Analysis Of Blow Mould Cooling System

对于几乎所有的挤出成型、注塑成型、吹塑及真空成型等成型方法,生产率很大程度上取决于塑料的加热与冷却的效率。吹塑成型过程中,通过模具带走融熔塑料的热量,使制品冷却定形,而吹塑成型中制品冷却时间占成型周期的60% 以上,对大型及厚壁制品高达90%。因此,提高吹塑制品的冷却效率,可缩短成型周期,降低能耗

For almost all of the extrusion molding, injection molding, blow molding and vacuum molding methods, productivity is largely determined by the efficiency of the heating and cooling of plastic. In blow molding process, the heat of melting plastic is taken away by the mold, the product is cooled and set, and the cooling time of the product is more than 60% of the molding cycle, and the large and thick wall products are as high as 90%. Therefore, improve the cooling efficiency of blow molding products, can shorten the molding cycle, reduce energy consumption.

  1. 模温对吹塑工艺的影响(the influence of mold temperature on the blow molding process)

过高的模温:会使冷却速率降低及热交换时间变长,不利于融熔料分子结晶,形成晶球且不断成长,会产生大小不一的晶体,使塑件冲击强度降低,导致使用寿命比较短。过低的模温:当模温低于4℃时,因受室温及空气湿度影响,模具表面极容易产生热气冷附现象,附着大量水珠,水珠的存在会影响塑件表面的光洁度,且容易使模具生锈腐蚀等现象,所以吹塑模具模温一般控制在10℃左右,可防止产生明显的热气冷附现象。冷却系统水路有无布置完善,也会导致冷却不均匀使得制品的各部位收缩率有差异,引起制品的翘曲、变形的问题。所以良好的冷却系统对于吹塑成型至关重要,它可使吹塑周期缩短,得到尺寸稳定、收缩变形小的制品,也能延长制品及模具的使用寿命。

High die temperature: the cooling rate decreases and heat exchange time becomes longer, is not conducive to the melting material molecular crystals, formed crystal ball and continue to grow, will produce size of crystal, plastic impact strength decreased, resulting in short service life. Low mold temperature: when the mold temperature is lower than the temperature of 4 DEG C, due to the room temperature and air humidity effect, the mold surface very easy to produce cold and hot attached phenomenon, attached to a large number of drops, drops of water will affect plastic parts surface is bright and clean degree and easy to mold rust corrosion phenomenon, so blow mold temperature general control in about 10 DEG C, prevent to produce obvious cold and hot attached phenomenon. Cooling system water is not arranged, it will lead to the uneven cooling of the parts of the various parts of the shrinkage rate is different, resulting in product warp, deformation of the problem. Therefore, a good cooling system for blow molding is essential, it can shorten the blow molding cycle, size stability, shrinkage deformation of small products, but also to extend the life of products and molds.

 

2.冷却系统的结构设计(Structure design of cooling system)

吹塑制品的冷却方法可分外冷却、内冷却与后冷却三种。我们公司模具主要冷却系统由外冷却及后冷却组成。1外冷却法外冷却是指在模具壁内开设冷却系统,通过外壁传热来冷却吹塑制品。在我们公司最常见的模具壁内开设冷却系统方式是在模壁内纵、横方向钻出冷却孔道,见图1

The cooling method of blow molding products can be cooled, with three kinds of internal cooling and cooling. The main cooling system of our company is composed of external cooling and post cooling. 1 external cooling method is to open the cooling system inside the mold wall, through the outer wall heat transfer to cooling blow molding products. In our company the most common mold wall open cooling system is in the in the mould wall from longitudinal and transverse direction drilled cooling channels.

1—冷却流体入口Cooling fluid inlet; 2—冷却流体出口Cooling fluid outlet; 3—管塞Tube plug;4—带塞子的横杆The bar with a tap

5—螺旋钢种片Spiral steel sheet

这种方式的冷却系统水路可以用机械加工制造,制造简单,方便,成本低。在孔道内设置的螺旋铜片增加流体的湍流程度,可以减少水垢的形成。冷却孔径一般取10  15mm,对于大型模具可达到30mm。孔径较大时要求冷却流体有较高的流率,既要求配置大功率的泵送装置,两相邻孔道之间的中心距为孔径的3  5 倍,孔壁与模腔之间的距离为孔径的1  2 倍,以均匀、充分地冷却制品。钻孔式冷却通道易于清理,便于修改。当有些模具内腔凸台比较高,热量比较集中,而模具不能做纵、横方向冷却孔道时,可使用冷却棒来使模具冷却。如图2

The cooling system of the method can be used for manufacturing the water by mechanical processing, and the manufacture is simple and convenient, and the cost is low. The spiral copper set in the pores increase the flow rate, can reduce the scale. The cooling aperture is generally 10 ~ 15mm, for large mold can reach 30mm. Larger pore size requires cooling fluid has high flow rate, pump configuration of large power transmission device, the distance between the center between two adjacent channels is 3 ~ 5 times of the hole diameter, the distance between the hole wall and a cavity for 1 ~ 2 times of the hole diameter, with uniform and sufficient cooling of the product. The hole type cooling passage is easy to be cleaned, and is easy to be modified. When some of the mold cavity boss is relatively high, the heat is more concentrated, and the mold can not do vertical and horizontal direction of the cooling channel, the cooling rod can be used to make the mold cooling.

D1 = D + 0 1  0 2mm( 方便冷却棒装拆且不易脱落)D2 = Dx2( 保证热量传导的快速性和稳定性)冷却棒有很好的热传递性能,可以将一端的热量迅速传递到另一端,安装冷却棒后,在合适位置上接通冷却水,就实现了一个热转换过程。在放入冷却棒时,棒上必须涂上专用导热润滑剂,其主要作用: 1、耐温使热导性好; 2、防锈、润滑,后期装拆方便。冷却棒底部用活动盲栓做堵头,可给以后的维修装拆带来很大的方便。

D1 = D + 0 1  0 2mm(Convenient cooling rod assembly and disassembly and not easy to fall off)D2 = Dx2(Ensure heat conduction speed and stability) cooling rods have good heat transfer performance, can be one end of the rapid heat transfer to the other end, mounted cooling rods, in the right position to connect with the cooling water, on the realization of the a thermal conversion process. When placed in the cooling rod, the rod must be coated with a special heat conductive lubricant, its main function: 1, temperature resistance, good thermal conductivity; 2, rust, lubrication, late loading and convenient. The bottom of the cooling rod is used as a plug for plugging, which can bring great convenience to the subsequent maintenance.)

2.1内冷却法Internal cooling method

吹塑制品在冷却中,外壁因与低温模腔接触而被较快冷却,内壁与吹胀空气接触,其传热量很少,故冷却较慢。内、外壁冷却速率的差异可能使制品出现翘曲现象。一种解决方案是在模具内保压时间长一点,让制品完全定型了再取出,这样做整个周期就延长了,影响生产效率。为此,研究并开发了各种内冷却方法,即把水雾、液态氮气或二氧化碳、制冷空气、循环空气或混合介质注入已吹胀的型坯内部,以快速冷却制品内壁。在内冷却中,最常用的是液态氮气与二氧化碳,因为他们干净,不起化学作用,适用于多种吹塑制品。如图3

Blow molding products in the cooling, the outer wall due to contact with the low temperature die cavity was faster cooling, the inner wall and blowing air contact, the heat transfer is very little, so the cooling is slow. The difference in cooling rate between the inner and outer walls may cause the product to warp. One solution is to keep the pressure in the mold a little longer, so that the product is completely finalized and then removed, so the whole cycle is extended, the impact of production efficiency. Therefore. Research and development of the various cooling method, namely the spray, liquid nitrogen or carbon dioxide, air refrigeration, circulating air or mixed media injection has been blowing expansion type billet inside, inside the rapid cooling of the product. In the internal cooling, the most commonly used liquid nitrogen and carbon dioxide, because they are clean, do not play the role of chemical, applicable to a variety of blow molding products.

德国Krupp Kautex 公司的吹塑机械采用液态N2把压缩空气冷却至- 185℃后注入型坯内,可提高生产率约30%N2 的初始温度为- 230℃,在热交换器中吸收压缩空气的热量后,以接近室温作为气体离开冷却器。

Germany Kautex Krupp blow molding machine using liquid N2 to cool the compressed air to – 185 degrees after the injection of green, can improve the productivity of about 30%. The initial temperature of N2 is at the temperature of the heat exchanger, and the heat of the compressed air is absorbed in the heat exchanger to close to the room temperature as the gas leaving the cooler.

2.2后冷却法Post cooling method

内、外冷却方法均针对处于吹塑模具内的制品而言的。若在较高温度下,尽快从模具内取出制品,置于后工位进行冷却,可明显缩短吹塑的成型周期。在脱模时,温度不能过高,一般可在经过正常冷却时间的一半后开模,以保持制品的形状。图. 4 为大型桶的切边与后冷却过程。

The internal and external cooling methods are aimed at the products in the blow mould. If at the higher temperature, as soon as possible from the mold to take out the products, in the post station for cooling, can obviously shorten the blow molding cycle. In the release, the temperature is not too high, generally in the mold after half of the normal cooling time, to keep the product shape.

1—取出机构夹持制品Take out mechanism clamping products;

2—第一工位切除余料First working position residual material;

3—第二工位后冷却制品Second station cooling products; 

4—输送制品Delivery products;

5—制品取出机构Product removal mechanism; 6—切除装置Removal device;

7—夹紧套Clamping sleeve; 8—中央冷却室Central cooling chamber;

9—冷却板Cooling plate

该系统具有自动取出制品的机构,其在模板开启之前夹持大桶顶部余料,并送至第一工位,在上、下端用被冷却的夹紧套夹持,切去上、下的余料。之后由夹紧套把大桶送至第二工位,这里,中央冷却室及上、下冷却板贴近并包紧大桶,使之冷却。大桶的开口朝下,可注入压缩空气( 压力最高为0 3Mpa) ,并可排除,这样,在大桶内产生了对热传热效应。大桶外壁与冷却室的内壁紧密接触而得到冷却,大桶被冷却后送至输送带。这种后冷却方法,大大减少了制品在模具内定型的时间,能很有效地降低生产周期时间,提高生产率。制品的好坏绝大数取决于模具是否合理的设计与加工,其中模具冷却系统的优良是一个重要的因素,它的好坏直接影响到模具的寿命、制品的质量及生产效率等等,所以在设计模具时冷却系统务必要考虑周到.

Mechanism for automatically taking out articles of the system, the clamping barrel residual material in the template before opening the top, and sent to the first station, In the upper and lower ends of the clamping sleeve is used for clamping the clamping sleeve, The remainder is cut up and down. After the clamping sleeve of the VAT is sent to the second station, Here, the central cooling chamber and the upper and lower cooling plate close and tight, to make it cool. The bucket opening down, can be injected into the compressed air (pressure up to 0.3Mpa), In this way, and could be excluded in the vat of the heat transfer effect. The inner barrel wall and the cooling chamber close contact cooling, cooling was sent to the conveyor belt. After this cooling method, greatly reduces the product in the mold the default type of time, can effectively reduce the production cycle time, improve the productivity. The good or bad of the product depends on whether the mold is reasonable design and processing, which is an important factor in the mold cooling system, It has a direct impact on the life of the mold, the quality of products and production efficiency, etc., so the design of the cooling system must be considered in the design of the mold.