The purpose of pre forging heating of hot forging die steel metal blank is to advance metal plasticity, reduce deformation resistance, make it easy to move and form, and obtain excellent post forging arrangement. Therefore, heating before forging has a direct impact on forward casting productivity, ensuring forging quality and saving energy consumption. According to the different heat sources selected, the heating methods of metal blanks can be divided into flame heating and electric heating.

火焰加热

Flame heating

火焰加热是使用燃料（煤、焦炭、重油、柴油和煤气）在火焰加热炉内焚烧发作含有很多高温气体（火焰），通过对流、辐射传给毛坯外表，再由外表热传导而使金属毛坯加热。

Flame heating uses fuel (coal, coke, heavy oil, diesel oil and gas) to burn in the flame heating furnace. It contains a lot of high-temperature gas (flame), which is transmitted to the surface of the blank through convection and radiation, and then the metal blank is heated by heat conduction on the surface.

在加热温度低于600～700℃时，毛坯加热主要是靠对流传热。所谓对流传热，是通过火焰在毛坯四周不断活动，凭借高温气体与毛坯外表的热交换，把温度传给金属毛坯。当加热温度超过700～800℃时，毛坯加热则以辐射传热为主。所谓辐射传热，是通过高温气体与炉膛将改变为辐射能，以电微波方法传播的辐射能被金属毛坯吸收后，再由辐射能改变成为而使毛坯加热。一般一般铸造加热炉在高温加热时，辐射传热比例高以上，对流传热只占比非常低。

When the heating temperature is lower than 600 ~ 700 ℃, the blank heating mainly depends on convective heat transfer. The so-called convective heat transfer is to continuously move around the blank through the flame, and transfer the temperature to the metal blank by virtue of the heat exchange between the high-temperature gas and the surface of the blank. When the heating temperature exceeds 700 ~ 800 ℃, the blank heating is dominated by radiation heat transfer. The so-called radiation heat transfer is to change the high-temperature gas and furnace into radiation energy. After the radiation energy transmitted by electric microwave is absorbed by the metal blank, it is changed from radiation energy to heat the blank. When the general casting heating furnace is heated at high temperature, the proportion of radiation heat transfer is higher than that of convection heat transfer, which is only very low.

热锻模具钢

Hot forging die steel

火焰加热办法的长处是燃料来源便当，炉子修造简略，加热费用较低，对毛坯的习惯规划广。但劳动条件差，加热速度慢，功率低，加热质量难于操控等。这种加热办法广泛用于各种毛坯的加热。

The advantages of flame heating method are convenient fuel source, simple furnace construction, low heating cost and wide habit planning of blanks. However, the working conditions are poor, the heating speed is slow, the power is low, and the heating quality is difficult to control. This heating method is widely used for heating blanks.

电加热是通过把电能来加热金属毛坯。其中有感应电加热、接触电加热、电阻炉加热和盐浴炉加热等。

Electric heating is to heat metal blanks by using electric energy. There are induction heating, contact heating, resistance furnace heating and salt bath furnace heating.

1.感应电加热

1. Induction heating

在感应器通入交变电流发作的交变磁场作用下，金属毛坯内部发作交变涡流。由于涡流和磁化发热（磁性改变点以下），便直接将金属毛坯加热。

Under the action of alternating magnetic field with alternating current through the inductor, alternating eddy current occurs in the metal blank. Due to eddy current and magnetization heating (below the magnetic change point), the metal blank is directly heated.

毛坯进行感应电加热时，内部发作的电流密度沿断面散布是不均匀的，中间电流密度小，表层电流密度大，这种现象称为趋肤效应。由此表层金属主要是因电流通过而被加热，心部金属则靠外层热量向内传导加热。关于大直径的毛坯，为了前进加热速度，应选用较低电流频率，以大电流透入；而对小直径的毛坯，由于截面标准较小，可选用较高电流频率，这样能够前进电功率。

When the blank is heated by induction heating, the current density inside is unevenly distributed along the section. The middle current density is small and the surface current density is large. This phenomenon is called skin effect. Thus, the surface metal is mainly heated by the passage of current, and the core metal is heated by the heat of the outer layer. For large-diameter blanks, in order to advance the heating speed, lower current frequency should be selected to penetrate with large current; For small-diameter blanks, due to the small section standard, higher current frequency can be selected, which can advance the electric power.

2.接触电加热

2. Contact electric heating

接触电加热的原理是以低压大电流直接通人金属毛坯，由于金属存在必定电阻，电流通过就会发作热量，从而使之加热。

The principle of contact electric heating is that low voltage and high current are directly connected to the metal blank. Due to the certain resistance of the metal, heat will occur when the current passes, so as to heat it.

关于必定标准的毛坯，要加热到规矩的温度，则需发作必定的热量。而一般金属的电阻值比较小，为前进生产率和缩短加热时刻，需要以大电流通入毛坯。为了避免短路，常采用下降电压的办法，以得到低电压的大电流。所以，接触电加热用的变压器副端空载电压只需2～15V。

For a certain standard blank, it needs a certain amount of heat to be heated to the regular temperature. The resistance value of general metals is relatively small. In order to advance productivity and shorten heating time, a large current needs to be connected to the blank. In order to avoid short circuit, the method of reducing voltage is often used to obtain high current with low voltage. Therefore, the no-load voltage of the secondary terminal of the transformer for contact electric heating only needs 2 ~ 15V.

接触电加热的特点是：加热速度快，金属烧损少，加热温度规划不受束缚，热功率高，耗电少，成本低，设备简略，操作便当。但毛坯的外表粗糙度和形状标准要求严格，特别是毛坯的端部规整，不得发作畸变。此外，加热温度的丈量和操控也比较困难。适用于长毛坯的全体或部分加热。

The characteristics of contact electric heating are: fast heating speed, less metal burning loss, unfettered heating temperature planning, high thermal power rate, less power consumption, low cost, simple equipment and convenient operation. However, the surface roughness and shape standards of the blank are strict, especially the ends of the blank are regular and shall not be distorted. In addition, it is difficult to measure and control the heating temperature. It is suitable for heating all or part of long blank.

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