Graeff｜熔体压力传感器的正确安装方式

The Melt Pressure Transducer Must Be Mounted Correctly

Damage to a pressure transducer is commonly caused by their installation into an improperly machined hole. In forcing a transducer into a too-small or eccentric hole, the transducer diaphragm may be crushed and as a result the instrument will not function.

Tool kits available for machining the mounting hole will help to make sure the holes are properly sized. A mounting torque of 100 to 200 inch pounds (for ½-20 UNF) is essential to form an adequate seal; however, excessive mounting torque will cause seizing. To prevent problems with seizing, a high temperature anti-seize compound should be applied to the transducer threads prior to installation. Transducers installed at a mounting torque above 500 inch pounds will be difficult to remove even when anti-seize compound is applied.

Ensure That the Mounting Hole Thread Size is Correct

The abrasion from screwing a transducer into a mounting hole with an incorrect thread size will damage the instrument’s threads. This damage may prevent a good tight seal, resulting in material leakage, and the instrument will not function properly or safely. The proper dimensions for the mounting hole must be used to avoid thread galling. (The threads are, generally the industry standard of ½ - 20 UNF 2B.) A mounting well gage plug should be used to verify that the mounting hole is correctly machined and cleaned.

The Mounting Holes Must Be Clean

It is important that the transducer mounting holes are kept clean and free of any plastic buildup. Before an extruder is cleaned all of the transducers should be removed from the barrel to avoid their being damaged. When they are removed, plastic is likely to flow into the mounting holes and harden. If this hard plastic residue is not removed extensive tip damage will result when the transducers are re-inserted. A cleaning tool kit can be used to remove the contaminant plastic. It should be noted that repeated cleaning may produce “too deep” holes and result in damage to the transducer tip. If this is seen, spacers should be used to raise the transducer.

Select a Good Location

Transducers may be located in the barrel, before a screen changer, before and after a melt pump, or in the die. When a transducer is positioned too far upstream in the barrel, un-melted plastic pellets may abrade against the transducer tip, resulting in damage. If a transducer is positioned too far back in the mounting hole, a stagnant pool of melted plastic will build up between the transducer tip and the screw flights. Over time this plastic will degrade to carbon, which will prevent the transmission of an accurate pressure signal. On the other hand, if the transducer extends too far into the barrel the screw flights can shear off the unit’s sensor tip.

Clean the Transducer with Care

All of the transducers should be removed before cleaning an extruder barrel with either a wire brush or special cleaning compounds. Either one of these can ruin the transducer diaphragm. The transducer should be removed while the barrel is hot and tip wiped clean with a non-abrasive cloth. The transducer hole should be cleaned at this time with a cleaning drill/guide sleeve.

Avoid Cold Starts

Both the transducer and extruder can be damaged if the extruder is not brought up to operating temperature before the machinery begins operating. A sufficient “soak time” must be provided for the plastic to go from it’s solid to molten state. In addition, it should be noted that if a transducer is removed from a cold extruder, material might adhere to the transducer tip causing the diaphragm to tear off the unit. Make sure the barrel is warm enough, that any plastic present will be soft, before removing the transducer.

Don’t Overpressure the Transducer

Even though transducers are designed to withstand 1.5 times overpressure, avoid the risk of applying too much pressure by making sure that you are using the correct model designed for your range of extrusion operation pressures. A good rule of thumb is to use transducers that are built to withstand twice the rated pressure in your process. Then the extruder will have to be operating at an extremely high (and unsafe) pressure level for the transducer to fail.

在化纤及塑料挤出系统设备中熔体压力传感器可以是仅测量一个点压力的单个高温熔体压力传感器，也可以是一系列用以测量整个生产线的传感器。高温熔体压力传感器与数据记录仪、声音报警装置相连，利用加制系统可以调整挤出机的加工参数。同时，高温熔体压力传感器也是非常灵敏的元件，如果得不到正确的安装和维护，就非常容易损坏。以下介绍一些高温熔体压力传感器安装使用注意事项，以确保高温熔体压力传感器测量精度和使用寿命。

选择恰当的位置

当高温熔体压力传感器的安装位置太靠近生产线的上游时，未熔融的物料可能会磨损传感器的顶部；如果传感器被安装在太靠后的位置，在传感器和螺杆行程之间可能会产生熔融物料的停滞区，熔料在那里有可能产生降解，压力信号也可能传递失真；如果传感器过于深入机筒，螺杆有可能在旋转过程中触碰到传感器的顶部而造成其损坏。一般来说，传感器可以位于滤网前面的机筒上、熔体泵的前后或者模具中。传感器的探头部分可耐高温，可外壳耐温在80℃以下，所以在安装使用过程中一定要注意将安装好的传感器外壳部分固定在室温环境中。外壳与高温区域隔离有利于提高传感器的测量精度和使用寿命。

正确安装

通常压力传感器的损坏都是由于其安装位置不恰当而引起的。如果将高温熔体压力传感器强行安装在过小的孔或形状不规则的孔中，就有可能造成高温熔体压力传感器的震动膜受到冲击而损坏。选择合适的工具加工安装孔，有利于控制安装孔的尺寸。另外，合适的安装扭矩有利于形成良好的密封。但是如果安装扭矩过高就容易引起传感器的滑脱，为防止这种现象发生，通常在传感器安装之前在其螺纹部分上涂抹防脱化合物。在使用这种化合物以后，即使安装扭矩很高，传感器也很难被移动。传感器的膜片是最容易损坏的部位，在安装之前请不要随意脱落其保护帽，同时在安装同时要注意保护传感器的膜片。安装孔的加工要根据安装孔尺寸图及尺寸表的技术要求加工，避免因安装孔不标准引起的膜片擦伤影响传感器正常工作。安装时要保证正确的安装孔内没有遗留的金属异物或塑料，在清理挤出机之前应将所有的传感器从机器上拆下。只有当聚合物成灼热的熔融状态下才能拆下传感器，拆下后立即用软布将传感器探头膜片擦净。在电气连接过程中，变送器的信号输出连接电缆必须单独通过布线槽进行连接，避免现场的扰乱。设备启动前保证充分的加热和熔化时间，以确保挤出机械工作前传感器的膜片部位的所有物料已融化。

检查安装孔的尺寸

如果安装孔的尺寸不合适，高温熔体压力传感器在安装过程中，其螺纹部分就很容易受到磨损。这不仅会影响设备的密封性能，而且使传感器不能充分发挥作用，甚至还可能产生安全隐患。只有合适的安装孔才能够避免螺纹的磨损（螺纹工业标准1/2-20 unf 2b），通常可以采用安装孔测量仪对安装孔进行检测，以做出适当的调整。

保持安装孔的清洁

保持安装孔的清洁并防止熔料堵塞对保证设备的正常运行来说十分重要。在挤出机被清洁之前，所有的高温熔体压力传感器都应该从机筒上拆除以避免损坏。在拆除高温熔体压力传感器时，熔料有可能流入到安装孔中并硬化，如果这些残余的熔料没有被去除，当再次安装传感器时就可能造成其顶部受损。Graeff清洁工具包能够将这些熔料残余物去除。然而，重复的清洁过程有可能加深安装孔对传感器造成的损坏。如果这种情况发生，就应当采取措施来升高传感器在安装孔中的位置。

仔细清洁

在使用钢丝刷或者特殊化合物对挤出机机筒进行清洁前，应该将所有的高温熔体压力传感器都拆卸下来。因为这两种清洁方式都可能会造成传感器的震动膜受损。当机筒被加热时，也应该将传感器拆卸下来并使用不会产生磨损的软布来擦拭其顶部，同时传感器的孔洞也需要用清洁的钻孔机和导套清理干净。

保持干燥

尽管高温熔体压力传感器的电路设计能够经受苛刻的挤出加工环境，但是多数传感器也不能防水，在潮湿的环境下也不利于正常运行。因此，需要保证挤出机机筒的水冷装置中的水不会渗漏，否则会对传感器造成不利影响。如果传感器不得不暴露在水中或潮湿的环境下，就要选择具有防水性的特殊传感器。

避免低温干扰

在挤出生产过程中，对于塑料原料而言，从固体到熔融状态应当具有充足的“浸透时间”。如果挤出机在开始进行生产前还没有达到操作温度，那么传感器和挤出机都会受到一定程度的损坏。另外，如果高温熔体压力传感器从冷的挤出机上被拆除，材料就可能粘附在传感器顶部引起震动膜的损坏。因此，在拆除传感器之前，应确认机筒的温度足够高，机筒内部的物料处于软化状态下。

防止压力过载

即使高温熔体压力传感器测压范围的过载设计能够达到50％（超出量程的比率），从设备运行的安全角度考虑也应该尽量避免冒险，选择被测压力处于量程范围之内的传感器。在通常情况下，所选传感器的量程应该是被测压力的2倍，这样即使挤出机在极高的压力下运行，也能避免传感器受到损坏。在实际压力控制过程之中，在额定压力之内，虽然传感器有一定的过载能力，当长时间的过载将影响传感器的测量精度和使用寿命。

01 Diaphragm damagedby a sharp edge

Causes:

· Damage through sharp edge contact (screwdriver or knife)

· Dropped

· Contact with degraded polymer in hole

Solutions:

· Use protective cap (transport, storage)

· Check hole with gauge plug for burrs or hardened plastic

· Clean hole with cleaning tool

02 Diaphragm ground off

Causes:

· Contact with abrasive material in process

· Cleaning with wire brush or wheel

Solutions:

· Dymax coating for abrasive applications

· Wipe tip while hot with cloth to remove plastic

· Never use wire brush or cleaning wheel

03 Diaphragm torn

Causes:

· Removal when the material was in a coldor hardened state - Shrinkage of adhesive materials

· Sensor located over flite (fatigue)

Solutions:

· Remove while hot to avoid adhesion

· Double-strength Diaphragm (T80) or TiN coated diaphragm

· Relocate sensor

04 Edge is crushed on the sensor tip

Causes:

· High shear tension

· Lateral crushing when installing (cross thread)

· Non-concentric mounting hole

Solutions:

· Check the install location

· Double strength Diaphragm (option T80)

· Check hole with gauge plug for burrs or hardened plastic

· Clean hole with cleaning tool

05  Seal surface is damaged

Causes:

· Poor mounting hole or cross-threading

Solutions:

· Check hole with gauge plug for burrs or hardened plastic

· Verify threads with gage plug

· Clean hole with cleaning tool

06 Shaft bent

Causes:

· External mechanical effect on stem

Solutions:

· Stem is too long – shorten stem to match depth

· Over-torqued

07 Shaft torn off

 Causes:

· Mechanical effect

· Thread has been fused in the hole (galled)

Solutions:

· Apply Anti-seize to thread prior to installation

· Follow torque requirements

· Use Hastalloy threads to minimize galling

关于Graeff

Graeff（格拉夫）是一家专注于熔体压力传感器、温度传感器、工业传感器、智能传感器、智能控制器以及自动化控制系统研发、生产和销售的英国跨国集团公司。

Graeff is a British multinational group company specializing in the research and development, production and sales of melt pressure sensors, temperature sensors, industrial sensors, intelligent sensors, intelligent controllers and automation control systems.

格拉夫（嘉兴）仪器仪表有限公司（简称：Graeff 中国）是欧洲企业Graeff 集团在中国的全资子公司，Graeff（格拉夫）专注于压力及温度领域的测量控制，Graeff（格拉夫）的技术研发核心成员在电子和力学领域有多年研究经验。是NTX环保型无汞填充高温熔体压力传感器领域的创变者。

Graeff (Jiaxing) Instruments Co., Ltd. (abbreviation: Graeff China) is a wholly-owned subsidiary of European enterprise Graeff Group in China. Graeff focuses on measurement and control in the field of pressure and temperature, and Graeff technology research and development The core members have many years of research experience in the fields of electronics and mechanics. It is an innovator in the field of NTX environmentally friendly mercury-free filled high temperature melt pressure sensors.