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The construction technology of alumina thermal welding

Sep 15, 2017

The heat welding of rail steel rail is a large amount of molten metal that is released during the chemical reaction process by aluminum and iron oxide, so that the metal is welded or surfacing. Aluminum thermal chemical reaction is REDOX reaction, the main reaction products of liquid aluminum hot steel and aluminum oxide slag, the reduction of iron with high temperature aluminum hot molten steel, aluminum was oxidized to alumina slag. The expression of chemical reaction of aluminum thermal welding is:

3FeO + 2A1 = 3Fe +Al2O3

Fe2O3 + 2Al = 2Fe +Al2O3 3Fe3O4 + 8Al = 9Fe + 4Al2O3

The aluminum thermal welding of aluminum powder, iron oxide, and other metal additives is used in the special crucible to ignite the aluminum heat reaction with a high temperature match. Reaction gives off a large amount of heat in the process of melting metal react, form the liquid steel, due to its dense drowned in the below, of slag is frivolous in upper part, steel in a very short period of time is full of sand mold, aluminum hot molten steel itself and as a filler metal, at the same time, cooling crystallization, together with the molten steel 2 period of rail form a whole.

Use appliances and materials.

1. Tools

(1) Sand mold side template and sand mold base plate

It is used for the clamping fixture of fixed sand mold, the side template is fixed to the side of the left and right sand mold, and the sand mold base plate is fixed to the bottom of the bottom, the side template is a pair, there are left and right sides.

(2) Fixed fixture of sand mold

Fixture with fixed and clamped mould side template. The mounting fixture has a point in front and back.

(3) Ash tray

Used to collect the steel and water waste from the sand mold during welding. When used, the bottom should be covered with a thin layer of sand.

(4) Crucible fork

Used to remove hot, discarded sand mold used in welding.

(5) Direct steel ruler (one meter)

Before welding, the positive ruler is made of alloy.

(6) Preheater and bracket

1) Preheating devices include preheating gun, pressure gauge, hose and joint. The bracket is used for the positioning and fixation of the residual heat device. And propane, oxygen air duct. Propane and oxygen pressure gauges (preheating for welding is a key device)

2) Preheater bracket preheating burner bracket is used to support and adjust the position of the preheater gun, and it is fixed on the rail to preheat the rail joint before welding.

2. Materials

(1) Aluminum thermal flux and sand mold, welding a welding head to use one set.

It includes: a package of flux, left sand mold, right sand mold, bottom sand mold, shunt plug.

According to different models of the rail, there are different matching flux and sand mold: 50kg, 60kg, 75kg;PD3, U71Mn, rare earth rail, etc. (in tongling iron pelletizing room 10t, it is 50kg)

(2) Disposable crucible - flux container

Welding a welding head USES a crucible, with the solder sand mold. Moisture-proof design, self-melting plug, environmental protection, fuel automatic decomposition.

(3) High temperature sealing box mud

The function is to seal the gap between the sand mold and the rail to prevent the leakage of the steel water. 10kg per barrel can be used for 3-6 times.

(4) Aluminum thermal ignition auxiliaries - high-temperature matches

Used to ignite aluminum thermal flux. Use one at a time, and take a few extra backups on site. It's 20 square boxes.

(5) Heat-resistant sealant

Apply between the bottom sand mold and sand mold for the sealing between the rail, sand mold and floor. 12 pieces per box. A sealant can be used for 6-8 welding heads.

3. The construction technology

(1) Construction preparation

1) The track will be adjusted, and once again, whether it meets the design and specification requirements. Check whether the two sections of the rail connection have a gap of about 15mm.

2) The two rails must be straight to the normal two rails with the right steel straighter.

3) Release the rail clamp screw from the position of the rail to the rail to make the rail and the driving beam.

There are some gaps.The general requirement is to be able to insert the bottom template and bottom sand mold.

(2) Clean the rail joint

Use file to cross section of the rail joint and the rust debris next to it.

(3) Install sand mold and fixture

Before installing the sand mold, install the bottom template and the side template to fix the sand mold. The sand mold base plate is fixed to the bottom of the bottom, and the side template is fixed to the side to the left and right sand mold. The side template is a pair of the left and right sides.

Installation sequence is:

The bottom die left and right side of the sand mold.

Adjust the fixed

(4) Sealing

1) Seal the gap between the steel rail and the sand mold with the high temperature sealing box, and then use the hand to rub the clay into strips in the sealing, then squeeze into the gap with the fine steel, and be sure that the seal is strong.

2) The gap between the front and rear bottom sand mold and the side die between the front and back of the sand mold and the gap between the front and rear modes.

3) Install cinder plates and seal the gaps between them.

A thin layer of sand is laid on the bottom of the ash tray, so as to avoid the leaking of molten steel and the crystallization of the ash tray. Then seal the gaps with high temperature resistant packing.

(5) Preheating

5.1 Installation preheater

Install oxygen and propane pressure gauges, and use oxygen and propane to direct the preheating gun.

5.2 Adjust the value of the propane and oxygen pressure gauge, ignite the preheating gun, and adjust the flame.

Fix the position with the preheating bracket. Start heating and timing, usually about 4 minutes or so.

5.3 The welding of aluminum hot solder is ignited.

1) Open the disposable crucible, install the aluminum thermal flux, and insert the hot match.

2) quickly prepare the ready crucible on both sides of the mould before preheating, and ignite the accelerant.

3) cover the top

5.4 Demolition of instruments

    General dismantling equipment room according to the first remove, first installed in the sequence of dismantling.

    1) After the reaction is completed, remove the discarded crucible with the crucible forceps, then remove the ash tray.

    2) Remove side templates and fixtures.

    3) The steel rail joint finished with welding is completely cooled, usually 2-3 hours, then the left and right side sand mold and bottom sand mold are removed.

    5.5 Polishing

      Cut off the excess steel flow above the rail gauge with gas cutting, and then polish the entire joint with a polishing machine.

      4. Matters needing attention

      (1) Technology

      1) Because of the particularity and complexity of the aluminum thermal welding of the lifting track, the technical content and operation requirements are relatively high, so the operator must hold the certificate and strictly prohibit the operation of the non-operator.

      2) Welding rail of gating system structure is complex, and because of the particularity of aluminium heat welding, aluminum hot molten steel pouring temperature is very high, molten steel during solidification shrinkage is bigger, the formation of shrinkage, porosity, cracking and other defects.As a result, the gating system of aluminium heat welding and welding of pre-heating and aluminum hot molten steel in casting solidification is particularly important in a cavity, and steel casting mold molding time is very short, usually done in 40 ~ 50 seconds.Therefore preheating can be called core in the whole welding work, and of course the preheating effect can only be reflected from the technical operation of the technician.

      (2) Security

      1) Crane rail generally on the basis of the steel crane beam, installed on the steel crane beam surface, such rail aluminothermic welding work is completed on steel crane beam, operation is very limited, and high technical content, operation difficulty is big.In this way, the safety of the workers is especially important. The staff should wear protective protective gear, wear safety helmet and fasten seat belts. Each welding technician shall be equipped with one or two auxiliary personnel.

      2) Often work there are on top of the crane beam cross homework, therefore, must pay attention to the safety of workers, under the crane beam may when installation, accessories slide in the fall, or when welding, steel spillover, cause harm.Therefore, during construction work, special security personnel must be equipped to guard, and no one will stay or pass from the bottom during the operation of the welding operation, and the operation below shall not be allowed.

      5. Summed up

      (1) Reliable quality

      By comparing the summary, crane rail aluminothermic welding connection is fused two rail by molten steel to form a whole rail, compared several kinds of common rail connection, welding quality is reliable.Through testing, the joints quality of aluminum thermal welding can achieve various performance indexes.

      (2) Mature technology and simple operation

      This process has been widely applied in bridge, railway and other engineering, the technology is mature, the operation is simple.Compared with welding, the process requirements are lower.The equipment model is relatively complete, easy to purchase in the material market.

      (3) Higher unit price

      Aluminothermic welding single rail joint in the unit price is more expensive, compared to common connection ways (clamp connection, special welding wire welding connection) in to discuss about rail aluminothermic welding construction technology for the above 2 times, aluminium heat welding cost mainly reflects in one-off crucible material cost, just in the process of the deficiencies.