area of 1 cm2 thickness of 1.3 cm of the billet, need to area of 1 cm2 blowhole rate 36% of gypsum model Xcm is below the thickness calculation:

Wet billet weight: 2.07 by 1.3 by 1 x 1 = 2.691 g

Porcelain body wet with dry material 2.691 x 0.83 = 2.2335 g

The formation of the porcelain body wet mud to 2.2335 ÷ 0.712 = 3.317 g

Wet mud formed porcelain body fluid loss 3.317-2.691 = 0.446 g


As the water loss for all that absorbed by model (actually they are not) and accounts for only of the model of the porosity one-third, or 12% (the actual also higher than this value)

Are: X multiply one multiply one X 12% = 0.446


So, one of the only eat plasma model X = 3.71 cm thick can, if double-sided eat slurry, every one is 2 cm enough. Visible, if use high strength, porosity rate at about 36% of the model, can design the single eat pulp thick 40 ~ 50 mm, double-sided eat pulp can design into thick 25 to 35 mm, according to the numerical calculation can use less than the current model 1/3 to 1/2 of the plaster powder, can greatly reduce the cost and weight.


Nine, the exterior gypsum model (not face) design should pay attention to

A factory model looks almost all is uneven, some similar heating flake. The thinking is very long revelation that design is quite science: 1, the model on the edge, the edges thicker, the rest place is thinner, easy to handle; 2, have thin have thick, thick with reinforced role, which helps to improve the overall strength, in line with the material mechanics principle; 3, bao hou is differ, may save the plaster powder lose weight, but strength insusceptible; 4 and increase evaporation area, be helpful for the rapid drying model. This kind of design such as can and thinning the feasibility of the model combining will more scientific and more perfect.


Ten, the choice of appropriate additive, can improve the plaster model of the openings porosity and water resistance and toughness


Note into gypsum piece immediately after stripping weighing for W1 (right now water evaporation not much), dry to the heng zhong again after the water to immerse to constant weight as fully W2. Common cream powder made into 256 cm3 trial piece of W1-W2 = 25 g, such as the use of adding additives made of gypsum plaster powder same gesso block, then W1-W2 = 10 g, even W1-W2 = 6 g. (this experiment is in the same conditions, gesso block bulk density were the same) is clearly put some kind of additive can make open blowhole rate increased by more than 5%, this just like model to improve the performance of water absorption capability and the increase.

Grouting with plaster model is in alternating wet state of the work. Plaster models and wet when when the flexural strength, compressive strength, surface hardness are very different. Usually gypsum model the flexural strength dry: wet = 3:1, hardness dry: wet > 5-1. Quite hard gesso block when soaked, and cork, bela model in wet when also easily broken, easy to fall off the surface. To improve the life of gypsum model, increase under wet strength and hardness of the wife is the key, should try to increase in additive gypsum model water resistance. According to data and experiment, we found that adding additives can make the flexural strength dry:?? Gt; 3:2, hardness and wear-resisting degree also have doubled. Add additive can also increase the toughness of the model and solve the model because of too brittle and cause damage in use of difficult problems