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You Are Here:Home > Solution > Compared Wax-base and Plastic-base Adhesive in MIM Feeding Process-Solution

FirstMixing Step

Wax-based adhesive

Plastic-based adhesive

1) Mixing temperature is lower than 120 ℃. Mixing time is shorter;

2) Sealed mixing. Airtight design to reduce paraffin heating loss;

3) Can be used for plastic mixing equipment, but the shear force should be according to temperature control.

1) Mixing temperature is greater than 150 ℃. A long time refining;

2) Using open mixing kneading;

3) Can not be used by wax-based mixing mixer. Less shear stress;

4) Special powder mixture need to be added with nitrogen protection;

5) High shear force can be fully softened plastic base material.

Wax-based adhesive is based on paraffin. Viscosity is small, easy volatile and mixing, but need to pay attention to the temperature that should not be too high (less than 120 ℃). With air tight design to reduce evaporation losses.

Plastic base adhesive to POM-based, high viscosity, less volatility; need to use a large shear mixer, and the temperature should be set higher (more than 150 ℃) to reduce the viscosity of the adhesive. Due to the high temperature, and its open type, in order to prevent some special metal powder oxidized, special circumstances need to use nitrogen protection.

Second, Injection Step

Wax-based adhesive

Plastic-based adhesive

1) Good lubricity; slow shooting can be reached; the hydraulic machine can also be injected;

2) Mold temperature and injection tube temperature is low;

3) High speed shooting easily lead to separation of powder shell obvious shell effect, which is due to the low viscosity of wax, so high brightness polishing parts are not easy to save their sand hole defects.

1) Needs high-speed motor to mix a good plastic-based feed;

2) The injection molding machines shooting speed is fast, shooting pressure is high and holding pressure can be a long time;

3) Screw compression ratio is very important. The screw length is shorter;

4) Mold temperature should be high (> 120 ℃), in order to reduce the residual stress of injection billet;

5) Tube temperature control to be more stringent. Should immediately reduce the temperature if no injection operation, to avoid POM cracking!

Similar to mixing, the high viscosity of plastic-based binders also makes injection difficult. Wax-based adhesives have the advantages of low viscosity, good lubricity, low pressure, low injection rate and low mold temperature, but high speed shooting would cause the separation of powder and binder which can lead to the defect of the final product.

Plastic-based adhesives need high-speed electric injection molding machine. The screw is shorter, the firing rate, injection pressure, mold temperature is high, and holding pressure need a long time; In addition, the tube temperature control must to be more stringent. Should immediately reduce the temperature if no injection operation, to avoid POM cracking!

Third, Degreasing Step

Wax base (dissolution / thermal off)

Plastic-based (acid-catalyzed off)

1) Products are easy to deformation in dissolution;

2) Low efficiency, poor security of dissolution equipment. Solvent fire prevention and recycling cause environmental and security issues;

3) Dissolution is suitable for large parts; the structure should have a support plane.

1) Rapid catalysis, suitable for thickness 5mm below, high efficiency;

2) The equipment is simple and high security;

3) By-products are gases (CO2, N2), easy to deal with.

The base solvent is degreased in the main solvent or in the hot atmosphere. The solvent will degrade the skeleton proppant. After the dissolution, the drying will tend to warp the billet. The solvent also needs to be fireproofed, the solvent recovery and the safety performance of the degreasing furnace need to be paid attention.

Plastic-based adhesive mainly through the catalytic role of acid degreasing. This method is fast, with by-products are gases (CO2, N2), easy to deal with.

Forth, Sintering Step

Wax base (dissolution / thermal off)

Plastic-based (acid-catalyzed off)

1) Wax-based binder sintering for a long time;

2) Product big deformation;

3) Low labor costs.

1) Wax-based binder sintering for a short time;

2) Product little deformation;

3) High labor costs.

Pre-sintering of wax-based binder(<600 ℃)

For a long time, resulting in nose-like, yellow wax residue; Due to the skeleton is deteriorated during degreasing, the products deform easily; Although the price for heat off wax-based binder is high, due to the use of degreasing sintering furnace, artificial Low cost, it is welcomed in Japan.

Pre-sintering of plastic-based binder(<600 ℃)

 For a short time, resulting in asphalt-like, dark green, yellow wax residue, and difficult to clean. In addition, the plastic-based binder is relatively little deformation.

Summary of the differences of above four processes, we can see that the wax-based binder mixing and injection molding process has simple requirements but sintered pieces deform largely; Plastic-based binder mixing and injection process requires higher standard. Because its viscosity is relatively large and other reasons, sintered pieces not easy deform. Of course, different specific parameters of different enterprises, there will be some discrepancies.

 Final, The Quota of Global Market Adhesive

Globally, there are six areas of concern. The following table explains:

Area

Catalytic degreasing / plastic base

Solvent degreasing/wax base

Thermal debinding / wax base

Mainland of China

80%

20%

 

Taiwan

30%

70%

 

Japan

 

 

Almost 100%

Europe

Most popular

 

 

North America

 

most

 

India

20%

80%

 

From the figure above, the acid degreasing is the most widely used in Europe, followed by China. In North America, mainly solvent degreasing / wax-based binder. Japan mainly use thermal degreasing / wax-based binder, but the two regions are also slowly accept the plastic-based adhesive since 2013. Plastic-based adhesives, because the product deformation is small, relatively difficult to produce sand holes and other defects, began to slowly get the global market recognition!

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